Looking to build a solar generator

Tom4Tom4 Registered Users Posts: 4
Attachment not found.I have landed 4 of these inverters that are all functional. They are the Prowatt 800 24VDC. I also have two barand new 12VDC deepcycle marine batteries at 125 AH rating. I was wondering what other components I would need to make a functioning solar generator. What size panel and what controls?
I am not incredibly smart, but can do simple math BUT high-tech nomenclature makes my brain glaze over. If someone can explain what I need in simple terms I would love to have an off the grid system started. Thanks!

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking to build a solar generator

    Welcome to the forum Tom.

    I think the first question would be "what do you want to achieve?"
    The reason being that old Statpower is a (pretty sure) MSW type inverter and those RV/Marine batteries aren't really top choice for a renewable energy application (they won't last).

    Now if you just want to do some experimentation and see how it works, you've already got enough to fire up one of those ProWatts and see what it will do: wire the two 12 Volt batteries in series and you've got 24 Volts. :D

    As for recharging them from solar ... maybe you want to see how well they work before investing in any panels and controller.

    BTW the Statpower equipment was actually good quality stuff. I still have an old 600 Watt unit and it still functions!
  • BB.BB. Super Moderators, Administrators Posts: 29,636 admin
    Re: Looking to build a solar generator

    For a 125 AH @ 24 volt battery bank, roughly a 5% to 13% rate of charge would be:
    • 125 amps * 29 volts charging * 0.05 rate of charge = 181 Watt array minimum
    • 125 amps * 29 volts charging * 0.10 rate of charge = 363 Watt array nominal
    • 125 amps * 29 volts charging * 0.13 rate of charge = 471 Watt array cost effective
    So, for a stand alone minimum solar array, around 181 Watt minimum (experimenting, weekend use, etc.).

    For 10% to 13% (roughly) rate of charge, good for daily power usage (other than the batteries are not probably true deep cycle).

    The solar array Vmp-array should be in the range from 35 to 39 volts with a less expensive PWM type charge controller. Or >=35 Volts to ~100 volts (depending on brand/model) of MPPT type charge controller.

    So, you could get 2x 140 Watt "12 volt" (really Vmp~17.5 volt) Kyocera (or similar) panels, connect them in series, and a 15+ amp PWM or MPPT solar charge controller for a ~280 Watt array.

    Note that there are some cost/configuration issues to work out... Not all solar panels are a good mix/match for all solar charge controller and 12/24/48 volt battery banks. There are certain combinations that work, and others that do not. And there are cost implications many times (expensive panels+cheap PWM charge controller vs cheap panel+expensive MPPT controller is one common mix--Either way, it is difficult to get away "cheap").

    Also, when shopping for solar panels (especially), check the costs delivered to your front door (unless you are picking them up locally)... Shipping costs can be very expensive for shipments of small numbers of panels (you are shipping large "glass windows"--Which must be packed well and shipped on the appropriate service--Panels over ~140 watts tend to ship only by truck).

    Solar panels:
    http://www.solar-electric.com/solar-panels-mounts-kits-accessories/solarpanels/hiposopa.html

    Solar charge controllers:
    http://www.solar-electric.com/inverters-controllers-accessories/chco.html

    Morningstar has both PWM and MPPT type charge controllers.
    Midnite makes a nice mid range and large MPPT series of charge controllers.

    Rogue also makes a nice mid size MPPT charge controller too.

    A 280 watt array with good fall/spring sun will have ~4 hours minimum of "solar noon" equivalent sun--Which gives you:
    • 280 Watt array * 0.52 system efficiency * 4 hours sun = 582 Watt*Hours per
    If you have, for example, a laptop that averages ~30 watts and a 10 Watt light bulb, that would run:
    • 582 WH * 1/40 watt load = 14.6 hours per day
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Tom4Tom4 Registered Users Posts: 4
    Re: Looking to build a solar generator

    So if I went with the Top Point Topoint Solar 190 Watt Monocrystalline Solar Panel, would this be acceptable?
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking to build a solar generator
    Tom4 wrote: »
    So if I went with the Top Point Topoint Solar 190 Watt Monocrystalline Solar Panel, would this be acceptable?

    Yes. That is a "true" 24 Volt panel with a Vmp of 36.5 so it will work on a 24 Volt system even with a PWM type charge controller. It's Imp is 5.2 so the charge rate on 125 Amp hours would be about 4% which is really too low for charging. Two of them in parallel would be fine, however.
  • Tom4Tom4 Registered Users Posts: 4
    Re: Looking to build a solar generator

    I am still learning here, but in that case it might be better to go with 2 of these instead...SolarWorld Sunmodule 240 Watt Monocrystalline with Imp of 8.22. to reduce charge time?
  • PhotowhitPhotowhit Solar Expert Posts: 5,011 ✭✭✭✭
    Re: Looking to build a solar generator

    What general area are you located, the only problem with the 190 watt panel is they are oversized for shipping, I think FedEx will ship them at an outrageous price, but if you check craigslist you might find someone changing out 12 volt panels, you'll need 2 of the same size in series to use the cheaper PWM Charge controller (CC). Also so wholesalers on the left coast, Miami and Norfolk areas... and others here might know of places other than those.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking to build a solar generator
    Tom4 wrote: »
    I am still learning here, but in that case it might be better to go with 2 of these instead...SolarWorld Sunmodule 240 Watt Monocrystalline with Imp of 8.22. to reduce charge time?

    No, that panel will not work because its Vmp is too low to fully charge a 24 Volt system (240 Watts / 8.22 Imp = Vmp 29).

    You have to have sufficiently high Voltage that the battery bank will reach Absorb (and preferably EQ) level after losses or else the current doesn't matter.
  • PhotowhitPhotowhit Solar Expert Posts: 5,011 ✭✭✭✭
    Re: Looking to build a solar generator
    Tom4 wrote: »
    I am still learning here, but in that case it might be better to go with 2 of these instead...SolarWorld Sunmodule 240 Watt Monocrystalline with Imp of 8.22. to reduce charge time?

    Tom, I think your looking at the wrong number those panels have a VOC (voltage open circuit) in the correct range, but you should be looking at the VMP number, Solar world uses VMPP to match up with MPPT charge controllers nomenclature. Also the max amps you could expect while charging is the 'working' number as well. If you look to the right of the rosy specs they list the NOCT values this is what you could expect from the panel on most days in sunny direct sun;

    Link to panel specs.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
  • BB.BB. Super Moderators, Administrators Posts: 29,636 admin
    Re: Looking to build a solar generator

    And here is where things get "complicated"... The solar world panel is Vmp~29.2 volts.

    Turns out, when you take battery voltage, charge controller voltage drop, wiring voltage drop, and that "hot panels" (over 75F) have Vmp voltage drop, that the "ideal" working Vmp ratings in the range of ~35-39 volts or so for a PWM charge controller.

    Drop the Vmp below ~35 volts, the panels will not charge the batteries very well on hot days.

    Raise the Vmp above ~39 volts, and you will use less of the arrays rated wattage. If if you have 24 volt battery bank and a ~70 volt array, you will only get ~1/2 of the array's rated wattage into the battery bank (as an example).

    So, your ~30 volt panels can either be connected two in parallel--And you have too low of voltage to optimally recharge a 24 volt lead acid battery bank. And if you put them in series for Vmp-array of ~60 volts, then you will lose almost 1/2 of the 480 Watt array power.

    A solution for this would be to use a MPPT (maximum power point tracking) charge controller. They have a "buck mode DC switching power supply" topology which can efficiently (~95% efficient) take high voltage/low current from the array and down convert to low voltage/high current needed to charge the battery bank.

    A Midnite "Kid" or a Rogue 30 amp MPPT charge controller will work nicely here with the two Solar World panels in series for Vmp-array ~ 58.4 volts (but more expensive than a PWM charge controller).

    Plus, you need to check shipping charges for two 240 Watt panels. It could be very expensive if you are not picking them up from the store/warehouse directly.

    And, for panels over ~175 Watts, you should consider having a friend help you move/install the panels. Large panels are very awkward and easy to destroy with a single person handling them.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Looking to build a solar generator
    BB. wrote: »
    And, for panels over ~175 Watts, you should consider having a friend help you move/install the panels. Large panels are very awkward and easy to destroy with a single person handling them.

    -Bill

    Note: I put up two 260 Watt panels by myself this Summer. Definitely awkward to handle on my own. Having an assistant would have been really nice, providing it was someone who would follow instructions of course. :D
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