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02 JANUARY 2016
Solar Thermal Energy Unlimited
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At a time when alternative heating methods are the only way, solar heat can prove to be "Manna from Heaven" for those who want to reduce their costs.
Hopefully, we have reached the first month of autumn and, of course, the idea of implementing alternative heating methods has its place of honor, as the impending rise in the price of heating oil is expected to greatly burden the family budget. In this regard, we have chosen to analyze the issue of solar heating, which is a simple way of heating and providing hot water that does not burden the environment and of course, does not involve any cost of use. So, in the following we analyze everything you need to know about this issue and the benefits it presents, while we have included detailed technical characteristics for the products that you will find in the Greek market (solar heating products for heating and hot water supply - solar water heaters).
What is solar heating?
Solar heating is the method by which solar energy is used to heat a space or to provide us with hot water. Generally in domestic heating applications the means of heat transfer is water, which is heated by burning oil or gas and circulating in radiators or underfloor heating in solar heating systems. The water for heating can be heated by solar energy to a large extent depending on the installation, with the direct result of reducing the consumed conventional fuel. Especially for our country, where sunlight is abundant throughout the year, this application seems like an ideal solution. We also emphasize that similar applications are found in countries in Northern Europe, where the sunshine is not so intense.
The parts of the system
A solar heating system consists of the following parts:
Solar panels
There are several types of solar panels. Depending on the intended use, we can choose flat-surface solar panels or vacuum collectors. In residential or commercial building applications where temperatures below 93 ° C are required, flat solar panels are commonly used, while in applications requiring temperatures higher than 93 ° C, solar panels with vacuum tubes are also used.
Thermal containers - Water tanks
The containers store hot water, the temperature of which can be used when we do not have sunshine.
Depending on the use we want, we place the corresponding reservoir, either for hot water or for heating support, or for a combination of both. In practice, these are storage water heaters for use and heating water that have a capacity that depends on the collector surface it has in the system and of course on the requirements of each owner. Most of the time they are made of steel and have a special inner coating that protects them from corrosion. In some cases, the heat sinks may be made of copper or may be stainless steel. They also have insulation on the outside to reduce heat loss.
Thermal containers - Water tanks
The containers store hot water, the temperature of which can be used when we do not have sunshine.
Depending on the use we want, we place the corresponding reservoir, either for hot water or for heating support, or for a combination of both. In practice, these are storage water heaters for use and heating water that have a capacity that depends on the collector surface it has in the system and of course on the requirements of each owner. Most of the time they are made of steel and have a special inner coating that protects them from corrosion. In some cases, the heat sinks may be made of copper or may be stainless steel. They also have insulation on the outside to reduce heat loss.
Solar controllers
Each solar heater has an electronic processor that periodically checks the temperature in the heating tank and, depending on the prevailing conditions, chooses whether the solar circulator or the auxiliary heating will work. The same accessory ensures that the temperature of the water used is maintained at the desired level.
How a solar heating system works
A solar heating system that we may install in our home takes advantage of the thermal energy produced by solar panels. In this way the heating water and the water circulating in the heating system are heated. It consists of three main parts: the solar panels and two hot water storage tanks, one of the use water and one of the space heating water and the solar one. Solar collectors absorb diffused sunlight, collecting solar energy even on cloudy days and converting 2/3 of solar radiation into beneficial energy. The hot water collected is transferred to the heat sinks to be kept at a constant temperature. The system takes care of the complete coverage of the needs in hot water and then, if there is too much energy, it heats the space heating water. In case the hot water is not enough to heat the space, then the conventional heating system is put into operation. Also during the summer months the hot water produced is used only for use. Most manufacturers have collectors with high absorbency glass that do not reflect radiation to ensure maximum heat transfer. The peculiarity of solar thermal systems lies in the fact that they operate by contributing to the heating produced by the use of other fuels and not by abolishing it. They can be combined with any conventional power source (oil or gas burners) or renewable energy source (biomass burners), and are integrated into an existing system, as long as there is space available for the installation of collectors and storage tanks. They can also be combined with any heating medium.
What the operation of the system depends on
The degree of contribution of solar heaters and consequently reduction of fuel use depends on climatic conditions, altitude, geographical location, installation size, building losses and other factors. Depending on the local climate and location of the building, the solar panel may capture more or less energy. Depending on the size of the facility, solar heaters cover from a very small to up to 80% of the annual heating needs. Of course, very high coverage is not yet a viable solution.
How large should the system be?
The ideal cost-performance ratio is to achieve a coverage of 40-60% of the total thermal load (space heating and hot water supply). In practice and based on the average sunshine in Greece and the average required heating energy of buildings, the area of solar energy collectors should correspond to 20% of the surface of the heated space, while the required storage volume is approximately tenfold, calculated in liters . In general, for a house of 100 sq.m., 20 sq.m. flat collectors and 1000 liters of hot water storage containers (approximately 200 l. for hot water and 800 l. for heating water). In the case of a roof, the required available area should be about 1.5 times larger than the surface of the collectors, ie about 30 sq.m., while for the installation of storage tanks about 3-4 sq.m. are required.
What are the benefits for the consumer
The cost of installing a solar heating system varies depending on the size of the installation and the rate at which one wants to reduce fuel consumption. The great advantage of such a system is that its size (and therefore its cost) can be tailored to the user's requirements and easily changed. For example, a system can be installed that takes up 30% of the heating load, and after a year can be expanded by installing additional solar panels to cover 60% of the heating. Especially in the case of installing solar panels in a newly constructed building, the money savings are higher, because a percentage of the thermal power needed is taken over by the solar system and the size of the conventional equipment (boiler and burner) required to be installed is smaller. That is, a portion of the money invested in solar heating is saved from day one when purchasing basic equipment. For example, it may be preferable to purchase a 20 kW boiler instead of 50 kW if a solar heating system with a 60% share is installed during the initial installation (newly constructed building).
Solar vacuum tube collectors
These products are used to reduce the heat loss found in flat collectors at high temperatures as well as for other uses of thermal systems, as their performance is much higher than other types of collectors. Each vacuum tube consists of two glass tubes made of transparent high-strength north-facing glass, so that it can withstand difficult weather conditions, such as hail.
Between the glass tubes there is a gap to enhance the thermal insulation of the collector and special heat-absorbing material for better performance. Also included is a copper heating pipe inside the pipe to transfer water to the system. The positives of this product category include, among other things, that they can absorb energy during cloudy days, through the infrared rays of the sun.
According to experts, when solar panels are placed in the North-South orientation, the pipes can perform all year round, while when they are in the East-West orientation, they can detect the sun all day long. Finally, we mention that the shape and in general the nature of their construction allows the sun's rays to fall vertically on them throughout the day.
Hot use
The well-known application of solar thermal systems is none other than the common solar water heaters that most of us have in our home. In these cases, the water is heated by the solar panels and then used by each consumer. The difference in density between hot and cold water does not require a circulator (as the water is transferred automatically), which is why in solar water heaters the storage tank is at a higher point than the collectors.
The overall performance of the solar water heater depends on the ambient temperature, the cloud cover and the efficiency of the thermal insulation of the system. An important factor for the good performance of the system is the absorption of solar panels in solar radiation and in general, the materials that offer the best performance-price ratio are the glass to the collectors and the surface made of aluminum or copper colored black.
What types of products are there?
As for the solar water heaters, we distinguish two types depending on the circulating circuit of the heated medium:
Open circuit: Direct heating of the used water (the heated medium is the water itself that we will use). Products in this category are simpler to manufacture and cheaper, but have some problems with low temperatures (we can't add antifreeze to them as the heating medium is the water itself).
Closed circuit: Indirect heating of the used water (the heated medium circulates in a separate circuit which heats the water that we will use without mixing them, through a heat exchanger). In closed circuit solar water heaters, the heated medium may be another liquid (eg oil). If it is water, it has antifreeze and anti-corrosion additives to protect the device.
Further categorization
In addition to what we mentioned, we can categorize solar water heaters and depending on the number of energy sources that can be exploited:
Double energy:
The water heater operates using either solar or electricity (eg during cloudy skies so the solar energy is not enough to heat the water). For this purpose, there is an electrical resistor mounted inside the storage compartment.
Triple energy:
It works like a dual-energy solar water heater but also has an inlet to use the hot water of the radiator produced by the central heating boiler as a heating medium. A prerequisite for the installation of triple energy solar water heaters is to have the appropriate infrastructure in the building in the form of separate pipes (per apartment if it is an apartment building) that connect the boiler room to the installation area of the solar water heater (roof or roof).
What does a solar water heater consist of?
Regardless of the type of product, each solar water heater consists of two main parts, the collectors and the boiler water storage tank.
These two parts are assembled together and connected by piping, but in larger systems they can also be separate and use pumps to circulate the heated medium, especially when the storage compartment is not in the same space as the collection compartment. The more expensive solar water heaters also have some control components, such as a pressure valve or automatic ventilation (to relieve the pressure on hot days).
Solar panels
The main part of a solar water heater is solar panels (or mirrors), ie the collection surface of solar radiation. It consists of four parts:
• The radiation collection plate
• Water flow pipes (serpentine)
• The cover (crystal) of the absorption plate
• The thermally insulated frame on which the other components are attached.
Boiler tank
The water storage tank has a capacity ranging from 100 to 200 liters for ordinary home applications. Its capacity is a function of the collector surface it has (in general, for a 4-member family, a 200 liter tank is required, ie 50 liters for each person). It is usually steel, with an inner coating to protect against corrosion. This coating is usually made of special plastic or epoxy paints or enamels. Alternatively, for more expensive systems, the storage tank can be copper or stainless steel. Externally, it has very good insulation usually made of polyurethane or fiberglass and usually has some electrical resistance built-in. In closed circuit systems, it also has a built-in alternator for circulating the heated medium or in more expensive systems it is double-walled (the heated medium circulates between the two walls).
Hopefully, we have reached the first month of autumn and, of course, the idea of implementing alternative heating methods has its place of honor, as the impending rise in the price of heating oil is expected to greatly burden the family budget. In this regard, we have chosen to analyze the issue of solar heating, which is a simple way of heating and providing hot water that does not burden the environment and of course, does not involve any cost of use. So, in the following we analyze everything you need to know about this issue and the benefits it presents, while we have included detailed technical characteristics for the products that you will find in the Greek market (solar heating products for heating and hot water supply - solar water heaters).
What is solar heating?
Solar heating is the method by which solar energy is used to heat a space or to provide us with hot water. Generally in domestic heating applications the means of heat transfer is water, which is heated by burning oil or gas and circulating in radiators or underfloor heating in solar heating systems. The water for heating can be heated by solar energy to a large extent depending on the installation, with the direct result of reducing the consumed conventional fuel. Especially for our country, where sunlight is abundant throughout the year, this application seems like an ideal solution. We also emphasize that similar applications are found in countries in Northern Europe, where the sunshine is not so intense.
The parts of the system
A solar heating system consists of the following parts:
Solar panels
There are several types of solar panels. Depending on the intended use, we can choose flat-surface solar panels or vacuum collectors. In residential or commercial building applications where temperatures below 93 ° C are required, flat solar panels are commonly used, while in applications requiring temperatures higher than 93 ° C, solar panels with vacuum tubes are also used.
Thermal containers - Water tanks
The containers store hot water, the temperature of which can be used when we do not have sunshine.
Depending on the use we want, we place the corresponding reservoir, either for hot water or for heating support, or for a combination of both. In practice, these are storage water heaters for use and heating water that have a capacity that depends on the collector surface it has in the system and of course on the requirements of each owner. Most of the time they are made of steel and have a special inner coating that protects them from corrosion. In some cases, the heat sinks may be made of copper or may be stainless steel. They also have insulation on the outside to reduce heat loss.
Thermal containers - Water tanks
The containers store hot water, the temperature of which can be used when we do not have sunshine.
Depending on the use we want, we place the corresponding reservoir, either for hot water or for heating support, or for a combination of both. In practice, these are storage water heaters for use and heating water that have a capacity that depends on the collector surface it has in the system and of course on the requirements of each owner. Most of the time they are made of steel and have a special inner coating that protects them from corrosion. In some cases, the heat sinks may be made of copper or may be stainless steel. They also have insulation on the outside to reduce heat loss.
Solar controllers
Each solar heater has an electronic processor that periodically checks the temperature in the heating tank and, depending on the prevailing conditions, chooses whether the solar circulator or the auxiliary heating will work. The same accessory ensures that the temperature of the water used is maintained at the desired level.
How a solar heating system works
A solar heating system that we may install in our home takes advantage of the thermal energy produced by solar panels. In this way the heating water and the water circulating in the heating system are heated. It consists of three main parts: the solar panels and two hot water storage tanks, one of the use water and one of the space heating water and the solar one. Solar collectors absorb diffused sunlight, collecting solar energy even on cloudy days and converting 2/3 of solar radiation into beneficial energy. The hot water collected is transferred to the heat sinks to be kept at a constant temperature. The system takes care of the complete coverage of the needs in hot water and then, if there is too much energy, it heats the space heating water. In case the hot water is not enough to heat the space, then the conventional heating system is put into operation. Also during the summer months the hot water produced is used only for use. Most manufacturers have collectors with high absorbency glass that do not reflect radiation to ensure maximum heat transfer. The peculiarity of solar thermal systems lies in the fact that they operate by contributing to the heating produced by the use of other fuels and not by abolishing it. They can be combined with any conventional power source (oil or gas burners) or renewable energy source (biomass burners), and are integrated into an existing system, as long as there is space available for the installation of collectors and storage tanks. They can also be combined with any heating medium.
What the operation of the system depends on
The degree of contribution of solar heaters and consequently reduction of fuel use depends on climatic conditions, altitude, geographical location, installation size, building losses and other factors. Depending on the local climate and location of the building, the solar panel may capture more or less energy. Depending on the size of the facility, solar heaters cover from a very small to up to 80% of the annual heating needs. Of course, very high coverage is not yet a viable solution.
How large should the system be?
The ideal cost-performance ratio is to achieve a coverage of 40-60% of the total thermal load (space heating and hot water supply). In practice and based on the average sunshine in Greece and the average required heating energy of buildings, the area of solar energy collectors should correspond to 20% of the surface of the heated space, while the required storage volume is approximately tenfold, calculated in liters . In general, for a house of 100 sq.m., 20 sq.m. flat collectors and 1000 liters of hot water storage containers (approximately 200 l. for hot water and 800 l. for heating water). In the case of a roof, the required available area should be about 1.5 times larger than the surface of the collectors, ie about 30 sq.m., while for the installation of storage tanks about 3-4 sq.m. are required.
What are the benefits for the consumer
The cost of installing a solar heating system varies depending on the size of the installation and the rate at which one wants to reduce fuel consumption. The great advantage of such a system is that its size (and therefore its cost) can be tailored to the user's requirements and easily changed. For example, a system can be installed that takes up 30% of the heating load, and after a year can be expanded by installing additional solar panels to cover 60% of the heating. Especially in the case of installing solar panels in a newly constructed building, the money savings are higher, because a percentage of the thermal power needed is taken over by the solar system and the size of the conventional equipment (boiler and burner) required to be installed is smaller. That is, a portion of the money invested in solar heating is saved from day one when purchasing basic equipment. For example, it may be preferable to purchase a 20 kW boiler instead of 50 kW if a solar heating system with a 60% share is installed during the initial installation (newly constructed building).
Solar vacuum tube collectors
These products are used to reduce the heat loss found in flat collectors at high temperatures as well as for other uses of thermal systems, as their performance is much higher than other types of collectors. Each vacuum tube consists of two glass tubes made of transparent high-strength north-facing glass, so that it can withstand difficult weather conditions, such as hail.
Between the glass tubes there is a gap to enhance the thermal insulation of the collector and special heat-absorbing material for better performance. Also included is a copper heating pipe inside the pipe to transfer water to the system. The positives of this product category include, among other things, that they can absorb energy during cloudy days, through the infrared rays of the sun.
According to experts, when solar panels are placed in the North-South orientation, the pipes can perform all year round, while when they are in the East-West orientation, they can detect the sun all day long. Finally, we mention that the shape and in general the nature of their construction allows the sun's rays to fall vertically on them throughout the day.
Hot use
The well-known application of solar thermal systems is none other than the common solar water heaters that most of us have in our home. In these cases, the water is heated by the solar panels and then used by each consumer. The difference in density between hot and cold water does not require a circulator (as the water is transferred automatically), which is why in solar water heaters the storage tank is at a higher point than the collectors.
The overall performance of the solar water heater depends on the ambient temperature, the cloud cover and the efficiency of the thermal insulation of the system. An important factor for the good performance of the system is the absorption of solar panels in solar radiation and in general, the materials that offer the best performance-price ratio are the glass to the collectors and the surface made of aluminum or copper colored black.
What types of products are there?
As for the solar water heaters, we distinguish two types depending on the circulating circuit of the heated medium:
Open circuit: Direct heating of the used water (the heated medium is the water itself that we will use). Products in this category are simpler to manufacture and cheaper, but have some problems with low temperatures (we can't add antifreeze to them as the heating medium is the water itself).
Closed circuit: Indirect heating of the used water (the heated medium circulates in a separate circuit which heats the water that we will use without mixing them, through a heat exchanger). In closed circuit solar water heaters, the heated medium may be another liquid (eg oil). If it is water, it has antifreeze and anti-corrosion additives to protect the device.
Further categorization
In addition to what we mentioned, we can categorize solar water heaters and depending on the number of energy sources that can be exploited:
Double energy:
The water heater operates using either solar or electricity (eg during cloudy skies so the solar energy is not enough to heat the water). For this purpose, there is an electrical resistor mounted inside the storage compartment.
Triple energy:
It works like a dual-energy solar water heater but also has an inlet to use the hot water of the radiator produced by the central heating boiler as a heating medium. A prerequisite for the installation of triple energy solar water heaters is to have the appropriate infrastructure in the building in the form of separate pipes (per apartment if it is an apartment building) that connect the boiler room to the installation area of the solar water heater (roof or roof).
What does a solar water heater consist of?
Regardless of the type of product, each solar water heater consists of two main parts, the collectors and the boiler water storage tank.
These two parts are assembled together and connected by piping, but in larger systems they can also be separate and use pumps to circulate the heated medium, especially when the storage compartment is not in the same space as the collection compartment. The more expensive solar water heaters also have some control components, such as a pressure valve or automatic ventilation (to relieve the pressure on hot days).
Solar panels
The main part of a solar water heater is solar panels (or mirrors), ie the collection surface of solar radiation. It consists of four parts:
• The radiation collection plate
• Water flow pipes (serpentine)
• The cover (crystal) of the absorption plate
• The thermally insulated frame on which the other components are attached.
Boiler tank
The water storage tank has a capacity ranging from 100 to 200 liters for ordinary home applications. Its capacity is a function of the collector surface it has (in general, for a 4-member family, a 200 liter tank is required, ie 50 liters for each person). It is usually steel, with an inner coating to protect against corrosion. This coating is usually made of special plastic or epoxy paints or enamels. Alternatively, for more expensive systems, the storage tank can be copper or stainless steel. Externally, it has very good insulation usually made of polyurethane or fiberglass and usually has some electrical resistance built-in. In closed circuit systems, it also has a built-in alternator for circulating the heated medium or in more expensive systems it is double-walled (the heated medium circulates between the two walls).
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