Solar panels energy efficiency is the percentage of sunlight that this particular system converts to electricity. New types of solar panel systems are being developed and improved constantly, and in laboratory conditions engineers are able to reach efficiency of 42%. While it's an impressive number, in general, the efficiency of most solar panels varies around 10%-25%. The performance of solar panels depends on a set of factors, such as the type of panels you're using, weather conditions and placement.
It's important to note that the efficiency of a solar panel system is determined in Standard Test Conditions (STC): 77 °F (25 °C) and irradiance of 1,000 W/m2. A solar panel system with efficiency of 20%, for example, gives out 200 Watts from 1 m2. The more efficient a particular system is, the less panels and therefore less space for them you need. It doesn't necessarily mean that you should always go for the most efficient choice: performance of a system greatly affects its cost so in some cases it is smarter to invest in a less efficient model that makes use of empty space on your roof.
In practice, an average annual electricity consumption for a utility customer is nearly 11,000 kWh, according to the US Energy Information Administration, which translates to around 30 kWh daily. 14-26 solar panels can cover these needs. Of course, some panels perform better than others, and their efficiency can also be affected by weather or positioning. Let's look in detail at different factors and their effects. There are several of them:
- weather conditions and shade
- positioning and angle
- type of panels