Solar Power MPPT

Discussion in 'General Electronics Chat' started by Vortex-8, Dec 20, 2013.

  1. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
    18
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    The Purpose of this Thread:
    =====================
    This thread is intended to be centered around understanding the management of the raw electrical power output from solar panels and tracking the electricity from the panels through the intermediate components to it's final delivery to the devices consuming the electrical power. The main goal is to create a discussion of the nuances involved so that a strong encompassing strategy for photovoltaic solar power system setup and component selection can be developed.


    Okay folks, this is my first time posting to All About Circuits. My goal here is to start a thread that can bloom into a theoretical discussion of managing the power output from various arrangements of solar powered photovoltaic systems on the scale of 'man portable' to large residential or homestead size systems and everything in between such as mobile truck mounted systems, RV modifications, or camping.

    In order to make this exchange and discussion possible, I think it is important for me to state my general knowledge and experience with the sciences and actual components that will likely be involved to form such systems.

    I have a formal education as a civil engineer, so I am not able to do complex circuit analysis. For me this is fine, because at this point I don't intend to try to design and construct the function performing component circuits. What I am looking to be able to do (ideally, so don't let this weigh down the discussion too much) is to become familiar with the entire spectrum of current commercially available relevant technologies so that I can plan for future applications, create basic systems that are flexible and modifiable by swapping components, and buy components that are strategic or wise purchases. I don't have money to burn at all to say the least, so in all things I do, I really have to have a good long term strategy before I begin to buy any components. Many of the specific reasons for these points will likely become understandable later in this post, I hope.

    Onto the actual topic.............
    ...............Solar Powered Photovoltaic Systems



    The Generalized Introduction:
    -------------------------------------
    Now, I will try to give some general goals and challenges of what I hope use the solar power systems for, so that readers can get their bearings on what is being sought, and to potentially find others with similar goals so that ideas and challenges and information can be shared.

    These goals are not related to electronics, they are related to our lives as humans, or at the least, my life and attempting to satisfy challenges in living circumstances. Concerning the physical needs of life, there are basic needs that need to be satisfied. Some of these physical needs are universal, such as Air, Water, Food, & Shelter (physical environment).
    Other needs could be considered supplemental needs due to the nature of how many of us must cope with modern systems in order to satisfy the previously stated more fundamental physical needs. One of these modern needs that most people are now dependent on is energy in the form of electrical power. Electricity has become something that most of us could hardly survive without, especially if you must function within modern society. When I refer to dependence on electrical power, I am not necessarily implying any scale of power that is necessary, but there are certain thresholds and challenges based on the scale and level of power consumption, depending on how one manages their use of electricity and what functions they try to perform with the aid of electricity. Maybe someone only needs a flashlight, some extra rechargeable batteries, a little portable radio, a basic cellular phone, and some low power lighting to satisfy their electrical based needs (it seems that even the base point reference of what the Amish do is still dependent on this minimum amount of reliance on electricity since to an extent, many of them still at various times use such devices.) So, I will leave this general orientation into the goals and motivations for what is being sought and now move into the more specific challenges of trying to meet some of these electrical power consumption needs with photovoltaic solar panels, and the related technical challenges and questions that must be understood and met to achieve this. There are many ways of harnessing power and converting it into electrical power, but this thread is to be focused on photovoltaic power systems and the challenges specific to solar panels.


    General Design Criteria & Examples of Potential Outcomes:
    ------------------------------------------------------------------------
    Now, I will just list some electrical power system needs that I am looking to satisfy with photovoltaics. This list is only to get a feel for what is generally trying to be accomplished and to get an idea of realistic parameters.
    - powering 12V based communications, information, and entertainment electronics (radio, digital TV tuner, small low power computer or laptop, audio power amplifier(s), speakers, scanners, two-way radios or Ham radio operations, data storage, monitor or video screen(s)
    - powering 12V, 24V, or 48V based food refrigeration device (ideally, a stirling cooler)
    - powering a 48V based stiriling heat pump (for relatively small volume cooling climate control, air-conditioning)
    - battery charging (basic lead acid batteries for large bank large capacity storage, charging AA, AAA type Ni-MH batteries for low power portable electronics like flashlights and radios, and for charging Lithium type batteries for cell phones or 18650 lithium batteries for flashlights and higher power consumption portable devices)
    - charging of a small super capacitor bank (i'm sure i'll figure out uses, likely in conjunction with batteries and other systems)
    - powering high power LED emitters for lighting such as Cree CXA series emitters for high efficiency (I have built some high power custom LED lights that are very efficient and better than even the lights commerical available, the power supply level I design for is usually an input of 48V but can range from about 12V to 60V, anything is possible with LED in terms of configuration)
    - charging batteries for vehicles (in the future we hope right), like an electric bicycle to start with and expand from there

     
  2. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
    18
    0
    My Personal Approach to this Discussion:
    --------------------------------------------------
    So now I will get into the specifics of the photovoltaic power output that I am trying to figure out the best way of managing. This is the main purpose of writing this thread. I am going to go through the process of describing the power being output from individual solar panels, down the chain of components, and being delivered finally to batteries (energy storage) or devices to be powered by the electrical output of the system. My personal preference for discussing almost anything technical is to try to keep the language as plain and simple as possible. I feel that if I can describe a process in wording that is intelligible while providing a solid understanding of what is being discussed in terms of simple language and analogies, then the descriptions and understandings are even more powerful and flexible and communicable to others. This is my personal approach, so I hope people don't take my descriptions as meaning that I lack understanding of the subject, I hope it actually reinforces the understanding instead. At the same time, I am no expert nor do I even want to pretend to have mid-level competence with complex circuit operations. Up until now, I try to understand all things just by spending a long time thinking about them in my head. I seem to be very good with converting electrical systems theories to their equivalent water systems and drawing analogies about the effects.

    Well........I apologize for the bloated introduction.......but I just want people to understand what I am asking and why. My current challenge with making selections and decisions for the photovoltaic system is in choosing the most effective components for processing and managing the power that comes out of the solar panels. I will describe what I understand, the questions I have, and hopefully people can respond with where I am wrong in my understandings or their advice or understanding about choosing components.


    My Assessment and Understanding of the Current Commercially Available Technologies of Photovoltaic Power Systems:
    (feel free to correct me on anything you feel is wrong, that's part of the point of going through this)
    ------------------------------------------------------------------------------
    The Solar Panels - Solar panels are a modular construction of many individual solar cells that are electrically connected together (probably usually in series). Most photovoltaic cells fall in the category of semiconductors because they are formed of a composite of very specific materials that have electrical responses that are dependent on the material that they are composed of. Light (specific regions of the radiation spectrum) have effects on the crystal structure of the photovoltaic material that causes the formation of voltage across the PV cell structure. If the light is applied over time to maintain the voltage and the voltage is connected within a circuit then power can be drawn from the photovoltaic cell(s). This is what a solar panel is for, and what it does.

    Because PV cells are semiconductors, they react like many semiconductors do in that they have unique responses over their operating parameters (incident light, voltage, current). This variation over the spectrum of operating parameters means that they will have (when graphed visually) regions where they have maximum efficiency in terms of what is desired as output (electrical power). (feel free to correct whatever you feel is wrong here)

    Since solar panels operate over a relatively wide range of parameters, this results in a wide range of available output power because the voltage produced and the current are effected. Extensive consideration for these variations needs to be taken in selecting the proper intermediate components for the solar power system so that power can be delivered effectively. For most applications of solar power systems (out in the sun) they are subject to cycles. The major cycles that effect the panels are the daily cycle and the yearly cycle. The daily cycle is the first and probably the most difficult challenge to meet since it causes a wider variation of input light than the yearly variation of input light. As discussed above, the photovoltaic panels are a semiconductor technology. Concerning the power system, due to economics and size and long term use, it is desired to get the most power out of them in comparison to what they are capable of producing. Being semi-conductors, and operating under multiple variables such as period of incident light, strength (flux) of incident light, and temperature of the cells (environmental temperature and heating from the light), there will be specific points (if graphed) where the panels will be able to put out more power per unit of incident light if the panels can be kept at or near those parameters. Another major variable that is necessary to consider is shading, or uneven distribution of incident light on individual solar panels or across multiple arrays of solar panels. A major complication caused by shading is that, since the individual PV cells in the panels are wired in strings (series), shading of a portion of the cells will have a huge effect on electrical flow through the entire chain of cells. (I am guessing that there are likely similar problems for cells that are in parallel as well, such as the voltage of unshaded cells applying their voltage to cells that have lower voltage due to shading.) This leads into the subject of the components that are to follow the solar panels in the power system.

    MPPT (Maximum Power Point Tracking) - Maximum Power Point Tracking refers to a process of automated modification to the general operating circuit parameters of the solar power system. By modifying the circuit parameters (such as, voltage, current, resistance, impedance), it is possible to have the solar panels (PV cell arrays) kept closer to the points (graphically) where they are operating near their maximum achievable efficiency. (Again, feel free to jump in here, since this is where I start to discuss things I don't know enough about, and I acknowledge that what I am saying could be very inaccurate.) I realize there are multiple methods or 'algorithms' to achieve identification of the maximum power point. Some methods may be more precise or faster adjusting than others. I am not very concerned with the specifics of the algorithm methods since one method in comparison to another is not likely to have a huge impact on efficiency, so long as they are able to perform their intended function.

     
  3. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
    18
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    The Nuances that Create the Hard Questions:
    -------------------------------------------------------
    This is where I deviate from the fundamentals of operation to the specifics of currently available technology. This is where many questions arise and I am in search of some detailed information.

    What is the actual method of modifying the power output to achieve the maximum power point. What I am asking is about the circuit types or components that are used to achieve this more than the algorithms. For instance, is some current bled off through resistors to increase power draw to actually end up increasing the efficiency of the PV characteristics. Is pulse width modulation (PWM) employed to modify the loading placed on the PV cells of the solar panel(s). Could someone fill me in on how 'shunting' can be part of the process. Depending on the method of MPPT, what is the resulting effect on the input voltage & current versus the output voltage & current for through an MPPT controller?

    Something that I want to discuss in depth that is causing some confusing for me is that it seems a majority of commercially available MPPT units are not simply just MPPT controller circuitry, but are a combination of common functions well beyond basic MPPT controlling. It seems like many of these MPPT units are intended to be connected to lead acid batteries. If they are meant to be connected directly to batteries, that would mean they have separate circuitry for battery charging control. As far as I understand, there are many approaches to charging and maintaining lead acid batteries. Some approaches are simple and use almost no circuitry, they simply feed in a voltage (say 13.8V) regardless of the state of charge of the battery. Other approaches ramp up the voltage so that the battery is not subjected to currents beyond a threshold. I own a Revolectrix PowerLab 8 battery charger. This battery charger is the best I could find through my research. It has the ability to charge almost any type of commercially available battery, batteries of various electro-chemistries, and custom battery packs with various cell configurations. The charge algorithms for the PowerLab 8 can be updated through a computer connection, so it is very adaptable and a flexible piece of equipment. The reason I bring up the PowerLab 8 into this discussion is that, if there are more flexible options for battery charging systems, I don't want to be limited to what is built into an MPPT unit. I only want the MPPT part, not the extra stuff. The PowerLab 8, like many other comparable hobby charges, takes input power in the form of DC, and it can handle (from memory so don't hold me to this) anywhere from about 10V to 36V, and the charger outputs whatever voltage is required to charge whatever battery type and configuration is specified before the charge cycle is started. I am guessing that the PowerLab 8 uses some form of PWM to achieve this, with other circuitry. Most of these hobby chargers require a separate power supply for people who are using them in them at home and want to provide power to the charger from their house's 120V receptacles. These charges are intended to be used 'in the field' as well as at home, which is why many don't have a 120V AC input built in, because many people supply power to them from a deep cycle lead acid battery to charge their other batteries (Lithium batteries for RC vehicles). I also have an inexpensive Schumacher battery charger for charging individual lead acid batteries. It has settings for basic lead acid, AGM, & (can't remember the other type right now). This charger plugs directly into a 120VAC outlet. The reason I bring up these charges is to show that, for some people, maybe they don't want the MPPT unit handling battery charging processes directly because they may have better stand alone chargers or they want more control over the process. This is important to me. As I stated in the introduction, I am looking for flexibility, upgradability, and swap-ability. I have many reasons for this, some of which are probably not obvious right now. So, getting back to the MPPT units..........What are they doing really, internally? What is available these days? What are the efficiencies of the MPPT systems. From what I have gathered, MPPT units may not increase overall efficiency if the total power output of the solar panel setup is under, say, 500 watts or maybe 300 watts. This would be due to the power loss associated with the circuitry and conversions going on in the MPPT unit itself in comparison to the gains achieved by getting the operation of the PV panels closer to the maximum power point.
    So, again, are the MPPT units usually using some form of PWM? Are they also DC-DC converters? What is the voltage & current output compared to the input?

    As of now.......I only have two 100 Watt each Renogy solar panels (200 Watts of solid output power). Apparently the operating voltage is around 17.5V and the open circuit voltage is 22V (I realize this is variable depending on lighting).

    Let's say I want to do a simple mobile setup where I can run a box I have built that has a bunch of 12V electronics in it (the first item of the original electronics list in the beginning) off of the solar panels I already have. Since this box is designed to be hooked up to a basic lead acid battery (automotive or deep cycle battery) it can take power from about 11V to 15V. Realistically, I don't need that much power unless I am trying to use a powerful amplifier. For this box, I am looking at a power draw under most circumstances of about 7 to 35 Watts. If I wanted to take a one of my solar panels outside, lean it against a wall towards the sun and hook it up to my box, at the least I would have to step the voltage down to something closer to 12V. There are many different ways to do this, and in this case I don't need something complicated, but for the sake of expandability, I want to understand my options. If I used a DC-DC converter (buck converter, buck-boost converter, etc.) I should be able to get a more efficient conversion process than other alternatives such as bleeding off current to drop the voltage. Maybe there are other options I am not aware of, but this would be the obvious methods, that is, without involving other intermediate components such as a battery.

    Now, let's say, in the future I am going to expand my number of solar panels to be able to have a greater power output so I can run more DC devices such as a small cooler or for charging a battery bank. At this point, MPPT should definitely be worth the effort and cost because of the added efficiency. So let's say I had the same setup, but now I want to include MPPT. What voltage would the commerially available MPPT units output? Are they adjustable? Do they all require a battery to be hooked up as an intermediate power regulation? Would I still need a DC-DC converter or regulator unit? One of the reasons for me asking these monotonous questions goes back again to being able to swap out components depending on needs. High watage and high efficiency DC-DC converters can be somewhat expensive and I may find in the future that I want either more power, or maybe a smaller package, so this would lead to needing to be able to select different converters depending on the setup. I generally buy components from Mouser and in terms of DC-DC converters I have been looking at Mean-Well, TDK-Lambda, & Cincon since they have products that could fit my needs well. The TDK-Lambda & Cincon units are small and are passively cooled through what they are mounted to, and seem to have relatively good efficiency. But again, good components don't usually come cheap. I don't want to just buy and try stuff if it's expensive.

    Another important aspect of maximum power point tracking that I have realized that can effect the overall solar power system setup strategy is that having more MPPT units for each solar panel or smaller groups of solar panels versus having only one higher power MPPT unit for an entire larger system can result in greater efficiency. This would happen because the MPPT unit is making adjustments for the efficiency of the solar cells, but not every cell will be under the exact same conditions at the same time. Effects such as shading, temperature, positioning and sun exposure, can cause variations across a solar panel and between groups of solar panels. By dividing up the MPPT, the adjustments of the MPPT system can be more precise and localized, resulting in higher efficiency. I have come across a newer strategy where MPPT units are being mounted directly to the back of solar panel units. The problem for me is that the ones that are setup like this currently, they output their power in 120VAC, and that is not what I want. I really don't need AC power. If I really need AC power it would only be for short periods and I can temporarily hook up an inverter or instead just run a small generator. So this is another aspect. I like the idea of having units attached to the back of each solar panel, even though it may cost more. This could also simplify expandability while increasing efficiency. It could also increase flexibility. For example, a person could grab a single solar panel to run some lower power electronics, or hook up the solar panel to a larger system and they integrate well while having good efficiency. Another thing I should mention is that, as of now, I am not concerned with feeding power back into the general electrical grid, so I am not concerned with MPPT units that have the added circuitry to do this. This is a complication I can ignore as of now, although later I will do what I can to consider it.
     
  4. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
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    A Partial Summary of my Questions:
    --------------------------------------------
    So again, some questions are....
    - What do the current MPPT units commercially available actually do?
    - Are there units that do 'only the MPPT function' without other functions?
    - What are the options for MPPT units for each solar panels instead of a single larger MPPT unit for a bunch of panels?
    - What kind of conversion is going on in the MPPT units?
    - What efficiencies of internal circuitry are many MPPT units working at?
    - What are the methods by which MPPT units perform MPPT?
    - What role do DC-DC converters play in solar panel power systems?
    - What is a good strategy for hooking up solar panels to electronics without intermediate batteries?



    Final Statements:
    ---------------------
    The first thing I want to do in closing, is to say wow, if you read all this that I wrote, you have some patients, so thank you. The second thing I want to say is of course that I appreciate anyone who has a contribution to make to this discussion and I appreciate the time and advice of people who are knowledgeable in this field.

    I also really hope that there are other people out there with similar goals so we can work on making our future better instead of waiting for other people to do it for us. This is for all the people who have identified the current difficulties of the modern era, those who have identified some solutions and simplifications, and who are willing to put their time, effort, and money where it counts. This is really what this is all about for me.

    -----------------------------------------------------------------------------------
     
  5. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    If you want only MPPT from solar then AC grid-tie or a system the presents a fixed DC voltage load with the capacity to sink whatever current your system can provide is needed. Most of the MPPT off-grid solar systems are 'battery charge controllers' so they must be able to switch from pure MPPT to a (PWM usually) regulation mode to charge batteries because most cell types require specific profiles of charging currents and voltages that's a function of it's electro-chemistry not electronics. The key to utility scale solutions in solar is not MPPT or charging/load sharing systems and designs, it's storage systems with low input/output conversion losses at a cost that's competitive with todays base load generation systems. You really can't have stable maximum solar power (an intermittent energy source) without storage. The level of storage needed can be adjusted by several ways but they usually require the solar panels to be run at less than MPPT levels to provide load buffering to simulate the rotation inertia seen in synchronous generators or the chemical energy storage of batteries.
     
  6. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    tl;dr

    (plus some extra letters to make the minimum post)
     
  7. eeabe

    Member

    Nov 30, 2013
    59
    9
    Here's a bit of feedback based on my experience with solar systems and charge controllers:

    First, I'd say that MPPT may not be necessary or even useful for a lot of systems. If you have a typical 12V solar panel that is 17V to 22V open circuit, it may be putting out maximum power at around 15V to 17V, which might be about the right voltage to charge a 12V battery through a typical charge controller. If you're keeping your system batteries charged and you can't use or store the extra power, there's no point in trying to get more from the panel.

    In my opinion, MPPT is a good option in a couple of cases:
    1) if you have panels and batteries that are not well matched in terms of operating voltage
    2) if you have a grid tied system where you are not limited in storage capacity, and the more energy you get, the better

    You asked, "What is the actual method of modifying the power output to achieve the maximum power point?" I would say the method normally involves a switching converter that can adjust the voltage and current at the panel to get the maximum power. If you've seen a solar panel voltage/current curve, and the associated power curve, you'll see that to get the maximum power, you need to be somewhere in between the maximum voltage (open circuit) and the maximum current (short circuit). Regardless of the algorithm used to find the best operating point, you would use some type of switcher so the panel basically "sees" a load that puts it at that best point on the curves. I don't think shunting power will help as it would just be a waste of power.

    As far as the output side, the voltage will depend on the switching topology, any transformers, and the load. You might want or need another switching stage to adjust and control the output voltage. For example, for a grid tied system, you need to provide power into a sine wave voltage, and you may want power factor correction.

    I believe some larger systems use micro-inverters, which is basically a small MPPT controller on each panel that allows it to feed power into a grid type AC voltage.

    Ok, I didn't read everything in detail :) but I will take a shot at your summary of questions:

    - What do the current MPPT units commercially available actually do?
    - Are there units that do 'only the MPPT function' without other functions?

    What I've seen are designed specifically to either charge batteries or to tie into the grid. It would be tough to make a generic MPPT controller without requiring some secondary unit to adjust the output as needed.

    - What are the options for MPPT units for each solar panels instead of a single larger MPPT unit for a bunch of panels?

    As mentioned above: microinverters. Also, it's a great idea to have each panel on its own converter in case one or more panels gets some shade or damage, so it doesn't bring down the entire system.

    - What kind of conversion is going on in the MPPT units?
    - What efficiencies of internal circuitry are many MPPT units working at?
    - What are the methods by which MPPT units perform MPPT?
    - What role do DC-DC converters play in solar panel power systems?

    As mentioned above, some type of switching conversion (PWM, DC-DC, etc.) so the panel sees its ideal load for the current condition; could be increasing or decreasing the voltage.

    - What is a good strategy for hooking up solar panels to electronics without intermediate batteries?

    Probably not very practical unless your electronics and systems can do without power when there's no sun, or maybe you could use some type of super-capacitor to keep stuff alive.
     
    Vortex-8 likes this.
  8. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
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    NSASpook & eeabe, thanks for the first replies.

    So far, what I gather from your responses is as follows.........

    Let me start with NSASpook's response since it was first....

    So, for MPPT to be effective, the MPPT unit is 'making the solar panels see' a constant voltage and constant current that correspond to the maximum power point (ideally). This means, for MPPT to be effective and actually 'do it's thing' the MPPT unit(s) ideally cause the solar panels to 'see' an ideal load (which I suppose would be the equivalent but opposite of an 'ideal power source') that is unchanging and non-responsive to whatever input is being provided. Otherwise, the MPPT would not be able to hold the panels at operating near the maximum power point since, regardless of the desired power use, the power (energy) must go somewhere.

    So in my example of trying to hook up one or two panels, as a test run, directly (no batteries or storage as buffer) to my 12V-based electronics box, an MPPT unit would likely provide no benefit since the electronics (such as a small computer, stereo, TV Tuner, equalizer, DC power outlets, etc.) have their specific power draw, and the power draw would fluctuate somewhat for these devices based on what the user is actually doing with them. The difference in power draw and output of the panels would not allow for any MPPT activity since there is nowhere to dump the extra power. That part, I admit, should have beeen obvious to me if I hadn't thought about it already in that way.

    Beyond the fundamental part of pairing an MPPT unit to something that can approach or be comparable to an 'ideal load', it seems that you are confirming that a majority of MPPT units are not simply MPPT circuitry as I suspected but are combing at least one other function within the unit, such as battery charging circuitry or grid-tie inverter circuitry (some do both I would assume). In the case of batteries, depending on the capacity of the battery (battery bank), the setup would deviate from MPPT based on the state of charge of the batteries since the charging circuitry would be adjusting the voltage and this would likely cause the current to change as well, which would change the power draw from the MPPT and throw off the system from the maximum power point of the panel(s). A grid-tied system would be similar but to a much larger scale and probably with more complex nuances effecting the analysis of what's actually going on.

    NSASpook, I appreciate the part where you brought up rotational inertia, even though to many that rotational inertia would seem to play little role in understanding what's occurring in a basic solar power PV setup. I will come back to that at the end to comment on that.

    Onto eebae's response......
    eebae, your response provided some very direct answers to some of my specific questions and you provided some helpful specific information, thanks. As strange as your initial comment may seem ("MPPT may not be necessary or even useful for a lot of systems") to the beginner in solar power, after thinking about your comments I think that was an excellent and very important statement to make based on what I am seeking.

    I will have to spend some time to think over your comment about MPPT being useful in situation where "you have panels and batteries that are not well matched in terms of operating voltage". The part of grid-tied systems and MPPT is easier for me to understand since it would be like a much larger place to dump energy. I need to consider many variations of battery setups and scales to understand the implications of this.

    I am also going to need to find and spend some time to find and review graphs of the solar panel power, voltage, & current graphs that you are talking about. I know I found that with LED's, understanding these kinds of curves allows for understanding what is going on very well and really effects a good design where other people may ignore it at the cost of efficiency (efficacy).

    You said that switching converters are likely to be part of what is occuring in an MPPT unit. Something I am guessing about, which is due to my lower level knowledge of converters, is that switching converters are in the category of PWM converters, is that correct? Are buck & boost converters considered to be in the category of PWM converters? That is a snag for me that I should understand before moving forward. Can anyone clarify this? I do understand the theory of PWM, in that it involves full power pulses that are limited to on and off time to modify the power draw, which is then smoothed capacitors into the voltage being sought. I hope that's correct. The reason I bring this up, is that with dimming LED's using PWM, this method of dimming results in current flow that is full on and full off, so it seems to not get the advantage of the usual increasing efficacy for LED's with reduced current draw (again, since it's full current to no current, versus dimming with reduced current). This makes me think of a similar situation for PWM conversion in conjunction with solar panels. What I am guessing happens with solar power units is that there are capacitors on the input side to smooth out the switching to create a constant voltage and current that the panels 'see', so that the panels are not being treated with sudden full draw and sudden full off, which wold mean the panels are not at functioning at the maximum power point. This probably is just picking things apart too much, but it's something good to understand still.

    Also, from what I gather of your comments, is that most MPPT units probably do output a certain constant voltage that is specific to the unit (I'm guessing some are adjustable). A unit might, for example, accept the range of voltage fluctuations form a solar panel array (maybe 17VDC up to maybe 140VDC), do the processing (the MPPT) and output maybe a relatively constant voltage like 15V. Maybe my understanding is wrong here. This would mean that the final output is somewhat regulated in terms of voltage. And, as you said, if the voltage level being output is not what the point of use electronics require, another DC-DC converter would be necessary to make the setup work.

    I think the other thing I have gotten from the comments so far is that some form of power output buffering in the form of energy storage (such as batteries or capacitors for example) is really necessary for a system to function. The part about the sun going down at night, I am not considering in the test case since I would just setup and take down the system over a course of some hours while doing testing. I don't have a house to mount my panels on yet, but acquiring a house is another matter to say the lest right. I purchased a set of Maxwell supercapacitors from eBay about 6 months ago knowing that they have so many applications and knowing I would find something to use them form. One thing I wanted to use them for was pairing them to a bicycle generator setup and also possibly in conjunction with a chemical battery, due to the nature of variable power being output when pedaling a bike and the instant uptake of power with low loss for capacitors. The same would apply well to PV panels. Even a relatively small set of supercapictors (possibly connected to the rear of the panels) with very limited actual energy storage capacity could be a great buffer for testing out systems where I don't want to be moving heavy batteries around. The capacitors may give me enough time to shut down my 12V electronics (very little time I know) and help to keep my electronics from shutting off suddenly due to sudden voltage drops, if, for instance, I walked past the panels quickly to grab something on the other side of them. Beyond that, most electronics (especially for vehicles) have capacitors to carry power through sudden and brief drops of voltage so they don't shut off unexpectedly.
     
  9. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
    18
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    Now........back to NSASpook bringing up rotational inertia.......
    What I have to say about that may not really be what you were trying to bring up directly, but it is something that is important to me for a bunch of reasons.

    One reason is that, rotational inertia is the ultimate form of stationary energy storage (it has mobile applications too though) as far as I can see. You may have already come across this........but I want to throw out there the subject of 'flywheel batteries' or 'flywheel energy storage'.
    Here's is a Wikipedia link to the subject:
    http://en.wikipedia.org/wiki/Flywheel_energy_storage

    The frustrating thing is that, i'm just some random idiot who realized that a heavy carbon fiber cylinder mass spinning at high rates of rotation and contained in a vacuum pressure vessel and supported by magnetic bearings and spun up and down by pulsing of electromagnets is the ultimate medium to large scale energy storage system. I spent a lot of time thinking about it years back and trying to see if anyone thought of it already. Then......I ended up finding that there is actually a company 'Beacon Power' that was building pretty much exactly what I was thinking. That's good, I just want the technology to be available. From what I have figured from rough calculations is that such an energy storage device the size of a large water heater has the ability to store and release enough energy for the operation of the average American single family home (even large ones, and also considering the current wasteful use of energy for most homes still) for a month.

    What this technology can do for distributed power generation is amazing. The technology is not complex and these things could lost 30 to maybe 80 years or maybe even more realistically. Pairing these things with solar, and wind, or really any variable source of energy solves so many problems that it makes me laugh due to it's simplicity and implications. I also suspect that these are what are used to supply the sudden and immense bursts of electrical power needed to launch aircraft from aircraft carriers using the new form of electromagnetic launch systems. There are probably sets of these things inside the ship directly bellow the launch site under the deck in a room I'm guessing. With that.......I have deviated from the original discussion too far........but since it is such a powerful technology that should be applied to distributed generation I wanted to comment on it.

    My major interest is in understanding energy physics and related sciences from a fundamental and even philosophical point of view and I have found rotational inertia to be one of the keys to understanding it all. There are many other aspects of 'rotation' itself I would love to discuss and even how it relates to circuits that are seemingly motionless, in understanding the theory of electricity and what is actually going on in a loop that we call a circuit, things related to focusing and defining points in space. I hope I haven't just thrown the discussion too far off topic.

    Thanks guys.......I'm hoping the original discussion about managing output power from solar panels can still be carried much further. There are many things to consider for a good setup.
     
    Last edited: Dec 24, 2013
  10. nsaspook

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    The technology is very useful as an energy buffer used to smooth out fluctuations in power during generation but as a primary energy storage system the physical stresses from very high speed/large mass operation and from large changes in stored energy quickly causing large changes in speed mean you have to deal with the problems of (very destructive) device failures like these seen inside vacuum chambers: http://www.flickr.com/photos/12772565@N05/sets/72157604136768179/with/2338386349/

    High speed MAG-LEV turbo pumps are notorious in the industry for total destruction at high speed.

    What you want is a way to store and use the energy in a way that only emulates a rotating mass generator powered from a energy source when responding to transient condition loads, with the actual storage method being a different physical process (like a battery or other type energy bank) that's converted to electrical energy as demanded by the control electronics. The physics and materials science needed to crack this nut is what's so hard, the electronics needed to control will be the easy part.
     
  11. Vortex-8

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    Dec 20, 2013
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    NSASpook.........I definitely realize that the rotational forces causing tension on the mass material is the main limiting factor of the technology. That doesn't mean that it's not feasible though. It just needs to be an extremely well balanced mass made from material with high tensile strength with good manufacturing quality control of the material and final formation of the mass. Carbon fiber would be an obvious option right? The other part that is a challenge is the bearings so that there is little energy loss. That's why they make them with magnetic bearings and the mass is encased in a vacuum pressure vessel. There are challenges to the technology, but there are similar challenges to developing an internal combustion engine in the same sense of needing to make the proper selections in design and materials. An engine reving too high will fly apart due to the same principles, based on the materials of the parts.

    There is always a limit to the maximum rotational speeds based on the materials. So you end up with a design that has a corresponding maximum operational rate of rotation. If you are at the maximum speed and need more energy storage.........then the next obvious option would be to make the mass larger so that it can rotate slower. But it's a basic geometry and dynamics situation where some functions are exponential, to the 2nd and 3rd power and some functions are linear so it would be helpful to graph the relationships to realize the limitations and choose the necessary dimensions and mass and rates of rotation.

    I'm really not saying that these things are available commercially nor am I saying anything about installing them in the basement of a house next to a furnace and water heater for general consumer use in such a simplistic approach. Never should something like this be in a standard consumer environment where it is placed near people. That is why the ones they currently install are set in the ground. There are simple things to overcome the safety concerns. The most basic is to dig a hole and pour a cylindrical concrete shell that probably has a steel inner lining and then set the unit into this. I think this mitigates most of the safety issues, and again, I'm not saying that this is something ready for the average home.

    This is currently better suited for distributed electrical grid energy storage and is a great for coupling with medium to larger scale energy production such as large wind turbines and wind farms or maybe large solar energy facilities, and also the common electrical generating utility plants. Beacon Technology Corporation already makes these units. I'm not sure in the last few years what has happened to the company. The last I know, they were installing sets of these near to a coal fired power plant (i think it was coal) somewhere in the state of New York. What they were doing was storing the extra energy from nighttime power production when consumer demand is less and when the electricity rates are cheaper, and then selling the energy back to the grid in the daytime when the energy rates are more expensive. So in this case they are using the technology to level out supply and demand with the available constraints of the power plant(s) (like you were saying it would be good for). That's a great use and application among the many potential ones.

    The place to start would be in updating the capacity of distributed grid energy storage. If it were to transition to a anything near the consumer level I would say the best place to start would be for people with large and more isolated properties such as ranches in the western region of the US for example. This would be a great technology for large manufacturing facilities and factories that have large bursts of current draw depending on what machinery they run. The thing flying apart in a sudden failure would be extremely dangerous though. But many currently used devices in and systems in industry are similarly dangerous. Many manufacturing facilities have high pressure tanks that could blow and kill a lot of people, but the engineering is done to minimize the risk.

    Here is one thing about this technology though. For power generation, often space and size is not as large a factor as it is for most other systems. Power plants usually already have large properties. Imagine a power plant having one of these an eight of a mile away from the main buildings and set in the ground. A well balance mass with a diameter of possibly 50 feet, or something on that scale could have a lot of potential. If it's a very large and massive cylinder, it could store quite a large amount of energy without having to spin up to such a high rate of rotation. The supports and bearings would be the main challenge in this case. I think it's a reasonable challenge though.

    I hope you didn't take it that I am saying let's give every average consumer one of these without thinking it through. The link to the vacuum pump is interesting. I haven't seen pictures of those like that before. That's pretty cool. At the same time, those vacuum pumps seem like they are much more complicated and have more components that could fail in comparison to flywheel energy storage. I should look into them and see how they are related to mag-lev trains because I don't know about the whole setup. I'm not sure what the vacuum pump does for mag-lev. It's definitely interesting to see.

    I hope you don’t take my comment in the wrong way. I’m definitely not trying to argue over anything. I’m just trying to have a discussion and you seem to have some diverse knowledge.
     
  12. Vortex-8

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    Do these mag-lev trains involve electromagnets rotating at high speed (in a vacuum to cut down on drag) in order to generate a pulsed magnetic field for the propulsion and levitation? I really don't know how these work.
     
  13. nsaspook

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    I've tinkered with cheap flywheel storage before using some old pumps from work to experiment on because I too was interested in the subject a few years ago. With a conventional self powered MAG-LEV pump turbine systems it took about 2W per kg to operate the spindle bearing at full speed. (~25,000 rpm) I don't remember all the details but the round-trip efficiency was less than 50% for a 200W cycle. If most bearing losses (with magical room temp super-conduction in the lifting magnets) were eliminated the round-trip efficiency might be up to 80+%. That sounds good but I could also easily get 70-80% efficiency with FLA batteries using smart charge and discharge profiles. Some of the new ideas are pretty cool if they actually work when scaled to full size.
    http://www.scientificamerican.com/article.cfm?id=new-flywheel-design

    The threat of flywheel explosion should be accounted for in the lack of enthusiasm for this form of storage as the liability for this kind of accident has a long history in the US.

    http://www.rustyiron.com/literature/Flywheel_Explosions.pdf
     
    Last edited: Dec 22, 2013
  14. Vortex-8

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    Dec 20, 2013
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    Okay, wow. I like the fact that you've experimented with the idea on your own. The numbers you are saying make a lot of sense. For some reason, through my limited searching, I seem to have gotten the impression that an 80% retention of the energy input may be possible with a high quality design. But as you are saying, about the magnetic bearings having losses.........that is really a major factor to consider. Especially since I am hoping to see the technology applied to being able store energy for a month versus a week or a day. Very interesting. I will definitely read through the articles you linked to. Skimming through the PDF article, I know I am going to really like that one. Thank you.

    I'm stuck in the world of theory and internet research. I don't have access to any substantial equipment or even most basic electronics equipment and components for that matter. That's pretty much why I'm here at this forum. So I'm all ears to someone who has practical experience or access to industrial equipment that they have experimented with.

    As far as solar PV......
    Do you have any advice on DC-DC converters for use in a PV setup? Maybe some advice on some specific DC-DC converter types?
    ...Or if you have any thoughts on specific Manufacturers like TDK-Lambda, Cincon, or Meanwell? Are the TDK-Lambda units overkill?

    I was considering these as some choices, maybe not necessarily as high of wattage to start with, but if I get something capable of higher wattage, it helps for expanding later.

    http://www.mouser.com/ProductDetail...=sGAEpiMZZMtwaiKVUtQsNZ/yu7DCXWZ1uFI3QCeWG80=

    http://www.mouser.com/ProductDetail...=sGAEpiMZZMtwaiKVUtQsNQ7X08mV/kuqc8b6Lc/Hj34=

    http://www.mouser.com/ProductDetail...=sGAEpiMZZMtwaiKVUtQsNWhyeQHiJKw7pYKetXQI35I=

    I seem to be drawn to the TDK units but I don't want to be wasting money if they aren't really intended for this kind of application.

    I like the idea of them being sealed and passively cooled if I wanted to retrofit something like a UPS type step van truck where I can integrate various components and systems into a relatively compact setup so that all the components don't take up too much space. This is honestly one of the design goals I am shooting for but it's not the only thing I'm interested in trying to do in the future, maybe a few years from now. That's why my initial posts were so long........because I may end up trying to take these things in various directions that start to diverge.....so I am searching for some broad knowledge but I still need some fairly detailed advice on components from some people with experience.

    I have to agree about the FLA batteries from what I have read. The commentary on the subject seems to point out that they are cheaper, have reasonably large capacities, and are longer lasting than many other options (even though they are initially viewed as old battery technology).
     
  15. ronv

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  17. nsaspook

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    It's much better to buy quality MPPT solar units (don't waste your money on the cheap Chinese junk) designed for solar energy as most have embedded control systems designed to track the typical parameters (via RS-232 or USB) you will need to understand what's happening with energy generation and usage unless you really want to send a huge amount of time to understand all the little details required to build your own DIY system. I've designed a few crude BMS systems for my own solar energy projects and am currently in the process of building a new data acquisition front-end prototype for my current system using a PIC32MX250 SPI master controlling several PIC18 slave units.
    Some demo code for testing the custom DAQ board.
    http://flic.kr/p/iwUDBY
    https://github.com/nsaspook/nidaq700/tree/master/mx_test.X
    https://github.com/nsaspook/nidaq700/tree/master/mx_test
    Some older designs: http://flic.kr/s/aHsjCgCD77
    As you can see it's not a trivial exercise to build these systems from scratch and for about the same price as a good DC/DC converter with a DAQ system you get the whole package.
     
  18. nsaspook

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    The pumps are not designed as energy storage devices but they show some current uses of a like technology and the countermeasures needed when things fail. One of the requirements is a very strong pressure vessel handle the implosion/explosion hazard during a flywheel failure. Here is another small (200mm inlet) pump that failed at 35,000 rpm due to a hub fracture in e-7 Torr vacuum. The MAG-LEV motor spindle seen in the lower half might be still ok but the upper vacuum housing (.5 inch min. stainless steel) is complete junk (warped).

    Dead pump inside view.
    http://farm4.staticflickr.com/3792/11524609976_9afd7f8b78_o_d.jpg
    Outside view of a good pump:
    http://www.ptb-sales.com/vacuum/pumps/turbo/seiko/stp1000.jpg
     
  19. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
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    Yeah I understand about any mass rotating a high speed is going to be like an explosion if it comes apart. These are all problems that are not so difficult to overcome. If someone is trying to put a small flywheel energy storage device in a room in their house, say.....next to their computer as a backup power supply, then yes.......that's a hazard to someone's life. I really think electro-chemical batteries or fuel cells would be a more appropriate direction to head off in for people wanting smaller or more easily moved backup power of a smaller scale. But for entire buildings, industrial, commercial, or residential districts, I think flywheel energy storage is appropriate.

    It really has been done. Beacon Power built them and installed units in that are just what I was thinking about. They went the way of Sylindra though, they went out of business in 2011. I think they were part of the same DOE program that was providing loans to a dozen or so companies. I don't think they went out of business simply because the technology wasn't do-able or feasible, they did, after, design, build and install the final product. Setting the units in the ground solves the problem of them being dangerous if there is a failure.

    Again, I'm not certain on this point, but I think this technology is what is being used for the magnetic launch of aircraft for the new system they are installing on aircraft carriers. If so, that would have to mean that the risks can be minimized. I doubt the navy would want to install a bunch of these on a ship if they will end up blowing up and sinking the ship. But then again, they do cruise around with loads of bombs and missiles so that really wouldn't say much would it.

    I was thinking about the potential implications of an earthquake on these units, but the article you linked to previously actually could easily solve that problem. That article, where it discusses mounting the devices in a gimbal is actually a great approach and it should allow them to be reliable in places where there are earthquakes. I had considered a gimbal configuration for a completely theoretic approach where the energy storage could be expanding from one axis and one dimension into possibly two or three dimensions to having greater energy storage density. I understand that doing just that would be probably 30 times more complex than the current approaches, but just for the sake of theory and potential expansion of the concept. But the article you linked to, they have the correct approach it seems..........which is to use the gimbal to stabilize the system. As they were discussing, it simplifies the manufacturing, the bearings necessary, and reduces the level of high precision balancing of the rotor (mass). The manufacturing tolerances they state in that article are surprisingly relatively loose, and everything else that is discussed in it seems to make the technology more realistic in the near term than even I had thought up to this point.

    If one considers the energy stored as inertia in such a device, like the actual kilo-joules, it can be relatively high, which is the intention and benefit. But, if the device fails, it will release all that energy almost instantly in an uncontrolled way. That would be like someone blowing off dynamite (comparing the energy of the flywheel to that of sticks of dynamite). But this is not much different than a tank of gasoline in a vehicle being dangerous if it were to be ignited and fail at once. But in the case of the flywheel energy storage, the unit can be set in the ground without raising the cost too much. Unless someone has the poor foresight of setting the unit in the ground right up against the foundation of a building, I don't think that it would pose a major hazard if it failed. There were need to be a strong cap or enough ground cover over it. That would not be too hard to take care of. It sure wouldn't be good for smaller property lots if that was the hope.

    Most of the safety concerns for these devices with this intended use could also be made for people who have large propane storage tanks. Having such tanks is not common everywhere. But in some parts of the country, having large propane and diesel or gasoline tanks is common for a lot of reasons. I would think they could blow up if someone does a bunch of irresponsible things, or if someone wants to start unloading a bunch of rounds from a rifle into one. Those tanks are not even set in the ground most often. They shouldn't be installed next to a person's house..........though I have seen them installed considerably close to a house, not that I would recommend something like that.

    The vacuum pumps that you bring up, while interesting, and I like the pictures, they aren't located in places that the flywheel energy storage systems would. It seems like those pumps are located inside in labs. If they are used as part of mag-lev trains like you brought up before, that would be much more complex and is a mobile application.

    Does anyone have any commentary on the DC-DC converters I brought up before, with the links to Mouser?

    "Do you have any advice on DC-DC converters for use in a PV setup? Maybe some advice on some specific DC-DC converter types?
    ...Or if you have any thoughts on specific Manufacturers like TDK-Lambda, Cincon, or Meanwell? Are the TDK-Lambda units overkill?

    I was considering these as some choices, maybe not necessarily as high of wattage to start with, but if I get something capable of higher wattage, it helps for expanding later.
    "

    http://www.mouser.com/ProductDetail/...uFI3QCeWG80%3d

    http://www.mouser.com/ProductDetail/...b6Lc%2fHj34%3d

    http://www.mouser.com/ProductDetail/...pYKetXQI35I%3d

    NSASpook, like you said about buying cheap Chinese equipment not being the way to go.....I don't want to buy throw-away components either or components with low efficiencies if higher efficiencies are available.

    Another basic question I have is......
    Can anyone recommend some good quality MPPT unit manufacturers or places that sell good quality solar PV equipment. This is really where I could use the advice of someone who works with this equipment. I don't want to buy knockoff junk.

    I also don't know how reliable eBay is for buying electronics equipment beyond basic components unless someone is trying to buy used reputable equipment at a good price.

    Maybe my approach here is wrong with me writing too much, maybe this site is or more geared towards more complex subjects for electrical engineers and the actual circuitry (after all, the title of it is All About Circuits right), and maybe me being an amateur is holding the discussion back. I have a textbook on PV systems

    (http://www.amazon.com/Photovoltaic-...0&sr=8-1&keywords=photovoltaic+systems+dunlop)

    I need to finish reading it but I don't think it will provide the answers to some of the specific questions I have brought up here. Thanks for the responses that I have been getting though. It's not like anyone has to help so I still have to appreciate people taking some time out to respond.
     
    Last edited: Dec 24, 2013
  20. Vortex-8

    Thread Starter New Member

    Dec 20, 2013
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    .....oh I left out also.......

    Maybe someone could direct me to a good website or forum that is more geared towards PV systems in general?

    That may be more appropriate so I can search through information to try to read and find out the answers to the questions I have instead of asking other people.

    As far as companies to purchase equipment from, I am somewhat clueless. Amazon sells PV equipment but I'm not sure if they list a wide enough selection of components. I don't know who the good MPPT unit manufacturers are. I am skeptical of eBay for this kind of stuff since I don't have the background. I don't think Mouser and Digikey deal in this stuff specifically. This is part of where I'm lost.
     
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