In the first part of his series on energy self-sufficiency, energy expert Dr. Martin Steiner island system. Now he devoted the second part to so-called grid-connected PV systems – the most common system design. Although they are not used to prevent blackouts, they are characterized by their particular cost-effectiveness.
Watch the video here or read the synopsis below:
Energy self-sufficiency in practice – Part 2: Grid-connected PV systems
A guest contribution by DI Dr. Martin JF Steiner MSc
This type of system is the most common. The reasons for this are:
- cheap inverters
- Inexpensive systems (as there is no storage)
- Simple and easy assembling and commissioning.
Grid-commutated inverters are connected to the electrical grid and synchronize themselves with it in terms of phase and amplitude. A built-in NA protection (grid and system protection) disconnects the inverter from the power supply as soon as a line break occurs.
The disadvantage of this system configuration is that in the event of a power failure, these systems also fail and cannot be operated. So unlike stand-alone systems, grid-connected PV systems are not used for blackout precautions.
A special form of grid-connected PV system is the “micro-inverter”. In terms of design, these are very similar to inverters from “Balkonkrafterken”.
The latter usually has the option of connecting one or two PV modules and thus a total power output of 600W or 800W. These are also the permit exemption limits for Germany (600W) and Austria (800W).
Micro inverters with the option of connecting up to 4 PV modules typically have 1400–1800 W of AC power. So if you want to set up a 4.5-5kW system, you can easily set up such a system with 4 PV modules and 1 micro inverter per phase – ie three pieces and 12 PV modules.
Another special feature when using micro-inverters is the PV module parallel – no more serial, as is the case with standard line-commutated inverters, – are connected. Therefore, in case of shading problems, among other things, the use of micro-inverters makes sense.
Energy is consumed first of all in the home network
The electrical energy provided by the PV system is firstly consumed in the home network (depending on the actual actual requirement). Excess energy flows into the grid (excess feed-in). For this purpose, a feed-in contract must be established with the relevant EVU (or with ÖMAG in Austria). The feed-in tariff is currently being recalculated and determined by ÖMAG for each quarter.
Different remuneration is offered for feed-in contracts with local energy supply companies. It is important to find the best version for the user (which cannot be completely simplified).
The grid-commutated PV system form is the most commonly used system form. This is because of its simplicity and because of the economy of this type of system. However, it should be remembered at this point that this type of system is not suitable as a blackout precaution: In the event of a blackout, these inverters provide no electrical energy.
When deciding on a grid-connected PV system, either blackout precautions should be taken, Or an additional (at least small) island PV system can be installed.
The next article will introduce grid-parallel systems, which can combine the advantages of stand-alone systems with the advantages of grid-connected systems.
Dr. Martin JF Steiner, 1. August 2023
About the Author
DI Dr. Martin JF Steiner MSc is a graduate of the Vienna University of Technology – he majored in electrical energy technology – and has been working for the past several years on the topics of renewable energy, energy self-sufficiency and the climate impact of various types of electrical power plants. 3 decades
https://www.str2030.at/Energie-Autarkie-Martin-Steiner
