National Grid forecasts low UK electricity demand this summer

* Summer electricity demand peak forecast at 35.7 GW

* Firms to be paid to use power

* Summer gas demand forecast at 34 bcm (Updates with details throughout)

LONDON, April 6 (Reuters) - Britain's National Grid (LSE: NG.L - news) expects low demand for electricity this summer and that there could be times when there is more generation than needed, the grid operator said on Thursday.

Summer electricity demand from the grid has been falling over the past few years due in part to a rapid increase in the amount of solar power generation on people’s homes and factory roofs.

In its summer outlook report, National Grid said peak transmission system demand for high summer (June-August) was forecast at 35.7 gigawatts (GW) and the summer minimum at 17.3 GW.

"In order to balance the system, we will need to curtail flexible generation this summer. It may also be necessary to instruct inflexible generators to reduce their output during these periods of low demand," the report said.

To prepare for the low demand National Grid, earlier this year secured 139 megawatts of "demand turn up" capacity through which firms are paid to either use electricity or produce less power during the summer months when output is high from renewable energy sources such as wind and solar.

Under the scheme the companies will conduct some operations overnight or at midday when there is a lot of renewable generation, or cut their electricity output when demand is weak.

As a part of the tender, companies were required to prove they need to carry out such operations and that the electricity would not be wasted.

The scheme was also open to small scale power generators that can also reduce their output at short notice, such as combined heat and power units, which generate electricity as a by-product of heating.

National Grid also forecast Britain's total gas demand for summer at 34 billion cubic metres, down 5.6 percent on last year partly due to a reduction in demand from gas-fired power stations.

Demand for gas storage is also expect to drop due to a prolonged outage at Britain's largest gas storage site Rough, National Grid said.

Gas is traditionally stored during the summer months to be used during winter when demand and prices are higher.

Centrica (Frankfurt: A0DK6K - news) owned Rough, which accounts for around 70 percent of Britain's storage capacity, will not be available for gas injection until at least July 1 because of tests on wells at the site. (Reporting By Susanna Twidale and Nina Chestney, editing by Jeremy Gaunt)