Varieties and selection of batteries for solar panels

What is a gel battery, its design, characteristics, service life

A gel battery is a lead-acid power source in which the electrolyte is in an absorbed, gel-like state between the plates.Gel-technology implies the complete sealing and maintenance-free of this power source, the principle of operation of which is no different from other types of batteries.

Gel battery design

In conventional lead-acid batteries, the electrolyte is a mixture of distilled water and sulfuric acid. Gel technology is different in that the acid solution in the battery is in the form of a gel. Such an electrolyte structure is achieved by adding a silicone filler to the composition, which thickens the mixture.

Several high-strength plastic cylindrical blocks, interconnected, form the body of the gel power source.

The main elements of the power supply:

• positive and negative electrodes;
• porous separator plates;
• electrolyte;
• valves;
• terminals;
• frame.

The principle of operation of the gel power source is similar to this process in conventional lead-acid batteries - a charged source gives off a charge. During this process, the voltage drops and the density of the electrolyte decreases.

Characteristics of Gel-batteries

When choosing a new gel power supply, you need to pay attention to the following parameters:

• Capacity - measured in amps/hours. Shows how long the power supply can supply 1A current.
• Maximum charge current - the maximum allowable current value when charging the battery.
• The maximum discharge current, also known as the starting current, shows the value of the maximum current that the battery can provide for 30 seconds.
• The operating voltage at the terminals is 12V.
• The weight of the power supply depends on its capacity and varies from 8.2 kg (26 Ah) to 52 kg (260 Ah).

Gel battery marking

An important parameter for choosing a new power source is the date of its production. The format of this information depends on the manufacturer. Let's look at the main examples:

1. Optima: numbers are embossed on the plastic: the first is the year, the next is the day of issue. For example: 3118 means 2013, day 118. On some models, the production date can be found on a sticker: the top row is the month, the bottom row is the year.

1. Delta: on a sticker with a set of numbers and letters, we are interested in the first four characters. The first (letter) is the year starting from 2011 (A).

The second (letter) is the month starting from January (A).

The third and fourth (numbers) are the day of the month

1. Varta: in the production code, the fourth digit is the year of issue, the fifth and sixth are the month (January 17, February 18, March 19, April 20, May 53, June 54, July 55, August 56, 57 -September, 58-October, 59-November, 60-December).

Service life of gel batteries

The service life of a gel battery, which is reported by manufacturers, is about 10 years. However, it should be understood that it may vary depending on the operating conditions.

Temperatures that are too low (below -30°C) and too high (above +50°C) will reduce the service life of the Gel battery. This is due to the fact that under such conditions, the electrochemical activity of the power source either decreases or increases. It should be noted that an increase in temperature entails an acceleration of the corrosion of the plates. Constant undercharging of the battery also leads to a decrease in battery life. However, excessive charges have a negative effect on the service life.

In order to use the gel power source as long as possible, it is recommended to avoid deep discharges and store the battery for a short time in dry rooms with a temperature regime of -35 ° C to +50 ° C.

Calculation of the required battery capacity

The capacity of batteries is calculated based on the expected period of battery life without recharging and the total power consumption of electrical appliances.

The average power of the electrical appliance over the time interval can be calculated as follows:

P = P1 * (T1 / T2),

Where:

• P1 - nameplate power of the device;
• T1 – device operation time;
• T2 is the total estimated time.

Almost throughout Russia, there are long periods when solar panels will not work due to bad weather.

Installing large arrays of batteries for their full load only a few times a year is uneconomical. Therefore, the choice of the time interval during which the devices will work only on the discharge must be approached based on the average value.

The amount of energy generated by solar panels depends on the density of the clouds. If cloudy weather in the region is not uncommon, then the lack of input power must be taken into account when calculating the volume of the battery pack

In the case of a long period when it is not possible to use solar panels, it is necessary to use another system for generating electricity, based, for example, on a diesel or gas generator.

A 100% charged battery can deliver power until it is completely discharged, which can be calculated using the formula:

P = U x I

Where:

• U - voltage;
• I - current strength.

So, one battery with voltage parameters 12 volts and a current of 200 amps, can generate 2400 watts (2.4 kW). To calculate the total power of several batteries, you must add the values ​​​​obtained for each of them.

On sale there are batteries with a high power rating, but they are expensive. Sometimes it is much cheaper to purchase several ordinary devices complete with connecting cables

The result obtained must be multiplied by several reduction factors:

• inverter efficiency. With proper matching of voltage and power at the input to the inverter, a maximum value of 0.92 to 0.96 will be reached.
• efficiency of power cables. Minimizing the length of the wires connecting the batteries and the distance to the inverter is necessary to reduce electrical resistance. In practice, the value of the indicator is from 0.98 to 0.99.
• The minimum allowable discharge of batteries. For any battery, there is a lower charge limit, beyond which the life of the device is significantly reduced. Typically, controllers are set to a minimum charge value of 15%, so the coefficient is about 0.85.
• Maximum allowable capacity loss before changing batteries. Over time, aging of devices occurs, an increase in their internal resistance, which leads to an irreversible decrease in their capacity. It is unprofitable to use devices with a residual capacity of less than 70%, so the value of the indicator should be taken as 0.7.

As a result, the value of the integral coefficient when calculating the required capacity for new batteries will be approximately equal to 0.8, and for old ones, before they are written off - 0.55.

To provide the house with electricity with a charge-discharge cycle length of 1 day, 12 batteries will be required.When one block of 6 devices is on discharge, the second block will be charged

Types of batteries

Virtually any battery can be used for solar panels. But the main thing is that it works for a long time. The functioning of the battery depends on the type of manufacture and materials.

The main types of energy storage devices:

1. Lithium.
2. Lead acid.
3. Alkaline.
4. Gel.
5. AGM
6. Jellied nickel-cadmium.
7. OPZS.

Lithium

Energy appears in them at the moment when lithium ions react with metal molecules. Metals are additional components.

These types of batteries are able to charge very quickly with a large capacity. These batteries weigh little and have a compact size. In addition, their cost is quite high. Because of this, they are almost never used in solar energy. They work 2 times less than gel ones. But serve even less if the charge exceeds 45%. It is at this point that they are able to keep the volume of the container at the desired level.

Such batteries operate in small voltage ranges. A significant disadvantage of such devices is the capacity decreasing over time. And this does not depend on compliance with all technical rules.

Lead acid

At the development stage, they were equipped with several compartments for electrolyte with an aqueous solution. Lead electrodes and various impurities are immersed in this mixture. Thanks to this, the battery turned out to be resistant to corrosion.

Such devices do not work for a long time. This is due to the speed of discharge.

alkaline

These batteries are low on electrolyte. Their chemicals are not able to dissolve in it. They don't even react to each other.

Alkaline (alkaline) batteries can last a long time. They are well resistant to power surges. Unlike gel batteries, these batteries are able to work stably at low temperatures. And in the cold they are able to work for a long time.

They must be stored 100% discharged. This is necessary in order not to lose capacity during future charges. This feature can seriously disrupt the operation of a solar power plant.

Gel

This type has such a name because the electrolyte in it is presented in the form of a gel. Due to the lattice layer, it practically does not flow.

This solar battery lasts a long time and can be recharged many times. Resistant to mechanical damage. All sorts of cracks will not interfere with its functioning.

It can operate at low temperatures down to -50 degrees and its capacity does not decrease. After a long period of inactivity, the gel battery does not lose its properties.

If this battery is to be used in a cold room, then it should be insulated. Under no circumstances should the charge level be exceeded. Otherwise, it may explode or fail. In addition, they are highly sensitive to power surges.

AGM

In fact, they belong to the type of lead-acid. But there is a difference - this is the fiberglass inside, which is in the electrolyte. Acid fills the layers of this material. This makes it possible for her not to spread. All this suggests that such a solar battery can be placed in any position.

These batteries have a good amount of capacity, last a long time and can be recharged up to 500 or 1000 times. It all depends on the manufacturer.But despite all the advantages, there is a significant drawback. They are sensitive to high current. This can inflate the body.

Cast nickel-cadmium batteries

They are alkaline and need to be filled with electrolyte. Unlike jelly-filled batteries, they are safer. Their cost is not high and the power is kept quite well. Able to withstand many cycles of charge and discharge.

The service life is quite short. The longer you use it, the smaller its capacity becomes.

Car batteries

These devices are quite profitable in terms of saving money. People who make their own solar power plant most often use them.

The disadvantage of these batteries is rapid wear and frequent replacement. As a result, they can be used for a short period of time and for low power solar modules.

Comparison table of batteries:

	Lead automotive	Lead AGM/GEL	Lead OPzS	Lead OPzV	Li-ion Li-ion	Lithium titanate LTOs	Lithium Iron Phosphate LiFePO4
pros	Low initial investment.	Sealed. Does not emit gases	Possibility of service. good performance for lead batteries.	Sealed. Does not emit gases. Good performance for lead batteries.	The highest energy density. Small weight and volume. Long service life.	Longest service life. It is possible to charge and discharge with huge currents. Completely safe	High energy density. Long service life. Large charging and discharging currents. Completely safe.
Minuses	Short service life. Give off gases. Slow charge. They are not capable of delivering high currents for a long time. Nonlinear bit characteristics.	Short service life with constant cycling. Slow charge. Not capable of delivering large currents. Small removable capacitance when discharging large	High price. Slow charge. Not capable of delivering long-term high currents. Small removable capacitance when discharging with high currents.	High price. Slow charge. Not capable of delivering long-term high currents. Small removable capacitance when discharging with high currents.	Hazardous if damaged or abnormally operated, give off fumes profusely and are a fire hazard. Cannot be used without a balancing and protection system.	The largest initial investment. Cannot be used without a balancing system.	High initial investment. Cannot be used without a balancing system.
Rated voltage 1pc, V	12	12	2	2	3,7	2,3	3,2
Number of pcs in series to get 12V	1	1	6	6	4	6	4
Specific gravity, W * h in 1 kg	45	40	33	33	205	73	95
Price for 1000 W*h, rub (for 2019)	7000	14000	16000	20000	14000	33000	16000
Number of cycles, at a discharge of 30%	750	1400	3000	5000	9000	25000	10000
Number of cycles, when discharged 70%	200	500	1700	1800	5000	20000	5000
Number of cycles, when discharged 80%	150	350	1300	1500	2000	16000	3000
The price of 1 cycle, with a discharge of 30%, rub	9,3	10	5,3	4	1,6	1,3	1,6
The price of 1 cycle, with a discharge of 70%, rub	35	28	9,4	11,1	2,8	1,7	3,2
The price of 1 cycle, with a discharge of 80%, rub	46,7	40	12,3	13,3	7	2,1	5,3

Based on all the above arguments and the comparative analysis, we can conclude that lithium batteries are superior to "lead" batteries in almost all respects. But which of the main three types of lithium batteries should you choose?

In our opinion, at the moment it is better to buy lithium-iron-phosphate batteries for a solar power plant, they have excellent technical characteristics, long service life and, unlike conventional Li-ion, are completely safe.Moreover, their cost is 2 times lower than that of lithium-titanate batteries, and despite the fact that LTOs are more profitable during operation, there is a high probability of buying a refurbished used LTO battery that was removed from electric vehicles in China.

Therefore, in most cases, batteries using LiFePO4 technology will be preferable.

Which ones to take?

In fact, batteries are the main brake on the development of alternative energy in general, its weak side. Modern technology has not made batteries smaller, lighter and cheaper. There are two types of batteries used in the solar power system:

• Acid;
• Gel.

There is a difference in price and in the internal structure, but the biggest difference lies in efficiency. A gel battery tolerates deep discharge much better, this is the normal mode of operation for it. The disadvantages of gel batteries include low starting currents at sub-zero temperatures, although such currents will not be needed under conditions of use in a home power supply system. Also, gel batteries are much more expensive.

Life time

In most cases with home solar panels, the cycle of the battery subsystem will be one day. As you operate in this mode, the ability of the battery to accumulate energy in the same volume will be reduced. It is believed that by the end of the battery life, the remaining capacity of the battery should be 80% of the nominal.

Given this feature, it is quite simple to calculate the economic feasibility of choosing certain batteries in a system with solar panels.

Effect of depth of discharge on service life (cycles)

Temperature effect on service life (years)

Types of batteries and their characteristics

Starter batteries

It is worth choosing this variety only if the place where the battery will be installed will have good ventilation. This type of battery, designed to work as part of a solar power plant, has a rather high self-discharge rate. They are used in cases where the solar battery is forced to function in difficult conditions.

Smear plate batteries

Such devices can be called the best option in such cases when it is impossible to carry out constant maintenance of the system. In addition, gel batteries are indispensable in case of installation in a poorly ventilated area. However, such energy storage devices cannot be called a budget option. In addition, the duration of operation of such batteries is relatively short. The positive qualities of such elements can be called small losses of electrical energy, which will significantly extend the operation of the station at night and cloudy weather.

AGM batteries

The structure of an AGM battery

The basis of the operation of these electrical energy storage devices are absorbent glass mats. Between the glass mats there is an electrolyte in a bound state. You can use the battery for its intended purpose in absolutely any position. The cost of such batteries is relatively low, and the charge level is quite high.

This battery has a lifespan of approximately five years.In addition, the distinguishing features of an AGM-type battery are: the ability to move in a fully charged state, the ability to withstand up to eight hundred cycles of full charge and discharge, relatively small size, fast charging (about seven and a half hours).

This battery operates in the temperature range from fifteen to twenty-five degrees. However, these batteries do not tolerate partial charge well.

Gel batteries

The electrolyte in this battery has a jelly consistency. The design of such batteries is highly resistant to charge and discharge. They do not need numerous maintenance activities. The cost of such an element is relatively low. Energy losses are also not significant.

Flooded (OPzS) batteries

The electrolyte in these batteries is in a liquid state. They do not need constant maintenance. In most cases, it is necessary to check the electrolyte level about once a year. Such electrical energy storage devices are designed to discharge at low currents and can withstand a large number of full charge and discharge cycles.

However, the cost of such devices is quite high, so it is advisable to use them in powerful power plants that convert solar energy into electrical energy.

What to look for when choosing

Power, number of LEDs

A very important parameter. The level of illumination, the brightness of the lamps, their number, the distance between them depends on it. Power is usually specified in Watts. As a rule, buyers best imagine the power of more familiar incandescent lamps.Therefore, there are tables with analogues of the power of LED lamps and incandescent lamps.

Based on such a table, it is not difficult to estimate how much power LED lamps are needed to create backlight or full-fledged lighting.

Degree of protection IP

Indicated on all electrical appliances. The first digit shows how the luminaire is protected from the penetration of dust, solid particles. The second marks the level of protection against moisture, splashes, water jets.

For safe operation, the case and batteries must be protected from dust and moisture. For outdoor installation, a protection class of at least IP44 is recommended. The higher, the safer. For fountain lights, the IP is at least 67.

glass type

Depends on the climate, the amount of sunlight. For the southern regions, where the sun is a frequent guest in the sky, you can choose panels with smooth glass.

If the weather is cloudy, then you should choose reflective glass. It will allow you to maximize the use of scattered sunlight for charging batteries.

Tempered glass is recommended for public spaces to protect panels from damage.

Type of silicon in fixtures

Depends on usage. More expensive multi-, mono-crystals are suitable for year-round use. For country summer use, polycrystals are enough.

If it is possible to install large-area solar panels, then thin-film ones can be used. They are inexpensive, produce fairly cheap energy.

Experts agree that properties of solar panels much more dependent on the quality of manufacture than on the type

It is better to pay attention to the reputation of the manufacturer to choose a reliable product.The Hungarian company Novotech, the Austrian Globo Lighting, etc. have proven themselves well.

Battery type and capacity

A standard charged battery with a capacity of 600-700 mAh is enough for 8-10 hours of work at night. Depending on your specific lighting needs, you can choose between smaller and larger batteries.

To do this, pay attention to the operating time of the lamps when the battery is fully charged. For lighting throughout the night, it is better to choose batteries with a voltage of at least 3 V

The type of battery does not play a role for the characteristics of lamps: both types are characterized by stable operation at temperatures from -50⁰С to +50⁰С. Nickel-metal hydride ones are more expensive, but last a little longer. The composition of the nickel-cadmium battery contains environmentally toxic cadmium, so it may be difficult to dispose of it.

Controller quality and additional options

The service life of lamps, autonomy, and other characteristics depend on the controllers. Additional devices, such as a motion sensor, a photo relay, allow you not to think about turning the lights on and off.

Appearance, installation method

Design is important for decorating the area.

The installation method is selected depending on the purpose. For garden lamps, a leg stuck into the ground is sufficient. More "serious" lighting fixtures require pendant mounting or a high support.

How to calculate battery parameters

Batteries make up a significant portion of the cost of the entire solar system. First of all, this is due to their regular replacements during operation. These devices have different capacities and service life, so the price is significantly different.There is a certain procedure that determines the calculation of a solar battery for a home, on the basis of which everyone decides to purchase a particular battery model.

The main parameters of any battery are the capacity and the number of charge and discharge cycles. Indicative calculations can be performed on the example of a conventional acid battery, the voltage of which is 12 V, and the capacity is 100 Ah. It is required to calculate the possible amount of energy accumulated at a time and the amount of the same energy given off for 1000 cycles that make up the battery life. All calculations are carried out taking into account compliance with the rules and operating standards. For example, an increase in temperature shortens the life of the device, and a decrease leads to a decrease in capacity.

So, how much energy can a battery fully charged and then fully discharged. To obtain a result, a capacity of 100 A * h is multiplied by an average voltage value of 12 V. The final figure will be 1200 W * h or 1.2 kW * h. However, in practice, the full depletion of the battery is considered at 40 percent of the balance of the initial capacity. In this case, the average capacity indicator for the entire period of operation will not be 100 A * h, but only 70. Therefore, the real supply of electricity is: 70 A * h x 12 V = 840 W * h or 0.84 kW * h.

The instructions for the battery indicate that it is undesirable to discharge it by more than 20% of the total capacity. That is, at night, only 0.164 kWh can be taken from the battery without consequences. Normal battery discharge should occur within 20 hours.If this process occurs under the influence of high current, then the capacitance will decrease even more. Thus, the most optimal discharge current will be 5 A, and the battery output power will be 60 W. If you need to solve the problem, how to calculate the power with an increased value, in this case the number of batteries increases or the mode of operation of existing devices changes.

Great importance in ensuring the operating mode is attached to the correct settings of the charge and discharge controller. When a certain charge voltage is reached, a shutdown is performed, otherwise the electrolyte will begin to boil and intensively evaporate. In the same way, consumers turn off when the battery is discharged up to 80%. Compliance with the operating mode and manufacturer's recommendations significantly increases the service life of batteries.

Main characteristics of batteries

In batteries for the solar system, it is necessary to perform reverse chemical processes. Multiple charging and deep discharging is not possible in every battery. The main characteristics of suitable batteries are:

• capacity;
• device type;
• self-discharge;
• energy density;
• temperature regime;
• atmospheric mode.

When buying a battery for a solar system, special attention should be paid to the chemical composition and capacity, be sure to pay attention to the output voltage. You should choose a convenient place for installation and maintenance of the battery

You should choose a convenient place for installation and maintenance of the battery

Premium options for gel batteries are able to painlessly leave the state of full charge discharge, and the cyclic service reaches five years.Due to the dense filling of the electrolyte on the surface of the electrodes, corrosion is excluded. High-quality batteries have low self-discharge and are able to operate under extreme temperature conditions.

How to choose batteries for solar panels?

Of course, the choice of battery for solar panels depends on the configuration of the system. However, there are a few principles that will point you in the right direction. First of all, in most cases, you should not give preference to AGM batteries. They tend to have significantly lower cycle life and are less tolerant of deep discharges, further shortening their service life. However, there are exceptions. Further, depending on the cyclicity of the system (i.e., the frequency of switching to battery operation), its internal parameters, the economic feasibility of choosing one or another technology is determined.

When choosing batteries, some features should be taken into account: how long the battery should last, how much power it should provide. Below are the most important criteria that should be used to compare different solutions.

What batteries are best for solar panels?

Among the classic solutions for industrial stationary batteries, there are several technologies that meet the requirements for pairing with solar panels. A small comparative analysis is given in the table:

Gel with tubular plates (OPzV)	up to 20 years	up to 3000	not required
Gel with spread plates	up to 15 years	before 2000	not required
Lithium iron phosphate (LiFePO4)	up to 25 years	up to 5000	not required
Nickel-cadmium	up to 25 years	up to 3000	water may need to be added

Gel lead acid batteries - the most adapted to cyclic operating modes and long-term discharges among sealed (maintenance-free). Tubular plate batteries meet more stringent quality and reliability requirements, so they are more commonly used in large and medium-sized industrial solar power plants. Plain plates are a simpler technology, however, due to their simplicity and less expensive, therefore, such batteries can often be found paired with low-power solar panels.

In lithium iron phosphate batteries iron phosphate is used to improve safety and thermal performance while achieving long cycle life. Since these batteries have low heat generation, they do not require ventilation or cooling and can be installed as part of solar power plants in ordinary buildings without special equipment.

Nickel-cadmium batteries have a simple and reliable design. Widely used in large solar power plants around the world due to their high efficiency, ruggedness and ability to operate in extreme temperatures. These batteries are suitable for demanding applications where reliability is a critical factor. They can do without regular maintenance, but require additional ventilation.

Solar Battery Selection Criteria

Everyone who has the goal of providing electricity to the house with solar panels is wondering which batteries are the best and most suitable option for creating a solar power plant.We will help you determine which battery to choose in this case.

When choosing a battery model, you must be guided by the ratio of these characteristics to the conditions of use

The parameters to pay attention to when buying are described below.

1. Resource of "charge-discharge" cycles. This characteristic suggests the approximate life of the battery.
2. An indicator of the speed of the charging and discharging process. This indicator also affects the service life of the device.
3. The self-discharge rate of the device. It also affects battery life.
4. Battery capacity. This parameter helps to determine the power with which the device can operate.
5. The maximum value of the current during charging and discharging. The charging value determines how much current the device can accept. The discharge value determines how much current the device can deliver without compromising performance.
6. Weight and dimensions of the device. These parameters are necessary to draw up a battery connection diagram, as well as determine their location.
7. Terms of use of the battery. This should be taken into account due to the fact that different models operate at different temperature conditions.
8. Service. The instructions should indicate what maintenance measures each specific model requires. But this is not the main parameter that may affect your choice.

For the full functioning of a solar power plant, the technical characteristics of all components of this system should be taken into account. We hope that the above information will help you choose the right battery for your solar power system.