Energy Harvesting
Solar Cell Utilization – Drawing on its many years of experience and its unique technical expertise, Ambient utilizes leading edge solar cell technology, proprietary algorithms and other techniques to maximize efficiency in energy harvesting and extend the state of the art in photovoltaic development and deployment. Utilizing this corporate expertise and technical know-how, Ambient designs and develops energy collection systems that are optimized to operate over a wide range of specific power requirements. For new applications, Ambient is utilizing high energy photovoltaic (HEPV) cells with operational efficiencies reaching 27% at one standard sun level (100mW/cm² at 1.5 Air Mass). To achieve this high efficiency, these HEPV cells operate over a wide spectral band as shown in Figure 1.
Figure 1: Relative Wavelength Efficiency for Various Solar Technologies (HEPV, SJ-Mono/Poly-Crystalline PV, Si-Amorphous PV)
HEPV cells can produce usable power at much lower light levels than mono/poly crystalline silicon PV cells. Mono/poly crystalline devices can provide usable power with light levels down to about 10,000 Lux (about 1/10 sun). HEPV cells produce usable power at light levels as low as 10 Lux. Low-light capability combined with superior power efficiency makes the HEPV cells the ideal choice in systems that have limited surface area or are required to operate in low-light environments such as rainforests. This capability also reduces the requirement to align the solar array as HEPV cells can produce power from highly occluded or reflected light sources.
Another area in which Ambient has pioneered the use of solar cells is the development of a patent-pending technology to use solar cells as ground planes for communication antennae. Finding enough area on a system for a solar array has always been a challenge in remote applications requiring a communications link. This patent-pending technology allows the area for a ground plane to be shared between the solar array and the antenna ground plane maximizing the available area for energy generation.
Energy Storage – Once the energy is generated it must be stored. Ambient has developed, through its internal research and development, a patented technology for battery-free, long-term energy conversion and storage. Traditional power supplies for remote sensing applications use primary batteries such as alkaline or lithium cells. These cells provide reliable power for short durations but have to be replaced periodically for continued operation. An alternative solution is the use of secondary or rechargeable batteries such as Lithium-Ion battery packs connected to solar cells or other sources. These also provide reliable power but are limited in the number of charge cycles they can endure. This limits their usefulness to less than a year. Recent developments in “Super” and “Ultra” capacitor technology have made the resulting products a viable alternative for energy storage. They have the advantage of a large number of recharge cycles and operational lifetimes of 10 years or more. When combined with photovoltaic modules, they provide a reliable, long duration energy solution for remote sensor applications.
Capacitor based energy storage has many engineering challenges. These capacitors operate within strict operating voltage limits When they are combined into capacitor banks, special care must be taken to ensure these limits are met. Failure to do so can limit the life of the capacitor bank. Ambient has the corporate know-how and has developed the technology to meet this requirement for low power applications.
Energy Conversion – In low-power solar engineering, the consistency and efficiency of the energy conversion between the solar cells and the energy storage components is often over looked. Ambient has developed a patent-pending Maximum Power Point Tracker (MPPT) designed specifically for medium to low power applications. The MPPT keeps the PV module operating at its maximum power point over variations in light levels and temperature. Power Trackers have been commercially available for several years but have been limited to high power applications, such as building power systems, where the power requirements are above 300 Watts. Ambient has been working in the technology forefront, developing a MPPT for medium, low and micro-power applications.
Ambient’s MPPT uses an electronic/software algorithm design that constantly monitors and adjusts the power output being delivered by the PV array to the capacitor storage array. The power tracking algorithm is dynamic in that it adjusts for variations in light and temperature and ensures that the PV array continually operates at its peak power point. When the storage array reaches full charge, the MPPT adjusts to a float condition maintaining this full charge status while preserving the lifetime of the storage array. The MPPT has an added feature that allows it to communicate power input level and charge status information to the host system providing for variable operational modes based on available energy. The use of capacitor-based storage introduces a challenge in handling the wide voltage variations that occur in the capacitor storage array. This may require the development of high efficiency, wide input voltage DC-DC converters. Ambient has the design expertise to develop such converters. With careful design, a linear regulator may be used. Ambient has the experience required to produce the optimum solution for any application.
Ambient’s technology is scalable and configurable to support a wide range of operational energy requirements. Examples provided in Table 1 illustrate the operational characteristics for a variety of Ambient’s energy management platforms designed to support a continuum of energy outputs. This data is presented for reference only. The precise characteristics will depend upon the environmental conditions within which the energy management platform will be required to operate. These illustrated systems are based on a 45°C maximum sustained (24 hours) operating temperature with an average illumination of 3 sun-hours per day at a 1.5 Air Mass (AM) level and with a 30% occlusion. These systems will have a minimum 10 year lifetime assuming a ground installation environment and an average 25°C ambient temperature.
Table 1: Example HEPV Power Subsystems
| Energy Output(W·hr/day) | PackageLength(in) | PackageWidth(in) | PackageHeight(in) | PackageVolume(in³) | PackageWeight(lbs) | Operating Temperature Range(°C) | Storage Temperature Range(°C) |
| 0.07 | 2.8 | 2.0 | 1.1 | 6.2 | 0.1 | -35 / +70 | -40 / +70 |
| 0.13 | 3.3 | 2.0 | 1.1 | 7.3 | 0.2 | -35 / +70 | -40 / +70 |
| 0.86 | 4.7 | 3.3 | 1.6 | 24.8 | 0.7 | -35 / +70 | -40 / +70 |
| 1.64 | 5.5 | 3.9 | 3.3 | 70.8 | 1.0 | -35 / +70 | -40 / +70 |
| 4.75 | 6.6 | 6.6 | 3.2 | 139.4 | 3.0 | -35 / +70 | -40 / +70 |
| 10.36 | 7.0 | 7.0 | 5.0 | 245.0 | 5.6 | -35 / +70 | -40 / +70 |
| 23.21 | 10.5 | 10.5 | 6.8 | 749.7 | 11.1 | -35 / +70 | -40 / +70 |
| 30.66 | 11.7 | 11.7 | 4.4 | 602.3 | 13.0 | -35 / +70 | -40 / +70 |
| 41.67 | 14.0 | 14.0 | 4.8 | 940.8 | 15.7 | -35 / +70 | -40 / +70 |
ALPC-10 - This power harvesting platform was developed for the US Special Operations Command in conjunction with the US Army CERDEC command. The ALPC-10 battery-free power module can power unattended ground sensors for 20 years in severe environmental conditions. The ALPC-10 harvests energy over a wide range of light conditions, while providing extremely high power reliability and survivability. Energy is stored in highly robust ultra capacitors providing a non-battery based solution.
The ALPC-10 employs HEPV photovoltaic technology and Ambient’s MPPT to optimize solar panel energy harvesting performance. All required energy is provided with horizontally emplaced deployment (tilting not required) under either direct sun, cloudy conditions or even under light forest canopy (30% occlusion). The ALPC-10 features Ambient’s battery-free ultra capacitor energy storage technology that is capable of delivering energy over 1,000,000 recharge cycles. The ALPC-10 supports continuous operation over a 20 year life cycle and provides high survivability in severe temperature environments (-35°C to +65°C). The Solar Control Module (SCM) and Energy Storage Module (ESM) can be integrated (see Fig.2) or separated (see Fig. 3) where both these modules are hermetically sealed.
The ALPC-10 provides 12 VDC @ 1.5 ADC of regulated output power with other output options readily available. It provides a separate charger input that allows rapid system charging in under 20 minutes. The unit’s power outputs can be cascaded in parallel or series for higher output power and increased system energy. The ALPC-10 was designed to provide high power reliability to support mission critical sensor operations and eliminate the risks associated with battery replacements in denied areas.
