RE<C - A Google.org Project to Develop Electricity from Renewable Energy Sources

RE<C Initiative

Video: Overview of heliostat research

In 2007 we launched our Renewable Energy Cheaper than Coal (RE<C) initiative through Google.org as an effort to drive down the cost of renewable energy. We’ve retired this initiative and continue to support renewable energy in a variety of other ways.

Our approach to RE<C

Through RE<C, we made several investments in companies working on potentially breakthrough technologies. For instance, we invested in companies like Brightsource Energy and eSolar to help expand their work on concentrating solar power technology, and in Potter Drilling to advance its innovative geothermal drilling technology. We also sponsored research to develop the first Geothermal Map of the US, helping better understand the potential for geothermal energy to provide renewable power that’s always available. And we’ve had an engineering team working to improve a type of concentrating solar power technology called the solar power tower.

The solar power tower is an exciting technology that works by using a field of mirrors, called heliostats, to concentrate the sun’s rays onto a solar receiver on top of a tower. This generates electricity from the sun’s concentrated heat. It’s been successfully demonstrated in the US and abroad at a small scale. We invested $168M in the world’s largest power tower project under construction -- Brightsource’s Ivanpah Solar Electric Generating System (ISEGS). The project is set to be completed in 2013, when it will generate 392 MW of clean solar energy.

Our RE<C engineering team focused their research on two areas of solar power technology: reducing the costs associated with heliostats, and reducing the cost and water consumption of the system. Our research demonstrates how overall costs could be reduced for this kind of technology.

Over the last few years, we’ve seen a lot of progress in clean energy. We’re excited that some technologies are so quickly approaching cost competitiveness with traditional forms of energy in parts of the US and the world. Power tower technology has come a long way, too. But the installed cost of solar photovoltaic technology has declined dramatically over the past few years, making solar photovoltaic technology a compelling choice for consumers.

In addition, we’ve reached a point in our engineering projects where we’re facing new challenges related to our solar receiver design. At this point, other institutions seem better positioned than Google to take this work to the next level. Therefore, we’ve retired our engineering work on RE<C and are sharing our key findings.

What we’ve learned

We’ve learned a lot about power tower technology, and we’re publishing our results to help others in the field advance the state of this technology. Some of our key findings include:

Smarter controls: In the past, the focus has been on making strong heliostat structures. We learned that using lower cost materials and smarter software controls can generate better performance at a lower cost. This ends up lowering the overall cost of the concentrating solar power system.
The Brayton engine: Concentrating solar power plants traditionally use significant quantities of water for cooling. This poses a challenge to scaling these technologies, especially in the desert. Our research shows that using a "Brayton engine" -- a jet engine that uses solar energy to heat air and does not require spray cooling with water -- significantly reduces water use and may reduce operating costs as well.
A systems approach: We took a system level approach to designing concentrating solar systems. By focusing on the cost and quality of the system as a whole, we tried to make cutbacks on some components, while compensating elsewhere to maintain performance. We believe this approach could reduce the cost of electricity generated by concentrating solar systems, rather than attempting to optimize each individual component, which can drive up overall costs.

For the scientists and engineers out there, we’re publishing several technical papers so you can dig into the details and find out about our work.

Heliostat project overview
Heliostat design philosophy and guiding principles

Heliostat reflector design
Heliostat frame design
Heliostat cable actuation system design
Heliostat control and targeting
Heliostat orientation estimation using a 3-axis accelerometer
Heliostat wind flow visualization experiments
Heliostat wind mitigation
Heliostat wind tunnel experiments
Appendix: Heliostat wind tunnel experiments
Multiscopic photometry for heliostat spot tracking
Pitch/roll heliostat control system design
Surface level wind data collection

Brayton project overview

Brayton system hardware summary
Brayton system performance summary

Google has also released two open-source projects to aid future researchers: one to help with heliostat optical simulation, and another to aid CSP heliostat R&D with wind data, heliostat aerodynamic behavior, and heliostat simulation and control software.

Additional renewable energy activities

Our engineering team is proud of the work we’ve done on power tower technology. And as a company, we continue to pursue a wide range of other activities in support of renewable energy -- from our on-campus efforts and energy for our data centers, to our more than $850 million in investments to further develop and deploy renewable energy technologies. We’re excited about contributing to the path toward a more sustainable energy future.