Solar panels and electricity output

There’s no question that a home solar powered system is a smart financial investment.  After all, relying on your own, independent source of energy will dramatically reduce, and often completely eliminate your electricity bill.  However, while owning a solar panel system has long term monetary benefits, the system itself requires a significant initial investment.

Before taking the financial leap towards such a large home improvement project, it is important to understand what to expect from your solar panel system and to make sure all your questions are both heard and answered.

How much you can save from switching to solar is directly tied to the amount of electricity that your PV system is able to generate, so inevitably, the first question that comes to mind is, “How much power can a solar panel produce?”

Understanding power ratings and factors that influence electricity production

A solar panel’s power rating (in Watts) is based on the amount of direct current power it can generate. Today, the majority of solar panels on the market have STC power ratings ranging from 200 to 400 Watts.  Now, this rating is based on the solar panel’s performance under ideal lab conditions, so it is difficult to know exactly how much a particular panel will produce for your home by looking solely at the power rating.

When determining a certain solar panel’s output in your home’s real world conditions, you need to look at many variables (in addition to the power rating) such as:

♦  Sunlight and temperature conditions – Solar panels need light not heat. If it is too hot, solar panels overheat, causing them to work less efficiently. Most solar panel systems need to be installed a few inches above the roof, allowing enough air flow to cool them down.

♦  Degree of shading on the roof – In essence, the less shade the better. If its possible to install your panels where there is absolutely no shade, you will certainly make the most out of your system.

♦  Tilt angle/azimuth of the roof – For optimal performance, your panels need to be close to a 35 degree angle, facing the south or southwest direction.

♦  Geographic location – A 5kW system may produce 6,000 kilowatt-hours (kWh) of electricity per year in Chicago, while the same system would produce 8,000 kWh per year in San Diego since the amount of sun each location gets is significantly different.

♦  Time of year – In the summer, thanks to longer daylight hours, your system will be able to produce proportionally more power.

PTC rating of solar panels

Of course, it may be hard to evaluate a panel’s output with multiple variables in mind.  If you want a shortcut to estimate a panel’s performance, you can look at the PTC rating.  PTC stands for PVUSA Test Condition, and is also commonly referred to as “Performance Test Condition”.

The PTC rating is generally recognized as a more realistic measure of PV output because the test conditions better reflect "real-world” climatic conditions, compared to the STC rating. During the test, everything is heated up and the solar cells within the panel are raised to their “normal operating cell temperature” which is typically around 113°F (45°C). The ambient temperature is set to 68°F, and a 2.2 mph breeze blows across the panel. The PTC rating value is used to figure out your available tax credit when you apply for a rebate.  You can find the PTC rating of almost any panel on the market in this CA database.

Production based on the size of your solar panel system

Exactly how much power you will generate is determined by the size of your system.  To give you the best idea of what to expect, let’s look at the data for average home solar panel systems.

Residential systems range from 1kW to 6kW in size.  A typical 1kW system will produce about 850kW units every year. If the average 3-bedroom house uses around 3,000kW of power per year, then a 4-5kW system would cover the home’s electricity needs.

Your solar installer can recommend an appropriate size for your solar system based on your average electricity bill and your individual preferences.

How will I know how much electricity my solar panels will generate?

You can monitor the performance of your solar panels with a meter. The meter is usually installed in an easily accessible location on the wall of your home and will record the amount of electricity produced by your solar panels as well as how much power is being exported back to the utility grid.

Today, solar manufacturers are becoming increasingly smartphone friendly, developing online monitoring tools, and allowing you to access your system’s performance data anytime, anywhere.

We recommend checking your system’s performance a couple times a month to ensure that everything is operating as expected.