– Source for quality information on efficiency, conservation, and clean energy

June 27, 2007

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

March 1, 2007

Mythbusters – Windmills vs. birds

Category: Mythbusters,Wind power – Dan 1:30 pm

A week ago, I caught the lead in to a conservative talk radio show. The commentator led in with an attack on windmills, and how “the environmentalists hate these things because they slaughter birds”. This business of windmills killing birds is repeated over and over as a reason why the nation, and especially the environmental community, should oppose windmills.

Since windmills are one of the most promising near-term renewable energy technologies, what’s the latest information on bird mortality? I want to approach this issue from two angles:

  • How bad is the problem?
  • Compared to what?

How bad is the problem?
The majority of controversy over bird mortality from windmills comes from early experiences at the Altamont Pass, a couple dozen miles east of San Francisco Bay. This was an early wind farm, and more than 5,000 turbines now dot the hillsides. These turbines are “believed to kill more birds of prey than any other wind farm in the world”[1].

It turns out that the Altamont Pass is a terrible place for a wind farm. After much study, reasearchers have concluded that Altamont Pass has a large bird population because of an abundance of prey:

The problem, many researchers say, begins with the abundance of small mammals in the area. “Altamont is a ground-squirrel refuge extraordinaire,” says Allen Fish, director of the Golden Gate Raptor Observatory. The plentiful mammals, combined with the mild California climate, attract large numbers of migrant and resident raptors; the area also has the highest density of wintering golden eagles observed anywhere in the world. Younger hawks and eagles, eager to hunt and build muscle and thus most enthusiastic about the fine dining available on the ground, seem especially prone to blunder into the moving turbine blades.[1]

All this said, there’s no controversy that windmills kill birds and bats. The solution to minimize the impact is careful siting studies, and avoiding areas where it will be a particular problem.

But there’s another dimension to this discussion…

As compared with what?

Yes, windmills kill birds. And as we build more windmills, the mortality rate will rise. But if we’re concerned about windmill caused bird mortality, we have to consider other man-made hazards to birds that we take for granted[2]:

  • Power lines are estimated to kill 130 to 174 million birds per year.
  • Collisions with cars and trucks are estimated to kill between 60 and 80 million birds per year.
  • Plate glass windows, especially in tall buildings and rural homes, are estimated to kill over 100 million birds per year.
  • Lighted communication towers are estimated to kill 40 to 50 million birds per year.
  • Pesticides are “conservatively estimated” to kill at least 67 million birds per year.
  • Cats kill millions of birds. A Wisconsin DNR study states that the “most reasonable” estimate is that cats kill about 39 million birds per year in Wisconsin alone.

These statistics are depressing, but my point is that windmills shouldn’t be singled out as a new and unique threat to birds. Indeed the article points out that the likely biggest man-made hazard are communication towers, and mentions one documented case where “a record 30,000 birds were estimated killed on one night” at a tower in Eau Claire, WI.

The bottom line. Yes, windmills kill birds. But the #1 threat to birds, and bats, and a host of other species, according to Birdlife International, is habitat destruction:

Habitat destruction and degradation threaten over 86% of GTBs and are currently the most serious pressures on the world’s birds. Over-exploitation and the effects of alien invasive species are also major threats and others – notably pollution and climate change – are of increasing concern. Some of these threats can be reversed, given enough resources, but others are difficult to combat and can become the final cause of extinction for species that are already reduced to tiny numbers.[3]

I’m not saying that the fact that windmills kill some birds is a good thing; we need to take measures to reduce the impact. But if committing to wind power reduces the impacts of global warming, strip mining, and air pollution, it’s the superior alternative by far.

For a more in-depth analysis of this overall topic, see the article on the Wind Energy Technical Info website titled Putting Wind Power’s Effect on Birds in perspective.

February 26, 2007

Wind power wimpy? NOT

Category: Wind power – Dan 10:07 pm

Critics use a variety of ways to discredit the potential contribution of wind power. Consider this text on the front page of

“As people start to examine whether such impact is justified, they find that the promoters of big wind are unable to show even minimal benefit. Despite decades of experience and substantial installations in Denmark, Germany, and Spain, the giant turbines have not been shown to reduce the use of other fuels — such as coal and nuclear, let alone gasoline and heating oil — or thus to reduce carbon dioxide emissions that contribute to global warming or pollutants that cause acid rain and health problems such as asthma.”

Wow. Sounds depressing. How then, can Denmark product 18%[1] of their electricity with wind and Spain over 6%[2]?

The fact is wind power has come a long ways. A single wind generator can exceed 2 MW, and a wind farm with 300 windmills can match the output of a typical coal-fired generating facility.

Wind power is variable, and critics will argue this is a reason that wind can never be significant. Yet there are several factors that mitigate this issue:

  • While one windmill may be quite variable, a wind farm will average out the variations.
  • While the power output from one wind farm will rise and fall with the available wind, multiple farms in multiple locations balance this variation to some extent.
  • Wind isn’t the sole source of energy. When other sources such as biomass, hydropower, and natural gas are added to the mix, a modern power grid can efficiently utilize power from wind sources.

Wind power today is the fastest growing source of renewable energy. Why? In the words of Javier Garcia Breva (recent director general of the Spanish Institute for Energy Diversification and Saving, a part of the Spanish government):

“…at the first analysis, the renewable energy plan has focused on increasing energy independence in Spain.” with a second goal of reducing carbon dioxide emissions in line with the goals of the European Union.[2]

Cost is also a driver. Wind power is already competitive in many locations at about 4 cents per kWh and are expected to drop to under 3 cents per kWh by 2030.[3]

But what about the viewscapes that will be destroyed? What about the birds that will be killed? These will be topics for a later post!