Self-supply with net-metering
Self-supply refers to electricity production from renewable energy sources whereby the consumer owns a self-supply generation unit connected to the building’s internal low-voltage installation. It is intended to cover end consumer’s electricity consumption, either a household or a small business consumer.
Self-supply with net-metering of electricity does not mean complete self-sufficiency of the end consumer with electricity. End consumers with a self-supply generation unit urgently need a grid that enables them to deliver the peaks of their production and the ability to consume energy from grid when their production is insufficient. In this case, the distribution network is in the role of a ‘virtual’ energy storage facility or battery because of the inconsistency between the consumer’s generation and consumption of the end consumer.
According to the revised Decree on the self-supply of electricity from renewable energy sources in 2019, self-supply with net-metering may be individual in the case of individual households or small business consumers. However, jointly acting renewables households and small business self-supplies with a self-supply generation unit are the matter of collective self-supply with net-metering:
- which may include self-supply of multi-apartment buildings or
- a RES energy community, to which consumers that consume electricity over two or more metering points, which are connected to a low-voltage network of the same transformer station, can be connected.
The maximum power of the self-supply generation unit must not exceed 0.8 times of the connection capacity of the metering point to installation is connected or 0.8 times of the sum of the connection capacity of the metering points included in the self-supply community. A self-supply generation unit may produce electricity using solar, wind, hydro or geothermal energy and cogeneration using renewable energy sources as a primary source. In practice, solar power plants strongly dominate.
Net-metering or netting
In the case of self-supply generation units, the calculation of electricity and network charges for consumed electricity is carried out on the basis of net-metering or netting in the accounting period of the calendar year. If the self-supply generation unit fully covers the consumer’s consumption during the billing period, these consumers are not charged for the consumed electricity, even though they use the network to a significant extent through their operating regime of consuming the electricity intended for final consumption.
The method of billing according to the principle of annual netting does not in any way encourage consumers to align electricity consumption and production at their metering points or to implement other measures, such as the installation of energy storage devices to minimize the exchange of electricity with the distribution network, thereby reducing the need to use the distribution network.
To reduce the exchange of electricity through the distribution network and thus the need for the use of the distribution network, self-supply generation units with monthly, weekly, or daily netting should be considered. These forms of netting are already in use in some European countries. In the case of net-metering daily netting, appropriate energy storage must be added to the production of the self-supply generation unit to cover the average daily consumption of an end consumer. Such energy storage will store surpluses of output from the self-supply generation unit during the day and offer them to the end consumer when there is insufficient production from the self-supply generation unit. Such netting will significantly reduce the need for the use of the distribution network and the consequent burden on the grid, as energy flows mainly between the self-supply generation unit, the storage device, and the end consumer. Besides, such distribution grid relief allows for the integration of more end consumers with self-supply generation units without further investment in grid reinforcement.
Similarly, European legislation through Directive (EU) 2018/2001 on the promotion of the use of energy from RES and Directive (EU) 2019/944 on common rules for the internal market for electricity require the EU Member States to be more proportionate and transparent, such as to provide a separate billing of the network charge for energy consumed and delivered, which can set the network charge that determines the use-of-the network actual costs per an individual consumer.