Starting Out: 230W panels and a PWM controller?

WYsolar · April 2013

List....

After many fits and starts I have the opportunity (about 90% sure) that I can begin building my small solar backup project.

I have the opportunity to purchase 2 good used Sharp 230w panels:

Max Power Rating: 230
STC: 230
PTC: 207.4
Vmp: 30.3
Imp: 7.6
Voc: 37
Isc: 8.24
TempCorrI: 0.053
Efficiency: 14.1
Max Fuse Rating: 15

I plan to feed 2x 6v 220Ah sam's club golf cart batteries in a 12v configuration.

I know a MPPT controller would be much better for my project...but they are just too expensive right now. As a result
I was hoping to use a 20A or so PWM controller like the SunSaver 20L.

QUESTION: Would a PWM controller work in such a situation?

It does not have to be the most efficient now...just work well enough to charge my batteries. The batteries are just for emergency backup (I plan on including a Morningstart 300w Ac inverter in the future)...and for running my small Ham Radio. When I save up more $$ I plan on purchasing a small MPPT controller (like the Phocos 100/20 or the new Rogue if the prices stay <$350 or so).

Thanks for the advice.

Cariboocoot · April 2013

Re: Starting Out: 230W panels and a PWM controller?

It will work. You'll just be wasting a lot of the power potential from the panels.

Essentially the PWM controller will simply pass the Imp of the panels but @ battery Voltage. So the maximum power will be about Imp * Absorb Voltage or roughly 15.2 * 14.8 = 225 Watts total. As such the charge rate would peak at about 6.8% on those batteries.

WYsolar · April 2013

Re: Starting Out: 230W panels and a PWM controller?

Thanks for the reply, Carib.

To clarify...are you saying that the total wattage of my two panels (460) would be derated to 225W total (over a 50% loss) if I use a PWM controller...or that each panel would be derated to 225W (a loss of 3%).

The 3% I could live with...but a loss of 50% would be catastrophic.

Cariboocoot · April 2013

Re: Starting Out: 230W panels and a PWM controller?

WYsolar wrote: »

Thanks for the reply, Carib.

To clarify...are you saying that the total wattage of my two panels (460) would be derated to 225W total (over a 50% loss) if I use a PWM controller...or that each panel would be derated to 225W (a loss of 3%).

The 3% I could live with...but a loss of 50% would be catastrophic.

That would be the total Wattage: two panels at Imp 7.6 each = 15.2 Amps current. The Voltage is then fixed by the system. With 14.8 Volts on Absorb .... 15.2 * 14.8 = 225 Watts total.

The massive loss comes from the panels' Voltage potential of 30.3 not being utilized by the PWM controller. It can't be helped. Sorry.

westbranch · April 2013

Re: Starting Out: 230W panels and a PWM controller?

the economics of the situation suddenly becomes clear, you are paying more for the MPPT controller to 'access' that > 50% 'lost' power. Pretty cheap power? $233 vs $78 Just no way get to that power when you have GT panels

Photowhit · April 2013

Re: Starting Out: 230W panels and a PWM controller?

WYsolar wrote: »

Thanks for the reply, Carib.

To clarify...are you saying that the total wattage of my two panels (460) would be derated to 225W total (over a 50% loss) if I use a PWM controller...or that each panel would be derated to 225W (a loss of 3%).

The 3% I could live with...but a loss of 50% would be catastrophic.

It's not as bad as all that, you can expect to get the 225 watts. The expected output from the 2 - 230 watt panels is likely 80-85% of their panel rating, This is called the NOCT value (Normal Operating Cell Temperature) as panel heat up their voltage is reduced, since you have plenty of voltage you won't have these losses.

I went and hunted down the spec sheet on What I suspect your panels are;

http://www.pvpower.com/pdf/datasheets/sharp/pv%20modules/sharp%20230.pdf

Your panels 230 watts at 25 degrees C operating temp, but looses .485% of it's voltage for every degree above 25, and the NOCT temp of 47.5 so you loss about 11% of your voltage...

Remember to that the charge controller typically, starts reducing the output as your batteries reach 85% of capacity, as we recommend you don't discharge below 80% on a regular basis, it will be at it's worse when you have significantly discharged your battery.

WYsolar · April 2013

Re: Starting Out: 230W panels and a PWM controller?

Wow.

Sure enough. Pricewise you just can't win.

BTW...what are "GT panels"?

niel · April 2013

Re: Starting Out: 230W panels and a PWM controller?

abbreviation for grid tie.

Cariboocoot · April 2013

Re: Starting Out: 230W panels and a PWM controller?

GT panels = grid tie as Niel said, meaning ones whose Vmp is not ideally suited for battery-based systems using a PWM controller.

WYsolar · April 2013

Re: Starting Out: 230W panels and a PWM controller?

Thanks again for the kind advice.

It seems to be a catch-22 situation.

12v panels = higher cost for given wattage, but can use lower cost controllers
"GT" panels = lower cost for given wattage, but require much more expensive MPPT controllers to harvest the same energy.

Hard to justify a $400+ controller for my little solar 220Ah battery project. Hmmm.

Rybren · April 2013

Re: Starting Out: 230W panels and a PWM controller?

Here's a sample calculation that I did when considering 12V panels v GT panels...

Four 210W @ $150 each=$600 + $500 60 Amp MPPT = $1,100 for 840 Watts and 54 Amps peak current on a 12 volt system

Or

Four 135W @ $300 each =$1,200 + 45 Amp TriStar PWM @ $150 = $1,350 for 540 W and maybe 30 Amps peak current on a 12 Volt system

For prices, I used the going rate here in Ottawa.

I ended up going with Option 1 and managed to pick up a Classic 150 for less than $500 at the Midnite Garage Sale. (I also decided to go with a 24V system)

vtmaps · April 2013

Re: Starting Out: 230W panels and a PWM controller?

WYsolar wrote: »

12v panels = higher cost for given wattage, but can use lower cost controllers
"GT" panels = lower cost for given wattage, but require much more expensive MPPT controllers to harvest the same energy.

Actually, you will harvest more of your panel's potential with the MPPT controller.

--vtMaps

KnowledgeSponge · April 2013

Re: Starting Out: 230W panels and a PWM controller?

As a newbie, may I assume (uh oh) that if MY panels are rated at only 18v (100W, 5.7A) that I would not have this massive loss using the same PWM controller?

Cariboocoot · April 2013

Re: Starting Out: 230W panels and a PWM controller?

KnowledgeSponge wrote: »

As a newbie, may I assume (uh oh) that if MY panels are rated at only 18v (100W, 5.7A) that I would not have this massive loss using the same PWM controller?

You are correct. The current stays the same, the Voltage changes:
5.7 Amps @ 14.8 Volts Absorb on a 12 Volt system = 84 Watts, only 16% less than the rating.

The "extra" Voltage of the panel is needed to overcome wiring and heat losses.

KnowledgeSponge · April 2013

Re: Starting Out: 230W panels and a PWM controller?

Cariboocoot wrote: »

You are correct. The current stays the same, the Voltage changes:
5.7 Amps @ 14.8 Volts Absorb on a 12 Volt system = 84 Watts, only 16% less than the rating.

The "extra" Voltage of the panel is needed to overcome wiring and heat losses.

Cool, thx :cool:

Starting Out: 230W panels and a PWM controller?

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