This paper discusses fundamental design issues for a photovoltaic-based, maintenance-free, highly available power supply for remote unattended loads. Example applications in rural settings include agricultural sensors and controls, geological and meteorological sensors, broadband internet hardware, and surveillance equipment for border patrol. Urban examples include traffic monitoring equipment and homeland security sensors. While the electrical power required by these loads is not high per se, the accumulated lifetime energy is high for many years of unattended operation. Conventional solutions require expensive pole-drop utility connections, incur high replacement cost of batteries, require regular preventative maintenance, or are extremely large and bulky. The system-oriented design described here uses a combination of energy storage, solar panels, power electronics circuits, and control algorithms.