Glossary: Solar Water Pumping Terms

By Windy Dankoff Courtesy of Dankoff Solar Products, Inc.

Basic Electricity

AC - Alternating Current, the standard form of electrical current supplied by the utility grid and by most fuel-powered generators. The polarity (and therefore the direction of current) alternates. In U.S.A., standard voltages for small water pumps are 115V and 230V. Standards vary in different countries. See Inverter.

DC - Direct Current, 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. Current - The rate at which electricity flows through a circuit, to transfer energy. Measured in Amperes, commonly called Amps. Analogy: Flow Rate in a water pipe.

Efficiency - 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.

Energy - 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.

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.

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.

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).

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.

Utility Grid - Commercial electric power distribution system. Synonym: Mains.

Voltage - The measurement of electrical potential. Analogy: Pressure in a water pipe.

Voltage Drop - Loss of voltage (electrical pressure) caused by the resistance in wire and electrical devices. Proper wire sizing will minimize 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 - 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.

Solar Electricity

Photovoltaic - The phenomenon of converting light to electric power. Photo = light, Volt = electricity. Abbreviation: PV.

PV - The common abbreviation for photovoltaic.

PV Array - A group of PV (photovoltaic) modules (also called panels) arranged to produce the voltage and power desired. PV Array-Direct - The use of electric power directly from a photovoltaic array, without storage batteries to store or stabilize it. Most solar water pumps work this way, utilizing a tank to store water.

PV Cell - The individual photovoltaic device. The most common PV modules are made with 33 to 36 silicon cells each producing 1/2 volt.

PV Module - An assembly of PV cells framed into a weatherproof unit. Commonly called a "PV panel". See PV Array.

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.

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.

Pumps & Related Components

Booster Pump - A surface pump used to increase pressure in a water line, or to pull from a storage tank and pressurize a water system. See Surface Pump.

Centrifugal Pump - A pumping mechanism that spins water by means of an "impeller". Water is pushed out by centrifugal force. See also multistage.

Check Valve - A valve that allows water to flow one way but not the other.

Diaphragm Pump - A type of pump in which water is drawn in and forced out of one or more chambers, by a flexible diaphragm. Check valves let water into and out of each chamber.

Foot Valve - A check valve placed in the water source below a surface pump. It prevents water from flowing back down the pipe and "losing prime". See check valve and priming.

Positive Displacement Pump - Any mechanism that seals water in a chamber, then forces it out by reducing the volume of the chamber. Examples: piston (including jack), diaphragm, rotary vane. Used for low volume and high lift. Contrast with "centrifugal". Synonyms: volumetric pump, force pump.

Impeller - See Centrifugal

Pump Jet Pump - A surface-mounted centrifugal pump that uses an "ejector" (venturi) device to augment its suction capacity. In a "deep well jet pump", the ejector is down in the well, to assist the pump in overcoming the limitations of suction. (Some water is diverted back down the well, causing an increase in energy use.)

Multistage. Centrifugal - A centrifugal pump with more than one impeller and chamber, stacked in a sequence to produce higher pressure. Conventional AC deep well submersible pumps and higher power solar submersibles work this way.

Priming - The process of hand-filling the suction pipe and intake of a surface pump. Priming is generally necessary when a pump must be located above the water source. A "self-priming" pump is able to draw some air suction in order to prime itself, at least in theory. See foot valve.

Pulsation Damper - A device that absorbs and releases pulsation in flow produced by a piston or diaphragm pump. Consists of a chamber with air trapped within it.

Pump Jack - A deep well piston pump. The piston and cylinder is submerged in the well water and actuated by a rod inside the drop pipe, powered by a motor at the surface. This is an old-fashioned system still used for extremely deep wells, including solar pumps as deep as 1000 feet.

Sealed Piston Pump - A type of pump in which water is drawn in and forced out of a chamber by a piston mechanism. The pistons have a very short stroke, allowing the use of flexible gaskets to seal water out of the piston mechanism. Check valves let water into and out of the chamber.

Submersible Pump - A motor/pump combination designed to be placed entirely below the water surface.

Surface Pump - A pump that is not submersible. It must be placed no more than about 20 ft. above the surface of the water in the well. See priming. (Exception: see jet pump)

Vane Pump - (Rotary Vane) A positive displacement mechanism used in low volume high lift surface pumps and booster pumps. Durable and efficient, but requires cleanly filtered water due to its mechanical precision.

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