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Solar PV Knowledge Bank

Micro-inverters and Solar Panel Optimisers

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Solar micro-inverters-1

Image source: Enphase.

Introduction

Micro-inverters and power optimisers are an upgrade on traditional PV system design, by maximising the electricity generated from each individual panel. They do this by shifting Maximum Power Point Tracking (MPPT) to the panel level. This is particularly beneficial on roofs with multiple orientations or shading, as the panels will have differing outputs.

Let’s see how micro-inverters compare to power optimisers, before taking a look at some of the most popular manufacturers.

Standard string inverters

Before diving into optimisation, it’s worth familiarising yourself with how a regular PV system is set up. The solar modules are connected in a string to a single inverter, which converts their DC power to AC for use in your house and the grid, while moderating the maximum output from the system as a whole with MPPT.

String inverter

The downside is that one poorly performing panel (due to dirt, shading, degradation etc) will bring down the system as a whole to its lower output.

What is a micro-inverter?

As the name implies, a micro-inverter is a small version of an inverter, converting DC to AC power from an individual panel. Each module in the system gets its own MPPT, meaning individual generation is maximised no matter its condition. They’re connected up in parallel, before sending AC current to your home and grid.

Micro-inverter

Advantages of micro-inverters:

  • Each module gets Maximum Power Point Tracking, giving 5-25% overall higher system output.
  • Micro-inverters usually have a longer lifespan than string inverters, which often have to be replaced during the lifetime of the system.
  • Warranties are typically 15-25 years vs 5-10 years for a string inverter.
  • It can be easier to extend the system later. A string inverter is sized for the system, so may need replacing with a higher power rating if the overall system size increases.
  • System components can be simpler - you don’t need large transformers, capacitors or cooling fans.
  • One module failing won’t take the whole array offline.
  • Arrays can include modules of different power ratings and harvest the maximum from each.
  • There is no high voltage DC current travelling across the roof, increasing safety (though a properly installed system will be safe regardless).

Disadvantages of micro-inverters:

  • A cost premium of 20-30% compared to a standard inverter. So there’s a higher initial cost per kWp, but this may be mitigated by the greater lifetime output.
  • Installed behind rooftop panels, they are harder and more costly to access and repair or replace.

What is an optimiser?

A solar panel power optimiser is like a halfway house between micro-inverters and a standard system set up. Each module has MPPT but there is still only one system inverter. An optimiser is attached to each panel and converts its optimum DC output to the optimum DC power for the inverter.

Power optimiser

Advantages of power optimisers:

  • As with micro-inverters, you can boost the system performance by up to 25%.
  • When optimisers are made by the same manufacturer as the inverter, they can communicate. For example, if one module’s output drops due to shading, the inverter can tell other panels to increase their output so the overall power going to the inverter remains stable.
  • On three phase commercial supplies, you can use double optimisers that take input from 2 panels. So there’s potential to reduce cost at scale.
  • If installing batteries at the same time then optimisers are better because they keep the output in DC, which is what the battery takes, preventing the need for a further inverter.

Disadvantages of power optimisers:

  • Again like micro-inverters, they’ll add around 15% to your system cost.
  • The array is still matched to the inverter’s power rating, so you typically can’t just add more panels later.

Enphase micro-inverters

  • Enphase is the most well established and respected micro-inverter brand.Enphase micro-inverter
  • Their products come with a 20 year warranty and are tested to last over 100 years.
  • You can monitor system production and health with the Enphase Enlighten web or mobile app.
  • Datasheet.

SolarEdge optimisers

  • SolarEdge is a combined inverter and optimiser system.Frame mounted residential power optimizer
  • Each panel has its own optimiser, connected in string to the SolarEdge inverter.
  • There’s a 25 year warranty on optimisers, 12 year on the inverter (with an optional extension to 25).
  • Full system monitoring and alerts.
  • Datasheet.

Tigo optimisers

  • Tigo optimisers can be used with many brands of inverter.Tigo optimiser
  • Their USP is that they can be placed selectively on modules where required to allow for a cheaper overall cost while still maximising the energy harvest.
  • Use the Tigo SMART app to monitor panel performance, see the contribution the optimisers are making, identify faults and predict future maintenance.
  • Datasheet.

Further advice

If you're interested in micro-inverters or power optimisers, please speak to one of our experts to discuss what's best for your solar PV system. Reach us on 0118 951 4490 or via the button below:

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