Solar water heating

As a solar thermal system solar systems are referred to, the heat from the sun that is available ( solar thermal). The heat is utilized in process engineering or building or used in solar thermal power plants to generate electricity.

The direct conversion of sunlight into electricity - for example, by means of solar cells - is, however, known as photovoltaics, the installations as photovoltaic systems.

2.2.1 Thermal Storage
2.2.2 Heat loss
2.2.3 structure
2.2.4 Long term storage
2.2.5 Dual-mode memory
2.2.6 Combination storage
2.2.7 Solar buffer

2.3.1 propylene glycol -water solution
2.3.2 Clean Water

2.4.1 Printing equipment
2.4.2 Drucklosanlagen

6.1 systems for DHW heating
6.2 systems to support heating ( solar thermal systems with return flow temperature increase )
6.3 promotion 6.3.1 Germany
6.3.2 Austria

Areas of application

Mostly solar thermal systems are used in domestic installations. The extracted heat is here mostly used for ' Trinkwasser' heating (dishwasher, shower and bath water) and for heating the living space.

In the industrial sector plants, most of more than 20 m² collector area for the production of process heat at temperatures up to 100 ° C or slightly above, about to accelerate biological and chemical processes involved in the biomass processing or in the chemical industry or for heating / preheating of air to operate.

Also among the solar thermal systems include facilities for solar air conditioning. Due to the high temperatures, they are similar to the process equipment.

A large technical use finds contrast instead in thermal solar plants as in Andasol. Most of these systems use concentrating collectors to focus the sun's rays on an absorber - point or a line absorber, in which, the temperatures of 390 ° C to 1000 ° C can be achieved. This heat is then either used as industrial process heat or converted via Generators in power ( solar thermal power ). Since concentrating panels need direct sunlight, they are only in sunny and dry regions used ( in Europe, for example in southern Spain ).

This article will focus in the following on the use of solar thermal for DHW heating and central heating, as this is the central Europe (still) most common and most widespread application.

Components

The solar thermal system consists of a collector, which converts the solar radiation into heat, a solar heat storage, which stores the heat and immediately used the connecting solar cycle over which the heat is transported from the collector into the memory. This consists of pipes, valves and drive units, ensure the proper operation of the system, and a controller which the heat transport on and off (except for gravity systems).

Collectors

The solar collector is the part of the solar system, which receives a large part of the energy of sunlight (absorption ), but at the same time - despite its own warming - only little of it back as heat emits radiation ( emission). He transfers the absorbed heat loss as possible on the so-called solar fluid in the solar circuit.

The main constructional distinction in between the panels is

With air -filled ' panels that are protected with conventional insulation materials against heat loss (insulation). They have been preparing for the efficient use of solar energy. They usually have a very long life; there should be manufacturers that provide a performance guarantee of 20 years.
Vacuum tube collectors; the most common variant operate according to the thermos flask principle: To the inner absorber tube, transport medium contained is set a second, outer (glass) tube. For better insulation of the gap, the air is removed (vacuum). You are more powerful than other types of buildings, especially at high temperature differences between the outside air and absorber. They are therefore used in the industrial sector, where process heat is required with constant above 80 ° C.

In Europe, air-filled flat plate collectors are spread much more frequently, and are mainly used in building technology. Vacuum collectors have a higher yield per square meter absorber surface. However, the difference in the conversion to the total area of the collector instead of the pure absorber surface melts together strong, as in air-filled collectors of the absorber has a significantly larger proportion of the total required for the installation area occupies. Based on the gross area of the yield with vacuum panels is theoretically about 20 % higher than the flat-plate collectors. In the most common use case of flat - plate and tube collectors - in a private family house - allows a vacuum tube collector only the realization of marginal income benefits. The addition of usable heat energy of a vacuum Röherenkollektors is then up to 2-5 % based on the total energy consumption of the house. Type-related performance differences exist with flat plate collectors and evacuated tube collectors. A comparison of the performance data that can be found in the Keymark certificates is unmungänglich. Vacuum tube collectors bring, especially in the transition period and in winter larger revenues because at low outdoor temperatures, the better insulation comes into play. Even with large temperature differences between outside temperature and storage medium temperature ( over 40 ° ), the efficiency of the evacuated tube collectors better. At low temperature spread of the flat plate collector has the advantage. Due to the better insulation thaw vacuum tube collectors from slightly slower. In regions with lots of snow this can be detrimental.

A mixed form are so-called vacuum flat solar panels. These represent an attempt to take advantage of the better insulating properties of the vacuum even in "normal " flat plate collectors. Due to the design, but these tend to leak, so that incoming air must be reduced, the thermal insulation and cleaned regularly using a vacuum pump.

In register- shaped absorber tubes or if multiple solar absorber / collectors are operated in parallel in a common hydraulic system ( for example, with a common circulation pump ), they must be tubes with each other after Tichelmann so that a reasonably uniform flow through all Absorber-/Kollektorsegmente is ensured.

Stagnation temperature

Is the temperature reached by the collector under standard illumination of 1000 W/m2 at idle without solar fluid. The height of the stagnation temperature of the collector depends on its quality. Mostly found in the certificates of collectors temperatures moving 170-230 degrees Celsius, with some collectors, this temperature is given as about 300 ° C. The better a collector is isolated the higher this temperature. Every collector must be designed so that these, these temperature extremes is also harmless. An accelerated aging but occurs more or less, depending on the design and brand forever. Collecting tubes made of copper oxidizing, with repeated prolonged stagnation. There are also panels with stainless steel manifolds. The insulating material may age prematurely depending on the material used. In the vicinity of the collector, the pipes must withstand this temperature without damage. If an in- stagnation collector but with solar fluid filled again as this can cause damage because of thermal shock may be too high. A filling of collectors should only take place when buried collector or in the early morning or in the evening after cooling of the collector.

Solar storage

In order to use the captured heat, regardless of the actual solar radiation, they must be stored. Important quality parameters are the capacity and heat loss.

Thermal storage capacity

The storage capacity is proportional to the storage capacity, the heat capacity of the storage medium and the usable temperature difference.

The storage medium is predominantly water. Water in comparison with other substances a high specific heat capacity of 4.187 kJ / (kg · K). A fully -heated 500 liter hot water tank contains a temperature difference of about 45 K, for example, a usable amount of energy from

Between the feed from the cold water pipe network and memory.

If a water reservoir for the heating mode are used, a maximum storage temperature and a low temperature heating and the use of a heating mixer is recommended in order to achieve the maximum temperature difference.

A fully -heated 800 liter cylinder with 80 ° C storage temperature and 30 ° C flow temperature of a floor could then, for example,

Hold.

Heat loss

A current standard 300 - liter tank has ( depending on the make and manufacturer ), for example, a heat loss of about 1.9 kWh / day, a 600 - liter tank with the same insulation standard about 2.4 kWh / day. Wherein doubled storage capacity so the heat loss increases only by about 30%. One reason for this is that the surface of a memory increases disproportionately with the volume.

Construction

From conventional hot water storage tanks, Solar memory differ primarily in:

Reinforced insulation; usual, 10 cm or more (up to about 50 cm ), partly from materials such as PU or PP foam with very low thermal conductivity ( λ <0.04 W / mK), partly two-layered, often compared to only 5 cm of mineral wool with conventional hot water tanks in central heating systems.
A high and slim design of the water tank, which allows the development of different temperature layers ( above hot water, cool water below )
A low -mounted, large-scale heat exchanger for transferring heat from the solar circuit.

Long -term storage

For long- term storage in a seasonal heat storage, as from summer to winter, even gravel is used in addition to water. The heat is on and applied by air. However, water and solids are only suitable when large volumes or masses are available ( about 20 tons ) for such longer-term storage.

An alternative is latent heat storage, this use of the phase transition solid / liquid, such as paraffins, for heat storage and require substantially less volume for the same amount of heat. For them, usually a large number of containers filled with paraffin in a water tank are installed.

Thermochemical heat storage use the heat of reversible chemical reactions: By adding heat the heat transfer medium used changes its chemical composition; in reconversion initiated from outside the main part of the supplied heat is released again. Thermochemical heat storage permit in contrast to buffer and latent heat storing the almost loss-free storage of large amounts of heat for extended periods. Therefore, they are, for example, as a seasonal storage for solar thermal applications in regions with high seasonal temperature differences.

Dual-mode memory

Frequently solar storage tank are designed bivalent, that is, in addition to the heat exchanger of the solar circuit, they have a means for reheating by another energy source, such as a second heat exchanger in the upper memory area for connection to a conventional ( fuel oil or natural gas), heat pump or biomass boiler ( pellet or firewood ). This reheating is always necessary when the sun does not provide enough energy to meet the hot water demand (for example, after several cold days with dense cloud cover ). Alternatively, to be used as an electric heater; water heating with electricity is but energetically very inefficient and not very environmentally friendly.

Combination storage

In addition to pure drinking water storage, there are also so-called combi storage tank or tank - in - tank systems that serve the heating support simultaneously. These containers are flowed through by the water from the central heating system, the solar- heated in the lower region, is reheated in the upper region of the boiler, if required. Inside this heating water storage is a second, much smaller container or a thick coiled tube through which the flows or the drinking water and - similar to a water heater - is heated by hot water. Such memories have a much higher total than pure drinking water storage ( at least double volume ); held before the share of heated drinking water is considerably lower (about 80 to 200 liters). Such systems are therefore also suitable for public buildings or guesthouses, which have a high demand for hot water, but do not want to rely on hot water tanks, with more than 400 liters that require special protective measures against Legionella.

Solar buffer storage

Solar buffers include heating water - not for drinking. A solar buffer storage has i.d.R. a heat exchanger in the bottom area of the memory. The solar heating system heats the heating water. Achieves the solar system is not sufficiently high buffer temperatures, can any other conventional heat source (eg, wood boilers, Elektroeinschraubheizstab, oil or gas heating) reheating the water buffer without the necessary use of a heat exchanger directly. Drinking water can be produced with the help of a fresh water station. The freshwater station used to the heat from the buffer memory. The fresh water station heats and maintains the required temperature for the tapped hot water. This is done to match the hot water demand sized plate heat exchanger in conjunction with a control unit for flow control. A legionella contamination of drinking water is virtually excluded from the DHW heating by buffer memory in association with a fresh water station.

Solar fluid

The heat transfer fluid transported - in liquid-filled systems - the heat from the producer to the consumer or memory. In general, under boundary conditions in hot periods it can come to the evaporation of the solar fluid which in turn leads to stagnation of the collector.

Propylene glycol -water solution

In most cases, the solar fluid is a water-propylene glycol solution that has a lower freezing point than water so that the plant will be protected from frost damage. The boiling point of the heat transfer fluid is substantially higher than that of pure water. Occur, especially in pressure systems characterized under marginal conditions during heat waves or with insufficient heat dissipation high temperatures (up to about 200 degrees Celsius ) and pressures in the solar circuit on. Line system and seals must be designed. If temperatures are too high, the solar fluid still in the vapor phase, this leads to plant shutdown and the stagnation temperature is reached; the pressure is then intercepted by the first diaphragm expansion vessel ( MAG) and when exceeding a limit ( usually 6 bar) solar fluid is discharged through the safety valve into a container. The state and the change of the solar fluid is checked during maintenance, since the solution is aging due to frequent aggregate change. The mixtures used today are non-toxic and chemically relatively stable.

The higher the glycol concentration is, the lower temperatures, the solar circuit withstand without damage. A concentration of about 50 % should be avoided, since the specific heat capacity of the mixture is reduced. Also, the pump is no longer reliably cooled. The viscosity of the mixture and thus the required pump work and power consumption increase. Overall, decreases the efficiency of the system. In extreme cases, it may be difficult starting the pump. Should the system be exposed to very low temperatures, so formed with sufficient glycol portion, a water ice, the lines but not destroyed. Heatpipes are not protected from the solar fluid. The frost resistance of heat pipes is depending on the manufacturer at approximately -30 ° C.

Pure water

There are systems that use water directly (more precisely pure water ) work as solar fluid. The purity need not be particularly high. Normal drinking water or filtered rain water is sufficient. When Duch directly carrying tube collectors with closed solar circuits where a residual amount of light on the water meets chemical additives are sometimes used to inhibit algae formation in the water. With pure water systems must be available not necessarily a heat exchanger between the solar cycle and memory. This also facilitates the integration of solar systems into existing heating systems. In the winter, make sure that the collectors do not freeze. To this end, the outside temperature is monitored and managed as needed warmer water through the collector. The energy required for this purpose (pump, hot water) can be offset with various savings such as the improved efficiency by dispensing with a antifreeze. The higher heat capacity and the reduced viscosity of pure water, therefore, has less pump work result. Similarly, " drain -back systems," where the solar cycle is automatically filled with water only work if the collectors are warm enough and the memory is receptive. Once the automatic control abstellt the pump, the water runs into an integrated receptacle. Under boundary conditions during heat waves, occur in the solar circuit to lower temperatures, since pure water has a boiling point depressants, as a propylene glycol -water solution. In particular, it is thus also possible Drucklossystemen pipes, pumps and other components to be used in polypropylene.

Pipes, valves and drive

In the context of single-family homes of nominal sizes DN 15 to DN 25 or corrugated stainless steel pipes generally used copper tubes, also can suitable composite pipes are used, which are both thermally stable and chemically resistant. Zinc in the pipe system may be used at any point when a glycol mixture is used. All cables are - although not mentioned - % provided thermal insulation, which is capable of permanently withstanding temperatures of at least 110 ° C - mostly after the Energy Conservation Act only with an almost 100. Outside, come sheet coated mineral wool shells and foamed EPDM in question, to reduce potential damage from UV radiation exposure, the effects of weather and bird repellents. Inside there insulation can not be used in heating technology since the very hot Kollektor-/Solarflüssigkeitstemperaturen would destroy them. There are also special insulation on airgel base ( Spaceloft ), thereby corresponding to 10 mm insulation EPDM insulation with 40 mm.

Volumeters to adjust the amount of liquid, temperature gauge, manometer and a filling and emptying device completes the solar system.

A strainer is not required; is a present, the strainer should only briefly because of the possible formation of an unnecessary drag on the system running - are used - a switchable bypass.

As circulation pumps Heating pumps are mostly used, which are set to protect against the high temperatures in the cold return. As the volume flow of the solar circuit is much smaller than that of a heating circuit, heating pumps are oversized for small solar installations often. Solar pumps are often controlled electronically through the solar control unit, also designed for small volume flows and therefore power consumption. For this use are almost all small heating pumps that do not have their own electronics, but also special pumps with electronics that allow an additional control voltage from the solar electronics PWM control. Thus, defective pump without draining the solar circuit can be replaced, this should be mounted between the two gate valves. A non-return valve in the return pipe prevents the possible gravity circulation, one avoids flow back flow and thus cooling of the memory.

In order to reduce heat losses in the connecting pipes through pipe internal circulation, the pipes should be arranged in the form of a thermosyphon convection - if the memory ports are not already constructed in this form. For drainback systems slightly different guidelines.

Pressure systems

The safety equipment includes pressure systems in the diaphragm expansion vessel ( MAG) and safety valve. The size of MAGs results from the expansion volume of water plus the complete liquid vapor the circuit. The derivation of the SVs is to ensure that hot water spray is not dangerous. A lockable Vents collection section at the highest point system ensures that accumulated air can be vented. This ensures that the heat can be continuously taken up and transported by only the liquid, and the cycle is not interrupted.

Drucklosanlagen

Drucklosanlagen have an open expansion tank without membrane at the highest point of the piping system. There is no pressure relief valve and also the additional vent. Evaporated water this must be refilled, which is usually done automatically. Although the oxygen transfer across the open unpressurized system is low, all parts are made possible from non-corrosive materials in the solar circuit.

Solar controller, solar station

A solar controller consists of various regulating and control circuits. It processes set temperature values , temperature measurements and measured temperature differences. In response to the set and the measured values of the pump and / or valves are switched. The temperatures are measured in simple systems with two sensors ( usually platinum sensor of the type " PT 1000 " = electrical resistance of 1000 ohms at 0 degrees Celsius ) at the collector (flow) and in memory; is the collector temperature is about 3-5 degrees Kelvin above the storage temperature, the pump is switched on when it falls below a threshold, it switches off. At a temperature detection in the return from the heat storage, the heat energy generated can also be detected for monitoring. Another sensor is isolated to determine the maximum store temperature is required. More complex controls can also manage multiple collector arrays with different orientation / exposure and / or more memory. Even an hour meter to profitability calculations is usually integrated. Some controller generate from the measured values trend and plausibility values .

For one- and two-family houses, the minimum equipment in one compact unit is offered, the called according to make solar controller, compact station or pump station. It is slightly larger than a shoe box and surrounded by thermal insulation, in which the four ports (front and return to the collector or memory ), usually two thermometers, pump, pressure gauge, safety valve with blow-off, the connection for the membrane expansion tank and the regulator with its power supply are located. These compact units, usually still with integrated air separator, are space-saving and easy to install.

Commissioning and maintenance

After completion of the plant commissioning, which requires that it be subjected to a leak test and a rinsing process is done. For pressure systems, a pressure test at 1.5 times the maximum operating pressure, which results from the static system height with 0.1 bar per meter and 0.5 bar is derived as the distance to the set pressure of the safety valve. The Flushing the system removes residual dirt and ensures a trouble- free flow. As is rinsed with water, it should be done in certain frost -free period. Jenach plant design could not freeze the remaining water. The filling of the collector system is done - depending on the absorber manufacturers and plant type - with ready-made mixtures or pure water the algae protection can be beigefüft. Mixtures and additives or treated water can be pumped via a charging hose and a filling pump in the system. Thereafter, the operating pressure is to be applied on MAG and adjust the plant flow. Full escape of air is important so that the circulation is maintained and operational noise are avoided. The oxygen contained in the air causes a rapid oxidation of the antifreeze agent. Prolonged emptying of the pump should be avoided and could possibly damage the pump. The maintenance of the pressure is carried out annually and the system pressure is restored. The control of the solar fluid concentration is two years old perform. The measurement is performed with Spindelaräometer and a pH measurement, which must be greater than 7 ( slightly basic ). If the mixture is acidic, the entire solar fluid must be replaced if necessary. The pollution of the collectors cover usually does not play a significant role and at best lead to a performance loss of 2 to 10%. A special purification of the panels is not required.

Building types and plant technology

The building types of solar systems can be classified according to various criteria.

In the field of building technology can be the intended use

Domestic hot water systems and
Systems in support of the space heating

Differ (see also below).

After the collector type used, a distinction is

Systems with flat plate collectors
Systems with vacuum tube collectors
Systems with air-filled collectors

Similarly, a distinction based on the storage technology is possible; Here there are a variety of different developments. These usually focus on the optimization of the temperature stratification in the memory or on the implementation of sampling strategies that avoid disturbing the stratification. Aim at a consistently high temperature in the upper memory area where the heat is removed, and a low in comparison to the collector temperature temperature in the lower memory area where the heat is supplied from the collectors, so that a continuous operation of the plant is possible.

After installation technology as such can be distinguished

Gravity systems ( thermosiphon )
High-flow systems
Low-flow systems

Gravity systems work without pumping station. Your circulation is driven solely by the heating in the collectors: The heated water in the collector is specifically lighter, rises and collects in the typically above the collector attached storage. On cooling it sinks downwards in the memory, and flows through the return pipe back to the collector.

The distinction between " high-flow " and " low flow " refers to the flow quantity in proportion to the collector surface per unit time. High Flow means that about 30 to 50 liters per hour per square meter of collector to be implemented at low flow is 10 to 20 Low can flow so that both a very slow circulation in the solar circuit and the quick turnaround at a very low overall volume in the solar circuit, respectively.

Most currently used smaller plants are high-flow systems using normal heating pumps ( circulators ) can be operated. You are able to dissipate large amounts of heat on low to medium temperature from the collector.

The technological advantage of low-flow systems based on the fact that in them higher temperature differences between collector and storage arise and persist even during operation. Thus, the collector efficiency decreases somewhat, but at the same time they can with less sunlight to produce heat at a higher temperature level and, as at medium irradiation must not be reheated to reach slightly higher levels of coverage throughout the year. Compared to high-flow systems of the same area a cheaper piping, smaller heat exchangers and weaker pumps can be used. Because of these advantages, large-scale systems are typically operated at low flow. Systems with very narrow tube cross sections can only be operated as low-flow systems, since the flow resistance may generate extremely increases. Within the absorber narrow tube cross sections are desired, so that the collector itself has a low heat capacity and heats up quickly.

Matched flow systems where the pump power is controlled in a wide range, are currently the exception. You must be technically equipped as a high-flow system expensive, so its advantage over this is only slight.

Outside Central Europe thermosiphon are often in use and mainly in warmer regions. However, with thermosiphon tube collectors can be operated down to -30 ° C without antifreeze and deliver even at very low temperature conditions in diffuse and indirect Sonnenbestahlung often still warm water. A frost protection must be provided in the first line of the pipe system. Thermosiphon often have an open circuit: the collectors are traversed in the simplest systems directly from the drinking water, which is then drawn off as hot water from the store. The slightly more complex variant used a Drucklosspeicher with integrated tube heat exchanger, can withstand the normal line pressure.

An exception drainback systems that provide a complete emptying of the panels in extreme temperatures or system halt. They can be operated with pure water. They, too, but mostly operated as a closed circuit, which emit the heat via heat exchangers to the hot water

Typical plant sizes

Most currently in use installations are installations for heating of potable water in one - family or two -family house. Goal in the design of the solar system is to achieve in the summer a full cover, so that the normal heating system can remain switched off completely. Due to the strong seasonal differences but would have a system that can meet more than 90 % of the demand in winter, be designed such that in the summer heat incur huge surpluses that could not be used. Since the system shuts down once in the solar storage tank a preset target temperature is reached, such plants would stand still common in summer. But if no more heat is removed, the panels heat so that the liquid contained solar transformed into steam. If, in this situation now in a cooling of the memory by high consumption, this can lead to the paradoxical situation that in the summer must be reheated conventional, because the system can be put into operation after nocturnal cooling of the collectors again.

A typical plant size in Germany and Austria is designed on a four -person household, has a 300 -liter tank and a solar collector area between 4 and 5 m. The next larger size of the plant with a 400 -liter solar tank and a collector 6-8 m² can power up to six people with normal water consumption with an annual coverage of about 70 %.

In the Netherlands, most systems are designed smaller by about a third; there are also systems with 150 - or 200 -liter solar tank to find, but then usually reach only a coverage ratio of less than 60 % on average.

In Austria, there are also systems with larger water reservoirs. In Germany this is rather unusual. The latter is also related that as a memory size of more than 400 liters requires the so-called " Legionella - regulation " of the German Association for Gas and Water special measures for regular sterilization of the drinking water system. Although this directive does not apply to single-family homes, yet you take as a result of health concerns often from the installation of larger storage distance.

Plants, which are expected to make in addition to the domestic hot water ( shower and bath water) and space heating, buffer need at least 700 liters capacity; these are, however, not drinking water, but heating water only circulates in a closed circuit of the heating system. The corresponding collector area can be set 9-12 m². Good performance values reach Combination tank systems with about 1000 liters total buffer capacity (of up to about 200 liters of drinking water in an internal tank) and a collector 12 to 15 m². In addition to a solar fraction of annual water heating needs of approximately 60-70% of such systems can provide up to a quarter of the annual heating energy use in low-energy house.

The differences between the sites (annual radiation), orientation / inclination of the collector (reduces or increases income), hot water demand of the household and heat demand of the building and ultimately the quality of solar systems ( efficiency of the panels, insulation quality of the solar storage tank, intelligence of the solar controller ) however, affect the required size significantly. Oversizing does not bring much more income years. Exceptions are steep and clear skies accurately aligned to South collectors. This can then be more captured on winter sun and summer overheating can be avoided. But summer overheating and the risk of system downtime can be reduced by excess heat by HKP is otherwise consumed. This requires a special regulation that responds to high return temperatures in the solar circuit.

Capacities worldwide and in Europe

The thermal solar energy is the most used in China and Europe. In the year 2007, the worldwide capacity growth at 126 GW, of which 67 % in China and 12 % in Europe. In China, they use the energy usually to produce hot water, in Europe often also for the partial solar space heating. The global installed capacity increased between 2007-2008, 15% (19 GW, 126 GW) to 145 GW. The European capacity increased between 2007-2008, 21% (3.3 GW, 15.7 GW) to 19 GW. The total European capacity increased in the turbulent years 2008-2011 with partly strong growth slumps to 26.3 GW

Since the end of 2011 is the world's largest solar power plant with 36,000 square meters of solar panels in Riyadh. You should provide the imaginary for 26,000 students plus faculty campus of Princess Nora Bint under construction Abdul Rahman University with hot water.

Economy

From the energy consumption of a private household accounts for approximately 61 % of the total heating energy demand (8% domestic hot water, 53 % heating energy demand ), about 31% for motor vehicles and 8% for electricity.

Systems for DHW heating

Today's solar thermal systems are primarily used for domestic water heating, this means they can in 55% to 60 % of the heating for DHW heating cover, which corresponds to about 8% of the total heating energy demand, or about 5 % of the total energy demand. The useful life of such a system is given as 20 to 25 years.

The energy consumption of a model family for DHW heating ( shower and bath water) is located at about 420 liters of heating oil per year ( or 420 cubic meters of natural gas). Of which can save about 55% to 60% of a solar thermal system, which corresponds to an annual saving of about 250 liters of heating oil and fuel oil at a price of 0.9 € / l (as of Aug 2011) in a saving of approximately € 225 per year leads.

Furthermore, a solar system save energy when the hot water is used for washing machine and dishwasher.

The cost of a solar thermal hot water system for a four -person household are dependent on technology and required effort between € 4,800 ( flat panel ) and € 8,800 (vacuum collector ), including transport and installation. If the installation is not carried out by professionals, but by the buyer, are the cost of the plant itself between € 2,880 and € 6,850.

As operating costs arise primarily the cost of electricity for the solar pump and depending on the system installer widely varying maintenance costs. Degradation and eventual disposal costs as a result of modernization of the plant may come in to play. Depending on the object of the solar system can often savings due to elimination of arrangements by the chimney sweep in the summer, extension of service intervals on the boiler due to the short time allotted loads in summer and extension of the boiler and chimney life can be credited.

Systems for heating support ( solar systems with return flow temperature increase )

In spring contact high solar radiation ( mid-April it about as high as the end of August ) and low external temperatures up together. Solar thermal systems are increasingly being used, therefore, the addition of heat engineering support for domestic water heating and space heating water warming in the transitional seasons (spring and autumn). These so-called " combined systems " are much larger and therefore more expensive than equipment for domestic water heating.

The costs and revenues fluctuate here much stronger than with pure drinking water systems, since temperature levels of the heating systems (flow temperature of 35 ° C for underfloor heating, 75 ° C for older systems ), heated area and specific heat demand from 0 to 300 kWh / (a · m ) per may vary according to house. In an old unrenovated a previous thermal insulation, production of the wind leak and any renewal of windows and doors is recommended.

At present, in Europe customary systems that save about 15% to 45% of the annual heating a house. Typical to matching memory sizes are in thermal Heizwasserspeichern about 1000 liters per 100 m² of heated living space.

Promotion

Germany

Since an economy with constant oil and natural gas prices often can not be reached, the BAFA promoted in Germany in principle the construction of solar plants. As part of the budget adoption, the promotion was set by the CDU / CSU / FDP coalition initially. Since July 12, 2010 Solar thermal systems for heating support are subsidized with reduced funding rates. Solar systems for hot water are conveyed only in conjunction with a complete heating system renovation. The promotion of investments in the new building has been completely deleted, as this has been regulated in Germany in the Renewable Energies Heat Act. The current conveyor frame of a solar thermal plant by the BAFA is published bafa.de on the website. Other funding opportunities offered by the states and partly also the cities and municipalities or local power company. The Reconstruction Loan Corporation promotes solar thermal systems with a collector area greater than 40 m² with a loan with a residual debt of 30%. Not all forms of support may be freely combined.

Austria

In Austria, the responsibility for promoting the installation of solar systems for single family houses in the competence of the provinces. This sway the non-repayable funding levels for solar systems for hot water production of 0, - € (Lower Austria ) to 1.700, - € (Upper Austria, Burgenland ), the promotion of auxiliary heating systems from 0, - € (Lower Austria ) until 3325, - € (Vorarlberg). Furthermore, some municipalities encourage the installation of solar systems.

Historical antecedents

The idea of solar radiation to "catch" to use their heat a target species is old. For centuries inventors employed with the capture of solar energy and here in particular with the use of focal glasses.

The Swiss naturalist Horace Bénédict de Saussure built in the 18th century a "simple solar collector ", which consisted of a wooden box with a black bottom and was covered with glass. His solar collector absorbed the sun's heat, and Saussure claimed to reach temperatures of approximately 90 ° C in its box.

1936 magazine reported the week of a developed Oven in California, who worked with bundled through a lens sun rays. The editors gave the solar energy no big chances for the future, but admits that under optimal levels of sunlight " should result in a lens radiation area of one square meter of a power capacity of 1 1/2 hp [ and ] sun machines are more profitable than -fired steam engines ."

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