Friday, April 17, 2015

Project Solar

I started doing some research into going solar at home. Not off the grid solar, but grid-tied solar. There are two basic types - off-grid and grid-tied. With off-grid, there are two options with or without batteries. Go without batteries if you're only interested in using electricity when the sun shines. Perhaps the whole house wouldn't be off-grid. Maybe only a sprinkler pump or something would. Off-grid completely likely means you'll need batteries, lots of them if your area doesn't get much sun. Grid-tied means you can have year-round power from multiple sources (the grid and your solar array). Grid-tied also means that you can sell the electric company your excess. Tying in with the grid means a few things, first you have to register with the electric company. There are certain compliance constraints that don't seem unreasonable. Some basic jabbing around the web turned up some good information. Some things were a little surprising actually, but make sense once you know how the cells work. Solar cells are gates. When the sun shines the gates open letting the electricity flow. All the cells in a panel are hooked together in a series. Think of a channel with locks for ships to pass through. If any of gates are not receiving sun, the whole panel is useless. A partial block reduces the effectiveness of the whole panel by half. Any shadows are bad, even from bare branches. Besides the financial considerations, I'll need to consider any technical constraints such as shadows, trees, arc of exposure during peak and off peak sun (summer and winter). This will translate to output which would equate to return on investment. A kit with an array of 10 270 watt panels costs about $6k for the equipment. There is a registration fee for the electric co. There would be incidentals, plus electrician to hook into the grid. Rough estimate for DIY (except the tie-in) is $10k for a system rated at around 400kwh/month with 5 hours of sun per day. I split that in half to 200kwh/month for my forecasts. Could probably refine that and adjust for seasonal differences. Without A/C my monthly usage is 800kwh/month. The electric co pays wholesale prices for electricity. One possibility is to take an option for $1k and set up a single off-grid panel and use it to charge batteries for light usage. Perhaps the garage can run on that or something. In that case it might be useful to have the battery system. Could be cost prohibitive if cut-overs are involved. It would be nice to have one in place to see what the actual output is for different times in the year. In any case, I believe that this would not yet be able to tie into the grid. There were implications that at least a 2000W rated system was necessary for selling to the grid. Perhaps there is a difference between grid-tied and selling back (also known as net metering). Next steps - - get wholesale price - price of application - can < 2kw systems be grid-tied without selling back? - measure space and arc of visibility - get hours of sun for locale - any local codes? This is going to be a three year goal since I have other things going on. I'll be looking to post follow-ups as things move along.

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