The sun is shining brightly on your rooftop solar panels (or the panels you hope to have). But how can you tell if those photons falling from the sky are actually turning into useful electricity? Since there are no moving parts to a rooftop solar system, it can indeed be difficult to tell if you are getting what you paid for. Fortunately, there are four easy ways to keep an eye on your system’s performance. Check the green light on your inverter, check to see that your meter is running backwards, check your electric bill, and check your monitoring system.

1. If you have an ordinary string inverter (that big box hanging on the wall near your electric meter), all you need to do is make sure the green light is on and that the inverter’s display indicates that power (measured in watts) is being generated. Usually you should see peak output around noon, and on a sunny day this output will usually be about 75% of the rated DC output of your system.

2. Another way to check your system’s operation is to see if your electric meter is running backwards on a sunny day -- but note that the amount of power you are sending back to the utility (usually in kw) is the net of what your solar generates minus what your house is currently using.

3. You should also keep an eye on your monthly electric bill -- a sudden increase in kwh billings from your utility could be a sign that your system is not operating properly (or the weather was hot and your AC was cranking).

4. Systems with monitoring are easier to manage, both for you and your installer. There are two types of monitoring: system level and panel level.

System level monitoring involves installing a gateway between your inverter (or microinverters) and your home internet connection. The gateway sends inverter data up to a webpage where you can check your output (at any time) and energy production (during any interval). Panel level monitoring gives you even more granular data, but this type of monitoring requires a microinverter or optimizer on the back of every panel. Although slightly more expensive, panel-level monitoring makes it easier for you or your installer to make sure your system is operating properly. It is important to note that the most common solar service calls are due to monitoring problems, and these monitoring problems do not necessarily mean that your system is not producing power (usually there is just a problem with your internet connection or gateway).

For more on the benefits of monitoring your rooftop solar system, please Listen Up to this week’s Energy Show on Renewable Energy World.