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AC: Alternating Current: AC is the standard form of electrical current supplied by the utility grid and by most fuel-powered generators (diesel or petrol “gensets”). The polarity (and therefore the direction of current) alternates. In the USA, standard voltages for small water pumps are 115V and 230V. In most of the rest of the world, standard voltages for small water pumps are 220-240V. In most of the world, the current frequency is 50 Hz (“Herz”, or cycles per minute), while in the US, current frequency is 60 Hz.

alternating current (ac): electric current in which the direction of flow changes at frequent, regular intervals

amorphous silicon: a type of thin film PV silicon cell having no crystalline structure

ampere (amp) (A): unit of electric current which measures the flow of electrons per unit time

ampere hour/Ah: a measure of total charge commonly used to indicate energy capacity in batteries. One amp hour is equal to the quantity of charge in the flow of one ampere over one hour.

appliance: a tool or other device such as radio or television which consumes electricity

array: an assembly of several modules on a support structure together with associated wiring For further info click here

audio-visuals: any of a number of appliances and associated equipment that include televisions, radios, video cassettes, film projectors, video recorders, microphones, speakers, electronic megaphones, and other appliances used to provide sound and visual information.


BOS: balance of system: the components and costs other than the PV/Photovoltaic array in solar power systems. This includes power conditioning unit (i.e., battery charge controller, inverter etc.), energy storage unit (i.e., battery), and, any supporting structure (e.g., tower, house, etc.) and the land the solar power system is placed on.

ballast inverter: a device which converts low voltage direct current to the type of high voltage ac current required by fluorescent lamps

ballast: Electronic part for fluorescent lights

battery capacity: the total number of amp hours that can be removed from a fully-charged battery or cell at a specified discharge rate. For further info click here

battery: a device that converts chemical energy contained in its active materials directly into electrical energy by means of an electrochemical reaction For further info click here

biogas: produced through anaerobic digestion, the bacterial fermentation of organic material. Biogas is often produced from animal and agricultural wastes. Biogas is used directly for lighting, for producing heat, and as a fuel source for fuel cells.

Biomass is one of the most plentiful and well-utilised sources of renewable energy in the world. Broadly speaking, it is organic material produced by the photosynthesis of light. For further info click here

blocking diode: a solid-state electrical device planed in circuit between the module and the battery when the voltage of the battery is higher than that of the module (i.e. at night)

butane: Either of two saturated hydrocarbons, or alkanes, with the chemical formula C4H10. Differences in structure between the two result in small but distinct differences in qualities. Both butanes occur in natural gas, petroleum, and refinery gases. They show little chemical reactivity at ordinary temperatures but burn readily when ignited in air or oxygen. They form part of gasoline and are sometimes added to propane to be marketed as bottled gas. [see petroleum products fact sheet]

by-pass diode: a solid-state electrical device installed in parallel with modules of an array which allows current to by-pass a shaded or damaged module


calorie: 4.1840 Joules (kilocalorie/kcal = 4.184 kilo Joules/kJ)

candela: Unit of luminous intensity (cd)

CCT: Correlated Colour Temperature = colour appearance of the light source. Unit: Kelvin For Further info click here

cell (battery): the smallest unit or section of a battery that can store electrical energy and is capable of providing a current to an external load (for further information click here)

cell (photovoltaic): see solar cell For further info click here

CFL: Compact Fluorescent Lamp For Further info click here

charge regulator: see charge controller. For further info click here

charge controller: a device which protects the battery, load and array from voltage fluctuations, alerts the users to system problems and performs other management functions For further info click here

CIE: International Commission on Illumination For Further info click here

circuit: a system of conductors (i.e. wires and appliances) capable of providing a closed path for electric current

cluster-LED: Recently-developed lighting technology based on output of Light Emiting Diodes. Cluster LEDs are more efficient and long-lasting than fluorescent lamps. They are best suited for task-lighting as their output is directional. For Further info click here

CO2: Carbon dioxide

concentrating solar power (CSP): Parabolic trough solar power systems, or CSP, are well suited for central, large-scale generation plants that connect to the electric transmission systems.

connector strips: insulated screw-down wire clamps used to fasten wires together in solar electric systems

converter: An electronic device for DC power that steps up voltage and steps down current proportionally (or vice-versa). Electrical analogy applied to AC: See transformer. Mechanical analogy: gears or belt drive. For further info click here

compatibility: the degree to which one component (e.g., a light, an inverter, a PV module, a battery, etc.) with another, or one system (e.g., water pumping, lighting, refrigeration) with another.

crystalline silicon: a type of PV cell made from a single crystal or polycrystalline slices of silicon For further info click here

cubic metre: one thousand metres cubed, i.e., 1 m3 = 1m x 1m x 1m

current (amps amperes, A): Electricity current is the rate at which electricity flows through a circuit, to transfer energy. Current is measured in Amperes (“A”), commonly called Amps. Analogy: Flow rate in a water pipe.

cycle life: of a battery, the number of cycles it is expected to last before being reduced to 80% of its rated capacity

cycle: one discharge and charge period of a battery


daily energy requirement: the amount of energy that a household, an institution, or any establishment requires to meet the sum total of its energy needs. Example: The daily energy requirement for a typical European household is approximately 45 kWh comprising demand from refrigerator, 20 light bulbs, a dishwasher, a washing machine, a clothes dryer, a TV, other household appliances. Typical energy requirements for an average East African rural household is on the order of less than 2 kWh. For further info click here

DC – Direct Current: DC is the type of power produced by photovoltaic panels and by storage batteries. The current flows in one direction and polarity is fixed, defined as positive (+) and negative (-). Nominal system voltage may be anywhere from 12 to 180V. See voltage, nominal.

deep discharge battery: a type of battery that is not damaged when a large portion of its energy capacity is repeatedly removed (i.e. motive batteries)

depth of discharge: a measure in percentage of the amount of energy removed from the battery during a cycle

diffuse radiation: solar radiation that reaches the earth indirectly due to reflection and scattering

direct current (dc): electric current flowing in one direction

direct radiation: radiation coming in a beam from the sun which can be focused

discharge: the removal of electric energy from a battery

domestic: Usually refers to the household sector. Example: Families use domestic lighting for reading in the home.

dry cell battery: can be made of alkaline cells, consisting of common dry cell carbon or zinc, of types “AA” “AAA”, “C”, “D” (most common torch/flashlight battery), others used for radios, cassette players, various other small appliances. A dry cell battery contains electrolytes that are in the form of paste rather than liquid. (see battery fact sheet)


efficiency: Efficiency is the percentage of power that gets converted to useful work. Example: An electric pump that is 60% efficient converts 60% of the input energy into work – pumping water. The remaining 40% becomes waste heat.

electricity: Energy that is generated by a number of forms, ranging from mechanical (e.g., wind mill), to thermal (e.g., diesel generator), to photovoltaic, and used to provide power for a number of applications. For further info click here

electric power: the rate at which energy is supplied from an electricity generating source. It is measured in watts (W) For further info click here

energy: Energy is the product of power and time, measured in Watt-hours. 1000 Watt-hours = 1 Kilowatt-hour (abbreviation: kWh). Variation: the product of current and time is Ampere-Hours, also called Amp-Hours (abbreviation: AH). 1000 watt consumed for 1 hour = 1 kWh. See power. For further info click here

energy calculations: any set of calculations typically used to determine the amount of demand or load that one has (e.g., the number and voltage required for appliances, equipment, etc.), and then defining the electricity that needs to be supplied to meet that demand/load, taking into consideration all losses in the system. For further info click here

EPI: the Expanded Programme on Immunization supported by the United Nations World Health Organisation, the United Nations Children’s Fund/UNICEF, and almost all international governments and development agencies. The goal of EPI is to provide immunisations to all the world’s children against the most important diseases (polio, tetanus, etc.).


FAQ: abbreviation for “frequently asked questions”. This is in wide use on the Internet. Good sites, particularly with technical information, will provide readers with an FAQ section in order to help guide them along.

fluourescent: light emitted from special inert gases (generally neon) when an electric current is passed through it. Fluourescent lamps are much more efficient than incandescent lamps, and are preferred over incandescent lamps for energy efficiency. However, not as efficient as halogen or LED.

fridge: Short for refrigerator.

fuse: a device which protects circuits and appliances in the system from damage by short circuits


g: gram (a unit of weight)

Gasoline: A mixture of the lighter liquid hydrocarbons, used chiefly as a fuel for internal-combustion engines. It is produced by the fractional distillation of petroleum; by condensation or adsorption from natural gas; by thermal or catalytic decomposition of petroleum or its fractions; by the hydrogenation of producer gas or coal; or by the polymerization of hydrocarbons of lower molecular weight. (see petroleum products fact sheet)

general lighting: Illumination of a large area. Unit lux = lumen/m2 For Further info click here

genset: a piece of equipment, powered by petrol/gasoline or diesel that generates electricity. Genset is short for generating set (gennys in North America). Often used for back-up power for hospitals, hotels, industries, but also used as primary electricity sources for isolated, off-grid applications, and in hybrid applications.

geothermal energy: energy that is generated by the heat of the earth’s own internal temperature. Geothermal energy manifests itself on the earth’s surface through hot springs and geysers. Geothermal energy has been used for thousands of years for heating in baths, houses and communal areas.

Giga: one thousand million units (in US terms, one billion units, in most European languages, giga = milliard), 109. Example: one gigawatt (GW) = one thousand million Watts (109 Watts); one gigajoule (GJ) = one thousand million Joules (109)

The Global Programme for Vaccines and Immunization (GPV): a programme of the World Health Organization. GVP recognises the fact that prevention is better than cure. It supports the development, supply and delivery of safe and effective vaccines at affordable prices in all countries.

grid: A network that connects a supply of electricity (water, transport, etc.) to a number of users. In electricity terms, a grid usually consists of some form of electricity generator, with electricity taken along a transmission line at high voltage, then stepped down to lower voltage on a distribution system that delivers electricity to end users (households, industries, etc.)


h: hour

halogen lamps: lamps with very low wattage, that generate high intensity light through a combination of specially coated, highly efficient reflectors. Very low voltage with high efficiency deliver of light for low power. For Further info click here

hand pump: a pump driven by human force, generally by hand, or by foot, or sometimes, by the weight of the human body.

heat transfer fluid: Heat Transfer Fluid (HTF) is a dense liquid, usually a synthethic oil that can be heated to very high temperatures on a repeated basis without degrading.

hybrid system: a hybrid system refers usually to the combination of two energy generating applications (e.g., diesel generator with PV system) to provide electricity at all times, or in all critical times. Generally, a hybrid system will be designed to ensure reliability (e.g., hospitals, industrial processes, computer operations), where one energy source (e.g., PV from the sun, wind) is intermittent, i.e., not always available.

hydraulic ram: otherwise referred to as an impulse pump. A device that uses the energy of falling water to lift a lessor amount of water to a higher elevation than the source, i.e. for water pumping.

hydropower: power generated by the flow of water. Water moving by force of gravity, either vertically (as in streams and rivers) or otherwise (as in tides and waves driven by the gravitation force between the earth and move, by the wind, etc.). Water power (see small hydro page)

hypertext links: a an area of selected text or graphic image that willl redirect you to another area of text, either in the same document, another document, a file, or anywhere on the World Wide Web.


illuminance: Luminous flux per unit area. Unit lux = lumen/m2 For Further info click here

illuminous efficacy: Efficiency with which a surface is lit. Unit: lux/Watt

incandescent: an incandescent lamp produces light when its wire filament is heated by electricity to ‘incandescence. Wire filaments are made of tungsten.

insolation: incident solar radiation. A measure of the solar energy incident on a given area over a specific period of time. Usually expressed in kilowatt-hours per square metre per day or indicated in peak sun hours

institutions: Usually refers to either publicly-linked or publicly-supported entities such as schools, hospitals, clinics, among others. Example: Institutional cooling needs for vaccines are often met by LPG refrigerators in remote areas.

institutional: Usually refers to institutions that are either publicly-linked or publicly-supported. Institutions generally include schools, hospitals, clinics, among others. Example: Institutional cooling needs for vaccines are often met by LPG refrigerators in remote areas.

interconnected system (ICS): Refers to an electricity system that connects one user to the next, and the source of electricity supply to consumers through the network or grid. An ICS is another word for a grid.

intermittence: when an energy source, such as sunshine, wind, even hydro or diesel, is not always available. Any system needs to be designed on the basis of how much constant, steady energy is needed, and whether demand can be served with intermittent supplies.

inverter: An electronic device that converts low voltage DC to high voltage AC power. In solar-electric systems, an inverter may take the 12, 24, or 48 volts DC and convert it to 115 or 230 volts AC, conventional household power. For further info click here

irradiance: the solar radiation incident or a surface per unit time. Expressed in watts or kilowatts per square metre


Joule: A joule is the energy required to push with a force of one Newton for one metre. A foot pound is the energy required to push with a force of one pound for one foot (1 joule = 1 Newton meter, 1 joule = .737562139 foot pounds, 1 foot pound = 1.355817967 joules)


Kelvin (K): Freezing point, 273.15 degrees K = 0 degrees Centigrade

kerosene: a light fraction petroleum product refined from the raw petroleum. Kerosene is one of the lighter “distillates” in a petroleum refinery, lighter than gasoil/diesel, and often in the same mix with jet fuel (e.g., Jet A1). It has been used for lighting, cooling and refrigeration for one hundred years. Kerosene is found throughout the world, and is one of the most common lighting fuels in the developing world. It is also often used for cooking, primarily in urban areas in the developing world.

kilocalorie (kcal): a measure of energy equivalent to 4.187 kJ/kilojoules, or 1.63 Wh/Watt hours

kilogram: one thousand grams (103 g)

kilo: One thousand units. Example: one kilowatts = 1,000 Watts; one kilojoule = one thousand Joules)

kVA: kilovolt ampere (one thousand Volt Amperes), the current flowing in a circuit multiplies by the voltage of that circuit, usually measured on a transformer. A measure of power whereby one kVA typically equals approximately 0.8 kWh (depending upon the phase).

kWh: kilowatt-hour = 3.6 MJ. An energy measure that indicates a Watt consumed or generated in one hour equivalent.


lamp: Light source (such as incandescent bulb, fluorescent tube)

LDC: a term used for ‘lesser-developing country’. This term has fallen out of favour, and the term ‘developing country’ tends to be preferred.

LED: Light Emitting Diode (a small, low-voltage light source) For Further info click here

light colour: the actual appearance of light emitted by lighting appliances. For Further info click here

light-emitting diode (LED): a type of diode which lights up when current is flowing through it. Commonly used as an indicator in charge controller For Further info click here

liquified petroleum gas (LPG): A mixture of butane, propane and other light hydrocarbons derived from refining crude oil. At normal temperature it is a gas but it can be cooled or subjected to pressure to facilitate storage and transportation. (see petroleum fact sheet)

lmh: Lumen-hour: luminous flux integrated over one hour For Further info click here

load: The amount of demand placed on an energy system. In the case of most electricity, load could be the set of equipment appliances that use the electrical power from the generating source, battery or module, and the amount of electricity (the load) that those appliances require. Load is often used synonymously with “demand”. Load is usually expressed in “watts”, so that, for example, if a refrigerator has a rating of 1 kW, the load is cited as being a 1 kW load. For further info click here

local lighting: Illumination of a (small) work area For Further info click here

localised lighting: Illumination of only part of an area For Further info click here

LOR: Light Output ratio = Luminaire efficiency For Further info click here

lumen: Unit of luminous flux (1m) For Further info click here

luminaire: Complete lighting system For Further info click here

luminous efficacy: Efficiency of lamp or luminaire. Unit: lumen/Watt For Further info click here

luminous intensity: Amount of light emitted in a certain direction For Further info click here

lux: Unit of illuminance For Further info click here


mega: equals 1 million units (106). Example: one megawatt (MW) = one million Watts (106 Watts); one megajoule (MJ) = one million Joules (106 Joules)

methane: A gas composed of carbon and hydrogen, the first member of the paraffin or alkane series of hydrocarbons. It is lighter than air, colourless, odourless, and flammable. Methane occurs in natural gas, as firedamp in coal mines, and as a product of decomposition of matter. It is a major component in the atmosphere of the outer planets. Methane is valuable as a fuel and in the production of hydrogen, hydrogen cyanide, ammonia, acetylene, and formaldehyde.

metre: unit of distance.

MJ: MegaJoule = one million Joules (106 Joules). An international energy measure that calculates the amount of


ni-cad battery: a nickel cadmium (ni-cad) battery. NiCad batteries have been used to power small electronic devices for a number of years. They are rechargeable, have higher energy densities than lead-acid batteries, and have higher energy densities that lead-acid batteries. Rarely used for PV applications for a variety of reasons including reduction in recharge voltage, the so-called “memory effect”, among others. [for further reading see:https://www.pfa.org.uk/ni-cad.html]

Non-Governmental Organisation (NGO): any number of organisations, associations, institutions that are non-profit, or non-for-profit, generally of a social service, benevolent basis. NGOs are extremely active in developing countries, and are very involved in the field of health, sanitation, water provision, education, and other social services in rural areas in off-grid situations. This makes them particularly interested in off-grid energy solutions.

Nox: Nitrous oxides


O&M: operations and maintenance. Refers to the level of effort required to operate an appliance, a piece of equipment or a system, and to maintain it as well.

off-grid: A situation when a consumer is not connected to an electricity grid. This is fairly rare in Europe or North America (limited to camping areas, very isolated sites, etc.), but is very common in rural areas, and many near-urban (peri-urban) areas of the developing world where electricity companies and suppliers have been unable to connect domestic, commercial, industrial and institutional consumers. The main thrust of this workbook is to provide “off-grid solutions”.

ohm (S): a unit of electrical resistance

open circuit voltage (Voc): the maximum possible voltage across a solar module or array. Open circuit voltage occurs in sunlight when no current is flowing

orientation light: Lighting which is just sufficient to recognise shapes


peak power (Wp): the amount of power a solar cell module can be expected to deliver at noon on a sunny day (i.e. at Standard Test Conditions) when it is facing directly towards the sun

petrol: See gasoline.

photovoltaic (PV): The phenomenon of converting light to electric power. Photo = light, Volt = electricity. Abbreviation: PV.

PLC: Type of CFL, with 2 or 4 tubes

power: The rate at which work is done. It is the product of Voltage times Current, measured in Watts. 1000 Watts = 1 kilowatt. An electric motor requires approximately 1 Kilowatt per Horsepower (after typical efficiency losses). 1 Kilowatt for 1 Hour = 1 kilowatt-hour (kWh). For further info click here

pressure lamp: a term usually used to refer to a kerosene lamp that is charged to a high pressure (usually by hand) in order to achieve vapourisation of the kerosene to aid combustion and generate a high intensity light. The kerosene is burnt and light emitted through the ‘mantle’. For further info click here

propane: A colourless, odourless gas of the alkane series of hydrocarbons, formula C3H8. It occurs in crude oil, in natural gas, and as a by-product of petroleum refining. Propane burns in air at high temperatures and is valuable as a fuel. When it is used as a fuel, propane is not separated from the related compounds, butane, ethane, and propylene. It is used also as so-called bottled gas, as a motor fuel, as a low-temperature solvent, and as a source of propylene and ethylene.

PV Array-Direct: The use of electric power directly from a photovoltaic array, without storage batteries to store or stabilise it. Most solar water pumps work this way, utilising a tank to store water. For further info click here

PV Array: A group of PV (photovoltaic) modules (also called panels) arranged to produce the voltage and power desired. For further info click here

PV Cell: The individual photovoltaic device. The most common PV modules are made with 33 to 36 silicon cells each producing 1/2 volt. For further info click here

PV Lighting System: a system that includes at least a PV module, a battery, an inverter and a light. Can include a large number of lights, preferably high efficiency fluourescent, LED, halogen lamps. For Further info click here

PV light suppliers: there are a number of international photovoltaic suppliers who range from specialist suppliers, to renewable energy equipment suppliers, to suppliers of leisure and camping equipment.

PV Module: An assembly of PV cells framed into a weatherproof unit. Commonly called a “PV panel”. See PV array. For further info click here

PV: The common abbreviation for Photovoltaic For further info click here



RA: Colour Rendering Index = Degree with which different colours can be recognised compared to a standard light source For Further info click here

RE: renewable energy. Energy from sources such as the sun, wind, water, waves, tides, biomass, that are renewable, that is, that can be renewed within a relatively short period of time.

reflector: Part of the luminaire with reflects light (usually downwards) For Further info click here

refrigerator: An appliance that cools an area, generally for food, beverage or vaccine storage.

resistance: the property of a conductor (i.e. a wire or appliance) which opposes the flow of current through it and converts electrical energy into heat. Resistance has the symbol R, and is measured in ohms, S.

RET: Renewable energy technologies. Technologies that utilise renewable energy resources such as the sun, the wind, biomass, geothermal, water, etc.


SEC: specific energy consumption, equivalent to the amount of energy consumed for a specific time in a specific area or for a specific purpose.

self-discharge: charge lost from batteries left standing due to reactions within the cells

shallow discharge batteries: batteries designed to supply high power for a short duration (e.g. automotive batteries); taking too much energy out of these batteries before recharging them is likely to damage the plates inside

silicon: a semi-conductor material commonly used to make photovoltaic cells For further info click here

solar cell module: groups of encapsulated solar cells framed in glass or plastic units, usually the smallest unit of solar electric equipment available to the consumer For further info click here

solar cell: a specially-made semiconductor material (i.e. silicon) which converts light energy into electric energy For further info click here

solar electricity: electricity that is generated by the sun’s rays. The most common form of solar electricity in use today is from photovoltaics. However, solar electricity is being produced from solar thermal arrays (typically mirrors focusing the sun’s heat on turbines) in several parts of the world.

solar energy: energy that is received from the sun.

solar radiation: see insolation.

solar module: a collection of PV cells wired to generate electricity from the sun, and read to be directly connected to a system, or arranged into an array. For further info click here

solar tracker: A mounting rack for a PV array that automatically tilts to follow the daily path of the sun through the sky. A “tracking array” will produce more energy through the course of the day, than a “fixed array” (non-tracking) particularly during the long days of summer.

Sox: Sulphur oxides

specific gravity: the ratio of the weight of a solution (i.e. battery acid) to an equal volume of water as a specific temperature. Used as an indicator of battery state of charge

Spectroradiometer: Device for measuring the spectral irradiance (the flux per unit of wavelength: W/m2/micrometer)

square metre: one metre by one metre on a flat surface (1 m2)

stand-alone system: any system that is not connected to a grid or distribution system. The term is most often used for systems not connected to the electricity or natural gas grids (see stand-alone solar electric system).

stand-alone solar electric system: a solar electric system that receives all of its energy from solar electric charge, and which is not connected to the grid or any other source of power

storage: any system by which energy is stored. Storage generally includes batteries, although more advanced storage systems can include heat pumps or water reservoirs. For further info click here

STC: Standard Test Conditions (here: ageing at least 100 hours; temperature in range 24-26C)

system: System usually refers to the integrated, connected range of electricity supply elements, the means of transmitting and/or distributing electricity, and the demand requirements or load. Example: A PV household system usually consists of a PV module array, a wiring system from the array to the inverter and battery, wiring from the inverter and battery to, say, lights, television, radio, etc.

system voltage: the voltage at which the charge controller, lamps and appliances in a system operate, and at-which the module (s) and battery are configured


total daily system energy requirement: see daily energy requirement. The amount of energy required to meet the daily electrical load plus the extra energy required to overcome system energy losses.

tracking: the practise of changing the position (i.e. angle) of the array at various times during the day so that is faces the sun and so harvests a larger amount of solar charge

transformer: An electrical device that steps up voltage and steps down current proportionally (or vice-versa). Transformers work with AC only. For DC, see converter. Mechanical analogy: gears or belt drive.

trickle charge: a low current charge. When the batteries are fully charged, some charge controllers reduce the energy from the module to the battery to a trickle charge so that the batteries are not overcharged, but so that they still get enough current to overcome self-discharge


UNICEF: United Nations Children’s Fund, the world’s leading children support agency, and the UN’s arm of support for children’s causes and welfare throughout the world. (see https://www.unicef.org )

utility grid: A utility grid is usually a commercial electric power distribution system that takes electricity from a generator (e.g., fossil fuel boiler and generator, diesel generator, wind turbines, water turbine, etc.), transmits it over a certain distance, then takes the electricity down to the consumer through a distribution system.


VAC: Volts alternating current.

vaccine: A liquid used to vaccinate people against disease.

vaccine refrigerator: Any of a variety of different types of refrigerators/fridges used to store and cool vaccines.

volt (V): a unit of measurement of the force given to electrons in an electric circuit; see potential difference. Analogy: Pressure in a water pipe

voltage drop: Voltage drop is the loss of voltage (electrical pressure) caused by the resistance in wire and electrical devices. Proper wire sizing will minimise voltage drop, particularly over long distances. Voltage drop is determined by 4 factors: wire size, current (amps), voltage, and length of wire. It is determined by a consulting wire sizing chart or formula available in various reference tests. It is expressed as a percentage. Water analogy: Friction Loss in pipe.

voltage, nominal: Nominal voltage is a way of naming a range of voltage to a standard. Example: A “12 Volt Nominal” system may operate in the range of 11 to 15 Volts. We call it “12 Volts” for simplicity.

voltage, open circuit: The voltage of a PV module or array with no load (when it is disconnected). A “12 Volt Nominal” PV module will produce about 20 Volts open circuit. Abbreviation: Voc.

voltage, peak power point: The voltage at which a photovoltaic module or array transfers the greatest amount of power (watts). A “12 Volt Nominal” PV module will typically have a peak power voltage of around 17 volts. A PV array-direct solar pump should reach this voltage in full sun conditions. In a higher voltage array, it will be a multiple of this voltage. Abbreviation: Vpp.

voltage: Voltage is the measurement of electrical potential. Analogy: Pressure in a water pipe


water pumping: The process of raising water, usual from a well, but also from any storage facility, from one point to another. Water pumping can be carried out by hand, electronically and manually with engines such as diesel pumps or by wind pumps. For further info, click here

watt (W): The internationally accepted measurement of power. One thousand watts are a kilowatt, and a million watts are a megawatt. A Watt is the power used when one Joule of energy is used every second (i.e., 1 Watt = Joule/second; 1 Joule = 1 Watt second; 1 Watt hour/Wh = 3.6 thousand Joules/kJ; 1 kWh = 3.6 MegaJoules/MJ)

watt hour (Wh): a common energy measure arrived at by multiplying the power times the hours of use (1 Watt hour/Wh = 3.6 kilo Joules/kJ; 1 kWh = 3.6 MegaJoules/MJ). Grid power is ordinarily sold and measured in kilowatt hours

WHO: World Health Organisation of the United Nations. The international health arm of the United Nations, recognised by virtually all countries in the world for setting standards for immunisation and vaccination. WHO-approved refrigerators are the world’s international health standards, and many international suppliers are certified by WHO for their solar refrigerators.

wind power: power generated by the movement of the earth’s rotation, and the temperature variations around the globe. Wind has been harnessed for power for thousands of years (e.g., sailing boats) and for mechanical power for a thousand years (wind mills).

wind turbines: turbines that are driven by the force of the wind to generate power, either mechanically (as for pumping) or electrically (as in wind electricity generators).