I have heard some of the hype about a proposed solution to all our energy (and economic) worries. My first reaction is to fire up the bullshit detector. Too often great publicity is given to fanciful schemes that hide more subtle attempts by people to dip their hands in the public purse. The guys that tout every few years for a multi million euro feasibility study on building a tunnel under the Irish sea which everyone knows will never be built are a good example. But I am an Engineer. I can do the maths on this scheme. So I can give a first estimate on whether it is a steaming heap of manure, or something that might have some promise.

The SoI guys quote a figure of 3500 MW generating capacity to be required from wind power. That number is enough to make a start on some calculations. Calculations that look at the feasibility of this is from a physics, and laws of nature stand point, before you ever get into things like the economics of the proposal, or the desirability of despoiling the mountains of the west with dams and massive construction projects.

MacKay and Hot Air
My handbook for the calculations is David MacKays “Sustainable Energy—Without the Hot Air“. He is a physicist in Cambridge University. Annoyed by people throwing numbers around about green solutions to energy problems he sat down and did some basic calculations to show what was and wasn’t possible. And then he wrote a book about his findings. To show how sincere he is about helping people understand this stuff, he has made the book freely available on his website withouthotair.com. He has several chapters on wind power, and uses Irish data (from Eirgrid) for much of his calculations.

Now a note on units. 1MW is a MegaWatt or a million Watts, a typical unit of power generation or consumption. You will know Watts from light bulbs or microwave power. This is an instantaneous measure – how much electricity is consumed in a second. The ESB prefers to measure your electricity consumption in kWh or kilowatt hours. This is equivalent to 1 kilowatt (or 1000 watts) used for one hour. The same principle is applied to the national power consumption amount and generation capacity, just the units are larger. Typically people use GWh (gigawatt hours = 1,000,000,000 Watts for one hour) or MWh. To simplify things I will work in GWh and MWh per month.

To convert a MW rating then so you multiply the MW by 24 (hours in a day) and 30 (days in a month). So Moneypoint , a 915MW power station provides 658 GWh of power to Ireland per month. Is that clear? :-)

The Questions
SoI state that we will need 3,000MW of wind generated electricity capacity. And that that will require 1% of Irish land area to generate.

Based on their estimates of the scale of the project I want to know, do their numbers add up, is this technically possible, and how big a project are we looking at?

My starting numbers

  • Current Irish power consumption from the CSO: about 2,500 MWh per month.
  • Area of Ireland from Wikipedia: 81,638.1 km^2 (square kilometres).
  • Average Irish wind speed, from Met Eireann: 7 m/s (from the chart on the top right of the linked page).
  • Current land use in Ireland from the EPA: 1.9% artificial (including all urban development, transport infrastructure, landfill, etc.)
  • Irish load factor for wind power from the Irish Wind Energy Association: 35% and I am being generous here as I assume that all the power is generated on the west coast. Note how similar the rest of their numbers seem to those quoted by SoI.
  • I am using MacKay’s calculations for the amount of power that can theoretically be extracted from the wind [Part III - Technical Chapters, B Wind]. He derives the formula to power output for a wind farm related to wind speed. You can review his calculations yourself, but as a mechanical engineer I can tell you they look sound to me. He is very generous with his view of 50% efficiency from turbines.

Well for starters the “current Irish power consumption is 2,500GWh per month. The SoI figure of 3,000MW is about 2,520GWh so they are planning to effectively double Irish electricity generation capacity. Can we get that much power from the wind?

I plugged a 7m/s average wind speed into MacKays formula and came up with an average power of 3.5W/m^2. You have to reduce that by the load factor of 35%, which gives you a net power of 1.23W/m^2.

Dividing that into the need to 3,000MW of power and you discover that the required wind farms will need 2,448km^2 of land. This is less than the Irish national land area, so I guess you can say that, yes, in theory we could generate enough power to run the country. The problem here is the size of the wind farms needed.

2,448km^2 is equivalent to 3.0% of the land area of the whole island, or 3.5% of the republic. For starters this means SoI’s figure of 1% is bullshit. But that 3.5% needs to be put into perspective. It is a tract of land greater than about the same size as (edited the typo) all of country Limerick (2,686km^2), covered with wind turbines. Today, a total of 1.9% of the country is “artificial” and has been built on. We are talking about taking pretty much the same amount of area again and covering it in wind turbines. Regardless of the cost of the hardware this is a massive undertaking that would totally change the entire western seaboard, even before you start to look at the economic cost of such a construction project.

And even then it isn’t sure that this would provide us with all the power we need. MacKay goes into the problems of intermittency in wind power at length in his book, using data from Ireland. This is the issue of the wind dropping, or just not being there when the power is needed. There are times when generating capacity drops to less than 2% because of light winds, sometimes for periods of up to 5 days. The SoI solution is pumped storage by damming glacial valleys. I haven’t gone into the calculations for that part of their solution yet. If I get a chance tomorrow night I will look at them.

The unspoken questions
In all of this I have not asked some very relevant questions. Would we want the western sea board, the most beautiful part of the country covered by thousands of square kilometers of wind turbines? And would we want the uplands there transformed by gigantic dams, lakes and power transmission infrastructure?

Don’t get me wrong. I am all for wind power, I do find wind turbines attractive. But the scale of what is being suggested here doesn’t seem to be grounded in reality at all. There will be a staggering price in terms in damage to our environment from building over more than 10% of the land of the 5 big western seaboard counties (Donegal, Mayo, Galway, Clare and Kerry). Even if the the turbines themselves were invisible just imagine the impact of service roads, transmission infrastructure, foundations and support structures? And there there would be the dams for the pumped storage facilities. Something I have not even got to looking at.

This scheme strikes me as an over the top think tank fantasy that has escaped out into the wild. What gives me hope, is that the whole scheme is so deranged that it will never be implemented. I just hope no-one in government decides that it might be a good idea to spend some real money looking into this crack pot idea.