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Comparing bids, hard to compare apples to oranges...

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  • Comparing bids, hard to compare apples to oranges...

    I've gotten 3 quotes from 3 different vendors for solar. I don't think looking at the total price (pre tax credit) is fair because some setups may cost more money, but produce more power.

    So I created a spreadsheet and ran some ratios as well:
    Vendor A (micro inverters):
    16panels - 4.720kW; 6,937 kWh annually with a 102% offset of my current needs
    Total cost: $24,225.40
    Cost per kW: $3.06
    kw produced per panel: 0.295

    18 panel - 5.310kW; 7,804 kWh annually with a 115% offset of my current needs
    Total cost: $25,199
    Cost per kW: $2.84
    kw produced per panel: 0.295

    Vendor B (optimizers):
    16 panels - 5.28kW; 7,854 kWh annually with a 116% offset of current needs
    Total cost: 20,189
    Cost per kW: $2.57
    kw produced per panel: 0.33

    Vendor C (micro inverters):
    16 panels - 5.7kW; 9,247 kWh annually with 94% offset (not sure why their offset is so low when they produce so much power)
    Total cost: 26,208
    Cost per kW: $2.83
    kw produced per panel: 0.35625

    14 panels - 4.5kW; 7,348 kWh annually with a 90% offset
    Total cost: $20,144
    Cost per kW: $2.74
    kw produced per panel: 0.32142857

    Based on the above cost per kW produced annually, I think VendorB is the best option. Am I missing anything here in my thought process?

    I'm also considering purchasing a battery at the same time. Mainly for backup purposes (selling back to the grid at peak times is a "bonus" and not my intention) since if the power goes out, I can't run the house on solar without a battery. (I guess a switch doesn't exist to cut power from being sent back onto the grid during outages.) Anyone have any thoughts on batteries and buying one?

    I'm in the San Francisco Bay Area if that makes a difference.

  • #2
    Hello noobie123 and welcome to Solar Panel Talk

    Sometimes a solar sales person will generate different kWh generation data so they can sell you more hardware. One place to check to see if they are giving you accurate data would be to go to pvwatts.nrel.gov and use the calculator there.

    If you decide to add batteries to your grid tie system you will need to have a different inverter then the ones that are being offered. Those Hybrid bimodel inverters are expensive and may not be worth the cost when you add the batteries.

    It is a pia that a grid tie system is turned off when the grid goes down but unless this happens a lot a cheaper action to have power is to go with a whole house generator. They will cost you a lot less money to install and run a couple of times a year then to go with batteries and a Hybrid inverter.

    Just something to think about.

    Comment


    • #3
      Originally posted by SunEagle View Post
      Hello noobie123 and welcome to Solar Panel Talk

      Sometimes a solar sales person will generate different kWh generation data so they can sell you more hardware. One place to check to see if they are giving you accurate data would be to go to pvwatts.nrel.gov and use the calculator there.

      If you decide to add batteries to your grid tie system you will need to have a different inverter then the ones that are being offered. Those Hybrid bimodel inverters are expensive and may not be worth the cost when you add the batteries.

      It is a pia that a grid tie system is turned off when the grid goes down but unless this happens a lot a cheaper action to have power is to go with a whole house generator. They will cost you a lot less money to install and run a couple of times a year then to go with batteries and a Hybrid inverter.

      Just something to think about.
      Hi SunEagle,
      If I do add a battery, the proper inverter is quoted in the price as well. So the cost is built-in if I do it now. The cost would definitely be higher if I add the battery later (new inverter and battery)

      Honestly a generator is cheaper to do. But harder to pull off as my wife won't know how to get it up and running if I'm not around.

      Comment


      • #4
        Originally posted by noobie123 View Post

        Hi SunEagle,
        If I do add a battery, the proper inverter is quoted in the price as well. So the cost is built-in if I do it now. The cost would definitely be higher if I add the battery later (new inverter and battery)

        Honestly a generator is cheaper to do. But harder to pull off as my wife won't know how to get it up and running if I'm not around.
        You did not mention the Hybrid inverter in your estimates and based on the low cost I figured they include only string or micro type which neither will work with a battery system.

        You better make sure they provide you the equipment information and cost associated with Hybrid inverter with batteries. Usually the cost will raise your blood pressure.

        There are whole house generators that will isolate the house from the grid and then start themselves automatically. The only thing you need to worry about is having fuel in the tank and the starting battery is ok. It will provide much more power then the batteries for a lot longer and for less cost.

        Comment


        • #5
          You are giving too much credence to their annual Kwh generation numbers. In order to win your bid, a vendor merely has to add another 1000 kwh to his estimate. If Solar PV systems generated exactly, or even somewhat close to estimated numbers consistently, then your method of evaluation would work. There are lots of variables that can greatly impact generation.. Did one vendor try to estimate some of these, did another assume best case? This is why pre ITC per KWH are used for a very good reason despite your insights. Play around with the website PVWatts and generate your own numbers to see if the vendors are giving your fair estimates. Vendor C might be so low because they used the most honest estimate of kwh?
          Last edited by cebury; 10-25-2017, 04:34 PM.

          Comment


          • #6
            Originally posted by cebury View Post
            You are giving too much credence to their annual Kwh generation numbers. In order to win your bid, a vendor merely has to add another 1000 kwh to his estimate. If Solar PV systems generated exactly, or even somewhat close to estimated numbers consistently, then your method of evaluation would work. There are lots of variables that can greatly impact generation.. Did one vendor try to estimate some of these, did another assume best case? This is why pre ITC per KWH are used for a very good reason despite your insights. Play around with the website PVWatts and generate your own numbers to see if the vendors are giving your fair estimates. Vendor C might be so low because they used the most honest estimate of kwh?
            Thanks for the insight. What's "pre-ITC"?

            Thanks!

            Comment


            • #7
              Spend $20 and buy "Solar Power Your Home for Dummies". As others have suggested or alluded, you need an education. Get knowledgeable and ask vendors questions you already know the answers to. After the reads, a session or 2 with PVWatts and some time back here filling in PV knowledge gaps, you'll learn a lot about PV and why your methods will lead you astray, and equally importantly, you'll be amazed at what you learn of the incompetence and ignorance of most vendors.

              Comment


              • #8
                Originally posted by noobie123 View Post

                Thanks for the insight. What's "pre-ITC"?

                Thanks!
                ITC is the federal tax credit. Just remember, trying to compare efficiency of panels (one step further is production efficiency per panel, your goal) is possible but an extremely difficult process. To even estimate this will take quite a bit more knowledge for you at this point. That is why we tell most residential solar PV buyers to consider panels a commodity and not sweat the brand name, the hype sales people try to lure you with certain high end panels. Some of the hype is bogus, some is questionable, a few are valid but matters a fraction of %, 1 or 2% tops in production for a hefty price tag. You left out the brand names of panels you were quoted. Vast majority will be ok but if you would like an opinion on whther folks here see those names a lot as decent brands, please include them.

                Comment


                • #9
                  Originally posted by noobie123 View Post
                  If I do add a battery, the proper inverter is quoted in the price as well. So the cost is built-in if I do it now.
                  The cost would definitely be higher if I add the battery later (new inverter and battery)
                  Honestly a generator is cheaper to do.
                  A battery?
                  To run your home for several hours ...
                  You will not have "a battery", you will have a Huge Bank of Batteries.
                  And you will be replacing that Bank of Batteries every 5 - 7 years for life, whether you use them or not.
                  And most likely, you will not be running your Central A/C from batteries.
                  Minimum $7,000 - $16,000 (every 5 years) for battery bank plus the upcharge for a hybrid inverter - to operate which appliances exactly?
                  Did you factor in that cost?

                  Comment

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