Photovoltaic Solar Glossary: What Is Insolation?

Photovoltaic solar energy, despite its increasing level of popularity, remains a bit of a mystery to many people. This is especially true with regard to the science of transforming the sun’s energy to usable electric power. In this version of our ongoing Solar Glossary, we explain the fascinating phenomenon of solar insolation.

To understand this concept, it’s necessary to back up a bit and examine its precursors. The amount of photovoltaic power at a given location is known as solar irradiance. Irradiance varies throughout the day as the sun moves through the sky, and throughout the year, as the earth moves around the sun. Weather also affects solar irradiance. The measurement of irradiance over a specific period of time is referred to as solar insolation.

Calculating Insolation

An acronym of incoming solar radiation, insolation is measured in hours, and for photovoltaic applications, is defined as kilowatt hours per square meter per day. Daily insolation levels can be calculated using data about the location’s latitude and day of the year.

Horizontal insolation also is widely used in the industry. For this calculation, the amount of irradiance received by a flat, horizontal surface ― such as a skyscraper rooftop, football field or swimming pool ― is measured over a period of time. Online photovoltaic charts and irradiance calculators can help consumers determine the daily insolation in their area of the country.

Why We Measure Solar Insolation

The purpose of calculating irradiance and insolation is to determine the amount of sunlight photovoltaic panels can absorb. This is useful in deciding upon the size of a photovoltaic system and the number of solar panels that will be necessary to provide enough electricity for a home or business.

Areas with high daily insolation, including Nevada, Utah and other sun-drenched Southwest and Intermountain states, will not require photovoltaic systems as large as those needed in Alaska and states in the Northeast. Knowing the insolation for a region can help consumers make informed decisions about using solar power for their homes and businesses.

How Insolation Affects System Design

To understand how this calculation affects PV system design, consider this scenario:

Take two identical homes with identical energy needs and place them in areas with different insolation levels. While a 3-kilowatt system may supply enough electricity for the home with a high daily insolation level, a larger system will be needed to provide enough power for the less-sunny home.

Photovoltaic systems are designed with this in mind, and their size is determined by dividing the number of kilowatts of power needed by the amount of solar irradiance at that location. This provides us with an idea of how many solar panels are needed to generate a sufficient amount of power.

You must consider solar insolation to create an effective photovoltaic system. Here at Intermountain Wind and Solar, solar is our specialty. Consequently, we understand irradiance and how it affects system output. This allows our engineers to design a photovoltaic system to meet your specific energy needs. Contact us today to learn more about photovoltaic solar energy.