18 Feb 2010 | United States
Energy harvesting in the dirt
Rarely do we think of soil as a battery or a source of power. However, Trophos Energy is successfully harvesting energy from soil, sediment and wastewater and, with the use of innovative power management electronics, is converting dirt into a useful source of clean reliable power.
As advancements in sensor and communication technology have increased power efficiency and reduced power consumption requirements, opportunities have arisen for low power energy harvesting solutions to replace conventional batteries. Trophos' Environmental Energy Harvesting (EH) technology offers a perpetual and maintenance-free power source for a wide range of commercially available electronics, sensors and communications devices employed in environmental monitoring and sensing applications.
Harvesting energy in an open, uncontrolled environment poses challenges. Systems often have to compete with other natural processes such as biofouling, micro-climate changes and animal interference, not to mention curious humans who tamper with visible systems. Trophos' approach is to take advantage of processes that are already present in nature - such as the metabolic activity of microorganisms or the energy that can be harvested from light sources - and to design systems that avail of these processes but also overcome the hazards of their surroundings.
Trophos Energy's Bioelectrochemical Energy System (BES) employs the natural metabolic pathways of microbes found ubiquitously in soil, sediment, and wastewater. In these environments, microbes act as biological catalysts to transfer electrons outside their cell walls, thus generating a small electrical charge in the surrounding substrate. This charge, measured as a Reduction-Oxidation (RedOx) potential, is directly collected by the BES electrodes, generating electrical current. With current and potential, you have power. In an open system, new food products and biological waste products ensure an endless supply of fuel for the BES, enabling persistent power generation. The location of the BES electrodes in the soil ensures that the power system is discrete and buried.
Another approach to addressing the issue of human tampering is to employ a discrete solar harvesting system. Trophos has developed the Discrete Photovoltaic (DPV) system which consists of a photovoltaic cell configured in such a way as to resemble rock or vegetation, rendering it virtually indistinguishable from the natural environment and making it suitable for many sensing and monitoring applications. This yields similar performance to a BES system but also works in dry and cold environments where BES systems may not be suitable.
Trophos' Environmental Energy Harvesting systems are custom designed to suit the environment of the given application and can be modified to meet a wide range of power requirements. System performance is ideally measured in terms of power density or power in relation to area or volume. Typical system performance ranges are as follows.
- Sized to provide 1-100mW of continuous power indefinitely
- Support power densities reaching 50 mW/m2 of soil footprint or 10 mW/liter, depending on the technologies used and the application environment.
- BES systems are typically installed by burying the system in soil. Marine systems can be deployed from the surface or by hand in shallow water.
- Constructed using non-corroding, chemically inert and environmentally compatible materials
Dirt to Useable Power - Integrated Power Management
Harvesting energy from soil alone is not sufficient to deliver the power requirements of today's electronics - the true value is in the ability to convert, store and manage this scavenged power so that it matches the requirements and duty-cycle of the specific application.
Trophos BES Power Management & Application Architecture
Because of the low voltage output of BES and other energy harvesting systems, low-threshold bootstrap and boost conversion topology is needed to reliably self-start and efficiently sustain power conversion of a low current 0.4V source to a more usable voltage. Due to the dynamic nature of BES and other scavenging systems, low-power circuitry has been developed to continuously monitor and adapt the poised potential, or power-transfer gain, to optimize EH performance and effectively manage the battery system.
Trophos is working with a wide variety of industry, government and educational institutions to explore and develop applications where low-maintenance, low-cost sources of power are of value.
For more information see www.trophosenergy.com .
Source and images: Trophos Energy
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