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Why buy a hybrid inverter for your solar PV system?

Posted by Aderanti Kudehinbu on 21 June 2017 at 9:45 am

The initial cost of a hybrid inverter is quite high, but this is offset by the ability to use your generated power more flexibly, rather than having to buy energy from the grid when the solar panel isn’t generating. Hybrid inverters have proven reliability across various grid types. Modern inverters have increased conversion efficiency compared to past models, with integrated safety and control features. A hybrid inverter will also future proof your system enabling you to connect a DC connected battery at minimal cost in the future.

The role of the inverter

Inverters are an integral part of domestic solar PV systems in the UK. Solar panels output electricity in the form of Direct Current (DC). However most of our electricity network relies on Alternating Current (AC). Consequently power from DC sources, such as solar panels, has to be converted to AC through the inversion process.

The inverter is the most technically complex part of a grid connected solar PV system. It is composed of a series of solid state components which oscillate the DC electricity to create an alternating current. Micro controller chips are programmed to maximise the power output from the PV panels, using an algorithm called Maximum Power Point Tracking. This outputs a clean 50Hz sinusoidal AC current which can then be used to power most electrical equipment. Different types of inverters have ways of optimizing performance. Solar Edge inverters allow for each panel to work independently which is the most efficient way to set a system up. Most standard inverters and hybrid inverters will effectively have two larger groups of panels wired separately in two strings.  

Solar PV set ups can be categorized into three types; Off-grid, grid-tied, and hybrid.

1. Grid-tied
Grid-tied systems have the ability to synchronize with the utility grid line. Electricity is converted to AC and any which is not used locally is exported to the grid. Individuals and residences are permitted to generate and sell their energy to the grid, and may be compensated for the amount of renewable energy they generate in the form of an export or Feed in Tariff (FIT).

2. Off-grid
In this case DC electricity generated may be used directly by 12V DC appliances or it will be converted to AC by the inverter for use by the household or business, without recourse to the grid. Electricity may be stored locally for use when the solar panels are not generating. This setup is frequently used in remote locations without a connection to the grid system. 

When installing such a system it is important to consider the battery bank voltage to ensure that everything is compatible. There must also be enough solar capacity to both run appliances and charge the batteries.

3. Hybrid 
Hybrid set ups combine the best elements of the other two types. They are grid connected, so excess electricity can be sold to the energy companies. However during periods of excess power generation, the extra generated power can be stored in a battery, rather than exported to the grid.  This can be particularly useful in areas where grid connections are unstable, as the stored electricity can provide power during a black out as long as the hybrid inverter and battery has the supporting software and changeover switches installed. Most do not come with this as standard and will need to be purchased as extras. If this is something you require make sure it is included in your quotation.

Benefits of hybrid inverters
Hybrid inverters produce the option for battery storage even for households on the grid. They are particularly popular in developing countries, where the grid systems are not very reliable. Hybrid inverters also reduce dependency on the grid, making them more versatile than grid-tied systems, but they still allow the export of excess energy, which off-grid systems do not.

With the advent of the 'smart grid' hybrid inverters should in future allow UK homeowners and businesses to take advantage of changes in utility electricity rates throughout the day. You'll be able to draw upon your own battery stored green electricity while electricity is expensive, then switch back to the grid when it is cheap.

When choosing a hybrid inverter it is vitally important that it performs well enough to allow the battery to function as designed. There are many different hybrid/battery combinations on the market all claiming to do the same but dig a little deeper and it’s quite the opposite.

The main thing to look out for isn’t actually just the storage capacity of the battery, it is the amount that you can draw from the battery at any one point that will have the biggest effect on your energy bills. Sometimes your hybrid inverter will also have an impact on this so it’s vital they are designed to work together.

Probably the best option for a hybrid setup at the moment would be a hybrid inverter such as the Solax hybrid or the Godwee hybrid paired with one of the batteries in the LG Chem Range.

Choosing a battery can be quite difficult but 95% of households should consider nothing less than 6KW with the ability to discharge continuously at 3.6kw.

This blog has been written in conjunction with SunGift Energy. Special thanks go to Ollie Gibbs, one of their experts for his contribution

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Image credit: National Renewable Energy Lab

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