Bright Energy Storage Technologies advances compressed air energy storage (CAES) technology

Bright Energy Storage Technologies (BEST), working with Czero engineers, has developed new technology for compressed air energy storage that will help wind and solar energy become more stable, profitable sources of clean power for the global electricity grid. This advanced positive-displacement compressor/expander and storage system has poised BEST to enter the market with a low-cost, scalable solution, at a time when renewable energy production is growing by more than 30% each year.

The energy industry’s “dispatchable power” mismatch

When Phoenix and Los Angeles turn on the air conditioning, utility companies need energy available to meet that spike in demand.

The requirement for on-demand, “dispatchable” electricity presents a huge challenge for the renewable energy industry. Utilities are willing to pay substantially more for “firm,” reliably available power from traditional sources, such as coal and nuclear power plants, than they are for inconsistently available solar and wind power. In other words, unpredictable supply compromises the economic viability of solar and wind power.

Right now, one of the problems with renewable energy is that it doesn’t count directly as ‘base load’ for utility companies, because the source, the sun or the wind, isn’t always ‘on.’… But stored energy can be considered base load. So there’s a big push now to develop better storage technologies for wind and solar, to make them a better fit for utilities. Jeff Rogers, Senior Engineer & Analyst

The inherently intermittent nature of wind and solar energy production, combined with the lack of efficient, cost-effective storage technology and capacity, means utility companies routinely buy more expensive energy to cover base load and peak demand when the sun or wind isn’t  “online.”

Yet during peak times for solar and wind power generation, production often exceeds consumer demand at that time of day.

For instance, in the Eastern Rocky Mountain corridor, prime wind-power generation peaks in the middle of the night, far too early to match the typical power-demand peaks that happen first thing in the morning, year-round, and during the hottest parts of the day, in summer.

This timing mismatch is one of the biggest innovation drivers for renewable energy storage technologies.

Load balancing: the challenges of heterogeneous grid-power sources

It’s quite challenging to balance energy production loads effectively using radically different power plant types. Nuclear plants and large coal power plants, for example, generally take hours, even days, to ramp production up or down: slow response, reliable output. Wind-farm power generation can vary minute to minute: fast response, unreliable output–or none, if the wind isn’t blowing. 

For the power grid, that means wind and solar power can’t be counted on as base load, and they certainly can’t be counted on to respond to spikes in consumer demand (“peaker” load). Currently natural-gas-fired “peaker plants”–fast response, inefficient energy conversion--often fill that gap, commanding a premium price for doing so.

In the clean energy equation, the intermittent availability of wind and solar power means they can’t reliably replace significant amounts of fossil fuel and nuclear sources in fulfilling base-load requirements, much less meet peak load demands.

Renewable energy economics

For utility companies, unfortunately, wind and solar power are of lower value because they aren’t dispatchable. In economic terms, this makes these energy sources less profitable for suppliers, limiting growth. Additionally, because the power grid must operate at equilibrium, any excess power that isn’t used or stored can’t be harvested, and that means lost energy, opportunity and revenue.

These two factors have made “grid firming,” stabilizing energy output through large-scale, cost-effective storage, mission critical for the financial viability of wind and solar power.

Currently, many renewables are on the edge of parity. Making them dispatchable will change the game. For people invested in renewables, making clean energy cost-effective and reliable is today’s number one goal. So for the renewable energy industry, this compressed air energy storage system innovation from Bright Energy Storage Technologies is big news. Guy Babbitt, CEO

Large-scale energy storage: approaches & limitations

Energy storage approaches to mediate variable or asynchronous supply and demand include pumping water into reservoirs (pumped-storage hydropower, PSH), DC storage in batteries (which is expensive), and compressed air energy storage (CAES), for later conversion back into to electricity.

In many cases, large-scale compressed air energy storage uses underground salt caverns as massive storage tanks, an approach also used for natural gas storage. This is only possible, however, in locations with the right geological formations, a major limiting factor. Pumped-water storage plants face similar geographic and environmental challenges.

Alternatives to salt-cavern  compressed air energy storage  include large metal tanks or underwater storage, another area where BEST is leading innovation.

The machines that make compressed air energy storage possible

In all cases, compressed air energy storage requires air compression/expansion machines. Historically, these highly specialized machines have been expensive because of low demand and correspondingly low manufacturing volume.

With global energy demand on the rise, however, the time is right for lower-cost compressed air energy storage technology. Smart engineering is vital in developing the efficient, low-cost energy storage that will make renewable energy economically viable on a large scale.

As part of an energy-storage system, a compressor uses electrical power to drive rotary motion that compresses air in a tank or vessel. Then, when the electricity is needed, the compressor is reversed: air expansion drives rotary motion that creates electricity.

Some energy is lost during each energy conversion step, and losing too much energy during the start-to-finish (round trip) process can kill any profits to be gained from using the system. Likewise, if the cost of the system is too great.

With this in mind, round-trip efficiency and total equipment cost were the top Czero design/engineering considerations in developing the new BEST compressed air energy storage system for market success.

BEST: advancing compressed air energy storage technology

Funded in part by the U.S. Department of Defense and leveraging concepts from multiple industries, BEST has pioneered a new technology that will significantly reduce renewable energy storage infrastructure costs.

Working closely with the Czero engineering team, BEST developed a novel high-volume positive displacement compressor/expander that directly addresses the cost, efficiency and scalability challenges that have hindered widespread adoption of compressed air energy storage.

Czero has been an invaluable and integral part of our program.  From component and subsystem design to detailed system performance analysis, Czero’s integrated engineering approach has allowed us to develop elements quickly to meet the very ambitious schedule challenges imposed by our U.S Department of Defense contract.   Scott Frazier, Co-founder and CEO
Bright Energy Storage Technologies

Czero: using cross-domain expertise to engineer innovation

BEST has worked with Czero on multiple projects over the last three years, and for this project looked to Czero for turnkey, design-to-prototype engineering R&D services. For compressed air energy storage innovation, Czero has a great team, with deep expertise in engines, compressors, clean-tech and energy-conversion technology. Based on experience, Czero’s engineers identified specific challenges expected to affect the project timeline and budget, helping BEST navigate the inevitable unknowns in engineering R&D.

Advanced modeling & simulation

The project kicked off with detailed thermodynamic analysis and system simulation, focused on achieving ambitious compressed air energy storage efficiency targets. Working closely with BEST engineers, the Czero team performed in-depth analysis of individual components (compressor heads, valve train, rotating group, etc.), each energy-conversion step in the round trip, and the compressed air energy storage system as a whole. Czero wrote special algorithms to determine optimal operating points, discovering multiple opportunities to increase system efficiency.

Designing low-cost, long-life compressors with novel valvetrains

Compressor/expander machine life, cost, reliability and efficiency are crucial factors in making renewable energy profitable: energy stored as compressed air isn’t dispatchable if the expander is down for maintenance, and losing energy to inefficiency erodes profits.

So designing a robust, high-volume positive displacement compressor/expander for BEST required extensive integrated design and analysis, including computational fluid dynamics (CFD) and finite element analysis (FEA) to identify structural, vibrational and thermal stress points in order to preempt potential problems through smart design choices. Czero used a quick-turn iterative design process, with integrated analysis, to optimize the compressor/expander and quickly arrive at a first prototype demonstrating the project feasibility.

Expediting time-to-market

Czero also worked directly with suppliers to source and assemble the system components, now in testing in Colorado labs, to expedite BEST’s time-to-prototype. And that fast time to prototype means a faster time to market. BEST will field test the first of these systems in Hawaii early this year.

And even better for BEST, Czero R&D directly contributed to the development of new, patentable technology, adding to the 30+ national and international patents that BEST has to date.