Renewable Energy Generation in Scotland - Assignment Example

RENEWABLE ENERGY GENERATION IN SCOTLAND: WHAT IS THE OPTIMUM FRACTION OF RENEWABLE ENERGY (RE) GENERATION IN SCOTLAND? TABLE OF CONTENTS 1. INTRODUCTION…………………………………………………………………….3 2. How does Renewable Energy generation Influence Demand Management in the Scottish scenario……………………………………………………………………….....3 3. What are the consequences of increasing or decreasing RE generation within the Scottish Grid?.......................................................................................................................5 4. Which mixture of RE generation (wind, solar, wave) would you suggest as being optimal in Scotland?............................................................................................................7 5. Are additional storage facilities needed in Scotland? If yes, then what technologies would you recommend pursuing and is it possible to identify possible sites?...................................................................................................................................10 6. CONCLUSION…………………………………………………………………… …11 7. REFERENCE LIST…………………………………………………………………..12 INTRODUCTION The amount of renewable energy generated in Scotland is increasing day by day, with onshore-wind energy being the single largest contributor. The present trends in renewable energy generation indicate that it would technically be feasible to achieve the Scottish Executive’s target of 40% energy generation from a range of renewable resources by 2020.While renewable energy generation will undoubtedly help meet Scotland’s commitment to addressing climate change, it also places a lot of constraints on the existing grid and power distribution system due to the intermittent generation of electricity from wind-mills, which calls for adequate interconnectivity build-up of the Scottish grid with its neighboring grid systems besides necessitating the introduction and implementation of energy storage and demand side management technologies. In addition to onshore-wind, other renewable technologies such as offshore-wind, wave and tidal energy also hold out promises of energy generation though to lesser degrees. This paper attempts to address some of the basic issues in renewable energy generation as applicable to the Scottish context. The influence of renewable energy generation on demand management, the effect of rise or fall in renewable energy generation on the Scottish grid, the accessory storage facilities and technologies required for renewable energy industry and their possible sites are also discussed. 1. How does Renewable Energy generation Influence Demand Management in the Scottish scenario? According to FREDS (2005,p2)The government of UK has set a target to cut CO2 emissions by 60% by 2050 to achieve which 30-40% of electricity would have to be generated from renewable energy resources. This requires that Scotland generate 40% of its electricity from renewable sources by 2020(ibid,p3). The Friends of the Earth Scotland (n.d., p4) point out that demand scenarios can be either of demand growth or of demand reduction. In the Demand Growth scenario, demand is expected to grow again in 2011 as the present recession is about to be over and the projected demand will attain a steady growth of 12.2% corresponding to 45,900GWh annually by 2030. In the Demand Reduction scenario, the demand will start diminishing from 2012 resulting in an annual electricity consumption of only up to 35,180GWh by 2030.The projected values for demand growth and demand reduction in Low Renewable scenario and High renewable scenario are shown at Table-1 while renewable energy generation as percentage of total consumption is shown at Table-2(Friends of Earth, n.d,p12). The projected electricity supply for 2030 in comparison with the projected demand which it is likely to exceed is shown at Fig-8. Both the UK Committee on Climate Change and the Scottish Government have set demand reduction targets of 20% and 12% respectively to be achieved by 2020. Reducing electricity demand in general and peak demand in particular, is the cheapest way to cut greenhouse emissions. The peak electricity demand has to be taken care of carefully, since this signifies the amount of electricity that should always be made available for security and it should be provided by generation or interconnectivity in transmission. Peaks and troughs in electricity demand can be smoothened out by making provisions for deferrable demand which makes possible the shifting of demand by a few hours. Smart meters can communicate signals to electricity consuming gadgets so as to facilitate or vary their consumption according to availability of power in grid so that overall energy consumption can be minimized during peak hours. Electric cars can also be used as energy storage devices to smoothen out peaks in demand and also by providing for energy to be drawn in from the batteries in times of shortage. Anaerobic digestion can be exploited to use biogas for reducing the contribution from renewable energy sources. In the context of a 100% renewable energy supply, the four methods to ensure security of supply are by Backup Generation to increase supply at short notice, by Deferrable Demand to reduce demand at short notice, by Energy Storage for storing electricity in other forms and by Interconnection to share reserve, and to smoothen demand and supply. The Friends of the Earth Scotland(n.d., p20) argue that Demand Management, in the context of Renewable Energy production requires of Scotland to aggressively pursue and exceed energy-saving targets in the Energy Efficiency Action Plan and ensure meeting renewable energy targets well in time. They recommend that target levels of ambition for both renewable heat transport power should be raised in proportion to achieved renewable energy production levels. Lastly, deferrable demand should be increased by state-of-art technology such as smart metering. 2. What are the consequences of increasing or decreasing RE generation within the Scottish Grid? The two main factors to be considered with respect to the effect of renewable energy generation on the Scottish grid are the availability of network import/export capacity and the availability of flexible generation within Scotland. The existing grid network has to be expanded so as to equip it with the capacity to export power out of Scotland when generation exceeds demand. Similarly, it is important to strengthen the capacity for importing electricity which would be required in times of peak demand exceeding generation output (FREDS, 2005, P9).Both these options call for increasing interconnectivity with the GB grid and to the continental grid. As per one view, there would have to be expansion in HVDC interconnectivity with the Irish, Belgian and French grids, which may have a destabilizing effect on the GB grid and may not be attractive from the point of view of political, strategic and security considerations(Select Committee, n.d. p231-232).This situation is explained by Fig-4 Fig-5 and Fig-7.The transmission wind farm connections and transmission reinforcements in the area of M/s SP Transmission, which is the company that provides 2.8GW of current transmission capacity from Scotland to England are shown at Fig-6. The high wind resource potential of Shetland can be tapped by a proposed Norwegian interconnection. The increase in the intermittent energy generation accompanying renewable energy production would have to be supported by increasing the proportion of spinning reserve generation plants with fast reacting response. Open Circuit Gas Turbines and pumped-hydro storage facilities are examples such fast response generation plants. Critics of renewable energy point out that the above options would jeopardize the predictable framework of the GB grid by destabilizing it(Select Committee, n.d. p231-232).This problem is accentuated by the absence of a single body overseeing the technical infrastructure or accountable for improvements being incorporated into the grid. The unpredictable and intermittent nature of renewable energy generation calls for positioning a mechanism for a firm backup generation such as standby diesel generators and open-cycle gas turbines as mentioned above, which would be readily available to replicate electricity generation from renewable source in case of failure of renewable energy plants. Thus it appears that adequate technical adaptation for standby capacity has to be provided to accommodate intermittent and unpredictable generation, while at the same time sacrificing grid integrity. The overall effect of increase in renewable energy generation, in such context would be one of destabilizing the integrity of the Scottish grid, which may have to be neutralized by improving interconnectivity with the GB grid and the continental grid. The impact of 32% wind power energy on GB system during 2006 winter peak is shown at Fig-3(Grid Conference Session 3B, 2011). A hypothetical example described below shows the consequences of decreasing and increasing renewable energy generation during an illustrative period of six hours of electricity output from a 40 MW wind farm supplying power to a town connected to the local grid shown at Fig-9(University of Edinburgh,2006,p44). The first one hour witnesses demand of electricity equaling generation. In the subsequent four hours we see a drop in generation of renewable energy and the electricity equal to the shortfall is meet by importing it from the grid. The remaining one hour period is characterized by renewable energy generation exceeding the demand which is exported through the grid. Since the generated amount of electricity exceeds the rated turbine power during the last one hour, the distribution network operator DNO takes steps to restrict the power generation values to lie within the rated power. 3. Which mixture of RE generation (wind, solar, wave) would you suggest as being optimal in Scotland? A study of numerical results from six technology scenarios and five area scenarios indicate that less than 6GW of on-shore wind plant in Scotland can supply 40% of electricity demand.(University of Edinburgh, 2006, p50).This study found that 23% of electricity demand could be possibly met by off-shore wind plants(ibid,p51). Another 20% of electricity could be supplied by wave energy plants generating 3GW of electricity(ibid,p52).The study also found that 5% of the total demand could be met from tidal wave plants generating 750 MW of electricity. Furthermore, it was found that by opting for a mix of these different types of renewable energy plants, 5.5 GW of electricity could be produced which would account for 40% of electricity demand in Scotland. The amount of capacity that is required to be installed at these plants can be reduced by utilizing the capacities of presently operational hydro and biogas plants and of those in the anvil. The above study has considered two mixed portfolio scenarios of renewable options arrived at from a combination of onshore-wind, offshore-wind, wave and tidal energy. In one option, the relative proportions of onshore-wind, offshore-wind, wave and tidal energy were held at 75-10-10-5% respectively, and the total renewable energy generating capacity was increased in four stages starting from 750MW, and ending at 6GW (University of Edinburgh,2006,p54). The graphs of this scenario are shown at Fig-1, a), b) and c). In the other mixed portfolio scenario, the combined capacity of the above portfolios were held constant at 6GW, but the relative proportion of onshore-wind was increased starting from 0% to 100%, corresponding to 0GW,750MW,1.5GW,3GW and ending at 6GW, while the remaining part of renewable energy from offshore-wind, wave and tide was fixed in 2:2:1 ratio(ibid,p55).The graphs for the second option are shown at Fig-2, a),b), and c).These options can be called the Fixed Mix option and the Variable Mix option. From Fig-1 b), it is evident that around 5.5GW of mixed capacity of renewable energy sources would have to be installed to meet the demand in Fixed Mix option. A shortfall of 10.4% of the total demand would still remain with a mixed capacity of 6GW. In the Variable Mix option, the values of plant capacity factor are found to remain more or less constant in Fig-2 a), with optimum values possible with 3GW of onshore-wind contribution. It can be seen from Fig-2,b) and c) that improvement in hour-by-hour matching is possible with lower contributions of onshore-wind. It is also seen that at lower onshore-wind contribution, lower levels of demand are exceeded more frequently while at higher contribution of onshore-wind, the higher values of electricity demand are more frequently exceeded. The above study indicates that that a balanced electricity generation mix with 3 GW from offshore-wind, 1.2GW from offshore-wind, 1.2 GW from wave and 0.6GW from tidal power in the ratio 5:2:2:1 can provide the optimum solution of performance requirements for meeting demand targets. The following pertinent conclusions have emerged from the above study (University of Edinburgh, 2006, p65): i) Based only on onshore-wind, offshore-wind wave and tidal power, electricity of up to 6GW, 3GW, 3GW and 1GW can be generated in Scotland ii) The annual plant capacity factors exceed 30%. There exists a seasonal variation for capacity factors due to variation in wind and tidal power with more potential for generation in the winter season. iii) 3GW electricity generation from onshore-wind, offshore-wind and wave alone can meet at least 50% of the 40% target demand while a 6GW output can comfortably meet the target of 40% demand by 2020. iv) There is no guarantee that the demand target would be met hour-by-hour at any time in a year by renewable resources alone. The renewable electricity generation would be characterized by shortfalls and excesses throughout its production due to the inherent variability which characterizes its generation. v) Only for a fraction of hours during any given year will the value of 40% of the actual demand be actually met by renewable energy. vi) A renewable energy capacity of 3GW will meet 40% of actual demand between 12-18% of the time while a renewable energy capacity of 6GW will meet 40% of the demand around 40% of the time. Q4. Are additional storage facilities needed in Scotland? If yes, then what technologies would you recommend pursuing and is it possible to identify possible sites? Additional storage facilities will necessarily have to be provided in view of the long term policy goal of the Scottish Government to steadily increase the contribution from renewable energy, the major portion of which, in the near future would be from dominated by the onshore-wind sector. Electricity generated from wind would be highly intermittent, it being a function of wind variability and predictability. Even though predictable to some extent for short term time frames, the inherent variability of wind generated power output calls for special efforts on the part of the system operator to match supply and demand. For example the system operator may have to encounter times when the output power starts to decline while the peak demand rises or conversely, the output power may start rising when the demand starts declining. According to a Scottish Government study, in 2020, intermittent power generation may constitute around 50% of installed capacity (Scottish Government, p15) which may play havoc with the integrity of the grid due to the high proportion of variable generation. This problem can be addressed by introducing corrective measures such as enhancing interconnectivity with other systems, restricting output of wind into the system, controlling the rate of change of wind generator outputs and introducing energy storage technologies. Many storage technologies have been recommended for Scotland. Fig-10 shows the storage capacities and discharge times of storage technologies applicable in the Scottish context. The three major technologies suitable for Scotland are Pumped Hydro, CAES and Flow Batteries (ibid,p74). The schematics of underground pumped Hydro Plant is shown at Fig-11 while that of CAES or Compressed Air Energy Storage Plant is shown at Fig-12. Pumped hydro plants are constrained by geographic and environmental requirements for compliance. However, Scottish &Southern Energy (SSE) has plans to set up 300-600MW pumped hydro storage plants at Balmacaan, 300-600MW at Coire Glas and 72Mw at Sloy. Development of CAES plants are also constrained by geography and are yet to be taken up, due paucity of suitable natural caverns in Scotland. Abandoned coal mines in the Central Belt of Scotland are being assessed for their suitability for being converted into CAES plants. Flow Batteries are being developed by Plurion based in Fife. SSE have commissioned a 100kW demonstration Flow Battery at their Nairn substation. There is on-going research in the field of Flow Batteries with Scottish Power being one of the participants in a project named “Development of Redox Flow Battery for Utility Energy Storage” (Scottish Government, p 29-35).A geographical estimate of Scotland’s possible storage plants by year 2020 is shown at Fig-14(Stocks S et al,2010) CONCLUSION Though Scotland is endowed with rich resources of wind, tidal and wave energy sectors, a careful balancing of these resource utilization is necessary to obviate intermittent generation of electricity, which is compounded by the present inadequate connectivity of Scottish grid with the grid systems of the rest of Europe. The peaks and troughs in energy demand will have to be smoothened out by increasing the deferrable demand, by smart metering, by provisioning for back up generation and by taking resort to energy storage technologies. Interconnectivity of the Scottish grid needs further augmentation so as to enable export of power out of Scotland when generation exceeds demand and import of electricity in times of peak demand exceeding generation output. A balanced renewable energy generation mix with generation from onshore-wind, offshore-wind, wave and tidal-power in the ratio 5:2:2:1 is found to be the optimum ratio for renewable energy generation in Scotland. A better hour to hour matching is achievable with lower contribution from onshore-wind, while higher contribution from onshore-wind is recommended to achieve higher values of plant capacity factor in summer. Though many storage technologies are available, only the Pumped hydro, CAES and Flow Batteries storage technologies are likely to be relevant in the Scottish context. REFERENCE LIST Scottish Renewables Grid Conference Session 1 available at http://www.scottishrenewables.com/static/uploads/publications/grid_workshop_presentations_2011.pdf Grid Conference Session 2 available at http://www.scottishrenewables.com/static/uploads/publications/grid_workshop_presentations_2011.pdf Grid Conference Session 3A available at http://www.scottishrenewables.com/static/uploads/publications/grid_workshop_presentations_2011.pdf Grid Conference Session 3B available at http://www.scottishrenewables.com/static/uploads/publications/grid_workshop_presentations_2011.pdf FREDS 2005 Available at http://www.scotland.gov.uk/Resource/Doc/54357/0013233.pdf Friends of Earth Scotland The Power of Scotland Secured Available at http://assets.wwf.org.uk/downloads/power_of_scotland_secured.pdf Select Committee on Economic Affairs, House of Lords, Great Britain, The Economics of Renewable Energy, 4th Report of Session 2007-2008 Vol II, Evidence University of Edinburgh Matching Renewable Electricity with Demand 2006 available at http://www.scotland.gov.uk/Resource/Doc/112589/0027356.pdf Scottish Government Energy Storage and Management Study available at http://www.scotland.gov.uk/Resource/Doc/328702/0106252.pdf http://www.scotland.gov.uk/Publications/2010/10/28091356/0 http://www.all-energy.co.uk/userfiles/file/steven-stocks-190510.pdf Stocks S et al available at http://www.all-energy.co.uk/userfiles/file/steven-stocks-190510.pdf 2010 Read More