Inverters

What is a solar inverter in detail?

As we have explained in the heading of this category, a solar inverter is in charge of transforming the direct current of the solar panels into alternating current for later use. The vast majority of the equipment used in the home and in the industries is supplied with alternating current with a given voltage and frequency (230V in single-phase and 50Hz in Spain) parameters that are not those given by the continuous part of the photovoltaic panels. The solar inverter is therefore in charge of carrying out the necessary transformations and adjustments so that our equipment can be powered by solar energy.

What are the types of solar inverters?

There are three main types of string solar inverters on the market:

Solar inverters for grid connection: this type of inverter is used in solar installations that are connected to the grid and can be synchronised with the voltage (V) and frequency (Hz) parameters of the grid.

Solar inverters for off-grid installation: as their name suggests, they are suitable for solar installations that are not connected to the grid. This type of inverter is capable of operating under a "grid" that it generates itself with the optimum voltage (V) and frequency parameters for use in conventional electrical appliances.

Hybrid inverters: Hybrid inverters are typically used in systems that need to operate both on and off the grid. They are often used in hybrid installations where the system can be connected to a grid, to different types of generators or operate temporarily as a stand-alone system. Typically, hybrid solar inverters can operate and manage batteries of different technologies, performing the function of back-up (backup system) when there is no solar generation or grid. Hybrid inverters can be grid-connected or stand-alone (without the need for a grid to synchronise with).

What to consider when choosing a solar inverter?

There are many brands, models and types of solar inverters on the market. But what should be taken into account when choosing a solar inverter?

Type of installation: Will our inverter be installed in a grid-connected or off-grid installation? Do we want to connect batteries and/or an electric generator to make our installation hybrid? Based on the above description, we will have to choose whether we need a grid-connected, off-grid or hybrid inverter (grid-connected or hybrid).

Inverter power: Depending on the needs and configuration of our solar installation, we will have to choose the power of the inverter that corresponds. The power of the inverter is usually stipulated in its description or name. It refers to the power in watts or kilowatts (or VA depending on the power factor) that the alternating current part of the inverter is capable of providing given a voltage, frequency and at a standard ambient temperature.

Depending on the loads we want to feed on the AC side, we will have to choose one power or another. It is important to note that the inverters also specify in their technical data sheet the power to be connected on the DC side, i.e. the solar panels. This power is given in Wp or kWp as the photovoltaic panels are expressed in peak power, the maximum power that the panel is capable of providing under certain circumstances of temperature and irradiation that are considered standard, although they are not very common.

This is why the power of panels is usually over-dimensioned with a DC/AC ratio that each inverter manufacturer describes in its technical data sheet. Generally, when it comes to maximising the generation of the solar system, the power of the solar panels in peak power is higher than the inverter power in Wac or VA. In this way we ensure that the inverter works most of the time providing the maximum AC power output. In the event that there is too much solar power and the inverter is reaching its limit, it performs the "clipping" action, which is to limit the solar input power and keep the output at the maximum.

Inverter input voltage (PV/Battery): In the case of the inverter voltage, we must understand what the solar installation will be like (grid/isolated/hybrid) and what loads and consumption it will be connected to.

In the case of off-grid installations or installations with battery storage, depending on each case, it will be more suitable to use:

- 12V solar inverters: usually for small installations of no more than 2000W. A low voltage (12V) implies more wiring to reduce losses, so this voltage is usually used for installations that mount batteries with low storage capacity, i.e. small installations.

- 24V solar inverters: usually for medium-sized installations of no more than 5000W.

- 48V solar inverters: usually for medium and large installations, up to 10000W. Although for very large installations it is usual to go to higher voltages, the standard step ends at 48V, beyond that the solutions are customised and with inverters that allow a varied range of voltages.

Maximum and output current of the inverter: It is important to know the maximum input current (DC) and output current (AC) of the inverter in order to understand how the strings/module chains should be designed on the DC side and to understand what overcurrent protections may be necessary on both the AC and DC sides.

MPPT number (if applicable): The MPPT number (Maximum Power Point tracking), also known as the number of MPPT trackers, refers to the number of solar panel string inputs that an inverter has in which the maximum power point tracking is performed, i.e. independently optimised.

Each series or string is the union of photovoltaic panels with a given current (I of the modules in the string) and a voltage given as the sum of the voltages of the panels connected in series (V).Therefore, a string will have a current and a voltage (V and I) corresponding to an inverter input. The MPPT consists of a series of electronic components capable of constantly searching for the combination of voltage and current that provides the highest possible power for each input.

Given that the production of the panels varies according to the radiation incident on them and the temperature, a greater number of inverter MPPTs will ensure greater performance of the panels of the entire solar installation.Moreover, the solar panels can be mounted with different orientations or inclinations only if each of these groups of modules is connected to a different MPPT tracker. So, for example, if we have a gable roof where we want to mount solar panels on both sides, we will look for an inverter with at least 2 MPPT inputs.

Efficiency: It is important to look for a solar inverter with a high direct current (DC) to alternating current (AC) conversion efficiency. The higher the efficiency of the solar inverter, the lower the losses and the faster the return on investment.Solar inverters already have high efficiency levels of around 95%.In any case, 1% or 2% more efficiency is an important difference when we are talking about long lifetimes. 

Monitoring and communication system: Opt for a solar inverter that offers a real-time monitoring system.This will allow you to monitor the performance of the solar installation and detect problems quickly.Some solar inverters offer online communication options or mobile applications to facilitate monitoring and performance.

Durability and Warranty: As we have already mentioned, it is very important to purchase an inverter from a first class manufacturer. The solar inverter is a critical piece of equipment because if it breaks down, the entire solar installation will be shut down, unlike solar panels. It is important to take into account when making any purchase of a solar inverter the years of warranty provided by the manufacturer. If appropriate in some cases inverter warranty extensions are available.

Battery Compatibility: If you want to install a hybrid solar installation using solar batteries, it is important to verify that the batteries and the inverter are compatible. Each battery manufacturer establishes a list of solar inverters with which their batteries are compatible. It is important to check compatibility to avoid communication problems between the inverter and the BMS (Battery Management System) of the batteries. 

Installation and Location: Installation and Location:For the installation of the solar inverter verify that the degree of protection is at least IP65.  It is also important to consider the ambient temperature at which the inverter will operate as well as ensuring good ventilation.

Inverter life and replacement

Solar inverters can have a life of more than 10 years without any problems. Depending on the conditions of use of the inverter and certain random parameters, the lifetime can be more or less than 10 years.

Typically, solar inverter manufacturers give factory warranties of 2 to 10 years. However, these can be extended by an additional 5 or 10 years by purchasing so-called "warranty extensions" from solar manufacturers or distributors such as Tienda Solar.

It is common in the industry for inverters to have a life of 10 years, and in the financial and life cycle approaches of solar installations it is often assumed that solar inverters will be replaced after 10 years. It is important to mention that this replacement is a reasonable assumption given the failure rate of these components and the experience accumulated in the industry over time.

What are the best brands of solar inverters?

There is a wide variety of brands on the market and it is true that sometimes it is difficult to choose which of them is the most suitable for our installation. Just as in the case of solar panels there is a classification of brands and manufacturers (the so-called Tier's published by Bloomberg) there is no such classification for solar inverters.

From Tienda Solar and given our experience in the sector (construction and operation of solar plants) we have selected a number of brands that offer good long-term performance and competitive prices. We usually recommend brands such as SMA, Victron, TBS, Studer, Solax, SAJ, Deye, GoodWe, SUNGROW, Huawei, Fronius, Solaredge, Kaco and Ingeteam. Some of them are cheaper than others, but the catalogue available on our website will ensure an efficient and long-lasting operation of your solar installation.

How many solar panels can be connected to an inverter?

The number of solar panels that can be connected to an inverter depends on several factors, including the inverter's rated capacity, the electrical configuration of the system and local conditions. Here are some points to consider:

• - Inverter capacity: Each inverter has a maximum rated capacity in terms of power output. This capacity is expressed in watts (W) or kilowatts (kW). The number of solar panels you can connect depends on the inverter's capacity. This is why the data sheets of solar inverters are divided into PV Power and Power Output. Solar power (also called PV input power) is expressed in Wp/kWp in the same way as solar panel power is expressed. Since panels rarely operate at their maximum power, inverters allow the input power to be oversized in Wp. Usually the input power in Wp is between 30% or 50% higher than the AC power. For example, if you have a 5 kW (5kWac) inverter, you could connect a number of panels adding up to 6.5kWp (+30%) or 7.5kWp depending on what the solar inverter manufacturer indicates.
• - Panel size and power: Solar panels vary in size and power. Larger and more powerful panels will generate more electricity, so the number of panels you can connect will depend on the total power you can handle with the inverter on the DC side (PV/solar input).
• - Electrical configuration: The way you connect the solar panels, either in series or in parallel, can influence the amount you can connect. Connecting panels in series increases the total system voltage, while connecting them in parallel increases the current. Make sure that the configuration is compatible with the capacity of the inverter. To do this, check that the maximum current that the solar inverter accepts per MPPT is always higher than the current of the string/s being connected. Similarly we have to verify that the string voltage is the same as the voltage accepted by the solar inverter (usually 1000Vdc or 1500Vdc).
• - Operating conditions: Weather and solar radiation conditions also affect the power generation of the solar panels. You may need to adjust the number of panels according to these conditions so as not to overload the inverter.
• - Regulatory and technical considerations: Local regulations and standards may influence the number of solar panels that can be connected to an inverter. It is important to comply with electrical and safety regulations in your area.

In general, it is recommended to work with a solar installer or professional in the field to determine how many solar panels can be connected to a specific inverter. They can make accurate calculations taking into account all relevant factors and ensure that the system is configured safely and efficiently.

In addition to the different types of solar string inverters, there are other types for residential and commercial solar installations and others for large solar plants. 

 What other types of solar inverters are there?

Central Inverters: These are inverters typically with power ratings between 1MW to 5MW used in the design and construction of large solar power plants (also called solar farms). These solar inverters have a large size (approximately the dimensions of a 20-foot container) and centralise the conversion from direct current to alternating current on a large scale. Central inverters tend to be more efficient in terms of cost per W compared to smaller string inverters or micro inverters. By concentrating the power conversion in a single device, they can achieve high levels of efficiency and DC/AC ratios compared to other types of solar inverters. 

Micro Inverters: Instead of using a single solar inverter for each string or string string concatenation, micro solar inverters are installed on the back of the solar panels to perform the DC to AC conversion individually. This allows each solar panel to operate independently and optimises energy production. If one solar panel, for example, is not working properly or is shaded, this does not affect the overall solar installation. The output of the micro inverters is already in alternating current, so there is no need for a large amount of cable to connect the output of the inverters to the power supply of the house or industry.

Battery inverters: These are inverters designed specifically for solar battery systems or energy storage. These inverters allow for efficient charging and discharging of batteries. Solar batteries store electricity in direct current, so a solar inverter is needed to be able to use the stored energy either in a home or industry. In this case the batteries can be charged either from the grid, with a generator or with solar energy but this does not necessarily have to be present.

In any case, if you would like more information, please do not hesitate to contact us at info@tienda-solar.es.