Waste Heat to Power as a Carbon Stabilization Wedge
How a small investment in waste heat to power can drive huge carbon savings
Our climate is already changing. With the backdrop of the COP21 climate talks in Paris this week the question still remains: how do we mitigate climate change going forward?
In 2004, Steve Pacala and Rob Socolow published the idea of “carbon stabilization wedges,” or eight approaches that, together, could stabilize the climate through reducing global carbon emissions by 1 billion tonnes each by 2050. The wedges included energy efficiency, solar, wind, and nuclear, among others — all important approaches that individually cannot do the entire job. Much has been argued since then about how these approaches are falling short and whether we need more wedges to tackle emissions.
Enter waste heat to power.
Waste heat is one of the most abundant untapped resources on the planet. Exhaust from industrial processes like factory furnaces and compression engines, as well as exhaust from vehicles, is so plentiful that turning the heat from this exhaust into electricity with presently available technology can comprise a carbon stabilization wedge on its own.
Executing on installing waste heat to power capacity globally is not as daunting as it sounds, in part because exhaust from industrial processes is on nearly all of the time. This subtlety has far-reaching consequences for the economics, and therefore adoption and ultimate total carbon reduction, that waste heat can yield.
In the electricity world we call “being on” the “capacity factor.” Waste heat is a renewable resource with 80–100% capacity factor. Solar power’s capacity factor is 25.9% on average worldwide (think of this as the fraction of the year that the sun is shining brightly), and wind power’s capacity factor is about 34% (the fraction of the year the wind is blowing significantly). A much smaller installed capacity of waste heat to power generation could generate as much electricity and offset as much carbon as solar. See the table below for an example analysis.
What this means is that, in the U.S. for example, we only need to install 6.5 GW of waste heat to power to match the yearly carbon emissions savings from solar — much smaller than the currently installed 22.7 GW of solar, most of which was installed in the past 5 years. Installing 6.5 GW of waste heat to power is achievable quickly if the effort is made.
We already have 0.77 GW of installed waste heat to power capacity in the U.S. industrial sector alone, mostly in the form of combined heat and power systems. Starting with this as a global baseline — a conservative assumption, since there is plenty of waste heat to power outside the U.S. — and assuming a mere 10% growth rate (contrast this to solar’s ~25% recent historical and projected growth rate), the world could achieve an entire 1.14 billion tonnes of CO2 savings by 2050.
What will make waste heat to power grow at a rate that we need — 10% annually overall, and faster for the newest technologies? New business models that are opex- rather than capex-driven, like leases and power purchase agreements that have done solar so well, can also do the same for waste heat to power. Technologies that have just reached commercial viability in the past couple years, like the PowerModule™ from Alphabet Energy or organic Rankine and CO2 cycles from various startups, generate power at similar scales (10–100 kW) to residential and commercial solar systems and therefore can benefit from financing-type business models similar to Solar City’s.
In the U.S., both House and Senate legislators have introduced the Power Efficiency and Resiliency Act (POWER) Act that would add waste heat to power to the list of renewable technologies that qualify for the 30 percent federal investment tax credit. More government efforts worldwide can help drive adoption.
Most importantly, waste heat to power can now see rapid adoption because its economics make sense. Payback times can be as low as one year and rarely more than five. Installed costs are currently $4–6/Watt — a very low number when the capacity factor is accounted for. At 90% uptime, a $6/Watt installation that lasts 15 years (like with solar, there are no ongoing fuel costs) yields an 8.7¢/kWh cost of electricity: on par with wind, and cheaper than solar.
In order to achieve over 1 billion tonnes of CO2 savings from waste heat to power by 2050, at an average cost of $4/W, a total investment of US$188.5 billion will be needed in 2015 dollars, cumulatively. US$270 billion was invested broadly in renewables in 2014 alone.
The world needs climate stabilization wedges that are executable and make sense economically, not just environmentally. Waste heat to power is now one of them.