Testing Solar Panels


Okay, you bought a solar panel.  How do you know it works?  How much power should it supply?  I'll show you simple ways to determine if it's working by using an inexpensive meter.  Then some more elaborate tools as your system grows.

The most basic tool for testing your solar panel is a Digital Volt Meter (DVM).  Don't run out and buy an expensive Fluke meter, a $1.99 Harbor Freight meter works just fine.  And if you hook it up wrong, you're out $1.99!


This is a 15 Watt panel from Harbor Freight.  Note the reflection of my flag, and the overcast sky...  Oh, and the meter that's connected directly to the wiring from the panel.


Most basic solar panels have a no load Voltage output of 18-23 Volts.  I have the meter set for DC Volts, 200 Volt range since this is beyond the 20V range.

An overview of the setup.

Clouds kept the output of the panel constantly changing.

To measure the current of the panel, disconnect the positive lead from the Voltage jack, and move it to the 10 Amp jack.  Then rotate the dial to the 10 Amp position.  Reconnect the meter to the panel.  During a cloudy period, the output measured 0.79 Amps.

A closer view of the meter settings for measuring current.  When the sun finally peeked out from behind the clouds, the output increased to almost 1 Amp.

130 Watt Kyocera panel on the left, 15 Watt Harbor Freight panel on the right.  The procedure for testing either of these panels is the same.

No load Voltage was almost 21V.

The short circuit current test was almost 7.5 Amps.  Most of my meters are rated at 10 Amps, some at 20 Amps.  Keep that in mind when measuring the current of your single panel, or an array.  You could exceed the rating of your meter, and blow an internal fuse, if you go beyond it's capabilities.

My array is presently 225 Watts.  This would exceed the rating of a 10 Amp meter.

Using another meter, with a 20 Amp range, I used the same method to measure the current.  Getting serious current at this point.  Making/breaking connections will throw a spark, be careful.


Bigger Setup, Better Tools

Two major problems with using a DVM to measure current are the limited range, and the meter must be in the circuit.  A clamp-on DC Ammeter has a much greater range (40A & 400A range on mine), and it simply clamps onto the wiring, nothing to disconnect.  This meter costs about $70, bought it at Northern Tool.  If you get such a meter, make sure it can read DC Amps, most only work with AC.  For more money, you can get one that will read both DC and AC Amperage.

If you look closely, you can spot this meter being used.

As my panels exceeded the 10 Amp rating of the MorningStar 10-L controller, I added a 30 Amp ProStar controller, with a built-in LCD meter.  It not only measures the system Voltage, but also the charging current and load current.

Solar array charging at 10.5 Amps.

At night, my outdoor lighting, security system, etc, all run from battery power.  Drawing 2.1 Amps.  This charge controller cycles through the three display functions every couple of seconds.

I added a remote display kit to my Xantrex Prosine 1800 Watt inverter.  This also shows the system Voltage, and discharge current.  It does not show the charging current.

The problem with measuring battery Voltage alone, is that it is a poor indicator of how much energy remains in the battery.  Unless the battery has had a few hours to 'rest', the numbers will be inaccurate.  A better way is to measure the current in/out of the battery bank.  The Xantrex LinkPRO does just that.  It comes with a shunt, allowing it to measure how much goes in or out, then gives a display of the amount remaining like a fuel gauge.  This product does a LOT more than I am willing to cover here.  For more information, check this out.

With both vehicles parked in the garage, access to my alt-power bench is limited.  So I installed a remote display for the inverter, and the LinkPRO, next to the door going into the house.  Now I only need to poke my head into the garage to see the status of my batteries and the inverter.

Details on the installation of the Xantrex LinkPRO is at this link.





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Last updated 2/02/09    All rights reserved.