String (or central) inverters have been on the market all the way since the introduction of solar panels. An inverter is an absolutely necessary component of a solar PV-system. Without it, we have no way of converting direct current (DC) into alternating current (AC), which is the required type of electricity for the vast majority of electrical applications today.
In the beginning of the 90’s the first micro-inverters were developed. However, it’s not until the last few years the technology has started taking ground. New models are out, some of them claiming as much as 25% better efficiency rates than conventional string inverters. Is this claim actually in line with reality? Are micro-inverters really better than conventional string-inverters?
Benefits of Micro-Inverters
Efficiency is optimized on a panel-by-panel basis
Usually, one conventional string inverter is enough to cover all your solar panels. This is the cheapest way to go, but unfortunately it comes with several problems. The string inverter is in charge of the optimization for every panel that is connected, but optimizes for the weakest link. As much as half of the power output can be lost if only one of the solar panels is covered in shading or dirt.
The main selling point of micro-inverters is that they are able to push more power out of a solar system than string inverters. One micro-inverter is attached to every solar panel – and performs optimizing algorithms for this solar panel alone. This way, every solar panel performs at its best, which can yield a significant boost in power output of the whole of the solar array.
Real-time reporting is incredible useful
Another major benefit with micro-inverters is the real-time reporting that both owners of the PV-system and installers can access to analyze and pinpoint any problems.
Safety is improved
There is quite a lot of voltage drop in a conventional string inverter. The DC output from every panel is connected and converted into AC at one point. This also happens on a with micro-inverters, but since there are so many of them, voltage is much lower and risk of harmful electricity and fire hazard is reduced.
Easier to scale
Lastly, adding solar panels to a preexisting solar system is not as complicated with micro-inverters as it is with string inverters. If you want to expand your power output you don’t have to fill up an entire new string invertor worth of solar panels. Simply add the number of solar panels you want and install the same number of micro-inverters
Micro-Inverters are More Expensive
There’s no doubt that a solar system that have micro-inverters will be more expensive than one that uses just one string inverter. The question is how the financial situation looks in the long run.
One micro-inverter for every each panel
For every solar panel you purchase you need to add a micro-inverter. These are composed of many of the same expensive components as string inverters, only in smaller scales. One micro-inverter is much cheaper than a string inverter; but micro-inverters for an entire solar array will be more expensive than one string inverter.
Enphase and Enecsys have started offering dual micro-inverters that still optimize power on a panel-by-panel basis, in other words have the functionality of single micro-inverters, but at lower costs.
Micro-inverters have longer lifespan than string inverters. Enphase and Enecsys offers micro-inverters with a warrant of 25 years, which is 5 years longer than the warrant of a typical string inverter.
Are Micro-Inverters Really Better?
It depends. String inverters can have an efficiency-rate of as high as 95%. This is under ideal conditions. Efficiency takes a significantly hit as soon as one of the solar panels starts underperforming – whether its from shading or technical issues. If you suspect that a solar array for your house would have high chances of any kind of coverage, micro-inverters should be seriously considered. On the other hand, if coverage is not an issue, string inverters can be the cheaper way to go.