Flat Panel solar water heater
The flat panel solar water heater is the most known type of solar heaters in the market, it depends on the greenhouse effect.
Because of the system’s low cost and easy installation, the flat panel solar water heater is more efficient and cost-effective, especially in hot water applications for residential and small commercial buildings.
How Flat Panel solar water heater works
The solar collector is a black aluminum or copper heat absorption plate, which absorbs solar energy and uses it to heat water. Underneath the surface, there are a number of copper pipes or tubes called risers, which contain the heat transfer fluid (usually water).
The copper pipes conduct heat when the surface plate gets hot, which is then transferred to the heating fluid to be then used in the building.
The risers are welded to the absorber plate to ensure maximum heat transfer whenever the absorbing surface is in contact with sunlight.
To create an insulating air space and protect the absorber plate and the risers, they are kept in an insulated metal or wooden box with a sheet of glass or plastic on the front.
The insulating air space is to prevent heat escape, as after heat is transferred from the plate to the fluid, the remaining heat can escape back to the atmosphere. In addition, high-temperature rigid foam or aluminum foil insulation is used to insulate the bottom and sides of a flat plate collector.
Flat Panel solar water heater parts
Solar collectors
To collect the sun's rays and heat up the water.
Thermal insulated tank
With a capacity that ranges between 100 - 500 liters for domestic use.
A metal mounting
That holds the solar collectors and the tank together.
Auxiliary Electric Heater
That works automatically using a sensor that measures the temperature of the water in the tank. It is used in winter or in case of a significant and temporary increase in water consumption in cloudy weather so the performance is not affected.
The capacity of this coil ranges between 2 and 4 kWh for most household uses.
Heating methods in Flat plate collectors
According to the way the heat is transferred around the system, solar water heating systems are classed as:
Direct system (active open-loop system):
This system uses a low voltage pump to circulate water throughout the system, as cold water is pushed from the building to the central water storage tank to be heated through the solar collectors and back to the tank and then to the building.
This system is more suitable for warmer climates, where chemicals can’t be added to the water to protect water in the pipes from freezing; as the same water that circulates through the flat plate collector is used.
The capacity of this coil ranges between 2 and 4 kWh for most household uses.
Indirect system (closed-loop systems):
In this system the heat exchanger in the tank is separate from the solar flat plate collector as the heating liquid inside it contains antifreeze solution so it can’t be mixed with the water supply.
There are two types of heat exchanger; a copper coil inside the storage tank or a flat plate exchanger outside the storage tank. It transfers heat to the water in the tank, which is then used in the building.
This system is most useful in climates where the temperature falls below the freezing point. It also protects the system collectors from corrosion, due to exposure to gases and various dissolved salts in untreated water that is usually used in the direct system heat exchanger.
Through adding a flat plate collector and a pump to the already existing gas heating system, it can be changed to a solar water heater.
This system depends on electricity to run the circulating pump. To make it more efficient, a small low voltage pump and photovoltaic panel can be installed with the collector.
The capacity of this coil ranges between 2 and 4 kWh for most household uses.
Flat Panel solar water heater benefits
- Flat panel solar water heater tend to be cheaper than other counterparts; because of their simple design and easy to manufacture.
- Can go for a 20 years warranty, because of the use of less sophisticated technology.
- Can be used in low-heat hydronic applications
- A better option in snowy climates; as it sheds snow easier than other counterparts.
Alternatives in the market
The main solar alternative to the flat panel solar water heater in the market is the vacuum tube solar water heating systems.
Other alternatives include gas and electric heaters.