Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. It is measured in watts per square meter (W/m²).
Peak sun hours, also called peak sunlight hours, are a way to measure how much sunlight a location receives. A peak sun hour is defined as one hour in which the intensity of sunlight (solar irradiance) averages 1,000 watts per square meter. This can be written as:
\[ 1 \text{ peak sun hour} = 1 \text{ hour of sunlight at } 1,000 \text{ W/m}^2 = 1,000 \text{ Wh/m}^2 \]
And because 1,000 watts is equal to 1 kilowatt, we can also write it as:
\[ 1 \text{ peak sun hour} = 1 \text{ hour of sunlight at } 1 \text{ kW/m}^2 = 1 \text{ kWh/m}^2 \]
Using historical data, we can estimate the amount of sunlight we expect a location to receive per day and express this value in peak sun hours. For example, Phoenix, AZ, receives around 5.8 peak sun hours per day on average. This means on an average day, the sun will pump out 5.8 kilowatt hours of sunlight per square meter.
Knowing the number of peak sun hours your location gets is useful because it lets you estimate how much energy a solar power system could produce. For instance, a 5 kW solar array in Phoenix could produce approximately:
\[ \text{Estimated output} = 5 \text{ kW} \times 5.8 \text{ peak sun hours per day} = 29 \text{ kWh per day} \]
Solar irradiance measures the power of solar radiation on a surface at an instant, while solar irradiation measures the energy received on a given surface over a period of time.
Solar irradiance is crucial for determining the potential electricity generation of a solar power system. It helps in predicting energy generation, climate modeling, and weather forecasting.
Solar irradiance is measured using instruments like pyranometers and radiometers. These instruments measure the intensity of sunlight hitting a surface.