48 vdc system

patrickp8616
patrickp8616 Registered Users Posts: 6
I have 4, 39" X 69" 225 watt each solar panels. These are of the "String Type" with a VOC of 36 vdc. What I'd like to do is make this a 24 or 48 vdc system but don't know which is the better route to take. The panels I got New at a yard sale for $50 total. I've not bought batteries, controller or inverter yet.
Since my RV just recently got a New EPDM roof, I went ahead and mounted the panel's but didn't wire anything up yet. I have a New Engel fridge that can run off either 12/24 vdc or 120 vac with a current draw of 1.5 amps and 3 led lights, that's it. My Winnie Minnie is only 23 ft long so it was my intent to cover the roof with 95% solar panels. There's no AC unit, fans or vents on the roof either, just the panel's. Over done and overrated? Yes, because I wanted the roof covered 95% with panel's. What would you do if you had this set up?
True, I have no loads in mind but the biggest thing I would probably run is the $60 Walmart microwave if I have the power then add other things if I have the potential to expand later.

Comments

  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    You would probably be best off with a 24 volt system... it really depends on your loads and your battery (which you have not specified).  You can probably also get by with 12 volts, but that will make expansion difficult... loads tend to grow with time.

    Assuming that you have no shading issues with your panels, as a first approximation your panels could support about 230 ah of battery at 24 volts... That would be 4 golfcart batteries in series.

    With those panels you will need to configure them as two strings (Voc = 72 volts) and use a 30 amp MPPT controller (for a 24 volt system).   You can put all panels in parallel with a 45-60 amp MPPT controller (for a 12 volt system).

    If partial shading of your rooftop panels is an issue, you might be better off at 12 volts because parallel panels deal better with partial shading.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    What vt said. 48V is overkill for an RV. 24V is ideal, 12V is what you settle for if you have 12V start electrics AND you NEED the alternator.

    For RVs I always prefer 36cell panels. 60 cell panels have an odd voltage that as said above pushs you to over long strings, and mppt controllers.

    If im reading this right while you have two panels so far, you plan is to actually employ 1+kW of PV?

    On our motorhome, it boiled down to the DC compressor fridge, and how often the vehicle (doesnt) moves.

    If, each day, you move the RV AND drive long enough each time to charge the house system, OR you have access to shore power, then go ahead and design around the alternator. Otherwise the logical conclusion is to build a solar system that is capable of running the fridge by itself.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar