Views:1 Author:sinoyin Publish Time: 2019-01-03 Origin:Site
The solar hot water heater makes use of the solar energy from the sun to generate heat which can be used to heat water for showering, space heating, industrial purpose as well as solar cooling.
Solar energy is the major source of energy for our planet as it is responsible for the provision of energy for plant growth and providing the warmth which makes our planet habitable.
While solar water heater devices have been around for more than 100 years, the last 20 years have seen a significant advance in absorber coating technologies which result into solar collectors that can reliably convert more than 50% of the available sunlight for domestic hot water supply. A solar water heater is one of the most effective ways of cutting a household’s carbon footprint by reducing reliance on dirty fossil fuel usage. By offsetting the use of electricity, gas or heating oil, the use of solar water heater can provide financial savings by reducing the energy costs.
The solar water heating collectors capture and retain heat from the sun and transfer this heat to a liquid. Solar thermal heat is trapped using the “greenhouse effect,” in this case the ability of a reflective surface to transmit short wave radiation and reflect long wave radiation. Heat and infrared are produced with the aid of short-wave radiation which is trapped within the collector. Fluid, usually water, in contact with the absorber collects the trapped heat to transfer it to storage.
Two principle govern the solar thermal collectors. Firstly, any hot object eventually looses its heat back to the environment. The efficiency of a solar thermal collector is directly related to the heat loss, mainly from convection and radiation. Thermal insulation is used to slow down heat loss from a hot object to its environment.
Secondly, heat loss is more rapid whenever the temperature difference between the hot object and its environment is larger, in this case between the temperature of the collector surface and the ambient temperature.
The most basic approach to solar heating of water is to put a tank filled with water into the sun. the heat from the sun would heat the metal tank and the water inside. This was how the earlier water heater work several years ago. However, this setup would be inefficient because the heat loss from the tank cannot be minimized. The addition of an insulated box around the tank, and adding glass above the top where the sun comes in would do a lot in heat retention.
A more common collector is called a flat plate collector. It has a large, flat surface area (absorber) to maximize exposure to the sun, and has small tubes bonded to it. Fluid runs through the tubes, collecting the heat from the absorber. The sides and bottom of the collector are well-insulated, and glass on top completes the insulation.
This is quite simple, but there are some very technical factors involved in making the collector as efficient as possible. One is the coating on the absorber, which is specially formulated to both absorb as much heat as possible, and to radiate back out as little heat as possible. Another is the glass, which is high-iron and specially coated to let as much light energy as possible through and to also prevent as much heat loss as possible.
Another popular type of collector is called evacuated tube, which has a long, skinny absorber that is inside a glass tube. The tube has the air evacuated out of it, which makes it highly insulated, this is not too different from a thermos used to keep drinks hot.
The final type of collector is a parabolic dish or tray, which increases heat potential by concentrating sunlight onto a small absorber. These are very rare in-home water heating systems, and more commonly used in utility-scale systems to create steam which runs turbines to make electricity.
The basic components in solar heating systems include:
Collectors to take the heat from the sun and pass it to a fluid
The heat transfer fluid which takes the heat from the collector for use or storage
Heat exchangers to transfer the heat from the fluid to a home’s domestic water.
Pumps to move the fluid through the collector and/or the exchanger, and sometimes to move the domestic water through the other side of the exchanger.
Controllers to run the pumps when there is collector heat available.
When all these components are available, the solar water heater would work effectively and efficiently.