Energy harvesting without batteries

In order to further improve the lifetime of the LightCatcher our customer asks us to design a battery-less power store to improve the lifetime of their product.

In a long life self-powered embedded system the batteries are one of the weakest links in the chain. Although recent innovations in battery technologies are promising, a battery still poses the following problems in the LightCatcher application:

  • batteries have a limited lifetime in situations where they are subjected to large temperature swing (freezing at night, +60 degrees C when the sun us shining during the day)due to temperature swings
  • batteries only have a limited number of charge/discharge cycles, and in this application the battery is charged daily. When they fail they typically cannot be replaced easily due to the mounting situation of the device (rooftop mounting).

So, what alternatives can we offer?

In our quest for a green battery pack replacement solution, we have developed a supercapacitor-based energy store. Although supercapacitors have a lower energy density than batteries, they win hands down when it comes to lifetime and change/discharge cycle count. Typical numbers are 10 to 15 years lifetime with unlimited charge/discharge cycles. For an outdoor application, where sunlight is abundant, this supercap charger is an excellent long life, green replacement.

Some of the features of the system we designed for this application:

  • charges any 2 supercaps in series from a solar panel input
  • MPPT (Maximum Power Point Tracker) to extract maximum energy from the solar cell
  • DC/DC boost convertor with low quiescent current boosts the supercap voltage (1V to 5V) to a constant 5V, required for the application electronics.

The system in now installed at the test-site of the customer for long-term validation.

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Solar panel provides the power

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Two ultracaps store the energy

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Maximum power-point tracker extracts the maximum amount of energy from the solar panel

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Ulta-low quiescent current DC-DC upconvertor generates the required 5V for the application