So-called grid-connected photovoltaic systems feed the solar power that is not used by the user into the public power grid. The operators receive a feed-in tariff for this. Pretty much all solar panels you see on homes and barns are grid connected. On this page we explain how the feed-in works technically and what needs to be considered when maintaining a system.
1. Feed in solar power – why and how?
As just mentioned, a solar power system is now designed in such a way that a large part of the solar power can be consumed itself. Why is that? In fact, your system will achieve the best return if you use as much generated electricity as possible yourself. This saves you the expensive purchase of electricity from the grid and instead uses the free solar power from your roof. In order to optimize self-consumption, the PV system can be expanded with a solar storage tank. This is very useful and should actually be offered by every solar technician! Further optimization can be achieved by using a heat pump.
But now we want to deal with how the excess solar power is fed in technically.
In addition, a sample solar calculator of a grid-connected photovoltaic system. You have sufficient roof space available and are planning on around $ 10,000. If you calculate with costs of $ 1,430 per kWp, the following results: $ 10,000 / $ 1,430 per kWp = ~7 kWp
However, the way the individual components are switched here is not always the most sensible. Under certain circumstances, an inverter should be used for each string. The connection concept differs from system to system. Simply leave the planning to your solar technician. Nevertheless, we would like to briefly explain what the individual parts are all about:
Components of the solar system:
Solar generator, generator junction box, inverter, feed-in meter
1.1. The generator junction box for feeding in solar power
Individual module strands (strings) of the solar system are brought together or switched in parallel in the generator connection box and transferred to a main line.
Grid connected parts
A main switch (load-break switch) is usually also installed here. This can be used to separate the solar modules from the rest of the circuit. In addition, systems for protection against overvoltage – so-called surge arresters – are often housed here. Fuses for the individual module strings can also be found here.
1.2. The inverter
The inverter ensures that direct current becomes alternating current. This is necessary because the public grid works with alternating current. The inverter can be chosen slightly smaller than the maximum output of the solar system, as this is only rarely achieved in the year (perfect position of the sun, time of day, season and cloudless sky). If the maximum power is then reached, that is not a problem either, since the inverter can reduce the power somewhat.
1.3. What does the feed-in counter do?
You also need an additional feed-in meter to feed solar power into the grid. Just as your electricity meter shows what you consume, this meter shows how much solar power you feed in and how much you are paid for.
What needs to be considered when feeding in depends on the respective grid operator and primarily on the EEG. The requirements can be found in the technical connection regulations (TAB).
1.4. Feed-in tariff
The EEG (Renewable Energy Sources Act) specifies certain remunerations that you receive for the electricity sold. Incidentally, the grid provider is obliged to connect your system to the grid and to buy the electricity for these statutory costs.
1.5. Feed-in contract
In addition, the question often arises as to whether a contract must be concluded with the grid operator for the sale of the electricity – i.e. for feeding it into the grid.
2. Monitoring of the photovoltaic system
The simplest and cheapest way to monitor your photovoltaic system is to regularly read and write down the meter readings on your feed-in meter with a piece of paper and a pencil. You can record weekly or monthly. Using IOT remote monitoring can also easily monitor your grid-connected grid system data.
The more often, the more you are on the safe side.
You can enter the read yield data in a table by hand.
Another possibility is the entry on the PC in a spreadsheet software such as Excel.
2.1. Monitoring with data logger
So-called data loggers are more convenient than self-maintained lists, but also more expensive. These are electronic data storage devices that permanently and automatically monitor the yields and other performance values of the PV system.
Many inverters today have a data logger integrated as standard. But they are also available separately.
The solar data loggers monitor and log the power that each individual inverter feeds into the power grid.
From the measured values, the data logger creates a daily report on the yield of your photovoltaic system.
He can also generate a monthly or annual evaluation from the log data.
In the event of irregularities, the data logger sends a signal to inform the system operator. Depending on the data interface, the data logger can send the system data to your mobile phone, your PC or an Internet portal via cable or wirelessly (e.g. via Bluetooth).
Other options are small displays that resemble radio alarm clocks that show the system data as a table or wall device. In larger systems, the data can be transferred to a large display that is visible to everyone.
There are also web-based or internet-connected data loggers. More and more inverter manufacturers are offering free internet portals on which all the data from the solar system can be analysed, presented and visualized. Data loggers regularly transmit the system data to the portal. The information pages can be freely configured, and reports or notifications can also be sent automatically by e-mail.
2.2. Should the PV system be monitored manually or with a data logger?
In the case of small solar systems with an output of up to 5 kWp, you should carefully consider the purchase of a IOT remote monitoring with a web connection, which costs around $500 , in terms of profitability. With a low photovoltaic system output, a failure of the solar system for several days does not have such a financial impact.
For larger PV systems from 10 kWp, the purchase is definitely worthwhile.