CAMPING - POWER & LIGHTING
We’re all familiar with solar camping power, but wind power is also a viable way of generating electricity. Why don’t we see many mini-windmills around campsites?
Commercial solar and wind ‘farms’ are familiar sights around the world and mini-solar, such as we have on the roofs of camper trailers and caravans, or pegged out in the sun beside a shaded camp, are also quite familiar. But we don’t see small-scale wind turbines being used very much.
That may seem odd, given that many cruising yachts have a combination of wind and solar power. Why not a campsite turbine, to complement solar panels, you may well ask.
There are some very good reasons why wind power doesn’t make it in the camping world, but the most significant are the output characteristics of wind turbines; the average wind speed around Australia and the ‘ground effect’ on wind turbines.
The average wind speed around Australia has been recorded since 1893 and sits between 12km/h and 18km/h.
Sure, there are storms that see wind strong enough to blow a dog off a chain, or the oysters off the rocks, but the average national wind speed is relatively low. Even worse, from a wind energy point of view, that wind strength is reduced by the very things we look for when camping: trees.
Ground-based obstacles reduce wind speed and change its direction erratically. It’s not a problem on a cruising yacht that’s floating on an unobstructed sea, but is a big problem for shade-loving campers.
Commercial wind generators aren’t made that huge size and height for fun: they need to be tall, to operate in unobstructed, higher-speed air flow and they need big blades, with huge swept areas, to maximise the effect of relatively low wind strength.
The few people who do use wind power as part of their camping kit do so usually by putting the wind turbines on tall masts, so they can spin in clear air.
That’s bad enough, but it gets worse, when you consider the nature of a wind turbine. Although not needing anything like turbocharger speed – yes, a turbocharger is a turbine – a wind turbine still needs to spin to at least 1000rpm, to generate electricity.
The typical giant commercial wind turbines we see dotted around the landscape rotate only five to 15 times each minute and are fitted with gearboxes to raise that input speed to suit their generators.
Typical small wind generators, of say 250-500-watt rating and with one-metre-diameter blades, may seem like a great addition to anyone’s camping-power kit, but the devil is in the detail.
Check out the specifications and you’ll see that 250-500W rating relies on 50km/h wind speed. Wind speed is often ‘hidden’ in wind turbine specifications as metres per second (m/s) and the simple conversion is to multiply that figure by 3.6 to discover the km/h speed.
If 50km/h wind speed doesn’t sound like much, check out the Beaufort wind-strength scale and you’ll discover it’s sufficient for the BoM to issue a strong wind warning. We sailors probably wouldn’t put up a big spinnaker in those conditions and most people would be unhappy campers, with double-roped-down tents and folded awnings!
There’s even more bad news, because wind turbine power output is calculated by multiplying the air density by the swept area of the blades by the wind speed cubed, then dividing that result by two. The fact that the wind speed figure is ‘cubed’ in this calculation means that the difference between low wind speed and high wind speed power output is huge.
For example, the 250-500W/50km/h wind turbine may produce as little as 20-30W in Australian average wind speed conditions and hardly anything at all in a 12km/h breeze. The investment cost of a wind turbine might be better spent on additional solar, or a small petrol generator, for when the sun doesn’t shine.
So, get some portable solar panels you can put out in the sun, while you’re camped in the shade and leave your wind generator on the boat!