Solar photovoltaic (PV) panels are a hot topic this summer, especially since many expect that the currently very generous financial support under the feed-in tariff scheme will be drastically cut for anyone who installs their PV roof after 1 April 2012, as the government will introduce new tariffs for systems installed after that date.
Apart from the panels themselves, the other major component of a grid-connected PV roof is the inverter.
Modern grid-tied inverters fulfil three roles:
The most common type of inverters for domestic PV installations in the UK are central “string” inverters: The PV modules on your roof are connected in one or more “strings” and wired to a single central inverter somewhere inside your house.
However, there is another, currently less common approach: Having a small dedicated inverter for each individual PV module, a so-called micro-inverter. Theoretically, this approach should have three main advantages:
However, all this is bought at the cost of currently higher capital costs – using micro-inverters will add somewhere between £500 and £2,000 to the cost of a domestic PV roof. Perhaps more critical, though, is the uncertainty about lifetime maintenance cost: While each individual micro-inverter may last much longer than a central inverter, the high number of individual inverters (10-20 in a typical domestic system) may still mean it’s quite likely that there will be dome failures during the life of the PV roof. And while the warranty could cover the cost of replacing the micro-inverter itself, the labour and scaffolding required to change micro-inverters on a roof may still make replacements very expensive.
At the moment, all of this is largely speculation. There simply aren’t enough micro-inverter systems, especially of the latest generation, which have been around for long enough on UK roofs for us to know how they pass the test of time. Anyone installing this technology at the moment should consider themselves an “early adopter” – with all the opportunities and risks associated.