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Batteries: What should be the ideal for an autonomous home?

Electrochemical batteries remain the most common energy storage for an independent power supply in the private sector. However, there are more than a dozen battery varieties on the market in which electrochemical reactions occur between substances other than conventional lead-acid batteries. Some performance models are more preferable in alternative energy systems.

Batteries in autonomous power supply systems

The nature and mode of operation of batteries in different systems reveal their advantages and disadvantages for specific conditions. 

Features of operating batteries in a non-volatile house

A full-fledged residential building requires electricity 24 hours a day, 365 days a year. Of course, there are some exceptions, but they only prove the rules. This is what distinguishes the operation of batteries in autonomous homes.

Another difference is the charging cycle.

The very principle of a non-volatile house is based on the use of alternative energy sources: the sun, wind, water flow, and partially geothermal technologies. Moreover, the first two options occupy about 95% of the private sector. And it is for them that cyclicality is characteristic! If for the wind it is poorly predictable, then for sunlight the day/night cycles are determined millions of years in advance.

In other words, the battery will be charged every day and will release energy at night. 365 cycles will pass in one year. Under ideal operating conditions, with the scrupulous observance of the depth and rate of discharge, as well as the charging mode, 1500 cycles for a good lead-acid battery can be extended to 4 years.

It is important to note that a single battery cannot be replaced from a lead acid battery pack!

For example, in a non-volatile house, the energy storage system is provided with a block of 4 batteries of 200 A * h each. In total, they give 800 A * h. If after one and a half – two years of operation one of the batteries fails, then it is impossible to replace it with the same new one! Indeed, during operation, all batteries in the system evenly reduced their capacity, which affected other characteristics. The smart charger adjusts the charging mode to these parameters. And the new element has “passport” operating characteristics that stand out from the general system.

The cost of the entire battery pack, with proper design, approaches the price of generating elements, in this case solar panels.

Requirements for batteries in an alternative power supply system

An ideal battery for a home energy storage system should:

  • Withstand the maximum possible number of charging cycles;
  • Have high energy consumption;
  • Be unpretentious in maintenance and operation;

And it is especially important that these parameters should be correlated with the cost of the battery. For example, there are two types of batteries with a capacity of 100 A * h and a voltage of 12 V:

  • Lead acid;
  • Lithium Iron Phosphate Battery (LiFePO4).

In an ideal system, with laboratory compliance with the operating mode, each of the batteries will be able to produce:

1 Permissible depth of discharge is 80%, the consumer receives 20% of the indicated capacity. To calculate the amount of stored power, multiply 20 A * h by an average voltage of 12 V, and we get 144 W * h.

The number of cycles is 1500, the battery will give out 216 kWh in total during operation

2 The   permissible depth of discharge is 20%, the consumer receives 80% of the indicated capacity. 80 A * h X 12 V = 960 W * h.

The number of cycles is from 2 to 7 thousand, let’s take an average of 4500 cycles, and we get: 960 W * h X 4500 = 4320 kW * h

The difference in the amount of accumulated energy is 20 times. The cost of a LiFePO4 battery with a capacity of 100 A * h is about 45 thousand rubles, and a regular lead-acid battery with the same capacity will cost 10 thousand rubles.

But at the same time, LiFePO4 battery is fully charged in just 1 hour, and when energy is released, the output voltage remains stable until it is completely discharged. Those. very unpretentious in operation.

The general formula for choosing the optimal battery for a non-volatile home looks like this: Purchase price ÷ (Useful capacity × Life cycle).

Types of batteries for autonomous power supply

Conventional lead-acid batteries may not be considered in detail, because the characteristics of their operation in alternative energy systems have been studied and described. But it is these batteries that will be taken for comparison, as the most common type, therefore, we recall that they have:

  • Maximum depth of discharge 20% (80% should remain);
  • The number of working cycles with ideal control of operation ≈1200;
  • High sensitivity to changes in the recommended operating mode (rate and depth of discharge, temperature and charging rate, etc.).

The only remark on the tricky move of marketers who guarantee the operation of such batteries in a buffer mode for 5 or even 10 years.

The fact is that the buffer mode and the non-volatile house are completely different categories. In the buffer mode, the battery is always recharged, and it turns on very rarely! Well, for example, on the towers of cell stations, the batteries work in a buffer mode, and they are turned on only in emergency cases when the voltage is lost in the network. This can happen once a month or quarterly.

In a house that receives energy from alternative sources, at best, there is a charge during the day, a discharge at night. If a wind generator serves as a source of energy, then the cyclicality can change more often – that’s why it and the wind, order to be unpredictable.