Controller for 30 Volt Solar Panel

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q127238
q127238 Registered Users Posts: 1
in Solar Beginners Corner #1
I recently obtained a Sharp 240 Watt solar panel rated at 8.75 amp made by Sharp. The specs states that the output is approx. 30 volts. I want to use in for charging one or two 12 volt deep cycle batteries. I have a project that has a load of 2 amp at 5 volts. Running 24 hours a day. I live in the Dallas area and the area of the panel is getting about 3 to 4 hours of sunlight. Any suggestions on a controller that can handle an output of 30 volts and charge 12 volt output.

Thanks in advance.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Controller for 30 Volt Solar Panel

    Welcome to the forum.

    If you want to make full use of the panel's power you will need an MPPT type charge controller such as the Morningstar SunSaver MPPT 15 http://www.solar-electric.com/inverters-controllers-accessories/chco/mochco/admpchco/mosumpsochco.html
    That will get you about 15 Amps from the panel on a 12 Volt system. If you use it with a PWM type controller you will get only the Imp of the panel, 8.75 Amps. The rest of the power will be lost due to the Voltage difference.

    What is the capacity of the 12 Volt batteries? It will make a difference on the viability of charging from this one panel.
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #3
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    Re: Controller for 30 Volt Solar Panel

    You are in "the gap". You can either maintain high efficiency by using an expensive MPPT type charge controller with your high-value large format PV panel, or you can lose a lot of its power with a low-cost PWM type controller. or you can get a relatively expensive 12V panel to go with a low-cost PWM controller. There is no good way to do a modest size solar array. If just a small array, PWM is ok, if more than 3 or 4 panels, then MPPT will pay for itself, but in-between - not so much.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #4
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    Re: Controller for 30 Volt Solar Panel

    Also--Question about the 3-4 hours of sunlight...

    If this is what we call "hours of sunlight"--That is hours of noon time sun equivalent per day... I.e., the array is in full sun and harvests 4 hours of noon time equivalent sun per day (3-4 hours of sun per day is typical winter average hours of sun per day).

    If the panels are in shade except for 3-4 hours per day--That is not good. It gives much less energy per day--And Lead Acid batteries really do better with more hours per day of charging (like 6+ hours). And 2-4 hours of charging current is difficult to keep lead acid batteries "happy".

    Other battery chemistries such as LiFePO4 (lithium iron phosphate) may be a better choice as they can take a lot of current in a short period of time to be fully recharged and do not need 2-4+ hours of "absorb voltage" (holding 14.5 volts or so for X hours on a lead acid) to recharge.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #5
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    Re: Controller for 30 Volt Solar Panel

    Interesting application, and YES, lifepo4 would be an excellent candidate for this. To the tune of about $2800.00.

    Even though the application has a low current draw, it is the 24/7 requirement that hurts. Let's figure on NO solar, ie one day without sun:

    Let's work in watts to make it easier (P/I*E formula).

    2A * 5v = 10 watts per hour.
    10 * 24hrs = 2400 watt hours daily.

    For a deep-cycle lead acid, you need to double that value for capacity so you don't run a battery down below half of it's rated capacity (if you want any decent cycle life). That means:

    4800 wh battery. For a 12v battery, that would be a capacity of:

    4800w / 12v = 400ah capacity. For lead acid.

    BUT, lifepo4 (such as a 400ah / 12v set of GBS, Winston or CALB cells) can go down to 80% DOD and will provide you some needed bad weather autonomy and provide some headroom for dc-dc voltage (12v > 5v ) conversion.

    A 400ah lifepo4 12v battery - about $2800. I'm a staunch advocate for lifepo4 with solar, but you must be able to absorb that upfront cost.

    As for charging, my charts show a "low" of about 5 hours in the winter in Texas. I believe you could make it with that panel setup - but ONLY with lifepo4, which doesn't mind being run in a "psoc" or partial-state-of-charge environment. With lead-acid, the battery would be quickly sulfating from a deficit charge given just one day of no sun.

    My recommendation would be to double up on your panel power, that way if you suffer longer periods of no sun, the lifepo4's will be able to play "catch-up" over the next few days quicker (no sulfation worries). Since they will easily accept up to 1C (in this case 400A) of charge current, your wallet is the limiting factor.
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  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    #6
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    Re: Controller for 30 Volt Solar Panel
    PNjunction wrote: »
    I

    Let's work in watts to make it easier (P/I*E formula).

    2A * 5v = 10 watts per hour.
    10 * 24hrs = 2400 watt hours daily.

    Wouldn't that be 240 watt hours?
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #7
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    Re: Controller for 30 Volt Solar Panel

    OH man, somebody slap me! Yes, cut everything by 10, including the battery cost.

    How about $250 for the 40ah battery? That's a LOT easier to digest. Your existing panel would be just fine.

    Better yet, an flooded or agm would be a nice start.

    Sorry about that, q127238. I don't know where my mind was on that one. :)
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  • mikeo
    mikeo Solar Expert Posts: 386 ✭✭✭
    #8
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    Re: Controller for 30 Volt Solar Panel

    If the OP needs 40 amp hours daily to power his loads, allowing for no more then 50% discharge for a lead acid battery, and 3 days of no sun max before having to find an alternative way to charge the battery then we are looking at a 240 amp hour battery (40 ah x 2 X 3 days). At a 10% charge rate that would be 24 amp worth of panels, so he needs at least two panels to start with. I have done a few of these small projects and I'm always amazed at how much battery and number of panels just to run a small project. Cheapest batteries for this project would be two 6 volt golf cart batteries. I would definitely would want an MPPT solar charger for this arrangement with 30 volt panels.
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  • jimindenver
    jimindenver Solar Expert Posts: 59 ✭✭
    #9
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    Re: Controller for 30 Volt Solar Panel

    I have used these little MPPT controllers for three years now. Somewhere on this board I posted a limited review of them.

    http://www.eco-worthy.com/catalog/mppt-solar-charge-controller-free-shipping-p-182.html

    They are the least expensive functioning MPPT controller I know of. Kind of limited in some respects with no remote temperature or voltage sensors ( temp sensor is internal) and the VOC limit is only 42v, but for a single 24v panel up to 270w it works great. I currently use two of them with two 245w panels in parallel while camping and know of a handful of others that use them, including one on this board I believe.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #10
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    Re: Controller for 30 Volt Solar Panel

    Jim wrote a review a few years ago--Seems like a very reasonable controller for ~$100 or so.

    Eco-Worthy 20a MPPT charge controller review.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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