TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The glass substrate contains less than 0.5 wt.% of boron oxide, preferably up to unavoidable traces of no boron oxide; less than 0.5 wt.% barium oxide, preferably up to unavoidable traces of no boron oxide; 2 wt.% of sum of calcium oxide, strontium oxide and zinc oxide; and at least 5, preferably 8 wt.% of sodium oxide. The molar ratio of the glass substrate component (comprising sum of sodium oxide, potassium oxide/magnesium oxide, calcium oxide, strontium oxide and barium oxide) is less than 6.5. The molar ratio of the glass substrate component (comprising silica/alumina) is 5-6. The glass substrate exhibits: a heat expansion coefficient of greater than 7.5x 10-6/K, preferably 8-9.5x 10-6/K at 20-300 degrees C; and an electrical conductivity of greater than 17x 10-12 second/cm at 25 degrees C, where the electrical conductivity of the glass substrate at 250 degrees C is greater than a factor of 104, preferably 106, than the electrical conductivity of the glass substrate at 25 degrees C. In the glass substrate, up to a surface depth of 20 mu m is replaced by sodium ion, at least partially by other cations, preferably potassium ion, such that the sodium ion content in the surface layer is less than the total content of the sodium ion in the glass substrate. The glass substrate comprises (in mol.%): silicon dioxide (63-67.5); alumina (10-12.5); sodium oxide (8.5-15.5); potassium oxide (2.5-4); magnesium oxide (3-9); sum of calcium oxide, strontium oxide and zinc oxide (0-2.5); sum of titanium oxide and zirconium oxide (0.5-1.5); cerium oxide (0.02-0.5); sum of arsenic trioxide and antimony trioxide (0-0.4); tin dioxide (0-1.5); and fluorine (0.05-2.6). In the glass substrate, the molar ratio of: silica and alumina is 5-6.8; sodium oxide and potassium oxide is 2.1-6.2; alumina and potassium oxide is 2.5-5; alumina and sodium oxide is 0.6-1.5; and sum of sodium oxide, potassium oxide/magnesium oxide, calcium oxide and strontium oxide is 0.95-6.5. The glass substrate is coated with at least a molybdenum layer having a thickness of 0.25-3, preferably 0.5-1.5 mu m.    TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The solar cell is a thin film solar cell based on silicon or a thin film solar cell based on semiconductor material, which is cadmium tellurium, copper indium selenide or copper indium gallium (di)selenide. The solar cell is in planar, concaved, spherical or cylindrical form. The solar cell exhibits functional layers comprising conductive and transparent conductive materials from photosensitive semiconductor compounds, buffer materials and/or metallic back contact materials. The solar cell comprises at least two solar cells, which are serially connected to a photovoltaic module and protected from the environment influences through encapsulation, preferably with silicon dioxide, plastics, preferably ethyl-vinyl-acetate, lacquer layer and/or by a further glass substrate. The solar cell has at least a photoactive semiconductor, which is applied on the glass substrate or precoated glass substrate at greater than 550 degrees C.