Although the design of solar water heater systems varies, they all include a solar collector and a storage tank. They are generally described by the type of collector and the circulation system used.
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Types of solar thermal collectors.
There is a wide variety of technologies that transform solar radiation into thermal energy and that use different operating principles.
Choosing the most appropriate technology for a residential, commercial or industrial application will depend on the amount of heat energy and fluid temperature required.
We talk about the most interesting systems.
Flat solar collector.
The easiest. It is used to heat water for residential and commercial applications.
This collector consists of a metal plate with a system of tubes through which the water circulates on the surface of the plate.
A special coating is applied to the tubes to better absorb solar radiation.
This tube plate is inside a box with a glass cover on the top surface and insulation on the bottom, to reduce heat loss to the environment.
Solar radiation is transmitted through the glass to the plate with tubes where its surface is heated, so that thermal energy is transferred to the fluid that circulates through the tube system, increasing its temperature.
Empty tubes.
Widely used in residential or domestic applications.
There is a system of inclined tubes connected to a storage tank.
The tubes have the characteristic of being under vacuum, in the manufacturing process, the air between the surface of the glass and the tube through which the fluid circulates is eliminated.
In this way, heat losses are reduced and greater efficiency is achieved than flat plate collectors.
There are different types of evacuated tube collectors which vary depending on the fluid used and the way heat is transferred to the fluid.
Parabolic of revolution and linear parabolic.
In the first case, the reflective surface has the shape of a parabolic disc where the solar radiation is concentrated in a small circular focal region.
In the latter, the reflecting surface has a curvature which remains constant in the axial direction and the solar radiation is reflected in a receiver tube in which a fluid circulates, whatever the type of solar concentrator.
To increase their efficiency, these concentrators are mounted on a structure with a control system that allows the reflecting surface to be oriented so that it receives the maximum incident radiation during the day.
Solar concentration tower.
It has in its upper part a receiver that receives solar radiation from a large number of reflective surfaces located on the surface of the base of the tower.
These reflective surfaces are programmed so that their orientation changes during the day to take maximum advantage of solar radiation.
The solar radiation captured in the tower’s receiver is used to increase the thermal energy of the liquid salts, which are used to generate electricity in a thermoelectric plant.
Hybrid solar concentrators.
These types of concentrators produce both electrical and thermal energy.
An advantage of these hybrid concentrators is that when the fluid circulates, the temperature of the photovoltaic panels decreases, increasing their efficiency.
Solar basins with saline gradients.
Solar saline ponds are a renewable technology that captures solar radiation at the surface of a salinity gradient pond and stores it as thermal energy in its lower zone.
When a salinity gradient is set up in the basin, the salt concentration in the water increases with depth, causing the heated water to rise because it is heavier than the water above.
In this way, vertical mixing of the fluid is eliminated and heat losses to the environment are reduced.
This thermal energy is extracted from the basin for various residential and commercial applications.
Sizing.
Your installer can help you calculate what you need, but generally choose 1.85m2 of collector area for a family of two.
Add 0.75 m2 for each additional person if you live in sunny regions, or 1.10 m2 in regions with cooler climates.
A small tank (200 liters) is recommended for one to three people and a medium tank (300 liters) for three to four people.
Tank size also increases with header size for active systems in hot climates to prevent overheating when water demand is low.
Frost protection.
Even in hot climates, where frost rarely occurs, it is recommended to install frost protection as a single frost can affect a sensor.
There are several methods, such as relief valves that evacuate water from the system when freezing temperatures occur, water recirculation, drainage systems, and antifreeze systems.
Certificates.
Water heaters are the second largest consumer of energy in the home; those that are ENERGY STAR certified have been tested for reliability and efficiency. In addition, only complete systems with auxiliary heating are evaluated.
Additionally, systems can also be certified by the Solar Certification and Qualification Corporation (ICC-SRCC), a third-party certification body for solar thermal products for safety, durability and performance standards.
Doubts.
- Do solar water heaters work in winter? Yes, but you will need a backup system, which you will need to use more frequently in the winter when there is less sunlight.
- Should I change my habits with a solar water heater? Yes, to maximize the use of solar energy, it is best to use the greatest amount of hot water at the end of the day when the system is operating at its peak. Also, if you tend to wash multiple times a day, you may want to spread it out to do fewer loads per day and reduce the amount of standby power needed.
- Can solar water heaters save you money? You will need to consider the cost of installation, which varies depending on the type of system you are installing and where you live. Long-term savings depend on several factors, such as the amount of water used, the size of the tank, and the price of fuel to heat the water. But since heating water represents 18% of the total consumption of an average home, it is estimated that it could reduce your energy costs by at least 50% of your bill corresponding to hot water.
- Should I buy a backup system for my solar water heater? In a word, yes! Unless cold showers don’t bother you or you live somewhere with a warm climate all year round, you still need a backup system that runs on electricity, gas, or propane, depending on the availability in your area.