Heating a liter of water takes some time. Therefore, it is necessary to have an accumulator to store the greatest amount of hot water for when it is needed . For example, at night, hot sanitary water may be required but solar radiation is not available to heat it.
When the system needs, for example, domestic hot water, the tank supplies this hot water and replaces it with cold water. Cold water will pass through the circuit of solar collectors exposed to solar radiation and will increase its thermal energy. The hot water returns to the accumulator for when it is needed.
How is a solar accumulator formed?
A solar storage tank is made up of a metal tank made from synthetic and insulated material.
In turn, the accumulator incorporates one or two heat exchangers or heat exchangers into your installation. These exchangers allow you to maximize your safety to avoid the risk of leaks and thermodynamic loss of energy.
How does an accumulator work?
The system works through two water circuits. The primary circuit is a closed circuit in which the same liquid always circulates, passing through the solar collectors (c) and through a heat exchanger (FG).
The secondary circuit is open. It has a cold water inlet (A) and a hot water outlet (E) which is the one that will be used in our heating or domestic hot water system.
Cold water enters the solar tank (B) as it empties when consumed. Cold water is slightly denser than hot water, so it tends to be at the bottom of the tank. Therefore, when hot water is needed it will be drawn from the top.
The liquid in the primary circuit passes through the solar collectors, which heat it thanks to exposure to solar radiation (D). In this way the thermal energy of the liquid increases. Then, the hot liquid is directed to a heat exchanger with the liquid from the accumulator.
In the heat exchanger the two liquids are in thermal contact, but do not mix. According to the second law of thermodynamics and Clausius's statement, heat can only be transferred from a hot body to a cold body. Therefore, the heat will always pass from the liquid in the primary circuit (hotter because it has been exposed to the Sun) to the accumulator liquid.
Why is the heat exchanger important?
A system that did not use a heat exchanger and the water that entered the collectors was the same as that stored in the tank would also work.
However, the heat transmission in a thermodynamic system, the efficiency is proportional to the temperature difference. In other words, the colder the liquid that passes through the solar collector, the faster it will heat up.
What is the best orientation of an accumulator?
If the accumulator is in a vertical position, the temperature stratification is carried out more easily and effectively, so it is not necessary that the entire tank be at the marked temperature.
In addition, installed in a vertical position of the accumulator, a higher thermal performance is obtained from the solar collectors, and thermal losses are again avoided.
Types of solar accumulators
The size of the solar installation is the most important element in choosing one type of accumulator or another.
Depending on the size of the installation
For small or medium-sized structures, it is common for the tank itself to also contain drinking water .
On the other hand, in large and complex thermal solar energy installations, it is essential that other buffer tanks are gradually established. The inertia tanks allow to store the thermal energy that will be transferred later to the solar accumulator.
Internal or external exchangers
In addition, depending on whether the heat exchangers are external or located inside the condenser, we can obtain other variants.
If the tank does not have a built-in exchanger, the water is heated outside. On the other hand, if it is included inside, both the accumulation of water and its subsequent increase in temperature occur within the same tank.
Depending on the location of the accumulator
The accumulator can be:
- Above solar collectors
- Elsewhere in the facility.
If they are above, it is a solar thermosiphon system; the fluid that circulates between the solar collectors and the accumulator does not require pumping.
If, on the other hand, the accumulator is located elsewhere, a contribution of electrical energy is required to pump the fluid . In these cases, the energy supplied can come from another renewable energy source or directly from the electricity grid.