The authors have drafted three alternative scenarios for the technological improvement and market penetration of photovoltaics in the next four decades, based on the preliminary results of the EU FP6 Integrated Project NEEDS, Research Stream 1a. The long-term diffusion of PV is foreseen to depend on the achievable module efficiencies and on the maturity of the different technologies in terms of their manufacturing costs, energy pay-back times, additional BOS costs, and even raw material reserves. Last but not least, the co-evolution of a suitable energy storage network (e.g. hydrogen) is also foreseen to be a mandatory requirement. Cumulative installed capacity worldwide is projected to reach 9,000 GWp in 2050 in the most optimistic scenario, which is reduced to 2,400 GWp in the intermediate scenario. In the third “pessimistic” scenario the current economic incentives are not assumed to be sustained long enough to allow PV to become competitive with bulk electricity, resulting in a stunted market growth (500 GWp in 2050). The resulting predictions in terms of costs range from 0.50 to 1.50 €/Wp in 2050, respectively corresponding to 2 - 8 €-cents per kWh in Southern Europe and 4 - 14 €-cents per kWh in Northern Europe. Within the framework of these three general scenarios, special attention is then put to the role that is likely to be played by thin film technologies, namely amorphous Si, CdTe and CIS/CIGS. These technologies are expected to collectively reach a market share of approximately 45% by as early as 2025 in all but the most pessimistic scenario, wherein the same goal is put off until 2050. Marked increases in module efficiencies and material and energy consumption are also expected, to varying degrees depending on the assumptions made in the three scenarios.