The daily energy production of a solar farm, a utility-scale photovoltaic installation that feeds power directly into the electrical grid, is highly variable. The energy yield is not constant because solar power depends entirely on the sun. Daily output is a complex calculation influenced by the farm’s fixed physical characteristics and fluctuating environmental conditions. To accurately estimate how much electricity a solar farm generates daily, the fundamental concepts of power capacity and energy delivered must first be understood.
Capacity vs. Actual Production
Understanding solar farm output requires distinguishing between capacity and energy. Capacity, measured in Megawatts (MW), represents the maximum rate at which the farm can generate electricity at any single moment under ideal conditions. This is the facility’s instantaneous potential, similar to the horsepower rating of a car engine. For example, a 100 MW solar farm is rated to produce 100 Megawatts when the sun is at its peak intensity.
Actual production is measured in Megawatt-hours (MWh), a unit of energy representing the total electricity delivered over time. This MWh figure is the accumulated output. If a 100 MW solar farm ran at maximum capacity for a full hour, it would generate 100 MWh. Since solar farms cannot produce power at night or during cloudy weather, the total daily MWh output is always significantly lower than the theoretical maximum.
The Role of Capacity Factor
The actual daily energy output is quantified using the Capacity Factor (CF). This ratio accounts for all non-production time and performance losses by dividing the actual energy generated over a period (day or year) by the maximum possible energy that could have been produced if the plant ran at nameplate capacity 24 hours a day. This factor is necessary because a solar farm’s instantaneous power output constantly changes based on the time of day and weather conditions.
For utility-scale solar installations, the annual Capacity Factor typically falls within a range of 18% to 30%. A higher CF signifies that the plant is generating energy closer to its maximum potential, while a lower CF indicates greater downtime or reduced efficiency. For instance, a solar farm in the sunny American Southwest might achieve a CF near 29%, while a similar facility in a less sunny region could be closer to 17%. The Capacity Factor is the most important metric for forecasting a solar farm’s energy yield and financial viability.
Primary Variables Affecting Daily Output
The wide variation in the Capacity Factor is driven by a combination of environmental and technical variables.
Environmental Variables
The most significant environmental factor is solar irradiance, which is the amount of solar energy that hits a given area, fundamentally determining the available resource. Geographic location, including latitude and altitude, dictates the average daily hours of sunlight and the angle at which the sun’s rays strike the panels. Areas closer to the equator and at higher altitudes generally receive more intense solar energy.
Local weather patterns, such as heavy cloud cover, can severely reduce output, often dropping a panel’s production to 10–25% of its rated capacity. High ambient temperatures also negatively affect performance, as the efficiency of photovoltaic cells decreases by approximately 0.4% to 0.5% for every degree Celsius above their optimal operating temperature.
Technical Variables
Technical considerations also play a role, including panel orientation and the use of tracking systems that follow the sun’s path throughout the day, which can significantly increase the total energy capture. Other losses occur through system components like inverters, wiring resistance, and the gradual degradation of the panels over their operational lifetime.
Translating Size into Daily Energy Yield
The concepts of capacity and Capacity Factor can be combined to estimate a solar farm’s daily energy yield using a simple formula: Capacity (MW) × 24 hours × Capacity Factor (CF) = Daily Energy Produced (MWh). This calculation converts the farm’s maximum potential into a realistic daily average. A 100 MW solar farm with an average annual CF of 25% would be expected to produce approximately 600 MWh per day (100 MW × 24 hours × 0.25 CF).
For example, a 50 MW farm in a high-insolation region with a 28% CF would yield around 336 MWh. Conversely, the same 50 MW farm in a cloudier region with an 18% CF would only yield about 216 MWh per day. Utility-scale solar farms typically yield an average of 4.3 to 7.2 MWh of energy per day for every Megawatt of installed capacity, depending on the site’s Capacity Factor and location.