Choosing the Best Solar Battery: Profitability, Types and Maintenance

Solar batteries are a very important component in self-consumption facilities since they are responsible for accumulating electrical energy and allow us to make the most of solar energy.

Below you will know all the important information about them in photovoltaic panel installations: what they are, the benefits they offer, their operation, the different types, which one you should choose according to your needs, etc.

Choosing the Best Solar Battery Profitability, types and maintenance

What is a photovoltaic solar battery?

A photovoltaic battery is a device that allows us to store the energy we generate through solar panels during sunny hours to make use of it when production is not possible, that is, during night hours or cloudy days. In this way, these devices contribute to having electricity when the solar panels are not in operation.

What are the benefits of the solar energy accumulator?

In addition to being a perfect solution to accumulate the energy produced by photovoltaic panels, solar batteries offer many other benefits. Some of them are:

  • Excellent behavior against variations in the appliances in use of the house regardless of the amount connected simultaneously.
  • They generate almost no pollution, helping to take care of the environment.
  • They have a very long lifespan; they can work properly for up to 15 years in some cases.
  • They will allow us to increase the self-consumed energy of our solar panels and thereby further reduce our electricity bill.

How do batteries for solar panels work?

As we have just seen, solar batteries are responsible for accumulating photovoltaic solar energy to use when solar panels do not produce enough electricity. But how do they do it?

The solar battery includes one or more electrochemical cells that convert chemical energy into electricity. The cells have a positive and a negative electrode and electrolytes that allow the movement of ions between the electrodes. In this way, the flow of current out of the battery is facilitated to perform its function.

All the surplus that has been generated from the solar radiation received by the photovoltaic panels will be stored in the battery belonging to the installation and can be used in times of low or no lighting.

The ability to store energy will depend on the download speed (the longer the download time, the greater the amount it can generate). Size, the battery’s capacity, and certain aspects that we will see later are usually taken into account, such as the type of use, whether the consumption is daily or sporadic, maximum installation power, etc.

When are batteries for photovoltaic self-consumption profitable?

The installation of batteries to store solar energy is an option that can help you make your photovoltaic system profitable. However, it depends on the type of installation:

1. Installation not connected to the grid: in the installations of isolated solar panels, they are essential so that you can store the energy you have generated.

Isolated installations are completely independent as they are not connected to the public network. Therefore, they do not have any contracted marketers and cannot benefit from the surplus compensation mechanism.

2. Grid-connected installation: it can be cost-effective or not. Of the hours of your consumption:

  • If your installation has high consumption during the night hours, it will be highly recommended that you make use of the batteries. 
  • If your installation has high consumption during the day, I do not recommend that you make this initial investment. Example: Office building.

Lithium batteries for photovoltaic systems

Lithium batteries are the ones that offer the best performance, and for this reason, despite being recent, they have positioned themselves as the undisputed leaders for solar energy in homes.

Advantages of lithium batteries

  • They lack the “memory effect,” so they can be loaded at any time
  • Allow higher energy density
  • Smaller size and weight than conventional batteries, being able to save up to 70% of space
  • They are the fastest to load
  • No maintenance required
  • Do not emit polluting gases

However, having more expensive manufacturing than the rest of the solutions, they are the most expensive. Its useful life is usually ten years.

Is it worth investing in a lithium battery?

If you prefer not to get involved in the maintenance of the battery and be able to opt for superior performance, it is worth investing a little more and opting for lithium batteries. Lead-acid batteries are cheaper, but they also require some care and attention from the user: monitoring the density of the electrolyte, monitoring levels, etc.

Other types of solar batteries: AGM, Monoblock, and Stationary

1. AGM Batteries (Absorbent Glass Mat)

This type of battery is ideal for installations that involve a high intensity of discharge, that is, that have multiple appliances with powerful electric motors connected simultaneously. They do not require any periodic maintenance. They have a long shelf life that ranges from 5 to 10 years.

Lithium batteries vs. AGM Batteries

In large installations, the choice between one battery or another is usually reduced to lithium vs. AGM batteries. The main disadvantages of AGMs compared to lithium are:

  • It is not advisable to download them more than 50% so that they maintain a decent useful life with proper operation. However, lithium batteries support a depth of discharge of 80-90%, so the energy utilization is higher.
  • On the other hand, we must take into account the concept that the discharge speed is related to the battery’s total capacity; that is, the higher the discharge speed, the amount of total energy granted by the battery is reduced. This effect is greater in AGM batteries, and therefore, the total battery power is lower.

2. Monoblock

Monoblock batteries are an economical alternative with very good performance for small installations and relatively low consumption to illuminate the house, television, computer, refrigerator, etc. However, it is not recommended to use it in places that contain complex devices (that is, that have a motor).

These batteries are contraindicated for the high starting peaks that some appliances such as washing machines or drills can produce. If they were used for this purpose, their useful life would be significantly reduced, usually around 4 to 5 years. We can find various classes within this typology: open lead-acid Monoblock, deep cycle, and gel Monoblock.

3. Stationary

Like the previous models, this type of solar battery is also lead-acid with the difference that their design is tabular because they are designed for installations that involve a constant input and output of energy.

These models are characterized by great durability and demand since they tolerate deep discharge cycles with very good results. Therefore, they are the perfect solution for daily use. They have a long service life higher than that of previous models, reaching up to 15 years.

The first impression is that the price of lead-acid over lithium is cheaper; however, lead-acid batteries offer fewer cycles than lithium batteries. When calculating the cost between the number of cycles, the long-term price will surely be lower in lithium batteries.

Lead-acid batteries vs. Lithium batteries

Feature Lead acid Lithium
Depth of charge 50-70% 80-100%
Number of cycles 2.000-3.000 4.000-6.000
Guarantee 2-5 years 10 years
Load Inefficient and slow
Very efficient and fast
Efficiency 80-85% 98%
Losses 15-20% 2%
Type of use Self-consumption and isolated installation
Self-consumption and isolated installation
Resistance to high temperatures Moderate
Better endurance
Gas emission Slight Nothing
Maintenance Newspaper Minimal
Price* Around 200 $ Around 1,400 $

How long do the batteries of a photovoltaic installation last?

There is no fixed duration of solar batteries. It will depend on the number of cycles that the battery is able to tolerate until it reaches a capacity of 80%.

Therefore, if we subject it to a task of multiple daily cycles, its useful life will be reduced. On the contrary, if your work is a few daily cycles, your useful life will be extended.

Example battery durability estimation:

Battery type Nº cycles*
Years (cycle/day)
Lead acid 1,500 cycles 5 years
Lithium 5,000 cycles 13 years

*Number of cycles conserving the residual capacity at 80% (capacity that remains in the battery after discharge, use and/or maintenance.

What should I take into account to choosing the ideal photovoltaic battery?

There are several types of solar batteries, and there are many concerns that we face when choosing one or the other: how much money should I invest, which will give me better performance, each when I will have to perform maintenance, consider the possibility of buying them second-hand, etc.

For all this, it is convenient to keep in mind a series of factors to make the right decision:

1. First of all, you must know if we are going to use them daily in our usual house or sporadically in our second home (for example, on weekends).

2. If you are going to move from one place to another, you must get a mobile battery. On the contrary, if it is for your regular residence, the smartest thing is that you opt for a fixed battery to get the most out of it.

3. As usual, price is a determining factor. The price of the batteries ranges from 150 to 10,000 euros (or more) in the models that offer the greatest performance. Therefore, it is important to know how much you are willing to pay depending on the use you want to make of them.

Indicative price of solar batteries

Battery type Price
AGM Batteries 200 – 600 €
Monoblock Batteries 200 – >1.500 €
Stationary Batteries 200 – >7.000 €
Lithium Batteries 500 – >10.000 €

4. Battery maintenance is a very important factor. Just like AGM batteries or stationary batteries do not need any maintenance on the user’s part, other models require some care on our part to regulate the level of electrolytes and other elements.

5. Finally, batteries ranging from 2v to 48v or more in power will inevitably influence their price and storage capacity. Therefore, it is important to know how much energy we will use to opt for one.

Which solar accumulator to choose: 12v, 24v, or 48v?

It will depend on your consumption. The 12V solar batteries are designed for small installations, where the consumption does not exceed 100 kWh per month and powers of 1 kW. The 24V is the most used and is ideal for consumption ranging between 100-150 kWh per month and a power of 1-5 kW. Finally, the 48V is designed for installations with high power demand for appliances with high demand (ceramic hob, oven, air conditioning, etc.), with consumption above 150 kWh and powers above 5 kW.

Maintenance of Monoblock and Stationary batteries

Solar batteries are an important investment in photovoltaic installations, so it is very important to carry out proper maintenance so that they work correctly and we can extend their functional life. Remember to read and follow the manufacturer’s instructions at all times before starting the battery maintenance process.

First of all, check that the place where the solar batteries are located is ventilated well and protected from solar rays. You mustn’t smoke or light lighters in the battery room.

Subsequently, you must monitor that the battery’s electrolyte level has not exceeded the maximum limits. For this point, use distilled water when you need to refill the tank and make it an electrolyte.

Suppose we do not replace the occasional loss of electrolyte. In that case, solar batteries can suffer irreparable damages. If we allow the electrolyte level to have very low levels and expose the plate having contact with the air, they are sulfated and destroyed.

Steps to carry out battery maintenance

As we said, some types of batteries do not require any attention; however, for Monoblock and stationary batteries, we must ensure their correct operation. To do this, you must carry out the following steps:

1. Separate the connectors from the terminals: Keep in mind that it is very important not to touch both poles simultaneously (first the positive and then the negative).

2. Use a clean, dry cloth to clean the top of the battery and the terminals. Subsequently, tighten the terminals.

3. If you need it, fill the accumulator with water (you should not exceed the indicated maximum point).

4. Strengthen the terminals.

5. Subsequently, check the status of the wiring and connections, checking that there is no anomaly.

6. Finally, we will carry out the equalization process; this step is very simple. You just have to activate the option in the regulator. If the load controller does not have automatic equalization, it will be done manually.

The periodicity of the equalization process will depend on each model and the use that has been made of it. Therefore, it is very important to follow each manufacturer’s recommendations so as not to cause any damage to the battery.

Recommendations when carrying out the maintenance process

  • Do not wear watches, rings, or other metal objects during this process, as they could touch the terminals of the accumulator.
  • Do not wear watches, rings, or other metal objects during this process, as they could touch the terminals of the accumulator.
  • It uses plastic funnels to refill the distilled water from the battery cups.
  • Do not replace distilled water with another type (e.g., boiled), as it could damage the battery.
  • If diluted acid comes into contact with the skin or eyes, immediately wash the affected area with plenty of water and seek medical attention.