In a perfect world, UK roofs would all face south, with a 35° pitch and no shading in sight. But we don’t live in a perfect world. As solar installers, we have to find clever ways to maximise the potential power from roofs of all make ups, orientations and shaded spots.
This is best achieved by using micro-inverters or power optimisers - nifty bits of kit, collectively known as Module-Level Power Electronics (MLPEs). As that name implies, these bring a degree of power optimisation at the module level (i.e. at the level of each individual solar panel). This means you can get the most from panels under different levels of sunlight (facing varying directions or affected by shading, dirt etc).
But which is the best solution? Let’s focus on our favourite brand of power optimiser, and compare SolarEdge vs micro-inverters.
What are micro-inverters and optimisers?
In a regular PV system, the panels are connected in a string (i.e. in series) with a single inverter to change their DC power to AC suitable for the home. The inverter continually tries to optimise the output of the string of panels using something called Maximum Power Point Tracking. Optimisation involves some ‘averaging’ across the panels, and if the panels are not behaving uniformly (e.g. some in shade, some not), this inevitably means that most individual panels do not achieve maximum output from the available solar radiation.
To work around this, we can shrink the inverter down and give each panel its own individual micro-inverter. Connected in parallel, they each send maximum AC power to the home.
Or, we can move the Maximum Power Point Tracking from the inverter and into a power optimiser placed alongside each panel. These send maximised DC power from the panels to a central inverter.
SolarEdge vs micro-inverters
SolarEdge is one of the leading brands of solar PV optimisers. Their optimisers communicate with a SolarEdge inverter for maximum benefit, and offer online panel-level monitoring for the customer.
The main brands of micro-inverters are Enphase and SMA. Each micro-inverter typically has a 190-220W rating.
The advantages of each are as follows...
- Most micro-inverters have a warranty of 25 years, longer than the standard SolarEdge inverter’s 12 year warranty (although this can be extended to 25 years, and the optimisers themselves have a 25 year guarantee).
- If one micro-inverter fails, the rest of the system still functions. But if a central inverter breaks, the whole system goes down. That said, in a micro-inverter system, there are a lot more ‘complex’ parts to fail - a 15 panel system means 15 inverters, compared to one inverter and 15 optimisers with a SolarEdge system. Failure tends to happen more to inverters than it does to optimisers.
- Since power is converted at the panel, there’s no high voltage DC going across the rooftop, which can be seen as a safety advantage (though any properly installed system should be safe regardless).
- It’s easier to extend the system with more panels at a later date, as you won’t have to replace an inverter rated to the current system’s size.
Image source: Enphase.
- You only duplicate the parts of the system that are needed for optimisation. As above, fewer components means less risk of failure.
- It also makes the overall system cheaper.
- The inverter is in a more accessible location for future maintenance or replacement.
- SolarEdge is directly compatible with our recommended domestic battery, the Tesla Powerwall 2.
In terms of cost, micro-inverters typically add about 20-30% to the project cost compared to a standard inverter. SolarEdge adds about 15%. The boost in output from either can be up to 25%, depending on the roof conditions.
The cost per watt decreases faster with power optimisers, as the panel-level component is much simpler. We commonly use them on larger systems, with micro-inverters reserved for very small systems (e.g. 1-2 panels).
In our experience, we’ve found SolarEdge a lot more reliable and less prone to failure than micro-inverters. Their online monitoring, allowing you to track performance and get alerted to any faults, is excellent. So for most PV systems that need the performance boost, we’d recommend SolarEdge.
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