Paul Eustace

A gigawatt of renewable energy.

Table of Contents

1 Abstract 2

2 Introduction 2

3 Evaluation of existing power sources 5

3.1 Thermal Generators. 6

3.1.1 Gas Turbines 6

3.1.2 Nuclear power. 7

3.2 Renewables 8

3.2.1 Wind 8

3.2.2 Biomass, Biogas 8

3.3 Transmission network improvements. 8

3.4 Combined Heat and Power 10

4 Future power sources 10

4.1 Wave and tidal power 10

5 Storage 11

5.1 Cost of electricity through the day 11

5.2 Types of storage 12

5.3 Short term 12

5.4 Hydro 12

5.5 Interconnectors 12

5.6 Electric vehicle batteries 13

6 Future Storage options 14

6.1.1 Spirit Of Ireland 14

6.1.2 Compressed Gas 15

6.1.3 Chemical storage 15

7 Demand reduction and Load balancing 15

7.1 Insulation 16

7.1.1 Health Benefits 19

8 Other Improvements. 20

9 Discussion 21

10 summary and conclusion 22

1 Abstract

Almost all of of Ireland's fuel is imported. At present the main uses of fuel in Ireland are for space heating, transport, industrial processes and the generation of electricity. This review will investigate current and future renewable contributions to these areas and which should be focused upon. One of the main uses of electricity and its most seasonal use is for heating. It will be shown that by improving the BER rating of buildings in Ireland that much of this seasonal variation could be removed. This would have benefits in reducing the peak generation capacity needed.

To a first approximation the difference between minimum and maximum demand for electricity in Ireland is one gigawatt. This is true of both diurnal peak to valley demand and seasonal peak to peak demand. At present the peak price for electricity can be up to ten times the base price due to supply and demand economics. The availability of wind power is also in the order of a gigawatt.

This report will investigate some of the renewable options for Ireland that are capable of matching this gigawatt difference through generation, storage and load reduction.

2 Introduction

Essentially the problem is to match supply and demand. The key challenge is that most renewables are not dispatchable though all are to some extent predictable. In comparison fossil fuel plants have agreed maintenance schedules for up to seven years in advance.

This report will look at methods of providing increasing supply and levelling demand. On the supply side the two main solutions are to generate more power or to store power until it is needed. Some technologies which have been successfully implemented abroad are evaluated on their applicability for use in Ireland. Some such as obtaining biomass from tropical salt water mangrove swamps in areas where fresh water is scarce would of course not be applicable here.

As Ireland moves to getting a larger percentage of its power from wind the instantaneous supply of that power may vary considerably. To some extent short term demand can be catered for by importing electricity from Northern Ireland over the existing interconnector or from pumped storage in addition to traditional fossil fuel plant.

Customer side storage is also investigated. The costs associated with electrical vehicle storage are considered. One promising area is thermal storage as the average demand for electrical domestic space and water heating is around the gigawatt figure. This could mainly be achieved by better insulation of existing housing stock. Using insulation for thermal storage may be the cheapest way to load balance electricity.

Energy use in Ireland November 2008 [1]. From this survey of 759 Irish sites it can be seen that most of the fuel they used was for heating. For industrial users about half of their consumption was for process heat. It can reasonably assumed that these users are very conscious about this energy use and would already have reduced it's use where practicable. [2] Many chemical processes are endothermic and so there is a limit to the amount of process heat that can be saved. For service and domestic customers the main usage of energy is for water and space heating.

The total domestic usage of electricity was 7,975,601 MWh. Averaged over a year this is 910 MW. But usage patterns of electricity are seasonal with usages increasing by fifty or even a hundred percent from summer levels. The services sector also uses electricity for heat so a reduction in demand could reduce the winter requirement by gigawatt.

From [1]

Illustration 1:

Text 1: Estimated Energy use in Ireland

From [1]

3 Evaluation of existing power sources

When considering current technologies for electricity generation the main focus will be the connected and contracted generators report as well as technology in use elsewhere. The all Island generation capacity statement 2011-2020 [4] outlines the probably generating capacity that will come online in the near future.

The Eirgrid all generators summary document lists [3] 37,266.6 MW of existing and proposed connections to the grid. The peak demand expected for the island for the 2011/2012 winter is 6,780MW which will be provided for by dispatchable capacity of 6,792MW in Ireland and 2,316MW in Northern Ireland.[5] With such a large difference between proposed supply and current demand it is extremely unlikely that all the generators listed would all come on line. It was felt therefore that other proposals which had not made it to the queue stage would not be considered in depth unless there were installations in the GW range in operation elsewhere. At present Eirgrid categorise the listed generators as wind and non-wind. Most of the non-dispatchable generators are wind and most of the dispatcatchable generators comprise of thermal and hydroelectric.

3.1 Thermal Generators.

There are three main types of fossil fuel plant in use in Ireland. The first type where steam is generated in a boiler using oil or coal as the fuel. Nuclear power plants are generally similar except in the nature of the heat source. The second type is an open cycle gas turbine (OCGT) where the working fluid is air instead of steam. The third type is a combination of the first two. In a closed cycle gas turbine (CCGT) the heat in the exhaust gases from the turbine is used to heat a boiler to produce steam. A CCGT is more efficient that the other types. [6]

Coal , oil and gas have different physical properties. Coal is a solid and can be stored easily but requires mechanical handling to move it. Oil is a liquid and has to be stored in a container, it can be pumped but the heavy fuel oils used in power production would need to be heated to reduce viscosity. Distillate is a lighter oil that can be used in gas turbines. In the quantities used for power generation natural gas is difficult to store because of its low volumetric energy content and is usually piped to its destination.

This range of physical properties is also reflected in the power plants using these fuels. Moneypoint is currently the last large coal plant in use. It has an output of 862.5MW and is the last coal fired stations plant with new ones proposed.

3.1.1 Gas Turbines

Open cycle gas turbines can have rapid startup times and provide reserve capacity to cover for outages elsewhere in the system, including wind power. While CCGT have higher efficiencies than OGCT they take longer to startup because of the time for the boiler to come to temperature. One proposal is get CCGT to work as OCGT when they are needed to provide reserve power to cater for wind load. [7] This is done by having the turbine exhaust bypass the boiler. The plant is then is less efficient under load but more efficient on standby that it would be if it was on standby in a closed cycle configuration.

3.1.2 Nuclear power.

This is unlikely to happen in Ireland for various reasons both political and technical. Nuclear power stations are in use world wide. The general trend since the first generation of them is to gain efficiencies through an increase in reactor size and coolant temperature. The larger size allows economies of scale. The higher temperatures means better Carnot efficiency.

One interesting aspect of nuclear power is the size of modern reactors compared to the grid demand. Back in 1998 the ESB planning criterion included the clause that not more than 35% of the generation capacity should be situated in one location [9] The summer night valley record is 1,786 MW.[10] The output from the European Pressurized Reactor design is 1,650MW [11], [12] Most other generation III reactors also have outputs above 1GW with the exception of the Westinghouse AP600. So it would be difficult to have the reactor running at capacity without a lot of stand by power. All current reactors are scaled up versions of those available in the 1950's [13] with efficiency improvements from 25% to 40% through the use of higher steam temperatures. This is sill far below the efficiency of a modern CCGT plant.

Looking to the future it is interesting to note the timescale of some of the generation IV reactors mentioned in [12] with prototypes of the pebble bed and molten salt reactors having being developed as far back as the 1960's. While [13] doesn't mention pebble bed the analysis on page 74 could be extended to cover it. Liquid metal cooling and pumping is also discussed. Given the long gestation period it's unlikely that any of the generation IV reactors will play an important role in Irelands power supply in the foreseeable future.

3.2 Renewables

3.2.1 Wind

There are plans for up to 19,758.4 MW of wind power including those in the queue. This completely outstrips all other proposed generation methods. As wind can be variable there have been many proposals to use large scale pumped storage to provide a backup to wind power. But modelling shows that the chances of having a 10 day lull country wide in the wind is once in every fifteen years.[8] This has implications for the scale of storage needed, if it is to handle such an event without a large capital cost.

As described previously one way to balance wind is to use fast starting gas turbines. Wind production is generally predictable hours in advance.

3.2.2 Biomass, Biogas

The total of biomass projected is 24.8 MW of this only 0.1MW is connected. Without a massive increase in the production of biomass this will not reach gigawatt levels. However, it should be noted that biomass in general can be treated like solid fuel. It is storable and dispatchable. It could be used in existing peat plants or perhaps as a booster fuel in CCGT plants.

Biogas is listed at 21.4MW but in contrast to biomass most of the anticipated supply is already connected up with just 1.5MW in the future queue.

3.3 Transmission network improvements.

This is not a power source as such, but reducing losses in the grid directly increases the effective power delivered to the customer. One advantage of that future fuel consumption is reduced by a capital investment. The current distribution loss adjustment factors vary from 1.015 at night on 38KV lines to 1.092 during the day for low voltage sales. [14]

Power loss from resistance is I²R . By doubling the voltage the same power can transmited with half the current. As its simplest this would reduce heating on power lines to a quarter of the previous value. And that since there is now current there will be a lower loss in voltage. Alternatively you could transmit twice as much power with the same amount of lost heat generated, resulting in a doubling of the capacity without doubling the losses.

There are other factors to take into account such as the voltage ratings of insulators, transformers and switchgear. The ESB are rolling out network improvements to sections of rural medium voltage 10KV network. [15] The changes include an improved conductor and new transformers to allow an increase to 20KV. Power losses should drop from 8% to 7.5% This is projected to save 132GWh per year. Averaged over a year this is equivalent to an extra 15MW capacity. Since winter loads are higher than summer the generation capacity saved would probably be in the order of 30MW and and so contribute at least as much capacity as that provided by either biomass or biogas.

The opportunity may also be taken to replace the conductors as well.[16][17][18] In this case the replacement was able to carry 50% extra current with the same size and weight as the original conductor..

The heating of cables limits the power that can be transmitted through them. During colder periods or when there is more wind the better cooling would enable more heat to be generated within the temperature limits of the cables. [19], [20] This means that up to 100% extra capacity could be handled under ideal conditions with a cross flow of 12m/s. This may be of benefit to wind farms in reducing transmission line costs as wind farm output increases during periods of high wind. In addition to modelling the transmission line temperatures can be monitored directly using fibre optics [21] Depending on the product used hot spots could be detected to within 0.5m

3.4Combined Heat and Power

The basic principle behind combined heat and power (CHP) is that there is a lot of waste heat in electrical production. If there is a use for this heat it may be more economical to forgo the economies of scale of a large generating plant and use a less efficient on site generator. An alternative viewpoint and perhaps easier to visualise is that if you are already using fuel to produceif the electricity generated was used on site then much of it would converted to heat as it is used so the reduction in heat production may not be as great as supposed.

However, it should be noted that in cold spells CHP operators may become nett importers of power as electrical generation is ramped back in favour of local heat production. At present Alumina have one 130MW CHP plant connected to the transmission grid. In the case of Alumina they had an on side demand for 390MW of heat and only for 42MW of electricity. [22] Overall they achieved an efficiency of 89% There is another 178.8MW existing and including all possible queued sources coming on line the total would be 990.4MW.

4Future power sources

4.1Wave and tidal power

Despite the huge potential for wave power the road map for 2020 only indicates a total of 75MW for the Republic and up to 300MW in Northern Ireland. The advantages of tidal power include the astetics since the generaters are out of sight. They are unlikely to be a thread to marine life as those living in tidal areas have to be able to swim fast

Because the Irish sea can have water entering from either end the tides aren't synchronous. This means that instead of having tidal stations peaking at the same time it could be used to allow continuous power production. The key factor in tidal turbines is that most tidal flows are quite slow and new turbine designs are needed. [23]

5Storage

5.1 Cost of electricity through the day

Storage is inefficient as power is lost during transfer and conversion to other forms of energy. Storage is also expensive. What makes it practical is that at peak time electricity is also expensive. The illustration shows that the cost can vary by a factor of ten over very short periods especially at peak system load. In order to receive this premium price an operator would either need to supply power very quickly as in the case of hydroelectric, or have unused spinning reserve in place before the power is needed. As more storage comes on line this price discrepancy may be reduced as there are more suppliers competing to supply.

Illustration 2: Single Market Electricity price 14 Dec 2011

http://www.sem-o.com/

Suppliers of base load power would receive the base price. This would particularity affect nuclear power plant as they can take longer than most other plants to change output level.

5.2Short term storage

There must be extra power available to the grid at all times to handle an outage of the largest component in the grid. There are several constraints to this mostly related to the amount of power that can be transferred across sections of the grid. [24] In the Republic the rules include having at least five high inertial machines on load, this is to provide some of the power needed for the first fifteen seconds of an outage. Another is that the open cycle gas turbines should between them have at least another 300MW of capacity ready to be used as reserve power. If an outage happens while pumping at Turlough Hill the pumps can be restricted to free up their electrical demand. The rules also hinder the use of a large nuclear reactor, as reserve capacity equal to it would have to be available within 90 seconds adding to the cost of operation.

5.3Hydro-electric

Most Irish rivers have been dammed to the extent that public support would allow so it's unlikely that significant hydro electric resources will come on stream in the future. The main pumped station in Ireland is Turlough Hill. It was originally built provide load balancing, possibly in anticipation of nuclear power at Carnsore point. It is still the only working pumped storage station on the Irish grid, though the 70MW plant in Cork should follow.

5.3.1Spirit Of Ireland

This is a proposal to setup large GW scale pumped storage reservoirs along the coast. To model how this would behave Dinorwig in Wales could be investigated using the East – West Interconnect. Only if this proved successful should construction be considered out here and even then it would have to be justified relative to building another interconnector to Wales. It should be simple enough to generate a short list of suitable sites using a computer [25]

5.4Interconnectors

The interconnectors are being treated as storage in the sense that electricity can be bought and sold across it. It can sink or source power. While interconnectors are usually more reliable than generators the Moyle interconnect between Northern Ireland and Scotland is currently off line [26] So at present there are no working interconnectors to Great Britain. Once the Moyle interconnector and the East-West interconnector are connected up there will be an import capacity of one gigawatt to the island.

The UK have a 2,000MW connection to France and a 1,000MW one to Belgium.[27] Because of language, cultural and time zone differences it is unlikely that the UK phenomenon of having a huge surge in demand due to kettles being put on at the end of a particular television program would also be matched by a synchronous sharp rise in demand on the continental side of the cables. In Ireland domestic consumers share many of the same attributes as those in the UK so there may be times when there are simultaneous demand spikes on both sides. The likely hood of this is probably decreasing since more consumers have access to time delay viewing solutions. Imera power have a license for two more interconnectors if the market demand is there. [28]

5.5Electric vehicle batteries

It has been proposed to use the batteries in electric vehicles to store electricity. There are several types of battery in use. First lead acid will be considered. [29] The REVAi car has a 9.6Kw lead acid battery. At a replacement cost of €2000 this would equate to a cost of €208/KWh. Its expected life time is up to three years. Assuming that they could take a 90% deep discharge every day with a 90% round trip efficiency this would work out at a cost of 23.5c per KWh stored. This cost is based on the assumption that the battery life is reduced on each full charging cycle and does not include the cost of the energy to charge the battery.

Illustration 3: Single Electricity Market 17 Dec 2011

The other major technology is lithium. Deutsche Bank have been reported as predicting a price drop for lithium batteries to about $250 per KWh by 2020. [30] This is still above the price of the lead acid. In a transport role the weight advantage of lithium to lead more than compensates for this. While some lithium batteries may have longer lives than lead acid, the most common use of lithium batteries would be in portable electronic appliances such as laptops, mobile phones, portable players and tablets where reduction in capacity is the norm common.

6Future Storage options

6.1.1Compressed Gas

Air can be compressed and stored underground in old mines. While it could be used to drive a turbine this would be inefficient as the cooling effect from expansion would reduce the temperature of the air leading to some volume reduction. One solution to this problem is to use a heat exchanger to bring the air back up to ambient temperature. Another is to use the compressed air to feed the a Combined Cycle Gas Turbine to increase its efficiency.

In Ireland the only suitable sites for underground storage would appear to be in the salt mines of Eastern Antrim [31] in the Larne area. It is unknown if the area near the Ballylumford power station would be suitable.

7Demand reduction and Load balancing

On the demand side the use of smart meters and variable pricing may change the behaviour of many domestic consumers but trials have shown little change in some commercial consumers. If peak demand could be reduced there are potential capital savings because less plant is required to cater for peak demand.

The results from the commission for energy regulation trial of smart meters include both good and bad news. [32] With domestic customers there was a significant response to usage reduction with 74% making major changes. In general there was a reduction in usage by 2.5% and a reduction in peak usage by 8.8% With SME customers no statistically significant reduction was noted for most customers. One of the most frequent reasons cited was that it was not possible to move usage to off peak times.

Another way to reduce peak demand is to pay some customers to not use electricity. Under the current Eirgrid Winter Peak Demand Reduction Scheme customers will be paid €224 per MWh that they reduce their demand during peak hours [33] , provided they keep to an agreed minimum reduction. The penalty clause is that if a reliability charge of €783 per MWh that they go over the agreed level during peak time. During the winter of 2010/2011 a total of 15,593MWh peak load was reduced.

7.1Insulation

Degree days are a simple metric to predict heating demand. [34] The air in a building is typically two or three degrees warmer than that outside. Since a minimum comfortable temperature is about 18° C then no heating would be required if the outside temperature was 15.5° C or higher. If the temperature was 5.5° C then ten degrees of heat would be needed each day. The sum of the degree days gives an indication of the heat load required.

Table of degree days for Dublin [35]

Looking at data for the UK as a whole [37] the correlation between temperature and demand can be recognised.

It should come as no surprise that domestic electricity usage increases in winter. [36] A survey of Northern Ireland usage showed significant increases in most homes surveyed of between fifty percent extra up to double the summer power usage. What is also noteworthy is that there was also some small widening of peak usage times.

Illustration 4: UK electricity demand

Illustration 5

From the above it can be seen that much of the increased winter demand for electricity is for heating purposes. Much of Irish building stock is poorly insulated and the average Irish dwelling had CO₂emission levels 104% more than the EU-27 average [38]. This is in part due to the use of solid fuel.

7.1.1Health Benefits

The 2007 All-Ireland policy paper on fuel poverty and health references 2,800 excess deaths each winter on the Island some of which can be directly related to the inability to afford heating. [39]

A BER rating is an indication of how much energy is needed to heat a building.

While most new domestic buildings are rated at B2 or B3, using between 100 and 150 kWh/m²/year most pre existing stock would have a rating below C1 and use substantially more power to achieve the same temperature. It is estimated that at an average cost of €30,000 per house, 500,000 older buildings could be brought up to a C1 BER rating. [40] This would help reduce both the daily and seasonal variability in electricity demand. In both cases this would be achieved by a reduction in the amount of heat needed and in the case of daily peak demand a better insulated house would stay warmer longer which offers further possibilities to reduce demand through the use of smart meter.

8Other Improvements.

As materials science progresses more options will become available. These may be in developing new materials and more economical methods of producing existing materials. In short there are areas where there is no need for us to invest heavily.

We should not invest in nuclear power plant research as we will not need multiple units. The semiconductor industry is investing continuously in producing more power efficient devices. Regarding nuclear fission we are already a participant in the European Fusion Development Agreement [41]

The International Technology Roadmap for Semiconductors[42] is the industry's guide to achieving that for at least the next fifteen years. Their More than Moore paper [42] also indicates other areas of technology they plan to develop in future.

One major use of power is in the cooling of rack mounted servers. A study by google into drive failures showed that temperature alone wasn't a predictor for failures.[44] Intel have demonstrated ambient air cooling for servers could save up to $2.87 million dollars and 76 million gallons (us) a year in a 10MW data centre. [45]

9Discussion

In an ideal world we would have freely available energy and not be bound by current constraints. The earth's crust contains far more aluminium than iron and our society could move from a world where rust is a large concern to one where vehicles lasted far longer than they do today. With enough energy many similar substations become possible. However, the world has a restricted supply of affordable energy and a growing population. But it's not all doom and gloom. At present only between 1.3% and 2% of primary energy is used to create fertilizer with most of the energy needed for the Harber process. Such levels are capable of being provided by existing renewables so at least there is no threat of global starvation in the future.

There is a finite supply of fossil fuel which is alternatives need to be sought before the supply runs out. Ireland is positioned at the west of Europe and has an abundant supply of wind from the Atlantic ocean. At present on land wind farms are the most efficient large scale way to harness renewable energy in Ireland. The wind doesn't blow all the time so there needs to be a mechanism to cater for that eventuality. A new pumped storage system would require considerable capital investment relative to using existing capabilities. The combination of the East-West interconnector, smart meters, allowing some degree of load shedding, existing pumped storage and quickly dispatchable plant should cover the discrepancy between forecast and actual wind.

Commercial buildings are generally poorly insulated. In some cases this is down to cost savings on the original building. A commercial premises that is only occupied during business hours will only need to be warm for a quarter of the time so payback times may be longer than for domestic buildings that are continually occupied. In Portugal it is now mandatory for commercial premesis above 1,000m² to display an energy certificate.

10summary and conclusion

Upgrading the thermal insulation of older housing stock will reduce the demand for heating in general which is particular relevant to peak electricity demand. The costs of doing this are quite high but would be financed by savings recouped later on. These would include taxes paid by workers, preferential loans taken out by householders to be paid out of cost savings as well as others such as reduced health care costs caused by complications of living in a cold environment.

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