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How is the Solar String Inverter working?
The English term solar string inverters is translated into Polish in two ways: inwertery stringowe or falowniki łańcuchowe. In fact, it refers to the device that converts direct current into alternating current (the current used in the house), to which a certain number of solar radiation absorbing modules are connected.
Solar Inverters are an integral part of every photovoltaic installation, whether low or high power. Its job is to convert the direct current generated by the panel into alternating current - which flows into a household electrical outlet. The direct current generated by photovoltaic cells is not suitable for powering domestic appliances, so it needs to be converted to a nominal voltage, which is 230 V. Using solar string inverters for PV - only one device supports all modules. The inverter market is divided into many categories - transformer and transformerless inverters, single and three phase phase, string and central. String inverters are also often referred to as "central inverters". This type of equipment has been used on the market for several years in the construction of most low power photovoltaic installations.
How does an inverter work and what are the types of inverters?
The inverter takes all the power from the panels and converts the DC to AC. Thanks to the electrical system, resistors, advanced electronics, it has additional functions: depending on the model, it protects against voltage surges and monitors the operation of the entire photovoltaic system.
In addition to string inverters, different types of operation, in photovoltaic installations are also divided into the following inverters:
String Inverter: This is the one main inverter for the entire system. It converts the current from the string of modules connected to it.
Island inverters: so-called off-grid inverters, dedicated to installations outside the grid, e.g. summer houses, industrial buildings, on plots. It directly powers the devices within its range.
Grid Tie Inverters: These allow you to store energy and transfer the rest of it to the grid.
Microinverter: This is a system where each solar panel has its own inverter. The most effective, safest, longest-lasting option, but definitely the most effective. However, subsidies and co-financing for PV installations can bring this investment closer.
There is no golden rule or one universal type of inverter that works perfectly with any type of solar panel. An interesting option is an optimizer that improves the efficiency of energy conversion and transformation processes. Their choice, as well as the choice of inverter, is a separate issue - in case of doubt it is worth consulting a PV expert.
Advantages of String Inverter Systems
1. Price advantage
String inverters can be purchased at affordable prices. It is the result of years of improving its production technology. For most installations, one solar inverter is usually enough to power each building. The situation is different, for example, in the case of microinverters, the number of devices is usually equal to the number of modules installed. A PV installation supported by a string inverter is usually around PLN 4,000 cheaper (in the case of a typical 5 kWp installation) compared to a PV installation built using microinverters or power optimizers.
2. Easy to replace
If a string inverter fails and needs to be repaired/replaced, we only deal with one unit and disassembly is simple, requires no access to the roof, and does not take long. This is important because usually the first component to fail is the inverter. Also, the cost of repairing one device will always be lower than the cost of repairing multiple devices (increasing the number of devices always increases the possible repair cost). Photovoltaic installations are made up of a few or a dozen elements - though their purpose is self-evident. It's supposed to get power, but to do that, it needs a device that converts the sun's rays into power, for example, to provide the proper current to a socket. Solar inverters, referred to as inverters or converters, play this extremely important role. It is an electronic system that converts the energy flowing from the battery. Its operation is critical to the smooth functioning of the entire installation.
3. String inverters are divided into off-grid series inverters and hybrid series inverters
The most identifiable criterion for choosing a solar inverter is the type of photovoltaic installation. For this, we distinguish between on-grid and off-grid inverters. Off-grid inverters are not synchronized with the electromagnetic grid, so they cannot feed energy back into it – however, they have the ability to charge batteries in the event of excess solar power. Grid inverters are synchronized with the public grid, so we can sell electricity on favorable terms, for example by using bi-directional electricity meters. Hybrid inverters are a novelty in the market which can work both in network and island mode. This is due to the built-in battery acting as an energy buffer. In this solution, if the building's current electricity demand is lower than the electricity generated by the photovoltaic installation, the inverter stores some of the energy in the battery. If the opposite is the case, i.e. the electricity supplied by the photovoltaic modules is lower than the building's electricity demand - the inverter draws the missing part of the energy from the battery.
Things to pay attention to when installing a string inverter:
String inverters are best suited for roofs that face in one or at most two directions and have no shaded areas. It should be noted that if a shadow falls on one of the panels connected to the same string, the efficiency of the entire string will be reduced and equal to the efficiency of the shaded panel. Imagine a large oak tree shades a panel or two in the system in the early afternoon. Since all panels are connected in a chain, if there is a shadow on these two panels, the performance of the entire system will be significantly reduced.
