String inverters vs Microinverters vs Power optimizers

String inverters vs Microinverters vs Power optimizers

What does an inverter do?

An inverter converts the direct current (DC) electricity generated by solar panels (or stored in batteries) into a more useful alternating current (AC) which is needed to power most of our electrical appliances.

Solar PV inverter types

There are three types of inverters that are available for solar energy systems:

  1. String inverters
  2. Micro inverters
  3. Power optimizers
Micro-inverters and power optimizers are also referred to as “Module-Level Power Electronics” or MLPEs.

String inverters are the most commonly deployed solar inverter on the market. However, module-level power electronic (MLPE) technologies are gaining in popularity as their costs come down.

Key Points: String inverters, microinverters & power optimizers

  • Inverters convert the DC electricity that solar panels produce into usable AC electricity.
  • The 3 main inverters available for solar installations are string inverters, micro-inverters and power optimizers.
  • Micro-inverters and power optimizers are more expensive than string inverters.
  • Micro-inverters and power optimizers are the best choice for solar panel installations where shading is an issue (modern string inverters incorporate a Maximum Power Point Tracking (MPPT) technology which also helps ), or where solar panels face different directions. Micro inverters also make it very easy to expand the solar system in the future, even allowing the use of multiple orientations, tilts and solar PV module types to be used without decreasing efficiency.
  • Micro-inverters and power optimizers allow generation monitoring of each individual solar panel.
  • Micro-inverters or power optimizers will produce slightly more electricity than an equivilant solar PV system using a string inverter.

String inverters


String inverters are the most cost effective inverter option in the UK. A string inverter is well suited to solar PV arrays that are free from shading (caused by trees, chimney stack etc) and does not face in multiple directions.

How a String Inverter Works

A solar PV array using a string inverter arranges it’s solar panels into subgroups connected by strings. Each string of panels then connects to a single string inverter, which transforms the electricity from DC to AC.

String inverters have been used in solar panel systems for decades, proving to be reliable, and a great choice for non-shaded solar PV installations.

A string of solar PV panels only produces as much electricity as the least productive panel – if one of your solar panels is shaded during part of the day, the power output from that entire string would be reduced to this lower level for the duration of the shading. For the same reason, solar panels installed facing different directions may not be well suited for a string inverter.

If your roof (or the location of your solar installation) is prone to shading during any part of the day, AC Gold recommend using micro inverters on each solar panel. Other more extreme options might be to remove the object causing the shading (such as cutting down a tree), or relocating the solar panels to a more suitable location.

However, modern string inverters are utilising a technology called Maximum Power Point Tracking (MPPT) which constantly monitors the solar panel array voltage and current to drive the operation point to the maximum power point, resulting in the highest energy harvest – so shading is not as big of an issue as it once was.

Maximum Power Point Tracker (MPPT)

How a Maximum Power Point Tracker Works:

Maximum Power Point Tracker is a high frequency DC to DC conversion which takes the DC input from the solar panels, converts it to high frequency AC (through a transformer – usually a toroid (doughnut) shaped transformer), then rectifying it back down to a different DC voltage/current using an output regulator – to better match the inverter or the batteries. MPPT’s operate at very high audio frequencies (usually 20-80 kHz range) which has the advantage that they can be designed with very high efficiency transformers and small components. Noise isolation and suppression are important in the design of MPPT circuits because the high frequency can act like a radio transmitter, broadcasting a signal and interfering with radio and television.

Micro-inverters


Micro inverters are gaining popularity, especially for domestic solar systems. Micro inverters are still more expensive than string inverters or power optimizers, but prices continue to fall with popularity, economies of scale and as the technology matures.

How Micro-inverters Work

Micro inverters are installed on every solar panel in a solar array. They convert the direct current (DC) electricity produced by the solar panel(s) into alternating current (AC) electricity on your roof, without the need for a large, separate inverter.

Micro inverters are the best choice for shaded roofs

With older string inverters, shading that falls onto a solar panel will reduce the output power of all solar panels wired to the same string down to this lowest voltage produced (you can think of it the same way as old christmas tree lights would go out when one bulb blew). This problem is solved by using micro inverters which convert the DC to AC electricity at each panel, meaning shading will only reduce the power in that one panel.

Micro-inverters also enable us to monitor the performance of every individual solar panel.

Power optimizers

Power optimisers are considered a compromise between more expensive micro-inverters and the standard string inverter.

How Power Optimizers Work

Like micro inverters, power optimisers are located at each solar panel, but rather than converting the electricity from DC to AC at the solar PV panel, they condition the DC electricity before sending it to a string inverter. Using power optimisers with a string inverter will produce a higher system efficiency than using a string inverter alone.

Power optimisers reduce the impact of panel shading on system performance, and also offer panel performance monitoring. Solar systems that use optimisers tend to be more affordable than solar PV arrays that use micro inverters.

How “smart modules” use micro-inverters and power optimizers

Increasingly, micro-inverter and power optimizers are being incorporated into solar panels to create smart modules with integrated MLPE equipment. This simplifies installation and cuts down on costs. Many of the world’s biggest panel manufacturers now have smart module options available, including Trina Solar, ET Solar, ReneSola and SunPower.

Visit Our Showroom

The AC Gold renewable energy showroom in Stirling offers an opportunity to see a range of renewable energy systems on display including solar PV, off-grid power solutions and a range of domestic biomass log and pellet boilers.

AC Gold Renewable Energy Showroom
11 Back O'Hill Industrial Estate, Stirling, FK8 1SH

Mon-Fri: 9am - 5pm