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Putting a Small Solar System on a shed (or awning) to Charge an Electric Car

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  • Putting a Small Solar System on a shed (or awning) to Charge an Electric Car

    Hi everyone, new member here.

    I already have a solar system now undersized for my needs. Lease company doesn't permit modifications without a buyout (a costly option after year 7). So I think the best route for me is to create a second system, maybe using surplus or used components I can cheaply source.

    Example: I saw Sunpower panels, which are higher end 360 watt, available for $149 each. Even if a used panel produced only 340 watts, a 4 panel system would then be ~1.36 Kilowatts. If I am able to get full output energy for 4 to 6 hours per day then I should certainly be able to charge up the equivalent of a Tesla Power Wall 1 which has a 6.4kW capacity.

    At night I would then plug in the car for slow 120v charging. If the car is rated at 23kW per 100 miles of range, this setup would give me 28% of that 100 miles, but after accounting for battery losses and battery degradation over time, we are more likely talking 23 to 25 miles. But, that's perfect for one person commuting 12 miles each way to work, or 10 miles each way plus an occasional grocery run.

    My goal here is to price out the cost of creating a small system of this kind. Please advise me and I will update the table below! I want to get a full parts list

    1. Solar panels -- $600 for used panels, 1.36 kW. Plus shipping.
    2. Inverters -- do I used microinverters, or am I better off with a single inverter, like a sub-$400 inverter with a 2kW capacity?
    3. Charge controller -- $400 for a 100 amp charge controller? Can I get a controller that works with AGM or Lithium batteries...
    4. Battery: most expensive piece. It looks like I can get 400Ah of AGM batteries (2 x 200 x 12v) for $724. Maybe go with that for 4.8Kw of battery storage, until the price of Lithium comes down?
    5. power outlet -- should I just run an extension cord from inverter, or should I set up the system to power a built in outdoor 120Volt outlet?
    6. excess power -- where would excess power be dumped when battery is full? I could send heat to the basement...
    7. direct charge -- is all the power to come from the battery circuit or is there an advantage to bypass the battery when the sun is available?
    8. mounting racks, cabling, etc.

    Thanks in advance for your help. Based on what I laid out above it should be possible to create a decent car charging system for $2500. What have I missed?

    Rick





  • #2
    Looks like your $2500.00 price tag does not include TPW1 add that in it's more like $7500-$9500?
    Why don't you just use your existing solar with dedicated hook up for EV. It would cost you a couple of $100.00s to have PV electric re-routed to EV Charger.
    If you can only charge EV at night set up battery bank charged off existing AC from PV, ie: 120v ac Charger + Batts.
    Last edited by Paul Land; 11-12-2019, 09:15 AM.

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    • #3
      You want to build an off-grid power system just so you can charge some batteries during the day and then use those batteries to charge some other batteries later that night? Sounds like a lot of work and expense when you already have grid-tie on the property. Does being around an EV have a negative affect on reasoning?
      Dave W. Gilbert AZ
      6.63kW grid-tie owner

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      • #4
        What is TPW1?

        And, I do need additional solar generation. I have a 4.8kw system and I need more like 6kW to meet my needs. So the purpose of the solar is to get my usage of the grid down to what I am already producing with the grid-tied system. Power here in MA comes out to around 22 cents a kilowatt-hour; the economics here are different from Arizona.

        Correct me if I am wrong but I think this would pay for itself in under 5 years.

        Rick

        Originally posted by Paul Land View Post
        Looks like your $2500.00 price tag does not include TPW1 add that in it's more like $7500-$9500?
        Why don't you just use your existing solar with dedicated hook up for EV.
        Last edited by leftlink; 11-12-2019, 09:49 AM.

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        • #5
          Originally posted by leftlink View Post
          What is TPW1?

          And, I do need additional solar generation. I have a 4.8kw system and I need more like 6kW to meet my needs. So the purpose of the solar is to get my usage of the grid down to what I am already producing with the grid-tied system. Power here in MA comes out to around 22 cents a kilowatt-hour; the economics here are different from Arizona.

          Correct me if I am wrong but I think this would pay for itself in under 5 years.

          Rick

          TPW1 = Tesla Powerwall

          If you plan on charging a battery system you should forget about micro inverters since they generate AC and not DC. You don't need an inverter for an off grid system. You need a quality Battery Charge controller that has the amp rating at least 1/10th of your battery Ah system.

          It sounds like you are just shooting in the dark without any good knowledge of what you really need. Why not just use your existing grid tie system and a grid tie battery charger to build up some type of energy storage system for your EV?

          Building a second off grid system for the EV seems like a waste of your money.

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          • #6
            IMHO Unless the lease prohibits another solar system being connected to the house, just add another grid tied system. Don't mess with the existing system just permit a second system.

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            • #7
              Originally posted by peakbagger View Post
              IMHO Unless the lease prohibits another solar system being connected to the house, just add another grid tied system. Don't mess with the existing system just permit a second system.
              I think the problem is that the first system is Leased probably due to cost. A second system may be outside the OP's price range which if so it makes sense to limit the cost of equipment and just look into an energy storage system to power the EV if that even makes financial sense.

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              • #8
                Originally posted by peakbagger View Post
                IMHO Unless the lease prohibits another solar system being connected to the house, just add another grid tied system. Don't mess with the existing system just permit a second system.
                You have a point with the idea of a second grid-tied system. I don't have roof space and don't really want to fill up the yard with ground mounts, so can I do a small system of four panels, expandable to 6 panels (in case I wanted to move the hardware to a new location some day)?

                There is a fixed cost per system: electrician for permitting. So I don't know whether a small system is economical. Also if I charge a battery I could add a switch to run the gas furnace off of it in the event of a power outage. So I am not throwing out the idea of an off grid system, yet!

                The TPW1 cost is not relevant here. I never intended to purchase a Tesla branded battery which is marked up far above Tesla's cost.

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                • #9
                  Originally posted by SunEagle View Post
                  I think the problem is that the first system is Leased probably due to cost. A second system may be outside the OP's price range which if so it makes sense to limit the cost of equipment and just look into an energy storage system to power the EV if that even makes financial sense.
                  I probably should never have leased and with a growing child, power usage has gone up. It was 7052kwh per year and if we use electric charging more often we could soon be at 10,000 kWh per year. I really want to see what is possible now, especially now when there is used equipment coming onto the market.

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                  • #10
                    Originally posted by leftlink View Post

                    I probably should never have leased and with a growing child, power usage has gone up. It was 7052kwh per year and if we use electric charging more often we could soon be at 10,000 kWh per year. I really want to see what is possible now, especially now when there is used equipment coming onto the market.
                    It is your choice to build an off grid system. Just be sure to know what you want and how to build a balanced system. You will need about 1/10th the Ah rating of your batteries for charging so make sure you have enough panel wattage and a quality MPPT CC. Batteries should not be wired in parallel so try to first size the system and then get 2V, 4V or 6V batteries at the correct Ah rating which can be wired in series to build your system. Good luck and let us know how it works out for you.

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                    • #11
                      A battery system will seldom, if ever, reach break even. The recurring cost of replacing batteries keeps resetting the payback clock over and over.

                      Your best bet is a an additional Grid Tie system independent of the existing system. If you have any shade issues, that reduces your power harvest and sets back the payback even further.
                      Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                      || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                      || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                      solar: http://tinyurl.com/LMR-Solar
                      gen: http://tinyurl.com/LMR-Lister

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                      • #12
                        Originally posted by Mike90250 View Post
                        The recurring cost of replacing batteries keeps resetting the payback clock...
                        Your best bet is a an additional Grid Tie system.
                        I get it. You make a good point, avoid the traditional batteries. There is another option: when not using the electricity output, dump the output of the extra solar panels (I am thinking just 4 or 6) into what is called a "heat battery." New technology and it uses a chemical that converts from solid to liquid at something like 56 degrees Celsius. This has been installed in thousands of homes in the UK and the Chinese government has a strong interest in expanding it for rural parts of China, maybe that will bring down the cost. It makes sense for me to experiment with this in order to reduce the power consumption of our electric water heater. It isn't absolutely necessary to get full payback on this investment, it is just to balance our system to be energy self sufficient again.
                        https://thermalbatterysolutions.co.uk/products

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                        • #13
                          While a phase change heat battery is an option, it squanders valuable PV electric power for simple thermal power. Thermal Solar panels for heating your heat battery are much more efficient than solar electric to heat with.
                          Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                          || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                          || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                          solar: http://tinyurl.com/LMR-Solar
                          gen: http://tinyurl.com/LMR-Lister

                          Comment

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