Oswald Consultancy Ltd Can Scottish hydro smooth wind and wave power? Oswald Consultancy carried out this assessment and would like to thank Scottish and Southern Energy for their invaluable assistance in providing operational data and explanation on the hydro plants they manage in Scotland. This 2007 study was originally commissioned by the Scottish Sustainable Energy Foundation who unfortunately went into liquidation.

Oswald Consultancy Ltd Can Scottish hydro smooth wind and wave power? It is known that renewables such as wind and wave deliver highly variable output of electricity due to fluctuations in British weather i.e. wind. We wish to know if Scotland’s existing hydro plant can make a significant contribution to smoothing this power delivery The paper concludes that this is not likely as there are already many existing constraints on the operation and power delivery characteristics of Scotland’s hydro plant and there is little scope to modify the plant’s behaviour –To understand this fully it is necessary to understand the constraints and power characteristics of the existing hydro plant in more detail Scottish wind output sufficient to meet 40% of Scotland’s electricity needs, Jan 2006, Ref Oswald Consultancy

Oswald Consultancy Ltd 5.2%5.5% 1.7% 2006 Scottish hydro contribution In % of Scotland’s electricity (4.3TWh) was generated by hydro plant Nearly two-thirds of this was generated by large hydro (2.5TMW) Here we consider the detail power characteristics of Scottish hydro plant –This has been compiled with the generous assistance of Scottish and Southern Energy who are the largest operator of conventional hydro in the UK SSE: 1050 MW conventional hydro plus 300 MW pumped storage Scottish Power: 500MW conventional hydro plus 540 MW pumped storage Large Hydro (no SROCs) 7.0%

Oswald Consultancy Ltd Hydro - Understanding fuel flow Hydro plants are fed by water which is collected in the catchment area and sent to the turbines. On route, the water may be captured in a reservoir, which allows storage and control of water flow and power. However, many hydro plants are supplied immediately by the river and there is little control over flow; these are called run of the river systems. –In designing a hydro plant the designer has a choice of fitting a large or small turbine relative to the maximum flow. A small turbine will spend more time at full power and so provide more consistent power, while a large turbine will provide a higher power but less consistently. In other words a small turbine will have a higher load factor over the year (higher percentage of full power) and a large turbine a lower load factor. –Understanding the physical constraints explains the power characteristics of different hydro plant. Reservoir Run of river Small turbine with high LF or Large turbine with low LF Controlled flow Uncontrolled flow Catchment area

Oswald Consultancy Ltd Constraints on operation of hydro plant The output of hydro plant is often determined by external constraints on operation, including the following: –Cascade hydro systems have stations in series along the same river and power delivery downstream is often decided by upstream control decisions. –Water flow is managed to avoid large changes in flow (and therefore power), as sudden changes in river height has ecological and safety implications, and can cause difficulties for other river users such as anglers or canoeists. –Operators are usually required to ensure a minimum flow is maintained along a river (called the statutory flow) to avoid the river running dry. –Some storage capacity is held in reserve in reservoirs to provide a buffer in case of extreme rainfall events and alleviate downstream flooding. –River flow affects wildlife; e.g. water spray is necessary for healthy algae, which are fundamental to the overall ecological health of the river. –Water storage levels in spring are monitored and the flow is managed to ensure some water is left over for the end of the summer. –Hydro plant designed for daily peaking power will have a low LF. These constraints mean each hydro plant has different characteristics in power delivery. –In the following section, different plants are considered in detail, with the plants grouped into plant having low, medium and high load factors.

Oswald Consultancy Ltd Low Load Factors<25% Sloy10% Errochty16% Livishie22%

Oswald Consultancy Ltd Sloy, 152MW Plant description –Large plant capacity and storage, never spills –Designed as peaking plant for Glasgow The half hourly data shows Sloy is typically used as peaking plant in late afternoon. The plant has high power (152.5 MW) but limited storage. Consequently, it generates for only a few hours per year but those hours are carefully chosen and traded when demand and prices are highest. The daily load factor plot shows winter months deliver more water and power than summer. Annual Load Factor is typically 10%

Oswald Consultancy Ltd Errochty, 75MW Plant description –Large plant capacity and storage, very rarely “spills” (a deliberate over flow of water without generating electricity) The large turbine and storage can be used to manage daytime demand for power. Daily load factor highest in wettest months, some days at 100%, some summer days at 0%. Annual Load Factor is typically16%

Oswald Consultancy Ltd Plant description –Run of river, very limited storage, spills very regularly The half hourly data shows Livishie is typically used for peaking in the early morning, afternoon and evening (it operates either at full load or does not operate). Livishie power station is supplied by a whole series of small dams, tunnels, aquaducts, and taps, and controls a series of small lochs, streams, and watersheds in the mountains to the North of Glen Moriston and the West of Loch Ness. The waters are taken to a small headpond on the Loch Bhlaraidh, which provides less than a days storage, and from there by pipe and tunnel to Livishe power station. Daily plot shows the plant generates little in the summer. Annual Load Factor is typically 22% Livishie, 15MW (

Oswald Consultancy Ltd Medium Load Factor 25 to 45% Kilmorack33% Fasnakyle37% Luichart45%

Oswald Consultancy Ltd Plant description: –Run of river, no storage, at the end of a large catchment. –Storage cascade, spills very regularly, runs continually to facilitate statutory requirements. The half hourly plot shows that the plant continually provides low base load power as it maintains statutory minimum flow level in the river. When high rainfall occurs, the plant operates at full rate and/or spills because it has no storage facility, as shown in daily load factor plot. Typical Annual Load Factor: 33% Kilmorack, 20MW

Oswald Consultancy Ltd Plant description: –Large plant capacity, medium storage, spills occasionally, runs to facilitate statutory requirements locally and within cascade The half hourly plot shows that the plant continually maintains some flow to maintain minimum river flow –Medium storage capacity gives the flexibility to increase generation by stages to a higher load when needed, which is usually from around the early morning until late at night. Daily plot shows plant never at zero flow and sometimes as high as 90%. Annual Load Factor is typically 37%. Fasnakyle, 69MW

Oswald Consultancy Ltd Plant description –Medium plant capacity and "pondage" storage, rarely spills, runs to facilitate statutory requirements within cascade. The Luichart plant typically runs with one of its two turbines at full load. This is done to maintain the statutory minimum flow in the river and not because of power reasons. Daily load factor plot shows never at zero load factor for a day. Typical Annual Load Factor of 45%. Luichart, 34MW

Oswald Consultancy Ltd High Load Factor > 45% Orrin50% Ceannacroc50% Cuileig61%

Oswald Consultancy Ltd Plant description: –Small plant capacity, medium storage, spills occasionally, can be required to facilitate statutory requirements within cascade. The half hourly plot shows that the combination of small plant capacity and medium storage allows the plant to operate at full power in January. The daily load factor plot shows water spilling in winter is common. Annual Load Factor typically of 50%. Orrin, 18MW Water spilling

Oswald Consultancy Ltd Plant description: –Small plant capacity, large storage, very rarely spills, runs to facilitate statutory requirements. The half hourly plot shows that the plant is used to provide bulk daytime power. The daily load factor plot shows that as a result of maintaining statutory minimum flow in the river the plant never operates below 15% load factor. Typical annual load factor of 50%. By comparison, Kilmorack has the same rated capacity (20 MW) but only an annual load factor of 33% –Kilmorack, is run of river and has much less storage. Ceannacroc, 20MW

Oswald Consultancy Ltd Plant description –Run of river, very small plant capacity, no storage, spills very regularly The half hourly plot shows that the plant is highly dependent on river flow (rainfall). Due to the small capacity the plant will spill water if the rain is heavy, while generation falls noticeably in low rain conditions. The daily plot shows the plant tends to run at either 100% whilst spilling water, or at 0% output. Annual Load Factor is typically 61% Cuileg, 3.1 MW

Oswald Consultancy Ltd Conclusions Hydro plants in Scotland were sized and designed to satisfy the normal variation in electricity demand of the local consumers. The plants are continually managed to: –Ensure that statutory minimum flow is maintained in rivers –Satisfy the requirements of other river users (e.g. wildlife and anglers) –Manage cascade hydro systems –Ensure reservoirs do not run dry before the end of the summer –Maintain reserve capacity in reservoirs in case of flood risk –Follow daily variations in electricity demand There is limited scope to use Scottish hydro to manage the substantial and uncontrollable power fluctuations caused by large scale development of stochastically variable renewables on the grid (e.g. wind and wave).