Hydro Energy

Hydro Energy

For those fortunate to have a stream or a river running through their property it may be feasible to invest in a small scale hydroelectricity (1kW or less) generating system. These can be relatively inexpensive to install. Because water is a lot denser than air the hydro unit will be a lot smaller than an equivalent output wind turbine. It has the further advantage of having the potential to produce electricity almost every day of the year for a 24 hour period.

A mass of water moving down a height difference contains energy which can be harvested using some waterwheel or turbine. The moving water drives the waterwheel and this rotation either drives machinery directly (e.g. mill, pump, hammer, thresher,) or is coupled with a generator which produces electric 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).

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 standardisation 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/estimate 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.

"Layman's book: How to develop a Small Hydro Site" may be a good start.

Estimation of height can be done easiest if there is a steep slope (waterfall) by rope.

HeadMeasurement

Principle of a step by step head measurement:
By measuring total height step by step, it's crucial to do the bearing strictly horizontally. Ensure that by using a level or a water filled hose. Widely available are hoses and pressure gauges which allow the easiest method of height measurement. As longer the hose as less steps have to be taken to measure the total head.

HeightMeasurebyLevelHeadbyPressureGaugeHeightMeasurebyHose

Estimation of flow is very difficult without measurement.

A quick and easy way to measure is the floating method:

  • First, measure the waters speed at a steady flowing part of the river. Therefore drop some item and stop the time it needs for a certain distance to float.
  • Second, do a sketch of the rivers cross section by measuring its depth every 20-50 cm so you come up with a grid showing the rivers profile from side to side. With this data its cross sections area can be calculated easily.
  • Finally the flow volume results from (water) speed x (section) area.

FlowMeasurement

Example:

A ball drifts 10 m in 12 s => speed = 10m/12s = 0.12 m/s.

Cross section => A1= 25 cm * 40 cm (0.25 m * 0.4 m) = 0.1 m²; A1+A2+ ... = A = 0.5 m²

Flow volume = 0.12 m/s * 0.5 m² = 0.06 m³/s => 60 l/s

To estimate a sites potential cost its necessary to know additionally:

Pipeline (penstock) length

Electrical transmission line length (from turbine to consumer). As smaller the sites power output as higher the power lines cost share

Leinster

Midlands

Munster

Ulster

Connaught