How Do Storage Systems in Photovoltaic Installations Work?

Those who equip photovoltaic installations with a storage system are mostly interested in increasing the on-site consumption of generated solar power. However, people often forget to consider that these kinds of battery systems only reveal their full potential through their multiple uses. In addition to allowing operators of photovoltaic installations to significantly increase on-site consumption, a storage system also enables them to reduce their dependency on utility companies and ensures that power will continue to be supplied without interruption should the public power grid temporarily fail.

Battery storage systems have long been common practice in off-grid photovoltaic installations (otherwise known as stand-alone solutions) in order to ensure that power is continuously supplied without interruption. In contrast, the use of storage systems in grid-connected solar installations, which are the norm for installations on private roofs and commercial businesses, is still a relatively new phenomenon. Electricity storage systems that are available on the market are suitable for use when retrofitting existing photovoltaic installations and can also be factored into the system design when planning new installations. All storage systems save excess energy and put it at the disposal of consumers at a later point in time.

Solar modules generate direct current, which is converted into alternating current by an inverter before being fed into the public power grid or being used by domestic power consumers. Battery storage systems can be integrated into both the direct current and alternating current sides of the installation.

If the operator knows that a storage system is required before construction works begin, the system will normally be integrated into the direct current side of the installation. This reduces investment costs, achieves a higher efficiency, and allows module output and storage capacity to be coordinated with each other in the system design. Specific inverters with an integrated charge and discharge control directly charge the (integrated) battery with solar energy. They also convert it into alternating current if the temporarily stored solar energy is to be used by power consumers at a later point. In principal, it is possible to integrate storage systems into the direct current side even when retrofitting existing installations. If the inverter present does not have the necessary configuration, then the battery can also operate with the help of an external charge controller.

In addition to the battery, a specific battery inverter must be installed for the storage system to be integrated into the alternating current circuit. This inverter converts alternating current into direct current, which is required for charging the accumulator. The disadvantage to this solution is that further losses occur when converting back from alternating current into direct current, thus minimizing the system’s efficiency. On the other hand, the plant operator has significantly more choice when choosing the battery capacity, which is advantageous, for example, if module output in an existing installation is given as a set amount.

The controller regulates the amount of generated power that is fed into the public power grid, the amount used to charge the storage system and the amount that is delivered directly to domestic power consumers. Normally, the controller is programmed to maximize the on-site consumption of electricity generated in the photovoltaic installation. Storage systems can contribute significantly to this by temporarily shifting the supply. Alongside load management on the part of the consumer, stabilizing the power grids could also increasingly codetermine the storage systems’ management in the future. In this case, storage system operators provide decentralized capacities, which are integrated into an intelligent power grid, and they are then remunerated as part of a capacity-dependent energy market.

This article was originally published on SolarEnergyStorage and was republished with permission.

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Before his occupation as Chief Executive Officer of the Deutsche CleanTech Institut (DCTI), Philipp Wolff advised several companies during many years of law practice – including providing legal advice to leading companies in the CleanTech field. With the founding of DCTI in 2008, Philipp undertook the role as CEO. Through extensive publications on the topic of CleanTech, Philipp has scrutinized the branches within CleanTech and, with the publication of the “CleanTech Yearbook”, has established the first German-language standard work in the field. Philipp is a leading personality in CleanTech: he is a significant networker and initiator in the German CleanTech movement.

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