Explaining terms, expressions and unusual words

Glossary | to help you understand the terminology

The amount of electricity used by a consumer in one year, typically measured in kilowatt-hours (kWh).

Method of flow measurement using a bucket of known volume and a stopwatch.

Is a measure of the “full power” capacity utilization of the turbine.

= actual kwh’s produced or expected annually

kwh’s produced or expected if turbine were at “full power” 100% of the time.

The quantity of CO2 emissions saved through the production of renewable electricity compared with grid electricity derived from fossil fuel sources.

Climate change refers to any significant change in measures of climate (such as temperature, precipitation, or wind) lasting for an extended period (decades or longer).

The rate of flow of electrons through a circuit;measured in Amps. The amount of current depends on voltage (consider it the same as pressure) and on the resistance of the material it is passing through.

Power (apparent) = Volts x Amps

This is selected by the designer by taking careful account of all project constraints.

Flow availability which has been determined by site survey and catchment study is the initial constraint. Typically, a value of Qmean (i.e. average annual flow ) or lower is used as the design flow rate. As a first estimate of site viability, Qmean can be used if an accurate historical value can be established. If no turbines are available because Qmean is too high, then reduce the value of the design flow rate in 10% steps until a suitable system is identified. Further factors affecting the design flow rate include:

  Environmental constraints (e.g. ‘hands off’ flow and/or flow split requirements)

– Grid connection constraints relating to the power export limit.

  Magnitude of user loads (“off-grid” schemes)

  Project finance and ROI requirements

Power (apparent) = Volts x Amps

The depleted reach (of the river) is the length of the river between intake to the leat and where the water re-enters the river.

A term used to describe localized or on-site power generation.

Wiring system which connects houses to the generator.

The word used to describe how all the power is converted from one form to another; it is the ratio of the output power to the input power expressed as a percentage; the efficiency of a pico hydro system is usually about 45%.

The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.

Energy = Power x period for which power is used.

kWh = Power in kW x hours for which power is used or produced.

Example: 1 Kilowatt hour = 1000 watts produced or consumed for one hour of time.

An independent regulatory agency within the U.S. Department of Energy that has jurisdiction over interstate electricity sales, wholesale electric rates, natural gas pricing, oil pipeline rates, and gas pipeline certification. It also licenses and inspects private, municipal, and state hydroelectric projects and oversees related environmental matters.

A policy mechanism designed to accelerate investment in renewable energy technologies. It achieves this by offering

1. a way for people to legally connect a generator and sell power to the grid

and by

2. offering long-term contracts for renewable energy producers.

A feed-in tariff is simply a guaranteed price set by the government for anyone who wants to sell renewable electricity to the grid, and a guarantee that they will have access to the grid to do so.

The price, or tariff, is set so that a modest profit is ensured, thereby unleashing the collective capital resources of the entire province, state or country to be part of the transition to renewable energy.

Feed-in tariffs exist in more than 20 countries. They are the most common policy for encouraging renewable energy systems, in part because “feed-in mechanisms achieve larger deployment at lower costs” than other policy mechanisms such as quotas, direct incentives or voluntary goals.

Measurement of the quantity of water flowing past a point in one second; measured in cubic meters per second or liters per second and used to calculate the hydraulic power. (Note: One cubic meter per second = 1000 liters per second.)

The volume of water passing a point in one second, measured in cubic metres per second or in litres per second if using metric units. One thousand litres per second is equal to one cubic metre per second therefore 50 l/s = 0.05 m3/s, for example.

A graph showing the percentage of time that the flow at a particular river location equals or exceeds certain values.

This is a method of characterising the flow variations at a particular site. A simple flow duration curve can be created by organizing all measured flow values in order of magnitude with the largest first.

The more data which is used, the more likely that the resulting graph will be indicative of future flow patterns. The Y axis is used to show flow rate and the X axis is divided into 100 percentage points. This is used to illustrate the probability of a particular flow rate being equalled or exceeded (PE or Probability Exceedence).

For example, the flow rate occurring at the 50 per cent mark (referred to as Q50) would be equalled or exceeded for 50 per cent of the time, therefore a period of six months of the year if flow data in complete years is used.

<a href=”“>More info</a>


The upstream pool before the intake within a hydropower generation system. It is a structure which is sometimes used for pico hydro at the start of the penstock ensuring that the water is sufficiently deep.

Fuels formed in the ground from the remains of dead plants and animals. It takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels.

The switching backwards and forwards of alternating current; measured in Hertz(cycles per second).

A device for converting mechanical energy to electrical energy.

Electricity that is generated from renewable energy sources is often referred to as “green power.”

The vertical drop between intake and discharge water level before any hydraulic losses are considered.

Similar to flow duration curve, except expresses the change in head and the probability of a particular value being equalled or exceeded. As the X axis is the same as for the flow duration curve, the two curves are often displayed on the same graph and therefore the relationship between head and flow can be illustrated. A head duration curve is important at some low head sites as the change in head levels will have a significant effect on energy capture.

The vertical drop of a water in a stream or in the penstock; measured in metres. 

Hedging is a risk reduction technique whereby an entity uses a derivative or similar instrument to offset future changes in the fair value or cash flows of an asset or liability. A hedged item can be any of the following individually or in a group with a similar risk characteristics:

    -Highly probably forecast transaction

    -Net investment in a foreign operation

    -Recognized liability

    -Unrecognized firm commitment

Hedge effectiveness is the amount of changes in the fair value cash flows of a hedged item that are offset by changes in the fair value or cash flows of a hedging instrument.

Source of ac electricity.

The total capacity of electrical generation devices in a power station or system.

Point where water enters the penstock.

Generation facilities whose output depends on a factor(s) that cannot be controlled by the power generator because they utilize intermittent resources such as solar energy or the wind.

A standard unit of electrical power equal to one thousand watts, or to the energy consumption at a rate of 1000 Joules per second.

A unit or measure of electricity supply or consumption of 1,000 Watts over the period of one hour.

Although definitions vary, large hydropower generally means facilities that have a capacity of more than 30 megawatts.

This is typically an open, nearly level channel for moving the water downstream to gain head.

The power required to run a defined system, such as a refrigerator, building, or an entire electricity distribution system. A device which uses the power produced by the generator.

One thousand kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.

One thousand kilowatt-hours or 1 million watt-hours.

A micro hydropower plant has a capacity of up to 100 kilowatts.

Some systems contain a pond, typically so debris can settle out of the water stream before entering the turbine. This is not necessary for Archimedes screw systems.

Allows the water to flow from the mill pond to the mill where turbine or water wheel is located.

A metal tag attached to a generation unit that contains information such as brand name, serial number, voltage, power ratings under specified conditions, and other manufacturer supplied data.

Gross head with all head losses subtracted.

The process of allowing electricity generated by a grid-interconnected renewable energy system to offset the electricity usage of the associated electric account at the same geographic location as the system.

Net metering is an electricity policy for consumers who own (generally small) renewable energy facilities Under net metering, a system owner receives credit for at least a portion of the electricity they generate.

Most electricity meters accurately record in both directions, allowing a no-cost method of effectively banking excess electricity production for future credit. However, the rules vary significantly by country and possibly state/province: if net metering is available, if and how long you can keep your banked credits, and how much the credits are worth (retail/wholesale).

In the U.S.A., as part of the Energy Policy Act of 2005, under Sec. 1251, all public electric utilities are now required to make available upon request net metering to their customers.[3]:

‘‘(11) NET METERING.—Each electric utility shall make available upon request net metering service to any electric consumer that the electric utility serves. For purposes of this paragraph, the term ‘net metering service’ means service to an electric consumer under which electric energy generated by that electric consumer from an eligible on-site generating facility and delivered to the local distribution facilities may be used to offset electric energy provided by the electric utility to the electric consumer during the applicable billing period.

Some systems might contain an overspill to control the water level within the leat system.

Rotating wheel with buckets around the outside which absorb the power of a water jet and convert it into rotating mechanical power; most Pelton designs require a head of 20 metres or more to work efficiently.

For turbines other than Archimedes screw based systems, a pipe decends steeply to the hydropower system/power house.

Hydro power with a maximum electrical output of 5kW

Measurement of energy supply and demand; given in Watts(W) or Kilowatts(kW); may be hydraulic power, mechanical power or electrical power.

Measures of Power:

1 Watt = Joule/second

Kilowatt (KW) = 1000 watts

Megawatt (MW) = 1000 kilowatts

Horsepower = 745.699872 watts

Reducing the reactive power requirements of loads such as induction motors and fluorescent lighting by connecting capacitors of certain value across the supply.

Building which contains the turbine, generator and any directly driven mechanical loads.

Energy derived from resources that are regenerative or for all practical purposes can not be depleted. Types of renewable energy resources include moving water (hydro, tidal and wave power), thermal gradients in ocean water, biomass, geothermal energy, solar energy, and wind energy.

A type of hydroelectric facility that uses the river flow without alteration and little or no impoundment of the water. Water flows are not managed, naturally occurring flows are maintained, even if containment areas are present – our projects are of this type.

Although definitions vary, small hydropower generally means facilities that have a capacity of 100 kilowatts to 30 megawatts.

Allows surplus water to flow past and over the dam once the pond is full. (Note: There are usually always a spillway and Millrace at old mill sites and sometimes an additional 3rd outlet for overflow from spring floods etc.

Water flows are managed, the containment areas serve as reservoirs to be drawn on when power is needed therefore water levels in the containment area vary.

The combined efficiency of the whole scheme, sometimes referred to as the “water to wire” efficiency.

A device which allows the voltage of an ac circuit to be charged up or down by a fixed amount (e.g. 240v to 12v) Sometimes the distribution voltage is raised so that houses further than 1km from the generator can be connected. Higher voltage reduces losses in the cables.

The channel that carries water away from the powerhouse in a hydropower generation system. The channel in which the water travels from the hydropower system back into the river.

The downstream water of the powerhouse.

The process of sending or moving electricity from one point to another.

Protective screen within a hydropower generation system used to prevent large objects from flowing into the generator.

Measurement of “electrical pressure” which is required in order for current to flow around a circuit; measured in volts(v).

The area of land where all of the water that is under it or drains off of it goes into the same place.

A hedge is an investment position intended to offset potential losses/gains that may be incurred by another  investment.

The flow which must be left in the river at the point of abstraction, for ecological purposes. Also referred to as the ‘residual’, ‘reserved’, ‘prescribed’ or a compensation flow

A structure for allowing migrant fish to travel upstream past a dam or weir, consisting of a ramp or a series of pools.

(or fish ladder) A structure for allowing migrant fish to travel upstream past a dam or weir, consisting of a ramp or a series of pools.

(Leat or Lade) An open channel that conveys water at a shallow gradient from a watercourse to the turbine forebay tank. (Also sometimes called Goit or Contour Canal). 

A vertical shaft slide gate, which can be operated either manually or by electric motors (there are other types).