Solar powered coffee maker

Discussion in 'The Projects Forum' started by risus, Jun 29, 2012.

  1. risus

    Thread Starter New Member

    Jun 6, 2012
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    [Warning this is a long read but it is fun if you like these sort of projects. I am listing my plans in detail before the questions, skip to the bottom if you just want to see them. And please use constructive advice and don't rant about how wrong everything is.. its just a geek project I wanted to do :cool:]

    STORY
    So my company moved buildings and the new building is LEED certified so they outlawed personal electronics including coffee makers. Problem is, what they do serve in the break rooms is really crappy. It's free I know.. but it's also terrible.

    Soooo I built a solar powered coffee maker on some basic numbers and through testing it I have a few <ahem> challenges :rolleyes:. It's been about 15 years since I worked with power conversion and circuits like this so I'm novice but rusty.

    PLANNING
    Ok here is what I have.

    I like the Keurig systems.. the coffee selection is awesome and the brew consistent. Plus one cup at a time would save on over all power and Ah needed. (for those concerned about recycling k-cups, I found a way to recycle.)

    So I got the Keurig B140 k-cup
    http://www.keurig.com/brewers/b140

    I saw that it was rated at 700w.

    The time it takes to brew 10 cups [not all for me :p] came out to around 30 minutes a day (I'm just assuming constant 700w but it is not 100% of the time)

    So I think that would be 70 watt hours needed for 10 cups so I purchased a 10watt solar panel which could charge 14 watt hours per hour at 100% or 7 watt hours per hour at 50%.

    http://www.amazon.com/Solar-Battery-Charger-Charge-Controller/dp/B006RE2KL0

    Ok for the inverter I saw that they have a .5amp constant draw with a percentage of efficiency with power inversion. 12*.5 = 6 watt draw (I have it switched so not to constantly drain) so to add all that up for the total watts 6 watts + (700 watt load / 0.85 inverter efficiency) = 830.5 watts total

    830.5watts / 12 volts = 69.2 amps draw from the battery.

    69.2 amps * .5 hrs = 34.6 Ah / 10 cups of coffee = 3.46 Ah per cup. So I figured I could get by with these.

    http://www.amazon.com/gp/product/B001TE0IMG/ref=oh_details_o03_s00_i01

    http://www.amazon.com/gp/product/B006LO7LV0/ref=oh_details_o01_s00_i00

    CHALLENGES
    1. The battery will be fully charged and show about 15 volts 14.5 rested. I start the coffee maker and the heating element turns on. The inverter and fan kick on and drop the voltage to about 12.5 and the fault light on the inverter turns on and the unit resets cutting power to the coffee maker. Click click click click.. that sort of thing.

    2. The sun that I get at the window is indirect and it stays between 11 - 15.5 volts throughout the day.

    3. I think that although I was going for 10 cups with my specs, I would be lucky to get 3 cups with some of the testing I've done over the week.

    QUESTIONS
    1. How bad off was I? :)

    2. I think I am going to get another panel and battery.Would another panel wired in series to help keep the voltage up and wire the controller it comes with a good idea? Or would I want to look to get more wattage in a paralell configuration for the duration of the day it is above 12 volts.

    3. Would getting another battery help sustain constant load to the inverter while the heating element is on so that it wouldn't fault? One other thing is the 8 gauge wire I have on it gets pretty hot, not melting but hot to the touch.

    4. I have considered a super capacitor as probably my best option to get the inverter working but still not sure I could get all the cups of coffee I want throughout the day.


    Let me know if there are any details I left out or could be helpful. Any insight is greatly appreciated!!
     
  2. Sensacell

    Well-Known Member

    Jun 19, 2012
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    I would say you are off by a factor of 4 in real-world terms.

    If the battery and panel you have now cannot support the load- double it.
    Then imagine 6 months from now when the solar panel is dirty and the battery is getting tired... double it again if you want it to continue to function and not be sadly idle- which would be an epic environmental travesty considering the situation.

    Just the idea that you are banned from having a coffee maker, in the name of "green architecture" kills me. You valiantly try to overcome the situation with the ultimate green solar solution- and look at the pile of technology it requires, and it still barely works. With all the energy (water too) that was consumed making all that hardware, you *might* break even in 20 years, but long before then, all that stuff will be leaching toxins into a landfill somewhere.

    IMHO- Green Technology is a myth.
     
  3. Markd77

    Senior Member

    Sep 7, 2009
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    I don't think you are ever going to charge the battery with solar and indirect sun. The power rating of the solar panel is for direct sun at midday, you will be lucky to get 1/10th without.
    With a bigger battery and thicker wires you might be able to brew a few cups, but you would have to take the battery home and charge it every day.
    My suggestion would be to make the coffee at home and use a vacuum flask to keep it warm.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    A perfect example of good intentions gone bad.
    Banning coffee machines/personal electronics is just STUPID..

    Funny how Starbucks roasting plants are LEED certified.
     
  5. wayneh

    Expert

    Sep 9, 2010
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    One concept sorely missed here is that the end-to-end efficiency of sunlight-to-consumed-electricity is under 5%. The panel itself is 11% at best, the battery charging/discharge process is 50% at best. Throw in an inverter and other losses and you're making a terrible waste of good sunshine. It's tolerated when there's no better alternative.

    If all you want is hot water, all that good sunshine should be used to make heat directly. You could probably capture 90+% of the heat you need for hot water with a passive collector such as a gallon glass jug placed onto a black surface in direct sun. Save your precious electricity for running the pump and the electronics.

    Feed your Keurig with pre-heated water and it becomes stunningly efficient, even if it is grid-powered.
     
    boomerlar and #12 like this.
  6. #12

    Expert

    Nov 30, 2010
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    I too rant about solar. The last time I did the math, it would take 75 years to sell enough electricity to pay for solar cells that have an estimated life of 20 years. So I say which is more ecological: Water running downhill in Tennessee or hundreds of pounds of exotic metals in the dump?

    Fortunately? the local electric utility (where I own 30 acres) refuses to buy solar power from the customers. That surely shoots solar power in the head!
     
  7. wayneh

    Expert

    Sep 9, 2010
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    I pretty much agree, especially when you get to the political implications.

    But I think this thread is a good example of where the appropriate "green" technology can actually provide a solution. If the OP's building has a hot water supply that was produced as efficiently as possible (perhaps 95% warmed by a solar collector followed by a 5% natural-gas tweak), and he feeds his Keurig with hot water so that electricity is not wasted heating water, then he has nothing to worry about.

    The idea that heating water with electricity is OK because you've made your own electricity is a false notion. Once you have electricity, it's a fungible asset, like cash. It doesn't remember where it came from. If you proceed to squander it, it's no different than pulling it off the grid and squandering it.
     
    boomerlar likes this.
  8. wayneh

    Expert

    Sep 9, 2010
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    Interesting. Are they making some sort of moral claim, protecting the environment or such?

    Don't tell Algore! ;)
     
  9. BSomer

    Member

    Dec 28, 2011
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    But they will buy other sources of power from the customers, such as wind???
     
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Its "sun tea" time.. :)
     
  11. wayneh

    Expert

    Sep 9, 2010
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    Ha ha, yes, this is exactly what I was thinking of when I said "gallon jug". Last time I made some, the jug was almost too hot to carry into the house.
     
  12. crutschow

    Expert

    Mar 14, 2008
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    So how do you explain all the solar panels and wind generators in use? :confused:
     
  13. wayneh

    Expert

    Sep 9, 2010
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    That's almost pure politics (subsidies, tax rebates, etc.). A few folks need off-grid power but that's the exception, not the rule.

    Alternative energy is at LEAST an order of magnitude more costly than natural gas, so those panels you see are NOT about economics.
     
  14. risus

    Thread Starter New Member

    Jun 6, 2012
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    Thanks everyone for their posts so far, here are some of my responses.

    A travesty? :eek: Well so I'm not worried about breaking even and I'm not even agreeing with the LEED certification it is just the building I am in now and I want a coffee maker that is off their grid so that it doesn't violate their policy. I would run an electric cord to the neighbor as long as it got me my coffee!

    So there is a building right next door that reflects the light pretty brightly into the building. And because of the LEED stuff we have big light flowing windows so I seem to get a good voltage and I did most of my calculations at 50% of the panel output. I do need to figure out what the watt output is I have that on my list.

    I bring coffee from home from time to time but I like the idea that my team and I can just brew whatever flavor whenever.

    Yeah we have flushless urinals,, you don't want to get me started about how lame this is. But still I can't change, I've /we've tried. Also as I understand the rules Starbucks can be LEED as long as they are not plugging in more than what is needed for the business to operate. And yes I pointed out that coffee helps me operate the business hehe :)

    NICE! I like it. Now this is in an office setting and limited to what type of light comes in but I am definitely going to do some research about how I can reduce the heating time needed.

    ---------------------------------

    OK so final note to everyone is that I'm not professing to make a green technology or appliance, I don't care if it is technically efficient or has a ROI as long as it works. I don't like that I have to do this other than I get to geek out on something I grew up with (I do software now), and I don't really care about the politics involved or what will work for an entire nation. My coffee maker will save the world in other ways.

    The LEED certification is just what I'm dealing with. There are tons of contradictions and inefficiencies I have identified in the building. For instance the water has a sign that claims to save 40% more water but really they just restrict it 40% which if you are running it and not using it is true. But I work with some fairly responsible people and we don't just let the water run.. so really this translates to 40% increase in the time it takes to fill our cups :confused:

    Does not have to be solar powered necessarily thats just what I started with, and I think wayneh had a great post because I'm having fun with this and if I have to build a solar water heating unit and pump it to the unit I will! I've even thought about an exercise bike with an alternator, or another hand crank type unit. Yeh it would be a workout for sure ;)

    Best way I can sum this up is I want a cup of coffee using the keurig system, and I don't want our facilities to cite me on using company grid. As I am writing this I am drinking a cup from this solar system,,, and it is good :)

    One other thing I have not heard about is peoples thought on using the super capacitor to power the inverter. I realize if I heat the water I won't have to worry about dumping so much power at once for the heating element but thought I would ask anyways. I was also suspicious of the inverter I was using and weather it was faulting prematurely or possibly if I could be using a better inverter. I thought about cracking that thing open and putting better heat dissipation and reducing the fan run time.

    Anyways thanks for the posts everyone.. I have some things I'm going to test out and try. Keep it fun! :cool:
     
  15. wayneh

    Expert

    Sep 9, 2010
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    If your current system is even close to working now, then preheating the water will take you across the goal for sure, since heating water takes the bulk of the energy needed by the Keurig. If all you want is coffee, you can probably just draw hot water from the tap and away you go. Assuming they don't ration your hot water, too!

    Forget the supercaps. Big, expensive, and nowhere near as good as a battery for this application.
     
  16. risus

    Thread Starter New Member

    Jun 6, 2012
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    The super cap I would use inline with the battery to supply the instantaneous load needed on first heating. It's the inverter that's getting titchy and starts faulting with the first load after a period of not brewing, and if I brew two in a row the second one (now that the water is mostly heated) is far smoother so I think your right, the more pre heat I can get the more efficient the overall power consumption will be.

    The break rooms where the hot tap water would be are about 100 y - 150 yards away so what I did is got a portable filter water canister and a pump. The idea is when the water light goes on it will trigger a photo sensor on a 555 timer (I have a slight issue with that I'll bring up later) and run the pump for 1.3 seconds which is enough to fill the reservoir to max every time.

    Soo I'll need to find a way to more efficiently heat what is in the heating chamber since it fills from the reservoir after a cup is brewed. But I like the idea overall. Nice call blue ;)
     
  17. wayneh

    Expert

    Sep 9, 2010
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    If you do the math to convert stored electrical energy into hot water energy, you'll find that even a "super"cap holds relatively very little.

    Each gram of water requires approx. 1 calorie to raise the temp by 1°C. So 2L would need 20,000 calories to go up 10°C. That almost 84,000 watt•sec. A 700W heater would need about 2 minutes, which sounds reasonable.

    I leave it to you to calculate how much energy a supercap could deliver. You know my prediction - a drop in the bucket.
     
  18. risus

    Thread Starter New Member

    Jun 6, 2012
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    Heh indeed. Thanks for the advice!
     
  19. wayneh

    Expert

    Sep 9, 2010
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    BTW, I think many visitors to this forum could benefit from seeing your project, limitations and all. Many come here hoping to get far more power from their small PV panel than is realistic. A "real world" example like your's would be a great thing to point them to. Consider posting it in the "Completed Projects" area.
     
  20. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    Have you seen all the "water cooled CPU manifolds" geeks are using in their PCs these days?

    Maybe you could hook a few PCs up as a water heater or at least as the pre-heater? ;)
     
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