Absorber

The absorber is the active surface in a solar collector. The absorber can be made of various materials and often the surface is applied with a selective coating that allow solar short wave (solar heat and light) to transmitt while long wave heat is reflected. Upon absorption, the solar energy transforms from short wave into long wave energy.

Accumulator

Accumulator is most often refered to as a solar heat storage. This is where you store all the surplus of energy that has been harvested by the solar collectors. An accumulator can be pressurized with a pipe heat exchanger for the solar liquid or none pressurized with a pipe heat exchanger for the pressurized tapwater.

Azimuth angle

The azimuth angle is often reffered to when a solar colletor surface is installed or engineered. The azimuth angle is a figure that tells you how many degrees out of south, the direction of the solar collectors are.

Bird and Hulstrom's Solar Irradiance Model

This model is widely used for estimating broadband clear sky irradiance at Earth's surface. It is based on empirical representations of radiative transfer equations and attempts to take into account the cumulative effects of aerosols, water vapor, ozone and other gases, and Rayleigh (molecular) scattering upon sunlight reaching Earth's surface. "I have substituted my own calculations for solar zenith angle and Earth-sun distance for the calculations included in published versions of code for the Bird model -- not because they are necessarily better, but because I had already written the code. However, I have retained the original calculation for relative air mass, which will be significantly different from my own calculations only at solar zenith angles very close to 90°".

Boundary layer absorption

A boundary layer absorption is opposed to surface absorption, an energy accumulation the the layer in direct contact with the refridgerant fluid that flows through the solar collector.

Circulation pump

A circulation pump is the pump that make the flow through the solar collector. The pump is operated via the system controll unit which monitor the temperatur in the solar collector as well as in the solar heat storage.

Concentrated solar thermal energy

See definition under Solar Power.

Cooling fluid

The cooling medium also named the refridgerant is the liquid that flows through the solar collector. When the liquid is flowing through the solar collector, the collector is cooled and at the same time, heat is transfered to the liquid and carried to the solar heat storage.

Diffuse radiation

Opposed to direct radiation that appears when the sun shine from a clear blue sky, diffuse radiation is solar energy that has been absorbed by the clouds, buildings or the terrain. These object are heated by the solar absorption and contrubute with a diffuse radiation as a result thereof.

Direct radiation

Direct radiation is the measurable solar energy that is radiated from a clear blue sky.

Drain-back

Drain-back is a method that allow a solar thermal energy system to drain when there is insufficient energy to harvest or in the case of stagnation caused by maximum temperatures in the solar thermal energy system.

Drain-back storage

A drain-back storage is used to hold the liquid that is drained from the solar collector when the solar circuit is not in operation. A drain-bak system provides much better environment for the solar thermal energy system and it prevent harmfull wear caused by overheating from the sun.

Efficiency

The efficiency of a solar collector determine the solar collectors abillity to capture solar short wave energy and pass it on to a circulating liquid that is used as the cooling medium or energy carrier. The formula of the efficiency is defined by n=n0-a1(?T/G)-a2(?T^2/G). The n0 is the solar efficiency at ?T=0, a1 is the heat loss coefficient and a2 is the emission from the solar collector.

Emisivity

Emisivity is the coefficient of long wave rediation form the surface of an object. In a solar collector it is important to reduce the emisivity to retain the heat inside the solar collector once the solar energy is captured.

Evacuated tube

See definition of vacuum tube.

ESTIF

The European Solar Thermal Industry Federation.

Flat plate heat exchanger

A flat plate heat exchanger is an installation where heated water on one side transfers the heat on to the other side of flowing water. Both sides must have a circulating fluid.

Fraunhofer Institute for Solar Energy (ISE)

Fraunhofer ISE is the most reputed science center for testing solar energy technologies.

Glycol

Glycol also known as ethylene glycol is an organic compound widely used as automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid. Glycol is toxic, and ingestion can be deadly.

kWh

kWh or 1 000 Watt during 1 hour is term for energy. 1 kWh equals 3 600 000 Joules.

Magnetic valve

A magnetic valve is a valve that is opened or closed via a magnetic pulse such as electricity.

None pressurized heat storage

A none pressurized solar heat storage is build to enable drain-back inside the solar heat storage. Typically the tap water will flow through a pipe heat exchanger in the storage.

Pipe heat exchanger

A pipe heat exchanger is an installation that allows for transfer of heat from one fluid to another. We recommend a pipe heat exchanger in the solar heat storages.

Pressurized heat storage

Pressurized solar heat storages holds the actual tap water and are heated through a pipe heat exchanger connected to the solar circuit. Because of the water expansion, you need an additional drain-back storage if your solar heat storage is pressurized.

Refridgerant

In a solar thermal energy system, the refridgerant has two functions. 1) The refridgerant will take solar thermal energy from the absorber and transfer the heat to a solar heat storage. 2) The refridgerant will also cool the absorber material and delay stagnation in the solar thermal energy systems.

Seasonal storage

On of the main challanges with solar thermal energy systems are the inverse ratio of energy. During the summer season, the solar collectors will provide more energy than what is typically needed, while the winter season will demand more energy that what you will receive from the sun. To compensate for the inverse ratio of solar thermal energy, a seasonal storage is benefitial. Such storages can be large scale water accumulation, melted salt, phase change materials or storage of surplus heat in a borehole or under ground.

Selective coating

Visible light represents different wavelengths that has various energies. In brief the wavelenghts belove 380 nm is UV-light, between 380 nm and 780 nm is visible light, 780 nm and 2500 nm is near infrared light and above 2500 nm is far infrared light. A selective coating transmites light in the range from 360 nm to 2500 nm while it will block light / energy above 2500 nm. In practise this means that the coating will allow short wave solar light to enter while long wave energy from the solar collector will be reflected back on the flowing liquid.

Solar air conditioning

See Solar cooling.

Solar cell

Solar cell, also reffered to as PV or photovaltaic systems are thin layers or doped silisium that provide a low voltage when exposed to sunlight. Opposed to solar thermal energy systems that produce heat, solar cells produce electricity. Solar thermal energy systems can provide more than 90% yield on the solar energy whilst solar cells that provide around 10%.

Solar combisystem

Solar combi systems are solar thermal energy systems where the hot solar water is utilized both for tap water and for space heating.

Solar collector

A solar collector is a flat surface that accumulates solar heat and transfers this heat onto a liquid flowing through the collector. There are several different technologies for improved efficiency. We use a special technology where solar heat is accumulated in the boudary layer where the liquid is flowing. In addition we use pure water which has an amasing heat capacity. Our solar collector is between 40% and 60% more efficient than the competition.

Solar cooling

While solar thermal energy is heat, it is possible to convert the energy to cooling without loss of efficiency. The conversion from solar heat to solar cooling is made with use of an absorption chiller.

Solar design

Solar design is a term used in architectural designs. A solar design is architecture that optimize the solar nergy in a building to gain as much passive solar energy as possible.

Solar energy

Solar energy is radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, account for most of the available renewable energy on earth. Only a minuscule fraction of the available solar energy is used. Solar powered electrical generation relies on heat engines and photovoltaics. Solar energy uses are limited only by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation and disinfection, daylighting, solar hot water, solar cooking, and high temperature process heat for industrial purposes.To harvest the solar energy, the most common way is to use solar collectors. Solar technologies are broadly characterized as either passive solar thermal energy or active solar thermal energy depending on the way they capture, convert and distribute the energy. Active solar technologies include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air.

Solar fraction

The solar fraction is the fraction of solar energy that is harvested with the solar thermal energy systems.

Solar heating

Solar heating is a term used about building that are heated with solar energy.

Solar heat storage

A solar heat storage can also be refered to as an accumulator or domestic hot water storage. This is where you store all the surplus of energy that has been harvested by the solar collectors. A solar heat storage can be pressurized with a pipe heat exchanger for the solar liquid or none pressurized with a pipe heat exchanger for the pressurized tapwater.

Solar hot water

Solar hot water is water that is heated by use of solar thermal energy.

Solar hours

Solar hours are the number of hours with a clear blue sky and sunshine during a timeframe. The number of solar hours for your project location is the most important factor for utilization of solar energy besides the direct solar radiation determined by the latitude.

Solar power

Opposed to solar thermal energy systems that typically utilize solar energy for heating purposes, solar power converts heat into electricity by use of a Stirling engine or a Peltier process.

Solar radiation

Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight and heat when the Sun is above the horizon. When the direct solar radiation is unblocked by clouds, it is sunshine, a combination of light and radiant heat. When it is blocked by the clouds or reflected from other objects, it is experienced as diffused light. The World Meteorological Organization uses the term "sunshine duration" which means the cumulative time during which an area receives direct irradiance from the Sun of at least 120 watts per m2. Direct sunlight has a luminous efficacy of about 93 lumens per watt of radiantion, which includes infrared, visible, and ultraviolet light. Bright sunlight provides illuminance of around 100,000 lumens per m2 at the Earth's surface.

Solar space heating

Solar space heating is space heating with use of solar thermal energy. Solar thermal energy is long wave energy that is very well suited for heating ie. by under floor heating.

Solar thermal energy system

A solar thermal energy system is an installation to harvest and utilize solar heat. Typically the system in made with one or more solar collectors, connecting pipes, a heat storage, a solar thermal system controller and some couplings and valves depending on the system setup.

Solar thermal energy

Solar thermal energy is solar energy in the form of heat and light, harnessed as heat. Solar thermal energy is different from photovoltaics, which convert solar energy directly into electricity.

Solar thermal energy calculator

A solar thermal energy calculator is a program that allows you to calculate your energy demand and solar contribution. You can download our solar thermal energy calculator free of charge from Solar thermal energy calculator

Specific heat capacity

A value that describes a material/fludiums energy storage potential. Ie. the heat capacity of water is 4.1796 J/cm3*K. That is; for each cubik cm of water, it takes an energy size of 4.1796 Joules to increase the temperature by 1 degrees. The higher the number, the better performance in a solar thermal collector. The specific heat capacity of glycol in water 50% is 3.4834 and that for air is 0.001297 Joules. This means that water has a capacity that is 3222 times higher than that of air.

Stagnation

During operation of a solar thermal energy system, stagnation will occure due to the solar heat storage reaching its maimum temperature. When the maximum temperature is reached in the storage tank, the solar thermal energy system must stop its circulation to avoid overheating and stagnation will enter. In a drain-back system, the fluid will drain out of the loop during stagnation and thus prevent any overheating of the flowing liquid.

Steam

Steam is the gas phase of water. In common speech, steam most often refers to the visible white mist that condenses above boiling water as the hot vapor mixes with the cooler air. The mist consists of tiny droplets of liquid water. Pure steam is a transparent gas. At normal temperature and pressure, pure steam occupies about 1,600 times the volume of an equal mass of liquid water. In the atmosphere, the partial pressure of water is much lower than 1 atm, therefore steam can exist at temperatures lower than 100 °C.

Tank in tank

A tank in tank is a staorage tank made of two tanks (one on top of the other) that are welded to each other with an intersection. A tank in tank heater can be very benefitial if you are planning under floor heating.

Tilt

The solar collector angle in the vertical plane is called the tilt. In a solar thermal energy stystem you may tilt the solar collectors between 15 degrees and 90 degrees depending on your energy needs and the architecture. Allthough you may gain some extra energy during the winter season with a larger tilt, the variations are very small. You may observe these variation with our Solar thermal energy calculator

Thermal energy storage

One of the main obstacles with solar thermal energy systems are the limited storages. A thermal energy storage aim to store solar heat so that this energy can be used when the sun is not contributing. Water storages are one of the most efficient storages, but there is a lot of experiments in the utilization of a borehole, melted salt, phase changing materials and sorbtion technologies.

Thermisifon

A simple form of solar thermal energy system is the thermosifon where water is convected by its own gravity.

Under floor heating

For optimized comfort and efficient utilization of solar thermal energy for space heating you can use under floor heating. As it says, it is small pipes circulating warm water under the surface of the floors, providing an efficient heat transfer and increased comfort level that may allow for a reduced room temperature and therby saving energy.

Vacuum tube

A vacuum tube solar collector is a collector where the cooling (typically glycol) is flowing inside a copper tube surrounded by an evacuated space and a glass tube on the outside. The theoretical benefits are lower convection and conduction from the heated copper through the evacuated space and the outer glass tube. In practise the vacuum tube solar collectors has shown efficient at temperture differences at more than 100 degrees K compared to the ambient temperatures.

Water trap

Water traps accure when a liquid is hindered from is flowing. This appears when a pipe has a bend or if one part of the piping is at a higher level than the rest of the piping. It can be a U-, S-, or J-shaped pipe located below or within a plumbing fixture. An S-shaped trap is also known as the S-bend.

Watt

Watt is a measure of the energy that is collected by the solar collector. In the summer with a clear blue sky, you may consider around 1000 Watt for each square meter of solar collectors that you have installed.