For 80 percent of Nepalis who have no access to electricity, the fact that Nepal has the highest per capita potential to generate hydropower has a hollow ring. And for the 20 percent who do, electricity is so expensive that they can't afford to use it much.

Enter: photovoltaic (PV) technology. This system of converting sunlight into electricity and storing it in batteries, could revolutionise Nepal's electricity use. All it needs is a solar cell set up on a sunny terrace or rooftop. PV cells used to be expensive, but prices have plummeted dramatically and it is now within reach of many Nepalis.

Hypothetically, if just 1,000 Kathmandu houses had PVs of 3KW per hour capacity, we'd have 15MW of power daily, taking into consideration that the average period of sunshine is five hours per day. This would mean that the rooftops of 1,000 houses in Kathmandu could generate three percent of Nepal's current installed hydropower capacity of 600MW. Multiply the gains by 365 days, add thousands of other rooftops all over Nepal and it would be the equivalent of an expensive new hydropower plant.

But how much does it cost? For starters, around Rs 1 million invested in PV modules, batteries, inverters for building integrated PV electrification systems and a monitoring system. For Alternative Current to get connected to the national grid all that is needed is stac equipment that costs even less.

The Centre for Energy Studies at the Tribhuban University's Institute of Engineering has demonstrated the technology in its own building with solar panels providing 27KW of power in a day, enough for lighting the building and the wireless local area network for computers (see pic, bottom). The excess energy is channeled into the campus grid. When there isn't enough power in its PV system, the CES building takes electricity from the campus grid, thus balancing the surplus and deficit and meriting the name Zero Energy House.

"What we did in our building can be replicated anywhere else," says the centre's director, Jagannath Shrestha (pictured, right). "We are creating awareness to encourage people to adopt this technology." PVs are something of a passion for Shrestha who thinks it will provide cheap solar power power for the masses.

At night, when there is no sunshine, PV users can get power from the national grid. "That way, people will pay less than their usual electricity bill," he adds. The idea is to calculate the difference between what you give from the PV system and what you take through the national grid.

But, for that there has to be some changes in the system and the law. For instance, Nepal Electricity Authority's distribution system has a one-way flow of power from the national grid to consumers. For a reverse flow there has to be changes made in the law too. "This could take some time," says Shrestha. "But, if the government understands its value, the necessary changes should not be a big deal."

Will it be worth the trouble? Hydro experts say that at the moment, the national power grid is cheaper than the PV system. But prices of solar panels are falling-the per watt power of a panel that cost $100 a few years ago now is $4. "The system is quite suitable for high value consumption like lighting, tv and refrigeration but not for industrial use," says energy expert Bikash Pandey. "It would be ideal for places that have no access to hydropower generation."

Professor Shrestha at CES says that installing a solar panel to produce the AC and connecting it to the national grid through stac will cost $5 per watt of power. The electricity produced through several run-of-river and storage plants in the country costs $4 per watt, on average. "Don't forget the politics and other hassles when it comes to constructing hydropower plants," reminds Shrestha.

In Germany more than 10,000 consumers already have solar panels under the Rooftop Program where roof tiles double as solar power collectors. Japan is promoting a Sunshine Program for solar electricity. By 2050, half of world's energy is expected to come from solar power.