How do I determine the kW system I need?

Discussion in 'Alternative Energy' started by SkizzlePig, Jun 25, 2006.

  1. SkizzlePig

    SkizzlePig Well-Known Member

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    Sandhills South Carolina
    After confusing several of you and certainly myself, I grabbed an old electric bill to determine our actual usage. Now, I don't have any clue how to translate this usage in the necessary size for a solar array.

    Here's what my bill indicates as my usage:
    May 2006: 1117kWh

    Daily average looks like it peaked in winter at about 42kWh per day.

    So, what does this mean for a solar system?

    Any help would be greatly appreciated. Thanks!
     
  2. JAK

    JAK Well-Known Member

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    New Brunswick
    That sounds reasonable and typical of most people on the grid. As usual you will want to reduce this before switching to solar or wind power or generator.

    Lets say you are now 1200 kWh/month as a year round average. At $0.08/kwh on grid that would be about $100/month, which is reasonable. If you get that down to 600 kWh/month, and go completely off grid at $0.50/kwh you will end up at $300/month over a 20 year life cycle, considering time value of money and all that. So there it is. Half as much energy for 3 times the money, and you get to pay for most of it up front. Sounds a little nuts, but no more twisted than a lot of other quirky things people do like commuting to work on the opposite side of the city in an SUV. :)

    Same thing only different.
     

  3. JAK

    JAK Well-Known Member

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    Joined:
    Oct 15, 2005
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    New Brunswick
    To answer the question more specifically.

    You are doing well to keep you winter peak not too much high than yout annual average. In Oregon you will still produce considerably more solar power in Summer than Winter. Let's say twice as much in Summer. So it would be reasonable to say that you system would cost twice as much if you want it to provide all you power year round and you will be throwing away half of what you produce in the Summer. That would be OK if solar energy was cheap, but it aint.

    Most likely one would reduce there summer demand down to say 24-36kwh/day and size a system that produces that much power on average in Summer. In Oregon you might average 8 hours of full power in Summer and 4 hours of full power in Winter. So that would mean 3000watts for a 24-kwh/day system, which is $15,000 for the panels alone, the greatest expense. If you still wanted 24-kwh in Winter you would spend $30,000, and I think you would still have some trouble. If you want to be completely off grid year round, and don't live in Phoenix, most people would get a small diesel generator system to produce up to 24-36kwh/day in winter. At up to 8-12 hours/day that would be 3kw. There are a lot of other advantages to such hybrid systems, such as allowing you to reduce battery storage somewhat, and also reduce your initial capital cost. If you have a high hill you can add wind power also, but it will add to your battery storage needs unless you keep it in balance with the others. One of the advantages of wind power is it can cost less, and it is something that can in theory be home built easier than the other two.

    Still, in theory 10% of the total value of a property doesn't seem like all that much if it would mean a system that provided all your energy needs. That might be $10,000 for a $100,000 home, or $100,000 for a $1,000,000 home. This is only in theory of course, because such systems need to be self-financed, and probably for good reason. I am not against banks not financing such renewable energy projects. I am against bank financing in general. :)

    Besides money, one of the reasons to reduce you energy needs before switching to off grid is because installing and operating and maintaining such a system is time consuming, and the novelty wears off once it becomes a job that is making everyone money but yourself. So most people would find that all of those so called conveniences of modern living are not only unneccessary once you are off grid, they are also not all that convenient. I think everyone eventually finds their own balance to suit their own needs. If you have lots and lots of money you could hire someone full-time to care for a very large and efficient system. Most likey that person would have drive to work and live on the grid, so there you are. :)

    Some people save 8 times more money by burning 8 cords of wood.
    Some people spend 8 times less money by burning only 1 cord of wood.