What role do energy audits play in off-grid planning?

Understanding Energy Demands

An energy audit begins by assessing the energy demands of the off-grid system, including the household’s power requirements, lighting, and appliance usage. This involves calculating the total daily energy demand in watt-hours (Wh) or kilowatt-hours (kWh). For example, a household with three 60W LED light bulbs and a refrigerator consuming 100W can be calculated as follows: (60W * 8h) + (100W * 8h) = 480Wh + 800Wh = 1280Wh per day. This information helps determine the required solar panel capacity and battery bank size.

Calculating Solar Panel Capacity

The solar panel capacity is calculated based on the energy demands and the amount of sunlight available at the site. A common rule of thumb is to allocate 1-2 watts of solar panel capacity per square foot of roof space. For a 10x10 foot roof space, this would translate to 100-200 watts of solar panel capacity. However, the actual capacity required depends on the location’s solar irradiance, which can range from 5 to 7 kilowatt-hours per square meter per day in different regions.

Battery Bank Sizing

The battery bank size is determined by the system’s energy storage requirements, taking into account the depth of discharge (DOD), which is the percentage of charge that can be drawn from the battery before it needs to be recharged. A common DOD is 50%. For a 2-day energy storage requirement, the battery bank size would be calculated as follows: (1280Wh * 2 days) / 0.5 = 5120Wh. This translates to a 5-kilowatt-hour (kWh) battery bank. The actual battery bank size may need to be adjusted based on other system factors, such as charging and discharging efficiency.