Solar inverters are one of the most important elements of any solar installation. Solar panels are often spoken about as if they were the only main part of the system, but without an inverter, the energy generated by the panels could not be used normally in a home, business or grid connected installation.
Their main function is to transform the electricity produced by solar panels into electricity that is compatible with everyday electrical equipment. In other words, they convert the direct current generated by photovoltaic modules into alternating current, which is what most electrical appliances use. In addition, modern solar inverters do much more than convert energy. They also control the performance of the installation, optimise production, incorporate protection systems and allow the operation of the system to be monitored in real time.
What are photovoltaic inverters?
Photovoltaic inverters are electronic devices that transform the direct current produced by solar panels into alternating current suitable for electrical consumption. Solar panels generate electricity in direct current, however, the electricity grid and most household appliances work with alternating current. The inverter acts as a bridge between both worlds.
In a self consumption installation, the inverter receives energy from the panels, adapts it and delivers it to the home, business, batteries or electricity grid, depending on the type of system.
It is also responsible for working within safe ranges. If it detects an anomaly, such as overvoltage, voltage drop or a frequency problem, it can disconnect automatically to protect the installation. In short, the inverter is not a secondary accessory, it is a very important technical part of a photovoltaic installation.
Types of solar inverters
Grid connected inverters
Grid connected inverters are the most common in self consumption installations. They are designed to work connected to the conventional electricity grid.
Their function is to convert the energy generated by the panels so that it can be consumed directly in the home or business. If the installation produces more energy than is being consumed at that moment, the surplus can be fed into the grid, provided that the system is legalised and configured for it.
These inverters need to synchronise with the electricity grid. That is why, if there is a power cut, they normally disconnect automatically for safety. This prevents the installation from continuing to feed energy into the grid while technicians are working on it.
They are a widely used option in homes, industrial buildings, shops and energy communities.
Off grid inverters
Off grid inverters are used in installations that are not connected to the electricity grid. They are common in country houses, shelters, agricultural facilities, pumping systems or installations located in remote areas. In this type of system, the energy generated by the panels is usually stored in batteries. Afterwards, the inverter takes that stored energy and transforms it into alternating current to power electrical loads.
The key in an off grid installation is to size the system very carefully. It is necessary to calculate the required power, battery capacity, available solar production and expected consumption. An off grid inverter must be able to cover the electrical demand even when there is no sun, as long as the batteries have enough charge.
Hybrid inverters
Hybrid inverters combine functions of grid connected inverters and off grid inverters. They are designed to work with solar panels, the electricity grid and batteries. They are an increasingly common solution in self consumption installations with storage, as they allow solar energy to be consumed during the day, batteries to be charged with surplus energy and that stored energy to be used at night or during periods of low production.
Some hybrid inverters can also provide electrical backup in the event of a power cut, provided that the installation is designed for this and has the necessary elements. Their main advantage is flexibility, allowing energy to be managed better and increasing the degree of independence from the electricity grid.
How a solar inverter works
A solar inverter works by receiving the direct current produced by photovoltaic panels and transforming it into alternating current.
The process starts in the solar modules, when they receive solar radiation and generate electricity in direct current. That energy reaches the inverter through the wiring of the installation. The inverter analyses the input voltage and current to work at the optimum production point. Many units incorporate maximum power point tracking, known as MPPT, which makes it possible to extract the greatest possible performance from the panels at all times.
Then, the inverter converts that direct current into alternating current with a voltage and frequency compatible with the electricity grid or with the loads of the installation.
In a home, that energy can be used directly to power household appliances, lighting, climate control or any connected equipment. If there are batteries, part of the energy can be stored and, if there is surplus and the installation allows it, it can be sent to the grid. Throughout this whole process, the inverter monitors the system. If it detects values outside the permitted range, it protects itself and may stop operating to prevent damage.
Characteristics of solar inverters
Before choosing a photovoltaic inverter, it is advisable to review its technical characteristics. These details appear on the manufacturer’s data sheet and help determine whether the equipment is suitable for a specific installation.
The main characteristics of solar inverters are:
- Nominal voltage: indicates the inverter’s usual working voltage. It must be compatible with the electrical system of the installation.
- Nominal power: this is the power that the inverter can deliver continuously under normal conditions.
- Overload capacity: indicates whether the equipment can withstand power peaks for a short period, which is useful when motors or demanding equipment start up.
- Start up input voltage: this is the minimum voltage required for the inverter to start operating.
- Minimum MPP voltage: marks the lower limit of the range in which the inverter can search for the panels’ maximum power point.
- Maximum MPP voltage: indicates the upper limit of the operating range for maximum power point tracking.
- Maximum input current: this is the maximum current the inverter can receive from the solar panels.
- Efficiency: expresses what percentage of the energy received is actually converted into useful energy.
- Monitoring system: allows production, consumption, alarms and the general operation of the installation to be checked from an app or web platform.
Efficiency of a solar inverter
The efficiency of a solar inverter indicates how much of the energy it receives is transformed into useful electricity. No inverter converts 100% of the energy, as there are always small losses during the conversion process.
An efficient inverter reduces those losses and helps make better use of the production from the solar panels. In practice, a small difference in efficiency can have an impact in the long term, especially in large installations or systems expected to operate for many years.
Efficiency is not always the same. It can vary depending on the power at which the equipment is operating, ambient temperature, input voltage and the real conditions of the installation. That is why it is better not to focus only on the maximum efficiency shown on the technical data sheet. It is also important to assess European efficiency or weighted efficiency, which provides a more realistic view of how the inverter behaves at different load levels.
An oversized or undersized inverter can work outside its optimum range for many hours, so sizing is just as important as the quality of the equipment.
Do solar inverters work when the power goes out?
It depends on the type of inverter and how the installation is designed.
In a grid connected self consumption installation, the inverter will usually disconnect automatically when the power goes out. This is due to a safety measure called anti islanding protection, which aims to prevent the photovoltaic installation from continuing to send electricity to the grid during a power cut. Although it may seem contradictory, a home with solar panels can be left without electricity during a blackout if it does not have a system prepared to operate independently.
To have energy during a power cut, you normally need a hybrid inverter or a system with backup function, batteries and a specific configuration. Having solar panels installed is not enough. In off grid installations, on the other hand, operation does not depend on the electricity grid. As long as there is energy available from the panels or in the batteries, the inverter can continue powering the loads.
Protections of solar inverters
Solar inverters incorporate different protections to ensure safe operation. These protections help prevent damage to the equipment, the solar panels, the electrical installation and users.
The most common protections include:
- Overvoltage protection: acts when the voltage exceeds the permitted values.
- Undervoltage protection: prevents the inverter from operating with insufficient or unstable voltage.
- Overcurrent protection: protects against currents higher than those allowed by the equipment.
- Short circuit protection: disconnects or blocks the system in the event of serious electrical faults.
- Overtemperature protection: reduces power or stops operation if the inverter becomes too hot.
- Anti islanding protection: disconnects the inverter from the grid when it detects a power cut.
- Reverse polarity protection: prevents damage if the positive and negative poles are connected incorrectly.
- Insulation fault protection: detects possible electrical leakage or insulation problems in the system.
- Out of range frequency protection: prevents operation if the grid frequency is not suitable.
- Out of range grid voltage protection: disconnects the equipment if the grid voltage does not meet the established values.
These protections do not replace correct installation design. The inverter must be accompanied by external protections, suitable wiring, earthing, circuit breakers, residual current devices and surge protection devices when necessary.
Sizing a photovoltaic inverter
Sizing a photovoltaic inverter means choosing equipment with suitable power and characteristics for the solar installation, because if the inverter is too small, it can limit production, but if it is too large, it can work for many hours below its optimum range and make the installation unnecessarily more expensive.
A common practical reference is to select an inverter with a power margin of approximately 25% more than the power of the panels, especially when future expansions are expected or there are demanding working conditions. For example, if an installation has 4 kW of solar panels, an inverter of around 5 kW could be considered, provided that the rest of the technical parameters are compatible. However, power is not the only important figure. It is also necessary to review:
- The working voltage of the strings.
- The number of panels per series.
- The maximum input current.
- The MPP range of the inverter.
- The orientation and inclination of the panels.
- Partial shading.
- The expected consumption.
- The possibility of installing batteries.
- The connection regulations and conditions.
In grid connected installations, the contracted power, export limits and system legalisation must also be taken into account.
Ideally, sizing should be carried out by a professional, because each installation has its own particular features. In short, photovoltaic inverters are a key component in any solar system. They transform energy, protect the installation, optimise production and allow the operation of the system to be controlled.
