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Glossary of Alternative Energy Terms

Definitions of many of the frequently used terms within renewable energy.

Basic Electricity | Solar Electricity | Batteries and Inverters | Hydro (Micro) Power | Pumps & Related Components | Solar Pump Components | Water Well Components | Water Well Characteristics | Pump System Engineering | Water Distribution|Wind Systems


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.


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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.

Short Circuit Current – The current measured when a PV module is not connected to a load or any other resistance. This is the basis for calculating the appropriate size for a charge controller. This is often abbreviated as Isc and the value can be found on the label on the back of each solar module.

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.


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Batteries and Inverters

Alternating Current (AC) – An electric current that reverses direction at regular intervals. Sources of alternating current are shore power, generator power, inverter power or household current. 

Ampere (Amp, A) -The unit of measure of electron flow rate of current through a circuit. 

Ampere-hour (Amp-Hr., AH) – A unit of measure for a battery’s electrical storage capacity, obtained by multiplying the current in amperes by the time in hours of discharge (Example: a battery which delivers 5 amperes for 20 hours delivers 5 amperes times 20 hours, or 100 Amp-Hr. of capacity.) 

AH Capacity – The ability of a fully charged battery to deliver a specified quantity of electricity (Amp-Hr., AH) at a given rate (Amp, A) over a definite period of time (Hr.). The capacity of a battery depends upon a number of factors including: active material, weight, density, adhesion to grid, number, design and dimensions of plates, plate spacing design of separators, specific gravity and quantity of available electrolyte, grid alloys, final limiting voltage, discharge rate, temperature, internal and external resistance, age and life of the battery (bank). 

AGM (Absorbed Glass Mat) Battery – A lead acid, maintenance-free battery. 

AWG (American Wire Gauge) – A standard used to measure the size of wire. 

Circuit – An electric circuit is the path of an electric current. A closed circuit has a complete path. An open circuit has a broken or disconnected path. 

Circuit (Series) – A circuit which has only one path for the current to flow. Batteries arranged in series are connected with the negative of the first to the positive of the second, negative of the second to the positive of the third, etc. If two 6 Volt batteries of 50 ampere-hours capacity are connected in series, the circuit voltage is equal to the sum of the two battery voltages, or 12 Volts, and the ampere-hour capacity of the combination is 50 ampere-hours. 

Circuit (Parallel) – A circuit which provides more than one path for current flow. A parallel arrangement of batteries (of like voltage and capacity) would have all positive terminals connected to a conductor and all negative terminals connected to another conductor. If two 12 Volt batteries of 50 ampere-hour capacity each are connected in parallel, the circuit voltage is 12 Volts, and the ampere-hour capacity of the combination is 100 ampere-hours. 

Current -The rate of flow of electricity or the movement rate of electrons along a conductor. It is comparable to the flow of a stream of water. The unit of measure for current is ampere. 

Cycle – In a battery, one discharge plus one recharge equals one cycle. 

Direct Current (DC) – Current that flows continuously in one direction such as that from batteries, photovoltaics, alternators, chargers and DC generators. 

Equalize Charge – A controlled overcharge of the batteries which brings all cells up to the same voltage potential, extends the battery life, restores capacity and mixes the electrolyte. This can only be done using the Freedom Remote Control Panel or a Link Instrument. 

Electrolyte – in a lead acid battery, it is a dilute solution of sulfuric acid (H2SO4) and water.

Gel Cell Battery -A type of battery that uses a gelled electrolyte solution. These batteries are sealed and are virtually maintenance-free. Not all sealed batteries are the gel cell type. 

GFCI (Ground Fault Circuit Interrupter) – A protective device that rapidly de-energizes a circuit when current to ground exceeds a predetermined value. 

Ground – The reference potential of a circuit. In automotive use, the result of attaching one battery cable to the body or frame which is used as a path for completing a circuit in lieu of a direct wire from a component. This method is not suitable for connecting the negative cable of the inverter to ground. Instead, route the cable directly to the negative terminal of the battery. 

Hydrometer – a tool used to measure the specific gravity of the electrolyte solution.

NEC – National Electric Code 

Negative – Designating or pertaining to electrical potential. The negative terminal is the point from which electrons flow during discharge. 

Ohm – A unit for measuring electrical resistance. 

Ohm’s Law – Expresses the relationship between Voltage (V) and Current (I) in an electrical circuit with resistance (R). It can be expressed as follows: V=IR. If any two of the three values are known, the third value can be calculated by using the above formula. 

Open Circuit Voltage – the voltage of a battery when there is no load attached (not receiving or delivering energy). This measurement is best taken when the battery has been at rest for at least 6 hours.

Parallel Connection – a method of wiring batteries together by connecting the positive terminal of the first battery to the positive terminal of the second and the negative terminal of the first to the negative of the second. The capacity for batteries connected in parallel becomes additive, while the voltage remains the same as the individual battery.

Primary Battery – an energy storage device that can deliver energy but cannot be recharged.

Positive – Designating or pertaining to electrical potential; opposite of negative. The positive battery terminal is the point where electrons return to the battery during discharge. 

Power Sharing – The feature of the charger to reduce its output when the AC power being consumed by the charger and external AC loads connected to the output of the inverter are in excess of the input breaker rating. 

Secondary Battery – an energy storage device that can deliver energy and can be recharged.

Separator – a divider made of porous material that is placed in between the positive and negative plates in a battery cell and allows current flow through it while preventing direct contact between the plates which would cause a short circuit.

Series Connection – a method of wiring like batteries together by connecting the positive terminal of one battery to the negative terminal of an other. The voltage for batteries connected in series is additive, while the capacity remains the same as the individual battery.

Series-Parallel Connection – a method of wiring batteries together in a combination of series and parallel connections.

Specific Gravity – the density of a solution relative to the density of water.

Stratification – a condition where the concentration of acid is greater at the bottom of the battery than at the top. This condition is caused by undercharging, and if not corrected can cause premature failure of the battery. This condition can be prevented by periodic equalization.

Sulfation – the formation of lead sulfate on both the positive and negative electrodes in a lead acid battery results during the discharge portion of the charge/discharge cycle and is a normal part of the battery process. If the battery is allowed to remain in a discharged state for a prolonged period of time, these sulfate crystals continue to grow. These larger crystals reduce the effective plate area and are difficult to dissolve back into solution with normal charging. Thus, they reduce the overall capacity of the battery. This condition can be prevented by effectively recharging the battery immediately following a discharge. This condition can also be prevented by periodically equalizing the battery.

TSC – Abbreviation for Temperature Sensitive Charging. The ability of the charger to adjust its charging voltage based on the temperature sensed at the battery bank if a temperature probe is used. 

Volt – The unit of measure for electric potential. 

Watt – The unit for measuring electrical power, i.e., the rate of doing work, in moving electrons by or against an electric potential.  (Watts = Amperes x Volts)

Watt-Hour (Watt-HR, WH) – The unit for measuring electrical energy which equals Watts x Hours. 

Wet Cell Battery – A type of battery that uses liquid as an electrolyte. The wet cell battery requires periodic maintenance; cleaning the connections, checking the electrolyte level and performing an equalization cycle. 


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Hydro (Micro) Power

Head – The vertical distance the water falls.

Flow – The rate at which water moves. Measured in liters per minute (I/m) or gallons per minute (gpm).

Pounds per square inch/ kilo-pascals -Units of pressure


1 imperial gallon (gal)

4.546 litres (L)
1 litre (L) 0.220 imperial gallons (gal)



1 cubic inch (in3)

16.387 cubic centimetres (cm3)

1 cubic centimetre (cm3) 0.061 cubic inches (in3)

1 cubic yard (yd3)

0.764 cubic metre (m3)
1 cubic metre (m3) 1.308 cubic yards (yd3)
1 cubic foot (ft3) 0.028 cubic metre (m3)
1 cubic metre (cm3) 35.315 cubic feet (ft3)


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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 multi-stage.

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.)

Multi-Stage 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 pulsations 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 that is still used for extremely deep wells, including solar pumps as deep as 1000 feet.

Sealed Piston Pump – See positive displacement pump. This is a type of pump recently developed for solar submersibles. The pistons have a very short stroke, allowing the use of flexible gaskets to seal water out of an oil-filled mechanism.

Self-Priming Pump – See priming.

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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Solar Pump Components

DC Motor, Brush-Type – The traditional DC motor, in which small carbon blocks called “brushes” conduct current into the spinning portion of the motor. They are used in DC surface pumps and also in some DC submersible pumps. Brushes naturally wear down after years of use, and may be easily replaced.

DC Motor, Brushless – High-technology motor used in centrifugal-type DC submersibles. The motor is filled with oil, to keep water out. An electronic system is used to precisely alternate the current, causing the motor to spin.

DC Motor, Permanent Magnet – All DC solar pumps use this type of motor in some form. Being a variable speed motor by nature, reduced voltage (in low sun) produces proportionally reduced speed, and causes no harm to the motor. Contrast: induction motor

Induction Motor (AC) – The type of electric motor used in conventional AC water pumps. It requires a high surge of current to start and a stable voltage supply, making it relatively expensive to run from by solar power. See Inverter.

Linear Current Booster – See pump controller . Note: Although this term has become generic, its abbreviation “LCB” is a trademark of Bobier Electronics.

Pump Controller – An electronic device which varies the voltage and current of a PV array to match the needs of an array-direct pump. It allows the pump to start and to run under low sun conditions without stalling. Electrical analogy: variable transformer. Mechanical analogy: automatic transmission. See linear current booster.


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Water Well Components

Borehole – Synonym for drilled well, especially outside of North America.

Casing – Plastic or steel tube that is permanently inserted in the well after drilling. Its size is specified according to its inside diameter.

Cable Splice – A joint in electrical cable. A submersible splice is made using special materials available in kit form.

Drop Pipe – The pipe that carries water from a pump in a well up to the surface.

Perforations – Slits cut into the well casing to allow groundwater to enter. May be located at more than one level, to coincide with water-bearing strata in the earth.

Pitless Adapter – A special pipe fitting that fits on a well casing, below ground. It allows the pipe to pass horizontally through the casing so that no pipe is exposed above ground where it could freeze. The pump may be installed and removed without further need to dig around the casing. This is done by using a 1 inch threaded pipe as a handle.

Safety Rope – Plastic rope used to secure the pump in case of pipe breakage.

Submersible Cable – Electrical cable designed for in-well submersion. Conductor sizing is specified in millimeters, or (in USA) by American Wire Gauge (AWG) in which a higher number indicates smaller wire. It is connected to a pump by a cable splice.

Well Seal – Top plate of well casing that provides a sanitary seal and support for the drop pipe and pump. Alternative: See pitless adapter


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Water Well Characteristics

Driller’s Log – The written form on which well characteristics are recorded by the well driller. In most states, drillers are required to register all water wells and to send a copy of the log to a state office. This supplies hydrological data and well performance test results to the public and to the well owner.

Drawdown – Lowering of level of water in a well due to pumping.

Recovery Rate – Rate at which groundwater refills the casing after the level is drawn down. This is the term used to specify the production rate of the well.

Static Water Level – Depth to the water surface in a well under static conditions (not being pumped). May be subject to seasonal changes or lowering due to depletion.

Wellhead – Top of the well, at ground level.


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Pump System Engineering

Friction Loss – The loss of pressure due to flow of water in pipe. This is determined by 3 factors: pipe size (inside diameter), flow rate, and length of pipe. It is determined by consulting a friction loss chart available in an engineering reference book or from a pipe supplier. It is expressed in PSI or Feet (equivalent additional feet of pumping).

Head – See synonym: vertical lift.

Suction Lift – Applied to surface pumps: Vertical distance from the surface of the water in the source, to a pump located above surface pump located above. This distance is limited by physics to around 20 feet at sea level (subtract 1 ft. per 1000 ft. altitude) and should be minimized for best results.

Submergence – Applied to submersible pumps: Distance beneath the static water level, at which a pump is set. Synonym: immersion level.

Total Dynamic Head – vertical lift + friction loss in piping (see friction loss).

Vertical Lift – The vertical distance that water is pumped. This determines the pressure that the pump pushes against. Total vertical lift = vertical lift from surface of water source up to the discharge in the tank + (in a pressure system) discharge pressure. Synonym: static head. Note: Horizontal distance does NOT add to the vertical lift, except in terms of pipe friction loss. NOR does the volume (weight) of water contained in pipe or tank. Submergence of the pump does NOT add to the vertical lift in the case of a centrifugal type pump. In the case of a positive displacement pump, it may add to the lift somewhat.


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Water Distribution

Cut-In Pressure and Cut-Out Pressure – See pressure switch.

Gravity Flow – The use of gravity to produce pressure and water flow. A storage tank is elevated above the point of use, so that water will flow with no further pumping required. A booster pump may be used to increase pressure. 2.31 Vertical Feet = 1 PSI. See pressure.

Head – See vertical lift and total dynamic head. In water distribution, synonym: vertical drop.

Open Discharge – The filling of a water vessel that is not sealed to hold pressure. Examples: storage (holding) tank, pond, flood irrigation. Contrast: pressure tank.

Pressure – The amount of force applied by water that is either forced by a pump, or by the gravity. Measured in pounds per square inch (PSI).

PSI = vertical lift (or drop) in Feet / 2.31.

Pressure Switch – An electrical switch actuated by the pressure in a pressure tank. When the pressure drops to a low set-point (cut-in) it turns a pump on. At a high point (cut-out) it turns the pump off.

Pressure Tank – A fully enclosed tank with an air space inside. As water is forced in, the air compresses. The stored water may be released after the pump has stopped. Most pressure tanks contain a rubber bladder to capture the air. If so, synonym: captive air tank.

Pressure Tank Precharge – The pressure of compressed air stored in a captive air pressure tank. A reading should be taken with an air pressure gauge (tire gauge) with water pressure at zero. The air pressure is then adjusted to about 3 PSI lower than the cut-in pressure (see Pressure Switch). If precharge is not set properly, the tank will not work to full capacity, and the pump will cycle on and off more frequently.


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Wind Systems

Turbulence – Wind that flows over obstacles such as trees or buildings gets churned up, and is no longer considered laminar (smooth) flow. Wind turbines do not handle turbulent flow well: power production can be dramatically decreased. To avoid turbulence, situate the turbine 30 feet above any obstruction within 300 feet. The higher the turbine, the less turbulence you will have and the greater the energy production.