Inverter

Everything you need to know about solar inverters

Solar inverters are a key component of any solar power system. They take the direct current (DC) of the electricity produced by solar panels and convert it into alternating current (AC) electricity, which can then be used to power your home. They also allow any excess electricity generated to be exported into the national grid, helping you to make a profit

How they work

Without getting too technical, solar inverters use a pair of “power switching transistors”, which are repeatedly turned off and on in order to make DC electricity seem like AC electricity. A receiver then processes the DC, converting it into AC before pumping the electricity into your system.
Efficiency is at the heart of all of the best solar inverters, which have a typical conversion rate of between 93% and 96%, with the remaining electricity used to power the inverter itself.

Types of inverter

There are two different types of inverter to choose from. The type you need will depend largely on the number of panels you have, the size of your home and the amount of money you are willing to invest in the technology.

String Inverters

These are ideal for households with a large number of solar panels that are operating under the same conditions. This means they are all facing in the same direction and are likely to receive the same amount of sunlight throughout the day. Depending on the size of your home, you may have to install a number of string inverters to achieve the best results.

Micro Inverters

In contrast to String Inverters, these are the perfect solution for properties that have a number of solar panels all facing in different directions, or smaller properties with just one or two panels. The cost per watt is higher for micro inverters, but they are easier to install initially.

Cost

As solar inverters are a new and necessary technology, the costs can be quite high, depending on the type of inverter you choose. Typical prices range from £500 for a smaller micro inverter to thousands of pounds for a top of the range, high-performance string inverter. Generally speaking, the more expensive the inverter, the greater the efficiency rating, although the lower cost models will still achieve around a 93% conversion rate.

Where to buy

There is a wide range of solar inverter outlets servicing the UK market, and a large selection of brands to choose from. SMA, one of the more popular manufacturers, have a number of inverters available, with the better Sunny Boy models ranging in price from £1,500 to £2,500. All models comply with UK regulations and achieve a conversion rate in excess of 93%.
You may also want to check out Mastervolt, who include a handy piece of free software to help you monitor the performance of your solar inverters, while charging considerably less than their SMA counterparts. You can typically find a high-performance Mastervolt inverter for around £400, while they also offer a budget, stand-alone option that does not need to be wired into your electricity system. These are available for around £100.

What are the different types of solar inverters?

Inverters are an important part of any solar installation; they are the brains of the system. Although the inverter’s main job is to convert DC power produced by the solar array into usable AC power, its role is only expanding. Inverters enable monitoring so installers and owners can see how a system is performing. Inverters can also provide diagnostic information to help O&M crews identify and fix system issues. These important components are increasingly taking on decision-making and control functions to help improve grid stability and efficiency. With the growth of solar + storage, inverters are also taking on responsibility for battery management. Here is a look at some different types of solar inverters.

Delta string inverter

String inverters

Solar panels are installed in rows, each on a “string.” For example if you have 25 panels you may have 5 rows of 5 panels. Multiple strings are connected to one string inverter. Each string carries the DC power the solar panels produce to the string inverter where it’s converted into usable AC power consumed as electricity. Depending on the size of the installation, you may have several string inverters each receiving DC power from a few strings.
String inverters have been around for a long time and are good for installations without shading issues and in which panels are positioned on a single plane so do not face different directions. If an installation uses string inverters and even one panel is shaded for a portion of the day reducing its performance, the output of every panel on the string is reduced to the struggling panels’ level. Though string inverters aren’t able to deal with shading issues, the technology is trusted and proven and they are less expensive than systems with microinverters. String inverters are commonly used in residential and commercial applications. Also, as technology improves allowing string inverters to have greater power density in smaller sizes, string inverters are becoming a popular alternative over central inverters in small utility installations smaller than 1 MW.
String inverters can also be paired with power optimizers, an option that is gaining popularity. Power optimizers are module-level power electronics meaning they are installed at the module level, so each solar panel has one. Some panel manufacturers integrate their products with power optimizers and sell them as one solution known as a Smart Module. This can make installation easier. Power optimizers are able to mitigate effects of shading that string inverters alone cannot. They condition the DC electricity before sending it to the inverter, which results in a higher overall efficiency than using a string inverter alone. Power optimizers offer similar benefits as microinverters, but tend to be less expensive and so can be a good option between using strictly string inverters or microinverters.

TMEIC central inverter

Central inverters

Central inverters are similar to string inverters but they are much larger and can support more strings of panels. Instead of strings running directly to the inverter, as with string models, the strings are connected together in a common combiner box that runs the DC power to the central inverter where it is converted to AC power. Central inverters require fewer component connections, but require a pad and combiner box. They are best suited for large installations with consistent production across the array.

Darfon microinverter

Magnum Energy inverter/charger

Microinverters

Microinverters are also becoming a popular choice for residential and commercial installations. Like power optimizers, microinverters are module-level electronics so one is installed on each panel. However, unlike power optimizers which do no conversion, microinverters convert DC power to AC right at the panel and so don’t require a string inverter. Also, because of the panel-level conversion, if one or more panels are shaded or are performing on a lower level than the others, the performance of the remaining panels won’t be jeopardized. Microinverters also monitor the performance of each individual panel, while string inverters show the performance of each string. This makes microinverters good for installations with shading issues or with panels on multiple planes facing various directions. Systems with microinverters can be more efficient, but these often cost more than string inverters.
Microinverters can also be sold through panel manufacturers already integrated into the panel, similar to Smart Modules but instead known as an AC Module. This makes installation easier and cheaper.

Battery based inverter/chargers

With the growth of solar + storage, battery-based inverter/chargers are becoming increasingly important. Battery based inverter/chargers are bi-directional in nature, including both a battery charger and an inverter. They require a battery to operate. Battery-based inverter/chargers may be grid-interactive, standalone grid-tied or off-grid, depending on their UL rating and design. The primary benefit of inverter/chargers is that they provide for continuous operation of critical loads irrespective of the presence or condition of the grid. UL1741 requires the grid-tied generation source to stop generating power in the event of a grid outage. This de-powering is known as anti-islanding, as opposed to ‘islanding’ which is defined as generating power to power a location in the event of a grid outage. Therefore, UL1741 grid-tie inverters will not generate power in the event of a grid outage, so a user will experience an outage irrespective of the availability solar harvest. Battery-based inverter/chargers will power the critical loads in the event of a grid outage, but will do so in a manner to not create the islanding condition. Further, UL1741 inverter/chargers may be rated as either interactive or standalone. The former export excess power to the grid, while the latter do not–by rating and by definition. In all instances, the battery based inverter/charger manages energy between the array and the grid while keeping the batteries charged. They monitor battery status and regulate how the batteries are charged.