Kerala's 10,000 Solar Rooftop Programme is already in full swing with almost half (4700) rooftops signed up by mid-January 2013. Any Keralaite with 15 square meters of unshaded rooftop area can register (http://ddr.anert.gov.in/index.php?option=com_content&view=article&id=116) to set up a 1 KW-peak system on their roof. The programme counts on each solar rooftop plant costing in total about Rs. 2.5 lakh with state and central subsidies covering 1.2 lakh, making the cost to consumer 1.3 lakh in all.
Each plant can last 20 to 25 years although batteries would need replacement every 5 years on average. A 1 KW-peak system can give an output of around 120 units a month. Without accounting for battery replacements but counting on only 20 year lifetime this would mean a cost per unit of Rs. 4.5 per unit produced, slightly above the average electricity tariff of Rs. 4.4 per unit for grid connected electricty. However with quickly increasing power tariffs in the long run the plant could save money, and not to mention that the solar power used would always cut the highest - most expensive - unit from the electricity bill.
For two groups of people a solar rooftop could be an enormous boon - those who use more than 300 units a month and those who otherwise rely on Diesel Generators (DG sets). As the Kerala utility has set the tariff for over 300 units per month at Rs. 15 per unit a solar rooftop could make back the investment (as compared to having to buy the more expensive power from the grid) in as little as 6 years, and earn a a total of 3 lakhs in savings over the lifetime of the plant!
As for those relying on DG sets the savings could be even higher as the cost of production of electricity from Diesel comes to more than Rs. 15 per unit according to market analysts. Not to forget either is the added benefit of a clean, and quiet power source as compared to Diesel.
There are of course risks - the output will go down during monsoonal months, batteries needs replacement and plants do degrade. However this will most probably be balanced out by the fact that any alternatives (including electricity tariffs) are only set to get more expensive. The cost of electricity has been increasing every year in India for at least the last 30 years and with coal getting harder to get by and gas running out power from the grid is only set to get more expensive.
By January 13 only 5295 subsidised solar roof-tops were left to be alloted, it is first come first serve, so go sign up!