NTT Research and Development 2008 Review of Activities

Photovoltaic cells are a typical example of a clean energy source, and they are being increasingly used in a wide variety of business and domestic situations as part of efforts to prevent global warming by reducing CO₂ emissions. At NTT Laboratories, we are conducting research and development into ultra-low voltage input boost technology to extract energy efficiently from these photovoltaic cells, and into stand-alone electric power supplies that use this technology. In this way, we intend to contribute to protecting the global environment.

With conventional photovoltaic solar panels, a number of cells must be connected in series to obtain enough voltage to operate equipment. A drawback of this approach is that if part of the photovoltaic panel is shaded from the sun or if part of a cell is broken or becomes dirty, then the solar panel is no longer able to generate electricity. NTT Laboratories have developed an ultra-low voltage input boost integrated circuit that is capable of boosting the very low voltage of 0.4-0.6 V from a single photovoltaic cell up to the range 4-8 V needed to operate equipment. This circuit makes it possible to use a single photovoltaic cell instead of having to connect multiple cells together in series, whereby the amount of electricity generated depends on the lit surface area of the cell. Moreover, we have equipped these cells with a function that tracks the point of maximum output power — a world first for this class of device (from a few watts up to 20 W). As a result, compared with conventional photovoltaic cell panels, it is able to increase the amount of power generated per day by a factor of approximately 1.5. This makes it possible to reduce the panel footprint and reduce costs, and is also expected to broaden the range of applications for photovoltaic cells.

In addition to this ultra-low voltage input boost IC, we also plan to provide stand-alone electric power supplies for driving systems that are situated outdoors, such as security lighting, surveillance cameras, and remote monitoring/sensing systems to provide early warnings of natural disasters along rivers, etc.