Is There a Best Practice for Sizing Solar Arrays with East-West Orientation?

Accounting for Azimuth

When sizing an east-west solar array, it’s essential to consider the reduced peak sun hours and energy production compared to a south-facing array. Studies have shown that east-west arrays produce around 10-15% less energy than south-facing arrays. To account for this, you can use the following formula to adjust the array size: Size_EW = (0.9 to 0.85) * Size_South, where Size_EW is the required size of the east-west array and Size_South is the required size of the south-facing array.

Using Performance Ratio (PR) and derating factors

A more accurate approach is to use performance ratio (PR) and derating factors to size the east-west array. A PR of 0.85 to 0.9 can be used to account for the reduced energy production. Additionally, derating factors for east-west orientation can range from 0.9 to 0.95, depending on the array’s tilt angle and the local climate. By applying these factors, you can size the east-west array more accurately and ensure optimal energy production.

Example Calculation

For example, let’s say we have a south-facing array that requires 10 kW to meet the energy needs of a building. Using the adjusted size formula, we can calculate the required size of the east-west array: Size_EW = (0.9) * Size_South = (0.9) * 10 kW = 9 kW. Alternatively, using the PR and derating factors approach, we can size the east-west array by applying a PR of 0.875 and a derating factor of 0.92: Size_EW = (0.875) * (Size_South / 0.92) = (0.875) * (10 kW / 0.92) ≈ 9.5 kW.