Which inverter is the best
PV inverters - cost and durability compared
Inverters convert the direct current produced by the solar modules into alternating current so that it can be fed into the power grid. Multi-string, module and central inverters:
If you want to install a photovoltaic system, you have many options with the inverter. But which inverter is the best and how long can a device work with the highest efficiency?
In the following you will get to know the different inverters better and learn more about their function, advantages and disadvantages.
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General information about the inverter
The inverter is the heart of a photovoltaic system. Basically it is needed for voltage conversion. The solar module generates direct current, but alternating current is required for the power grid.
To create a transition here, the inverter converts the photovoltaic direct current into alternating current. Inverters today work with very little loss, and the best devices now achieve an efficiency of 99%.
That means: only one hundredth of the direct current power is lost during the conversion. The inverter is therefore important in order to make a photovoltaic system usable in the first place. Regardless of whether it is for private use or for feeding into public networks, the inverter is indispensable.
Inverters can basically be divided into three types. If the inverter offers the option of connecting several strings at the same time, it is referred to as a multi-string inverter. With a multi-string inverter, several strings of series-connected photovoltaic modules are connected. A module inverter is connected directly to a single solar module.
A central inverter is usually only used for very large photovoltaic systems. It is housed in its own technical room and often takes up many square meters. It is mainly used in the systems of professional operators.
If you privately install a photovoltaic system with an output of around 10 kilowatts peak (kWp), a multi-string inverter is recommended. The individual output of a module inverter is quite simply too low. So many models would be needed that costs skyrocket.
When do I need a photovoltaic inverter?
An inverter is necessary as soon as you decide to use a photovoltaic system. The inverter is required to convert the direct current generated by the photovoltaic modules into alternating current. The electricity can be used for private consumption or fed into the public grid.
Which inverter do I need?
For an average single-family house, you can expect electricity consumption of around 4,000 kilowatt hours (kWh) per year. Here you would probably install approx. 10 kWp photovoltaic power, for which a multi-string inverter is ideal. Which inverter ultimately fits your photovoltaic system depends on the number of solar modules and the output of the photovoltaic system. Full utilization is strongly recommended for the economic efficiency of the inverter.
Inverters: manufacturers and prices in comparison
The inverter must always match the photovoltaic system. The power, i.e. the maximum input voltage, of the photovoltaic system is decisive here.
The inverters also differ primarily in terms of their equipment, quality and cost-effectiveness. Due to the differences in applicability, the cost of inverters also varies.
Module inverters are not recommended. Since you need a separate module inverter for each solar module, the costs multiply quickly. Multi-string inverters are therefore more recommended. Multi-string inverters also have a higher average efficiency and last longer than the small module inverters.
|Inverter||power||For system size||Price (CHF)|
|Fronius Symo 6.0-3-M||6 kVA||6 - 7 kWp||CHF 1'800|
|SMA Sunny Tripower 10000 TL-20||10 kVA||10 - 12 kWp||CHF 3,000|
|Kostal Piko 15||15 kVA||15 - 18 kWp||CHF 3'300|
For string inverters, the average costs are CHF 1,600. With an output of around ten kilowatts, the costs for an inverter are around CHF 2,200.
In the case of the modular inverter, cost-effectiveness plays a decisive role. Although the costs are well below the string inverter, several units are usually required. The costs of CHF 200 to 450 are only offset by an output of 250 to 500 watts.
There are now hundreds of inverter manufacturers around the world. In German-speaking countries, at least 40 manufacturers offer inverters. In addition to the costs, the products naturally differ in quality, durability and variety.
Probably the most important criterion when comparing the inverters is the efficiency. Since it is highest at a certain operating point, it should also be correctly dimensioned. The cost, economy and performance of the products are also important criteria. In order to provide an overview, some manufacturers and their prices are listed above as examples.
Durability of modern inverters
It is very unlikely that the inverter will reach the service life of the connected photovoltaic system. The electrical stress caused by the constant loop lashing is simply too high for this. In addition, wind and weather play a major role in durability.
The inverter reacts more strongly to external environmental influences than the associated photovoltaic module. You should therefore plan an additional inverter when purchasing a solar system. Photovoltaic systems last around 25 years on average. The average warranty period for an inverter is 7 to 10 years. If used properly, however, the shelf life increases by a few more years. Manufacturers recommend setting up the inverter in closed rooms for optimum durability.
However, these must offer enough space to ensure good ventilation conditions for the inverter. Basements, for example, are very suitable. Basement rooms in particular can be heated in parallel with the heat emitted by the inverter. So you save costs for additional heating energy. In general, the inverter should be set up in a cool room. If the ambient temperature increases permanently by around 10 degrees, the expected shelf life decreases by up to 50%.
For example, Fronius specifies the following temperatures for its inverters: -40 to +60 ° C (Fronius Symo) and -25 ° C to + 60 ° C (Fronius Eco). So it shouldn't be too cold or too warm. Always observe the manufacturer's specifications in specific individual cases!
|Cool (-10 ° C to 20 ° C),|
|7-10 years||10-15 years|
|Too warm (40 ° C to 70 ° C), poor ventilation||Often not applicable||5 - 7 years|
This is how you can tell that the inverter is broken
After a while, the inverter will show signs of wear. Although this is completely normal, it is also the most common cause of malfunctions in a photovoltaic system. The inverter reacts very sensitively to external environmental influences. In addition, there can be voltage fluctuations, both from your own household and from external influences.
Malfunctions are normally indicated directly on the inverter display by means of error messages. A look at the manual usually helps here. First of all, the system owner should check which error the display shows. After that, it is often enough to take a look at the troubleshooting guide. Otherwise, a specialist can often identify the problem based on this data.
Once you have found the type of error, it is important to get to the bottom of the cause. If it is an internal operational damage, you should consult an expert. This can happen, for example, after a storm by a lightning strike.
|Overheating||Alarm (overheat)||Wait until the converter has cooled down and restart|
|Short circuit||Output voltage too low||Test connections, polarity and voltage. (A technician may be needed)|
Which replacement inverter to buy?
There are now several hundred different manufacturers of inverters. In the German-speaking area alone there are over 40 manufacturers of inverters with a range of more than 1,000 products. If the defective inverter is still available as a new device, replacement is usually not a problem because the device can be exchanged without any problems. If there is no original replacement inverter, you usually have to look for an alternative.
Your photovoltaic professional will be happy to advise you on the use of the right inverter. And we would be happy to advise you on the right installation partner.
Long service life for inverters
- Pay close attention to the manufacturer's specifications
- Take the installation site into account when planning
- Avoid extreme temperatures in general
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