An energy transfer device for solar power systems operates to draw power from high-producing photovoltaic devices and apply that power across low-producing photovoltaic devices. An embodiment is a self-regulating energy exchanger using bidirectional DC-DC converters that operates to maintain uniform voltage across each series-connected photovoltaic device. An alternative embodiment is an energy exchanger that is controlled to maintain each of several series-connected photovoltaic devices at a maximum power point by drawing power from high-performing devices and applying that power across low-performing devices to provide uniform current among series-connected photovoltaic devices.