Not to be confused with solar panels / solar cells, which convert sunlight into electricity. Flat solar panels recessed into the tile roof
Solar panels are built to concentrate the heat of solar radiation and use it to heat facilities of various kinds, mainly houses, hot water and pools. A suitable medium, usually a water-based liquid, passes through the solar collector, which carries the heat further. Usually the heated liquid is primarily transferred to some kind of storage space, directly or indirectly, via heat exchangers. In most cases, these are so-called accumulator tanks. There are also solar panels that use air instead of liquid. These are most often used in holiday homes where these systems can be combined with ventilation and thus drive out cold and moisture on sunny days even when the house is empty.
By using liquid, the heat can be stored more easily than when air is used. This means that liquid-based systems have a greater impact. The heat is stored in accumulator tanks for sun-poor days and can thus be used better, especially during the summer. It is more difficult to store excess heat from the warm part of the year until winter. There are attempts with long-term storage of the heat energy in well-insulated heating magazines, but this is so far very unusual.   Letting the solar panels work against a rock heat hole is something that is discussed and where studies have been done.  The conclusion so far is that this is not so effective.
- 1 Different types of liquid-based solar collectors
- 1.1 Pool solar collector
- 1.2 Flat solar collector
- 1.3 Vacuum tube solar collector
- 1.4 Concentrating solar panels
- 2 See also
- 3 References
Different types of liquid-based solar collectors
Flat solar collectors, vacuum tube solar collectors and concentrating solar collectors are the different types available, the most common are flat solar collectors. There are also solar collectors for pools and so-called heliostat plants for the production of electricity (thermal solar power plant).
Pool solar collector
In its simplest form, a pool solar collector is a black hose. The insulation is not the best of course, but gives more effect than you might think. An easy and cheap way to raise the temperature in the swimming pool or for the hot water in the summer cottage.
Flat solar collector
En plan solfångare består av en hel absorbatorplåt som på baksidan är försedd med en rörslinga för värmebäraren (glykol/vatten). Hela absorbatorpaketet sitter i en välisolerad låda med en glasskiva framtill. Lådan kan monteras direkt på takets ströläkt och ersätter därmed tegelpannorna på samma yta. Isolationsförmågan hos en plan solfångare som kan monteras integrerat i taket blir betydligt bättre än för fristående konstruktioner. Den plana solfångaren fångar upp all infallande strålning mot panelen medan till exempel vakuumrörssolfångarpaneler har ett glapp mellan vakuumrören där solinstrålning går förlorad. Dagg, snö och frost avdunstar snabbt från en plan solfångare genom att glaset värms upp underifrån. Så kallade full-plate absorbatorer har en enda hel absorbatoryta vänd mot solen och kan läggas kant i kant och utnyttjar därmed maximal del av den infallande strålningen per takyta. Den plana solfångaren får därmed en lägre arbetstemperatur per ytenhet på absorbatorn/värmeväxlaren och är inte beroende av upparbetat vakuum för att fungera. Detta ger en avsevärt längre livslängd för plana solfångare jämfört med vakuumberoende konstruktioner av likvärdigt tillverkningsmaterial.
Vacuum tube solar collector
Vacuum tube solar collector
A vacuum tube solar collector consists of a number of vacuum tubes. The vacuum tubes are designed as a thermos, ie there are two tubes with a vacuum between them. The outer tube is transparent and the inner is the absorber itself. In the center of the inner tube, the air becomes extremely hot. This is where you pick out the energy. There are mainly two ways to transport the heat out;
U-tube: A copper tube goes down into the vacuum tube and turns into a U. In the copper tube, a heat carrier (glycol mixture) circulates which cools the air in the vacuum tube and transports the heat away to, for example, an accumulator tank.
2. Heat-Pipe: A copper piston containing a liquid is inserted into the vacuum tube. The top of the piston is inserted into a heat exchanger. As the heat rises in the vacuum tube, the liquid in the piston evaporates and rises upwards until it reaches the heat exchanger. Then it cools and condenses and flows back down into the piston to heat up again. A solar collector with heat pipe must therefore be mounted inclined. The heat is transferred from the heat exchanger to, for example, an accumulator tank.
The stagnation temperature of the vacuum tube, ie when it is allowed to stand in full sunshine and without heat dissipation, becomes very high: 230-250 degrees Celsius. About 80% of the solar radiation towards the tube can be picked out in the center.
The efficiency of all types of solar panels is negatively affected by how much lower the ambient temperature is compared to the solar panel temperature. How the efficiency decreases depends partly on the solar collector's insulation. A black hose is very poorly insulated and a large part of the energy disappears into space, a plane is better, but the vacuum tube, calculated on active surface, is so far the best in the comparison. The good insulation capacity of the vacuum tube in the first years means that the efficiency is in class with a flat solar collector, even though the illuminated surface is less calculated on the building surface on the roof. At the same time, this means that the vacuum tube is cold on the surface and thus does not "freeze off" like other constructions, which is important in the Nordic countries. 
In summer, with full solar radiation, there is less difference in efficiency between the different types of solar panels. Even a black hose is quite competitive, not least in terms of price!
The differences in performance between U-pipes, Heatpipe and flat solar collectors are not generally measurable in terms of annual exchange. There is a greater difference between different brands than between the different types.
Solar collectors can be hung directly on a wall where it stays snow-free in winter and can catch the low sun of winter. If you attach the solar collector with hinges, you can change the angle according to the seasons -winter 80˚, summer 30˚ and spring / autumn 60˚ relative to the ground level.
There are some manufacturers that manufacture vacuum tubes that can be mounted 360 degrees with a closed system. Ie also on flat roofs and on a facade. Then they can be integrated into the architecture in a more exciting way without losing efficiency as the pipes can be adjusted individually in the best position to the sun.
Concentrating solar panels
The efficiency of the solar collector can be increased with reflectors that collect the light. With solar tracking and reflectors, a solar collector can deliver many times more energy than a normal flat installation, but it takes up more space and becomes more expensive. An advantage of these is that they can simultaneously produce electricity. Sweden has a long research tradition on concentrating solar heating systems. 
- Solar heating
- Solar heating
- Solar machine
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