For a very long time, men have been using solar energy to heat water. The thermonuclear reaction on the Sun is the source of solar radiation. Solar energy is released by way of electromagnetic rays.
To make use of this energy, one must decide how to catch its largest flow, store and transfer heat to a consumer without losses.
Solar energy is inexhaustible. According to the available data, the amount of solar energy reaching the Earth`s surface within a minute is greater than the world`s total energy produced by other energy sources over a year. Solar panels are the basis of many solar energy systems. A panel absorbs solar sunlight and converts it into thermal energy, that is transferred to a refrigerant (liquid or air) and further is used for heating and hot water supply. Solar panels can be used virtually in every process that requires heat energy. Solar panels can entirely cover hot water demand in summer. In autumn and spring, up to 40% of the required energy for heating and up to 60% for the hot water supply could be received from the sun.
For the time-being, there are two types of solar panels: flat plate solar panels, which are simpler and cheaper, and vacuum-tubular solar panels, which are more complex and expensive. On sunny days, there is virtually no difference in operation of these two types of solar panels. However, the advantages of vacuum solar panels become evident on cold, cloudy days. There is a difference between maximum temperature of water in these types of solar panels even in summer. Whereas, a flat plate solar panel`s maximum temperature can`t exceed 80-90°C, in vacuum solar panels refrigerant`s temperature may exceed 100 ° C. This requires constant heat removal from a vacuum solar panel, to avoid boiling. As a rule, systems with flat plate solar panels are used seasonally (spring through autumn). In winter, the flat plate solar panels system efficiency drops due to heat losses. Vacuum solar panels are usually used in the year-round solar water heating systems, although, it is also possible to use flat plate solar panels with thorough heat insulation. The main advantage of a flat plate solar panel over a vacuum one is a lower price and its service life of about 50 years comparing to 20-30 years of a vacuum solar panel.
Review of vacuum solar panels and flat plate solar panels
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A flat plate solar panel is to be placed into a casing with a protective glass to reduce heat losses. Air-filled space between glass and the absorbing panel of a flat plate solar heat generator causes significant heat losses, especially on cold days (up to 80% of the total heat flux).
A flat plate solar panel has high hydraulic resistance, for a refrigerant circulates through a long, ramified system of pipelines with small diameter. Thus, an increased energy consumption is required to drive a circulating pump of a flat plate solar panel.
A flat solar water heating panel without a controller, can recover the accumulated heat (i.e. self-discharge), once its temperature becomes lower than the temperature of water in the accumulation tank.
A flat plate solar panel is to be mounted with its face tilted directly towards the South at a specific angle to the surface (e.g. a rooftop)
A flat plate solar heating device efficiency drops substantially if the glass is damaged. In such a case, it shall be demounted right away and its glass replaced.
A flat plate solar panel is difficult to transport and to mount, as it must be lifted and installed in block.
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Each heat–transfer tube of a vacuum solar collector is placed inside a glass vacuum flask to minimize heat losses (thermos principle). Due to this fact, a vacuum solar heat generator efficiency increases substantially compared to a flat one, especially in winter.
Superconductive heat-transfer tubes, which effectively remove heat from an absorbing surface, are used in a vacuum solar panel. Usage of these tubes enables to lower hydraulic resistance of a vacuum solar system by 10 times and consequently to decrease power consumption of a circulating pump.
A heat-transfer tube of a vacuum solar heating device operates under the principle of a thermal diode. Even without a controller of a solar system, heat flows exclusively in one direction: from a vacuum solar panel to a refrigerant, and never in the reverse direction.
A vacuum tubular solar panel does not have to be placed at a strict angle or direction and allows for a certain architectural and aesthetic freedom while mounting a solar system.
A vacuum solar heater efficiency does not drop substantially, when several glass tubes are damaged. A solar panel need not be disassembled, since the replacement of the tubes can be done on-site.
A vacuum solar panel is easy to transport and install, as its disassembled units can be hauled separately, ensuring that a panel would stay undamaged. Lightweight detachable tubes can be assembled directly on-site. |
Solar heating systems are believed to be among the most reliable and durable systems, given that they are correctly selected and installed using efficient and qualitative equipment. A slightest mistake can quickly lower the amount of power being generated and damage a system.
Houses powered by the alternative energy are starting to emerge worldwide and they are referred to as passive (net zero-energy) buildings. Over a year, a zero energy building consumes no power and, moreover, generates the spare power which can be supplied to the external network. In Europe, a program under which majority of houses are to use alternative energy, thus becoming ultra-low energy buildings by 2030 was developed.
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