A Comparison of String Inverter Systems, Microinverters, and Optimized Inverters
The main components of a home solar system are solar PV panels. These panels interact with sunlight to generate electricity. However, the electricity generated by solar panels is in the form of Direct Current (DC). Unfortunately, almost all modern appliances utilize Alternating Current (AC). Fortunately, there is an easy solution to this in the form of a device called an inverter. This device converts the DC into AC, for use in the home.
Besides the solar panels, one of the most important decisions you will need to make is the type of inverter to use. This decision can be difficult since there are three primary types of inverters from which to choose. The guide below will help you understand the different types of inverters so that you can make an informed decision.
String inverters remain the most commonly used type of inverter around the world and in NZ. They are the most economic option where individual strings of solar panels can be installed facing the same direction. However, the do not offer much flexibility, such as in cases where solar panels need to be installed on separate roof areas facing different directions, or in partially shaded spaces.
With a string inverter, the solar panels are connected in series with each other. They then deliver their cumulative DC voltage to one inverter, which transforms the DC from the entire solar array into AC power, which is then fed into the grid. While string inverters are a time-proven technology, their main downside is that if a single solar panel fails or works below its optimal output (shaded, covered by dirt, or has a failed diode), then the entire system will suffer. In short, the maximum output of the system is determined by the poorest performing panel in the system.
Optimized inverters systems, such as Solaredge, allow solar power production and monitoring to be done at the level of each panel. Solaredge achieves this by using a simple Optimiser under each solar panel, all wired to a central Inverter. This system offer the benefit of ensuring that if one panel goes down, it will not affect the output of the whole system. Additionally, these devices are located under the solar panels just like with microinverters, described below. However, there are some differences.
One of the key differences is that they can start operation at a lower voltage. As a result, they can achieve each panel’s Maximum Power Point, even when it is partially covered or shaded. Another major difference is that the optimized inverters are connected to a central string inverter.
This setup reduces the quantity of sensitive electronic components out in the open, while taking advantage of the cost-efficiency of string inverters. With these optimized inverters, the output of each solar panel is optimized before it is sent to the central string inverter. The result is high overall efficiency than would be possible if the DC output of each panel went directly to a central string inverter.
If you opt to use SolarEdge power optimisers, there are a few benefits that you will get. For instance, the optimisers come with a 25 year warranty, which in practice means the entire life of the solar system. Another benefit of SolarEdge power optimisers is the proprietary safety technology built into them. This technology is called SafeDC, and it automatically switches to safety mode when the AC shuts down. SafeDC also ensures that output voltage from each module is reduced to a touch-safe 1V whenever the AC power is switched off. Another safety feature is the arc fault detection and interruption, which helps to cut the risk of fires. In other words, if the DC cable gets damaged for any reason (hurricane, rodents, etc),and comes into contact with the roof or other conductors, the inverter will automatically decrease panel voltage to 1V in order to prevent arcing.
A major benefit of Optimisers s is that they have fewer parts, which means they have few points of failure. It also means they require simpler roof wiring, which means they last longer statistically than microinverters.
A microinverter is an alternative to the string inverter. It is a good option for situations where one or more of the panels is shaded or installed in a different direction to the other panels. Microinverters, unlike string inverters, are attached to a single panel or two panels on commercial systems. Consequently, there is no central inverter in such a system.
The microinverters are connected in parallel and the AC power they produce travels upstream via a branch circuit to the distribution board. One of the main advantages of this system is that it isolates the output from each panel. As a result, the loss of output from one panel will not affect the output from the other panels. Each microinverter maintains optimal output for its panel by performing MPPT for its solar panel. A major benefit of this setup is more flexibility in the solar panels. If a single panel fails, it will not affect the overall performance of the solar system.
The main drawback of a microinverter setup is that it costs more upfront to install. In a micro inverter, all of the delicate electronics are on the roof, exposed to higher temperatures and weather, thus there can be a higher failure rate. Wiring can be expensive as proprietary cable and connectors are used. Microinverters tend to be less efficient and are normally rated lower in power that the solar panels, so there are higher power losses. The cost of replacing such a device is high and can take a lot of man-hours since each microinverter is located under the panels, which are mounted on the roof.
When picking the best option to use in your solar system, it often comes down to site characteristics and the client’s needs. An expert determines the best options based on factors such as the need for smart devices such as relays, EV charging, and hot water diverters. One of the best companies to source these devices from is SolarEdge, which produces a complete suite of devices for solar systems.
Finally, the unique characteristics of the roof will play an important role in the choice of the inverter to be used. Some homes have a simple sloping roof design, which makes it easy to install solar panels facing the same direction. In such an instance, a simple string inverter will suffice. However, some roofs have complex roof designs, or obstacles near the roof, which necessitate the need to have panels facing different directions to maximise the solar energy captured by the system. In such a situation, it would be necessary to use power optimizers.
The choice of which inverter system to use often comes down to site conditions, your needs, and the advice you will receive from your installation expert. Always pick the option that feels appropriate for your needs and budget.