SOLAR BATTERIES, ENERGY STORAGEElectricity storage devices can help you save even more money by making electricity available when it is not on the distribution operator's grid. As housing costs continue to rise, people are thinking about measures to help them pay less for their homes. One option is electricity storage, or what is sometimes mistakenly called "solar panels". An electricity storage device (solar panel) is an additional device for households with an installed solar power plant that can reduce electricity costs by a further 10-40%, depending on the amount of energy consumed and the size of the panel. This investment would also provide peace of mind by changing the billing method with the operator from net-metering to net-billing. Energy storage would then allow the use of cheap energy (batteries are charged when energy is cheap and discharged when it is expensive).

Advantages of electricity storage

So what are the advantages of solar batteries? Combining a solar power plant and an electricity storage system in a household offers additional benefits for the consumer:Excess electricity generated at home can be stored in an energy storage system for use in the evenings and at night. This would help to reduce the use of the electricity grid, thus saving the cost of storing electricity on the grid.

A household with a solar power plant

The energy consumption of a household using a conventional solar power plant is reflected in the first graph. The blue line shows that household energy consumption is typically higher in the morning and evening, but not when the solar power plant is producing energy. The orange colour indicates the generation of the solar power plant. In this case, in a net-metering system, the energy is exported to the  grid for "storage" and "retrieved" in the evening, when domestic consumption starts.

Household with solar power and storage battery

The solar battery is fully charged and the surplus is then exported to the grid. If the energy storage device is of sufficient size (kWh), only a small amount of surplus energy can be exported to the grid.The household uses the energy from the solar batteries in the evening, at night and in the morning - when there is no solar power generation.An electricity storage (ECE) system can also reduce the amount of power you can supply to ESO's electricity grid. This allows you to connect a solar power plant with a higher capacity than ESO's distribution grid allows without additional reconstruction. This effectively increases the installed capacity of the solar power plant without changing the amount of power that can be fed into the grid.

Reducing the power fed into the grid by a solar power plant

By installing an energy storage device, you can use the excess energy (which you would not be able to feed into the grid, for example due to a limitation on the amount of power that can be generated) and store it until the time you need or want to feed it into the grid, for example in the evening.

Choosing a solar power system

It is recommended to consult installers or equipment dealers before planning to install an ECE. So what is worth discussing?

•   For a house already equipped with a solar power plant, it is important to check whether the existing inverter has the technical capacity to integrate an energy storage device. If the existing inverter has this capability, assess whether the system will only work with the grid (Grid Tie) or whether it can also work without the grid (Off Grid). Perhaps additional system accessories are needed - Retrofit inverter, EPS (emergency power supply) switchgear, etc.?
• How much of the electricity generated is fed into the  grid (if the consumer has installed a solar plant).
• It is also important to assess the cost of the  system with installation works and the potential payback period.
• Potential electricity savings through increased energy autonomy.
• What are the performance characteristics (e.g. energy conversion losses, capacity, etc.) of the household electricity storage  systems for the specific system selected.
• Whether there is sufficient space in the home to install an  system. Is adequate cooling, if any, required for the selected system? Can the system operate in our winter conditions if the system is installed outdoors?
• The installation requirements set by the manufacturers of the storage systems (including distances from walls and ceilings, ambient temperature or ventilation conditions, recommended size of the solar plant, etc.).

 

Capacity and selection of energy storage devices

The capacity of electricity energy storage  is usually expressed in kilowatt-hours (kWh) and is one of the indicators that can be compared between different ES systems on the market without much technical knowledge. However, it is important to note that each ECE system may have a different depth of discharge or amount of energy available for use, which indicates the actual amount of energy that can be stored for use or fed back into the grid. Systems from different generators may have different operating topologies - different energy conversion efficiencies, different topological 'depths' that determine the overall system efficiency. Therefore, when selecting an ECE system, it is necessary to take into account not only its total capacity (kWh), but also its depth of discharge or amount of energy used, voltage, number of guaranteed charge-discharge cycles, chemical composition of the battery, maximum capacity, and system topology in order to select the most efficient system.Lithium-ion batteries are the most common and popular category of energy storage (ESS) system on the market, especially in the central European market, where they account for more than 95% of the total ESS segment.

Recommended discharge levels for different technologies

It is recommended that you choose the capacity of the Energy Storage System (ESS) based on the average daily electricity consumption (kWh) during summer. For example, if your annual electricity consumption is 5000 kWh and you have a 5 kWp solar power plant, it would be optimal to install an electricity storage system with a useful capacity of 7.5 kWh, according to the recommendations of the German HTW Berlin University.When a consumer intends to use an solar batteries as a back-up power supply, it is important to choose the capacity of the system according to the desired autonomy period. This refers to the number of hours the ECE system can supply power to, for example, a 2 kW appliance, independently of other sources of energy supply. It is also important to be aware that the power supplied by the storage unit gradually decreases - it is necessary to assess how long a building will need a given power. Perhaps it will be sufficient to supply only the back-up power lines, providing power for essential appliances such as the fridge, lighting, internet etc.?

Selecting the solar batteries of an energy storage device

The power of the ECE inverter affects the charging and discharging speed of the storage device. This parameter affects the energy autonomy of a dwelling with ECE. In homes without high power electrical equipment, such as electric car chargers or fast electric water heaters, a 0.5 kW/1 kWh energy storage system (e.g. a 10 kWh storage system with a 5 kW inverter) is sufficient. This ensures efficient storage of electricity in the home.The previous recommendations are applicable to cases where the aim is to increase the energy autonomy of the household through an ECE system. However, if the ECE system is planned as a back-up energy source, then the capacity of the ECE inverter should be determined on the basis of the most powerful electrical appliances in the household (i.e. the appliances for which the ECE system will supply energy autonomously in the event of a power outage).

Selecting the solar batteries installation location

For the installation of the stacker, the room must be selected in accordance with the manufacturer's instructions and the specified safety distances. Once the ECE system has been properly selected, it can be wall-mounted or floor-mounted, depending on the design. It should be noted that the weight of the ECE system may vary and, for example, a 10 kWh lithium-ion ECE system may weigh around 135 kg or more.Lead-acid batteries (we do not recommend this technology) are generally larger than lithium-ion batteries and are most often placed in non-residential areas such as garages or basements. In addition, when installing an ECE system, it is important to consider the operating temperature of the system. For example, the operating temperature of a manufacturer A ECE system may be between 0 °C and +30 °C, while the operating temperature of a manufacturer B system may be between -10 °C and +50 °C.According to the previous example, it is recommended that the manufacturer A system is installed in a warm room with good ventilation. However, the system of manufacturer B can be installed even in unheated rooms where the temperature does not fall below -10 °C in winter. For example, our SolaX H3.0 T30 batteries can be installed outdoors and have a preheating system, so they can operate in outdoor temperatures as low as -30C.

General requirements for energy storage devices, solar batteries

The equipment must be CE-marked and comply with EU standards, including eco-labels, energy labels and other technical standardisation frameworks established by EU standardisation bodies. In addition, the power used and generated by the energy storage device must be in accordance with the technical conditions issued by ESO (Electricity Supply Operator) in order to comply with the power consumption and generation limits set for the generating consumer.