This paper describes a class of power electronics architecture for scalable photovoltaic power processing. The proposed power processing technique can provide extreme improvements in power conversion density. The architecture enhances energy delivery and system reliability compared to conventional methods. The strategy leverages the best attributes of conventional methods with a fundamentally different approach that also overcomes their major drawbacks. This differential power processing approach converts power only once, using small local converters to process the limited mismatch between adjacent solar elements. When a grid tie is desired, a simplified large inverter provides this interface. The method supports local protection and diagnostics, while optimizing power production.