Conventional and Transformerless Inverters

Our earlier article, ˜Solar Panel Installations are changing!‘ discussed the modern evolution of solar technology. As noted, one big change that may increase efficiency and lower costs is the shift from conventional inverters to transformerless (TL) models.

Inverter basics

The inverter is the center of your solar energy system, responsible for converting the direct current (DC) electricity produced by your panels into the alternating current (AC) that flows through the grid and powers your washing machine and electric razor.

Standard inverters have a transformer within them that synchronises the voltage with that of the grid and your appliances.

Transformerless inverters use a computerized multi-step process and electronic components to convert DC to high frequency AC, back to DC, and ultimately to standard-frequency AC. TL inverters dominate the European market and work on the premise that in a grid-connected system, transformers are already in place in buildings or just a short way down the line. As such the individual transformer within the home-scale inverter becomes redundant.

Transformerless Advantages

As seen by the image above efficiency levels of TL inverters are around 97%, up 2% from conventional inverters.  This might not sound like much, but any increase in efficiency results in increased power supply, which can be quite significant when calculated over the life of the system.

Additionally, without the transformer, the inverter becomes much lighter, more compact, and more affordable. TL inverters use electronic (rather than mechanical) switching, thus reducing the amount of heat and ˜hum’ generated by the unit.

A further advantage is that many TL inverters have two maximum power point trackers, which allow the inverter to treat your installation as two separate systems. This means that you can place some panels on a north-facing roof, for example, and more on a west-facing roof, without worrying about lower irradiance on one side dragging the whole system down. In other words, the dual MPP tracker enables you to install more panels”and generate more energy”on a limited roof space.

Safety

Unlike their conventional counterparts, transformerless inverters lack electrical isolation between DC and AC circuits. This may raise safety concerns. However, safety mechanisms such as isolation resistance tests and residual current measurement can lower the risk of shock.

In Australia, the installation of photovoltaic systems is regulated under AS 5033 and must comply with safety standards. It is important to note that TL inverters have been common in Europe for the last decade or two, even though they are relatively new to Australia. As technology evolves, it is imperative that the standards committee monitors concerns to provide for the public safety.

Transformerless inverters may also create marginally stronger electromagnetic fields than transformer-based inverters. Nevertheless, EMF strength lies well below recommended limits and may be further minimized with advancing technology.

As always, care should be taken around all electricity-generating systems and on rooftops.

To sum up¦

Transformer-based inverters are still very common in Australia. They are widely used and well-understood, and have a long track-record as a component of solar energy systems. Transformerless inverters are becoming more popular, particularly in home solar installations. Their greater efficiency, smaller size, and lower costs make them attractive to home-owners and solar engineers alike.

Written by John Yurasek

Solar Energy Consultant

Solar Choice

© 2010 Solar Choice Pty Ltd

Sources:

Burger, B. & Kranzer, D.  ˜Transformerless PV topologies,’ retrieved 12 June 2010 from http://www.powersystemsdesign.com/index.php?option=com_content&view=article&id=453&Itemid=83.

Calais, M., Ruscoe, A., Dymond, M. (2009), ˜Transformerless PV inverter issues revisited,’ retrieved 12 June 2010 from http://www.rise.org.au/pubs/Solar09Paper165_MCalaisARuscoeMDymond.pdf.

Envirogroup, retrieved 12 June 2010 from http://www.envirogroup.com.au/content/transformerless-inverters.

German Energy Society (2008), Planning and Installing Photovoltaic Systems: A Guide for Installers, Architects and Engineers, Earthscan, London.

Robertson, H. ˜Optimising photovoltaic systems,’ retrieved 12 June 2010 from

http://www2.electronicproducts.com/PrintArticle.aspx?ArticleURL=fapo_Avnet_apr2010.html.