Questions about Solar equipment

SystemSystem Posts: 2,511 admin
Hello everyone my name is Ryan and I have some questions about what solar components I need to get. I am a college student that is part of renewable energy club on campus. We were donated 4 solar pv panels 3 of them the glass is shattered on the inside but the plastic is still holding everything together. Here are some specs for the panels

Prated = 190 Watts
Vmax = 26.7 Volts
Imax = 7.12 Amps
Voc = 32.8 Volts
Isc = 8.05 Amps

Our project is we want to build a solar trailer , with panels, a charge controller, battery pack, and modified sine wave inverter. The purpose of this trailer will be able to take it to club events and show it off so running a fan, blender, stereo would be the things we would power and it would be for hardly any time at all. the Max would I roughly calculated with a stereo and blender on at once was around 800W.

I would like to know the best way to arrange the panels, parallel series or both, and which charge controllers and inverters I would be able to pick up for cheap.

My thought would be to get a charge controller that could step down the voltage to 12 volts so our inverter would be cheaper and we could hook 12 volt batteries in parallel but I am not sure what I am looking for.

Any comments would be greatly appreciated.

Ryan

Comments

  • System2System2 Posts: 6,290 admin
    Re: Questions about Solar equipment

    First thoughts - - before you spend any money, or go further with the project as it's now planned, is to verify the panels with shattered glass are working. In almost all posts I've seen here re broken glass, the panels are next to useless. You may be lucky, but verify, so you'll know where you can with it go first.
    You have to check BOTH the output voltage, AND the output current. Don't be surprised if the voltage seems within reason, but the amperage is next to nil, or way down on the ones with shattered glass.
    Let us know what you find.
    I'm sure others will have input here too.
    It's my opinion that you did come to the right place to ask your questions. The people on this form are awesome. They know what they're talking about, there is no BS and they will be glad to help you if they can.
    Good luck with your project.
    Wayne
  • System2System2 Posts: 6,290 admin
    Re: Questions about Solar equipment

    Thank you for the reply. We did check out the voltage and current on the shattered panels and were able to get about 1/3 the current maximum from them. The voltage stayed pretty much the same.

    Ryan
  • BB.BB. Super Moderators, Administrators Posts: 32,009 admin
    Re: Questions about Solar equipment

    About the only use for the shattered panels would be to carefully pick the glass off of the solar cells and cut the cells into loose parts (and maybe some solvent to remove the backing) for projects (maybe a give-a-way project like 2-3 cells and a RED led or a few cells connected to a little AM/FM radio, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,973 ✭✭✭
    Re: Questions about Solar equipment

    I think you will find the 1/3rd current was an Isc measument ( short curcuit ) not at the Vmp voltage. 75% of the module could be non-functional and the ISC could still be measured thanks to the bypass diodes

    I would be very surpised if you get 10% of the rated wattage, hook up an electronic load to each panel and set the load for contstant voltage load, set to the manufactures listed Vmp value and then you will get the true power the panel can produce

    As other have suggested, they are probably worthless for your portable power project
  • System2System2 Posts: 6,290 admin
    Re: Questions about Solar equipment

    I really feel badly about this man, but unfortunately, these guys are telling you the truth. I wish it weren't so. Your project was a noble one. Hopefully something will turn up that will allow you to carry on with it. It is worth doing, but you need good panels. I believe in it enough, that if I lived close by, I would be willing to lend you a couple of mine.
    Hopefully something will turn up.
    Wayne
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Questions about Solar equipment

    even if by some miracle the pvs were workable by you, i doubt they'd survive going over the road or handle the weather. at least you didn't have to buy them, but as bb suggested, the parts may be useful for something.
  • System2System2 Posts: 6,290 admin
    Re: Questions about Solar equipment

    Well if what you guys say is true, I still have 1 panel that has not been damaged. Would I still be able to provide enough amperage through the charge controller to charge up a couple of 12V batteries. Time would not be an issue because we would keep the unit outside most of the day and would only use the batteries maybe 30 minutes if that.

    This weekend I will see if I can get some of the guys together and we can test out the panels more. What do you suggest I use as a constant voltage load to verify the status of the broken panels?

    Thanks again for the input if worse comes to worse we build the trailer and hopefully down the road some solar companies will give us better luck with donated panels.

    Ryan
  • BB.BB. Super Moderators, Administrators Posts: 32,009 admin
    Re: Questions about Solar equipment

    When all is said and done, you will get, very roughly, 400 Watt*Hours of useful energy out of your system per sunny day with the one 190 watt panel and MPPT solar charge controller...

    Battery wise, it should be sized around 1/5%-1/10% of charging capacity (10-20x the available charging energy). So that would be 4 to 8 kW*Hour of storage battery for, roughly balanced/optimum storage capacity (if this were designed as a real off-grid application).

    But, you don't really need 3 days of no sun (poor weather) performance for a demonstration system.

    Another way to look at sizing of the battery is how much power do you wish to draw from it... Normally, if you can discharge the battery by 20% or less per day (80% State Of Charge)--it will last a good long time. You can discharge it as much as 50% maximum in a day, but it will not last that many cycles (but if you are only doing this a few times per year--it probably does not matter). And if you can recharge the battery quickly (like within 24 hours)--the sulfates will not harden (which kills the battery).

    Also, you could look at AGM batteries--they will take deeper discharges without damage (but--deep cycling will kill them faster too).

    So--if you want 800 watts for 30 minutes per day--the one panel will just about support it (or 100 watts for 8 hours per day, etc.)... Exact numbers really depend on where you are at (San Luis Obispo, CA?). And the time of year (winter, summer, etc.)...

    There are still quite a few issues in your decision (flooded cell requires watering once per month, AGM's are 2x as expensive).

    And, you may want to experiment with the Mod Sine Wave inverter (MSW). For some electronics (radios, TV's, digital clocks, some motors), you may have problems with noisy audio/video, clocks may not keep correct time, and some motors and electronic devices may overheat. Most items will probably work OK--but you should "pre-test" your setups before you go out for a demo (or get a true sine wave inverter which will pretty much support anything within its power rating).

    Also, watch the maximum power you want to use--800 watts is going to be close to 100 amps from 12 volt batteries (even more if surge is above 800 watts--such as starting a motor). For a small battery bank, that is quite a large current--which will quickly flatten a battery (battery energy discharge curves are non-linear--the larger the current, the less energy the battery can deliver).

    Keeping loads small (CFLs, fans, boom-box, laptop computer, etc.) will help--You don't want to give the idea that a few solar panels is equivalent of a 120 VAC 15 amp wall outlet.

    And, if you plan on adding more panels later, it would be helpful if they are the same Current or Voltage rating (depending on if you will be adding these is series or parallel--which depends on the solar charge controller you have or will be replacing when adding on). And, if you add more batteries, you will have issues of the new batteries not lasting much longer than the original batteries (all will begin to fail around the same time).

    In the end, what is it you want to do? Make a simple demo tool for sunny weather, a slightly more sophisticated power station for night time demos and some light emergency work. Or, a full blown design/installation project with automated charge/load control with full monitoring (Battery Monitor) and an automatic start electric generator for periods of no sun...

    -Bill

    PS: One other possibility would be to use the extra space for a solar thermal hot water heater--that would be different and cheaper too (plus more solar design/build experience)... Add a solar panel, pumps, insulated tank and watch the temperature rise--put a hot water faucet on the side (you may need to temper with cold water to prevent scalding).
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Questions about Solar equipment

    if that pv is good you may be able to charge up a battery or 2 as this would depend on losses presented if a standard pwm controller is used. if using a downconverting mppt cc i'll say up to about 250ah in battery capacity at 12v. a 100ah battery at 12v for sure could be charged with it. as to what you can power with it depends on the strength of the sun and the number of hours it presents itself to the pv. remember there will be losses in charging too, but otherwise watts in to provide watts out. this means for you to consume x number of watts in loads that you need at least that much power plus some for losses provided by the pv. you won't be able to do all you had planned for it because of this. keep in mind that you should have around a 5% charge or more (without exceeding any manufacturer's maximum) to properly charge the battery. if that pv is not providing the proper charging amperage for your batteries that you already have there needing a charge then you will need to get more pvs to charge them. there's no doubt that the load requirements you list will require more pvs and do note that it will depend also on how long you draw on those loads as a factor in how much pv and battery will be needed.
    as i had said, the ones with broken glass will not be able to be put into a trailer even if they output properly as the weather and road shock would destroy them in short order.
    please if you would pm me as to who gave you the pvs?
  • TelcoTelco Solar Expert Posts: 201 ✭✭✭✭✭
    Re: Questions about Solar equipment

    Ya know, since this is a school solar club with the intent of building a project, why not just test the broken panels, then tear them down and try to repair them? Since your ultimate goal in building this trailer is to learn about alternative energy, the time and trouble taken to do a full teardown, test and repair would be a good one to undertake. It also helps to learn how to handle unexpected problems in a project. Who knows, you might even be able to get the panels back to their rated power. Detail the repair process and make a web page about it, and it might help you land a job you otherwise might not have had a chance with. If nothing else, write a book on how to evaluate and repair damaged solar panels and make a few bucks.

    The skills you pick up may also be useful to you at some future point where you might need to get a damaged panel working for a mission-critical need. When all is lost and the mission is failing, the guy that can pull a working system out of a pile of scraps and keep it going till the replacements get in is the guy that gets the promotions and bonuses, AND gets put at the top of the do-not-touch list when the company has layoffs.
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