Plug-in grid connect solar inverters have begun appearing in Australia – so what are they, how do they work and should you use one?
A solar inverter is a box of electronics that takes the electricity generated by an array of solar panels and converts it from Direct Current (DC) to Alternating Current (AC); suitable for use by home appliances and for export to the mains grid.
A traditional solar inverter can handle the output of multiple solar modules and is usually installed close to the meter box. Microinverters, a more recent development, are much smaller units that work with single panels and are located on the back of the module itself; creating what is often referred to as an AC solar panel.
The most common type of solar inverter used in home power installations needs to be installed by a qualified person as they are hard-wired into to the meter board.
The new “plug and play” inverters are very different – these are a portable device that allow you to connect solar panels or small wind turbine to the inverter and then plug the inverter directly into a standard power socket in a home; making the power generated available to appliances. While not having as much capacity as a standard residential solar inverter, multiple units can be used.
It sounds like a great idea, but consumers considering purchasing a plug and play grid tied inverter may need to be cautious.
In a discussion concerning these units on Energy Matters’ forum, one of the points mentioned is while plug and play inverters may be listed by the Clean Energy Council (CEC) and approved for Renewable Energy Certificates (RECs), their certification under an important safety standard still appears to questionable.
The standard, AS-4777, deals with grid connection of energy systems via inverters. In order to be listed by the CEC, inverters “must be tested against AS 4777.2 and 3 – 2005 (or equivalent) and AS3100 (or equivalent) by an appropriate testing laboratory.”
However, in AS 4777.1 (Installation Requirements, Clause 5.3.1), it apparently states “the inverter shall be connected by fixed wiring to a dedicated circuit on a switchboard”. This would seem to prevent the use of any plug-in type device if AS-4777 is strictly observed.
Another important issue involves electricity distributors. Before any electricity generator can be connected to a network (which includes your house when solar panels are capable of exporting electricity to the grid), permission from the distributor must be gained. This permission doesn’t consist of a quick call to the company and a verbal “yep, you’re good to go” – there is paperwork involved.
Additionally, safety of these units has also been raised. While a plug-in inverter may have anti-islanding features that prevent the unit from delivering power in a blackout, electricity may still be delivered for up to 2 seconds. If the plug were pulled from the outlet, it could still potentially deliver a nasty shock.
Finally, consumers considering installing a plug and play grid connect inverter should check with their insurance company to ensure using such a device doesn’t impact on home insurance policy coverage, particularly as a DIY project.
While a great idea in theory, it’s these potential issues that have led some to refer to plug in grid tie inverters as “plug and pray”.