Solar Basics

Solar Glossary
I - J - K - L - M - N

The U.S. Department of Energy has an extensive glossary of energy related terms including the definitive explanations of the basic solar energy terms listed below.

Incident Solar Radiation
The amount of solar radiation striking a surface per unit of time and area.
Indirect Solar Gain System
A passive solar heating system in which the sun warms a heat storage element, and the heat is distributed to the interior space by convection, conduction, and radiation.

 

Indirect Solar Water Heater
These systems circulate fluids other than water (such as diluted antifreeze) through the collector. The collected heat is transferred to the household water supply using a heat exchanger. Also known as "closed-loop" systems.
Insolation
The solar power density incident on a surface of stated area and orientation, usually expressed as Watts per square meter or Btu per square foot per hour.
Instantaneous Efficiency (of a Solar Collector)
The amount of energy absorbed (or converted) by a solar collector (or photovoltaic cell or module) over a 15 minute period.
Integral Collector Storage System
This simple passive solar hot water system consists of one or more storage tanks placed in an insulated box that has a glazed side facing the sun. An integral collector storage system is mounted on the ground or on the roof (make sure your roof structure is strong enough to support it). Some systems use "selective" surfaces on the tank(s). These surfaces absorb sun well but inhibit radiative loss. Also known as bread box systems or batch heaters.
Intermittent Generators
Power plants, 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.
Intrinsic Layer
A layer of semiconductor material (as used in a solar photovoltaic device) whose properties are essentially those of the pure, undoped, material.
Inverter
A device that converts direct current electricity (from for example a solar photovoltaic module or array) to alternating current for use directly to operate appliances or to supply power to a electricity grid.
Irradiance
The direct, diffuse, and reflected solar radiation that strikes a surface.
Isolated Solar Gain System
A type of passive solar heating system where heat is collected in one area for use in another.
I-V Curve
A graphical plot or representation the current and voltage output of a solar photovoltaic cell or module as a load on the device is increased from short circuit (no load) condition to the open circuit condition; used to characterize cell/module performance.
Langley
A unit or measure of solar radiation; 1 calorie per square centimeter or 3.69 Btu per square foot.
Liquid-Based Solar Heating System
A solar heating system that uses a liquid as the heat transfer fluid.
Local Solar Time
A system of astronomical time in which the sun crosses the true north-south meridian at 12 noon, and which differs from local time according to longitude, time zone, and equation of time.
Low-Flow Solar Water Heating Systems
The flow rate in these systems is 1/8 to 1/5 the rate of most solar water heating systems. The low-flow systems take advantage of stratification in the storage tank and theoretically allows for the use of smaller diameter piping to and from the collector and a smaller pump.
Microgroove
A small groove scribed into the surface of a solar photovoltaic cell which is filled with metal for contacts.
Mixing Valve
A valve operated by a thermostat that can be installed in solar water heating systems to mix cold water with water from the collector loop to maintain a safe water temperature.
Multijunction Device
A high-efficiency photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum.
Net Metering
The practice of using a single meter to measure consumption and generation of electricity by a small generation facility (such as a house with a wind or solar photovoltaic system). The net energy produced or consumed is purchased from or sold to the power provider, respectively.

About the list of terms on this page.

The U.S. Department of Energy Efficiency and Renewable Energy Home Page is a great starting point for learning about renewable energy methods and sources. To assist the educated consumer, the website provides calculators and guides of all kinds to assist the consumer in saving money, saving energy and making the most of the renewable energy sources available. The solar energy terms and definitions on our glossary pages were extracted from the extensive DOE EERE glossary of terms about all aspects and forms of energy.