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Аккумуляторные батареи для фотоэлектрических систем

Most off-grid PV systems use batteries to store power for use during periods of low or no sunlight. Certain specialized applications (e.g. some pumping and ventilation systems and calculators) do not require storage because power is needed only during periods of light. Some pumping applications use pumped water as the storage medium rather than electricity. However, most PV systems in Canada use batteries.

Your choice of battery size and type is an important design consideration, particularly for systems that have no backup power source. The batteries alone can represent 25 to 50 percent of total system cost, so it is essential to select the right type. You can use different types of rechargeable batteries, depending on the system's requirements. Batteries with a long expected life have higher initial costs but should cost less in the long run. Several batteries on the market are designed for use with renewable energy systems, such as PV and wind systems. Deep-discharge marine, golf cart or recreational vehicle (RV) batteries may also be suitable and are generally more affordable up front. An experienced PV dealer can advise on what type of battery is best for your needs.

Most PV systems use lead-acid batteries such as deep-discharge lead-calcium or lead-antimony batteries. Do not use car batteries as they are not designed for repeated deep discharges. Nickel-cadmium (Ni-Cd) batteries are rarely used in residential applications. Although they can be deeply discharged many times without harm and are less affected by temperature changes than lead-acid batteries, Ni-Cd batteries are more expensive and very expensive to recycle. As a result, their use is primarily restricted to applications where their increased reliability and low maintenance are worth the premium price.

Battery storage capacity is generally rated in ampere-hours (Ah). This is the amount of current that a battery will deliver over a given number of hours at its normal voltage and at a temperature of 25°C. The rated capacity of any battery drops with temperature. The size of battery you require is determined by the total anticipated drain on the battery. You can calculate this if you know the following information: the voltage of the battery, the wattage of the load, the length of time the load is operated and the ambient temperature of the batteries.

Operating batteries at temperatures below 25°C implies that you will need more nominal capacity. (This will vary, according to the type of batteries and rate of discharge applied.)

For example, to run a 25-W bulb for eight hours from a 12-V battery that is maintained at 25°C, you would need a battery with a capacity of at least 16.7 Ah (200 Wh at 12 V). If the battery must operate at temperatures as low as 0°C, then at least a 20-Ah battery would be required for the same load. But in practice, to protect the battery against accelerated aging, a larger capacity is used to avoid a complete discharge. For deep discharge batteries, do not use more than 80 percent of their nominal capacity. Also, car batteries start to be damaged if discharged more than 20 percent of their nominal capacity; therefore, they are not well suited for this type of application.

PV battery systems are usually designed to provide several days of storage in the absence of sunlight. In cases where longer overcast periods are anticipated, such as in the Far North, it is usually wiser to use a hybrid system rather than trying to provide enough battery storage. In this and many other cases, your most practical approach may be to use a combination of backup power and batteries.

In so-called stand alone solar electricity systems or solar home systems (SHS) batteries are used to store electricity so it can be used at night for lighting or to watch TV. Also batteries are used to supply electricity during periods when little or no bright sunlight is available to produce electricity with the solar panel. The amount of electricity needed and the size of the battery storage determine the duration of the dark period that can be bridged.

In solar electric backup systems batteries are used to bridge periods of black outs of the electricity grid (see also solar electric backup systems). Ordinary grid connected systems (where the electricity grid is reliable) do not use batteries.

Batteries are available in many sorts and sizes. 12V batteries are used most. Provided that the batteries are new and of the same type and size, they can be connected to increase the capacity of the battery storage. A trained professional only should do this.

Some solar electricity systems come with special solar batteries. Other systems use ordinary car batteries. Solar batteries are to be preferred as they are adapted for use in a solar electric system and will last considerably longer.

Batteries are often the weakest point in a solar electricity system and they are often the part to break down first. Here are some hints to help extend the life of your battery:

1. The use of a charge controller is highly recommended. It switches off loads when the battery is almost empty. All standard Solar Home System kits come with a charge controller.
2. Make sure that the number of solar panels, the size of the batteries and the number of loads (lights, appliances) and their consumption matches. Your supplier can help (also see sizing).
3. Observe your charge controller to check the state of charge of the battery (how full it is), usually there is a red light that will come on when the battery is empty and a green lamp when it is full. Try to keep the green lamp on as much as possible. This will extend the life of the battery.
4. Have the battery maintained (filled with distilled water) at least 3 times a year (provided it is not a maintenance free battery).
5. If you have the opportunity to have the battery charged completely with a battery charger/ generator, doing so (once a month) helps to extend the life of the battery.
6. Never by-pass the charge controller to get the last bit of energy from the battery: doing so will ruin your battery.
7. WARNING: Batteries should be stored in a cool (but not freezing!), well vented place, out of reach of children. Remember that batteries are dangerous as they contain harmful acids and electricity. Old batteries should be turned in with the supplier or disposed off as chemical waste
   

The amount of electricity needed and the size of the battery storage determine the duration of the dark period that can be bridged. This period is called the autonomy period: the maximum period with which the basic electricity needs can be met when there is no electricity produced by the solar panel. The autonomy period is a parameter that is used for system sizing.

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