Tom Murphy is an associate professor of physics at the University of California, San Diego.  His blog, Do the Math, takes an astrophysicist’s-eye view of societal issues relating to energy production, climate change, and economic growth.

With the exception of tidal energy, our focus thus far has been on land-based energy sources. Meanwhile, the ocean absorbs a prodigious fraction of the Sun’s incident energy, creating thermal gradients, currents, and waves whipped up by winds. Let’s put some scales on the energetics of these sources and see if we may turn to them for help. We’ve got our three boxes ready: abundant, potent, and niche (puny). Time to do some sorting!

Thermal Gradients

Wherever there is a thermal gradient, our eyes light up because we can create a heat flow across the gradient and capture some fraction of the energy flow to do useful work. This is called a heat engine, the efficiency of which is capped by the theoretical maximum (T_h − T_c)/T_h, where “h” and “c” subscripts refer to absolute temperatures of the hot and cold reservoirs, respectively. In the ocean, we are rather limited in how much gradient is available. The surface does not tend to exceed 30°C (303 K), while the depths cannot get much cooler than 0°C (273 K; pressure and salinity allow it to go a few degrees negative). The maximum thermodynamic efficiency therefore tops out at 10%, and in practice we might get half of this in a real application. The general scheme of producing energy from thermal gradients in the ocean is called ocean thermal energy conversion (OTEC).

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The Future of the Electric Grid was published this week by the MIT Energy Initiative.  The 268 page report aims to provide a comprehensive, objective portrait of the U.S. electric grid and the challenges and opportunities it is likely to face over the next two decades.  It also highlights a number of areas in which policy changes, focused research and demonstration, and the collection and sharing of important data can facilitate meeting the challenges and seizing the opportunities that the grid will face.  The report shows that with new policies, the electric grid in the United States could handle the expected influx of electric cars and wind and solar generation.

Much of the report relates directly to developments in the San Diego region.  Chapter 5 is about The Impact of Distributed Generation and Electric Vehicles.  Chapter 8: Utility Regulation touches on the current challenge in San Diego to have a rate structure for distributed generation which is equitable for all parties.

(From page 182 of the report), “The distortions caused by these implicit subsidies rise with the penetration of distributed generation and with energy conservation more generally.  Consider, for example, proposed “zero net energy” buildings: if network costs continue to be recovered on a per-kWh basis, these customers could in theory receive all the benefits of being connected to the grid, drawing and injecting power on demand, while paying little or nothing toward the cost of the system or the option to use the network.”  Of course, the opposite side of the issue is also compelling.

Click here for the complete report and here for the abstract.

The multidisciplinary effort of the MIT Energy Initiative to generate The Future of the Electric Grid included economists, engineers and, of course, graduate students from MIT and from without.  Click here for an excellent video of the introductory presentation by the study c-chairs of the report. 

The last two sections of the report include a useful Glossary plus a list of Acronyms and Abbreviations.

Over the Fourth of July weekend while I was in Ohio for a family get-together I had the thrill of seeing a barge of wind turbine towers being towed up the Ohio River at Ripley, OH.  Where they came from and where they went remains a mystery to me.

About 200 miles up-river from Ripley, construction has begun on a new hydroelectric power plant in St. Marys, WV.  Previously I was under the impression that we had seen the last of new hydroelectric facilities in the U.S.  Most of the good sites for hydro plants have been taken.  Under current environmental and seismic regulations most of the hydroelectric dams constructed in the last century could not be built today.  Environmental groups have opposed hydroelectric projects that put new dams on bodies of water.  However, 350MW of new “run-of-the-river” hydroelectric generation plants will be built on the Ohio River to harness the energy of water flowing over existing dams.  Since no new dams or reservoirs are required the usual impediments to project development are side-stepped.  Click here for the full report.

Facing Kentucky, Ripley, OH is a one hour drive up-river from Cincinnati.  The town was an early stop on the Underground Railroad, a network of citizens helping slaves escape north to freedom. A number of prominent abolitionists lived in the town in the 1800s, mainly on Front Street near the river.  My sister and her husband have restored the Thomas Collins house which served as a hiding place for slaves escaping to Canada.  The character Eliza in Harriet Beecher Stowe’s book, Uncle Tom’s Cabin, was inspired by a slave woman who crossed the frozen river to Ripley in 1838.

This morning I participated in the latest CleanTECH San Diego SCRUB session.  SCRUB is an opportunity for early stage clean tech companies to present their business story to a group of CleanTECH San Diego members.  Three local emerging clean tech ventures made their case this morning to a panel of 28 CleanTECH San Diego members representing a mix of venture capitalists, engineers, marketing specialists, intellectual property attorneys as well as local leaders from industry, research and government.  The objective of SCRUB is to provide immediate feedback and assistance to take each company to the next stage. 

Today’s SCRUB showcased three distinctly different clean tech businesses.  Marine Power Partners has developed a patent pending waterwheel that generates continuous base-load electricity from flowing water at lower capital and operating costs than either solar or wind systems.  A Smart Grid innovator, On-Ramp Wireless, is a systems provider for low-power wide-area scalable sensor networking and location tracking.  New Leaf Biofuel collects waste cooking oil from 1,100 San Diego restaurants to manufacture biodiesel, which is used to fuel diesel vehicles with little or no conversion. 

In the past four quarterly SCRUB sessions CleanTECH San Diego has provided advice, introductions and critical evaluations to fourteen future clean tech stars.  If you have a clean tech enterprise that would benefit from a good SCRUB you can submit your request to CleanTECH San Diego today.