National Grid has warned that record low demand for electricity during Britain’s coronavirus lockdown could lead to windfarms and power plants being turned off, in order to avoid overloading the electricity grid.

The energy system operator has forecast that the lockdown could cut demand for electricity 20% below normal levels, potentially leading to an oversupply of electricity at times.

British households are using more electricity than usual through the lockdown but overall demand for power is far lower since schools, offices, factories and restaurants were forced to close last month.

Roisin Quinn, the head of National Grid’s control room, said low demand could put the network under high levels of stress. She said: “The assumption will be that lower demand makes it easier for us to do our job, with less power needed overall and therefore less stress on the system. In fact, as system operator, it’s just as important for us to manage lower demand for electricity as it is to manage the peaks,” she said.

The combination of high levels of power generation and low demand can raise the risk of overloading local energy grids and also reduces the energy system’s resilience to sudden changes in frequency – a measure of energy intensity – which can lead to temporary blackouts.

The National Grid control room expects to pay flexible windfarms – which can power down quickly – to switch off at short notice while cutting electricity imports through subsea cables from Europe to avoid overwhelming the electricity grid.

The energy system operator said it will also pay hydro power projects to act as giant “virtual batteries” by using the extra electricity to pump water up into lakes before releasing it again later if power supplies threaten to eclipse the country’s demand.

National Grid’s director, Fintan Slye, said that although the situation was “very fluid” the company was “implementing a number of measures so that consumers in the UK will continue to receive secure and reliable electricity supplies during these uncertain times”.

Many of these measures have been used in the past, particularly in regional networks in the north of Scotland where demand for electricity is often low while wind power levels are higher, but these are likely to be used “more frequently and for longer than in past summers”.

On some days this summer electricity demand may fall below the “baseload” output from inflexible power plants, such as nuclear power reactors, which can take hours to shut down safely, meaning there is a risk that National Grid may be forced to issue emergency orders to turn off power plants to avoid overloading the grid.

National Grid set out its forecasts for the summer days after electricity demand fell to record lows of 15.2GW over the Easter weekend, sharply below its forecast lows of 17.6GW for this summer due to the mild, sunny weather.

“We know that millions of people rely on us every day to keep the lights on and we want to reassure everyone that we do not expect the operation of the electricity system to be adversely affected,” Quinn said.