Sil­i­con, the mate­r­ial used in most of today’s solar cells, is a semi-con­duc­tor. This raw mate­r­ial is common in the earth’s crust in the form of sil­i­con diox­ide (quartz, sand), making it avail­able in almost unlim­ited quan­ti­ties. Monocrys­talline, poly­crys­talline and amor­phous sil­i­con can be pro­duced from high purity sil­i­con. These base mate­ri­als are in turn used to pro­duce solar cells with vary­ing prop­er­ties. Solar cells made from amor­phous sil­i­con offer low effi­ciency at a cor­re­spond­ingly low cost; solar cells made from monocrys­talline sil­i­con may be more costly, but they are also more effi­cient. The right cell type depends on the spe­cific appli­ca­tion. Lumi­naires with a decen­tralised power supply require a com­pact design and high effi­ciency, which is why hei solar lumi­naires from Selux use highly effi­cient solar cells gen­er­ally made from monocrys­talline sil­i­con.

The nom­i­nal power of pho­to­voltaic instal­la­tions is mea­sured in Wp (Watt-peak). Wp refers to the per­for­mance under test con­di­tions that approx­i­mate the max­i­mum solar radi­a­tion in Ger­many. These stan­dard test con­di­tions (STC), used to com­pare dif­fer­ent solar mod­ules, are defined as a cell tem­per­a­ture of 25°C, radi­a­tion of 1000W/​m² and an air mass of 1.5. A typ­i­cal PV-instal­la­tion on the roof of a family home (with 40m²) yields around 4 – 5kWp; the PV cells on a hei-solar lumi­naire from Selux have nom­i­nal power rat­ings in the range of 100 to 250Wp. Pho­to­voltaics are ide­ally suited to regions within what we call the solar belt, where there are high levels of solar radi­a­tion irre­spec­tive of the season. These include south­ern areas of Europe and North Amer­ica, Cen­tral and South Amer­ica, Africa, Asia and Aus­tralia. Pho­to­voltaics are also a cost-effi­cient alter­na­tive in neigh­bour­ing regions such as Cen­tral Europe, as has been demon­strated in recent decades. Sev­eral cities and regions in Ger­many and else­where are record­ing pho­to­voltaic yields in solar land reg­is­ters.

Solar power is not only sus­tain­able from an eco­log­i­cal point of view, it is now also finan­cially com­pet­i­tive. Over recent decades, tech­ni­cal advances have improved the per­for­mance of solar cells, as well as other system com­po­nents such as invert­ers, con­trol and charg­ing elec­tron­ics and bat­tery stor­age. At the same time, the eco­nom­ics of scal­ing pro­duc­tion mean costs have fallen con­sid­er­ably: solar cell prices today are 90% lower than in 2010. In many regions with cor­re­spond­ing light inten­sity, pho­to­voltaics are already con­sid­ered the cheap­est way to gen­er­ate elec­tric­ity. In appli­ca­tions such as making road or path light­ing self-suf­fi­cient (»off-grid«), addi­tional fac­tors pos­i­tively impact eco­nomic effi­ciency and the eco­log­i­cal bal­ance sheet: not only are there no elec­tric­ity costs per se, nei­ther are there any line charges or wiring instal­la­tion costs.