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August 11, 2007

Clean energy – Reaching a tipping point?

Category: Alternative Power – Dan 9:31 am

I just finished reading an article on RenewableEnergyAccess by Ron Pernick that took a very positive viewpoint of the sea change with alternative and renewable energy.

[Clean energy sources] will they represent the highest growth and innovation opportunity in the energy sector and double-digit chunks of our energy infrastructure…

He quotes a number of statistics to back up this viewpoint:

  • PV – In 2003 the solar industry was valued <$5 billion globally with ~600 MW of solar manufactured worldwide. By 2006 that number had more than tripled to nearly $16 billion with more than 2 GW of solar manufactured globally.
  • Wind – In 2003 new isntalled generation was about 8,000 MW worldwide. THis nearly doubled to more than 15,000 MW in 2006, and last month T. Boones Pickens announced plans for a 4,000 MW wind power plant (equal to the total annual global install less than a decade ago) and FPL announced that it will develop 10,000 MW of new wind power projects between now and 2012.
  • China has a new renewable energy law is targeting 120 GW (that’s equivalent to 200 or more coal fired plants) of new renewable energy generation capacity by 2015.

Ron closes his story with this conclusion:

As I look out over the next 5-10 years I’m confident that the most important development in the clean-energy sector will be the scaling of manufacturing, systems integration, and equally important, technology deployment. Millions of jobs and billions of dollars will be generated in the process if policymakers, investors, corporations, and innovators get this right.

Let’s do what we can to get U.S. policy makers behind this, so that the U.S. can join the rest of the world in helping drive this innovation and adoption!

August 6, 2007

Why isn’t there more Solar Thermal?

Category: Solar Thermal – Dan 6:06 pm

In terms of what you can do at home to make a difference, one of the top items on the “more expensive but worth it” list is solar thermal — essentially hot water generated by rooftop collectors.

We like our hot water. We talk about taking a “long hot shower”, we rely on it to clean our clothes and dishes. A typical family of four uses an estimated 65 to 75 gallons of hot water per day[1]. According to an article by the Renewable Energy Resource Center in Vermont:

By installing a solar water heater, a family of four, who currently use an electric water heater and consume an average of 80 gallons of hot water per day, will prevent 3,400 pounds of greenhouse gas emissions each year. This represents a reduction in household greenhouse gas emissions of 20% or more for a typical household.

If the goal is to achieve 80% reduction in greenhouse gases by 2050, that requires a 2% reduction per year. So solar hot water can buy you the first 10 years down this path. The investment can range from $3,000 to perhaps $10,000, depending on if it’s for new construction or a retrofit, and depending on the size of the installation.

How does Solar Thermal work?

Solar thermal is one of the simplest green technologies. Basically, you pass water through a collector on the roof during the day. Whenever the sun is shining (and really whenever it’s relatively bright outside), the collector heats the water. This water is then stored in a tank for later use. Depending on the configuration, the solar portion of the system could be the only source of heat (if the tank is large and the collector is sufficiently large relative to the daily demands), or a traditional water heating system is provided to boost the heat from the solar system to acceptable levels.

Why is the US so far behind?

The US investment in solar thermal collectors is incredibly small. Look at this chart of data from the German Solar Energy Industry Association for 1999 installations (m2 of collectors):

Country Total Per Person
China 4,000,000 3.09
India 2,000,000 1.92
Japan 1,000,000 7.84
Europe 890,000 1.23
South Korea 500,000 10.55
Turkey 430,000 6.27
Israel 400,000 63.46
USA 25,000 0.09

How depressing. And while I fear China’s ongoing construction of coal fired facilities, you have to admit that their investment in solar thermal is impressive. But it’s not limited to developing countries like India and China, and it’s not limited to mid-latitude countries like Israel or Turkey.

I’d postulate three reasons why the US is so far behind here:

  • Cheap energy – Why worry about additional stuff in your house when gas and electricity is inexpensive.
  • Lack of policy – We don’t have any incentives to encourage developers, homeowners, or businesses to invest in solar thermal.
  • Lack of feedback – Those homeowners who do have solar thermal systems don’t get any sense of how well it’s working, or how much money they are saving by having it.

Installing Solar Thermal

If you can afford the investment ($3K to $10K, depending on your home and size), where do you go and what can you do? Here are several leads for systems:

  • Heliodyne Inc has been manufacturing solar thermal products for 30 years, primarily flat plate collectors and heat transfer appliances. They sell both components and off-the-shelf packaged systems ranging from smaller residential systems to large pool or commercial heating systems.
  • Alternate Energy Technologies, LLC manufactures flat plate solar thermal collectors and fully integrated solar hot water systems for medium and high-temperature commercial, industrial and residential applications. They have a nicely integrated system that reduces the number of overall components and therefore the installation costs.
  • Conergy is a supplier of flat panel collectors and systems for domestic hot water, space heating, and pool and spa heating. Their applications include use of solar powered water pumps to ensure reliability and eliminate dependence on grid power for their operation.

There are many more. You can find companies like this at, or by doing Google searches.

June 27, 2007

More on Geothermal

Category: Geothermal energy – Dan 10:52 am

I’ve ignored geothermal in the blog for some time, so it’s time to make up for that. I just read an article in Technology Review titled “Abundant Power from Universal Geothermal Energy“. The article is essentially an interview with Jefferson Tester, professor of chemical engineering at the MIT Laboratory for Energy and the Environment.

Here are some of the key points Tester touches on:

  • Plenty of energy – The available energy in theory exceeds 100 million quads (a quad is one quadrillion BTUs). Even if you could only tap 1/10th of 1%, that’s still 100,000 quads or 250 times current world energy use of about 400 quads.
  • Available almost everywhere – New oil-field stimulation technology should make it possible to tap this energy by creating artificial geothermal reservoirs many kilometers underground.
  • Key advantages – Because the resource is widely distributed, Tester talks about this as “universal geothermal” energy because the reservoirs could be created near high-demand locations. In addition, the power would be on tap 7×24, and work like current base power sources like coal and nuclear.
  • Technology getting there – Much of the required technology is coming from research into extending oil production and tapping oil shale deposits. Tester says “we know how to create the reservoirs”, and now “we need to connect them better, to stimulate them better than we have in the past using some of these hydraulic methods and diagnostics that are now available to us”.

The challenge here, of source, is more economic than technical. Current geothermal technology takes advantage of naturally occurring reservoirs of hot water in places llke Iceland or the Geysers (in California). It will take considerable investment to build the first few plants. As the price of oil rises, and when we (hopefully) get carbon trading or a carbon tax in place, these investments will start to make sense.

Hybrid Power Solutions

One challenge for solar and wind sources is that they are intermittent — power is only generated when the wind blows or the sun shines. Utilities prefer what they call “firm” power — essentially power that is comes with a future delivery commitment. Because wind and solar are intermittent and the available power may not be known in advance, utilities are sometimes reluctant to assign capacity values to these sources. The result is utilities often don’t consider solar or wind output as firm[1].

This is not a major technical problem today, since these intermittent sources constitute only a fraction of the total electricity provided to the grid. Indeed many experts believe that these sources could exceed 20% of all power on a grid and still be manageable[2]. It is unfortunately still a perception problem however, and sometimes and institutional problem.

There are at least three solutions that help mitigate the fact that renewable sources are often intermittent. I’ll classify all of these as hybrid solutions, although what is being combined is different in each case.

Matching source to use

One approach is to co-locate intermittent power sources with applications that don’t need a firm power source. Such applications include water treatment, water pumping, desalinization facilities, some energy-intensive industrial facilities, and so forth. Consider water pumping; indeed the dutch have using wind power to drain their polders since the 16th century. The point here is that not every energy consuming activity has to be done right now. One reason that a number of these hybrid solutions are associated with water is that the demand for that water is also intermittent, so storing water for later use is common, and nicely complements that fact that your energy supply is also intermittent.

Source/demand synergies

To some extent, this is similar to the above point on matching source to use. Given that peak demand for electricity in warm sunny regions (for air conditioning) coincides almost exactly with peak output from photovoltaic and concentrating solar power sources, these become perfect complements to provide incremental supply when it’s most needed.

Hybrid energy sourcing

Another approach to this issue is to match an intermittent source to a controllable alternative source. This is commonly proposed as an approach for concentrating solar power (CSP). By pairing up CSP with natural gas (which is a relatively simple technical extension as the gas could heat the same working fluid as the solar energy), you can convert CSP into a firm source that essentially behaves like an ultra efficient gas plant. Not, strictly speaking, a renewable energy source, but better than pure gas-fired electricity.

What hasn’t been explored to any extent is hybrid solutions using paired renewable sources, such as wind and geothermal. This likely requires geothermal power technology to move ahead further (it’s still relatively expensive for most locations), but such combinations would provide the best of all worlds, and serve as a long term power source with virtually no negative environmental impacts.

June 19, 2007

NREL “Wind to Hydrogen” Facility

Category: Hydrogen,Wind power – Dan 6:31 am

NREL (the National Renewable Energy Lab) recently published information on their new experimental “Wind to Hydrogen” facility. This is an idea that has been promoted for some time by the Leighty Foundation, and it’s a clear example of “Smart Green Energy”.

The challenge: Wind power is intermittent. The solution: Use unneeded power to generate hydrogen which is stored on-site. This hydrogen is then converted back to electricity in a fuel cell when the wind isn’t blowing and power is needed.

“By marrying wind turbines to hydrogen production, we create a synergy that systematically reduces the drawbacks of each,” Richard Kelly, Xcel Energy chairman, president and CEO

While mobile hydrogen storage is a problem (see “Mythbusters – Hydrogen will fuel our cars?“), there’s no problem with industrial-scale hydrogen storage, especially where wind power is generated (which by it’s nature is out in the wide open spaces).

NREL’s Wind2H2 project is designed to analyze the tradeoffs using different types of wind generators, different approaches to convert the electricity to hydrogen, and issues related to the integration of these technologies as well as the operation of electrolyzers with different gas output pressures.

The NREL site also has a very cool animation to show the different configurations being tested.NREL “Wind to Hydrogen” Animation

What about geothermal power?

Category: Geothermal energy – Dan 6:11 am

Geothermal is a seldom discussed alternative source of power. Yet there is a vast potential geothermal energy resource located as heat in water and rocks at drillable depths of about 2 to 6 miles[1]. Interest in geothermal comes and goes. Just this past week, U.S. Rep. Jerry McNerney, (D-Pleasanton CA), is sponsoring a bill that would support the development of geothermal power[2].

This figure shows the geographic distribution of geothermal energy potential across the continental US at a depth of 6 km. Geothermal distribution in the US The best potential is in the more geologically active intermountain west. Data from the ASES shows that there is theoretical potential to supply all of US energy needs (total US demand in 2003 was about 98 quads, whereas the potential geothermal resource storage is about 14 million quads). So the good news is that even low geothermal energy recovery could displace substantial fossil fuel use. Geothermal has a second advantage because, unlike the wind or the sun, the resource is always available. In effect, we don’t have to figure out how to store the energy resource, because it’s already stored within the earth.

“Unlike other environmentally friendly sources, geothermal energy does not depend on wind or sunshine. This system can provide an uninterrupted supply of electricity, day or night.”
Jeff Tester, professor of chemical engineering at MIT

The challenge is making productive use of this energy. As with wind and concentrating solar, much of the resource is “stranded”, that is the best geographic locations are far from the demand (not to mention that it’s several KM deep!). And while the heat reservoirs within the earth are vast, it mostly constitutes low-grade heat that is harder to utilize.

17 geothermal technology specialists recently performed a study of geothermal potential on behalf of DOE’s Geothermal Technologies Program. The resulting report estimates that 2% of the energy could be recovered as electricity with current stimulation, drilling, and energy conversion technologies, assuming that these technologies advanced further to cut costs. At this 2% level, the study estimates that as much as 2.4 terawatts might be generated over the long term – easily enough to retire all the coal plants in the US. In the mid term (40 or 50 years), the study concludes that 100 GW (about 200 500MW coal plant equivalents) is feasible. This estimate takes into account practical implementation problems with geothermal technology.

While geothermal has the advantage of being a constant (vs. intermittent) power source, it needs much more research and early investment to become a proven alternative to traditional sources. It’s encouraging to see that this is becoming part of the energy proposals in congress, and with luck and support we may yet see a comprehensive energy bill that includes this promising and complementary source as part of the package.

June 2, 2007

Local vs. Regional vs. National Sources

Category: Alternative Power,General – Dan 9:24 am

I just spent 2 days in New York City. It’s quite a stark contrast in some respects (at least from an outsider’s viewpoint), because the SF Bay Area is so conscious about energy efficiency and alternative sources, whereas you find plenty of incandescent lights powered by coal fired plans in New York.

Yet in some ways, New York City is inherently efficient. The population density is high, and the city so crowded that car travel is impractical so vast numbers of people ride the subway or walk to work. Indeed according to the “Inventory of New York City Greenhouse Gas Emissions” report, carbon emissions measured per capita are only 7.1 metric tons per person in New York, less than San Francisco at 11.2 metric tons and far below the national average, at 24.5.

From an energy source standpoint, however, New York is not a place where power will come from rooftop solar cells and backyard windmills. I’ve been to meetings where concepts like Community Choice Aggregation are discussed, and often (maybe a bit too often), the idea that every community should strive to be energy independent is raised. While nice in concept, there’s a reason why people, communities, and nations trade, and energy is another commodity that is often best produced in one location and moved to where it is needed. Indeed in a recent Stanford Magazine an article titled “A Crude Awakening” looked at the issue of national energy independence, and concluded that while oil addiction is a threat to national security, a “go it alone” attitude is even worse.

I agree that calling the problem “energy dependence” and therefore seeking energy independence is the wrong way to think about this problem. Talking about energy independence feeds the xenophobic impulse that occurs all too easily in American politics. And it suggests to other countries that they should seek independence rather than a more cooperative approach.

In practical terms, smart green energy solutions need a mix of local, regional, and national energy sources. When it is possible and practical to use local solar and wind resources, it makes tons of sense; local sources don’t require long distance (and inefficient) energy transmission, and they create some redundancy in the system that reduces the effect of outages and supply disruptions.

But at the same time, the vast wind resources in the midwest, the untapped solar potential of the southwest, numerous geothermal sites, and other sustainable sources can and should contribute to the overall national energy picture. Cities like New York will never be “energy independent”, nor should they. National energy policy should take into account these regional and local differences, and create a framework for smart and often very different solutions can thrive.

May 29, 2007

Categorizing solutions

Category: Alternative Power – Dan 12:21 pm

Here are some ideas for general categories for smart green energy solutions:

  • Local solutions – Technologies like photovoltaic cells and ground source heat pumps are inherently local in nature. It makes the most sense to employ these right where the energy use will take place. Local sources don’t require (and don’t incur the costs) of energy transmission, and they are inherently more secure than centralized industrial-scale facilities.
  • Transportation solutions – Energy for transportation must consider that the energy use (primarily creating motion) means that the energy supply must be portable. Transportation solutions must combine high efficiency with high density fuel sources and/or infrastructure that facilitates using stationary sources in some fashion.
  • Solutions for stranded energy resources – Both wind and concentrating solar power have vast potential to supply electricity at an industrial scale. But these sources are generally far from the demand (hence the industry term “stranded”). Solutions here must combine these sources with technology for energy transmission and storage, to make the energy available when and where it is needed.
  • Efficiency – Regardless of the energy source, efficiency is now the least expensive source of power in many (most?) cases.

This categorization scheme will be used in the next few posts to look at workable solutions in each area.

April 19, 2007

Ethanol? Good? Bad? Ugly?

Category: Ethanol – Dan 9:29 pm

While hanging out at the Sierra Club’s booth at last weekend’s Step It Up event in San Francisco, someone asked me “Can you explain the deal with Ethanol? Is it a good idea or not.”

As with many things, the answer is “it depends”.

Drawing from “” (the industry group promoting corn-based ethanol):

Ethanol is a clean-burning, high-octane fuel that is produced from renewable sources. At its most basic, ethanol is grain alcohol, produced from crops such as corn. Because it is domestically produced, ethanol helps reduce America’s dependence upon foreign sources of energy.

Ethanol is grain alcohol, the same alcohol, in pure form, that you get from fermented grapes, wheat, potatoes, or rye. Instead of mixing it with water, it’s mixed with gasoline.

There’s two issues to discuss here. First, why do we care about ethanol. And the second, how do you make it.

Why do we care about ethanol?

Ethanol, like gasoline and diesel, is a high energy density liquid fuel. It’s a potential substitute for gasoline to power our vehicles. And unlike diesel or gas, it’s made from biomass. The theory here is that growing plants uses the energy of the sun to take CO2 out of the air and convert it into biomass, you then convert the biomass into ethanol, and you essentially have a carbon neutral energy source.

This is the big appeal of ethanol. That said, it’s not a perfect fuel by any means:

  • It has a lower energy density than gasoline or diesel (roughly a third less). If you got 300 miles on a tankful with gas, you’d only get 200 miles on a tank of ethanol.
  • Ethanol is not compatible with some fuel system components. This is one reason that cars need specific adaptations to use E85 fuel
  • Ethanol absorbs water, whereas gas and diesel do not. Most existing petroleum pipeline are (surprisingly) not water free (water is heavier, and can collect in low spots). Putting ethanol or gas/ethanol mixtures in these pipes causes the water and other contaminants to be taken up by the fuel. Consequently, ethanol today is transported by truck, not pipeline.[3]

OK, not perfect. But a reasonable choice for a liquid fuel based on renewable biomass.

How do you make ethanol?

In the US today, ethanol is almost synonymous with corn. But corn has two issues: first it’s a relatively water and energy intensive crop to grow, and second we currently only produce ethanol from the grain. The result is that it takes nearly as much energy (mostly fossil fuel energy) to create the ethanol as you get from it[4]. I guess you could call this dumb green energy.

Brazil is also making large investments in ethanol, but it’s based on using Sugar Cane. The overall energy yield is roughly 8 times what you put into it, making this a much greener source of liquid fuel.

But to really make ethanol successful, one needs to look at what crops yield the most potential fuel per acre for the least input of energy and water. Here are some choices:

Crop US Gallons/acre
Miscanthus 1500
Switchgrass 1150
Sugar Cane 662
Corn 370

This is why switchgrass is often mentioned as the long term ethanol feedstock. The challenge is in making production from non-starch based sources. The term for this is cellulosic ethanol. Much work is now being done to generate ethanol from these alternate sources, and if this can ramp up to an industrial scale, then ethanol has great promise as a future liquid fuel.

March 19, 2007

The solar variety show

Category: Concentrating Solar,Photovoltaics – Dan 7:38 am

Like many people, what I knew about solar power was limited, and in particular was limited to knowing about flat panel solar collectors. Oh, and one article that I’d read years ago about a “power tower” being built somewhere in the southwestern US with a bunch of heliostats (sun tracking mirrors).

Turns out that solar is an area with not only vast potential, but extensive innovation on a number of different approaches to turning solar energy into useful power. Here’s my list:

  • Flat panel technologies – All flat panel technologies have some key characteristics. They do not require direct sunlight, and generate energy regardless of where the light source is located. As a result, they don’t need to track the sun (although efficiency will be higher if they do), and they generate some power even on cloudy days. There are several types of flat panel collectors:
    • Flat panel crystalline silicon solar cells – These are what most people think of when they think solar. Cystalline silicon is grown into rods, which are sliced into wafers that form the cells. Arrays of the cells are built into flat panels.
    • Thin film technology – The high cost (both dollars and energy) of crystalline solar cells prompted development of a new approach where thin films of semiconductor materials are deposited. Although these generally have lower efficiencies than crystalline cells, the costs are also significantly lower, both in terms of manufacturing the active material, and in terms of the required support structures (thin film cells are much lighter). Thin film cells are also flexible, and can therefore be bonded directly to roofing materials; an example of this is the BIPV Solar Electric Roofing produced by SolarIntegrated.
    • Non-traditional photovoltaics – There is a new generation of semiconductor solar cell devices that work differently than the above two options. Companies doing this development include Konarka Technologies, Nanosolar and Nanosys.
  • Concentrating Photovoltaics – If the most expensive component of a traditional solar cell is the collector itself, then why not use mirrors or lenses to concentrate sunlight on the collectors. The advantage of this approach is lower costs. This does, however, make it more important that the collectors track the sun, and this technology clearly works better in southwest locations that have relatively cloudless skies. Companies working on concentrating photovoltaics include SolFocus, Silicon Valley Solar, and Sharp Electronics.
  • Solar Thermal Technologies – If what you need is heat and hot water, why go to the trouble of converting sunlight to electricity? This is the theory behind various solar thermal technologies. Solar thermal has been around for generations, and unfortunately this seems to be the unglamorous stepsister of solar technology. Solutions range from basic arrays of black tubing on the roof to help heat swimming pools, to modern sophisticated devices using glass evacuated tubes coated with advanced materials and integrated with ethanol-filled heat pipes. This is worth an entire article, so I won’t write more here.
  • Concentrating solar power – If you think big, it’s possible to create facilities that gather sunlight over a large area to create high heat that then is used to generate electricity. The three primary types of facilities here are:
    • Parabolic Trough – Long parabolic trough-shaped mirrors focus sunlight on tubes that heat a fluid to well over 500 degrees F; this heat creates steam to power a turbine generator and produce electricity.
    • Power Tower – A circular array of sun tracking mirrors focus sunlight on a central receiver on tower, heating a fluid which powers a generator.
    • Dish Engine systems – A mirrored dish focuses sunlight on a stirling heat engine at the focal point that directly generates electricity.