Harnessing the winds of change
Cape Town - It’s an ill wind that blows no good, they say – so next time you want to curse the Cape Doctor or a north-westerly gale, stop for a moment and think, because this very wind might be powering the kettle for your cup of tea or providing the electricity for your lights and television.
That’s because two major commercial wind farms are now in operation close to Cape Town and are feeding power into the national electricity grid, which in turn supplies the city’s homes and businesses.
One of them is the Hopefield Wind Farm 5km south-east of Hopefield in the Swartland, a 66.6 megawatt facility that achieved “COD” – commercial operation date – on February 1. The other is the Dassiesklip Wind Energy Facility, just outside Caledon in the Overberg, which has nine wind turbine generators with a total 27MW capacity and was officially opened on February 18.
They are among already approved wind farms in South Africa that will be providing up to 1 983MW of power through more than 700 turbines over the next 20 years. Countrywide, five new wind farms are already in full operation, 15 large-scale wind farms are currently under construction, and another seven are approaching financial closure.
According to the SA Wind Energy Association (Sawea), power produced by these wind farms will be significantly cheaper – as much as 30 percent – than electricity generated by the new coal-fired mega-power stations, such as Medupi, when they eventually come on stream. And that’s not counting the huge indirect pollution costs of coal.
Also, communities living within a radius of 50km of these new wind farms will benefit through compulsory shareholdings of between 2.5 percent and 40 percent of the projects as well as from more than R5-billion that the wind farms will spend on socio-economic (R4.2bn) and enterprise (R1.2bn) development over the next 20 years.
The cheaper generating cost of wind power is “good news”, says Sawea chief executive Johan van den Berg.
“(But) the really good news story is that wind power and its sister renewable energy projects in South Africa (like solar power) will unlock rural development and socio-economic upliftment at a scale that is almost certainly unmatched by anything the private sector has achieved or attempted in this country before.
“That (R5bn) is a pretty staggering number, so if we can get it right, it will be good.”
The Hopefield Wind Farm has been developed by Umoya Energy, a company established specifically for this venture and that was one of the successful bidders in the first round of the government’s renewable energy independent power producer procurement programme. This is the vehicle for achieving 3 625MW of electricity through large-scale renewable energy projects, such as wind and solar, throughout the country over the next two decades.
Three rounds of bids under this programme have already been completed and, for wind power, have already proved so popular with investors that the bids in the third round were hugely over-subscribed.
The price the government will pay for wind-generated electricity from approved projects has dropped by up to 42 percent: from R1.14 per kilowatt hour in the first round of bids to 89c/kWh in the second, to an average of just 74c/kWh in the third round, where the lowest price was just 66c/kWh.
A fourth round is scheduled to be completed in mid August.
One of the reasons that made the Hopefield site attractive – all proposed wind farms are subject to environmental impact assessments – is its proximity to the national grid: Eskom’s 132kV (kilovolt) Moorreesburg to Aurora line is just 2km away.
Another was its easy access from Saldanha Bay port, where the Chinese-manufactured hubs, blades and nacelles (the housing for all of the generating components, including the generator, gearbox, drive train and brake) for the 37 turbines were delivered.
The hubs of these turbines stand at 95m, but at 1.8MW they are not particularly big as far as wind farm turbines go.
The industry average turbine is about 2.3MW; those at the Caledon plant stand on 100m hubs with a 113m rotor diameter that generates a huge 3MW; while the true giants of around 6MW – with 75m blades – are found in offshore wind farms. Prototypes of 8MW are already being tested.
Sam Cook, Umoya’s technical manager, says there is “quite a bit of variability” in the wind speed on their 900ha Hopefield site, averaging around 6.5m a second to about 8.5m/s.
But the blades are adjusted – technically, “feathered” – so that there is not that much variability in the operation of the rotor which is designed to turn at between nine and a maximum of 17rpm in low to moderate winds.
To the eye, the blades appear to be turning quite slowly, but their 100m diameter means that at maximum revs, the tip of the blade will actually be turning at more than 300km/h.
The turbine cuts out if there is prolonged wind speed of more than 20m/s – “It can happen, but it’s very seldom,” says Cook.
But the wind doesn’t always blow, right? So how can we depend on wind power?
This is an argument that is frequently made by opponents and sceptics of wind power, especially relating to the so-called “base load” electricity requirements of the country.
“We’re so far away from that (argument) we don’t even need to talk about it,” responds Cook, and Van den Berg agrees.
The wind is always blowing somewhere and Eskom already manages a great deal of variability in the power supply. In fact, one of its gas-fired “peaking plants” that is designed for short-term, peak demand time generation but that is actually being used almost constantly, is just around the corner from the Hopefield Wind Farm, they point out.
Renewable energy generation in the form of wind and solar can be brought up to at least 20 percent of the supply to the national grid by 2030, as envisaged by the government’s IRP (integrated resource plan for electricity) 2010-2030, says Van den Berg. “And we’re a long way from that now.”
He points out that on Christmas Day last year – admittedly when commercial demand was probably not at its peak – Denmark’s wind energy production was 112 percent of total demand in the country.
And on “good days”, highly industrialised Germany is able to meet its total energy demand from renewables, he says.
There are still some doubting Thomases about wind power’s potential and it does have environmental impacts – bird and especially bat mortalities are major concerns in some areas, for example. But given the global imperative for clean energy generation, it’s… well, arriving locally like a breath of fresh air. - Cape Argus