The reliability challenge for solar energy

Solar power is an intermittent way to generate electricity because the sun does not shine all the time, and therefore cannot be relied upon to meet peak demand, especially in winter. 

The challenge

Solar photovoltaic (PV) panels only generate electricity while exposed to sunlight. They cannot generate electricity at all during the night, and even during the day how much they can generate depends on the weather.

Due to cloud cover, the sun only shines for 34% of a typical day in a typical UK location – but our demand for electricity does not always coincide with times when the sun is shining. In winter, we need more light and heat, but the days are shorter, colder and likely to be cloudy.

The solution

Energy storage may be the way to address the intermittency of solar power. If the energy generated by solar photovoltaic (PV) cells could be stored when demand is low and released when demand is high, their overall output would be more consistent and predictable.

Solar energy could be stored as heat – concentrating the sun's rays to heat a substance such as oil or salts – or as electrical energy in rechargeable batteries connected to PV cells. Research shows that molten salts may offer an effective way to store heat. There are a number of projects using this technology, but further development is required before the technology becomes more widespread. 1Some homes with rooftop solar panels use rechargeable batteries to store electricity, and research continues to improve their efficiency and lower their price, and progress appears to be being made in this area.

Surplus power from solar panels could be used to pump water uphill into a reservoir, releasing it when needed to generate electricity via a hydroelectric turbine. But incorporating pumped storage would be likely to increase the upfront cost of installing solar panels.

Until these storage technologies become more commercially viable, solar energy in the UK must be backed up by other, more reliable energy sources.