Virginia Electric and Power Co. is looking for 2,000 volunteers to test residential electrical rates based not only on how much power they use but when they use it.

Under the time-of-usage (TOU) rates, consumers potentially could lower their electric bills by running appliances between 9 p.m. and 9 a.m. when there is less demand for electricity.

Eventually Vepco wants to use time-of-usage rates for all its customers. The Virginia Corporation Commission has tentatively approved the phase-in of TOU rates starting in 1980 with large residential customers and gradually spreading to smaller ones.

To test the impact of the new method of charging for electricity, Vepco is asking for 1,000 volunteers for each of two separate programs. One involves total electricity use, the other just water heating.

In the water heating program, special meters will be installed which prevent the heater from running during peak demand hours - 9 a.m. to 9 p.m.

In return for using their water heaters during hours when demand for electricity is relatively low, the volunteers will be charged lower rates.

"This plan is recommended for customers whose electrical water heaters have a large storage capacity," said William Berry, Vepco's executive vice president.

The program is geared for Virginia customers who already have a separate meter base in their homes from the time when Vepco had special rates for electric water heaters.

The second test is more complicated and gives consumers the potential for saving on their electric bill by controlling when they use electricity and how much they use at any one time, as well as total electric consumptions. In the thousand test homes, special $270 meters will be installed which measure all three factors.

The volunteers will pay 1.5 cents per kilowatt hour of electricity used during off-peak hours (9 p.m. to 9 a.m.) and 2.39 cents per kilowatt for peak use (9 a.m. to 9 p.m.).

"The key to saving on monthly bills depends on how much the customer can shift his use of electricity from the on-peak and more expensive hours to the off-peak hours," said Berry.

The volunteers' bills will also depend on their maximum electrical consumption - what utilities refer to as "peak load demand" - the electricity used when the water heater, the washer, dryer and other appliances are used all at the same time, explained Bob Gay, Vepco's executive manager for rates.

The goal of both electric rate experiments, Vepco people explain, is linking electric charges to the cost of providing service, and reducing the utility's peak load.

Utility companies have to build generating plants to handle the peak load demand. During off-peak hours - mostly at night - the costly generators sit idle.

By shifting the electrical use to off-peak hours, the need for peak generating capacity is reduced, and along with it the amount customers must pay for the power plants.

Vepco's board of directors yesterday approved spending $546 million this year to build new facilities and another $54 million for fuel for nuclear power plants.

About $109 million will be spent to complete - on a speeded-up timetable - a massive peak load generating station in Bath County. Originally set to be finished in 1983 and 1984, three units of the Bath County project will be ready in 1982 and three more in 1983.

Acceleration of the project was needed to provide adequate reserves for summer peak loads during 1982 and 1983, said Vepco chairman John McGurn. Without the plants, Vepco would have less than an 8 per cent reserve during the summer "which would have been an unacceptable level," he said.

Vepco's 1978 construction budget included $54 million for pollution control equipment, $212 million for work on its North Anna nuclear plants, $79 million for other production facilities and $144 million for lines and distribution facilities.

For the 12-months ended Dec. 31, Vepco's operating revenues increased from $1.1 billion to $1.3 billion, common stock earnings grew from $122 million to $142 billion and earnings per share rose from $1.80 to $1.92, the company reported yesterday.

For the last three months of 1977, operating revenues were $328 million compared with $286 million the previous year; common stock earnings increased from $30 million to $32 million, but earnings per share declined from 43.5 cents to 43.3 cents due to an increase in the number of shares outstanding.