Spirit of Ireland and Pumped Storage Proposals

Spirit of Ireland more than a few wires short of a connection

A number of articles in the Irish press have been marketing something called Spirit of Ireland. The product being offered is not a racing horse, not an an alcoholic beverage, new brand of deodorant, or trendy docklands night club, but a series of immense elevated inland lakes filled with seawater. It is claimed these lakes, when emptied through turbines, will enable Ireland meet all of its electricity needs from renewables by balancing out the fluctuating supply from intermittant renewable sources of energy. The proposal is also predicated upon the erection of many of thousands of huge wind turbines, in order to provide the electricity necessary to pump hundreds of millions (or possibly billions) of tons of sea water from the Atlantic Ocean into the inland lakes, or to feed directly into the national grid.

The proposals are the latest in a long line of fantastic 'solutions' to the vexing issue of long term energy security. Like many other science fantasies, at first glance they may appear to have some credibility.

As stated,the proposal is predicated upon erecting enough wind turbines to meet Ireland's electricity requirements, either directly through supply directly to the grid or indirectly via the pumped storgae facilities (the inland lakes filled with seawater).

Ireland currently uses some 27 TWh (Terawatt hours, equivalent to one billion kilowatt hours) of electricity per annum. The current installed wind capacity is about 1100 MW (Megawatts), delivering some 2.7 TWh of electricity per annum or about one tenth of the total demand. The Spirit of Ireland proposal is to massively ramp up wind capacity.

Wind is an intermittent resource and unfortunately output cannot be adjusted to match demand like a conventional power station. Electricity demand is often highest during winter anti-cyclones, in other words during periods of cold settled weather when wind speeds are typically very low.

Wind output is often highest during the milder conditions associated with cyclonic Atlantic weather systems. Also, during any given day, electricity demand varies enormously. It is lowest during the middle of the night when most people are in bed, work-places empty, and industrial output is at its minimum.

This winter, output from Ireland's wind farms was particularly low, and often failed to reach 5 percent of demand. On occasion, output from the wind sector was below 1 percent of total demand. The average for the period from the start of December to the end of February was about 9 percent. This should not be taken to imply that 11 times the current installed capacity of 1100 MW would have met Ireland's electricity requirements during this period, as an installed capacity of 12000 MW would have led to massive oversupply on occasion, whilst still only contributing a small fraction of electricity requirements during periods of settled weather.

In order to fully utilise wind-generated electricity surpluses, one must store the energy until it is needed.

A cursory examination of Eirgrid data shows that maximum output (output within 20 percent of the maximum possible) occurs less than 5 percent of the time. By comparison, average output from wind installations is only one quarter to one third of maximum output. This relationship between the average and maximum is usually referred to as capacity factor. Capacity factor is highest on sites with good wind regimes (high wind speeds and low turbulence) and where down-time for maintenance and repairs is at a minimum. In Ireland, the overall capacity factor of the large wind sector is around 30 percent. However, this will fall in the future as the best sites become fully developed and poorer sites have to be used.

Even at a very optimistic 30 percent capacity factor, to produce an equivalent amount of electricity from wind as is currently used by Ireland would require an installed capacity of around 10,000 MW (10,000 MW x 8760 hours per year x 30 percent capacity factor).

That is not to say an installed wind capacity of 10,000 MW could actually meet Ireland's electricity requirements as even with adequate storage capability, there would still be wastage and conversion losses during the storage and transmission processes of anything up to 30 percent. In reality, 10,000 MW of installed capacity would be nowhere near enough. Taking into consideration wastage, conversion losses and lower capacity factors, Ireland would need approximately 16,000 MW of installed wind capacity to meet current electricty demand from wind and pumped storage alone ( other independent estimates put the necessary installed wind capacity even higher).

As explained below, there would also be enormous difficulties on the storage side.

The only proven technique for storing electricity on a large scale is pumped storage. Surplus electricity is used to pump water to (relatively) high altitude storage dams. When extra electricity is needed, the water is let out of the dams through turbines. Ireland already has one such pumped storage facility, at Turlough Hill in the Wicklow Mountains. Built between 1968 and 1974 at a cost of around £20 Million, it comprises two reservoirs. The upper reservoir - the one used for electricity generation - contains 2.3 million cubic meters of water. In today's money, afacility similar in size to Turlough Hill would cost around €200 Million.

The purpose of Turlough Hill is to provide some balancing capability between day and night time supply and demand. This it achieves. The facility is able to deliver up to 292 MW of electricity - about one tenth of the average national demand - continuously for about five hours. Not weeks or even days: hours. At this point the storage facility is fully depleted, just the same as a rechargeable battery that has been fully run down.

The total energy storage capacity of Turlough Hill is thus about 1.6 GWh (Gigawatt hour: one million kilowatt hours), or roughly one two-hundredth of one percent of Ireland's annual electricity demand.

In order to balance out seasonal variations in wind energy, Ireland would need storage capacity of 2000-2500 GWh (2-2.5 TWh) to meet current national electricity demand solely from wind ...about one tenth of annual demand or equivalent to 1500 times the capacity of Turlough. 

Using seawater in pumped storage at inland locations is a new and largely untested idea. Currently, there is only one (experimental) seawater-based pumped storage facility in the world - at Okinawa in Japan. The Okinawa facility is tiny - only one tenth the size of Turlough Hill. The reservoir is only 250 metres in diameter and in many respects resembles a large outside swimming pool (it is even lined with rubber sheeting). Maximum output is 30 MW. This output can be maintained for about 5 hours. In other words, it would meet the electricity requirements of a small Irish town for a few hours. It reportedly cost $200 Million to build, which makes the Turlough Hill facility look positively good value for money.

Further info

In response to the many requests for more details, further information has been provided below:

Monthly variation in energy from wind installations

As a consequence of seasonal variations in wind speed, approximately two thirds of the total annual electricity delivered to the grid from wind installations occurs during the October to March period.  Wind electricity delivered in December and January is up to three times the delivery in June and July.

Although demand for electricity also varies on a seasonal basis, the differences are not so dramatic.  For wind installations to provide Ireland with electricity all year round, a storage capacity of up to ten or fifteen percent of total annual demand would be necessary.

For the sake of argument we will assume a storage requirement of 2.7 TWh: ten percent of annual demand.

Storage Potential

Ignoring the efficiency of the turbines for a moment, the potential energy (pe) of water in pumped storage is expressed by the formula:

 pe = MgH

Where M = mass, g = acceleration due to gravity (9.81 m s-2), a H = height (head)

Thus 1kg of water raised 1 metre has potential energy of 9.81 joules

1m³ of water (1000kg) raised 1 metre has potential energy of 9810 joules

1 m³ raised 100 metres has potential energy of 981,000 joules

Converting to kWh:

1m³ raised 100 metres has potential energy of 0.27 kWh

10,000,000,000m³ raised 100 metres has potential energy of 2.7 TWh

This is equivalent to a lake of 1000km² in area and 10 metres deep, raised to an elevation of 100 metres above turbine height.To allow for evaporation losses, seepage, sedimentation, and wind turbine to water turbine energy losses, one might wish to increase volume by a further 25 percent.

Hence a lake of 1250km², or three times the area of Lough Neagh. The construction of an artificial lake of this size, at a raised elevation, would present some interesting challenges.

Spirit of Ireland proposals

If one extrapolates down to the rather smaller Spirit of Ireland proposals, one finds that a 10 metre deep lake (or combination of lakes) of 32 km² in area, with a head of 100 metres (the height difference between the lake and the turbines), would have an electrical energy potential of (at best) about 75 GWh: about enough energy to meet Ireland's electricity needs for one day.

To extrapolate down from the calculations above:

320,000,000m³ raised 100 metres has potential energy of 86.4 GWh. This is before turbine energy losses (usually taken to be about 15 percent) are factored in.

This raises the question what is the Spirit of Ireland proposal really about, as clearly it cannot come remotely close to its implied objective of meeting Ireland's electricity requirements solely from wind energy. One explanation offered is that the purpose of the  facility would be  to store up  short term wind electricity surpluses, for selling to the Irish grid at peak times (typically between 4 and 7 pm on weekdays) when the tariff is highest.

A different explanation is that the project's main purpose is to make corporate-owned wind farms more profitable, by utilising more of the output during periods of high wind. This scenario is predicated on a lot of the associated costs being met from the public purse.

This raises the further question of what happens when the storage facilities are full and there is excess wind energy.

Surpluses may end up being sold to the UK via electricity interconnectors. Given that the Irish state would be expected to provide the grid infrastructure, and possibly some of the funding for the turbines and pumped storage facilities, this would create a situation whereby the Irish public subsidise Britain's electricity, whilst simultaneously enriching the shareholders of the companies owning the project.

How much would it really cost to meet Ireland's electricity needs from wind and pumped storage?

Each 1 MW of installed wind capacity would cost €2 Million. Hence 15,000 MW of additional installed wind capacity would cost €30 Billion. If the money is borrowed, interest replayments might add another 50 percent to installation costs.

The reconfiguration and strengthing of the existing grid infrastructure, and construction of multiple interconnectors to Britain capable of handling potential surpluses of 10 GW would cost nearly as much again.

The construction cost of 1250 km² of elevated inland lakes filled with seawater, having never been attempted anywhere in the world before, is hard to estimate. Extrapolating from Turlough Hill, €100 Billion appears very conservative, even before interest repayments are factored in. Thus we are looking at a total spend of in the region of €200 Billion at today's prices - equivalent to six times the annual state income, and more than the annual global spend on renewable energy.

In order to break even, the average unit price of energy supplied would be €250-300 per MWh, some 3 to 4 times the current wholesale price for wind electricity. This estimate is based on an average infrastructural life expectancy of 30 years, annual output of 27 TWh, and total costs (including maintainance) of €200-250 Billion. As this average figure would have to include cheap electricity off-loaded to the UK, the unit price to the Irish state would be considerably higher.

Ireland has already found out to its cost, what happens when it buys into speculative bubbles. The construction industry so lost the run of itself it was building 6 times as many new houses as were needed in Ireland. Just as there is an optimum amount of houses in Ireland, there is also an optimum capacity of wind turbines. This optimum capacity may lie at around 1500-1750 MW, although some analysts put the figure significantly higher. Above the optimum capacity, there is a law of diminishing returns that delivers progressively less benefit for each additional sum invested. Compared to houses, which might remain functional for many decades, turbines have parts that wear out, suffer from corrosion, and have relatively short lives. There is an on-going need for maintenance and replacement, which in turn requires additional investment.

Can the Irish state afford an investment of this scale? Irrespective of the outcome, the answer is unequivocally no. There are many other, much smaller, investments the Irish state could make into renewable energy, that would deliver much better outcomes. In particular, investments into sustainable forestry and anaerobic digestion would revitalise local economies, strengthen local communities, create employment, enhance the environment, and offer much better long term energy security prospects.

Spirit of Ireland proposals do not add up

On its website, Spirit of Ireland claims that its proposed project would allow Ireland to "achieve energy independence within 5 years". Not merely independence in electricity generation, but energy independence. It is important to note that electricity consumption accounts for only one third of total energy consumption.

Yet as demonstrated here, the pumped proposal outlined (two 4 x 4 km lakes each containing 160 million cubic metres of water) could only meet Ireland's electricity requirements (alone) for just one day.

The Spirit of Ireland proposals, quite simply, are unworkable. For politicians and the media alike to endorse this project, in the absence of any proper independent evaluation, or detailed appraisal of long term energy requirements and options available, is folly in the extreme.

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