Specific yield (kWh/kWp) is one of the most commonly used performance metrics for all sizes of solar systems. It’s used for many things such as comparing different locations, analyzing different designs, and assessing the health of an array. Specific yield refers to how much energy (kWh) is produced for every kWp of module capacity over the course of a year. Typical values can range from 1,000 kWh/kWp to over 2,000 kWh/kWp, but the actual value is driven by many factors, which include location, module selection, and balance of system efficiency.
A project’s location determines the amount of sunlight or irradiance it will receive. Irradiance is usually the biggest driver of specific yield because it can vary a lot. It depends directly on the location of a solar array, as well as other factors such as location, exposure to shade, soiling, and snow. With module selection, the modules are often described by a single number called module wattage. All modules lose efficiency in hot and low-light conditions, but at different rates. A module with a better temperature coefficient can improve the yield of a project by two to four percent. Balance of system efficiency includes inverter efficiency, inverter clipping, MPP tracking losses, DC and AC wire losses, mismatch losses and more. The balance of system is all components of a solar system except the photovoltaic panels, so it includes wiring, switches, the mounting system, solar inverter(s), a battery bank, and battery charger.
These factors all have an impact on a solar system’s specific yield. In each location, there’s a difference of 20 percent or more between the lowest and highest yield designs. These designs have different impacts of shading and temperature among many other things, and are important to look into once you decide to go solar!