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Scotlands Aim For Renewable Electricity Environmental Sciences Essay

In the words of Ben Murray, "...it is possible to have a clean, green energy supply in Scotland. By 2030 renewable energy can meet between 60% and 143% of Scotland's projected annual electricity demand, depending of the level of investment in energy saving and new renewables. ...it is entirely plausible that no large-scale fossil fired generating capacity would remain online by 2030."

Taking up the challenge to forestall the impacts of climate change and achieve a largely de-carbonized energy supply, the Scottish Government has set energy targets for 2020; a reduction in GHG emissions by 42%, 20% total energy use coming from renewables with electricity getting 80% of the total while heat and transport have about 10% each (Garrad Hassan: 2010).

The general direction of research into ways of achieving this target tend towards

demand reduction and management including changing user behaviour and improved energy efficiency programs, appliances etc.

carbon capture and storage (Scotland has huge potential for storage options),

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updated electricity transmission and interconnection infrastructure,

thermal electricity generation,

and promotion of renewable generation, micro- and macro-scale.

It might seem a bit far fetched to expect a 100% delivery of renewable electricity by 2030, however, the role of renewables in the Sottish energy targets cannot be overstated. A plus for Scotland is the fact that there is a myriad of renewable energy sources waiting to be tapped. These technologies however are restricted by the scale of costs, speed of approval of suggested projects and public awareness and acceptance. After a drop from 2002 levels, the total electricity generated from renewable sources (renewable contribution to electricity) has steadily risen from 9% in 2003 to 27.4% in 2009; find below (Figure 1) the distribution of the various sources.

As can be seen in the figure (adapted from a document by the Scottish Government) the share contribution of each renewable resource has increased steadily with ample room for more growth. Scotland has large hydro resources (including waves and tides), abundant wind energy (including onshore wind and offshore wind), biomass and energy from waste. Each of these obviously has varying degrees of availability and it is generally accepted that matching energy demand with supply from renewables however difficult can be done with either of two possible scenarios. Utilizing a capture area larger than the community to be served or reducing that community's demand such that it is commensurate with RE generation (Born, FJ et al: 2001). The bottom line is that 100% RE generation (or more) is possible with aggressive DSM measures. Find below a table showing potential RE generation capacity for Scotland on the assumption that constraints do not exist and generation is favourable.

As can be seen in the figure (adapted from a document by the Scottish Government) the share contribution of each renewable resource has increased steadily with ample room for more growth. Scotland has large hydro resources (including waves and tides), abundant wind energy (including onshore wind and offshore wind), biomass and energy from waste. Each of these obviously has varying degrees of availability and it is generally accepted that matching energy demand with supply from renewables however difficult can be done with either of two possible scenarios. Utilizing a capture area larger than the community to be served or reducing that community's demand such that it is commensurate with RE generation (Born, FJ et al: 2001). The bottom line is that 100% RE generation (or more) is possible with aggressive DSM measures. Find below a table showing potential RE generation capacity for Scotland on the assumption that constraints do not exist and generation is favourable.

Presently, Demand Side Management (DSM) programs in Scotland are of the following kinds

customer side measures

network-driven DSM

incentives and grants

Renewable energy generation can enhance all of the existing measures depending on applicability.

Micro-generation (CHP): About 29% of energy consumed in Scotland goes to the residential sector for space and water heating, electric appliances, cooking and lighting. A large percentage of CHP in Scotland runs on gas, however, they can be made to run on energy from fuel (e.g. biogas). Using such technologies as grey-water treatment, micro-CHP, micro wind turbines, solar PV cells etc. micro-generation can be installed as a self sufficient system for a house. An example that incorporates renewable generation and energy efficiency is the Aurora House design collaboration between South Lanarkshire College, Dawn Construction and over 50 private sector partners. Find diagram of design below. This kind of installation will encourage awareness of electricity consumption as well as reduced reliance on central generation and transmission.

Distributed Generation: these are generation technologies typically small scale of the range of 3kW - 10000kW designed to provide an alternative to and thus ease dependence on traditional power generators. DG used in the Kerman PV Plant in the USA has been shown to have benefits including increased capacity and system reliability, avoided fuel costs, reduction in CO2 emissions, reduction in losses from reactive power etc. As a demand management strategy, DG is in effect in some small communities in Scotland. The Isle of Eigg off the west coast of country has put a cap on residential and businesses energy consumption at 5kW and 10kW respectively. Eigg has seen a reduction in carbon emissions and has achieved this through a range of renewable energy technologies installed to feed into the local grid. The mix of technologies includes a 100kW micro-hydro system, a 10kWp solar PV and four 6kW wind turbines. They also have a bank of batteries to store energy in over supply and a backup of two 64kW diesel generators (Ashden Awards: 2010). The result from the energy demand cap is ensuring that consumption is regulated and kept effectively low.

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Fuel Substitution: Fuel substitution projects have the effect of reducing total demand, i.e. changing the shape of the electricity demand curve. At the utility level, fuel substitution may not have the desired effect of demand management if the supply stays the same. For example a utility switching from coal burning to wind power to supply energy for peak periods will only affect the bottom line cost and emissions, but it doesn't affect the demand for energy. However, when substitution is taken to to the residential or business use, it radically changes the demand figures. Take space heating as an example, the substitution of electric resistance heating with ground-source heat pumps or water heating with direct solar power instead of electric heaters. Such substitution will reduce demand on the main grid yet provide consumers with the heating required.

Behaviour Change: In 2001, the European Commission funded a project "Changing Behaviour" that investigated a practical model to influencing change in consumers toward energy use and policies. The aim was to develop a practical tool-kit for improving DSM. The efforts of the consumers is invariably important. Distributed renewable generation appeals to end consumers mainly because it is becoming attractive to be "green". The image of living in harmony with nature will be a factor to consider as small renewable power generating units located at customer sites are likely to lower both the energy and peak demand. Tariffs designed to give incentives to the consumer for demand at RE peak generation and charge the consumer for high demand at low RE generation could also contribute to active demand management.

Incentives and policies: The DECC through the Renewable Heat Incentive planned to be in effect in April 2011, plans to encourage the widespread commercial use of renewable sources for heating. The Government expects a rapid growth of the industry and thus resultant reduction in demand for electricity for heating.

The Scottish grid, owned by Scottish Power and Scottish and Southern Energy, comprises of all the different points from electricity generation to final delivery to consumers, thus it includes the power plant, transmission and distribution system. As noted by Scottish Renewables (2008) the choice of increasing or decreasing RE generation must deal with these issues

distance from market

access to networks

charging for network use

supply chain and planning

inter-connection levels

Considering the need to decrease the effects of climate change and ensure energy security, reducing RE generation is implausible. It is highly unlikely that the target for reducing carbon emissions around the world can be achieved without fuels that have almost zero carbon emissions.

Ofgem and DECC convened a joint review of current Great Britain (GB) transmission framework, the Transmission Access Review (TAR) with the main objective of its being able to support renewable electricity generation by 2020. Given the remote locations of some RE generation sources and distribution points (e.g. Orkney Islands, Western, Shetland and Eigg Isles), the existing grid will need expansion and co-ordination, thus introducing the need for smarter meters and a smarter grid. A smarter grid (one that reinforces onshore and creates lines sub-sea or offshore), as shown in Figure 3 will sufficiently shorten connection queues, improve power delivery, reliability and efficiency. High levels of flexibility in the transmission system are important if Scotland is to achieve high RE generation.

Currently, Scotland transmission system is a 132kV network. Usually maximum and minimum voltage limits are set to prevent damage to equipment from over-voltage and voltage collapses respectively. It may therefore be necessary to invest in voltage control equipment or to require renewables generation plants to have control capabilities similar to conventional generators.

Automatic Generation Control (AGC) is responsible for matching power demand with plant production using the system frequency. Whenever there is an increase in one over the other, the AGC can increase production to match demand (in decreased system frequency) or reduce production in over supply`(increased system frequency). RE generation cannot be matched up in this way as their production is not dependent on system frequency. In cases where conventional generators also produce alongside RE generation, there will almost always be instances where they are off-loaded to absorb excess power from RE generations. With increasing RE generations, utilities would need to invest in load following plants to supply load in the instances where wind dies down for example and RE generation does not meet demand.

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Reports on Scotland's targets are positive given the increased RE generation which at the end of 2009 stood at 10,744.3GWh (Scottish Renewables: 2011), with Wind and Hydro constituting over three-quarters of the total. Currently, the country has 436 sites of RE generation with more planned for the near future as can be seen in Table 2.

The optimal mix of RE generation for Scotland would have to be one that performs as reliably or more effectively than conventional generation sources. It is evident form the table that wind energy receives the most attention. Thus given Scotland's location, a mix of Wind energy for base load, Hydroelectric for intermediate load and Biomass for peak load would be optimal.

Technological considerations

Demand for energy varies with time of day (daytime and night-time), weeks (weekdays and weekends) and seasons (spring and summer versus autumn and winter) every year. Thus it is easy to find that there are two peaks of demand per day in winter and just one in summer. To match these variations in demand, utility companies usually would designate power plants to supply base load. These plants in theory are to produce power 24 hours a day, all the year round to compensate for capital intensity needed to keep them in operation. There are plants that are run only at peak demand and just to supply energy for the length of time the peak lasts and to supply energy for unpredictable demand. These have low capital costs but high average costs mainly from the fuels costs. Then there are stations that exist to produce intermittent power supply, these smooth out the gaps between the base and peak load stations. They run mostly during the day and are started more often than peak load stations.

Offshore wind is capital intensive, however, wind energy as a whole is the largest RE source in Scotland. With wind energy supplying base load, the energy produced from turbines set up onshore and offshore can be directed straight to the grid eliminating the need for storage (which would be the case in any other situation). Variable wind power production will cease to be a problem when there is a large number of wind farms across the country. Conventional power plants experience technical difficulties ranging from long downtime for refuelling as is the case with nuclear power plants to a 10 - 15% service outage for the average coal plant. Research shows that wind and solar systems have a technical availability of about 97% and can easily replace regular base load plants. To effectively replace a coal base load plant, it will be necessary to install wind turbines to supply at least 150% the equivalent of 100% load. This will make up for the variations in wind power.

Hydroelectric power is the second most available resource in Scotland and when PHS is included, can conveniently supply intermediate load. As a result of the storage capability of PHS and the fact that there are not that many natural reservoirs (or available locations for artificial ones) or run-of-the-river hydro that can be utilized to supply base load, hydro electric can easily smooth out any gaps in supply from wind energy. In most countries, especially in the UK, PHS is used to supply energy at peak times. The Glendoe Hydroelectric Power Station located in the Highlands of Scotland (although currently shut down due to rock falls in the tunnel mouth) is predicted to generate about 180GWh annually, enough to supply 250,000 homes with electricity with full capacity reached in 30 seconds.

Thermodynamic considerations

Thermodynamic efficiency where there are minimal energy losses must also be considered in the choice for the optimal RE generation mix. The energy payback ratio (also known by other authors as energy ratio, energy return on investment etc.) can be used to determine the thermodynamic efficiency of generation technologies. It is simply defined as the ratio of energy delivered by a process to the energy input to the process.

Gagnon L (2008) found that the life cycle energy payback ratio of electricity for hydroelectric was highest compared to all other forms of generation, both conventional and renewable. The ratio was between 205 - 280 for hydro-power with reservoir and between 170 - 267 for run-of-the-river hydro. His results for wind took into account a use factor of 35% thus the low ratio of between 18 - 34. Biomass had a ratio of between 3 - 5 for plantations and 27 for waste. His analysis for solar PV and other conventional generation fell below the ratios for the three afore mentioned.

Economic considerations

Any investment in RE technology has to be considered based on marginal levelized cost and maximum CO2 saved. Wind energy may well be the cleanest form of RE generation and with advances in the learning curve, the cost of installation and management will get lower as time progresses. Find below Table 3 showing capital cost of selected power plants and the marginal (average) levelized cost of electricity from said power plants; all calculated based on US markets.

It can be seen from the table that among other RE generation, wind biomass and hydroelectric are among the cheapest to build. When measured against CO2 emissions saved, the costs drop even farther.

As one of the cheapest energy sources, using biomass power plants to supply peak demand will make eventual costs to the consumers lower. Biomass can in fact supply more power than that required for peak load, however, the ongoing debate between the proponents of food crops against energy crops is yet to be resolved. The answer lies in the opportunity cost of one over the other.

In the end, without demand management it would be impossible for any mix of RE generation to adequately meet energy needs no matter how many biomass plantation exists or how many wind farms are built or indeed, how much hydroelectric power is produced. It may yet be difficult to have 100% electricity from RE generation, thus the need to have a few efficient conventional power plants for necessary fall back plans.

To succeed at the challenging task of turning the whole country (at least the majority of the industries, electricity and transport) green by 2050, Scotland must invest in more energy storage options. The AEA in research for the Scottish Government has projected a possible need of at least 7,000MW (worst case scenario) of storage for 2030. Given that current PHS is of 400MW, there would need to be about 18 more installations of the same kind to meet this prediction. It is unlikely that there are sites that can adequately supply this using PHS alone. Thus the need to explore other energy storage facilities.

Pumped hydro energy storage in Scotland is used to supply peak demand and presently takes the form of two large schemes, 300MW (Foyers) and 400MW (Cruachan). There are another two large-scale schemes planned for the Highlands with another 900MW capacity and much smaller schemes with planning areas distributed across the country. The advantage of PHS is that energy can be stored for long periods and can also be released upon demand with little downtime. There is yet some opportunity for increased PHS in Scotland, like sea water PHS, and underground PHS. A 30MW sea-water PHS is being used in Japan with another planned 480MW for Ireland against 2013. Scotland has limited potential for this kind of storage facility because of its geographical constraints, yet its use of sea water can be incorporated to off-peak wind energy for pumping and other forms of RE generation, thus increasing its appeal. It would be more suited to offshore wind generation thus can be situated in areas near the Beatrice Wind Farm at Moray Firth or the Robin Rigg Wind Farm at Solway Firth. The cost of sea-water PHS are about 15% more that conventional PHS.

Vanadium Redox Battery although a fairly new technology has already found application in a number of countries. It was first tested for a house, integrated with solar PV in Thailand. In other countries like Kenya and Japan it is being used as back-up storage. Being a battery system, it can be integrated with any form of electricity generation and thus finds unlimited application for Scottish utility companies. There is ongoing research into the technology and its application for Scotland.

Even though Hydrogen has only been investigated for energy storage on a small scale, there are extensive possibilities for its use. In January of this year, the First Minister of Scotland officially opened the Hydrogen Office, a research facility set up to show the roles renewables, energy efficiency and hydrogen can play to guarantee the reduction of the effects of climate change. There are other projects that utilize hydrogen as storage for conversion to electricity by fuel cells and for use in electric vehicles. As a result of it still being tested worldwide and the absence of a learning curve, the capital cost of the technology is high.

Compressed Air Energy Storage (CAES) in spite of site constraints has some potential for development in Scotland. The issue however is its inherent use for natural gas turbines. The target for 2050 may involve some fossil fuel generation and thus CAES could be an investment towards that time. However, the government is still looking into the perfect mix of generation technologies (for all sectors) to achieve its targets.

Other energy storage facilities like flywheels and Superconducting Magnetic Energy Storage (SMES) also have application for Scotland as the former can support fluctuations from RE generation and the latter can be used for power quality for industries. However, flywheels have little advancements in Scotland and SMES come with the attendant environment issues.

In conclusion Scotland has the opportunity to act as leader in this era of climate, energy security and price worries; the combination of renewable resources, terrain and island network may well be the driving force to championing change in energy technology for the rest of the world.

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