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  • #16
    Originally posted by CessnaTPA View Post

    So are you saying the numbers I'm getting from pvwatts should be higher or lower?
    I think JPM is talking about is how pvwatts calculates the $ savings based on some type of $/kWh input. Those number may be skewed so first determine the kWh savings and then run your own calculation of $ savings based on a realistic cost per kWh. Remember whatever is generated above your usage will be sold to the POCO but they may pay you a lower $/kWh that what they charge you.

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    • #17
      Originally posted by CessnaTPA View Post

      So are you saying the numbers I'm getting from pvwatts should be higher or lower?
      One or the other.

      The production numbers are estimates of long term average system output. Actual annual (or 12 month, or running 365 day) output will be different than PVWatts estimate.

      That portion of the model seems to do a fair job if the input is reasonably correct. GIGO applies.

      What I was referring to is what PVWatts calls "Energy Value". Read the help/info screens for details. My experience is that those $$ estimates of how much the modeled system will save per year are way off. Since most folks do PV to lower electric bills, having reasonably accurate cost saving estimates are kind of important. My opinion based on experience with what PVWatts thinks my POCO is doing as well as looking through the NREL utility rate data gives me the opinion that the data is unreliable as cost data or system design.

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      • #18
        Originally posted by SunEagle View Post

        I think JPM is talking about is how pvwatts calculates the $ savings based on some type of $/kWh input. Those number may be skewed so first determine the kWh savings and then run your own calculation of $ savings based on a realistic cost per kWh. Remember whatever is generated above your usage will be sold to the POCO but they may pay you a lower $/kWh that what they charge you.
        what is even more important they will pay you for excess below your cost of production so any excess becomes negative revenue generator. The bigger excess the worse it looks. Your cost even DIY is $15,000 / 15,000 kWh / 10 years = 10 c/kWh if it lasts 15 years it would drop to 6 c/kWh but Pocos typically pay < 4 c/kWh for excess.
        Last edited by max2k; 07-23-2017, 12:49 AM.

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        • #19
          Originally posted by max2k View Post

          what is even more important they will pay you for excess below your cost of production so any excess becomes negative revenue generator. The bigger excess the worse it looks. Your cost even DIY is $15,000 / 15,000 kWh / 10 years = 10 c/kWh if it lasts 15 years it would drop to 6 c/kWh but Pocos typically pay < 4 c/kWh for excess.
          Probably more important still, the best way around overgenerating is to not oversize in the first place. As long as the reimbursement for overgeneration is < the NEM credit, overgeneration will always hurt the bottom line and always hurt the ROI/cost effectiveness. And, system size, because it's an easily controlled parameter, makes oversizing a self inflicted injury. One of the reasons why better information about system capabilities and utility billing methods, both now and into the future is important.

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          • #20
            Originally posted by max2k View Post

            what is even more important they will pay you for excess below your cost of production so any excess becomes negative revenue generator. The bigger excess the worse it looks. Your cost even DIY is $15,000 / 15,000 kWh / 10 years = 10 c/kWh if it lasts 15 years it would drop to 6 c/kWh but Pocos typically pay < 4 c/kWh for excess.
            That is why you know exactly what you are getting into when you sign the contract with the POCO. A true Net Metering contract will pay you the same amount per kWh that the POCO charges you.

            Just be careful because your "cost" may include the generation, distribution, fuel and grid maintenance values but their payment may only include the generation and fuel. Distribution and maintenance costs per kWh may not be given to your for your generation.

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            • #21
              Originally posted by SunEagle View Post

              That is why you know exactly what you are getting into when you sign the contract with the POCO. A true Net Metering contract will pay you the same amount per kWh that the POCO charges you.

              Just be careful because your "cost" may include the generation, distribution, fuel and grid maintenance values but their payment may only include the generation and fuel. Distribution and maintenance costs per kWh may not be given to your for your generation.
              As in, you gotta' do yur' homework, and really understand what you're getting into.

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              • #22
                Originally posted by max2k View Post

                what is even more important they will pay you for excess below your cost of production so any excess
                becomes negative revenue generator. The bigger excess the worse it looks. Your cost even DIY is
                $15,000 / 15,000 kWh / 10 years = 10 c/kWh if it lasts 15 years it would drop to 6 c/kWh but Pocos
                typically pay < 4 c/kWh for excess.
                I am having a hard time thinking of that as negative revenue. The plant was expensive, but now paid for.
                Cost of generation is near zero. In my case they pay me zero for excess; I don't care because I paid zero
                for it. The local problem is that the harshness of winters varies so greatly. I am equipped to deal with the
                coldest, which leaves quite a surplus after a mild one. Bruce Roe

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                • #23
                  Originally posted by bcroe View Post

                  I am having a hard time thinking of that as negative revenue. The plant was expensive, but now paid for.
                  Cost of generation is near zero. In my case they pay me zero for excess; I don't care because I paid zero
                  for it. The local problem is that the harshness of winters varies so greatly. I am equipped to deal with the
                  coldest, which leaves quite a surplus after a mild one. Bruce Roe
                  PV don't last forever so if its amortization period is close to its life expectation you'll be exactly where you started but with 'that thing' on your roof or in your case- on your property. If it had ROI of 5 years - no problem, as you said I'd care less if I'm not making much but reality is I'm investing upfront and if I over- invest I'll never see those money back simply because my bill was not that high to begin with.

                  As normal politics go this problem has another solution- increase your consumption to justify expense but that usually works well if the investment money belonged to the public.

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                  • #24
                    Originally posted by bcroe View Post

                    I am having a hard time thinking of that as negative revenue. The plant was expensive, but now paid for.
                    Cost of generation is near zero. In my case they pay me zero for excess; I don't care because I paid zero
                    for it. The local problem is that the harshness of winters varies so greatly. I am equipped to deal with the
                    coldest, which leaves quite a surplus after a mild one. Bruce Roe
                    Bruce: Think of the money you spent on PV as prepaying your electric bill. The cost of generation can be anything you choose to call it, incliding zero - your money, your table, your game. But, what you, I and lots of other folks have done is commonly amortized over some time span (payback period is one way name). There are many ways to calculate that cost and spread it over a period of time, often years. In one sense, you're hoping the current and future cost of electricity is higher than you projected, particularly with a high offset, because that will give you a better actual ROI for what you generate than you projected it would be (rates went up more than you guessed). For large but < 100 % offsets you're a happy camper. At 100% offset (which BTW, is often/usually less than the most cost effective system size), you don't care what happens to rates - your entire bill is effectively a sunk cost with a variable ROI - with that ROI dependent on what happens to rates.

                    Now, if excess generation is paid to you at a rate that's less than the cost of electricity your PV is replacing (as it almost always is @ ~~ $0.03-$0.06/kWh for excess generation), that is indeed system revenue, but that revenue for the overgeneration in excess of use is a lot less than the value of the power you're "undergenerating" up to the limits of your use, with that undergeneration subsequently either offsetting POCO delivered power, or feeding to the grid, again up to the limits of your use.

                    I'm not an accountant (and I don't play one on TV), but I think I understand what Max is writing. I'm not sure I'd call the difference between NEM rates and overgeneration reimbursement rates negative revenue as much as simply a poor use of resources or assets by knowingly spending more on excess PV that is known (or ought to be known) to have a lousy ROI and thus a poor investment for the excess incremental generating capacity.

                    As a practical matter, overgeneration almost always lowers ROI. It's a choice a lot of solar ignorant folks make not knowing the consequences of what they're doing and kind of ironic - bitching about their electric bill and getting a bunch of quotes, and then making decisions about sizing (and other things - or leaving those details to the vendor, which is a formula for getting big time screwed), and doing things in such a way that will usually and commonly almost guarantee a greater long term cost of electricity than what they're bitching about in the first place. Seen it up close and personal about 100 times so far and counting. But, not my money, decision or life.

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                    • #25
                      All true, but there are other approaches. Nothing wrong with increased electric consumption along with
                      solar, if that was the plan; mine has gone up more than 5 times. With the price of propane varying from
                      $1 to $5.25 already (who knows for the future), its just a guess how many gallons I won't buy, and at
                      what price. The heat pump is quite competitive with propane most of the year, and at $2.25
                      a gallon even resistance heat matches it. Bruce Roe

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                      • #26
                        Originally posted by SunEagle View Post

                        Sounds like you have a plan. Let us know what TECO allows you to do on the installation.

                        Where I am now, Duke would not allow me to do anything which made it expensive and very hard to justify an installation. But maybe my new POCO, Withlacoochee Electric will allow me more flexibility on installs next year.
                        I found out I can pull my own permit as a home owner and do the whole install myself.

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                        • #27
                          Originally posted by CessnaTPA View Post

                          I found out I can pull my own permit as a home owner and do the whole install myself.
                          That is good to know. It looks like Fl has relaxed it's rule of needing someone that is Solar Certified to do the install.

                          The change may have happened because the State refund credit for a solar install dried up and there is no longer any cost reduction except what you can get from the Feds.

                          Still make sure your TECO rep agrees with your design on the interconnection along with allowing you to land the wires in your main panel.

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                          • #28
                            In hydro-rich WA, the power rates are pretty reasonable, but there is a tiered rate structure that gets more expensive with more consumption. We have full net metering. My goal is just to eliminate my POCO consumption at the third tier ($0.09/kWh). Considering our dark winters and clouds and trees, it's not exactly an ideal solar location, so I'm not trying for more than that (plus some very expensive backup capability, but that's another topic).

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                            • #29
                              Originally posted by CessnaTPA View Post

                              I found out I can pull my own permit as a home owner and do the whole install myself.

                              Hey how can i get in contact with you. I am in Pasco and also on Withlacocchee and was thinking of doing my own install. The costs here are easily 25k for a 7KW system. I have worked on roofs most of my life helping friends and have all the tools necessary to do my own. I also was thinking of pulling my own permit in Pasco as well. I can help you if you need .

                              Lu

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                              • #30
                                Have you upgraded your home yet?

                                Every dollar you spend on upgrading like energy efficiency appliances, HVAC, Insulation, Windows, and Doors will save you $2 in RE installation cost. Not only that has immediate positive net gain on your home. Solar in FL is likely to have negative net equity gain.

                                At 70 Kwh/day you either have a very large luxury home, or one in need of energy upgrading.
                                MSEE, PE

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