Arrays of thin-film solar cells based on dye-sensitised nanocrystalline oxides (DSC) promise low-cost electricity especially where continuous direct insolation is unavailable. However, the optimisation of arrays of DSC is not straightforward because of the lower power levels obtained and the corresponding increased stringency needed when calculating the production tolerances permissible in the individual cells. This paper describes the first stage of project to devise and build a DSC array simulator driven solely by a phenomenological model of individual DSC behaviour at the level of infinitesimal cells. The simulator numerically extrapolates this behaviour to real finite cells and thence to a real physical array. In the process it is observed that optimisation of infinitesimal cells is only possible when the size of the real cell is first decided, and that the relationship between the conducting oxide transparency and electrical resistance is critical for the optimisation to be effective. The results obtained using the simulator are compared with the behaviour of real test cell assemblies manufactured by STI, a DSC Licensee, and are found to be in good agreement. Their effects on the costs of delivered power are discussed. (c) 2004 Elsevier B.V. All rights reserved.