Out of the Box. Solar: the cool way to cut power costs

The blazing sun can be a cool way to generate electricity, if you set up rooftop solar equipment. With the cost of the devices dropping drastically in recent years, setting up a solar system in your home may be an economically viable option, especially with power bills ballooning. Here’s telling you how to get started.

Rooftop installations may be suitable if the bulk of your power usage is during the day, say for a school or office.

This way, your overall power bill will reduce drastically. It also helps those of us who want to be earth-friendly and reduce pollution or carbon footprint.

By saving three units of conventional electricity a day, you would have conserved over 700 kg of coal in a year.

And considering the emission, this would be equal to saving 225 litres of petrol emissions, says R Ramarathnam, Chairman, Basil Energetics, a solar energy start-up.

You need open space that gets good sunlight.

The rule of thumb is that, to generate one unit of power an hour, you need 10-15 sq m (around 120-160 sq ft) of space.

This number can vary based on factors such as the solar panel technology and where you are located, says Chandrashekhar Mishra, Managing Director, Crux Power, a start-up working on renewable power.

Basically, you need three appliances. One, solar panels, which can cost ₹40-50 per unit of power.

Two, you need an inverter to convert solar power into the form that appliances can use. This can cost around ₹18-20 per unit of power. Finally, if you choose to have battery back-up to have power in non-day hours as well, it will add to around ₹15 per unit of power.

As easy as wiping glass! Solar panels lose efficiency when they are dusty. Their lifetime is over 20 years, although over time they generate less power.

Inverters have a warranty period of around five years and don’t require much maintenance. If you use batteries, some upkeep, such as topping up distilled water every quarter or so, is required.

Yes. But to run large loads such as motor, refrigerator or air-conditioner, you need something extra. These appliances draw a lot of current when you switch them on, placing a heavy load on the power generator. To manage that, additional circuits are used to balance the demand.

Alternatively, Basil Energetics uses re-designed appliances with electronics to lower the peak power drawn. While you do have to replace your existing appliances for this, your rooftop unit cost is lower due to smaller panel need.

Changing your appliances to be more power-saving can also be considered. For example, Basil Energetics’ solution for a 330-litre refrigerator, three fans, and eight lights costs ₹1.5 lakh. This is without battery but inclusive of new appliances.

The bulk of the savings comes from reducing the peak power demand from the rooftop panel — to 360W from 2,000W — due to better electronic control.

It all depends on your usage pattern. If most of your consumption is during the day, between 9 a.m. and 4 p.m. when the solar unit generates power, you can save a lot. During rains and cloudy days, you may not generate power; so be aware of the seasonal variations.

Ramarathnam says that there has been an average 50-70 per cent reduction in power bills for office settings. However, do a detailed analysis of your usage amount, hours and local tariff to understand what you are likely to save.

To evaluate the suitability of solar power, first assess your power needs.

Talk to a local contractor who can tell you the size of the units you should buy, based on local weather conditions. You can then get cost estimates for different solutions and analyse what works best.

For instance, the cost of the system and the ongoing maintenance can be low if you do not have batteries; you need to evaluate if that'll work for you.

The Ministry of New and Renewable Energy provides 30 per cent capital subsidy on project cost. You pay only 70 per cent and the empanelled contractors get the rest from the Government.

The contractors list is available at http://mnre.gov.in under Public Information.

State Governments such as Tamil Nadu offer additional subsidies. But the reality is that no subsidies have been paid in the last year, according to Mishra. Contractors are now only willing to take up projects if the customer pays the full amount. So, do not count on subsidy money.