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I finally finished a project in which I designed a 55 kW of PV system for a 50 kW load and I finally calculate costs and revenues over 20 years. I found that with a 25% of incentives for the cost of inverter and PV panels, I have a negative NPV (net present value, is the sum of the net cash flows over some years actualized, in my case over 20 years) of -75k€ more or less while without the PV plant the NPV is -52k€ more or less. I tried to increase the incentives up to 75% and at this point, the NPV is almost the same in the case of the PV plant and not. So if incentives increase from now on, after 20 years we will have a positive profit. I have 2 questions, especially for those that have a bit of experience in this field:

  1. Do these results sound reasonable for you?
  2. If yes, from an ECONOMICAL point of view ONLY, why one person should buy solar panels without incentives? I live in Italy and here the incentives are 110% but ONLY on PV plant with a size that is less than 10 or 20 kW (I don't remember exactly the size) and with a lot of other constraints. Yes PV panels have a great positive impact on the environment, but nobody will buy solar panels without 100% at least of incentives.
Samuele Benito Di Gioia
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    Please dont assume that everyone knows that PV stands for Photo-Voltaic. Also, this is not an electrical engineering related question and so does not belong on this site. – Vinzent May 08 '21 at 00:02
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    this question is not about electric current, or energy, or any other engineering topic. – Jasen Слава Україні May 08 '21 at 01:06
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    I think it depends a lot on where in the world you are. In the tropics, a PV setup can pay for itself in just a few years. I have a small one (3x380W panels, 1.5kW grid-tie inverter) and I get 3-5kWh on most days. With the local electricity cost, it should pay for itself in 5 years. However, this one is sized based on our consumption. A larger number of panels and a larger inverter wouldn't make sense in this case as it would exceed our consumption, and exporting to the grid is not economically attractive here. – KristoferA May 08 '21 at 04:17
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    As an example (also EU), my small 700W grid-tie solar setup was installed by me in 2013 without any incentives and it has already paid itself back. It’s delivering around 3-4kWh on (partially) sunny days but much less in winter. – StarCat May 08 '21 at 06:47
  • @StarCat You said that your photovoltaic system has already paid itself back, but have you thought in terms of actualized cash flows or not? In the sense that the value of money of tomorrow is not the same as today, every year you should consider an actualization rate of 1.2^(number of years from the investment). Because If we think that the value of money is the same every year ok, also my PV plant pays it back after 11 years in my case but is not correct to do the investment without actualizing the cash flows over the years; I can invest my money in another way! This is a problem for RES – Samuele Benito Di Gioia May 08 '21 at 09:34
  • @KristoferA yes, the load that my PV plant should supply is 50 kW and my PV plant is 50kW (even if due to technologies and efficiencies of the inverters and panels the effective size is 38 kW more or less), so most of the load is supplied by my PV plant and when it produces more I sell it or I store it and use it after. I live in Italy, here there is a lot of sun during the year, so the geographical problem doesn't exist in my case. About you PV plant, have you read the answer that I gave to Starcat? Have you thought in terms of actualized cash flows? – Samuele Benito Di Gioia May 08 '21 at 09:42
  • The results do not sound reasonable; financial rates of 1.2^(years since investment) sounds like you're putting it on a credit card. In which case, it's the credit card that doesn't make sense, not the solar panels. –  May 08 '21 at 12:41
  • @user_1818839 Sorry I didn't understand your answer very much, do you mean that the actualization rate of 0.20% is too high? – Samuele Benito Di Gioia May 08 '21 at 13:43

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