Hydro-electric Power: Types, Generation, and Challenges

1. Energy and the New Reality, Volume 2:C-Free Energy SupplyChapter 6: Hydro-electric power L. D. Danny Harveyharvey@geog.utoronto.ca Publisher: Earthscan, UKHomepage: www.earthscan.co.uk/?tabid=101808 This material is intended for use in lectures, presentations and as handouts to students, and is provided in Powerpoint format so as to allow customization for the individual needs of course instructors. Permission of the author and publisher is required for any other usage. Please see www.earthscan.co.uk for contact details.

2. Kinds of hydro-power • Run-of-the-river (no reservoirs) • Reservoir-based

3. Power production: • Mechanical power of flowing water is equal to Pe = ρg Q H where H is the “head” and Q the volumetric rate of flow • Electric power produced is equal to Pe = ηeηtρg Q H where ηe and ηt are the generator electrical and turbine mechanical efficiencies, respectively

4. Figure 6.1a Low-head hydro-electric system Source: Ramage (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford, 183-226 )

5. Figure 6.1b Medium-heat hydro-electric system Source: Ramage (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford, 183-226 )

6. Figure 6.1c High-head hydro-electric system Source: Ramage (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford, 183-226 )

7. Figure 6.2 Impellors Source: Ramage (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford, 183-226 )

8. Figure 6.3 Impellor Space Source: Ramage (1996, Renewable Energy, Power for a Sustainable Future, Oxford University Press, Oxford, 183-226 )

9. Figure 6.4 Hydro Efficiency Source: Paish (2002, Renewable and Sustainable Energy Reviews 6, 537–556, http://www.sciencedirect.com/science/journal/13640321)

10. Figure 6.5 Hydro-electricity generation

11. Current hydro-electricity • About 19% of global electrical generating capacity in 2014 (1174 GW out of 6154 GW) • About 16% of global electricity generation in 2014 (2838 TWh out of 18000 TWh) • Almost 60% of the total expansion in hydro capacity over 2013-2016 was in China

12. Annual additions to hydro capacity

13. Buildup to total hydro capacity at the end of 2016. About 1/3 of the global capacity of 1096 GW is in China.

14. Figure 6.8 Percent of total electricity generation as hydro-electricity

15. Total small-hydro (< 10 MW)

16. Figure 6.9 Hydro-electric generation potential

17. Hydro-electric generation potentials Table 6.1 Potential energy generation (TWh/yr), existing (2005) and future generation (TWh/yr), total electricity demand (TWh) in 2005, and percent of total electricity demand met by hydro power in various continents and selected countries (listed for each continent in order of decreasing technical potential). UC=under construction. Source: WEC (2007) for hydro generation, UN (2007) for total generation.

18. Figure 6.10a Hydro reservoir power densities

19. Greenhouse gas emissions • Methane is produced from the decomposition of organic matter already on the land when it is flooded to produce a reservoir (this emission decreases over time) • Methane is also produced from decomposition of organic matter that washes into the reservoir and decays anaerobically • For some projects, the GHG emission per kWh, averaged over the lifetime of the projected, is greater than that from a coal-fired powerplant! • Accurate assessment of the GHG emissions is, however, very difficult

20. Figure 6.10b GHG emissions from dams in Brazil (except for “Boreal”)

21. Figure 6.11a GHG emissions vs power density for reservoirs in Brazil

22. Figure 6.11b GHG emissions vs power density for reservoirs in Quebec

23. Capital cost of hydro powerplants • Small hydro, $1000-3000/kW, developing countries • Small hydro, $2000-9000/kW, developed countries • Large hydro (involving dams and reservoirs), $2000-8000/kW (including access roads for high estimates)

24. The problem with reservoir-based hydro power is that capital costs have risen enormously, at least in Canada. In particular, • The 824 MW Muskrat Falls project in Newfoundland is now expected to cost $11.7 billion ( $13,900/kW ! ) , compared to an estimate of $5 billion when it was approved 5 years ago. Electricity will cost 23.3 cents/kWh before taxes (Globe and Mail, 24/6/17). • The 695 MW Keeyask project in Manitoba is now expected to cost $8.7 billion ( $12500/kW ) Globe and Mail, 7/7/17). • The 1100 MW Site C project in British Columbia is now expected to cost $9.0 billion ( $8200/kW ) Globe and Mail, 7/7/17). Once (and if) these projects are all completed (Site C is under review), we can assume that there will be no new hydro dam projects in Canada. Thus, the focus will need to be on making better use if existing facilities, and in freeing up (through more efficient use) some existing supplies of hydro-electricity that are currently used inefficiently.

25. Factors reducing the final unit cost of electricity: • Operating costs are essentially zero, and maintenance costs are very low • The project lifespan – and hence the length of time over which it is financed – is 50 years or longer (compared to 25-30 years for wind, solar and geothermal)

26. Using hydro-electric dams as a backup for fluctuating wind and solar • The output of hydro powerplants can be changed very quickly, and so can quickly go up when wind or solar electricity production drops and vice versa • However, there are limits to how fast the electricity can be reduced, related to the need to avoid “pressure hammers” • The turbine can only be slowed down a little before being disconnected from the grid, but because the grid and turbine frequencies are “interlocked”, the grid serves as a brake on the turbine, so the turbine will tend to speed up when disconnected – causing pressure surges that can damage the concrete water shafts if not done carefully

27. Linking Quebec hydropower with Ontario • To add AC power to the AC electricity grid from a new source, the new source must not only have exactly the same frequency as the grid, but the voltage crests and troughs must be exactly in phase. • Because they developed independently, the AC grids in Quebec and the rest of eastern North America are not in phase • So, to transfer power from Quebec to Ontario, the power has to be converted from AC to DC, and then from DC back to AC but this time exactly synchronized with the Ontario grid. This linkage is called an “intertie” • Western and eastern North America, and Texas, are also separate regions, and interties are needed to connect them • An advantage of having regions separated by interties is that if power is lost in one entire region due to a cascade of instabilities (such as happened in eastern North America in 2003), the cascade stops at the intertie (so Quebec did not lose power in 2003).

28. Quebec and Ontario recently signed a “capacity swap agreement”, whereby Ontario will supply Quebec with 500 MW of power during the winter, and Quebec will supply Ontario with 500 MW during the summer. This can be done with minimal investment.To add a brand new intertie with 2000 MW capacity would cost $1.4 billion, which is $700/kW- near the low end of the cost of wind farms.However, to transmit electricity efficiently requires high voltage DC (HVDC), and to do that required converting from AC to DC, transmitting, and the converting back to AC – which has to be done anyway just to cross the border from Quebec to Ontario.So – an HVDC line from wind farms + hydro in Quebec to, say, the Toronto area, would serve as the “intertie” that needs to be built anyway if we are going to make use of Quebec’s enormous hydropower (and Quebec also has lots of windy regions – so that wind power production would serve to keep the transmission line “full”)