Power plant owners notice that sometimes the instantaneous efficiency of a power plant does not reach its maximum installed capacity. It is a common perception that the sunnier and hotter the day, the higher the solar power plant's generation will be. In fact, the power plant needs the sun, but on hot days, the solar modules heat up and the efficiency of the module drops, so you will see a lower instantaneous power output. However, it is natural that on hot days, even if the instantaneous output of the power plant is lower, it will generate more kWh, because the power plant's output will be constant.

How do weather conditions affect the weather?

Environmental conditions have a big impact on the amount of energy a solar power plant produces. The PV modules produced are tested under STC (Standard Test Conditions) conditions. These conditions correspond to a module temperature of 25 °C and an illuminance of 1000 kWh/m2/year.Please note that in UK conditions, the illuminance varies between 800-900 W/m2. However, at high illuminance, solar modules can heat up and their temperature can increase up to 60 °C. With each degree increase in temperature, the efficiency of the module drops, so that on a hot day, the instantaneous power output of the plant is about 20% lower than the installed capacity of the plant.The ideal conditions for instantaneous power are when the clouds on a cloudy day "cool" the modules and the sun shines directly on them. In this case, the sun shines with high intensity on the cooler module and for a few minutes the instantaneous power output of the plant can even rise above the maximum installed capacity.Cool and sunny weather is particularly favourable for solar power plants to generate electricity. This means that there may be days when your power plant is even more efficient on a sunny autumn day than in summer, when outside temperatures are much higher. Although it is common to expect fewer sunny days in autumn, it is worth noting that solar power plants can still generate electricity, even when it is more cloudy or foggy.

Leapfrog instantaneous generation - an example of a 10 kW solar power plant

In the example above, the instantaneous (hourly) generation of the plant is higher on a cooler day than on a hot day with an air temperature of +27 °C.The hourly readings are different in the two graphs, with the cooler days generating 0.93 kWh more electricity (9.77 kWh - 8.84 kWh). However, it is important to note that the total daily generation on a hot and sunny day is significantly higher than on a cool day - 74.54 kWh and 50.01 kWh respectively.This means that although the instantaneous (hourly) generation is higher on a cool day, it is the result in the long term that matters.

Most favourable weather conditions in UK

In UK, the ideal orientation of a solar power plant is south and at an inclination angle of 36-39°. This is the most common orientation for ground-mounted solar power plants. When installing a solar power plant on a roof, it is often not possible to match the ideal orientation and tilt angle of the modules. We suggest choosing the most favourable roof slope towards the south and laying the modules on aluminium profiles, which will help to artificially create the ideal tilt angle of the modules. This way the system will be long lasting and the losses due to less than ideal orientation and tilt angle will be only about 5-10%.