Solar batteries are devices that allow the energy produced by solar panels to be accumulated. In this article we explain when they are necessary and what factors you should take into account if you are thinking of acquiring them.
What are solar batteries?
Batteries for solar panels allow the electrical energy produced by solar panels to be stored . The purpose of photovoltaic accumulators is to be able to use energy at any time of the day, mainly when photovoltaic installations are not in operation (for example, at night).
Installing solar batteries allows you to completely disconnect from the electricity grid. Therefore, this photovoltaic component is essential in isolated photovoltaic installations . In this way, all the energy consumed will be completely free and renewable.
Solar batteries last between 5 and 15 years depending on the model. Therefore, they must be replaced at least once throughout the useful life of the solar panel installation .
How do photovoltaic batteries work?
The operation of photovoltaic batteries is based on a process of reduction – oxidation. Solar accumulators are made up of a positive and a negative pole, as well as electrolytes that allow the flow of electrical current to the outside of the battery. Thanks to this, the electricity generated in times of low demand can be stored to supply it when needed.
The ability to accumulate energy and generate electrical current is determined by the following parameters:
▷ Loading / unloading speed: measures the speed with which the accumulator fills and empties. The more discharge cycles, the shorter the battery life will be.
▷ Charge depth : measures the amount of electrical energy that can be introduced into the solar battery in each charge. The deeper it is, the shorter the battery life will be. For this reason, it is advisable not to download more than 50% of them.
What is the capacity of a solar battery?
The capacity of a solar battery for photovoltaic self-consumption is the amount of energy that the device can accumulate and is measured in Ampere-hours (Ah). It is calculated by multiplying the voltage by the amperage of the accumulators, however, the energy supplied will also depend on the discharge rate. Factors influencing capacity are:
1. Amperage : represents the intensity of electrical current or the flow supplied by the solar battery.
2. Voltage : is the potential difference (or force) with which the current provided by the battery circulates.
3. Battery discharge rate: the higher the discharge rate, the less power supplied by the battery. The amount of amps the accumulator can supply is described in the CX format indicating discharge times.
|Amperage / hour
Solar batteries typically refer to discharge times of approximately 100-120 hours to last between 3 and 6 days.
What types of solar batteries are there?
There are multiple types of solar batteries that are classified according to manufacturing technology, among them, we distinguish:
▷ AGM solar batteries : indicated for small installations (for example, self-consumption in motorhomes ) and do not require maintenance. They are very versatile and although they undergo deep discharge cycles, they perform very well and can be recharged. AGM accumulators have a useful life of between 5 and 10 years.
▷ Monoblock photovoltaic batteries : they are usually used in isolated installations with low consumption or sporadic use (such as lighting). Its useful life is approximately between 4 and 5 years.
▷ Stationary solar batteries : they have an excellent quality-price in the photovoltaic sector. This type of accumulators is designed for homes, since they are indicated in installations with high and continuous consumption.
▷ Lithium battery for solar panels : light, compact and with fast charging times. This type of accumulators can be used in any installation and do not require any maintenance. In addition, they do not emit any type of polluting gases, so they are very sustainable. As a disadvantage, it is the accumulator that has a higher price.
What is the charge level according to the voltage of the solar battery?
▷ 12V solar batteries : indicated for monthly consumption less than 100 kWh and powers of 1 kW. In these cases, it is advisable to use monoblock batteries as they are designed for second homes where consumption is occasional and low (for example, country houses).
▷ 24V solar batteries : indicated for consumptions ranging between 100 and 150 kWh and with powers between 1 and 5 kW. It is recommended to use stationary batteries in this type of self-consumption systems.
▷ 48V solar batteries : indicated for consumption above 150 kWh per month and with powers greater than 5 kW. In these installations it is advisable to use stationary batteries or lithium batteries.
Is it possible to connect two solar batteries?
Yes, two solar batteries can be connected in series, always adding the voltage and keeping the amperage constant. Therefore, if we have 4 6V and 900Ah batteries, we have a total of 24 Volts and 900 Amps.
What are the best batteries for photovoltaic panels?
There are more and more manufacturers in the solar battery sector. Here are some of the models that offer the best results:
|LG Chem Resu 10
|One of the best lithium batteries on the market with more than 6,000 cycles of autonomy.
|48V 910 Ah at C100
|HOPPECKE 6 * 6 OPzS 600
|Stationary battery with a lifespan of approximately 15 years
|2V 910 Ah at C100
|WccSolar AGM U-Power TFS
|It does not require maintenance and can be used with temperatures ranging between -20 and 55º C.
|12V 250 Ah
What is the price of solar batteries?
The price of solar batteries will depend mainly on two factors:
- The photovoltaic accumulator model (AGM, Monoblock, stationary or lithium).
- Of the battery capacity.
Therefore, there are important variations in the cost of batteries for solar panels. It is advisable to ask a specialist for advice to choose the battery that best suits our consumption needs and thus avoid future worries. To give you an idea, in the following table we indicate the existing price ranges depending on the accumulator model:
|€ 500 – € 1,500
|€ 200 – € 2,000
|200 – 7,000 €
|€ 500 – € 10,000 (or more)
How many solar batteries do I need for my photovoltaic installation?
When sizing the capacity of the solar batteries that we need for our solar installation, it is important to take into account the following factors:
The photovoltaic installation must produce enough energy in winter to cover the energy demand for the entire month. For this reason, it is important to determine the amount of energy that is consumed in this station.
Calculate the daily consumption in the months with less solar irradiation (normally, December or January) by two. This will prevent the batteries from discharging more than 50% on a regular basis. Subsequently, multiply the result by three to guarantee a sufficient amount of energy in our home for three days without solar production.
Determine the voltage that is most suitable for the installation (12, 24 or 48V) based on the advice we mentioned above.
Calculate the amperage of solar batteries by dividing the total energy by the amperage.
Next, we are going to show an example for a single-family home that has a consumption of 250 kWh per month in January and a contracted power of 4.6 kW:
1. Calculation of daily consumption: 250 kWh / 31 = 8 kWh per day.
2. We multiply the January consumption by 6 = 8 kWh * 6 = 48.
3. We are going to select 48V batteries. With this, we calculate the amperage of the batteries = 48,000 / 48 = 1,000 Ah. As a result, the accumulator to choose will be with a voltage of 48V and an amperage of 1,000 Ah.
It is not possible to increase the capacity of the solar batteries.
When are solar batteries necessary?
Solar batteries are essential in isolated photovoltaic installations so that we do not run out of electricity at night or on very cloudy days. On the other hand, accumulators are optional in installations with connection to the electrical network, however, they are not usually economically recommended. In the following table, we show the advantages and disadvantages of installing solar batteries depending on the type of photovoltaic system:
|Type of photovoltaic system
|House with network connection
What to consider when comparing solar batteries?
When buying solar batteries, it is essential to compare various manufacturers and models to choose the one that best suits our energy needs. Here are the factors that must be taken into account to choose the ideal accumulator:
1. Compare the amperages at the same discharge rate :
- Since this information varies depending on the battery discharge rate, it is important to find and check the C100 value on the device.
- However, not all solar batteries provide the information in C100. If you cannot find this value, it is advisable to compare the closest one, such as C50.
2. Compare the energy the battery is capable of supplying (kWh)
- This data is essential to cover our energy demand at times when the solar panels are not in operation.
3. Compare the useful life and / or number of charge cycles.
- This point is important to take into account to know the number of times we must replace the batteries in our solar installation.