Producing a reliable, more efficient and less costly PV panel is an important step in making solar more competitive. But it is only part of the bigger picture, or the ‘balance of system’. An array of other components, including inverters, converters and the associated hardware that go towards making it work – as well as the people who install them – can account for half an installation’s cost.
Manufacturers and installers know only too well that these items must be made simpler, smarter, more integrated, more efficient and more reliable to reduce overall costs and speed up the rate of return for customers.
Some of the most significant recent technological advances are in the area of inverters, with several firms racing to market with micro-inverters, devices that convert direct current (DC) from a single solar module (panel) to alternating current (AC).
Drawbacks in Central Inverter Architecture
Shortcomings inherent to the central inverter architecture are creating opportunities for a range of new technologies, with a growing number of companies developing products and technology to generate more power from the PV panels already on the market.
One of them is Enphase, which claims to have been first to develop a commercially available micro-inverter. The company has shipped more than 300,000 units to date, grabbing 13% of the under-10 kW market in a remarkably short time.
Unlike a central, or string inverter, that aggregates and converts the power generated by an entire array of solar modules, a micro-inverter converts the DC power from a single solar module to AC. When connected to a central or string inverter, modules are typically connected in series; when they have micro-inverters, the modules are all connected in parallel.
Enphase, like others developing micro-inverters, claims there are numerous advantages, particularly for smaller — domestic and commercial — applications. The concept of panels delivering AC power has significant appeal for small-scale home project applications at lower voltage levels. But the technology is rapidly sizing-up, and the company, which recently completed a 223-kW build, is currently working on a further installation about twice that size.
Several producers are now promoting grid-tied PV micro-inverters, which ensure that the power supplied will be compliant with the grid code. It means that in geographic locations where buyback agreements are in place, installations with surplus power can sell it to the utility. In net-metering environments the meter turns forward during normal consumption, such as at night or in the day when local loads demand more than the PV system can supply, and backwards when PV production is greater than the load.
Micro-inverters are not new, but advances in electronic components have made them commercially viable for the first time, enabling manufacturers to penetrate lower-end markets while addressing some of the challenges associated with standard central inverters. A distributed approach to inverter technology reduces the effect of dust, debris and shade on the array. As the modules are installed in parallel via the AC connection only, any issues with a single module no longer disrupt the rest of the array as had occurred in previous designs using a central inverter. As a result, the solar installation is no longer subject to the ‘Christmas light’ effect in which shading or failure of a single module affected an entire string.