How to assess sunlight availability for off-grid solar?

Determining Location and Time of Year

To assess sunlight availability, first consider the location and time of year. The closer you are to the equator, the more sunlight you will receive throughout the year. However, even locations at higher latitudes can receive significant sunlight during the summer months. For example, in the northern US, a location at 45° latitude can receive up to 6 hours of direct sunlight in December. Use online tools such as the NASA Surface meteorology and Solar Energy dataset or consult with a solar expert to determine the maximum daily solar irradiance for your specific location.

Evaluating Shading and Obstructions

Shading from trees, buildings, or other obstructions can significantly impact sunlight availability. To evaluate these factors, create a site plan and identify potential shading sources. Use tools such as Google Earth or SketchUp to visualize the site and identify areas of shading. Consider installing a solar pathfinder or using a smartphone app to measure the amount of sunlight received on a south-facing surface during different times of day.

Calculating System Size

Once you have determined the maximum daily solar irradiance and evaluated shading and obstructions, you can calculate the required system size. A general rule of thumb is to size the system to provide 1-2 kWh of energy per square meter of array size per day. For example, if you have a location with 6 hours of direct sunlight and a maximum irradiance of 200 W/m², you would size the system to provide around 1.2-2.4 kWh of energy per day. This helps ensure the system is sized correctly and meets your energy needs.