DEBUNKING ENERGY MYTHS:Can it be that simple? This question dominates your thoughts when talking to Prof David MacKay. And it will creep up on the lucky few who gather at Trinity College Dublin on Wednesday, as MacKay discusses the 21st century's greatest challenge – energy – using language we can all understand, writes RICHARD GILLIS

When he takes questions at the end, he may, as he did during this interview, get out his pen and paper to work out the answer: “Right, there are four million people . . . one moment . . .”

His clarity is striking, because a debate as important, and valuable, as energy quickly becomes mired in claim and counter-claim, as vested interests – government, venture capitalists, tech providers, eco campaigners – attempt to shape the agenda to their own ends. MacKay is a curious physicist; he is not pushing anything, other than the facts.

Last year the British physicist published a book called Sustainable Energy – Without the Hot Air, first on the internet and then in print form, using £10,000 (€11,200) of his own money. It has been described as "the Freakonomicsof energy and climate" and received rave reviews from the Economist, among others. As a result, his media schedule is filling up quickly: The Irish Timeswaited in line with CNNand the New York Timesfor his attention.

A professor in the Department of Physics at the University of Cambridge, he studied natural sciences at the university and then obtained his PhD in Computation and Neural Systems at the California Institute of Technology. He returned to Cambridge as a Royal Society research fellow at Darwin College.

He is known for his research in machine learning, information theory and communication systems, including the invention of Dasher, a software interface that enables efficient communication in any language with any muscle. He has taught physics at Cambridge since 1995. Since 2005, he has devoted much of his time to public teaching about energy. He’s also a member of the World Economic Forum Global Agenda Council on Climate Change.

The secret ingredient of MacKay’s book is that he allows the facts to speak for themselves and enables the reader to make like-for-like comparisons. All forms of power consumption and production are described using a single unit of measurement – kilowatt hours per day (kWh/d). As a guideline, 1kWh/d equals one 40-watt lightbulb, kept switched on all the time. Drive a car for 50km and you consume 40kWh/d, or 40 lightbulbs on all day.

On his website there is a short film that should be required viewing in every school and college in the country, in which he compares instances of everyday energy usage and gently undermines our “eco gestures”, such as feeling worthy for turning off the mobile phone charger. A charge uses as much energy as driving an average saloon car for one second.

And if the simplicity of the maths is entertaining on a micro level, it pales when compared to the impact it has when discussing the energy needs of countries such as Ireland.

“The area of Ireland per person is 17,500 square metres, so if around 2.5 per cent of Ireland was covered with wind farms, it would give us 22kWh per day per person or roughly one sixth of Irish consumption today, which is 120kWh per day per person (that’s energy in all forms, including transport and heating, not just electricity). If we cover 10 per cent of Ireland with wind farms, it would account for more than half of Ireland’s current total of energy consumption, including transport and heating and electricity. If you wanted to deliver all of Ireland’s consumption, assuming no reductions, entirely from wind power, it could be delivered, on average, by about 60 gigawatts of nameplate capacity wind farm. If each turbine is a 2 megawatt turbine, which is the standard size today, we would need 30,000 turbines .”

The cost of one turbine is about £2 million (about €2.25 million) for a 2MW turbine.

“The total cost would be in billions, but if that is spread over 40 years, running up to the target date of 2050 to decarbonise ourselves, then the spend rate would be a couple of billion per year, so, not outrageous when put against current energy spend and a fraction of what the governments have paid to bail out the banks.

“Let’s be realistic. What fraction of the country [in this case the UK] can we really imagine covering with windmills? Maybe 10 per cent? Then we conclude: if we covered the windiest 10 per cent of the country with windmills (delivering 2W/m²), we would be able to generate 20kWh/d per person, which is half of the power used by driving an average fossil-fuel car 50km per day.”

If Ireland were to go for windpower in a really big way, we’d need a method of coping with fluctuations in wind, requiring storage systems, which add to the cost substantially.

“The fluctuations mean we’d need a big cable to Britain to allow Ireland to export and import electricity according wind power. Would Britain be able to provide that missing power? That’s not clear, so probably Ireland would need to link to Iceland or France, in addition. It’s not easy to make a plan that adds up without making some implausible sounding assumptions.” These might include solar farms in foreign deserts, for example.

The barriers to successful decarbonisation are being removed slowly. “In Britain, putting up wind farms is perfectly profitable, thanks to the Renewables Obligation, giving a subsidy to wind. It gives people loads of money to do so. What makes it difficult is public opposition and getting through the planning process. There are similar subsidies in Ireland. As long as subsidies are in place to recognise that fossil fuels are not paying their fair way, in that they are allowed to pollute for free, and if the market is structured favourably, it should be economical to set up storage units too.”

Wind, he says, is the technology with the biggest potential to “scale up”. Wave is an undeveloped technology: “The bottom line is that the amount of energy you could get from wave is very small, in Britain it works out to be around 4kWh/d per person, or 4 per cent of our total energy consumption. In Ireland it would be a bit more, but still a partial contributor. Tidal power I’m very excited about – there are large tidal resources in the Irish Sea, and underwater windmills could be inserted under the sea and work in much the same way as windmills do on land, without spoiling the view. Again its potential contribution is only a part of our current needs to sustain our European lifestyles.”

The debate is confusing because people use different units of measurement. “If they want to sound impressive, they say they are providing energy for so many thousands of homes. Using nebulous phrases like ‘the home’ makes it hard to compare things. The lack of a single unit is the problem. Almost always, people are put on sides of a debate, and are trying to score points over each other to make their argument sound good,” says MacKay.

“It is rare to come to this without an agenda. With numbers you can always make anything sound wonderful or awful. Putting up 10 nuclear stations in the UK would power all our energy needs. Alternatively, they would only reduce carbon emissions by 4 per cent. Both of those points of view are true. You can make the arguments for wind farms. The wind farms that Britain is perhaps going to have by 2020 could power all of Britain’s homes, or you could say they would only reduce carbon emissions by 4 per cent.”

Simple then. MacKay detests hype and he is now devoting his life to debunking it. So, to call him brilliant would probably irritate him. But he may have to get used to it.

• David MacKay is talking at Trinity College, Dublin on Wednesday, May 13th. His book Sustainable Energy – Without The Hot Air, is published by UIT (£19.99, paperback; £45, hardback), or can be downloaded free from withouthotair.com

Greenwashing and the kingdom of codswallop - Prof MacKay

WE AREinundated with a flood of crazy innumerate codswallop. The BBC doles out advice on how we can do our bit to save the planet - for example "switch off your mobile phone charger when it's not in use". If anyone objects that mobile phone chargers are not actually our number one form of energy consumption, the mantra "every little helps" is wheeled out. Every little helps? A more realistic mantra is: if everyone does a little, we'll only achieve a little.

Companies contribute to the daily codswallop as they tell us how wonderful they are, or how they can help us “do our bit”. BP’s website, for example, celebrates the reductions in carbon dioxide (CO2) pollution they hope to achieve by changing the paint used for painting BP’s ships. Does anyone fall for this? Surely everyone will guess that it’s not the exterior paint job, it’s the stuff inside the tanker that deserves attention if CO2 emissions are to be significantly cut? BP created a web-based carbon absolution service, targetneutral.com, which claims that they can “neutralise” all your carbon emissions, and that it “doesn’t cost the Earth” - indeed, that your CO2 pollution can be cleaned up for just £40 per year. How can this add up? If the true cost of fixing climate change were £40 per person, the government could fix it with the loose change in the Chancellor’s pocket.

Even more reprehensible are companies that exploit current concern for the environment by offering “water-powered batteries”, “biodegradable mobile phones”, “portable arm-mounted wind-turbines”, and other pointless tat.

Perhaps the worst offenders in the kingdom of codswallop are the people who really should know better: the media publishers who promote the codswallop - for example, New Scientist, with its article about the "water-powered car".

In a climate where people don’t understand the numbers, newspapers, campaigners, companies, and politicians get away with murder. We need simple numbers and we need them to be comprehensible, comparable, and memorable.