1. Ipsun Solar Library
2. Solar 101: Everything You Need to Know About Solar Energy

Why is my 10kW solar panel system not producing 10kWh?

There is a fundamental difference between kW and kWh. The kW of a solar system referred to the installed capacity and the kWh is the energy it actually produces.

There is a difference between kW and kWh and that difference is what causes a lot of confusion. What's the difference between kW and kWh?

Analogies 1: A car

When you're talking about a car, you could talk about the amount of horse power a car has. Some powerful cars can have 300 or 400 horse power, but when you drive with that car you rarely use that 300 horse power. There is a difference between the nameplate horse power and what you actually use.

Analogies 2: An airplane

When one talks about an airplane one can talk about the maximum altitude the plane can reach like 10,000 feet or 45,000 ft or the maximum speed an airplane can travel at. This doesn't mean the airplane will always be at that altitude nor does it mean it will always travel at that maximum speed.

What does this mean for a solar panel?

A solar energy system is composed of individual solar panels. Each solar panel has a nameplate Wattage. We currently install a standard 380W panel (this is 0.38kW) at Ipsun Solar. We also use LG's 425W panel and have commercial panels of 450W etc. This is similar to the car analogy of 300 horse power. This is what the nameplate of the machine says. Once sunlight hits the solar panel, then it produces energy. If you have a little bit of sunlight, the panel produces a little bit of energy  If more sunshine hits the panel more energy comes out of the wires of the solar panel.

Standard Condition for a solar panel.

A solar panel gets "flashed" with a big light simulating the sun. The test happens at a specific atmospheric pressure, temperature and light intensity. Imagine a big light flashing 1,000W on a solar panel and the test then measures what comes out of the panel. You guessed it, for a 380W panel flashed with 1,000W, 380W comes out of it. Flashing has different standards and ways to measure things. Example of flashing standard: Measurement tolerances PMPP ±3%; ISC; VOC ±5% at STC: 1000W/m2, 25±2°C, AM 1.5G according to IEC 60904-3 ∙ 2 800 W/m², NMOT, spectrum AM 1.5G

From kW to kWh

Your solar energy system and solar panels have an installed capacity measured in watts or killowatts (kW) installed. If the sun hits your system with a specific sun intensity called solar irradiation for an hour your panels and solar system will produce a certain amount of kWh. That's the wattage for 1 hour. We all know the sunshine hitting your panels is not contant. It varies over time on a single day. It also varies per season. The tilt (the angle towards the sun) of your solar panels also has an effect on how much sunlight is hitting your panels and thus the energy production coming out.

I wrote another article about "The Effect of Solar Panel Orientation and Azimuth on Their Performance" https://blog.ipsunsolar.com/the-effect-of-solar-panel-orientation-and-azimuth-on-their-performance

Conclusion:

A solar panel has a nameplate capacity measured in Wattage just like a car has an amount of horse power or a plane has a maximum altitude or maximum speed. The amount of horse power you use while driving the car depends on your speed, the inclination of the road and other factors. Your solar panel's energy output measured in kWh depends on the sunlight intensity, tilt, temperature and other variables. That's why a solar energy system of 10kW will produce an electric energy measured in kWh that is most of the time different than 10kWh as the energy produced by the solar panes depend on multiple factors like the sun intensity, tilt, temperature, azimuth etc.