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Solar inverter

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The inverter converts the generated energy from solar panels into usable electricity. Below you can read more about the inverter and which inverter you need for your solar panels.

Solar inverter

Every energy from solar panel requires an inverter. The main task of the inverter is to convert the direct current generated by the solar modules into alternating current. For some years, inverters have also had to take over some control tasks in order to improve the integration of photovoltaics into the power grid.

Everyone who purchases solar panels has to deal with an inverter. Solar panels convert sunlight into direct current, also known as ‘direct current’ (DC). However, we cannot use direct current, because all electronic devices in our household use alternating current, also known as ‘alternating current’ (AC). The inverter converts direct current to alternating current, after which the electricity can be used by the household appliances, or can be supplied back to the electricity grid. This means that the inverter has an indispensable function.

Types of solar inverter

Depending on the application, there are different inverters for grid-connected photovoltaic systems:

  • String inverters: In these models, several module strings are routed to an inverter.
  • Multi-string inverter
  • Modular inverters: In this design each solar module has its own inverter.
  • Central inverter (for large photovoltaic systems)

The efficiency of solar inverter

The efficiency of an inverter indicates how much of the DC side input power is delivered as AC side power. The definition of the efficiency is a little complicated because it depends on the instantaneous input power, which changes during the day and also depends on the weather. So little meaningful is the peak efficiency, which is achieved practically only under ideal conditions on the measuring stand. Considerably more practical is the so-called European efficiency , which describes the actual achievable average efficiency under typical Central European weather conditions. Transformerless inverters achieve efficiencies of more than 98 percent, for models with transformers 96 percent are a good value.

How does solar panel inverter (or inverter) work?

The operation of a solar panel inverter (or inverter) is very simple. The direct current generated by the solar panels is led to the inverter, where it is converted to usable alternating current. Electric devices only work on alternating current. An MPP tracker (Maximum Power Point) connected to the inverter ensures that the panels achieve their maximum efficiency and also maps the yield of the system. We distinguish here three types of inverters, of which the central or string inverter is the most common:

The inverter ensures that direct current is converted into usable alternating current. Realization: 

Solar Panel connected to an inverter?

For private rooftop systems, the answer is most: yes! Here, all modules are combined in series to a string and connected to the inverter, which is therefore also called string inverter. In the string inverter provides a ” Maximum Power Point Tracker”(MPP tracker) ensures that the inverter is always set to the optimum operating point for the currently generated power.

However, this procedure leads to performance losses if the modules of the system deliver very different performances. This may be the case, for example, if the plant comprises an east and a south roof. Here it is recommended to switch separate strings for both roofs. Instead of operating a separate inverter for each string, a multi-string inverter that uses its own MPP tracker for each string comes into consideration. Only marginally is the concept of the modular inverters mentioned, in which each individual module is connected directly to the roof with its own inverter. In terms of performance optimization, this concept is quite logical,

Which inverter do I need?

If you purchase solar panels you always need an inverter. Countless different inverters are available. Each inverter has a manufacturer-specified interval of input voltages on the DC side within which it operates. Which inverter you need depends on the capacity of your solar panels. The capacity of the inverter is adjusted to this. It is important that the yield of your solar panels does not exceed the capacity of your inverter. 

Also take into account the direction and slope in which the solar panels will be located and any shadow that the solar panels will catch. This always has an effect on the yield of the solar panels, so a smaller inverter may also be sufficient. In principle, the inverter is a maximum of 20% smaller and a maximum of 10% larger than the capacity of your solar panels, but it is always advisable to have a solar panel specialist advise you on this. Also take into account the amount of decibels that the inverter produces in sound, especially when the inverter hangs close to a living room or bedroom, for example, and the inverter guarantee scheme. A guarantee period of 5 years is normal. It should be noted that the maximum voltage depends on the module temperature. The required information can be found in the datasheet of the modules.

Which size of inverter do I need for my House?

For an average family home, one can count  and calculate on a power consumption of about 4,000 kilowatt hours per year. Here you would probably install about 10 kilowatt-peak solar power power, what a multi-string inverter offers. Which inverter finally fits your solar power system depends on the number of solar modules and the power of the solar panel use. For the efficiency of the inverter a full utilization is absolutely recommended.

Inverter with or without transformer?

While earlier in photovoltaic systems almost exclusively inverters with transformers were used, nowadays more and more transformerless models prevail. These have numerous advantages. First, the voltage conversion in a transformer is always associated with power losses, which is why transformerless models usually have a slightly higher efficiency. In addition, they are lighter, smaller and cheaper. However, there are tough exclusion criteria that in some cases make their use impossible.

A special feature of a transformer is that the power transmission from the DC to the AC side is done inductively, so there is no conductive connection between the two circuits. This is called galvanic isolation. Galvanic isolation allows the module strings to be grounded on the DC side. Some solarmodules mandate such grounding, especially thin-film modules .

The second advantage of the inverter with transformer is that on the DC side actually almost perfect DC current prevails and only minimal voltage fluctuations occur. In transformerless models, this separation between the AC side and the DC side is not quite as perfect. Some types of modules are sensitive to this, in particular solar modules made of amorphous siliconbelong. In this case, either a model with transformer or a transformerless inverter should be chosen, in which this problem was solved by means of the so-called “quiet rail technology”.

The final advice on the subject of transformers is therefore very simple from a pragmatic point of view: Transformerless inverters are usually a good choice if the module manufacturer has issued a corresponding release for his modules.

Where to place an Inverter?

Inverters are usually placed close to the meter board. This is because there is always some power loss when the electricity is transported through the cables to the meter cupboard. This loss is greater with alternating current than with direct current, so that it is favorable if the inverter hangs close to the meter board. The alternating current then only has to travel a small distance to the meter cupboard, so that little power loss can occur. If the inverter has a capacity that is higher than 600 watts, the inverter needs its own group in the meter cupboard.

When do I need a solar inverter?

An inverter becomes necessary as soon as one decides to use a solar energy system. The inverter is needed to convert the direct current generated by the photovoltaic modules into alternating current. Thus, the electricity can be used for private consumption or fed into the public grid.

Lifetime and Durability of Solar inverters

The fact that the inverter may reaches the lifetime of the connected solar panel is very unlikely. The electrical stress due to the constant re-tensioning is simply too high. In addition, wind and weather play a big role in durability.

The inverter reacts more strongly to external environmental influences than the associated solar panel module. Therefore, you should already consider the purchase of a solar panel with an additional inverter.

Solar panel last around 25 years on average. The average warranty period for an inverter is 7 to 10 years. Although solar panels nowadays have a lifespan of around 25 years, inverters last an average of 10 to 15 years. The inverter must be replaced after this period. The costs for having the inverter replaced depend on many factors, but you can take into account an average price of between € 1,000 and € 1,500.

Thou, if used properly, shelf life will increase for several more years. For optimum durability, manufacturers recommend installing the inverter indoors.

However, these must provide enough area to guarantee the inverter good ventilation conditions. Cellars are very well suited. Especially basements can be heated in parallel with the heat emitted by the inverter. This saves costs for additional heating energy. Generally, the inverter should be placed in cool rooms. If the ambient temperature permanently increases by about 10 degrees, the expected durability drops by up to 50 percent.

Maintenance of solar inverter

Picture: Repair of an inverter

So you notice that the inverter is showing faulty After some time, the inverter will show signs of wear. Although this is completely normal, but also the most common cause of a photovoltaic system fault. The inverter is very sensitive to external environmental influences. In addition, there may be voltage fluctuations, both from your own household, as well as external influences.

Faults are normally displayed directly by error messages on the display of an inverter. Here is usually a look in the manual. First of all, the system owner should check which error the display outputs. After that, it is often sufficient to have a look into the troubleshooting manual. Otherwise, often a specialist can already recognize the problem on the basis of these data.

Having found the type of error, it is important to get to the bottom of the cause. If it is an internal operating damage, you should consult an expert. This can happen after a storm due to lightning.

Inverter Fault description
Overheating. Wait until the converter has cooled down and restart. Alarm (overheat)
Short circuit. Test connections, polarity and voltage. (Maybe a technician is needed) Too low output voltag

Central or string inverters

String inverters: in most cases, solar panels are connected to each other in series so that they form one circle or “string”. Hence the term “string inverters”. This circuit is further connected to one central inverter. However, there are circumstances where the use of string inverters is detrimental to the efficiency. This is, for example, the case with shadow: if shadow falls on a single panel, it has a negative impact on the yield of the entire system. You could therefore choose to place panels that simultaneously capture shadow on a separate circle than panels that get full sun. Each string is then connected to the inverter with a separate MPP tracker. This way all panels achieve their maximum efficiency. You can also consider switching to micro-inverters or power optimizers.

Print effect shadow on string inverter

Shadow is very detrimental to the efficiency of string inverters

Microinverter

microinverters. Microinverters are mounted directly behind the solar panels and one microinverter is connected to one or a maximum of two solar panels. It convert direct Current DC from the solar panel to AC Current. A solar panel system therefore works with several micro-inverters. This has advantages and disadvantages. An advantage is that the system is less susceptible to malfunctions. If one inverter does not function properly, the entire system does not immediately stop, but the other microinverters can continue to convert electricity without being disturbed. In addition, the solar system can easily be scaled up. 

Extra panels with new microinverters can then simply be installed. With the regular inverter it can be difficult to add extra solar panels, since this inverter is bound to a maximum capacity. The lifespan of microinverters is also longer on average. Some manufacturers even provide a warranty period of up to 25 years. The microinverters, on the other hand, are more expensive to purchase. For a micro-inverter you quickly pay a price of between € 150 and € 250 per micro-inverter, excluding installation. Bear in mind that for a system of 10 solar panels, in most cases you also need 10 microinverters.

Inverter Power optimizers

When you place an inverter, keep the following points in mind:

  • the capacity of the inverter must be matched to that of the solar panels (max. 20% smaller or 10% larger). If you have a solar installation with a capacity of 3.5Wp, you better go for an inverter with a capacity between 2.8 and 3.85Wp.
  • the efficiency of inverters drops slightly every year. That is why you have to replace it after about 10 to 15 years (= about once during the lifetime of your solar panels).

To maximize the service life, place your inverter in a cool and ventilated area . High temperatures are detrimental to the service life of inverters. An inverter can also produce quite a bit of sound . Are you someone who could experience this noise as a nuisance? Then place the inverter in a room that will not cause much trouble to you (eg in the entrance hall).

Conclusion

You cannot avoid choosing an inverter for your solar panels, as this is an essential part of the solar panel. However, it is advisable to have your solar panel specialist advise you properly. A specialist knows enough about inverters to quickly know which inverter best fits your solar panel system.

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