Situation. Photovoltaics is considered as the most promising renewable energy species in the Worlds Solar Program 1996-2005. In EU White Paper (Energy for the Future: Renewable Sources of Energy) the capacity of photovoltaics equipment in EU has to be increased by 100-fold till 2010.
At present the efficiency of commercial solar cells converting solar radiative energy into electricity consists ~15%, that of experimental cells - ~20%, in experiments with multijuncture semiconductors ~30% efficiency has been documented. 150 kWh/m2 of electrical energy from one square meter can be produced annually using modern commercial solar cells.
The efficiency of photovoltaic system does not depend on it's power. Consequently, in Lithuania, where an electrical grid is well developed, photovoltaic equipment should be gradually connected to the grid.
At present there are no photovoltaic equipment in Lithuania. Joint venture company "Saulės energija" has realized some 3 kW overall power photovoltaic modules in Lithuania in 1994-1998. However, they are used in tourism or for feeding specific electronic devices and cannot be regarded as demonstration energy objects. Low-power (25-100 W) equipment are already established or being under construction in MSI, LZUII, KTU.
The development and deployment of solar energy technologies are hampered by a very high cost of installed one watt that is several times higher than that of conventional electric energy. At present the cost of 1W-power solar cell is ~8-12 Lt, the cost of installed 1W-power in solar elements reaches 20-40 Lt.
Main objectives. Reducing the photoelectricity price is a basic and global task aimed at promoting the photovoltaics development world-wide. This can be accomplished in two ways: enhancing the solar cell efficiency and thereby obtaining more electric energy from the same area or diminishing the cell production cost. Cosmetic upgrading is insufficient in this case. The situation can be changed radically by introducing new materials and appropriate technological principles. According to the program, scientific research and technology development are carried out in three directions:
Studies in the field of self-formation in artificial systems (theory and application) create opportunities for the development of new and effective solar cell production technologies (MSI). The self-formation principles in artificial systems have been elaborated in Lithuania, Lithuania was a leader in this field in the former Soviet Union. The self-formation technology was in the stage of introduction in the whole microelectronics industry by minister orders.
- self-formation principles in solar cell technology (the end objective - increased efficiency and production cost reduction);
- new three-component semiconductor solar cells (the end objective - increased efficiency);
- new organic materials and amorphous silicon for solar cells (the end objective - production cost reduction).
The self-formation principles were commenced to be applied in solar cell technology within the framework of the earlier mentioned program "Solar and alternative renewable energy sources for agriculture" (1996-1999).
It is essential to continue scientific research on new inorganic materials suitable for solar energetics. For example, three-component chalcopyrite semiconductors may become very effective material in solar element technology. Amorphous silicon is currently the cheapest material and its further investigations are promising too. The dependence of efficiency of these semiconductors on layer formation conditions as well as their electric and photoelectric behavior are planned to be investigated. This project will be carried out by united efforts of scientists from Greece, Bulgaria and Lithuania (VU, PFI).
The synthesis, investigation of photophysical properties and application of photosensitive organic compounds suitable for molecular solar cells (FI, VU, KTU, MTMI, MSI) are aimed at substantial reducing of photovoltaics-driven electricity.
The widely used monocrystalline silicon technology for solar cells has been elaborated in the country. The approach is able of producing a new self-formation-based technology resulting in higher efficiency (15%) of solar cells and by one third diminishing their production costs.
The country is capable of manufacturing currently widely used world-wide (85%) solar cells based on monocrystalline silicon of overall power 1-2 MW per annum. This would meet not only Lithuania needs but might become one of high-technology products suitable for export.
The country is able to produce solar modules for local needs as well as for export taking advantage of solar elements manufactured in Lithuania (Joint venture company "Saules energija").
Current situation. At present the solar energy for thermal purposes can be used through establishing solar collectors for water warming, solar collectors for drying agricultural products and systems for room heating. There are several water warming systems using solar thermal collectors assembled in Lithuania. Their overall area is about 1000 m2. The enterprise "Santechnines detales" (sanitary engineering parts) manufactures solar collectors employing stamped steel heating radiators. The comparative price of such collector amounts to 300 Lt/m2, energetic efficiency - about 250-290 kWh/m2 per season. The model project is intended to be put into operation with assistance of Danish Energy agency: 150 m2 of solar collectors for water warming in Kacergine children sanatorium. Under present conditions, when there is no incentives and support, the use of solar collectors for water warming is in most cases economically unjustified. Recently film solar collectors for drying of products have been designed and commenced to be employed in country agriculture. Their seasonal capacity - up to 200 kWh/m2, they pay off in 1-2 years. Yet, such collectors are inconvenient in terms of assembling and storing, the polymeric film itself is not everlasting. Small farmers might use such collectors. The overall area of collectors for drying of agricultural products at present is 180 m2 in Lithuania.
Research is launched aimed at substantiating solar energy employment for house warming. However, such recommendations are yet in preparatory stage and actually operating heating systems are absent.
In National program on increasing the energy utilization efficiency, the utilization potential of solar energy for heating is evaluated assuming that this energy can meet 10% of heating and about 30% of hot water preparation needs, i.e., 3.0 TkW per year. It is most appropriate to use solar collectors and receivers of domestic production for water warming. The price of the system is about 400-500 Lt/m2, efficiency 150-300 kWh/m2 per year, the service lifetime 10 years. It is also possible to arrange local industrial production of collectors making use of imported absorbers. The price of such a system would be about 1000 Lt/m2, efficiency up to 330-400 kWh/m2 per year, service lifetime about 15-20 years. In addition, polymeric absorbers (without transparent coating) could be more widely used for swimming pools, fishery and vegetable watering.
Solar collectors have a good outlook when used for drying agricultural produce. In 1997 more than 3 Mt of grain and more than 2 Mt of hay were produced in Lithuania. Using thermal dryers, about 1.1-1.7 kWh of energy need to be consumed to evaporate 1 kg of water from grain, whereas using active ventilation with solar collectors - only 0.33-0.39 kWh of energy. Drying one ton 24%-moisture grain to 14%-moisture level with thermal dryers requires about 184 kWh/t, using active ventilation with solar collectors - only about 47 kWh/t of energy. High-quality fodder can be prepared employing active ventilation with solar collectors for hay drying. Estimates show that the potential of drying agricultural produce in the country makes up about 4 million of square meters of collector area. Such collectors should be matched in future with building constructions.
In Lithuania the overall annual heat losses in dwelling houses totaled 23.2 TWh of energy in 1995. Preliminary estimates show that, making use of passive systems for house heating with solar energy and under favorable position and orientation of a building, the energy expenditure for heating can be reduced by 20%. Besides, such passive systems can be employed for heating water and air used in various technologies.
Main objectives. It is planned that in 2005 the heating equipment area will reach the figure over 1000 m2 and more than 260.000 kWh of thermal energy will be produced annually.
For the implementation of the program should be performed researches:
While introducing into production measures relating to solar energy utilization for thermal purposes, it is suggested to design a solar collector matched with building constructions for a grain store. Such a design could be used in series.
- of solar collectors matched with building constructions designed for drying of agricultural products;
- of passive building heating systems capable of complex heating of water and air used for technological purposes;
- to evaluate opportunities and identify measures aimed at accumulating in a greenhouse of thermal energy taken away from greenhouse in daytime.