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System Size - Totally Confused

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  • System Size - Totally Confused

    I am in the process of evaluating solar and have had a number of companies prepare proposals. We live in SoCal and the house has a perfect 180 degree south facing with almost no shade issues. Our annual usage is about 14K kwH, with the peaks in July/August of about 1,800 each month. Overall, I don't see our usage changing much as we already have two electric cars. If anything, it might be reduced slightly as we are going to install an energy efficient roof with insulation as part of the move to solar and we just put a whole house fan in to reduce the need for AC on cool nights. I have had system sizes recommended from a low of 6.96 kwH to a high of 9.5 kwH. At the low end, they are estimating base production of about 11K kwH, but say that the system will actually produce about 106%of that amount. Overall, they are recommending that I should be in the low 90's % of my needs, i.e., never produce more than you need. SCE does not do anyone favors on over-production, so I tend to agree with this premise. At the the other end, I am being told that I should size a system to produce the full 14K kwH of my estimated usage. They believe that once I move to solar, I will actually use more than I am using now. I don't know if it makes any difference, but I am leaning towards using the LG335NIC-A5 panels. They are rated at 335 watts and have an efficiency rating of 19.3%.

    Thanks,
    Dave

  • #2
    1.) Download a free "Solar Power Your Home for Dummies", or buy an updated/revised version at bookstores/Amazon for ~ $20.
    2.) Get familiar with SCE's tariffs. You will be on T.O.U. soon and those rates and times are much less favorable to PV users than in the even recent past.
    3.) Download and run PVWatts. Read the help/info screens a couple of times before making any runs.
    4.) Under T.O.U. be aware that, depending on your hourly use pattern, perhaps a system that produces less than 100 % of your annual use, may offset 100 % of your annual bill.

    There are few one word or one sentence answers. Do 1 to 3 above and come back and ask informed questions to fill in knowledge gaps beyond the basics.

    Get your own answers. Most of this stuff is far from rocket science.Relying of those w/skin in the game for advice is letting the fox guard the henhouse.

    Welcome to the neighborhood and the forum of few(er) illusions.

    Comment


    • #3
      Originally posted by CLLACAB View Post
      . At the low end, they are estimating base production of about 11K kwH, but say that the system will actually produce about 106%of that amount.
      Trust NOTHING that the SAY, trust only what they put in writing.
      Contact someone with a similar sized PV Array in your area and
      ask to see and read their actual KWHr PV generation on their 12 Monthly Electrical Bills for an entire year.
      Then, and only then, will know the facts.

      Comment


      • #4
        Originally posted by NEOH View Post
        Then, and only then, will know the facts.
        Or, if you're real lucky, maybe a few of them.

        Comment


        • #5
          All depends on what your goals are: Most cost effective? minimum use of grid power? lowest cost? ability to expand? storage ready?
          My guess in your case is to put in a max sized inverter (7.7kW) that is capable of adding batteries on in the future, and start with a comfortable size array that you can add on more to later if you want. Yes, LG panels are some of the most high-efficiency PV panels, but are also expensive - there are many other good brands with just as good durability and reliability at a much lower cost/watt if you have the roof space to fit a few more.
          BSEE, R11, NABCEP, >1200kW installed

          Comment


          • #6
            Originally posted by solarix View Post
            All depends on what your goals are: Most cost effective? minimum use of grid power? lowest cost? ability to expand? storage ready?
            My guess in your case is to put in a max sized inverter (7.7kW) that is capable of adding batteries on in the future, and start with a comfortable size array that you can add on more to later if you want. Yes, LG panels are some of the most high-efficiency PV panels, but are also expensive - there are many other good brands with just as good durability and reliability at a much lower cost/watt if you have the roof space to fit a few more.
            I'd suggest goals can be identified better with more information and knowledge. Getting more information before making decisions can lead to better goal setting.

            If the OP is like many/most, minimizing the long term cost of providing reliable electricity in an quantities necessary and consistent with lifestyle choices is often one usual goal.

            More information and the knowledge such information brings can help point a path to such goals.

            Comment


            • #7
              My usage almost mirrors yours. A couple of installers was suggesting I go with a 7kw system but that was partly based on using the utility bill credit within about 7 years. In other words, those would have been intentionally undersized but still obtain the max credit available. Running the numbers @ 8.4kw, the projected yearly production was coming close to my yearly usage. Some months I don't produce enough and some months I should over produce some. However, considering the insolation charts I have seen, CA gets more sun than TX. I also have zero shade issues.

              As my system is only a couple of months old, the jury is still out as to production vs usage. It looks like I will be a little under the projected. Counting degradation and heat issues I should stay a little short of actual usage. One thing though, I'm trying to shift most of my usage while the panels are producing so that may help from an under production standpoint. No TOU issues here currently or projected AFAIK.

              If I were to make a suggestion, perhaps 7-8kw system with a 7.6kw inverter and then evaluate it for a few years and add panels later if needed. PVWatts is a good place to start but it is only an estimate and does not take into account any shading issues (from what I have seen).

              I too agree that using 330w, 19+% efficiency panels may be a bit more expense than is necessary but it is your money.

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