The ability to combine solar, thermal and vibration energy sources is useful because many of these sources are intermittent and therefore a multisource architecture is able to capture and deliver power under a wider circumstances. However, the energy levels and optimization and control strategies are also diverse. According to MIT thermoelectric harvest sources typically produce only 0.02 to 0.15 volts, while photovoltaic cells generate 0.2 to 0.7 volts while vibration sources can produce up to 5 volts.
Up until now the simplest and commonest strategy has been simply to switch between the highest energy generation source, but wasting the energy input from other sources.
Co-ordinating the energy sources in real-time to produce a constant usable output requires a specialized control system which has been designed in a chip developed by doctoral student Saurav Bandyopadhyay, under MIT professor Anantha Chandrakasan, is described in a paper published in the IEEE Journal of Solid-State Circuits.
It has a dual-path architecture allowing energy to be used directly or to be stored and the switch matrix and the control circuits are implemented in a 0.35-micron CMOS process.