Storage of renewable energy , solar , heat

Most of renewable energy sources to have an average energy balance (averaged over one year cycle) a very low or even zero .
All renewable energy sources like wind , sun , heat , etc. . are temporary and require storage and accumulation ,much later than is the ” overproduction ” .

this means , that the use of any surplus energy ( heating , solar , renewable ) , requires its storage for a long period of time .

Lets consider closed solar system .
When we do not accumulate and buffer heating energy in an insulated tank with hot water : what we have gained in a hot and sunny day, We would give back to the atmosphere at night .
Despite the temporary production of kilowatts or megawatts of power by the receiver or heat exchanger , average energy recovered from organic sources tends to zero .

The easiest and cheapest way of storing is thermal energy, which does not require any special processing technology to another type of energy.
It can be used for heating water (eg. washing ), and to heat your home throughout the year.
The first step is to ensure that you can use energy for current needs and then store the excess, because storage is always associated with energy losses, and accumulate energy for months is rather non economic.

Depending on the length of storage time and the amount of energy is required for different volume “energy storage” . this depends , also the approximate amount of energy needed to heat .

We must consider efficiency of thermal energy storage project taking into account the percentage of free energy , in relation to the total energy of the inserted heating . The real value is between 70 – 80 % .

To produce hot water , it is necessary to heat it to a temperature above 45 ° C and storage directly in the hot water tank. Storage of larger amounts of hot water for more than 2 – 3 days is not viable due to the large losses resulting from high difference of temperature .
Seems more sensible to long-term storage of energy with lower temperatures ( losses are proportional to the temperature difference between the tank and external temperature. However, this requires a large volume of buffer energy and large heat transfer coefficient .

We can gain maximally of the heat energy from the solar systems, which have a relatively high efficiency. Recovery time is also much lower , than other devices using renewable energy sources such as heat pumps.
Reception of energy is also very simple , by flowing the liquid through a solar collector and returning it to the tank, or the energy transfer via a heat exchanger .

If you wish to store thermal energy throughout the year the number of receivers of solar energy (heat) much bigger then only for spring,summer,autumn. We must consider the year-round demand and estimated losses. The most optimal is to combine solar panels with independent segments and their individual control, especially when they are turned in different geographical directions .

The most sensible is heating farms or homes on large plots, where we have lots of space , both the deployment of solar collectors and heat storage systems . Are known energy storage (gels tanks ) , that can store several times more heat energy , then the water tank of the same volume.
However, these are very expensive solution and at the stage of thermal energy storage, together with the construction of a house from scratch , can be much simpler and cheaper to implement such a magazine. In addition, it will allow us to accumulate heat throughout the spring , summer , autumn and putting it through the winter.

This magazine is best done during the construction of the building at the stage of basement.
Given that basement has depth of about 1.5 meters at our latitudes , between the foundations of the building to the planned floor space we obtain a volume close to the surface of the foundation of the building * (1 to 1.3m of height) which make quite big space for tank.

The best do it with loamy earth , which dominates in Poland, Europe and has a good coefficient transfer of heat energy.

To do this, whole ground inside basement footprint must be removed to the depth of basement. Basement walls are made standard way, by insulating them from the outside only.
The whole of the bottom must be isolated against water with thick foil .
The bottom we also has to isolate thermally with LECA and other insulating materials , which can withstand the pressure of the earth with a height of 1.5m.
Expanded clay can be replaced by other isolation material. For thermal insulation again put a thin layer of polystyrene foam and foil insulation.
At the bottom of the Heap created put a thin layer of clay.
Then spread the heat exchanger ( water pipe for underfloor heating ), which would transmit solar energy and return it from the energy store to the accumulator.
Then, very carefully fill the coil 20cm layer of soil and thicken it .
After this point it is good practice to test the tightness of the pipe with the help of a compressor and a pressure gauge .
The entire space between the continuous footings fill it with clay thickening every 20 – 30cm .
For security, you can put more than one coil to allow switching to a second heat exchanger in case of damage of the first.
The upper part of the energy storage must be thermally insulated with foil and Styrofoam (10cm minimally), to the planed floor level.
The use of another coil in the floor allow for more optimal use of solar energy in winter to low-temperature reheating home .

This self constructed “warehouse” of heat energy is slowly transferred through the walls of the building bearing up through which significantly reduces the heat escapes of home through the walls and basement floor and warms itself for few months of the year.
Good insulation from the bottom of the energy store and the outside of the building directly affects the efficiency of such a solution and reheating time of the building with free energy of the sun .
Since the volume of such storage is limited , to increase free time building heating , You can at most increase the active surface area of ​​solar collectors and energy storage to a higher temperature.
In this case , it may turn , that the building will be additionally re-heated at times when this is not required (in the summer) .

The use of such a store of heat supplied by energy from multi segment of solar collectors – require the use of
home automation heating as RoomManager and or a dedicated
home automation controller for solar collectors that would lead to maximum efficiency. Taking into account that every square meter of collector “dearly” costs , achieve efficiency 50% instead of 100% is equivalent to double the surface of solar collectors. It should be also be considered busy area of ​​the solar collectors on the plot that did not occupy a large area of the plot or roof.
In the case of installation on the roof , the surface of the roof are usually sufficient.
The performance of the system is particularly important in the case of the transition periods (mostly fall) optimal control of the heating system allows the storage of a large supply of energy before winter. In winter low efficiency and suboptimal control can even generate energy losses so it is worth fighting for.
In winter to increase the efficiency of solar heating ( solar farms ) it is best to power the underfloor heating through a heat exchanger , allowing for the use of such a low-temperature energy source directly at the minimum loss. smart home