Your guide to the cost and benefit of a rooftop power system, based on the Renergy 2013 expo in Chennai

So you are thinking of going solar. We will take a short tour of the state-of-the-art on this sunshine technology, about which this newspaper produced a feature recently.

The Renergy 2013 conference in Chennai features an exhibition of solar products that is drawing massive crowds. Many of the visitors are from the deep south of Tamil Nadu and neighbouring States. In some towns of Tamil Nadu, which has a 'solar policy', there is a power cut that lasts several hours. The solar option looks really bright to these suffering millions who include small and medium industries who are having to scale down production or shut shop.

This is the line-up on solar photovoltaic systems.

What you need: Roof or open space of about 100 to 120 square feet to place the panels on metal frames.

How much power can it produce? About eight points of light loads such as lights and fans, including a television, but not air-conditioners.

What are the components of the system? Solar photovoltaic panels on the roof, an inverter that supports 3KW, suitable battery for solar charging. A solar battery costs about Rs. 11,000.

How long will the system work? The manufacturers warranty the panels for five years, and their life is estimated to be at least twenty five years, with a power production ability of 85 per cent from the 20th year, output being higher in the earlier period.

Is there a subsidy? The Centre provides a 30 per cent subsidy through the manufacturer, while Tamil Nadu has announced a 20 per cent subsidy over that.

How much does it cost? The range for a 1 KW system quoted at the expo by various solutions providers is between Rs. 1.20 lakhs to Rs. 1.8 lakhs.

Small solar systems of Rs. 45,000 promise to run three lights, a couple of fans and a TV. Newer products in the sub Rs.25,000 range and an intermediate system at Rs. 75,000 are soon to be announced.

Tamil Nadu, which has a stall by its Energy Development Agency at the expo, so far seems more focused on government-run streetlighting and green home schemes, than on consumer-level subsidies. The manufacturers are clear that without a transparent subsidy scheme that help consumers shift to solar - without the need to approach government departments to avail the subsidy - it may not make major impact.

Other sidelights of the expo are small panels of 3 watts, 5 watts and so on, at a price point of Rs.60 per watt. So if you have a Direct Current bulb, such as an LED, you can get a light running for a total cost of Rs. 300 for the panel, and Rs. 400 or so for the bulb. There are AC-DC fans also which can be plugged into a solar panel, or run off the mains. These go for about Rs. 4,200.

Have the Centre and the States done enough to popularise solar? The answer is no. Until they have proper net-metering (the surplus you produce from your panels go to the electricity grid and you get a net balance in your favour including actual cash), this is nowhere near the revolution it can actually be.

What is also interesting that the manufacturers say the panels are assembled in India, but the circuits are imported from China, Taiwan and also from Japan. Where does that leave India's fabrication industry?