[en] Solar scientist are well aware of the low energy density of solar radiation. A fully tracking collector at the sunniest spot on this planet will receive a little excess of 3000 kWh per year per m² of solar radiation (beam plus diffused). In most places the figure is far lower. Conversion efficiencies, from solar radiation to electricity, vary from a fraction of 1% for a photo-synthesis-hybrid-thermal converter, to to a maximum well below 40% for the highest temperature thermal systems. It is this low output per unit area that presents the major problem in achieving economic viability, discontinuity in the energy supply being, by comparison, a minor inconvenience. The economics of various solar conversion systems is presented, using an unsophisticated approach in order to see more vividly the issues involved. Economic viability depends not only on cost and output but on the cost of alternatively energy supplies at site in question