As “balcony power plants” are meant small “Plug & Play” photovoltaic systems with an output of less than 800 watts, which are being plugged into appropriate power connectors and of which the generated electrical energy is fed into the household network.
The advantage of these systems is that their operation does not require approval from the electricity grid operator and that no particular electrical skills are required for their connection.
If used correctly, these devices can help a household to consume self-generated sustainable electricity and to reduce the need to purchase energy from its electricity supplier, which can result in cost savings.
However, in order for these advantages to occur, a few things must be considered when connecting such a system.
Three-phase network
Almost all households in Luxembourg have a three-phase mains connection, which consists of three live conductors (L1, L2, L3) behind the electricity meter, as well as a neutral conductor (N) and a grounding conductor (PE).
While the electricity meter belongs to the electricity grid operator and is maintained and read by him, the electricity grid operator is not responsible for the technical installation behind the electricity meter.
Instead, it is the professional electrician’s responsibility to ensure that the installation behind the electricity meter conforms to technical regulations; in particular, the “Technical connection conditions for high-voltage systems with a nominal voltage of up to 1.000V in the Grand Duchy of Luxembourg” must be respected.
During the electrical installation of a household, the electrician has to make sure that the circuits in a new building (or in the case of a renovation or extension) are distributed evenly over the three phases L1, L2 and L3 so that none of the three phases is disproportionately overloaded. In this context, one speaks of avoiding an “unbalanced load”. According to Article 9.1 of the above mentioned technical connection conditions, the maximum permissible asymmetry limit of 4,6 kVA between two phases at the connection point must be respected at all times.
Electricity meter
The intelligent “Smarty” electricity meter, installed in a household, measures all electrical energy that flows into the household from the grid, but it does not measure the energy that is transmitted through each of the three phases (L1, L2 and L3) individually.
Because no separate electricity meter is installed for a Plug & Play system, no dedicated measurement occurs of the electrical energy generated by such device. The electrical energy, generated by such a system, thus flows into the overall household without being measured.
However, the Smarty electricity meters have a compensatory effect, which means that the consumption (import) can be reduced by the simultaneous feed-in (export) of electrical energy from a Plug & Play PV system, even if the consumption is distributed over several phases and regardless of which phase the Plug & Play PV system is connected to.
Nevertheless, if the production of electrical energy is bigger than the current consumption in the household and a surplus of energy is therefore generated by a Plug & Play PV system, the household will not be reimbursed by the grid operator for the energy fed into the grid.