Portable tester for measuring the IV curves of solar cells and modules. It is controlled and powered through a USB cable with any computer such as a laptop or netbook, so can be used outdoors for sunlight testing for several hours with no AC power cord. The big benefit of this design is that it is fast enough to be used indoors 24/7 with a low cost commercial grade flash lamp to test any photovoltaic device from small cells to full size modules. It has been used for crystal-Si and III-V Triple Junction cells and circuits. Light intensity is calibrated with a reference cell of the same spectral response. 8 engineering prototype units have been sold and are being used for product development and production at beta test locations.