Original URL: http://www.theregister.co.uk/2009/06/24/mcelroy_globo_windfarm_paper/

Prof: Global windfarm could power entire human race

Provided most of it remains in misery, that is

By Lewis Page

Posted in Science, 24th June 2009 10:32 GMT

Analysis Harvard University boffins have published an analysis of how much energy the human race could possibly produce from wind power, and we thought we'd have a bit of a play around with their numbers.

Career Harvard enviro-prof Michael McElroy, assisted by Xi Lu and Juha Kiviluoma (now working in Finland) published their paper Global Potential for wind power in the Proceedings of the National Academy of Sciences (free pdf). They say:

A network of land-based 2.5-megawatt (MW) turbines restricted to nonforested, ice-free, nonurban areas operating at as little as 20% of their rated capacity could supply >40 times current worldwide consumption of electricity, >5 times total global use of energy in all forms.

This statement has been widely taken to mean that "Wind Farms could supply planet's power", or even "wind power could provide for the entire world's current and future energy needs".

So can it? Bottom line, according to the Harvard trio, how much energy can the planet Earth possibly generate from wind?

Well, McElroy and Co say that if wind farms were be built absolutely everywhere onshore they possibly can be where the turbines can operate at a load factor of 20 per cent or better - that is, over time they produce an average 20 per cent of their maximum rated capacity - you get a grand worldwide total of 690 petawatt-hours every year. At the moment, people don't generally bother building a windfarm unless they think they'll get 30 per cent, but no matter.

Six hundred and ninety PWh is certainly a lot of energy. Five times the present-day human usage, as the profs say, sounds reasonable.

But hold on. There are 6.7 billion people in the world - and counting. The only reason they get by with a measly 140 PWh a year or so is that the majority live incredibly unpleasant lives. Half a billion in sub-Saharan Africa alone have no access to grid electricity at all, for instance. Electricity, roads, rails, industries, homes, laundry, food, water, welfare states, medicine, education, coolness for the hot and warmth for the cold - even the smaller things like IT and aviation - it all needs energy and plenty of it.

Profligate powerhog Americans, indeed, each use a hefty 91 megawatt-hours annually (according to Professor J C MacKay of Cambridge University). Even relatively restrained Europeans burn through 46 MWh/year.

If everyone on Earth aspires one day to live at the sort of level Americans do now, and assuming the world's population stabilises at 7bn, we're looking at global demand of 637 petawatt-hours - almost all of Professor McElroy's best-possible global output for onshore wind. Even a European lifestyle would gobble half the total possible production, leaving a rather uncomfortable margin for mistakes, future progress etc.

However, Prof McElroy then adds in bigger 3.6 megawatt offshore turbines on every bit of sea where they could do load factors of better than 20 per cent. He's not wildly unrealistic, though: he sternly restricts himself to waters less than 200m deep [!] and within 50 miles of the shore. (The most heavily-trafficked seas of all; but pass on.) That bumps the total up to 840 petawatt-hours annually.

Surely we're there now? Provided the world's population doesn't triple, everyone alive could live at European levels of energy consumption just on wind power. Problems solved, assuming we can persuade the Americans to live in apartments more often and get out of their cars now and then.

Just a 100m-tall windmill tower for every twenty families and we're set

Worryingly, though, the world's population tripled just in the last century. And McElroy's global windfarm is going to take some time to build, as it requires the erection of massive 100m-tall turbines on every single piece of land where the load factor would be better than 20 per cent. By our calculations that would require around 60 million turbines for a present-day world population living at European levels of energy use. We're talking about a turbine as big as a cathedral for every hundred people on the planet; and unlike cathedrals, these things wear out and have to be replaced every couple of decades.

We won't only need turbines, either. Just as the turbines were absolutely everywhere, so too would the high-capacity power grid need to be - covering the vast bulk of the US interior, the Siberian tundra, the Himalayas, the Andes, the Sahara - everywhere that doesn't at the moment have trees, glaciers or buildings on it. The grid will also need to go underwater to cover much of the continental shelf.

Then remember, to have wind turbines and a power grid you must also have transport - good transport, capable of moving huge pieces of machinery. In the all-electric world of the future there won't be much aviation (there isn't any significant amount now which can move wind turbine parts, for that matter). Thus we need high-capacity roads or rails criss-crossing all those mountain ranges and deserts.

Not only will every hundred people alive (twenty or fewer couples of working age) need to save up for a new hundred-metre-tall wind turbine every couple of decades - many of us struggle to pay for a relatively poxy little house on such a timescale - they'll have to pay for the upkeep of a hell of lot more road and power line than Americans or Europeans now do. And these will be expensive roads and powerlines, all the more so as large areas of the world are occasionally subject to days-long calms, meaning that the global grid backbone will need to be very high-capacity indeed so as to carry in huge amounts of juice across continents at need. Or alternatively one would need another world-girdling mega-engineering complex of pumped storage artificial lakes, dams and hydropower machinery.

Even McElroy and his colleagues admit that:

Given the inevitably greater expense of establishing wind farms in remote locations and potential public opposition to such initiatives, it would appear unlikely that these resources will be developed in the near term.

And we haven't even yet got into the fact that McElroy takes his windspeed data from boundary layer analysis, a method which has the advantage of easily covering the whole world but which has produced seriously overblown (cough) windpower results in the past.

So actually there's a big, big further cut to be made to McElroy's bottom-line figures - probably one or more orders of magnitude. But the figures can't take such a cut and remain meaningful. Be nice and say the best that global wind can do is a tenth of what McElroy says - already it's well down below present-day use with us mainly living in poverty and squalor, let alone the human race's actual reasonable requirements.

The people of the world simply can't live decent lives on wind power, QED. Wind power cannot, in fact, provide for the world's current and future energy needs. It seems evident that it's going to be part of the solution, but something else - probably several very large somethings - will be required to go with it. ®