# 12v or 24v panels?

Solar Expert Posts: 225 ✭✭✭
I was talking to someone today who said that 200 watt PV panels were always 24v. So, can I use a 200watt panel with a 12v appliance?

If not, what is the maximum wattage panel that I can use that is still 12v?

thanks!

• Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
Re: 12v or 24v panels?

Some, but not all, ~200 W modules are considered “24 V” modules. These typically consist of 72 cells wired in series, although there are exceptions.

24 V Example: http://store.solar-electric.com/so230wamosop.html
24 V Exception: http://lib.store.yahoo.net/lib/wind-sun/BP-SX3200.pdf

There are many other exceptions. These ~200 W module consists of 60 cells in series, and are considered “20 V” modules.

See: http://store.solar-electric.com/casocs200was.html
And: http://store.solar-electric.com/shsondsopa1.html

And, there are “12 V” modules rated at ~200 W.

See: http://store.solar-electric.com/ev180wasopa.html
And: http://lib.store.yahoo.net/lib/wind-sun/ESA-200.pdf

What kind of charge controller are you planning to use?

HTH,
Jim / crewzer
Re: 12v or 24v panels?

If you are placing one or more 200 watt panels in service... Then you are in the area of running a MPPT type Solar Charge Controller. Most will take "24 volt" panels and down convert them to "12 volts" for your system very nicely and efficiently.

If you are looking at 400+ watts of solar panels--then you are looking at "full sized" MPPT type charge controllers (60-80 amps each). And--at 48 volts, a "60 amp" charge controller will hand 4x the wattage of solar panels vs a 12 volt battery bank (60 amps * 60 volts charging equals ~3,600 watts of solar panels; 60 amps * 15 volts equals ~900 watts if solar panels).

Define your loads first (number of watts--peak and average--, for how many watt*hours per day, 120/240 VAC or 12, 24, 48 VDC or whatever...).

Once you do that, then the inverters, converters, charge controllers, and solar panels will sort themselves out just fine.

My personal rule of thumb--try to limit maximum continuous battery current to 100 amps max... As the current increases much beyond 100 amps--the costs for wiring, switches, breakers, fuses goes up dramatically.

At 12 volts--that would be a 1,200 watt inverter/load. At 48 volts, that would support a 4,800 watt load/inverter.

Also, voltage drop (at high currents) is a huge problem at low battery bank voltages... A 12 volt system with 2 volt drop will turn off most inverters. A two volt drop on a 48 volt system is not much of a problem at all.

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