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September 17, 2007

More on energy storage – Flywheel Batteries

Category: Flywheels – Dan 8:03 pm

Energy storage is the least talked about, and most challenging problem facing green energy today. There’s plenty of potential power from either wind or solar, but these sources are intermittent. What’s needed is reliable storage.

There are four broad general ways to store energy[1]:

  • Chemical, with batteries being the most popular form. But in truth all fossil fuels are, in effect, chemical energy stores, and storing hydrogen is another effective chemical means of storing energy.
  • Mechanical, which might be water pumped uphill, compressed gas, or kinetic energy in a flywheel.
  • Electrical, either capacitors or inductors.
  • Thermal, which is not particularly efficient but if your source is thermal (as with CSP), this might be a cost effective approach.

There’s clearly a lot of research going on around batteries, especially since they are suitable for any mobile application. Electric or hybrid cars rely on batteries, and alternatives (such as flywheels or compressed hydrogen) so far do not look nearly as promising. There’s also considerable research going into storing hydrogen.

One option that gets far less press are flywheels, which store energy in a disk spinning at high speeds. These are commonly called “Flywheel Batteries”. Currently traditional lead-acid batteries today have an advantage in terms of cost, but flywheels have far longer service lives (>20 years vs. 3 or 4 for lead-acid batteries), a wider range of operating temperatures, and high power density.[1]

25 kWh Flywheel from Beacon Power

Imagine for a moment the potential of combining a solar PV system with a modest flywheel battery with a 25 KWHr capacity. This combination installed in a small energy-efficient home would have the potential of providing nearly all of the power needed over a 24 hour period. Properly sized, the PV panels could provide sufficient power during the day to both power lights and electric appliances, and spin up the flywheel in the basement. Peak AC requirements would closely coincide with peak PV generation. When the sun goes down, load could be pulled from the flywheel battery. A grid connection covers any under or over generation during the course of the day.

What’s the advantage of such a system? There are several:

  • Near continuous power – The flywheel battery effectively extends the power generating time of the PV system, providing a nearly continuous power source.
  • Long service life – Both the PV system and the flywheel battery are virtually maintenance free and have >20 year service life given today’s technology.
  • Modular design – Both the PV panels and the flywheel batteries are produced as manufactured components that can easily be shipped to a site and installed. Need more capacity — add more units.
  • Local source – There are no transmission losses, because most of the power generated on site is used on site.
  • Grid Stability – From the grid connection’s perspective, the system is relatively stable. The combination of flywheel battery and PV panels means that the house can handle much of it’s own power regulation. Could these systems work off of the grid? Certainly, but having them on the grid provides advantages with local power regulation.

Flywheel batteries are manufactured today, but are primarily sold as short-term high current uninteruptable power supply sources to even out fluctuations in the grid. Some manufacturers include Tribology Systems, Powercorp, and Beacon Power.

What’s not to like? Cost is the primary objection, but as with PV systems, the prices are falling as quantity ramps up. 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August 29, 2007

Homes without heat?

Category: Efficiency – Dan 2:12 pm

Efficiency is the ugly stepchild of solving our energy woes. While solar panels and windmills are high profile and focus on alternative sources of energy, efficiency focuses on needing less in the first place. How dull.

How do you spice this up? How about the idea that you don’t actually need any home heating. What, you say? Maybe in moderate climates, but that’s not going to cut it in Minnesota! But the hotbed (no pun intended) of this technology is in Germany, which is anything but warm in the winter.

Germany has several home heading standards in place[1].

  • A “Low Energy House” (Niedrigenergiehaus) cannot require more than the equivalent of 7 litres of heating oil for each square meter of room for space heating annually (in US terms, 15,850 Btu/ft²/yr)
  • The German Passivhaus ultra-low energy standard, is set to less than 1/3 this level, with a maximum space heating requirement of 4,755 Btu/ft²/yr. These homes are generally built with no central heating system, because it’s not needed.

Compared with buildings that follow the 2003 Model Energy Efficiency Code in the United States, these ultra-efficient homes use 75% to 95% less energy for heating or cooling.

Yes, you say, but what are the costs of building this way. Data on this varies widely, but seems to be in the 3% to 8% range. The challenge (as I saw in one article) is that the developer is generally not the owner.[2]

What to do in the near term? When buying new homes, demand higher energy efficiency! Be willing to pay the additional costs. But more important, we need to lobby for higher efficiency standards and incentives for developers to implement higher standards. The US has just come off a massive housing construction boom, and the sad truth is that a majority of those homes were not particularly energy efficient.

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.

July 27, 2007

Mythbusters: What about Liquid Coal?

Category: Mythbusters – Dan 5:47 pm

Wow. There’s been so much press lately about liquid coal. Between “liquid coal” and “clean coal”, there’s almost a buzz, especially among non-technical people. Gee, this stuff sounds great.

OK, my analogy for “clean coal” is it’s as if you referred to sewage that’s had 90% of the feces removed as “clean water”. I suppose it would be legitimate to call it “cleaner“, but I can’t see anyone wanting to drink it.

Liquid coal, is in almost every way even worse. In the August 2007 issue of Scientific American, there’s an article that dispassionately goes down the many reasons.

  • One ton of coal produces only two barrels of fuel
  • Besides the CO2 produced while using the fuel, the production process creates almost a ton of CO2 per barrel.
  • MIT researchers estimate it will cost $70B to buile enough plants to replace 10% of US gasoline consumption.

The article concludes as follows:

The country would be spending billinos in loans, tax incentives, and price guarantees to lock in a technology that produces more greenhouse gases than gasoline does. This is unacceptable at a time when leading scientists from all over the world are warning that greenhouse gases must be cut by at last 60 percent over the next half a century to avert the worst consequences of global warming. Instead of spending billions to subsidize a massively polluting industry, we should be investing in efficiency and in renewable energy technologies that can help us constrain global warming today.

What’s the deal? Isn’t this obvious? Unfortunately, too many senators come from states where coal production is a major economic force, and a major campaign contributor. These members of congress talk (generally not understanding the technical details) about both “clean coal” and “liquid coal” being solutions. Know the facts here, folks. Not clean. Not smart. Liquid coal? Consider that the title of the SciAm article is “Worse Than Gasoline”…

The Rebound Effect

Category: Efficiency – Dan 4:32 pm

Now here’s a challenge. In the recent issue of Scientific American, there’s an article about the “rebound effect”. This is something straight out of Economics 101: “If prices decline, consumption will increase”.

When applied to efficiency, what this means is that, as energy consuming devices, like cars and our homes, become more efficient, will we drive more and turn up the heat? Studies listed in the article had conflicting results, but the conclusion was that indeed there was some rebound effect. The article concludes, in part, by stating:

To compensate for the rebound effect, energy efficiency must be couples with other policy solutions to lower emissions.

On a parallel thread, I’ve seen some companies, or companies-to-be working on solutions to this of another kind. Some of the contestants in the 2007 CleanTech competition are working on ways to make your energy consumption more visible. Primarily at the home level, these folks are looking to provide a real-time monitor for your home’s resource consumption, be it gas, electricity, or water. In the presentation at the most recent CleanTech event on green building, one of the speakers mentioned a case were simply by posting daily energy use on the bulletin board of a college dorm, that day by day the usage fell as awareness grew.

So maybe the answer to the Rebound Effect is better awareness. Instead of simply seeing the monthly bill, you see a red light on the wall every time you’ve left too many lights on, regardless of how efficient they are. Food for thought.

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.