36 v panel

Re: 36 v panel

Welcome to the forum Patrick,

We have to be careful with solar panels... Your panel, in our terms, is not a 36 volt panel... It is a ~30 volt Vmp (voltage maximum power) panel.

System Rating: 250 Watts
Watts (PTC): 227.5 Watts
Max Power Voltage (Vmpp): 30.1 Volts
Max Power Current (Impp): 8.31 Amps
Open Circuit Voltage (Voc):37.4 Volts
Short Circuit Current (Isc): 8.83 Amps
Max System Voltage: 600 Volts
Module Efficiency: 15.4%

While it is a perfectly good panel--It is not one that can use an inexpensive PWM (pulse width modulation) solar charge controller and efficiently charge a 12 volt battery bank... If you used a PWM controller, you would lose about 1/2 the energy from the solar panel. A "true" 12 volt panel will have Vmp~17.5 to 18.6 volts or so. Solar panels, when they get hot, will have their output voltage fall (upwards of 20% on a very hot day). And 12 volt flooded cell batteries need >~15.0 volts to fully recharge (plus allow for voltage drop in your wiring).

And, Vmp=30.1 volts is not high enough to charge a 24 volt battery bank (you need Vmp~35-40 volts to do that).

So--To efficiently use this panel with a 12 volt battery bank, you would need to look at MPPT (maximum power point tracking) solar chargers. Some examples of smaller charge controllers:

Morningstar SunSaver 15 Amp MPPT Solar Charge Controller
Rogue 30 amps MPPT 12/24/48 volt charge controller
Charge Controllers from Midnite Solar - KID (should be available in a month or two???)

And, there are of course larger MPPT charge controllers in the $500-$600+ price range.

-Bill

Re: 36 v panel

We usually like to suggest that people start with paper designs before the purchase hardware... There are a lot of issues that need to be understood/resolved before you open your wallet. It is easy to get components that may not play well together.

The 250 Watt panel is very good--It is just to work (efficiently) with a 12 volt battery, you need a more complex/expensive MPPT type charge controller.

MPPT controllers are (usually) digital switching power supplies (buck mode down converters--technical jargon)--Which can efficiently (~95% efficiency) take the high voltage/low current from your Vmp~30 volt panel and down convert it to low voltage/high current needed to charge the battery bank. Think of an MPPT charge controller like a variable AC transformer for DC circuits.

And with solar, we are frequently in a bind--You can get "cheap" 250 Watt panels ($$$/Watt) and use "expensive" MPPT Charge controllers to "match the array" to the battery bank.

The other "main usage" for MPPT charge controllers is you can run a "high Vmp Voltage Array" and send the power much longer distances with smaller gauge copper wire (if your array is 10's to 100's of feet away from charge controller+battery bank).

But you have to do a paper design of both types of systems (PWM with "12 volt" panels vs MPPT with non-12 volt panels) and see which system has the best cost/benefit ratio for your needs.

The 250 Watt panel will work very nicely with the MorningStar MPPT 15 amp 12/24 volt controller (very nice small MPPT controller for ~$230). Or you can get a pair of 130 watt panels and a "cheap" PWM controller for ~$100 or less...

So, before you toss the panel, or get too frustrated with my replies ()--I like to start at the beginning--What are your needs? We typically start with the loads which define the battery bank. Then we use that information (plus distance between array/battery bank/loads) to size the solar array, AC inverter (if used), charge controller, etc... Then we start looking for hardware that will meet those needs.

However, we can work other ways too... Give us a battery bank and we can suggest an array+charge controller. Or give us a solar panel, and we can do a paper design for a system and then tell you how well it will perform.

Once we go through a paper design cycle, all of this should make a lot more sense... There will be some math--But it is all pretty easy stuff.

How would you like to proceed?

-Bill

Re: 36 v panel

By the way, loads on solar are critcial to getting a cost effective/working system.

For example, a Coleman cooler that draws 60 watts is about the same amount of energy per day that a full size 17+ cuft Energy Star refrigerator takes:

60 watts * 24 hours = 1,440 WH per day = 1.44 kWH per day
1.44 kWH per day * 365 days per year = 526 kWH per year (standard 120 VAC US fridge >~350 kWH per year)

I see that Marc has already commented about the small fridge--There is the Propane Fridge option--Great for use for a few days/weeks/months at a time... Going to solar refrigeration is usually a better bet when looking 9 months or more per year of off grid living.

There are options--Get a smaller chest freezer, change the thermostat to ~35F range, and you may get down towards ~250 WH / 0.25 kWH per day...

In general, off grid solar costs around 5-10x as much as utility power--So looking at conservation/high efficiency appliances can really save you a lot of money overall (smaller solar array, smaller batteries, etc.).

-Bill