home solar pv system queries

Discussion in 'General Electronics Chat' started by robert.guttormson, Dec 27, 2010.

  1. robert.guttormson

    Thread Starter New Member

    Oct 3, 2009
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    Hi everyone,

    I am conceptualising a solar system for my home. The wattage it needs to support is 4kw. In this context, i had some questions regarding connecting with the grid. First of all I dont plan to install net metering as i dont plan to feed electricity back into the grid. What i am looking at is a pv system (panels + inverter) feeding power into a distribution panel. The distribution panel also has input AC from the utility. I need to know how i can accomplish prioritising usage of solar power over utility AC when the total amount of load is less than 4 kw. In other words, I want my home to first utilise solar power and start using utility power only when the demand from the loads goes beyond what the solar power system provides.

    Any pointers/links are welcome.

    Best,
    Bob
     
  2. iONic

    AAC Fanatic!

    Nov 16, 2007
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    In other words you need to connect the "grid" when you do not have enough power available?
     
  3. blueroomelectronics

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    Jul 22, 2007
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    You need a Grid Tie Inverter. They start around $5k
     
  4. robert.guttormson

    Thread Starter New Member

    Oct 3, 2009
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    Well yes i need to draw power from the grid when what the solar system is generating is not enough. But my confusion is with regard to prioritisation of usage of pv power, I need to first use my pv power and then use the rest from the grid.

    Going for grid tie inverter is not in my reach and i plan to go for a cheaper off grid inverter.
     
  5. retched

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    Dec 5, 2009
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    ATS

    or Automatic Transfer Switch will switch between the Utility company and your solar array once the conditions of the switch are met.


    If your current draw hits 70% of your available PV power, then the ATS can switch to the POCO (POwer COmpany)

    Are you going to charge batteries or with the solar while the POCO is being used? or something else?

    Why not use a grid tie and become a Customer Generator.

    Any power you are not using would be sold to the POCO resulting in credits against your bill.

    Look into the enphase micro-inverter system.

    1 inverter per 2 panels, auto grid-tie and full regulation. It also data-logs performance of EACH panel over time and at a time.
     
  6. robert.guttormson

    Thread Starter New Member

    Oct 3, 2009
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    Ahhh ATS was what i was looking for. Thanks a lot. There are a couple of problems with the Grid tie inverter schema, first is it is expensive, second is the location of this installation. This is for a relative's home in Nicaragua and there is no clear set of guidelines from the utility on feeding power back to the grid. I will revert back after googling for ATS. Thanks once again.
     
  7. retched

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    Im here to help... and be helped ;)
     
  8. marshallf3

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    Jul 26, 2010
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    Here's one of those cases a good old telephone can be your friend. You may find that, through a few simple phone calls, that your local power company may be more than willing to help out, often even giving you cash rebates back for taking the effort to do this.

    When we finally decided the best method to convert from the HID lighting in our warehouse over to the very new CFLs that will run directly off of 277V they sent a guy out who looked over our plans and we're going to end up with a cash check outright that will more than pay for the materials involved in the conversion so long as we stick to our own labor which is totally doable for me and my helper.

    Thank goodness I've got him. I didn't used to have a fear of heights until I fell off a two story roof and severely messed up both my ankles. Over the years I've worked my way up to where around 18'-20' doesn't bother me on the large (not one of those flimsy ones) scissor lifts I bought a while back but it still seems like getting all the way up to the 26' I need to be in for a majority of the areas is still just too far over the edge for me.
     
  9. thatoneguy

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    Feb 19, 2009
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    I don't like heights, but I really hate being close to the ceiling in a lift. Guy on the ground running it though I said "bit more" when I said "hold it", if I hadn't ducked, I'd have gone through the ceiling instead of the lift denting it. I've stayed away from any that don't have the remote since.

    On Topic: In a country with spotty power, biggest thing would be to get GOOD battery banks and a proper charge controller, not just a bunch of old car batteries tied together connected to an old UPS. At low usage levels and with a lot of sunlight, a good PV array can run a good deal of stuff. Put high draw items on the grid breaker panel, and lower draw/necessary items on the PV Array breaker panel and outlets.
     
  10. marshallf3

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    Jul 26, 2010
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    Yea, mine's remote and I can actually drive the thing around while it's up in the air but if I do it has to be for a very short distance and at a very slow speed or I get nervous. It has a huge work platform on it thus it's built a lot sturdier than most, however it still has a little sway to it when you're up at any distance.

    Ideally you'd want to find a still fairly good forklift (traction) battery for a big PV system but the 6V golf cart batteries are fairly reasonable in price and deep cycle by nature. Very few know this but our local "Pull-A-Part" auto salvage yard sells the batteries out of the cars they buy for $10 or so and if you hit them up at the right time you can find several that haven't even seen but a few months of use before someone gave up trying to fix whatever was really wrong with the car.
     
  11. timrobbins

    Active Member

    Aug 29, 2009
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    You run into a variety of compromises if you don't want to do a normal grid-tie scheme (ie. have an arrangement with the power company, and have a fully standardised grid-tie inverter). One issue is that pv modules are expensive so you probably want to use every W from them. But that means special switches and a battery or heat storage scheme (that all come with the need for controls and expenses), and short breaks in your mains supply, and limited peak power ratings for starting certain loads, and....
     
  12. iONic

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    Nov 16, 2007
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    All the added expense of managing grid tied systems tends to nudge one in the direction of all-or-none. In other words grid free or no tied PV sources with separate distribution boxes. Just a $5K expense for a grid tied inverter could take years to pay back depending on your electricity costs.
     
  13. retched

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    Dec 5, 2009
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    BUT as the OP said.. This is going to be installed in Nicaragua.

    Good luck finding details, or a POCO giving out free grid-tie equipment.
     
  14. marshallf3

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    Jul 26, 2010
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    Yea, that could prove to be quite the problem as they'd probably prefer to just sell you the power rather than worry about reducing the strain on their grid. The philosophy of our local power company is two fold, they love to brag about anyone that's done something that substantially reduces their electric bill and in return they get paid back by not having to add capacity to it. I think my two huge outdoor ground mounted transformers are about 5' cubes but then again they convert what I think is around 20KV 3 phase incoming down to the 480V 6,000A 3 phase that can be drawn from each of them.

    As I look at last months utility bill we used 156,800 KWh and my power factor was 97% - far above the penalty level for falling under 85% but I can also see from the previous bill that I saved almost $3,000 during the summer by participating in the "time of use" program. We share the building having around 63% of the warehouse and 60% of the office areas so the bill is divided up between us in a number of ways as we've got individual meters on some of the distribution panels so it can be separated with a half decent set of formulas. We're hoping the other company will go under or move in time as at the rate we're growing we'll probably need all 100% of the 234,000 square feet within a couple of years. Oddly enough, if we have another cold winter my natural gas bill is going to exceed my electric bill but my main boiler is only around 70% efficient and I rarely ever use the other one as it feeds an area of the warehouse that's in the center of the building thus it doesn't get that cold in there due to the surrounding areas being heated. I've got a fair amount of free-hanging heaters in some of the warehouse areas as well but they rarely need to be used either, when the people in those areas are working they prefer it to be fairly cool.

    When I get my roof cooling system into operation this spring I expect even further reductions on the KWh I need to feed my main chiller and in time I hope to get the city to pull in another 4" main for me so I can cover a lot more of the warehouse area with roof cooling as only a small amount of it gets air conditioning.

    I also have a 205,000 gallon water storage tank in the system that would allow me to charge it up with cold water during the off-peak hours and draw on it during the peak time of use period but since I don't have the chiller capacity online to properly use it and I don't cool most of the warehouse areas it would end up costing me money just to initially buy and maintain all the chemicals involved necessary to keep the water bacteria free and pipe corrosion in an unfriendly state. I'm squeaking by with a mere 90 tons of chiller capacity but I've got two 400 ton ones I could eventually bring back online with a lot of work and another large cooling tower outside. They're about the size of small locomotive engines and just looking through the full manual sets for them scares me.

    I've also got a plate heat exchanger I could be using during the winter to even further lessen the load on the chiller during the colder months by taking the heat out of the chilled water loop and directly transferring it to the cooling tower feed instead of relying on having the water to water chiller do that. Sadly I've got a small leak in it I may or may not have cured, just haven't brought it and the associated pumps back online to see if I've cured it. It wouldn't save me that much money anyway so I'm not in a big hurry to get it back online. Due to the way the air handlers operate and the fact that the company we share the building with requires chilled water for some of the process machinery they use I've got to keep the chilled water loop around 45*F even during the winter. The chilled water loop probably comes out to be about 3/4 of a mile of mainly 10" pipe not counting the 15 or so areas it's choked down at to go to the cold decks of the air handlers.

    Some day the company is going to get to the point that the extra money involved isn't going to bother them and cooling the rest of the warehouse will be attractive to them, that's when I'll have to get at least one of the 400 ton chillers back into operation and I've got water switching options for the East and South warehouse areas so they can run off their own chiller, in that case I'll probably find a nice used 150 or so ton water:air self contained chiller I can simply mount on the roof in that area but that in itself would be at least a $100,000 project when all is considered.

    When I get everything set back up to my liking now that my office has been moved upstairs I'll get one of my spare PCs back online that has pictures of some of this stuff and put them on my website, they can actually be somewhat scary to look at but nothing like having to deal with all of it in person.

    All in all, with a lot of help, since we fully moved in about 3 years ago I've increased the energy efficiency of the HVAC systems I'm using at present by nearly 40% but it was a mess to begin with with so many leaking control valves and little in the way of control systems. The previous business operated 24x7 so they didn't need to do much but maintain everything at a year round level, I've designed and installed a ton or electronic controls integrated into the pneumatically controlled systems such that I can pull selected energy drains to a minimum during the nights and weekends. Converting all the MH fixtures over is going to be an immense help as well and once I'm done this is going to be one heck of an efficient building considering it's around 40 years old and has virtually no insulation between the black membrane roof and the inside.
     
  15. thatoneguy

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    Feb 19, 2009
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    If you don't mind my asking, what type of business is this?

    Pics would be awesome, seems like quite a setup and an amazing level of power.

    Some of the larger local banks run their generators for 2 hours a day for a big discount on the bill. This has the side bonus of keeping the backup generators in good condition.
     
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Kind of hard to explain. We operate a 59 year old business that, believe it or not, designs, manufactures, produces, markets and ships designer children's & teen's socks, tights and slippers for almost every store in the US with the exception of Wal Mart, Costco & Target although we do a lot for Sam's Club. It would be rare to see our company name on anything as 99% is custom labeled for the stores so the products appear to be their own brand. Our home office and specialized warehouse operations are here although a fair amount comes off the boat and get shipped directly from California out to the customer's distribution centers. No order or request is too small for us so in addition to perhaps a million of something going out to one we've got a ton of orders that may only contain a few pairs of socks going to a particular small store. Although about as computerized as we can be it's a labor intensive operation to hand pick, pack and ship the thousands of smaller orders we fill in a week's time. We've got sales people and a few offices spread out over the US.

    Most product is contract ordered from textile mills overseas in about 26 countries but some is still made in the US. It's highly involved as once a design is finalized, approved etc it can take as long as three months for us to receive shipment after the initial order is placed and sample production runs are approved. Sometimes a product comes in that didn't get done correctly so we've got to hand re-package &/or re-label tons of stuff, that or there are some common lines we sell to several customers that we get in raw and label according to who they're going to right here. Some companies have to have specific oddball UPC code conventions, some are even specific as to different codes for different shipment dates on an identical product. A lot of these larger companies require every individual box to be labeled such that they can receive the pallets at their distribution centers then separate and distribute them out to their stores from there. It's highly complicated but somebody's got to do it and we're often thought of as the best in the business as we're extremely picky about quality and accuracy.

    So that's it in a very small nutshell. Luckily I have virtually nothing to do with any of that, I'm in charge of keeping the building in operation and making changes as needed as well as helping out on some of purchasing decisions related to warehouse equipment.

    The company we share the building with builds cooling towers for HVAC systems. These are really nothing more than heat exchangers that remove heat from the recirculating condenser cooling water side of liquid to liquid chillers and transfer it to the outside air. I'm sure you've seen plenty of these on larger buildings, they really boil down to the hotter water being pumped in at the top and then goes through a complex grid of baffles that break it up into droplets and the heat is removed by the huge fans that circulate air through them. A lot of companies make these but what this company produces is far more efficient and trouble free than most.

    I (and especially our MIS) has wanted a backup generator for ages just to power the server room. I've got an area outside that's ideal for one, has natural gas access and I'd only have to do a minimal amount of new wiring and changes to get that power to an automatic transfer panel in the server room. Seeing that we're growing and have to keep our eyes on every penny it's going to take a major extended power outage before it'll ever happen though, in the meantime he's got to deal with his UPS setups and shutting all the servers down should it ever happen.

    We've got some pretty darn reliable rock solid electrical service coming in and the worst scare I've ever had was when the power company lost one phase on their main lines, that sure played hell with everything for the short time it took them to get it fixed. People from other companies up and down the street were all out looking at the lines but of course that was no help. I never have traced down exactly where the substation is that feeds us but the only thing I could do was to call their emergency line and tell them that we'd lost a phase all up and down the street. I about went and killed the main breakers but it kept coming back as if they had a circuit breaker on that phase that was either failing or a load somewhere down the line was shorting out.

    What kills us around here is when we get a bad ice storm and a tree falls onto a live line but they tend to keep anything near them pretty well trimmed down on a regular basis. Mine comes in underground from the outside poles that are about 50' high but should a smaller step-down transformer somewhere on those lines fail in just the right way it's going to arc internally and create one heck of an amount of havoc until the fuses leading to it fail.

    Considering I've got the capability of about 1 MW from the outside step downs, limited to about half of that internally and I'm only using a very small amount of that capacity I tend to think I'm fine as far as my end goes. The building was previously occupied by a huge printing company that had an extremely high power demand so I've got plenty of 480 I'm not even using. I do have one area in the upstairs area of the South warehouse that is going to give me a problem in the future, I've got a 50 KVA stepdown to common 240/120 but barely have enough to feed it since the copper thieves stole some of the wiring out of the building while it was vacant for about 6 or so years. They got the main feed to the panel that provided for it so I had to get creative and took advantage of another run to feed it. It may be sufficient for them, then again it may not be as I've calculated the draw of that area and they aren't going to have much spare capacity at all. I may even have to increase the capacity of the common split system HVAC systems they've got up there and, if so, it's going to be a shock to the company to wire that distribution panel in the way it was originally much less buying a 75 or 100 KVA transformer that should have been there in the first place along with installing another common breaker panel. I suppose it may be cheaper to just add some additional HVAC capacity with a 480V unit but even then it's not going to be easy and that's not the way to do it properly. If I recall I've got 60A of 480 available to that transformer which would provide the full 50 KVA but it's running through kind of a "go here then come back there" setup that would by nature cause me to derate the true capacity. It will be a challenge but if my nimble little fingers don't like the temperatures I'm feeling when we take that area online, or if they need more capacity I'm going to have to call foul. I think I've got another spare 300A of 480 not far away but I'm not good at pulling that gauge of wire through conduit even using ropes and a forklift for the pulling and if I bring that panel online again I'd far rather have the extra capacity in it. I suppose, if need be, I could pull some #1 or #0 over to it on my own but I'd far rather have 4/0 in the event I need it somewhere else in that area. The major cost won't be the wire but replacing that transformer.
     
  17. thatoneguy

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    Feb 19, 2009
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    Sounds similar to K-Products, but they make shirts and stuff. I did a bit for them about 15 years ago. Lots of embroidery machines and sewing machines out on the floor.

    Wow, we got off topic. Sorry, OP!
     
  18. marshallf3

    Well-Known Member

    Jul 26, 2010
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    OT's no problem around here, it gets back to the topic when the original poster appears again.

    We don't sew or do anything like that although they did back in the early days and I've got an antique sock knitting machine to prove it. When you're selling around 4 million pairs of socks a year not to mention the other stuff I guess we keep a lot of the smaller countries rather busy. I hate to think that child labor is involved but I really doubt it is, most of the places we order from are huge textile mills that have the automated machinery to whip this kind of stuff out in no time at all. We hold a lot of patents and trademarks of our own but I'd say that most of it is conceived through a combination of our design and art departments along with the existing or potential customers.

    You'd never know it but if you've got anything from a newborn up to around 16 year old in your house chances are you've got some of our product. As I've previously mentioned, when I get the building into the shape I want it in and as automated as I can make it I'll be semi-retiring to where I can work a half day for them and a half day on my own projects. Given the 4,000 square feet I've got to work in, (minus all the equipment present) I've got tools, storage space etc that exceeds what I'll ever need. (and I've got tons more other storage space nobody's interested in) I have rarely ever brought one of my true Snap-On tools from home, I only buy the cheaper stuff for what I keep around up there and there's a ton of it considering the big stuff I occasionally have to work on. Profits on my projects will be minimal at first as I'll be investing in even more designs I need to get into production but in time I'll be feeding money back to the corporation targeted towards the needs and comforts of the hard workers we have out in the warehouse areas.

    Although warned many times upper management will be hesitant at first when they figure out what I'm doing but I think if they start seeing some returns they'll just leave me alone as they have for so many years.
     
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