AC and DC Power Storage: Differences and Benefits

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Solar storage systems are becoming increasingly popular around the world. Because they allow the operator of a solar system to use it, most of the solar power is generated himself. Thanks to battery storage, the energy generated by the PV system can be stored. Solar power can also be used when the sun is not shining.

Due to the significantly higher photovoltaic self-consumption, electricity costs can be saved. In addition, system operators with a power storage system become significantly more independent of the public power grid. Since self-generated solar power is emission-free, every kilowatt-hour consumed from your solar system is important to climate protection.

It is not without reason that the market for solar storage is growing. The number of manufacturers and models is increasing while prices are falling. Many providers have different solutions to offer, which are not always easy for interested parties to distinguish from one another.

Lithium-ion batteries instead of lead batteries

For years, solar power storage devices based on lead-acid or lead gel were the standard for photovoltaic systems. Storage tanks with lead technology were mostly used in industry and vehicle construction. This was mainly due to the low price. The devices were often cheaper than comparable models that used other technologies.

Since then, however, a lot has happened. As a rule, electricity storage devices with lead-acid or lead-gel technology are no longer used in single-family homes. Instead, storage devices with lithium-ion batteries have been on the market for a long time. Almost every major memory manufacturer now relies on this modern technology, which has caused their prices to drop sharply.

After all, lithium-ion storage can usually be charged and discharged much more often and must therefore still have a usable capacity of 80 percent even after 10 years. Added to this are efficiencies of up to 95 percent and more.

The values promise a significantly higher performance over a longer period than would be the case with lead storage. Lead-acid batteries are usually only designed for around 3,000 full cycles. A maximum depth of discharge of 80 percent also significantly reduces the usable storage capacity. At less than 90 percent, the degree of efficiency is also generally significantly lower than with lithium-ion power storage devices.

What type of building should the solar system be installed on?

Conventional lithium-ion batteries

Lithium-ion batteries are currently the most commonly used battery cells worldwide. They are used in solar storage systems and millions of other electronic devices, such as mobile phones. Lithium-ion technology conducts lithium ions from the positive to the negative electrode. They remain here until they are discharged.

Modern lithium iron phosphate batteries

Lithium iron phosphate batteries use a so-called lithium iron phosphate cathode instead of the conventional lithium cobalt oxide cathode in a lithium-ion battery. Instead of lithium cobalt oxide, lithium iron phosphate is used as the positive electrode. The negative electrode usually consists of graphite or specially hardened carbon.

For the operation of a solar storage tank – and thus indirectly for the system operator – this initially has no other effects. However, lithium iron phosphate storage systems are particularly convincing with high discharge currents, cycle stability, and increased robustness. In addition, there are short charging times and a particularly low risk of overheating. Overall, however, both the lithium-ion and lithium-iron-phosphate storage systems impress with their high level of safety and maximum performance.

AC or DC storage systems?

Investing in a 12V battery storage system pays off in the long term. But the decision for or against an electricity storage system is not the only one that a system operator has to make. There is also the question of what type of storage system it should be. We are talking here about the so-called system topology. A basic distinction can be made between AC and DC systems.

In this context, the terms AC and DC stand for Alternating Current and Direct Current, i.e., alternating current and direct current. PV modules always generate direct current – and the energy in electricity storage is also stored as direct current.

However, the power grid runs on an alternating current – and so does household electricity. For this reason, so-called inverters have to be connected between the roof, on which the solar powered generator generates the direct current, and the household, in which household electricity is consumed. These are responsible for converting direct current into alternating current.

We will explain exactly what the different storage systems are all about.

How does an AC storage system work?

AC side storage systems are installed on the AC side of the solar array. Therefore, the solar storage tank is not connected directly to the solar modules but is connected to the house power grid via an interposed battery inverter.

AC storage systems are ideal for storage upgrades because they are independent of the PV inverter and can easily expand an existing system. Thanks to their flexibility, AC systems can also prove useful for new installations. It is best to discuss with your solar technician whether this solution is also suitable for you.

The direct current generated is first converted into alternating current by the solar inverter, which means that it can be used in the home. Excess electricity not used directly is converted back into direct current by the battery inverter and stored in the solar storage system.

How does a DC storage system work?

Unlike AC-side storage systems, DC storage systems combine solar and battery inverters. One, therefore, also speaks of the so-called hybrid inverter.

The solar system’s direct current is not directly converted into the alternating current but can first be absorbed by the solar storage tank. If this electricity is now required in the household, the storage tank is discharged with the help of the integrated solar inverter. Since the electricity only has to be converted once, the conversion losses are usually lower, and the system becomes more efficient.

In most cases, DC storage systems are only suitable for new installations since existing systems are often equipped with conventional photovoltaic inverters that do not have a hybrid function and therefore do not allow a direct connection to a storage system. Overall, the system impresses not only with its high-efficiency level but also with less space and less complex installation. This is because there is no battery inverter, and DC storage systems have fewer components.

However, you should always note that with DC storage systems, the storage and the hybrid inverter must inevitably be placed next to each other. In the case of AC systems, on the other hand, the battery inverter and battery can be hung separately from the PV inverter, which can be particularly advantageous if space is a problem.

During your consultation at solar, we focus on finding the optimal storage size concerning your system performance and consumption.


Lead-acid or lead-gel batteries have long been obsolete in private homes. Instead, high-performance lithium-ion power storage devices are used today. A special type of lithium-ion battery is lithium iron phosphate storage. Both technologies are used by major manufacturers today and promise high performance over a long period.

DC-side storage systems are increasingly used today, especially for newly installed solar systems. These not only promise simpler and more cost-effective installation. A DC system also usually impresses with a particularly high-efficiency level and, thus, maximum yields. However, installing an AC storage system can also make sense in new buildings, as it offers a high level of flexibility concerning the installation location of the system.


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