Abstract. The conversation of solar energy into electricity using photovoltaic panels and into heat energy using solar collectors is the challenge of the time. Presently widely used fossil energy is unfriendly to the earth environment and its amount is limited. Both solar panels and solar collectors produce more energy, if direct solar radiation strikes its working surface perpendicularly during all the operation time. For that special device -the sun tracking stands or trackers, automatically keeping their working surface perpendicular to the sunbeams, are used. Different constructions of solar trackers and actuators are known: trackers based on the clockwork principle, based on the principle of freon evaporation and condensation, based on the principle of spring made of shape-memory alloys and others. The trackers act on a control unit and actuator, changing the position of the panels or collectors in azimuth, or azimuth and zenith plane. Different constructions of the actuators are in operation. Driving mechanisms with one electric motor (turning only in one plane) or with two electric motors (turning in two planes) are widely used. In the Ulbroka Research Centre a solar tracking stand of a new construction has been developed. There only one electric motor with a gearbox and a crank mechanism simultaneously is turning solar panels in two planes (Latvia patent LV 15245 A, 2017). The device has been made, experimentally investigated in field conditions on the roof of a house and positive results have been obtained. The amount of electric energy produced by two solar panels placed on the developed stand during the summer time of 2017 has been compared with the gain of electricity produced by in the same conditions working stationary fixed panels of the same type. Tracking the sun panels had produced around 1.48 times more electric energy than the fix ones, but in September 1.3 times more.Keywords: photovoltaic, panels, electricity, trackers. IntroductionThere are many possibilities of the use of solar energy. One of them is the use it for production of heat and electricity. The conversion of solar energy into electricity using photovoltaic panels and into heat energy using solar collectors can help decrease the consumption of fossil energy, which is widely used up to date but is unfriendly to the earth environment. The technology for production of heat energy from sunlight has been known and used long time ago. The transformation of solar energy into electricity is another possibility to use it for practical needs. The main task of the technology used for both transformations is to do it with as high as possible efficiency and low costs. Solar energy in that way is widely used in many countries all over the globe, particularly in Southern countries and large amount of international experience is collected [1]. Solar panels and collectors produce more energy, if direct solar radiation strikes the working surface perpendicularly during the whole operation time [2]. On cloudy days, if there is no direct radiation, ...

Two years (2009-2010) experience of the experimental use of alternative energy sources in technological processes of agriculture is analyzed. Water was heated by an outside air heat pump with passive evaporators, and used for new born piglets resting place floor heating. Experimental data were obtained by the reckoning consumption of electric energy for the operation of the heat pump’s compressor and electric heater, and by a heat meter registering the consumed heat energy. The obtained data show that the outside air heat pump with passive evaporators is working successfully during summer months, when the coefficient of performance (COP) of the heat pump exceeds 3.5. When the outside temperature decreases under +10˚C, the heat pump evaporators become covered with hoarfrost and ice. The value of the COP and produced amount of heat energy reduce, and the electric heater often switches on. During the experimental research one of the heat pump evaporators was supplied with a ventilator, air flow from which was washing the surface of the evaporator’s plates. So the satisfactory operation of the heat pump was provided till December 10, 2009 and November 25, 2010.

Abstract. Lithuania medium rotation plant plantations are started to breed relatively recently, so reliable data on suitability of these crops for biofuel production cannot be found. Studies have established wild cherry chop physical properties. 8-16 mm particles make the main, chopped by a drum chopper, wood fraction; on the average, it makes 84 % of total chop mass. Experimental results show that humidity has greater impact on the wild cherry wood chop collapse angle: with decrease of the moisture content the collapse angle increased from 65 ± 1.0 to 82 ± 2.0 degrees, when humidity is lower, the influence on the natural slope angle is lower. It fell accordingly from 36 ± 1.0 to 42 ± 2.0 degrees. Chop bulk density variation with the change of wood humidity was determined; with increase of humidity of wild cherry from 35.1 ± 1.0 to 6.4 ± 0.1 % the density varied from 342.67 ± 4.81 to 236.67 ± 2.6 kg·m -3 . Wild cherry ash content is low, and it does not increase 1.87 ± 0.18 %, and the calorific value of wood reached 18.70 ± 0.36 MJ·kg -1 ; it is close to the standard accepted in Lithuania -birch caloricity. The determined elemental composition of wild cherry wood showed that carbon (C) quantity reached 49.16 ± 1.10 %, nitrogen (N) quantity does not increase 0.23 ± 0.10 %, and quantity of sulphur (S) does not exceed 0.01 %. Having determined and evaluated the main criteria for biofuel (finesse of chop, calorific value, ash content, elemental composition), it is possible to state that wild cherry wood fully complies for production of qualitative biofuel. However, from the economic point of view, it is purposeful to use only branches and tops of wild cherry trees for biofuel, and valuable part of wood may be used for production of furniture or in other industry branches.

A flat plate solar collector with cell polycarbonate absorber and transparent cover has been made and its experimental investigation carried out. The collector consists of a wooden box, into which, a layer of heat insulation with a mirror film and 4 mm thick cell polycarbonate sheet, as the absorber, are placed. The coherence between collector’s efficiency, heat carrier and ambient air temperature, as well as intensity of the solar radiation and heat power in the experimental investigation has been obtained. During the experimental examination the maximum temperature of the heat carrier reached 80˚C at the intensity of solar radiation about 0.8 kW/m2 and ambient air temperature around 32˚C. The efficiency of the collector reached 33-60%, depending on the intensity of solar radiation and surrounding air temperature.

Usual constructions of solar energy receivers are not efficient enough in Latvia and others northern countries, and new constructions are required, that would be able to collect energy from all sides as well as to use the diffused radiation more efficiently. The aim of the paper is to elaborate method for calculation of energy received by solar collector, usable for developing of new constructions of solar collectors, and to develop a new construction of solar collector using this method. Such new construction can be a semi-spherical solar collector. Such collector has been made, and measurements of water heating have been carried out. Method of calculations of received energy has been elaborated. Theoretical calculations of the energy gain from semi-spherical solar collector have been performed and verified by comparison of calculated daily energy sums with measured ones, and good coincidence has been obtained. Method of calculations allows calculating not only integral received energy, but also distribution of the received energy along the surface. The measured distribution of surface temperature of the semi-spherical solar collector corresponds to the calculated one. There are no spot on the semi-spherical surface which would never get warm. Such semi-spherical solar collector could be appropriate for use of solar energy in Latvia and other countries with similar geographical and climatic conditions.