Hydro Power 101

Principle of Hydro Power

Hydro power is probably the first form of automated power production which is not human / animal driven. Moving a grind stone for milling first, developed into the driving of an electrical generator. Next to steam it was for long the main power source for electricity.Its continual availability does not require any power storage (unlike wind / solar power). It is mainly mechanical hardware. This makes it relative easy to understand and repair-/maintainable. In smaller units its environmental impact becomes neglect-able (see: environmental impact assessment and pros and cons of micro hydropower).

Mesaure the Head & Flow

In order to create electricity from hydropower, two parameters are critical:

  • Flow; or the minimum amount of water that is constantly available throughout the entire year

  • Head; the difference in height

These specific conditions limit generalising and standartisation of "how to install hydropower plants". Choosing the right location and planning requires some specific knowledge. With knowledge of water flow and height difference the potential power can be estimated.

The first step to judge a sites hydropower potential is to measure or estimate the head and flow.

  • Head (the vertical distance between the intake and turbine)

  • Flow (how much water comes down the stream)

Head is very often exaggerated as is the flow rate, which varies over the year!

Wrong data occurs frequently. Confirmation of existing data is highly recommended!

Head and flow are the two most important facts of a hydro site. This will determine everything about the hydro system - volume of civil constructions, pipeline size, turbine type and power output. Inaccurate measurements result in low efficiency, high cost and scarcity of power.

Units and Power Estimations

Power: watts [W] or Kilowatts [kW] 1 kW = 1000W
Flow: 1 m³/s = 1000 l/s
Gross heat: height difference the water "falls down"
Net head: a little smaller than gross head. Gross head deducted by energy loss due to friction in penstock

Potential power ('electric)' is calculated as follows:
Power [W] = Net head [m] x Flow [ l/s] x 9.81 [m/s²] (est. gravity constant) x 0.7 (turbine/generator efficiency)
Potential power is estimated as follows:
Power output [W] = height [m] flow [l/s] 7

More accurate estimations take into consideration:

  • exact net head (intake to powerhouse)

  • exact flow (constant during the year?)

  • combined efficiency of turbine and generator (depends on quality, est. 70% = 0.7)

A 6 m high waterfall has 300 liter/sec => potential power est. : 6 m 300 l/s 7 = 126000 W = 12.6 kW

Classification of Hydro Power

For the United Nations Industrial Development Organization (UNIDO)and the European Small Hydropower Association (ESHA)and the International Association for Small Hydro (IASH)a capacity of up to 10 MW total is becoming the generally accepted norm for small hydropower plants (SHP). In China, it can refer to capacities of up to 25 MW, in India up to 15 MW and in Sweden small means up to 1.5 MW, in Canada 'small' can refer to upper limit capacities of between 20 and 25 MW, and in the United States 'small' can mean 30 MW.

Small hydro can be further subdivided into mini, micro and pico:

  • Mini (MH) < 1 MW, grid connected, special know how required

  • Micro <100 kW, partially grid connected, professional know how required

  • Pico (PH)< 10 kW island grids, small series units produced locally; professional equipment available

  • Family (FH)< ~1 kW single households/clusters often locally handmade solutions; professional equipment available

Hydropower Potential

Hydropower potential means: an amount of water (flow) which flows down a certain height.
To utilise such, the produced electricity is to be transportet by powerline to potential users.

Hydropower offers a significant potential of renewable energy production. In 2009 electricity production from hydropower was about 16% of the global electricity production. The undeveloped capacity ranges from 30% in Europe up to 88% in Africa.

If reading such numbers please keep in mind:

  • There is a structural difference between small and big hydropower;
    the first is mainly decentralised - the later is usually utilized by big structures, which have usually massive environmental impacts

  • Hydropower potential is bound to specific sites, which may be far from potential energy usage

Small hydropower potential is given in hilly or mountainous regions, where rivers do not fall dry during the year.
Where gravity fed irrigation is practiced small and micro power plants find suiting conditions.

Mountainous regions often have bad infrastructure and are least to be connected to a electric grid. If there is water available it may be a suitable source for decentralised hydro power electrification. Such setups may even get support from governmental or major electricity supplier. The costs to connect remote areas are high, whereby the revenue, due to little amount of electricity utilised, is low.

The above basic Hydro Power 101 video and contents are from the site: https://energypedia.info/wiki/Hydro_Power_Basics#Classification_of_Hydro_Power

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