Knowledge Centre – Passive Strategies

Solar and Off-grid Appliances

Appliances based on renewable forms of energy will go a long way in saving consumer’s money through lower energy bills and reduce dependence on the electricity grid. Government is providing incentives and subsidies for many of the solar appliances in order to make them more affordable, especially for the rural applicants.

Solar appliances fall in two broad categories; one, solar photovoltaic based appliances that produce electricity to power DC type of electrical devices, and the other, solar thermal systems that use the heat to produce heating which can be used for generating hot water or for cooking.

Solar Lighting

Solar lighting systems can be as simple as a single lantern with integrated PV module and a battery, to a full fledged lighting system for the entire building with flexible sizes of battery, PV, and lighting fixtures.

The Solar Lantern is portable, light-weight device, mostly used for rural applications and can be used indoor as well as outdoor lighting. The Lantern comprises of 3 elements: a CFL, of 5W or 7W; PV module and a maintenance free battery.

A solar lantern can lead to savings of approximately 50 liters of kerosene in a year by replacing the traditional kerosene lantern. It can be used for upto 3 to 4 hours per day.

The solar lighting system can be extended to provide internal lighting in one or more rooms in a building. These systems are often sold as a package with other solar devices like a DC fan and mobile chargers. A typical system comprises of a PV module, a lead acid battery and CFLs of 9W or 11W rating. There are several systems with 1, 2 or 4 CFLs.

The PV module is typically fixed, mounted on the roof, directed towards the solar radiation. The system are sized to run for 3 to 4 hours daily. The PV panel has a life of 20-25 years.

The Government provides incentives for installing this system to individual users and NGOs. For example, MNRE provides subsidy of Rs. 2,400 on purchase of solar lantern in North East and special areas.


Solar Street Lighting

Small photovoltaic modules can be used for powering of external lighting. A typical system, comprising of an 11 W CFL, with a 74 W photovoltaic module and a 12 V/75 AH battery, costs Rs. 22, 000 to 24 000. When fully charged, the battery can power the street light for 8-10 hours.


Solar Cookers

Solar cookers are used to cook food by utilizing the heat energy of the sun’s rays. Efficient use of soalr cookers can lead to saving of 3 to 4 LPG cylinders per year. Solars cookers have high durability and are simple to use. There are two types of solar cookers, namely:

Box type- This cooker can be used to cook most of the food except chapatis or frying. It is ideal for cooking on sunny days but stops functioning on cloudy days. Some box cookers with electrical backup are also available in the marked and are handy during cloudy days. The lifespan of this cooker is 10 to 12 years ant the cost could vary from 1200 Rs. To 2500Rs.

Dish type- This cooker has a parabolic dish for concentrating the incident solar radiation. This is also known as the ‘SK-14’ solar cooker. This has a higher capacity than the box type cooker and can make food for upto 15 people and can operate from 8 to 9 hours in a single day. This cooker can be used for roasting, frying and boiling. The lifespan of the metallic structure is 20 years but the sheets have to be replaced every 5 years. The cost varies from Rs. 4300 to Rs. 5000.

To encourage the utilization of dish type solar cookers, an incentive of 50 per cent of the cost of the dish solar cooker is provided by the government, which is limited to Rs. 2,500 per cooker.

Solar Water Heaters

Solar Water heaters use energy from the sun’s rays to heat water for domestic & commercial purpose. This appliance consists of a collector which collects solar energy and an insulated water tank to store hot water. The collector on receiving solar energy transfers heat to the underlying pipes containing water which in turn goes to the insulated storage tank. This water is recirculated to increase the temperature of the water. There are two categories of solar water heaters, namely closed loop and open loop.

The closed loop system has installed heat exchangers for protection against hard water obtained from borewells. In the open loop system, the water is open to the atmosphere at some point in the cycle. The open loop systems are suitable for domestic as well as small industrial purposes.

The lifespan of a solar water heater designed as per BIS specification is between 15-20 years but a lot depends on the maintenance of the heater.

The Ministry of New & Renewable Energy (MNRE) provides subsidized loans at rates of 2 percent to domestic consumers, 3% to institutions and 5% to communities with an additional Rs. 100 per square collector area as incentive.