The Housing Board is working on its largest single solar-leasing project to date - and is also looking into households being able to buy electricity made from the sun's energy.
Last month, it called its largest solar-leasing tender: for a company to own and operate panels on some 125 blocks in Ang Mo Kio, Sengkang, Serangoon North and Buangkok.
These would produce 5MW of electricity in optimum conditions, or 5 megawatts-peak (MWp), enough to power more than 1,000 four-room HDB flats.
The HDB will offset up to 30 per cent of the start-up costs, and, in turn, buy the electricity for 20 years at a 5 per cent or greater discount off the prevailing market price. This electricity would power lights in corridors and common areas, lifts and water pumps, among other things.
Another tender in May, to generate 2MWp for 40 blocks in Jurong East, includes a possible new option of allowing households to buy the excess electricity generated during the day, again at a discount off the market rate.
"HDB is studying the feasibility of enabling residents to obtain green energy from the vendor directly," a spokesman said. No details are available yet, she added.
Currently, solar panels installed on HDB rooftops in Punggol by leasing company Sunseap generate enough to fully power common area services - such as lifts and lights - in the day; the extra electricity is sold to the grid.
Energy Studies Institute research associate Shiva Susarla said leasing companies would make more profit if they could sell the power to households.
"And if the tariff being paid by the households for solar energy is slightly lower than what they are already paying to SP Services, it is good for them, isn't it?" he added.
The project is large for Singapore, though much larger solar "farms" exist in Thailand, India and elsewhere, said Mr Susarla.
Both the Ang Mo Kio and Jurong East projects are scheduled to start next year and be completed in 2015, the HDB said.
The housing agency's $31 million, five-year scheme to test solar energy in 30 precincts around the island has been able to take advantage of the plummeting prices of solar panels. These have come down in the last few years from more than $5.17 per watt installed to about $2.10 today.
Other large projects include a 1.2MWp array atop the distribution centre of supermarket giant Sheng Siong, and a 1MWp one on the Ulu Pandan Newater plant.
Last month, the HDB also called a solar leasing tender for panels that use newer copper indium gallium selenide thin-film technology, which is more energy- and cost-efficient than conventional solar cells, to be put on blocks in Sengkang West, Chua Chu Kang and Yishun.
Already, the existing solar panels in Punggol mean common services in those blocks run almost completely on solar energy in the daytime, and the panels generate enough in the day to offset what lifts, lights and pumps use at night, the HDB said.