Q&A: Small wind considerations

In the article on small wind power in ReNew 122, I found it odd that there is no mention of the possibility of lightning strikes nor maintenance considerations, especially when we are told that tower heights of 36 to 42 m are the norm in some countries.

I had a grid-feed PV system installed in Grafton and a stand-alone system in Coonabarabran. Both companies advised against wind, claiming that the electrical surge from a lightning strike could flow to the inverter and other equipment and damage the whole system.

Pending sale of the Coonabarabran property, I hope to install a stand-alone system at a different site that lacks neither sun nor wind and where the only turbulence would be created by the house itself which, though small, is two storeys at the rear, with the ridge being just under 6 m. Of the two installers I have spoken to in this district, one said the same as the two companies mentioned above and the other more or less said that by the time anything happened to the turbine it would probably have paid for itself, which to me is a completely unsatisfactory attitude.

I am probably better to stick to PVs but, as the article says, you do see numerous small turbines around the countryside apparently in good order. For that matter, what happens with the old Southern Cross mills or the commercial wind turbines? I find it very puzzling that, at this relatively late stage, there seems to be no consensus view as to what does or does not work with small wind, and would suggest that it merits an article in itself.

Dick Varley

Lightning protection is a complex area. In my experience, there are loosely three schools of thought for tall objects including wind turbines. The first two cost money. They are:

  1. Divert the lightning, e.g. using a finial and earthing (not very practical for small wind turbines) and/or MOV surge protectors (effective but have limited lifespan).
  2. Insulate/isolate the turbine and electrical installation from earth as much as possible so the lighting naturally takes another route.
  3. Do nothing—which costs nothing up front obviously but of course carries far higher risk of expensive damage later.

Neither options one nor two are guaranteed to work; in locations not prone to lightning some argue neither are guaranteed to be necessary either, hence school of thought number three.

Because lightning is not predictable and the level of risk is location-specific, there is no clear ‘best’ approach for lightning protection of turbines. I’ve known of one wind turbine on a 20 m tower on a coastal hill to get struck almost annually, but many other turbines that have never been hit. I’ve worked on 80 m wind monitoring towers and found that, on average, these seem to get struck once every five to ten years.

Lightning risk is only one of a long list of environmental considerations you would make when assessing a site, and the point of Katie’s article is about avoiding the main pitfalls of choosing a wind site. So, while clearly lighnting protection is a consideration for designing a turbine system, I would only consider the highest risk locations to be absolute showstoppers for wind, and only where there are clearly other energy options.

Most people do find solar to be the best option, given how much cheaper it has become in recent years and the fact of it being solid state and therefore lower maintenance, quieter etc—but wind energy can still be the best choice for some locations.

Craig Memery, ATA Policy Team

EOFY ReNew 2017