constructing a smallish, stand-alone solar powered electric source

Comments

• stamptrol Posts: 1,731

  2010-06-15 18:19 edited 2010-06-15 18:19

  Start out by looking for the Energuide figure for a fridge like the one you want to run. That will give you an idea of the required Kwhr per month in normal operation.
  
  Depending where you are in the world, look up the solar insolation for the least-sunny month of the year. You can also check on the number of sunny days you have to decide on how long your fridge has to run on batteries. The hours of sunshine and the area and efficiency of your panels will determine how much of the sunshine gets converted to electrical energy.
  
  You can work out a rough storage capacity by knowing your installed amp-hours of battery and the system voltage. Books by Michael Hackelman put it in easy-to-understand, barnyard terms.
  
  Use some of the "living off-grid" websites to get a feel for what works in practical terms.
  
  Not a trivial or inexpensive project, but a great learning experience!
  
  Cheers,
  
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  Tom Sisk
  
  http://www.siskconsult.com
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• davejames Posts: 4,047

  2010-06-15 18:37 edited 2010-06-15 18:37

  Thanks Mr. Sisk,
  
  I'll check Hackelman's books - "barnyard terms" is good!
  
  Living in the south San Fransisco bay area offers many, many sunny days during the year. And the ONLY item that must remain "on" is the fridge. Granted, the cost of the solar solution may swamp the savings from not being tied to a utility; especially for such a focused objective.
  
  But, that's what I'm attempting to figure out.
  
  
  Regards,
  
  DJ
  
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• Beau Schwabe Posts: 6,572

  2010-06-16 01:49 edited 2010-06-16 01:49

  davejames,
  
  Look into grid-tie units also ... not to tie back into the grid per say, but these units make it easy to 'tie' literally several units together. In other words, you can spend a lot of money buying a single Sinewave inverter capable of delivering several thousand watts, but if the unit goes down you are SOL.
  
  If you want to go completely off-grid you can still use a grid-tie inverter despite what the name implies. Here is how: Use a single true-sine wave inverter as your 'master'. It does not need to be huge 300-400 Watt is fine, but it must be a true-sine inverter. I would scope it just to make sure, Chances are that the clerk behind the counter would know anything. Modified-sine or anything else simply won't work. Now for your 'slaves' use a grid-tie inverters (these are all sine wave), as many as you need to get the power demand you want. Again, these don't need to be huge 300-400 Watt is fine. With this type of a setup, if of the grid-tie units go out, it won't kill the entire system, and it's cheaper to repair.
  
  
  Edit:
  
  Something else to consider is the efficiency of the converter(s) itself. The grid-tie inverters that I have currently run at about 85% efficiency directly from the panels ... For example, I currently have 615 Watts of Solar panel on my roof and on a bright sunny day I 'see' 520 Watts ... I know this because I have a meter and have been able to measure at least that much.
  
  Also, I don't know what the haze conditions are there in San Fran, but I know that in the mid-west even what appears to be a bright sunny day, the solar panels will tell you otherwise. And it's not pollution in the air, it's humidity that can lessen the efficiency. ...So there are many things that need to be factored in when applying your solar panels.
  
  Here is food for thought... If you simply turn 'off' the equivalent of a 100 Watt bulb that would normally be on
  24/7 and eliminate that amount of usage. You would save 2.4kWH per day ... 876kWH per year <--- I say that, because in many cases it's easier to do something like that than to add a solar panel. You could of course do both
  
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  Beau Schwabe
  
  IC Layout Engineer
  Parallax, Inc.
  
  Post Edited (Beau Schwabe (Parallax)) : 6/16/2010 2:36:52 AM GMT
• davejames Posts: 4,047

  2010-06-16 18:01 edited 2010-06-16 18:01

  Mr. Schwabe,
  
  Thank you very much for the input - the "I've done this" aspect is very helpful.
  
  My wife and I are out of the house for the majority of the day, so there's not much going on electricity-wise. I guess I could do an experiment and see what happens over a few weeks by turning off completely the computer monitors (LCD), unplug the 2 computers, unplug the TV (CRT), VCR (yup - still lhave one!), DVD, and digital tuner. All of these have "stand by" modes. Other than that, it's the fridge that remains on.
  
  
  Just looking for more ways to be "green" - meaning, save the green in my WALLET!
  
  
  Later,
  
  DJ
  
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• stamptrol Posts: 1,731

  2010-06-16 19:20 edited 2010-06-16 19:20

  Along those same lines of thinking, if the fridge door stays closed during the day, it won't run much anyhow.
  
  As an early experiment, hook up a timer to monitor the fridge run time or energy consumption during the day.
  
  After all, its better to be smart and green; using electricity for the preservation of food and avoidance of food-borne disease is a pretty good use of resources!
  
  Urging your town to turn off unnecessary lighting and encouraging car-pooling, walking and cycling has a large "greening" effect for us all.
  
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  Tom Sisk
  
  http://www.siskconsult.com
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• Lawson Posts: 870

  2010-06-16 21:09 edited 2010-06-16 21:09

  Whenever I think of making anything solar I think of reducing energy consumption first. Some extra insulation around the fridge would cut heat gain so the compressor will run less. Improving the air flow over the condenser will make the cooling loop more efficient so the fridge coos more each time the compressor runs. Might also find a way to dump the heat from the fridge outside so it won't make the house air conditioner run.
  
  Once on solar power, you might not need batteries. A couple of gallons of frozen salt water in the freezer should work just as well to keep food cold all night. (might still need a bit of power for fans)
  
  Lawson
  
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  Lunch cures all problems! have you had lunch?