May 21, 2019


The installation of a solar appliance, covers almost all the needs of a home for hot water, but also a large part for its heating.

Proper exploitation of the sun can lead to an alternative way of heating, with significant economic benefits for every home.

With the sun now permanently occupying its place in the Greek sky, the issue of its use for our benefit is again set on the “table” of current events. In a country where sunshine lasts most of the time, its non-exploitation is a serious mistake, which even tends to turn into a “crime” at this time, with the economic crisis affecting almost all citizens and the price of oil “shouting” for turning to alternative forms of energy. This category also includes solar heating, with the relevant technologies being developed to such an extent that they guarantee the discharge of a large part of the heating and hot water costs, while the investment is depreciated in only a few years. But let’s take a closer look at what sunlight means and how to exploit it in its own interest.

The method of solar heating

The use of solar energy to heat a room or to convert hot water to hot is the method we call solar thermal. Generally, in domestic heating applications the heat transfer medium is water, which is heated by combustion of oil or natural gas and circulates in radiators or floor heating in solar heating systems. Water for heating can be heavily heated by solar energy depending on the installation, with the direct effect of reducing the conventional fuel consumed. Especially for our country, where sunlight is abundant throughout the year, this application seems to be an ideal solution. We also point out that similar applications are also found in northern European countries where sunshine is not so intense.

The solar thermal system

A solar thermal system consists of three parts, the solar energy collector, the reservoir storing the water we want to heat (either use or heating) and the processor that controls the temperature. More specifically, there are the following parts:

  • Solar collectors

Depending on the intended use, we can select flat panel solar panels or vacuum collectors. In residential or commercial applications where temperatures below 93 ° C are required, flat solar collectors are commonly used, and in applications requiring temperatures greater than 93 ° C, solar panels with vacuum tubes are also used.

  • Water Heaters-Water Tanks

They are the containers in which hot water is stored, with its temperature being utilized when there is no 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 water storage heaters that have a capacity that depends on the collector surface they have in the system and of course the requirements of each owner. Most of the time they are made of steel and have a special internal coating that protects them from corrosion. In some cases, the pots can be made of copper or stainless. They also have insulation on the outside to reduce thermal losses.

  • Solar controllers

Each solar heater has an electronic processor that regularly checks the temperature in the heating tank and, depending on the prevailing conditions, selects whether the solar pump or auxiliary heating will work. The same fitting ensures that the water temperature is maintained at the desired level.

The operation of a system

A solar heating system that may be installed in our home exploits the thermal energy produced by the solar panels. In this way, the water and the water circulating in the heating system are heated. 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 pots in order to keep it at a constant temperature. The system takes priority of full coverage of hot water needs and then, if there is excess energy, the space heating water heats up. If the hot water is not enough to heat the space, then the conventional heating system is switched on. Also during the summer months, the hot water produced is used only for use. Most manufacturers have collectors with high absorbency glass that does not reflect radiation to ensure maximum heat transfer. The peculiarity of solar thermal systems is that they function by contributing to the heat produced by using other fuels rather than by removing it. They can be combined with any conventional source of energy (oil or gas burners) or a renewable energy source (biomass burners), and are integrated into an existing system as long as there is space available for the installation of the collectors and hot water storage tanks. They can also be combined with any heating medium.

The performance of the system

The degree of contribution of solar thermal and, by extension, reduction in fuel use depends on climatic conditions, altitude, geographic location, plant size, building losses and other factors. Depending on the local climate and location of the building, the solar collector can capture more or less energy. Depending on the size of the installation, solar heating covers up to 80% of the annual heating needs. Of course, very high coverage is not yet economically viable solutions.

 The extent of a system

The ideal cost-effectiveness ratio is to achieve a coverage of 40-60% of the total heat load (space heating and hot water supply). In practice and based on the average sunshine in Greece and the average required heating energy of the buildings, the surface of the solar energy collectors should correspond to 20% of the surface of the heated space, while the required storage volume is approximately 10 times, calculated in liters . In general, for a 100m2 house, 20m2 is required. flat collectors and 1000 liters of hot water storage tanks (about 200 liters for hot water and 800 liters for heating water). In the case of a roof, the required available surface should be approximately 1.5 times the collector surface, that is, about 30 square meters, while about 3 to 4 square meters are required to install the storage containers.

The benefits of solar heating

The cost of installing a solar thermal system varies depending on the size of the installation and the percentage you want 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 can be easily changed. For example, a system can be installed to take up the heating load by 30%, and after one year to expand by installing additional solar panels so as to cover 60% of the heating. In a typical residential building of 180 square meters with a system consisting of solar panels of a total area of ​​12.55 square meters on the roof of the house, a boiler for the heating of a capacity of 800 liters and a storage tank for hot water with a capacity of 250 liters , the amounts are as follows:

With an annual oil consumption of 3,000 liters and with a price of 1,4 Euro / liter, annual heating costs are 3,000 x 1,4 = 4,200 Euros plus 250 Euros per year for hot water from an electric water heater. That is, we need 4,450 euros. With the installation of the solar thermal system, these amounts are reduced to 3,000 x 1,4 x 0,75 = 3,150 euros for heating plus 0 euros for hot water production. So we have an annual savings of 1,300 euros. The total cost of supplying and installing the system (solar collectors, mixed tank, collector mountings, other parts, installation and adjustment works) amounts to approximately EUR 7,500. The extinguishing of the solar thermal system is estimated at 6 years, but this time is calculated at an oil price of 1.4 euro / liter, a price that, if climbed, will make the depreciation time even smaller.

Vacuum tubing solar panels

These products are used to limit the heat losses detected in flat collectors at high temperatures as well as for other uses of thermal systems, since their performance is much higher than the other collector types. Each vacuum tube consists of two glass tubes made of transparent borosilicate glass of high strength, so it can withstand difficult weather conditions, such as hail. Between the glass tubes there is a vacuum to enhance the collector thermal insulation and a special heat-absorbing material for better performance. Also, a copper heater tube is included in the tube to transfer water to the system. The positive features of this product category include, among other things, that they can also absorb energy during cloudy days through infrared sun rays.

As experts say, when vacuum tube solar panels are positioned in the North-South orientation, the tubes can perform all the time, while when they are in the East-West orientation, they can detect the sun all day. Finally, it is worth mentioning that the shape and generally the nature of their construction allows the sun’s rays to penetrate vertically over them throughout the day.

Solar Water Heaters

The well-known application of solar thermal systems is none other than the common solar heaters that most of us have in our home. In these cases, the water is heated by the solar panels and then used by the individual consumer. The difference in hot and cold water density does not require a circulator (as water is automatically transported), therefore the storage tank is at a higher point than the collectors in the solar water heaters.

The overall efficiency 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 in the collectors and the surface, made of aluminum or copper, colored black.

Solar water heaters can be divided into two types depending on the circulating circuit of the heated medium:

  • Open circuit. Direct heating of water for use (the heated medium is the same water that we will use). Products belonging to this category are simpler to manufacture and cheaper at cost but have some problems in low temperatures (we can not add antifreeze mixes as the heated medium is the water itself).
  • Closed circuit. Indirect water heating (the heated medium circulates in a separate circuit that heats the water to be used without mixing through a heat exchanger). In closed circuit solar water heaters, the heated medium may be another fluid (e.g., oil). If it is water, it has antifreeze and anti-corrosion additives to protect the device.

Solar water heaters can be further categorized and depending on the number of energy sources they can exploit, as follows:

  • Dual energy. The water heater works by taking advantage of either solar power or electricity (eg during cloudy weather, so the solar energy is not enough to heat the water). For this purpose, there is an electrical resistance located inside the storage section.
  • Triple energy. It works like a dual-energy solar water heater, but it also has an inlet to use as the heating medium the hot water of the radiator produced by the central heating boiler. A condition for installing a three-energy solar water heater is to have the appropriate infrastructure in the building in the form of separate pipelines (per apartment if it is a block of flats) connecting the boiler room to the solar heater (roof or roof).

Parts of the solar water heater

Irrespective of the type of product, each solar water heater consists of two main parts, the collectors and the water storage tank (boiler).

These two parts are assembled together and connected by piping, but larger systems may also be separate and pumps used to circulate the heated medium, especially when the storage part is not in the same space as the collection section. Most expensive solar water heaters also feature control components, such as overpressure valve or automatic vents (to relieve pressure on hot days).

“Renewable energy source with … Greek identity”

On the occasion of the tribute to Solar Thermia, the new president of the Association of Solar Energy Industries, Panagis Konstantinidis, gives his own views on this alternative form of energy.

“The energy model on which the modern development of human activity is based has reached its limits. The unreasonable use of fossil fuels has multiple unpleasant consequences. Economic dependence of the state on oil exporters, aggravation of climate change and economic bleeding of low and middle income due to constantly rising prices.

Solar thermal energy is the cleanest and most efficient form of renewable energy. The rate at which we can take advantage of solar thermal energy is over 80%. This, coupled with the significant advancement of Greek industry in this sector, which has led to very competitive prices for its products, makes the use of solar thermal energy as the most economical and advantageous. It is a fact that the purchase of a certified solar water heater, with an average life span of 15 years, is extinguished in just 3-4 years.

However, solar thermal applications are not limited to hot water. Our total energy requirements for low- and medium-temperature thermal energy can be covered by the sun in 50%. One of the most common applications is to assist in space heating. Solar thermal collectors can work perfectly in conjunction with an oil or gas burner or pellet, as well as a heat pump, geothermal systems, etc. The economy ensured in such an application is remarkable. It can surpass 30%! There are many other cases where the use of solar thermal energy is required by economic terms. Commercial applications, mainly hotels and hospitals, and industrial applications (where thermal energy is needed) are the ones with the most growth, given their backwardness in previous years.

Solar thermal energy, as the most economical among all renewable energy sources and with a wide range of applications, is leading the country’s effort for sustainable development and is based on our own human and material resources. ”

Heating and cooling of areas with solar energy

Thermal solar systems can, in addition to hot water, ensure:

  • space heating, as the radiator
  • cooling areas, replacing air conditioners

In heating systems, oil and gas are basically saved, while electricity is cooled. However, as both oil and gas costs rose in 2012 and are expected to rise even further in the coming winter due to the equalization of heating and traffic oil prices, many consumers heat their homes by using local of air conditioners that spend electricity. Therefore, a significant proportion of the total energy consumed for heating and cooling is made up of electricity. The heating and cooling of areas with solar energy has an increased initial installation cost. This cost is depreciated by saving the energy that is achieved. The cost of a 20 m² home heating system is about 8,000-10,000 euros. The savings it can make is about 1.3 tonnes of oil or 1.340 euros per year. With current oil prices, the depreciation time of the system is about 8 years. Corresponding to solar cooling, depending on the size of the system, there are also amortization times of 15 years.