Hydro Power

Illustration of Hydro Electricity Generator As with wind and waves, hydro energy is also indirectly solar energy. Hydro power stations capture water flowing from a height, either in rivers, water falls or artificial dams.

The power that can be captured by a water flow is

Formula for hydro power

 

with constants r=1,023kg/m3 and g=9.81m/s2. Q denotes the water flow volume per second and h is the drop height, called the head. Twice the head, doubles the power, the same goes for water flow.

Natural ranges for these parameters are wide: E.g.
  • Niagara Falls: Q=1,420m3/s, h=52m
  • Val Strem (Switzerland): Q=0.71m3/s, h=216m

 

 

Hydro Electricity Market

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Hydro power is the most mature of the renewable technologies to generate electricity and still by the most prominent, as 88% of all electricity generated from renewable sources comes from hydro energy.

Growth

The installed base of hydro electricity capacity has increased steadily to over 900GW in 2009. While growth rates might be modest in comparison to wind or solar, its large base means it will be the dominant renewable source for some time to come.

Global spread

With 26% of the total of hydro electricity generated, Asia-Pacific is the region with the largest share, followed by North America(22%), South America (21%) and Europe (19%). The Top-4 countries (China, Canada, Brazil, USA) account for almost half of the market! However, hydro energy is utilised world-wide, as shown in our map. In large parts of South America and Africa, as well as Norway and Iceland, hydro accounts for more than 50% of the consumed electrcitiy.

Salient Benefits

Apart from attractive economics, there are some other distinct advantages:
  • Water supply fluctuations are far less random than in wind power or pronounced as in tidal power.
  • Water can be held in or pumped up into high reservoirs. This valuable energy store is used to iron out fluctuations in water supply as well as electricity demand, making it a popular choice for peak supply.
Turbine Technologies
Three main dominant turbine designs have developed to reflect the vast ranges of head levels (from as little as a few meters to more than 2,000m in mountain regions) and water flows.
Kaplan: low head - high flow

Where the head is only a few meters, axial flow Kaplan turbines are most common. The turbine in entirely immersed, as there is no need for water to be fed from the side.

Kaplan Turbine
Francis: high to medium

In the most common device, the Francis turbine, water enters in radial direction, but exits in axial direction.

 

Francis Turbine
Pelton: high head - low flow

Where there is a high head, but generally low flow, water is directed, through a nozzle (to increase pressure), on a wheel with double cups, the Pelton turbine.

Pelton Turbine
Applications
Run-of-the-river

Run-of-the-river hydro power plants have a low head without reservoir capacity, often with a by-pass for ships.

 

Up to 2GW, but many small from 200kW

Run-of-the river hydro plant Iffezheim

The power station Iffezheim on the Rhine is powered by 4 Kaplan turbines(5.8m diameter) with a maximum throughput of 1,100m3/s. The dam is 20m wide.

Pumped Storage

In plants with pumped storage, water can be moved up to a high reservoir for grid energy storage and released back.

 

Up to 2GW, but many 100MW - 200MW

Pump storage in Vianden

The hydro power station with pump storage in Vianden, Luxemburg: With a head of 290m 10 Francis- turbines with 9x 100MW and 1x 200MW, generating 13GWh per annum.
Conventional

Conventional hydro power stations utilise dammed water with a reservoir, though no pumped storage.

 

Up to 22GW (China)

Pelton Turbine

The power station Silz (Austria) uses a head of 1,240m with 2 Pelton turbines of 255MW each, generating 718 GWh per annum.

 

Economics
Economics

Cost Structure

In general, the turbine accounts for just 10% of the total capex, with 15 - 20% spent on site development and environmental studes and the remaining 65 - 75% on civil engineering.

 

Capital Costs

Costs for hydro electricity vary widely from €/kW1,000 - 4,000. For instance, in 2009 a Pelton-based power plant ValStrem in Switzerland for 2MW cost €7m, which is at the higher end. Economies of scale prevail, driving the cost per kW down to much more attractive levels.

 

Operations

Hydro plants tend to have a long live - similar to gas power stations. O&M costs are roughly 1 - 2% of capex.

Environmental Issues

 

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