Solar Panels

As has been mentioned before, many factors enter into how much power a solar panel setup will produce. total wattage of the array, latitude, time of year, angle of the array in relation to the sun, quality of the panels (mono crystalline, poly crystalline), age of the panels (most panel will decline a few percentage points each year as they age) Distance from battery bank, size of wire used, type of controller and so on.

I would suggest doing the math. Make a chart of how much power you will need, check your panel output, design your installation so you have the shortest distances from panels to controller, from controller to battery bank, make sure you have the correct wire size for the current produced.

If you are using an inverter (12V DC to 120V AC) decide whether you can use modified sine wave or if you will need a pure sine wave inverter). If you are using an inverter, you will need a sub panel or some form of circuit protection.

The key is to take the time to do all of the calculations and plan ahead for your installation. Good quality electric wiring is expensive and going cheap or trying to save money by using undersized wire is a recipe for disaster down the road. There is a lot of experience and expertise on this forum. Ask the questions before you do an installation. You ill get a lot of good advice!

I am pretty much convinced the numbers on the panels are for both panels in parallel. I was watching you tube videos and they can be confusing. HA

(on a side note @ 2manytoyz, i've been reading your website for years. Very impressive. I just realized you were on this forum..

Thanks everyone

wd wrote:
I have 2 65w panels connected through a controller. I am testing them with the connection wires disconnected. I am getting 20.5 VOC and 3.5 ISC from each panel. The back of each panel says it should have 21.6 VOC and 8.31 ISC. Anyone know how much charging power i am losing? Are the panels worn out? I've had them about 9 years from Solarland. Don't have a lot of knowledge about these so any help would be appreciated.

Your Isc of 8.31 is for both panels in parallel (add the amps, volts the same). One 130w panel will have an Isc about 8.2 amps.

Moved from Technology Corner

Many of the better quality panels have a 20 or 25 year guarantee on performance.

But as others have mentioned, time of year, time of day, and angle to sun play a huge role in the output of the panel.

I used to buy Kyocera panels when they sold 12V panels to the public.

Here's how my 135W panel tested:





Here's another panel, same rating, tested a different day:



Both tested about the same on yet another day. Yours are probably fine. Check again during the peak of the day during the Summer.

They are stored in a suitcase. I was just looking at the numbers on the back of the panels that’s probably the max output. Each panel showed the same readings. I’m pretty well convinced the panels are ok. Really appreciate the feedback. Thanks to all. WD

SoCal? Sun is a bit low in the sky this time of year so less energy available. Are the panels mounted flat on the roof or facing direct at the sun? As said above the measurements sound normal. Check it again in June pointed direct at the sun.

mike-s wrote:
Unless you know for a fact that your solar irradiance is 1000 W/m^2 on a panel at 25C, you can't expect to get the numbers on the label. That ISC sounds about 2x too high for a 12 V (nominal), 65 W panel. What does it show as Vmp and Imp? When I Google "solarland 65W", the first relevant hit says 21.6 Voc and 4.21 Isc.

Are the panels part of a folding suitcase, or some such? The rating might be for the pair, not the individual panels.

I fully agree with what Mike-S said. Sounds to me like there is nothing wrong with the two solar panels if the OP is getting 3.5A ISC on each 65W solar panel.

Unless you know for a fact that your solar irradiance is 1000 W/m^2 on a panel at 25C, you can't expect to get the numbers on the label. That ISC sounds about 2x too high for a 12 V (nominal), 65 W panel. What does it show as Vmp and Imp? When I Google "solarland 65W", the first relevant hit says 21.6 Voc and 4.21 Isc.

Are the panels part of a folding suitcase, or some such? The rating might be for the pair, not the individual panels.

Panel watts are computed by multiplying maximum power current and voltage, not short circuit open circuit parameters.