The sun is the most powerful source of energy in our Solar System. India is fortunate to be blessed with a sunny weather for a major part of the year. Solar energy is not only renewable, but also clean and free. So, if properly utilised, solar energy could be the panacea for all our power woes. One way to do this is through solar water heating systems, as they are economical, easy to install and convenient to use.
A solar water heater utilises solar energy to heat water for daily use. It is usually installed on the terrace or in an open space where it can get uninterrupted sunlight during the day. Heated water is stored in an insulated tank for consumption whenever required. Solar water heaters do not use electricity, which results in lower power consumption in a residence.
Solar water heating systems have two major components: collectors and storage. In solar water heaters, the collectors capture and retain the heat from the sun and transfer it to a liquid, which is usually water. It works on the principle of greenhouse effect, to trap the heat. The water which absorbs the trapped heat is transferred to a storage tank from where it can be employed for domestic use. The aim of the collectors is to absorb maximum heat and radiate as little it as possible back to the atmosphere. The coating of the absorber and the glass is especially made to achieve this. The heated water will lose heat to the environment, which is reduced by using thermal insulation.
Types of collectors
Flat plate collectors: These have a large flat surface area as an absorber for maximum exposure to the sun. The fluid runs through the small tubes that are bonded to it. The glass on the top and thermal insulation on the sides and bottom complete the arrangement. This system is strong and durable as it is made of metal.
Evacuated tube collector: In this, there are parallel rows of transparent glass tubes. Each tube contains an outer glass tube with an inner metal absorber tube attached to a fin. The air from the outer tube is evacuated much like a thermos for higher thermal insulation. This system is fragile as a glass can break, but it is more economical than the flat plate one. Also, it takes up lesser space than the flat plate system.
There are many readymade options that are available in both these types of solar water heating systems.Solar water heating systems are available in various capacities starting from 100 litres per day (that is sufficient for a family of four). Solar water heating leads to a saving of around 1500 units of electricity in a year for a 100-litre capacity. The initial investment on the solar water heater can be easily recovered in a few years.
In both types of collector systems, Passive and Active options are available. Passive option works without pump and active one uses a pump to transfer the water to the storage tank.
For domestic use, the Passive option is usually employed, as it is easier to maintain and is more economical. The passive system uses the principle of thermosiphon, in which the warm water automatically rises into the storage tank that is placed above the collector system.
Solar water heating systems work even on cloudy days as they use diffused radiation in the atmosphere. But for prolonged periods of overcast lasting more than a couple of days, a backup is required. Usually, a conventional electric water heater can be employed for this purpose.
Proper maintenance of the system is required for its smooth functioning. The glass needs to be cleaned and should be replaced if it breaks. In case of hard water, scaling might take place, which needs to be removed periodically.
Photovoltaic systems for power generation
Photovoltaic (PV) panels are made of a group of photovoltaic cells. Photovoltaic cells are made from layers of silicon or any other semiconductor.
When sunlight falls on the PV cells, they convert it into electrons and direct current (electricity) is generated. These electrons then flow out from the solar panel into the inverter where it is changed to alternating current power that can be used for domestic consumption. A pure sine wave inverter is more efficient than modified wave inverter in converting the current. There are two types of PV systems:
Grid-connected systems: In this, the PV system is connected to the electric supply of the power company. The excess electricity generated by the PV system is sent to the power grid. At night or on cloudy days when the PV system is not producing enough current, you will be drawing power from the grid. Net energy metre keeps track of how much power from the PV system goes into the grid and how much is used from the grid. You will be billed for the net consumption only.
Off-grid systems: They are standalone as they are not connected to the electric supply. They require batteries to store the electricity. These batteries are an expensive component of the PV system and need to be changed every few years. This system is suitable if there are a lot of power cuts in your area. Deep cycle batteries are the best suited for storing electricity generated from solar panels.
Other solar products
If you are not keen to set up a PV system, you could go in for a solar generator for standby power. These take up less space and work silently without causing any disturbance. They save on the cost of diesel which is used in most generators and do not emit fumes that pollute the atmosphere. Other solar products like lamps, water pumps, cookers, garden lights and street lights can also be used in homes.
Investment: The investment for the system includes the capital cost involved in installation and the operating cost for its maintenance. This would depend on the type and size of the system employed and the solar resource available. The PV systems do not require much maintenance other than removing dust and debris from the panels. These systems can last for many years without giving any trouble.