Renewable Energy Glossary

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Feathering

In wind generators, this refers to an adjustment of the blade angle so that blades produce less lift force. This can control speed and prevent damage to the machine in high winds. Feathering can be achieved by increasing the blade pitch angle so the blades are “edge on” to the wind.

Feed-In Tariff

A grid-connected system with meters for both consumption and production; also called a buy-all/sell-all system, because all energy produced is sold to the utility, and all energy consumed is purchased.

Feed-in Tariff Connection

Similar to a supply side connection, but the inverter output is run through a fused service disconnect and a production meter before being connected to the grid on the utility side of the existing electrical meter.

Feed-in Tariff System

A grid-connected system with meters for both consumption and production; also called a buy-all/sell-all system, because all energy produced is sold to the utility, and all energy consumed is purchased.

FFV

A flex-fuel vehicle (FFV) is a vehicle that can run on a range of fuels from 100% gasoline to 100% ethanol, but is generally optimized for an 85% ethanol mixture.

Fixed Guyed Tower

A guyed tower that does not tilt down or up. The most common tower type is a guyed lattice tower. We also see fixed-guyed tubular towers, especially in home-built applications.

Flagging

Noticeable deformation of trees from prevailing winds. Flagging is an indication of an effective wind site. Lack of flagging is not necessarily an indication of a poor wind site.

Flashing

A piece of impervious material installed to prevent water from entering a structure through a joint or penetration.

Flat Plate Collector

A solar heating collector that converts the sun's radiation into heat on a flat absorber. A glazed collector has a glass or plastic covering and an unglazed collector has no glazing; both have fluid or air passages to allow the circulation of a heat transfer fluid.

Flex Fuel Vehicle

A vehicle designed to run on a range of fuel mixtures, from 100% gasoline to 100% ethanol. The fuel is stored in a single tank, relying on electronic sensors to determine the specific mix of gas to alcohol and adjust engine tune to suit.

Flexible Fuel Vehicle

A vehicle designed to run on fuel mixtures ranging from 100% gasoline to 100% ethanol, stored in a single tank, with the mixture detected electronically. FFVs are typically optimized to burn E85, a fuel made up of 85% ethanol and 15% gasoline.

Flooded Lead Acid Batteries

Batteries that have cell caps that can be opened, allowing access to refill the cells with distilled water periodically.

Flow

In hydroelectric terms, flow refers to the volume of water supplied to a water source or exiting a nozzle per unit of time. Commonly measured in gallons per minute, or liters per second.

Flow Duration Curve

A chart showing the number of hours per year at any given flow. This can be used to calculate energy production and decide the most economic size for the turbine and penstock. The flow determines the power (kW) at any moment and the duration determines the energy (kWh).

Flow Rate

A measure of the quantity of fluid that moves through piping during a fixed period of time.

Fluorescent Light

An electric lamp coated on its inner surface with phosphor and containing mercury vapor. When bombarded with electrons, the vapor emits ultraviolet light that causes the phosphor to emit visible light.

Forest Stewardship Council

A nonprofit third party that certifies that wood products are made from lumber harvested in a sustainable manner. Other third-party certifying bodies include the Sustainable Forestry Initiative and the Canadian Standards Association.

Fossil Fuel

A non-renewable form of energy, such as coal, petroleum, or natural gas, which has high carbon content and is formed by the decomposition of organic matter.

Francis Turbine

A type of reaction hydro-turbine used in low to medium heads. It has a cast rotor with vanes that are parallel to the shaft. Water enters through a spiral passage, is controlled by adjustable guide vanes, then flows down through the vanes and out sideways. Francis turbines are uncommon in domestic-scale hydro systems.

Freestanding Tower

A wind generator tower with no guy wires. This can be either a lattice tower or a monopole. Freestanding towers are the most expensive type, requiring large excavations and large amounts of concrete and steel. They are also often considered to be the safest towers to install and live with, and some find they are the most aesthetic.

Freeze Protection

Only antifreeze and drainback systems exhibit true freeze protection. Other methods of protection are known to have widespread failure depend on valves or controls.

Freeze Tolerance

A freeze tolerance temperature that manufacturers list with their SRCC OG-300 system certification.

Friction Loss

Lost energy due to friction. For a given size of pipe, friction loss rises rapidly with increased flow. (It varies roughly with the square of the flow.) There will also be friction losses in belt drive systems.

Frictional Head Loss

See dynamic head--the loss in pressure or head from the friction of the fluid on the interior walls of pipe.

Frictional Head Loss

The amount of pressure lost due to friction in a pipe. The "dynamic head" (operating pressure) is equal to the "static head" (or gross head) minus the head loss. Loss depends on both pipe bore and flow. Head loss can be reduced dramatically by using a larger bore pipe, but there are diminishing returns once it has been reduced below about 10%.

FSC

The Forest Stewardship Council (FSC) is a third party that certifies that wood products are made from lumber harvested in a sustainable manner. Other third-party certifying bodies include the Sustainable Forestry Initiative and the Canadian Standards Association.

Full Sun

Equivalent to a peak sun hour or 1,000 watts per square meter for one hour.

Furling

Adjusting a wind generator's blades to protect it from high winds. Common furling methods in small turbines are to tilt the rotor (blades) up and/or to yaw sideways out of the wind. The term is also used for changing the blade pitch to reduce loads.

Fuse

An overcurrent protection device that can interrupt a circuit and protect against excess electrical current.

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