Introduction

Solar collector is a device for receiving heat of the sun and transfer it through the solar system to the tray with the water utility.  Heat from the infrared radiation field is taken up by the absorber surface and then transferred to the heating medium flowing through the collector head.  Heated in this way factor is transported in a closed system using solar pumps to pressure accumulation tank.  Here, the surface of a spiral coil of the tank, heat is the water and brought to the current needs of the household.  Working principle of solar vacuum tubes is to stop the energy captured in a trap, which is a vacuum.  Collectors of this operating principle makes a very low rate of heat loss makes that they are effective for 365 days a year.  The geographical Polish from November to the end of February are very difficult working conditions and the collectors are doing much better in them was the era of vacuum tube solar collectors.

The first generation of solar collectors, flat plate solar collector operates on the principle of the coil, in which the liquid heating element covered with a copper plate, which in turn is covered with a layer of absorbing solar radiation, all covered with solar glass shielding device.  The energy yield from solar collectors flat fully dependent on external temperature, practically, this means that in periods when the low temperature outside and the sun shines all the intense heat that is absorbed is given to the environment before it is forwarded to the installation.  Flat plate collectors can successfully work efficiently throughout the year in countries with high sunlight where the temperature differences between seasons are very small, precisely in these areas their use is justified.  Flat plate collectors are still in their application in our country mainly because of the price, and their evolutionary successors are vacuum tube solar collectors.

The collector with direct flow vacuum in which the heating agent is transported directly into all vacuum tube.  Working as a factor in a flat manifold is directly heated in a copper tube, with the difference that, thanks to vacuum all the heat losses are eliminated.  Such a solution allows for higher temperature factor, and hence higher energy yields.  This technology has its drawbacks, however, a large quantity of heating medium and very high temperatures reached by the collector at a time when there is no way to receive heat (eg: travel holiday) cause the possibility of overheating the system, it is veiled in the drain of inaction.  More working for the heating medium increases the time needed to start the collector, in case of accident or of the installation of the vacuum tube is necessary to empty the entire solar system with liquid.  The disadvantage of this type of collector is the potential for sediment that lowers the efficiency of the device.

Heat pipe collectors where the heating element does not flow directly through the collector and the receiving heat only in the head unit.  This type of collector consists of a few to several dozen glass tubes with high vacuum inside.  In each vacuum tube is built with fixed absorber tube, the substance contained in it already at 30 ° C is brought to a boil, bubbled in on the end of the condenser, evaporator, heats it and through the anchoring of the bus provide the bulk of its heat pusses  the working factor.  The vacuum ensures minimal loss of heat to the environment, which enables the collector work throughout the year, even during the frost in winter.  Technology and materials used in modern collectors "heat pipe" allow for a rapid start-up and allow for high values of power devices.  The energy yield from a single square meter of collector can be up to three times greater than the yield from the same surface in a flat manifold.  Ultimately, this means that the heat the same amount of water we need much smaller numbers of collectors.  Another advantage of such devices is the possibility of energy dissipated by the collector which fulfills its function even during cloudy days, when outdoor temperatures prevailing positive.  In the case of this technology has reduced the problem of overheating in the installation.  Heating agent flows only in the head collector, this means exposure of a small number of very high temperature.  In this system there is no need for covering the surface of the collector in the absence and the absence of consumption.  Solutions used in the collectors 'heat pipe' guarantee high operational reliability even over long periods of stagnation during the installation and the high sun, which translates directly into high security in the whole system work.  These collectors use the latest solar technology solutions, characterized by the highest optical efficiency and the highest annual energy yeld.

---

---

Factors describing the flat plate collectors

Optical collector efficiency factor

Optical efficiency of solar collectors is determined by the absence of temperature difference between absorber and the surroundings. The higher the optical efficiency of the better utilization of solar radiation reaching the device. Describes the optical efficiency of the penetration of solar radiation by covering the collector (eg glass collector) and the degree of efficiency of the absorber surface (shell absorption capacity). The actual efficiency of the solar collector depends on the efficiency of optical minus the heat loss.

Coefficient of heat loss

K 1 - the linear heat transfer rate [W/m2 x K]
Designates the collector heat loss when the temperature of the absorber is close to ambient temperature such as heating season in our climate from April-September.
K 2 – square (non-linear) rate of heat loss [W/m2 x K2]
Designates the collector heat loss when the temperature of the absorber is much higher than ambient temperature. This factor is particularly important in a climate of Central and Eastern Europe where in cold season of X-III, low ambient temperatures are recorded. For collectors, vacuum of this ratio is 2 / 2, 5 times lower in comparison to flat collectors, which is why they remain much higher efficiency in the first half of the cold.

Gross area

Collector surface resulting from its external dimensions, including the basic frame.

Absorber area

Effective absorber surface which is covered with a selective coating and is not shaded.  It is cold as the effective collector surface. In the case of tubular collectors assumed that this is a portion of the vacuum tube circuit or a flat surface for the collector absorber Sunti EV. To calculate the surface area of solar installations always take up the absorber area.

Collector efficiency factor

Represents the percentage ratio between the heat abstracted by the collector to the power of solar radiation reaching. Its value depends primarily on the quality of the shell from absorbing heat and energy losses have already collected heat. Its mathematical description of the indicators used in k 1 and k 2.

Thermal performance of solar

It’s checked for good weather conditions, where differences in comparison of flat collectors and vacuum are slight (order of 10 +15 W / m 2). However, the heat efficiency (instantaneous) must be distinguished from full-year energy yield (for changing conditions), which for vacuum collectors may be higher by as much as 50-60% of collectors flat.