Photovoltaic cells under concentrated illumination experience a high heat load which must be dissipated efficiently in order to maintain a low cell temperature. Tower and dish solar concentrators typically use arrays of densely packed cells where all of the heat must be removed in the direction normal to the surface. This book identifies jet impingement cooling as a promising technology for this type of configuration. A prototype cooling device is manufactured and the heat transfer and flow characteristics of this device are tested in the laboratory. Correlations for average heat transfer coefficient and pressure drop are established and combined to form a model for required pumping power at a given average heat transfer coefficient. This model is used to make general predictions for the optimal cooling device configuration and to propose an optimising design procedure. Combining this model with a model for PV output as a function of temperature gives the optimal system operating range. The effect of a nonuniform heat transfer coefficient distribution on single and interconnected PV cells is investigated and found to be minor.