This follows the success of solar hot-water systems in southern Viet Nam in recent years where more than 20,000 are reported to have been installed.

The new campaign, launched in the central city of Da Nang, is part of a national programme to conserve energy. It aims to reduce the total amount of energy produced by stations powered by water and oil by 5-8 per cent within five or six years.

If it is successful, the Government will promote solar heating in the north of the country, but heavy cloud will limit its usage in winter.

Dr Phuong Hoang Kim, deputy director of MoIT’s Sciences and Technologies Department, said central Viet Nam enjoyed plenty of sunshine all year round - more than 2,000 hours a year.

The introduction of solar water heaters is expected to help reduce the overloading on regional hydro-power plants.

Solar water heaters can be a cost-effective way to generate hot water as the fuel they use – sunshine – is free. But installation costs can be high, especially for poorer people.

Solar heating systems require well insulated storage tanks, like most hot-water systems. They can use a separate storage tank or be connected to a main tank heated by conventional power supplies. In one-tank systems, the two sources of hot water are combined.

Kim said a family solar water heating system cost around VND5-6 million (USD280-330) and could lead to yearly savings of more than 800kWh of electricity, equivalent to USD50.

"For houses under construction, the cost of solar installation is much cheaper than installing normal electric water heaters," said Kim. 

But 51-year-old Nguyen Thi Hanh, a resident in Quan Hanh Town, Nghi Loc District, central Nghe An Province, said she had no intention of spending so much on new technology.

"It costs too much. Our monthly electricity bill is around VND300,000-500,000. I’m happy with it and would rather stick to a normal electric water heater than spend a fortune on something no-one in town uses," said Hanh.

Director of the Ha Noi Energy Efficiency Centre Dao Hong Thai said the cost was a little high considering the low income of Vietnamese people, especially in rural and highland areas.

But he was adamant that the use of solar energy for water heating - and eventually for cooking, lighting and heating - was a perfect idea and would become popular in the future.

"The success of this programme depends on Government subsidies to lower the cost of heaters," said Thai.

Kim said about 20,000 new solar water heaters were installed last year in the country, mostly in the south. About 3,000 were partly subsidised by the Government.