Alex Murphy

Can we rely on renewables?

Abstract

This work seeks to determine the potential of renewable energy in Ireland. Estimates for energy consumption as well as production from renewables are determined; first based on the methods used in MacKay's "Sustainable Energy - Without the Hot Air", and secondly from a number of other sources.

It is seen that the potential of renewable energy in Ireland is enormous but our so is our energy consumption. A number of technologies, such as wave and tidal stream, are untested on a large scale. The current production from other technologies such as wind or solar would need to be increased by hundreds or thousands of times to meet our total consumption.

To be able to rely on renewables completely a vast increase in the current production would be needed, as well as some presently undetermined solution to the issue of storage.

Introduction

I chose this subject because I was wanted to investigate how far we can go with renewable based energy. One target of the European Unions climate and energy package is to have 20% of EU energy consumption to come from renewable resources by 2020. Although this is generally seen as commendable it does beg the question what happens after 2020? Is the goal to rely on renewable energy completely at some point? And if not how what will be used to make up the difference?

Although there is much debate about when it will happen, there is no getting around the fact that fossil fuels will run out at some point. Items related to renewable energy appear regularly in the media but there seems to be very little coverage on long term goals and strategies. When presented with the fact that a commodity on which we rely so heavily is due to run out in the not to distant future, the logical step is to determine how we are to survive without it.

These questions are clearly very broad. In order to reduce the scope of this project to a more manageable size I have chosen to focus solely on the Republic of Ireland. We are told frequently that we have a huge potential supply of wind and ocean energy due to the position of the country relative to the Atlantic. I wanted to investigate how large this supply actually is. Would we be able to rely on it solely in the future? If not how large would the shortfall be?

Sustainable Energy - Without the Hot Air

In his book “Sustainable Energy – without the hot air” [MacKay 2009] David MacKay seeks to gain an insight into the renewable energy debate focusing on the U.K. I agree with is assertion that vague adjectives such as 'huge' and 'vast' are often used when describing the potential of renewable energy resources, but do little to give any great insight into the debate. One of the questions that MacKay seeks to address is “Can a country like Britain conceivably live on its own renewable energy sources?”. It is clearly necessary that some consistent method be used in order to compare the various forms of energy that we consume, with the potential energy that can be gained from renewables. MacKay's method (which I shall refer to it as from now on) is as follows. Two columns are created. The first represents the energy consumption of the population of Britain and is broken down into eight sections: cars, planes, heating and cooling, light, gadgets, food and farming, stuff and finally public services.

The second column represents the total potential from renewable sources and is broken down into seven sections: wind, solar, hydroelectricity, offshore wind, wave, tide and geothermal.

The energy consumed/produced for each section is determined through various theoretical means. Finally the two columns are compared to determine if the potential energy from renewables outweighs the consumed energy. MacKay's book views the renewable energy debate at a macro level and there are many assumptions made when determining figures. This is perhaps a necessary consequence of looking at the 'big picture'.

If you don't to spoil the ending than look away now. After an initial assessment the two totals are similar. However MacKay purposefully attempts to boost the renewables column in his assessments and after taking common objections to renewable sources into account (e.g. 'not in my backyard') the production column decreases dramatically. MacKay concludes that unless there is a massive reduction in energy consumption, the U.K. will not be able to rely on energy from its renewable sources alone.

I will initially begin by applying to Ireland a similar method to the one used by MacKay. I will then look at estimates from some other sources, as well as statistics from renewable sources that are actually in use to determine how they compare with the theoretical ones.

Units

There are a number of different units commonly used to measure energy, some examples being Joules (J), kilowatt hours (kWh), tonne of oil equivalent (toe). In order to simplify the comparison of values, MacKay converts energy consumption and production per unit time (i.e. power) into one unit throughout his book. This is the kilowatt hour per day, per person (kWh/d/p). I find values in this unit are more intuitive than others. For that reason, and in order to aid comparison with figures used in MacKay's book, I will use the same units here.

In doing so however something immediately becomes apparent – there is a large difference between the population of the United Kingdom and that of the Republic of Ireland. As a result when converting an amount of power to kWh/d/p, there will be a different result depending on the region in question.

MacKay uses 60 million as the population of the UK. for the purposes of his book (the population at the time of writing is just over 62 million [WorldBank 2010]. The population of Ireland is under 4.5 million, although this is the value I will use for simplicity's sake [WorldBank 2010]. For a given amount of energy therefore, the kWh/d/p will be 13 times higher for the ROI than for the UK.

Some basic calculations to get started:

1 watt (a unit of power) is defined as 1 Joule per second.

Converting from kilowatt hours to Joules (both units of energy):1 kWh = 3.6 x 10⁶J

Converting from watts to kilowatt hours per day:

1 watt = 1 J/s

= 60 J/min

= 3600 J/hr

= 86400 J/day

= 0.024 kWh/day

Therefore 1 gigawatt = 24 x 10⁶ kWh/day. Using 60 million as the population of the UK, 1 gigawatt equates to 0.4 kWh per day per person. Using 4.5 million as the population of the ROI. 1 gigawatt equates to 5.3 kWh/d/p.

Consumption

MacKay's estimates for each of the sections in the consumption column are given in kilowatt hours per person per day. As the standard of living is similar between the ROI and the UK I will use the same estimates for the consumption column for Ireland. Data from the World Resources Institute [WRI 2005] shows total energy consumption to be very similar for the two regions.

What follows is the final value used for each of the consumption sections in “Sustainable Energy – without the hot air”, along with a brief summary of how they were reached. Note all values for consumption are shown in red).

Cars

MacKay uses the following formula to estimate the energy use per person per day due to driving car:

33 miles per gallon is (12 km/litre) is used for the distance per unit of fuel and 10 kWh/litre for the energy per unit of fuel. The distance travelled per day is assumed to be 50 km. This gives a figure of 40 kWh/d/p.

Planes

This section takes into account personal flights only – the energy used in transporting goods it accounted for later. MacKay assumes that every year each person flies the equivalent of one 10,000 km return trip in a plane that is 80% full and uses 240,000 litres of fuel which gives 10 kWh/litre. This results in a figure of 30 kWh/d/p.

Heating/Cooling

MacKay assumes 12 kWh/d/p are used for 'hot water' which takes into account cooking and cleaning. 1 kWh/d/p is assumed for 'cooling' which includes refrigeration and freezing. Finally 24 kWh/d/p is taken as the value for building heating. This gives a total of 37 kWh/d/p.

Light

Lighting for home and work, using a mix of incandescent and low energy bulbs is given a value of 4 kWh/d/p.

Gadgets

This section takes into account digital and household appliances such as computers, televisions, vacuum cleaners etc. The total is 5 kWh/d/p.

Food, Farming

MacKay assumes a diet consisting of vegetables, dairy, eggs and meat. Along with an estimate of the contribution made may fertilizer this gives 15 kWh/d/p.

"Stuff"

This section is concerned with the energy cost related to the manufacture and transport of everyday goods. Transporting is given a value of 12 kWh/d/p which includes road transport and freight brought in through ports. Manufacturing of goods is given 12 kWh/d/p.

This section also includes the energy costs associated with imported goods which adds up to a massive 48 kWh/d/p (more than for cars). If a similar analysis was performed on country with a large manufacturing industry it may be the case that energy due to imports would decrease substantially. The value for manufacturing goods would increase in turn however. The total of this section is 60 kWh/d/p (48 for manufacturing, 12 for transport).

Public Services

Despite the title this section is mostly concerned with the energy used for defence purposes. This is one area where the R.O.I are the U.K. are not comparable. MacKay estimates a value for energy use based on the cost of government expenditure. He assumes 6% of the budget is spent on energy, the cost of which is 2.7p per kWh. This gives a value of 4 kWh per day per person. In 2010 the U.K. expenditure on defence was $57.4 billion, compared with $1.3 million for the ROI [SIPRI 2011]. Assuming there is some correlation between expenditure and energy use I feel the energy related to defence for the ROI would be negligible compared to the rest of the consumption column.

Production

Note all values for production for the ROI are shown in green. MacKay's figures for the UK are shown in blue

Solar

MacKay includes a section the chapter on solar energy somewhat pessimistically entitled 'Fantasy time: solar farming'. He takes the power of sunshine per square metre (insolation) in the U.K. to be 100 W/m². From this he calculates the conceivable energy production from covering 5% of the U.K. with 10% efficient panels, which yields 50kWh/d/p.

Using 4.5 million as the population of the R.O.I. and 70,282 sq. km. as the area [Nolan 2007] the area per person is approximately 15,000m², 5% of this being 750m² per person. Multiplying this by 10 W/m² gives 7500 W/person or 180 kWh/d/p. Note that 5% of 70,282 sq. km. is about 3500 sq. km. - just over the size of County Clare.

As hare-brained as such an idea is it does illustrate the difference in population density with the U.K. Mackay’s estimate of 50kWh/d/p is about a quarter of the estimate for total energy consumption. Such a scheme in Ireland would nearly match consumption.

Additionally we may consider the contribution that solar PV could make were all south facing roofs covered with panels. Mackay estimates this to be 5 kWh/d/p assuming 20% efficient panels (i.e. 22 W/m²) and 10m² of roof space per person.

The above estimates assume that the insolation for the UK is the same as that for the ROI. Insolation is a measure of the energy received by the earth's surface due to solar radiation and is measured in W/m². Insolation is dependent on the angle between the surface in question and the incoming rays of the sun. The cosine of the latitude of the surface gives the reduction in insolation compared to a surface at the equator. For example Mackay uses Cambridge which is situated at a latitude of 52°. The cosine of this angle is 0.61566 – in other words the intensity of the suns radiation is at Cambridge is 61.5% of the intensity at the equator. The latitude of Dublin is 53°, the cosine of which is 0.6018 (not radically different from Cambridge).

NASA's website provides a database of solar insolation at any point on the globe [SMSE 2011]. The table below gives a 22-year average of insolation (in kWh/day/m²) between 53°/54° latitude and -7°/-8° longitude (approx. the centre of Ireland). There is obviously a significant difference between the winter and summer months, which is out of sync with energy demand for heating. The average over the 12 months is 2.4 kWh/day/m². This is 101 W/m² – almost exactly the same as the 100 W/m² used by Mackay.

Above: 22-year average of solar insolation [SMSE 2011]

The Met Éireann website [METSun 2011] gives annual global radiation figures for various locations within Ireland. These are around 320,000 J/cm² per year which works out at 101 W/m². Again very close to the figure used by MacKay.

Above: Mean Global Radiation in Joules/ cm² 1981 -2000 for locations in Ireland [METSun 2011]

Above: Annual average solar insolation [UNEP 2007]

The United Nations Environment Programme website provides a map of solar insolation for Europe [UNEP 2007]. England receives higher levels of solar radiation than Ireland although the average over the UK would be decrease given that it includes areas further north than the ROI. Note: 1 kWh/day/m² is approximately 42 W/m².

Biomass

Simply put biomass refers to living matter and bioenergy is a term for energy derived from biomass materials such as crops (e.g. maize, sugar cane, corn) or animal waste. Energy can be extracted directly from such materials or they may be converted into biofuels.

As part of the chapter on solar energy MacKay gives an estimate on the potential power that could be gained from solar biomass. Instead of specifying the means of extracting power from biomass (combusting, converting to biodiesel etc.) he uses an average power output per unit area of 0.5 W/m², which is higher than sugar beet but lower than tropical crops. This is clearly small compared to 10 W/m² that was used for solar PV. For land area he uses the amount of land devoted to agriculture in the UK which is 75%. This gives 3000m² per person which corresponds to 36 kWh/d/p (UK). MacKay says himself that this is an overestimate, used to boost the renewables column. Converting all the land used for agriculture to grow biofuels would obviously create some other problems i.e. what will we eat? He also does not mention the effect on CO2/SO2/NOx emissions from burning this much plant matter.

The section appears, more than anything, to demonstrate how inefficient solar biomass is as a form of energy production. Even so, what would a similar assessment for Ireland yield? One source [TEAGASC 2010] states that 64% of total land area is taken up by agriculture. This corresponds to 44,890 km² or just under 10,000 m² per person. Using a power density of 0.5 W/m² this would theoretically yield 120 kWh/d/p.

Wave

MacKay uses a broad estimate that the wave power off the west coast of the U.K. is 40 kW/m. Arranging 50% efficient wave-machines (MacKay ignores which type) along 500km of Atlantic facing coastline yields a paltry 4kWh/d/p (U.K.).

What about Ireland? At a rough estimate a distance of 500km fits reasonably well around coastline facing into the Atlantic (although the exact length of coastline along the west coast would be subject to some debate and would be much greater if every bay and peninsula were taken into account). Assuming as MacKay does that wave power of 40 kW/m is captured using 50% efficient machines this yields a total power of 10 GW or 53 kWh/d/p (ROI). Again a contribution that is quite small when set against the population of the UK becomes significant when compared to the population of the ROI.

How accurate is the figure of 40 kW/m? One estimate [Boyle 2004 p307] states “In water 100m deep at South Uist (Hebrides, Scotland), for example the annual average is around 70 kW/m, whereas closer to shore where the depth is 40m, the average power density is about 50 kW/m.” A figure on the same page illustrates averages of global wave power with the west coast of Ireland somewhere between 62 and 70 kW/m.

Left: Wave Energy Power per metre [MacKay 2009 p.73]

Tide

Methods of obtaining power from tidal sources can be seen as making use of either the kinetic energy of the moving water, e.g. tidal stream generators, or the potential energy due to the difference in height between low and high tides e.g. tidal barrages [IWEATide 2011]. MacKay uses the following formula to determine the theoretical power per unit area that can be obtained from a tidal stream farm.

ρ = Density of fluid

v = Velocity of fluid

This is the same formula used to determine the power per unit area of wind farms (see next section) although in this case the density will be the density of water which is approximately one thousand times greater than that of air. The power is clearly very dependant on the speed at which the water is travelling. MacKay gives estimate of 9 kWh/d/p (UK) for potential power that could be obtained from tidal stream farms. Details of the area used, or how it was calculated, is not given however and so I will not make an equivalent estimate for the ROI. Estimates from the SEAI will be looked at in the 'Other sources' section.

Onshore Wind

“Wind farms are hopelessly inadequate to the UK as a source of energy” - James Lovelock, The Vanishing Face of Gaia [Lovelock 2009]

The theoretical power produced by a wind turbine can be determined as follows. Consider the kinetic energy of a 'cylinder' of air that passes through the turbine blades in time t. The kinetic energy of this cylinder is ½mv², where m is the mass of the air and v is the wind speed. This can be rewritten as ½ ρ V v² where p is air density and V is the volume of the cylinder. Rewriting volume as cross sectional area (A) times v times t yields ½ ρ A t v³. The power (energy per unit time) is therefore:

It is important to note that (theoretically) wind turbine power is proportional to the cube of wind speed. In his estimates MacKay states that wind turbines cannot be spaced closer than 5 times the diameter of the blades. This enables him to workout the power per unit area of a wind farm, regardless of the size of the turbines and the spacing between them. He uses the following formula for the power per unit area of a wind farm (the same as in the Tide section):

Assuming the density of air is 1.3 kg/m³ an average wind speed in the U.K. of 6 m/s this yields 2 W/m². Covering an area equivalent to 10% of the U.K. MacKay reaches a figure of 20 kWh/d/p (U.K.).

How would a similar calculation work out for the R.O.I? As determined previously the amount of land per capita is approximately 15,000m². If 10% of this were used for wind farms this results in 3000 W per person or 72 kWh/d/p. A substantial portion of the power consumption per person. However 10% of the area of the R.O.I is about 7000 sq. km – almost the size of county Cork

How accurate is the use of 6 m/s for the average wind speed? Wind is notoriously volatile and wind speed is relative to height from the ground – “doubling the height typically increases wind-speed by 10%]” [MacKay 2009] . According to Met Éireann [METWind 2011] “Average annual wind speeds range from 7 m.p.h. (~3 m/s) in parts of south Leinster to over 18 m.p.h. (~8 m/s) in the extreme north”. A wind speed map courtesy of SEAI is to the right (click for a bigger version) [RENEWBL 2009]. Onshore wind speeds in low lying areas range from 6.5 to 8 m/s.

Right: Wind speed map around Ireland [RENEWBL 2009]

Offshore Wind

MacKay breaks up the chapter on offshore wind into two types. The first is shallow water offshore which covers depths less than 25m. He indicates that this is roughly twice as costly as onshore wind generation but still economically feasible. The second is deep offshore which covers depths from 25 to 50m and not economically feasible. 3 W/m² is used as an estimate of power per unit area for offshore wind. This is 50% larger than the 2 W/m² used for onshore, although it only corresponds to an increase in average wind speed from 6m/s to 6.6m/s. This is due to power scaling relative to the cube of wind speed.

MacKay estimates that the area around the UK with waters less than 25m is 40,000 km². One third of this (equivalent to a strip 4km wide around the entire coastline) at 3 W/m2 results in an estimate of 16 kWh/d/p (UK). He estimates an area of 80,000 km² contains water depths of 25 – 50m. One third of this at 3 W/m² results in 32 kWh/d/p (UK). It should be noted that the estimate for deep offshore involves covering an area larger than Wales with a technology that is not economically feasible.

Ireland is frequently mentioned as having huge potential offshore wind resources. See the figure below right [WINDATLAS 1989] for one example. What would the figure be if, like MacKay's estimate for shallow water offshore, we placed a strip of turbines 4km thick around the coastline? Taking the coastline of the ROI to be ~2800km [ORACLE 2011] and reducing to a third (933 km) this gives and area of ~3733 km2. Using 3 W/m² this corresponds to a total power of 11.2 GW or 60 kWh/d/p (ROI). Clearly this is significantly more than the figure that was reached for the UK of 16kWh/d/p, but is only one third of the estimate for total power consumption. I would imagine that a 4km strip of wind turbines around the coastline would understandably cause some consternation among environmental groups.

I was unable to find figures for the area of waters around Ireland less than 25m and between 25 and 50m. However there is a large amount of bathymetry data for Ireland available at http://www.infomar.ie. See the figure below for an overall view of the ROI [Infomar 2011]. Although the information in incomplete around the west coast it can be seen that the water depth increases rapidly to 100m (shown in yellow) only a few kilometres from the shore. The only areas less than 50m (red/orange) are either very close to the shore, or in bays. An image for Galway Bay is also shown [InformarGB 2011]

Above Left: Batymetry map around Ireland [Infomar 2011], Above Middle: Bathymetry map of Galway bay[InfomarGB 2011], Above Right: Wind speed around Ireland [WINDATLAS 1989]

How much wind power could these areas potentially generate? Some estimates using 3 W/m² (and assuming nobody minds the view from our coastlines consisting largely of wind turbines):

Dingle bay: 580 km², 1.7 GW, 9 kWh/d/p (ROI)

Galway bay: 675 km², 2 GW, 10.6 kWh/d/p (ROI)

Donegal bay: 480 km², 1.4 GW, 7.6 kWh/d/p (ROI)

Result of using 'MacKay's Method'

Even based on rough estimates there is clearly a sharp contrast between the UK and the ROI in terms of the contribution that renewables could make towards matching energy consumption. In every section in his book MacKay attempts to boost the renewables estimates as much as possible, and yet still comes up short in comparison to consumption. A summary of the figures in MacKay's book for the UK and my figures for Ireland is given below. All figures are in kWh per day per person for the respective region. It is important to emphasise that this is not an assessment of total power, but rather power per capita. It should be noted that MacKay also includes a substantial estimate of 32 kWh/d/p (UK) for deep offshore wind farms in his evaluation, which I have not provided an estimate for. He also provides values for geothermal, tidal, hydro and solar heating sources.

As already stated MacKay's figures are deliberate overestimates. Most (probably all) of the ideas discussed above will seem ludicrous. Covering 5% of the country with solar panels, as well as 75% being used to grow biomass being two such examples. MacKay notes that after “public consultation” a figure of 18 kWh/d/p (i.e. 10% of the initial estimate) is possibly more accurate. Other sources that he cites give evaluations ranging from 12 to 27 kWh/d/p. Clearly is it worth considering other estimates to get a more rounded picture and where possible observed data. The next section attempts to do so.

Other sources

Consumption

MacKay's estimates of energy consumption for all the sections in his book was carried out per person per day. I assumed that as the standard of living is not radically different between the UK and the ROI, energy consumption per capita would not be either. As a result I didn't not do any calculations specific to the ROI other than to leave out the 4 kWh/d/p for “defence”. The total figure for consumption was therefore 191 kWh/d/p.

It is important to note that electricity consumption is not the same as energy consumption. MacKay's estimate for the energy used in manufacturing goods was 48 kWh/d/p. If this was all taken from the electricity grid it would still only account for 25% of 191 kWh/d/p total. In terms of domestic electricity MacKay estimates 37 kWh/d/p for heating and cooling (hot water, hot air and refrigeration), 4 kWh/d/p for lighting, and 5 kWh/d/p for 'gadgets' (TV, computer, vacuum cleaner etc.). This gives a sum of 46 kWh/d/p or 25%. Therefore going by MacKay's figures electricity consumption accounts for less than half of the total energy consumption.

What about other sources? The figure shown below is from the Sustainable Energy Authority of Ireland (SEAI). In addition to total primary energy it also shows the final consumption after losses due to refining, transformation, transmission etc. The losses here account for 17.8% of the primary consumption. How does this translate to kWh per day per person?

Above: Energy Production vs Consumption for Ireland [SEAIEE 2009]

1 ton of oil equivalent (toe) = 11630 kWh

1 ktoe = 11.63 x 10⁶ kWh

1 ktoe/yr = 31863 kWh/d = 7.08 x 10^-3 kWh/p/d (ROI)

The 16,132 ktoe for primary energy requirement therefore corresponds to 114 kWh/d/p. This obviously substantially less than MacKay's estimate. However MacKay takes into account the energy consumption due to the manufacture of imported goods.

The World Resources Institute provides statistics for total energy consumption per capita for most countries [EARTH 2005]. According to the WRI each person in Ireland consumed 3656 kgoe (kilogram of oil equivalent) in 2005.

1 toe = 11630 kWh (as before)

1 kgoe = 1/1000 toe = 11.63 kWh

1 kgoe/day = 0.03186 kWh/day

Therefore 3656 kgoe/d/p corresponds to 116 kWh/d/p (ROI). According to the technical notes on the WRI's webpage:

“Total energy consumption per capita measures the amount of primary energy consumed, on average, by each person living in a particular country or region for the year indicated. All primary sources of energy, including coal and coal products, oil and petroleum products, natural gas, nuclear, hydroelectric, etc., are included here.”

Again the energy used in the manufacture of imported goods would not be included here. The same site also gives statistics for electricity consumption per capita. In Ireland in 2005 each person consumed an average of 6,248.7 kWh. This works out at 17 kWh per day per person (I will use yellow to represent consumption of electricity only) – just under 15% of the total energy consumption.

The Irish Wind Energy Association (IWEA) uses a “median demand forecast” of 27,206 GWh for 2010 [IWEAFAQ 2011]. This equates to 16.5 kWh/d/p.

I find the use of statistics related to electricity consumption to be somewhat disingenuous. Regardless of the exact figure total energy consumption is substantially greater than that accounted for by total electricity consumption.

Wind

According to the SEAI are “currently 110 on-shore and one offshore wind energy projects in operation in the Republic of Ireland with a total installed capacity of 1,379 Megawatts” [SEAIWind 2011]. It is important to note that installed capacity represents the maximum amount of power that can be generated. For a wind turbine this would only occur were the wind to be blowing constantly at the fully rated wind speed. The capacity factor is defined as the actual output divided by the maximum potential output, a value of 0.25 (25% efficiency) being typical for the UK [Boyle 2004, p152, p279]. The IWEA indicates a capacity factor of 31% for Ireland [IWEAFAQ 2011].

A report from the SEAI states that 2955 GWh of electrical energy was generated by wind resources in 2009. This equates to just under 1.8 kWh/d/p (ROI). Compared to the amount of electrical energy that we consume 1.8 kWh/d/p does not seem too bad - it is over 10% of the electricity demand given by the IWEA.

So if we increase our wind output by a factor of 10 we could be completely reliant on renewables? Unfortunately not. 1.8 kWh/d/p corresponds to 2% of total energy demand given by the CSO and less than 1% of the figure that was reached using MacKay's method. Increasing our wind generation by a factor of 100 would seem to be more realistic estimate. It should be noted however that the energy generated by wind has been increasing dramatically over the last decade - see the figure to the right [SEAIRE 2010].

Above: Increase in wind generated electricity [SEAIRE 2010]

The quote from the SEAI used above mentions one offshore wind farm. This is Arklow Bank which is located 10 km off the coast of Co. Wicklow. It consists of seven 3.6 MW turbines giving a total installed capacity of 25 MW [LORC 2011][CEOE 2004]. One source states that the annual energy output is 95 GWh/year [OSWE 2002]. This equates to just under 11 MW, which means that the capacity factor is 43%.

95 GWh/year also equates to a 0.0578 kWh/d/p (ROI). If we use 191 kWh/d/p as our total energy consumption then we would need over 3000 'Arklow Banks' to meet our needs (ignoring the contribution from other sources). There were plans to increase the installed capacity of Arklow Bank to 520 MW [Airtricity 2007]. Using the same capacity factor this would equate to 1.2 kWh/d/p.

Wave

At present the SEAI is looking to develop the “Atlantic Marine Energy Test Site (AMETS)” off the coast of Belmullet, Co. Mayo [SEAIB 2009]. The site is in the planning stage at present, with completion of environmental impact studies, submission of planning permission etc. to be complete before 2012. It is due to be operational and ready to test full scale wave energy converters by 2014.

An ocean energy strategy document is also available on the SEAI's website, although it dates from 2005 [SEAI 2005]. Figure 1 of the document indicates that wave power per unit length is 70kW/m along the west coast, and 50 kW/m in waters north of Ireland. These are similar to the values discussed previously.

The report states “The practical wave energy resource offshore is estimated at greater than 6000MW”. This corresponds to 32 kWh/d/p (ROI) . A more conservative estimate is shown in a table (D1) which provides a projection for cumulative installed capacity. A figure of 84 MW is given for 2020 which corresponds to 0.4 kWh/d/p (ROI). An enormous increase in shown in the following decade with a figure of 1744 MW for 2030, or 4 kWh/d/p (ROI).

Another document, the 'Ocean Energy Roadmap to 2050' [SEAIO 2010] gives some very optimistic estimates of potential wave power by 2050, that are achievable “without likely significant adverse effects”. A figure of 12,500 – 13,600 MW is given for waters 10 - 100m in depth. The lower estimate corresponds to 66 kWh/d/p (ROI). A figure of 15,000 – 17,500 MW is given for waters 100 - 200m in depth. The lower estimate corresponds to an enormous 80 kWh/d/p (ROI).

As with a number of resources there is clearly a huge amount of potential power to be tapped into. Equally clear however is the fact that more research needs to be done into this area. The accuracy of projections ten, twenty or forty years into the future is at least very questionable, considering that a testing facility for this technology has not even been built off the coast of Ireland yet.

Tide

In the 'Tidal Current Energy Resources in Ireland' by the SEAI [SEAIT 2004] a theoretical potential of 230 TWh/yr is given for tidal currents between the 10m depth contour and a 12 nautical mile territorial limit. This figure was obtained from a computational model of current flows around Ireland and corresponds to 140 kWh/d/p (ROI). This estimate also makes use of the same formula (for the power in a tube of moving fluid) that was used by MacKay when discussing wind and tidal energy:

In addition it is noted that the “maximum power which can be extracted from the flow is 59% as the fluid must have sufficient kinetic energy to leave the power extraction region”. The report also provides an analysis of how this estimate changes when technical, practical, accessible and viable constraints are taken into consideration.

The technical constraints mean that only areas where the peak velocity is above 1.5m/s are taken into account and device efficiency is limited to 39%. The revised estimate is 10.46 TWh/yr or 6.4 kWh/d/p (ROI). The technical estimate is a mere 4.5% of the initial, theoretical estimate.

Practical and accessible constraints exclude waters whose depth is not between 10m and 40m, excluding areas which contain shipping lanes, military zones, pipelines etc. and taking environmental considerations into account. This give a new estimate of 2.633 TWh/yr or 1.6 kWh/d/p (ROI).

Left: Averaged Peak Spring tidal currents around Ireland [SEAIT 2004]

Finally viability constraints exclude areas where mean maximum spring tide current is less than 2.5m/s and also involve commercial constraints such as development costs. This further reduces the estimate to 0.92 TWh/yr or 0.56 kWh/d/p (ROI). It is important to emphasise how much of a decrease there is between the initial theoretical estimate (230 TWh/yr) and the final 'viable' estimate. The viable estimate is less than half of one percent of the theoretical one. Below right: SEAGEN power turbine, Strandford Lough [Guardian 2008]

The SeaGen turbine in Strandford Lough provides one example of how tidal stream turbines can function in practice. Built in 2008 at a cost of £8.5m it consists of a central tower, which rises 40m from the seabed, connected to two 16m diameter rotors [PowerTech][SEAGEN]. The power generated to the grid is given as 3800 MWh/yr which corresponds to 0.0023 kWh/d/p (ROI). Our estimate for total energy consumption (191 kWh/d/p) equates to over 83,000 SeaGen turbines.

The power station at La Rance in France provides an example of how tidal barrages can function in practice. Completed in 1966 it has generated an average of 0.54 TWh/yr [BHA 2009]. This corresponds to 0.33 kWh/d/p (ROI) although I am unaware of any sites in Ireland that would be suitable for such a project.

The 'Ocean Energy Roadmap to 2050' [SEAIO 2010], mentioned in the previous section provides a figure of 1,500 – 3,000 MW for potential tidal power by 2050. The lower estimate corresponds to 8 kWh/d/p (ROI).

A target of 500MW of ocean energy (tidal and wave) to be installed by 2020 has been set by the government which corresponds to 2.6 kWh/d/p (ROI) [Marine].

Solar

According to the SEAI, in 2008 solar accounted for 3 ktoe of the 581 ktoe contributed by renewables to gross energy. To put this in perspective the total primary energy requirement for that year was 16,356 ktoe (or 114 kWh/d/p as mentioned previously) [SEAIKey 2009]. The contribution made by solar PV is not given although according to another SEAI report there were 15 solar PV micro-generation sites connected at the end of 2009, with a total installed capacity of 33.9 kW. This equates to a minuscule 0.00018 kWh/d/p (ROI). It is noted that “There are not many photovoltaic installations in Ireland, as it is an expensive way of producing electricity here relative to other renewable energy sources.”[SEAIRE 2010].

Figures for 2010 show a doubling of the contribution by solar to 6 ktoe. This is still very small, the contribution by wind power was 242 ktoe for example.

Interestingly Germany has been making great strides in its installed solar capacity, and a map of photovoltaic solar electricity potential (see figure: Annual average solar insolation) indicates that the amount of irradiation received by German is not dissimilar to Ireland.

Solar PV in Germany contributed 12 TWh of electricity in 2010, or 2% of the total supply. It should be noted however that this is 2% of the electricity supply, not total energy [REW 2011]. Solar PV are heavily subsidised in Germany and there are those who suggest the money would be better spent on other more cost efficient technologies: “By 2008 solar PV was producing a grand total of 0.6% of Germany's electricity for €35bn. Hands up all those who think this is a good investment” [Guardian 2010].

A more thorough analysis of why solar so well supported in Germany is out of the scope of this paper. In terms of the ROI however it is clear that solar power is not seen a viable way to significantly contribute to our energy needs.

Left: Increase in renewable contribution to GFC [SEAIRE 2010 p13]

The SEAI divides bioenergy into two categories: biofuels and combustible renewables. Figures for 2008 show 55 ktoe was gained from biofuels, which equates to 0.4 kWh/d/p (ROI) [SEAIKey 2009]. It should be noted however of this 57% was produced indigenously while 43% was imported. The proportion of production to imports depends on the fuel although for bioethanol imports represent almost seventy times the amount produced in Ireland [SEAIRE 2010 p26].

Combustible renewables contributed 186 ktoe to gross energy in 2008 which equates to a 1.3 kWh/d/p (ROI). Figures for the amount of land used where not provided however. Of the186 ktoe, 95% was related to solid biomass which involves the combustion of organic, non-fossil material. This is usually wood, wood wastes (wood chips, sawdust etc.) and other solid wastes such as straw and oat hulls. The majority of the solid biomass is used for thermal energy in the industrial sector [cite last link (2010 update)]. Solid biomass has been one of the most consistently used forms of renewable energy over the last two decades with a contribution of 105 ktoe in 1990.

Biogas contributed the remaining 5% of the figure for 2008. This comprises of gas from sewage, as well as from animal slurries, abattoirs, breweries etc.

A contribution of 26 ktoe, or 0.18 kWh/d/p (ROI), was made by gas from landfills, although this is regarded as a waste energy source and not a renewable source.

The SEAI report does not mention crops grown for energy use specifically. A 2007 report by the School of Natural Sciences, Trinity College Dublin [EPA 2007] states that “current energy-crop utilisation in Ireland is virtually non-existent”. An assessment is given for the electricity that could potentially be gained from miscanthus as well short-rotation coppice willow (SRCW). Using miscanthus an area of 33,784 hectares would yield 850 GWh/annum of electricity. Using SRCW an area of 59,381 hectares would yield 987 GWh/annum. These values equate to 0.12 W/m² and 0.28 W/m² respectively which are even less than the 0.5 W/m² used by MacKay. Although biomass has made a substantial proportion of our renewable energy production to date it does appear to be an inefficient use of land area.

Above: Contribution to gross energy by source [SEAIKey 2009]

Storage

My primary focus in this work is the potential of renewable sources. The problem of energy storage in relation to renewables is a very significant, but also broad subject, and due to time constraints I will only be to give a short assessment of it.

In his chapter on fluctuations and storage, MacKay provides a graph of the power output from wind farms in Ireland from April 2006 to April 2007 (see right). The output is clearly very variable and MacKay splits these fluctuations in two types. These are short term variations, known as slews, and long term variations known as lulls. The longest lull in this period lasted for 5 days during which the output was less than 5% of its peak.

Left: Wind energy production Ireland 2007 [MacKay 2009]

MacKay extrapolates the data for the UK and determines that 1200 GWh would need to be stored in order to cope with a lull of five days. He notes that for Ireland the total capacity of the wind farms in 2007 was 745 MW. As stated previously the SEAI gives a figure of 1,379 MW for 2011 [SEAWind 2011] which I will use here. Using a capacity factor of 0.3 (as MacKay does) this equates to an average output of 414 MW. In order to continue to supply this power over a lull of five days, 50 GWh would need to be stored.

Details of the largest hydroelectric plants in the UK are given by MacKay. Dinorwig in Snowdonia is the 'Queen' of these facilities which is capable of storing 9.1 GWh. There is only one pumped storage facility in the ROI which is located at Turlough Hill, Co. Wicklow [Turlough 2001]. A rough estimate of the amount of energy stored can be gained by using the following formula:

Where V is the volume of water, ρ is the density of water (about 1000 kg/m³), g is the acceleration due to gravity (about 9.8 m/s²) and h is the geodetic head (i.e. the difference between the high and low lakes).

Above: Details of pumped storage facilities [MacKay 2009 p191][Turlough 2001]

Details of the Dinorwig and Turlough Hill facilities are shown in the table above. To store for 5 days we would need 28 times the capacity of Turlough hill. Unfortunately we have already “harnessed 75% of the country's water power potential” according to the ESB [ESB]. For a more sobering picture the total consumption of electricity and energy can be analysed. 17 kWh/d/p (an estimate of electricity consumption discussed previously) corresponds to 383 GWh which is 214 times the capacity of Turlough Hill. Using our estimate of 191 kWh/d/p for total energy consumption gives approximately 4300 GWh, or over 2000 times the capacity of Turlough Hill. Although all of the above are obviously rough estimates, there is not getting around some basic laws of physics.

The Spirit of Ireland website indicates that a combination of wind energy and pumped storage could provide enough power to meet our electricity demands. This does not appear possible going by the above estimates, and the idea is severely rebuked on another site www.sustainability.ie. This latter website states “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”. It also indicates that a lake of 32km², 10m deep and with a head of 100mm would only provide 86.4 GWh.

Another potential solution is mentioned by MacKay, which involves using a country sized fleet of electric vehicles. The theory is that, assuming the uptake of EVs is successfully in the future, the batteries of this fleet could be used to store electricity when excess is being produced, and supply electricity when there is a lull. Obviously a minimum amount of charge would need to retained in the vehicles for people to be able to go to work, pick up the kids etc. MacKay assumes that an average EV battery can hold 40kWh. In 2007 there were 2.5 million cars on Irish roads [BNews 2008] . If all these had such a battery this would equate to a storage capacity of 100 GWh. Twice what we would need to compensate for a 5 day lull in wind power, but not enough to store 5 days worth of electricity use.

Conclusion

I hoped to provide some level of clarity into the debate on renewable energy. I purposefully chose to examine this subject at a macro level as I wanted to look at the bigger picture and avoid getting bogged down too much in the details of one particular technology. There are other areas such as economics, which although hugely important have not been discussed due to time constraints. MacKay also discusses the potential of nuclear energy as well as solar power from deserts, which are outside the scope of this work.

I found the use of one unit of measurement to be beneficial amongst all the toes, ktoes, Ws, MWs, TWs, kWh/yr, GWh/yr. As stated I chose to use the kWh/day/person in order to aid comparisons with Mackay’s estimates, and because figures per person are generally more intuitive. A number of other units could equally be utilised of course.

Another general conclusion is that, even with broad estimates, electricity use is not the same as energy use. I do not find figures quoted in 'electricity to power X homes' to be useful and I would argue that they in fact obscure some important details of the argument.

The most obvious conclusion that can be drawn from applying MacKay's analysis to the Republic of Ireland is that population density makes an enormous difference. Where MacKay consistently provided very generous assessments in order for the renewables estimates just to come close to the consumption estimates, a similar analysis for the ROI shows renewable production to be multiple times larger than consumption.

Having said this it is also clear that estimates of the potential energy to that can be extracted from a particular resource can be wildly different from what can be viably gained. The difference between the 'theoretical' and 'viable' estimates from the SEAI's assessment of tidal energy illustrates this. Access to data from technologies that have actually been tested in the field is invaluable. Technologies which fall into this category are onshore wind, biomass and to a lesser extent tidal stream and shallow offshore wind. Biomass appears to be a hugely inefficient use of land. Wind has shown itself to be at least viable, but an increase of a hundredfold, if not more, would be needed to come close to our present energy consumption.

In theory there is huge potential in wave energy off the west coast, although making vague sweeping statements like that is part of the problem. It will be interesting to see the data that is obtained from the Atlantic Marine Energy Test Site near Belmullet.

Although predictions in such a rapidly changing field can be wildly off the mark I will none the less stick my neck out and make some conclusion based on the information discussed above. In the long term if vast sums of money are invested in renewables (we have after all become more familiar with hundreds of billions of Euro in the last few years), and some viable solution to the issue of storage can be reached, then it may be possible to rely on them fully. The alternatives are to purchase solar/nuclear energy from abroad, or resign ourselves to building nuclear power stations on the island. While each of these may be vehemently opposed by some people they may begin to change their minds as the supply of oil and gas begins to run out.

Bibliography

Books

[MacKay 2009] David JC MacKay (2009). Sustainable Energy - without the hot air. 1st. ed. Cambridge, England: UIT Cambridge Ltd. Also available from: <http://www.withouthotair.com/>.

[Boyle 2004] Godfrey Boyle (2004). Renewable Energy Power for a Sustainable Future. 1st. ed. Oxford, England: Oxford University Press.

[Lovelock 2009] James Lovelock (2009). The Vanishing Face of Gaia. 1st. ed. London, England: Penguin.

Websites

[WorldBank 2010] The World Bank Data Indicators [online]. (2010) [Accessed 4 December 2011]. Available from: <http://data.worldbank.org/indicator/SP.POP.TOTL>.

[WRI 2005] Earth Trends, World Resources Institute [online]. (2005) [Accessed 4 December 2011]. Available from: <http://earthtrends.wri.org/text/energy-resources/variable-351.html>.

[SIPRI 2011] Stockholm International Peace Research Institute [online]. (2011) [Accessed 4 December 2011]. Available from: <http://milexdata.sipri.org/>.

[Nolan 2007] Prof. William Nolan (2007). Geography of Ireland [online]. [Accessed 4 December 2011]. Available from: <http://www.gov.ie/en/essays/geography.html>.

[SMSE 2011] NASA Surface meteorology and Solar Energy [online]. (2011) [Accessed 4 December 2011]. Available from: <http://eosweb.larc.nasa.gov/cgi-bin/sse/sse.cgi?%20s01>.

[METSun 2011] Met Eireann Sunshine [online]. (2011) [Accessed 4 December 2011]. Available from: <http://www.met.ie/climate-ireland/sunshine.asp>.

[METWind 2011] Met Eireann Wind [online]. (2011) [Accessed 4 December 2011]. Available from: <http://www.met.ie/climate/wind.asp>.

[UNEP 2007] UNEP GRID-Arendal Solar insolation [online]. (2007) [Accessed 4 December 2011]. Available from: <http://maps.grida.no/go/graphic/solar-insolation>.

[TEAGASC 2010] Teagasc: Agricultural and Food Development Authority [online]. (2010) [Accessed 4 December 2011]. Available from: <http://www.teagasc.ie/agrifood/>.

[IWEATide 2011] Irish Wind Energy Association Tidal Energy FAQ [online]. (2011) [Accessed 4 December 2011]. Available from: <http://www.iwea.com/index.cfm/page/tidalenergyfaq>.

[RENEWBL 2009] Wind Speed Map of Ireland at 50 metres [online]. (2009) [Accessed 4 December 2011]. Available from: <http://www.renewbl.com/wp-content/uploads/2009/05/ireland_wind_speed_map.jpg>.

[WINDATLAS 1989] European wind resources at 50 metres [online]. (1989) [Accessed 6 December 2011]. Available from: <http://www.windatlas.dk/europe/landmap.html>.

[ORACLE 2011] Oracle Ireland [online]. (2011) [Accessed 6 December 2011]. Available from: <http://oracleireland.com/Ireland/about/snippets.htm>.

[Infomar 2011] Infomar: Ireland Coverage [online]. (2011) [Accessed 8 December 2011]. Available from: <http://www.infomar.ie/documents/Ireland_Coverage_Chart_21Sep11.pdf>.

[InfomarGB 2011] Infomar: Galway Bay [online]. (2011) [Accessed 8 December 2011]. Available from: <http://www.infomar.ie/data/Charts/Galway/GalwayBay.php>.

[SEAIEE 2009] SEAI Energy Efficiency in Ireland [online]. (2009) [Accessed 6 December 2011]. Available from: <http://www.seai.ie/Publications/Statistics_Publications/EPSSU_Publications/Energy_Efficiency_in_Ireland_2009/Energy_Efficiency_Report_2009.pdf>.

[SEAIWind 2011] SEAI Wind Energy [online]. (2011) [Accessed 7 December 2011]. Available from: <http://www.seai.ie/Renewables/Wind_Energy/Wind_Farms_in_Ireland/>.

[SEAIRE 2010] SEAI Renewable Energy in Ireland [online]. (2010) [Accessed 7 December 2011]. Available from: <http://www.seai.ie/Publications/Statistics_Publications/SEI_Renewable_Energy_2010_Update/RE_in_Ire_2010update.pdf>.

[SEAIB 2009] SEAI: Belmullet Wave Energy Test Site [online]. (2009) [Accessed 8 December 2011]. Available from: <http://www.seai.ie/Renewables/Ocean_Energy/Belmullet_Wave_Energy_Test_Site/>.

[SEAI 2005] SEAI: Ocean Energy in Ireland [online]. (2005) [Accessed 8 December 2011]. Available from: <http://www.seai.ie/Renewables/Ocean_Energy/Belmullet_Wave_Energy_Test_Site/>.

[SEAIO 2010] SEAI: OCEAN ENERGY Roadmap to 2050 [online]. (2010) [Accessed 8 December 2011]. Available from: <http://www.seai.ie/Renewables/Ocean_Energy/Ocean_Energy_Information_Research/Ocean_Energy_Publications/Ocean_Energy_Roadmap_to_2050.pdf>.

[SEAIT 2004] SEAI: Tidal [online]. (2004) [Accessed 8 December 2011]. Available from: <http://www.seai.ie/Publications/Renewables_Publications/Tidal_Current_Energy_Resources_in_Ireland_Report.pdf>.

[SEAIKey 2009] SEAI: Energy in Ireland KEY STATISTICS 2009 [online]. (2009) [Accessed 8 December 2011]. Available from: <http://www.seai.ie/Publications/Statistics_Publications/EPSSU_Publications/Energy_in_Ireland_Key_Statistics.pdf>.

[EARTH 2005] Earth Trends - Total energy consumption per capita [online]. (2005) [Accessed 7 December 2011]. Available from: <http://earthtrends.wri.org/text/energy-resources/variable-351.html>.

[IWEAFAQ 2011] IWEA FAQ [online]. (2011) [Accessed 7 December 2011]. Available from: <http://www.iwea.com/index.cfm/page/technicalfaqs>.

[LORC 2011] Lindoe Offshore Renewables Center [online]. (2011) [Accessed 8 December 2011]. Available from: <http://www.lorc.dk/Knowledge/Offshore-renewables-map/Offshore-site-datasheet/Arklow-Bank-1-Offshore-Wind-Farm/000015>.

[CEOE 2004] University of Delaware: Arklow offshore wind park [online]. (2004) [Accessed 8 December 2011]. Available from: <http://www.ceoe.udel.edu/windpower/docs/arklow_infosheet_final.pdf>.

[OSWE 2002] Offshorewindenergy.org: Arklow Bank [online]. (2002) [Accessed 8 December 2011]. Available from: <http://www.offshorewindenergy.org/windfarms/display_data_windfarm.php?id=6>.

[Airtricity 2007] Airtricity: Offshore Wind Farm Development [online]. (2007) [Accessed 8 December 2011]. Available from: <http://www.airtricity.com/assets/Uploads2/Press-Releases/Offshore-support-press-release1.pdf>.

[Guardian 2008] Guardian.co.uk: First tidal power turbine gets plugged in [online]. (2008) [Accessed 8 December 2011]. Available from: <http://www.guardian.co.uk/environment/2008/jul/17/waveandtidalpower.renewableenergy>.

[Guardian 2010] Guardian.co.uk: Solar PV has failed in Germany and it will fail in the UK [online]. (2010) [Accessed 8 December 2011]. Available from: <http://www.guardian.co.uk/environment/georgemonbiot/2010/mar/11/solar-power-germany-feed-in-tariff>.

[PowerTech] Power-Technology.com: Strangford Lough Tidal Turbine [online]. (?) [Accessed 8 December 2011]. Available from: <http://www.power-technology.com/projects/strangford-lough/>.

[SEAGEN] seageneration.co.uk: The SEAGEN Turbine [online]. (?) [Accessed 8 December 2011]. Available from: <http://www.seageneration.co.uk/downloads/recent/General Documents/Seagen Facts EXTERNAL 2.pdf>.

[BHA 2009] La Rance Tidal Power Plant [online]. (2009) [Accessed 8 December 2011]. Available from: <http://www.british-hydro.org/downloads/La%20Rance-BHA-Oct%202009.pdf>.

[Marine] marine.ie: Ocean Energy Strategy [online]. (?) [Accessed 8 December 2011]. Available from: <http://www.marine.ie/home/services/operational/oceanenergy/OceanEnergyStrategy.htm>.

[REW 2011] Renewable Energy World [online]. (2011) [Accessed 8 December 2011]. Available from: <http://www.renewableenergyworld.com/rea/news/article/2011/03/new-record-for-german-renewable-energy-in-2010??cmpid=WNL-Wednesday-March30-2011>.

[EPA 2007] EPA.ie: Energy Crops in Ireland [online]. (2007) [Accessed 8 December 2011]. Available from: <http://www.epa.ie/downloads/pubs/research/econ/styles%20report%20ertdi%2070%20for%20web1.pdf>.

[Turlough 2001] Pumped Storage Station of Turlough Hill [online]. (2001) [Accessed 15 December 2011]. Available from: <http://www.scep.ensmp.fr/more-care/activities/turlough_hill/turlough_hill.html>.

[ESB] ESB Hydro development [online]. (?) [Accessed 15 December 2011]. Available from: <http://www.esb.ie/main/about-esb/hydro-development.jsp>.

[BNews 2008] Breaking News [online]. (2008) [Accessed 15 December 2011]. Available from: <http://www.breakingnews.ie/ireland/mhqlkfauidgb/rss2/>.