Under normal conditions, the solar energy produced by a photovoltaic installation can only be partially used directly by the household. A typical three-person household with a 5 kW net-bill installation directly consumes about 20 to 30 percent of the solar energy produced by the installation.

In this case, the excess solar energy flows out to the power grid (surplus to the energy consumed). Therefore, given the current net-billing system, it makes sense to use one's own solar energy for autoconsumption. The autoconsumption of photovoltaic energy can be increased (more than 20-30%) when using battery storage systems, since this means that solar energy can be consumed when the sun is no longer shining. Thus, battery systems make it possible to use electricity during the morning and evening hours, when the photovoltaic system produces little or no electricity. The use of battery systems can help relieve the load on the grid and help absorb the power peaks of photovoltaic systems occurring during the midday hours (between 10 a.m. and 2 p.m.). Some battery systems also provide access to electricity in the event of a grid power failure - backup power. A high level of self-consumption with a good cost-benefit ratio can be achieved when the battery capacity is well-matched to the capacity of the photovoltaic system and to the household's electricity demand. When planning a battery system, at least 1 kWp of photovoltaic system output and at least 1 kWh of storage system capacity can be planned for every 1,000 kWh of annual energy consumption. In this case, we will be able to achieve a level of self-consumption of between 50 and 60 percent. We recommend a calculator that allows you to calculate the basic parameters of a battery installation:

An additional increase in the level of self-consumption can be achieved by deliberately switching on electricity consumers during the photovoltaic plant's energy production hours (self-consumption can reach a value of 80%). A battery charge controller is required to control the charging and discharging of the battery. The battery can be installed in front of the inverter on the DC side of the photovoltaic system (DC/DC inverters) or behind it, and then it will be connected on the AC side (AC/DC inverters). Connecting battery systems on the AC side is characterized by the occurrence of higher conversion losses during charging. On the other hand, they often achieve higher efficiency during discharge compared to DC systems. In addition, AC-connected systems are particularly suitable for retrofitting existing photovoltaic systems, as they can be very flexibly designed for connection to an existing photovoltaic installation. Energy storage systems can be integrated into the home grid as a single-phase or three-phase system. Battery systems never store solar energy without losses. Up to 20% of electricity is lost irretrievably during the charging and discharging processes. A higher level of losses is achieved in low-voltage battery systems, which have higher charging/discharging currents (thus experiencing higher thermal losses), compared to high-voltage systems (the voltage of the battery system is at least 98 V). The market mainly offers storage systems with lithium-ion batteries for household use. In addition, there are also lead-acid batteries on the market, which are not compatible with all hybrid inverters on the market. At the same time, in the case of lead-acid batteries, we have to reckon with almost double the capacity (in order to achieve similar amounts of energy storage).

Parametry pracy baterii

Important manufacturer specifications for battery size design are the maximum depth of discharge and the usable capacity of the battery. In the case of LION batteries, the depth of discharge reaches values of 80%, which are significantly higher than in the case of lead-acid batteries (in the latter case it is about 50%). In addition, batteries are also characterized by the number of cycles (the number of charge and discharge cycles), after which the capacity of the battery reaches about 80% of the original capacity. For LION batteries, calendar aging usually determines the end of their life before a possible number of cycles ranging from 2,000 to as many as 15,000 charge cycles. For home energy storage systems, a life span of 10 to 15 years can be assumed. For lead-acid batteries, the number of cycles is about 600-1000 cycles.

The average household achieves about 250 charge-discharge cycles per year.

Since batteries age faster at higher temperatures, it is worthwhile for battery systems to operate at temperatures not exceeding 25-40 degrees Celsius. Therefore, it is very important to properly choose the location of the storage system (in domestic applications, the best place to locate the battery system is the basement, while always remembering to properly ventilate this room).

Energy storage systems cost from 3700 to 6400 PLN/kWh, of which the battery and its BMS management systems account for about 1500 PLN/kWh (at least 25% of the total cost). Thus, the battery along with the BMS management system represent the largest cost of the entire storage system.

Systemy bateryjne