Whether on or off the grid, using solar panels (also called solar PV panels, PV panels, or PV modules) is one of the simplest and cleanest ways to convert the sun's energy into electricity. Solar panels are clean, quiet, direct, and incredibly durable, with a maintenance-free lifespan of decades. And solar has declined in price by more than half in just the last 10 years.
Real Goods' legacy is directly linked to the practicality and reliability of off-grid solar panels - we sold the first off-grid solar panel in the U.S., after all. But we've also built solar PV systems for thousands of customers across the country since 1978, and most are still going strong decades later.
We literally sold the first retail solar panel in the U.S. back in 1978 (a 9-Watt panel that cost $900!) and have been an industry leader in helping people go solar ever since. In those 40 years, we've seen PV design and manufacturing trends come and go, and we've watched the cost per Watt fall dramatically. We know what quality and value in solar panels looks like, and that's what we carry.
STC stands for Standard Test Conditions, which is the industry-standard performance test run on PV modules after manufacture. The test hits the panels with 1000 Watts per square meter of simulated sunlight at 77°F. Unfortunately, real-world conditions are usually not this favorable - meaning panels tend to perform below their STC results.
This is why it's important to check solar panel spec sheets for output or power "tolerance", which is the amount a given panel's power output can vary from its STC-rated power. For a 300-Watt panel, a tolerance rating of +/- 5W means the actual maximum power output of the module will be between 295W - 305W. A tolerance rating of +5/-0 means the module will put out between 300W - 305W. So to get the most out of your modules, avoid those negative power tolerances!
PTC stands for Photovoltaics for Utility Scale Applications Test Conditions. It's newer set of test criteria that more closely mimics real-world conditions by testing at a higher PV cell temperature (113°F compared to 77°F) and with a slight 2.2 mph breeze blowing across the panel.
If STC and PTC values are both listed on a solar panel spec sheet, the PTC values are more likely to reflect the performance you'll actually get.
NOCT stands for Normal Operating Cell Temperature. It is yet another set of test conditions and, like PTC, more closely mimics real-world conditions than STC tests.
NOCT test conditions are an irradiance of 800 Watts per square meter, ambient temperature of 68°F, and a 2.2 mph breeze.
Our Solar Techs have answers! Contact them at 800-919-2400 or [email protected]
Our Solar Living Sourcebook is an excellent one-stop resource for solar PV and everything else off-grid.
To rack and mount your solar PV panels: