The objective of this renewable energy security demonstration program was to show that a recently emerged, micro photovoltaic (PV) cell based, high concentration solar electric technology was poised to transition into cost effective use at Department of Defense (DoD) installations situated in sunny climate zones.

The key HCPV module technology is a m-transfer printing approach, which allows the use of micro-cells. Micro-cells have a number of advantages over conventional cells, some of which are mentioned below. The approach has the following cost, performance and reliability benefits over existing approaches such as:

• m-transfer printing which allows the GaAs substrate to be used several times, reducing cell cost
• High concentration of solar flux which reduces cell size and hence cost
• Unique high efficiency two-stage refractive optics implemented with inexpensive material stock which reduces cost
• Short optical path which enables a thin module profile and reduces cost of structural materials
• Distributed zero-cost thermal management which reduces cost by eliminating supplemental heat sink and heat spreader, decreasing module cost
• Low current and low temperature and thin film metal interconnects increases reliability
• Highly scalable and parallel, capital efficient and automated manufacturing process

The module has a dimension of 636 mm x 476 mm and is 66 mm thick. It has a rated power of 87.5 W and a concentration ratio of 1100 suns. The efficiency of this module was determined to be 33.9% by Instituto de Energia Solar at the Universidad Politecnica de Madrid (IES-UPM).

The HCPV system was to use modified commercially available dual-axis solar trackers from STi Norland, providing optimum solar alignment with high angular accuracies as tight as 0.1 degrees, allowing for the maximum capture of the solar energy throughout the day. This high accuracy is necessary for HCPV applications in high DNI regions in providing lowest solar electricity production cost. The dual axis tracker also provides > 30% more energy yield than a fixed installation with the same nameplate rating.

For the storage battery, the Princeton Power Systems' equipment was chosen. Princeton supplied the batteries along with the battery controller, the inverters, air conditioning unit, fire extinguisher system and the data acquisition computer all inside one equipment container.

The opportunity to measure and develop experience with HCPV technology did not materialize with this project. An insurmountable amount of site permit requirements and delays associated with the site selection resulted in the project losing momentum and becoming vulnerable to cancellation. In addition, the HCPV module manufacturer (Semprius) went out of business during the project, further cementing the non-viability of the technology going forward after this demonstration project.

Rocketdyne has conducted in-depth levelized cost of energy (LCOE) studies for a wide range of solar options and estimates a nearly 20% LCOE cost advantage if the approach is implemented at commercial scale. Finally, Rocketdyne recognizes that the most likely transition of HCPV cost and energy security benefits to the DoD will be through purchase power agreements, energy savings contracts, or other contract mechanisms requiring the capital expenditures to be provided by third party financing. The key to bankability of future privately financed activities is a comprehensive commercial scale demonstration activity to be provided by this ESTCP project.