Transparent Solar Windows Versus Conventional Windows

In the IN2 NEXT project, researchers tested NEXT Energy Technology's photovoltaic coated windows against conventional commercial windows and tracked performance against their respective solar heat gain coefficients (SHGC), the industry standard performance metric for commercial windows. The results showed that the technology could reduce the SHGC of equivalent windows to less than 0.20.

The California-based company is developing transparent energy-harvesting window technology with the goal of making glass curtain walls a source of low-cost, on-site renewable energy in buildings. As part of the Wells Fargo Innovation Incubator (IN2), the company is involved in a multi-year PV window project that compares the overall energy efficiency performance of the company's transparent PV windows to that of conventional commercial windows.

Commercial buildings account for 36% of total electricity consumption in the US, consuming more than $190 billion annually. In addition, according to the Department of Energy, windows account for 30% of the energy used to heat and cool commercial buildings, costing US building owners approximately $50 billion annually. Considering the potential savings, it is important to reduce SHGC to 0.20 outside of energy production. SHGC measures the amount of heat generated by sunlight passively entering a building through windows, or solar heat gain. Too much solar gain can lead to overheating of spaces and inefficient energy management throughout the building.

"These are extremely important results for the energy efficiency of insulating glass. Achieving a SHGC of less than 0.20 while providing neutral aesthetics is a huge challenge for all manufacturers of vacuum deposited coated glass. Balancing performance and appearance is at the heart of the ideal harmony and it appears that NEXT has achieved this," said Garret Henson, Vice President of Sales and Marketing for Viracon, a North American manufacturer of commercial architectural glass.

In making these windows, photovoltaic technology is achieved through proprietary organic semiconductor materials, which, according to the company report, are abundant and inexpensive on the planet. In a high-speed, low-cost, low-energy process, this material is applied evenly to the glass like ink, allowing the glass to collect sunlight and convert it into electricity rather than heat.

"The results of the collaboration with NEXT give us data on how to redefine the way architects and building owners measure the performance of commercial windows," said Trish Cozart, IN2 project manager and director of NREL's Centre for Innovation and Entrepreneurship, "If building windows can be used to Promisingly, this will mark a new chapter in the generation of significant amounts of electricity. The goal now is to evaluate SHGCs to take into account the impact of electricity generation as well as solar heat gain."