In a Pike Research webinar held at the event, Andres Carvallo, the chief strategy officer of smart grid network software provider Proximetry, noted that the smart grid has “reached the teenage years” and is “still evolving.” As it grows up and reaches its full potential, I’ve put together five important ways in which how we interact with our utility can be revolutionized and why they matter.

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• What the utility of the future looks like
• Green IT Q4: solar, subsidies and the outlook for EVs
• Cleantech, meet connectivity: a new era of energy efficiency

Data centers are increasingly requiring energy capacity of close to 100 MW of power, which is the equivalent power for about 80,000 U.S. homes, says Greenpeace. While most Internet companies don’t disclose the details of their facilities’ energy consumption, Apple’s billion-dollar data center in North Carolina is estimated to require 100 MW, according to Greenpeace. Google’s data center in North Carolina is estimated to require between 60 MW to 100 MW when the second phase of it is fully built out, and Facebook has another data center in North Carolina, which is estimated to be smaller with a capacity of 40 MW.

A large coal plant, or even a really large solar thermal plant, can produce 500 MW of power. So a 100 MW data center would consume a significant portion of the output of a large power plant.

How dirty the power is that goes to these data centers depends on the region. As Greenpeace explained in its report last year: North Carolina, which is housing some of these Internet companies’ new data centers, “is one of the dirtiest in the country, with only 4 percent of electricity generation from renewable sources and the balance from coal (61 percent) and nuclear (30.8 percent).”

All of these numbers highlight just how energy-intensive the Internet has become, and how always-on servers will require increasing amounts of power to be sustained as more people get online and spend more of their time online. While the energy consumption growth of data centers was hampered slightly by the recession in recent years, according to Jonathan Koomey’s report on the subject last year, electricity used by data centers worldwide grew by 56 percent from 2005 to 2010, and by 36 percent over that time period in the U.S.

The total electricity use by data centers in 2010 was 1.3 percent of all electricity use for the world, and two percent of all electricity use for the U.S. At one point, the Environmental Protection Agency predicted data center power consumption in the U.S. would grow to 12 gigawatts by the end of 2011, or the output of 25 large power plants.

At the same time, Internet companies are starting to be more conscientious about making data centers more energy-efficient, and some are even investing in clean power, too. For example, Apple has been building a solar project near its data center in North Carolina, and both Facebook and Google are aggressively cutting their cooling power needs by using outside air for cooling for some of their data centers.

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Demand response is when the customers of utilities agree to let their energy-consuming devices — like thermostats, pool pumps and smart appliances — to be turned down during peak events (like the hot summer months), in return for financial compensation or other benefits. Residential demand response projects aren’t all that common these days, but the numbers of customers enrolled in these programs are growing. Energy Hub says it already has 100,000 smart thermostats under management and the company plans to add another 100,000 this year.

The e5 service will launch in Texas this summer and use a WiFi-connected thermostat from 3M. The consumer is the one who enrolls in the program and installs the thermostat, which can be obtained at retailers or online. The consumer can benefit through energy savings, and the utility can benefit from better demand response. EcoFactor has developed a similar service using weather data, smart thermostats and real-time demand response.

Earth Networks was formerly called AWS Convergence Technologies, and the firm refocused last year to start working on building a network of greenhouse gas emissions monitoring stations throughout the U.S. Those stations will use gas-detecting sensor boxes from Picarro, a startup in Santa Clara, Calif. However, clearly, Earth Networks’ weather data is still important to its business.

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• Smart Grid Apps: Six Trends That Will Shape Grid Evolution
• Green IT Q1: Cleantech Breaking Out — and Bracing for Hard Times
• The Smart Energy Home

Over the weekend, the Cleanweb hackers created applications like NYC BLDGS, a web data base of the energy consumption of buildings in New York that pits the best and worst buildings against each other in friendly competition. Econofy, a web site created over the weekend that enables consumers to compare the energy consumption of appliances, won both the audience choice award and the judges’ award for best overall hack.

The first Cleanweb Hackathon was held in San Francisco in September of last year, and the New York event this weekend was a slightly more high-profile affair. Judges of the hacks included investor Fred Wilson and Rachel Sterne, New York City’s chief digital officer. United States Chief Technology Officer Aneesh Chopra made an appearance as a special guest.

The event is the latest sign the ecosystem around clean technology is changing. As investors look back at the mistakes that have been made and money lost in capital-intensive investments like next-gen solar, biofuels and electric cars, some investors are taking a different route and looking to make cleantech investing look a lot more like web and mobile investing — literally. Paul’s firm Spring Ventures invests in Cleanweb companies like Solar Mosaic.

The Cleanweb is an attractive way to attack the problem of climate change and resource management for an age of 9 billion people. Information technologies are available now — compared to the science experiments in biofuels and parts of clean power — and thanks to Moore’s Law they are cheap, and will get increasingly cheaper. Now it’s time to tap into the innovation of the developer community to try to create new ways to leverage IT to solve the world’s problems.

Check out the video of the event below and Paul’s explanation of the Cleanweb at our Green:Net 2011 event:

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San Jose-based Varentec, incorporated in June 2010, is working on what it calls “power routers,” which will allow utilities to channel electrons to whichever transmission or distribution lines they deem suitable to deliver the necessary amount of power and meet demand at any time of the day or night.

“If people want green electrons, then we can guarantee the electrons are green,” Deepak Divan, president and chief technology officer of the company told us. “We can route power around a congestion point. If there is wind being curtailed, we can route the wind to different places to make sure the wind power gets to market.”

Varentec is using a $5 million grant from the U.S. Department of Energy’s ARPA-E program (for high-risk early-stage research) to develop its technology for both directing and adjusting the amount of power that flows all the way from a power plant to a home or business, said Divan. Varentec plans to both unveil the equipment and announce a pilot project with a utility in 2013, said Andrew Dillon, Varentec’s head of business development and marketing.

Dillon declined to name the utility, whose involvement could not only help demonstrate the tech but also to market it to other utilities. Utilities are known to shun the use of new (and sometimes expensive) equipment unless they have to do so for regulatory compliance.

Varentec also raised a $7.7 million Series A round last year and counts Khosla Ventures as a lead investor. Varentec is one of the rare smart grid startups that Khosla Ventures has funded.

The current power grid

Currently, the grid isn’t set up to allow utilities to have this dynamic control of the power flow. And there really isn’t a major need for it — yet. The majority of power today comes from fossil fuel-based power plants, which can produce electricity consistently 24/7, and can meet utilities’ demands predictably.

But with the emergence of wind and solar power, there could be a potentially huge headache. Wind and solar power production is variable because it depends on whether the sun shines or the wind blows. If the sun hides behind the clouds or the wind dies, utilities may not have enough time to crank up their coal or natural gas power plants to make up for the temporary loss of power supply, or to direct that power to certain neighborhoods quickly. They also will have to cut power production at these fossil fuel plants quickly once the sun comes out from hiding or the wind kicks up again.

“You don’t want your lights to go off just because wind has died down somewhere,” Divan said. “Utilities are forced to route power from a different place.”

In addition if electric cars become more popular, utilities will have figure out when and where in their territories they will have to provide the necessary amount of power to accommodate car charging. Utilities face penalties for not delivering power reliably – that means, for example, they can’t have too many outages and have to restore power as quickly as they can.

Varentec’s secret sauce

Varentec’s got some ideas about controlling the direction and volume of the power flow, but Divan declined to describe exactly how that could be done. We do know, however, that its power router technology will come with silicon-based converters that Divan said will be more efficient at adjusting the voltage, current and other characteristics of power as it courses through the grid. Power losses happen with each power conversion step, but Varentec’s converters will reduce that loss to less than 1 percent, compared with the 3-5 percent of converters today, Divan said.

Varentec also says its power routers will be more efficient and cost less in other ways. “To regulate 10 MW of power, we only need 1 MW of the equipment. We can get a 10x cost reduction, and that’ll become more economical,” Dillon said.

For an idea of what Varentec is working on, you can check out this presentation from the Georgia Institute of Technology, which is a partner in Varentec’s project and has done its own, separate research in power electronics for the grid. The presentation counts Divan as a co-author but describes another ARPA-E funded project to use a “power converter-augmented transformer” using silicon-based “direct AC converter cells” to control power flow.

Photo courtesy of Florian via Flickr

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The transition, though the company said it’s planned, still raises questions about the company’s well-being. Nanosolar is among a group of thin-film startups that have received hundreds of millions of dollars in venture capital but have yet to become meaningful players in the solar market. Corrales replaces Geoff Tate, who arrived at the helm of Nanosolar two years ago in 2010. Before that, the company was led by its colorful founder Martin Roscheisen.

The company makes copper-indium-gallium-selenide (CIGS) solar panels, and it has built a reputation for making promises it can’t deliver. Part of that came from Roscheisen, who said the company began commercial production of solar panels in Dec, 2007, which meant it should have begun to steadily increase its shipments, line up more customers and expand production. But he then divulged few details that would show progress, such as its technology, factory capacities, customers or projects, and he did so for long enough to draw suspicion, then ridicule from analysts and competitors.

It turned out the company wasn’t ready for prime time. Nanosolar announced in Sept. 2009 that, for sure, it was entering mass production that time around. The company became more circumspect about its work and opened its factory in San Jose, Calif. for tours to show it was making progress.

Nanosolar has announced some big contracts, technology improvements and completion of projects by its customers since Tate took over, but the company also was trying to right itself during a time when the solar market was beset by an oversupply of panels and falling prices for solar panels. Many of the much larger solar manufacturers have closed factories, laid off a big percent of their workforce, or gone bankrupt (see our list). Whether Nanosolar can survive remains a big question.

Corrales started at Nanosolar in 2010 and the company says, “under Corrales, cumulative shipments have gone from zero to 10MW; and median panel efficiencies are now 11.5%,” the company said in a statement. Tate is “returning to retirement.”

Corrales previously worked for two other solar companies, including SolFocus. Before that, she was the VP of operations at Cisco Systems.

“Eugenia’s track record at Nanosolar and prior speaks for itself, and this planned transition will allow the company to maintain its momentum and trajectory. We are confident that under her stewardship we can grow the market for Nanosolar Utility panels and expand our global footprint,” said Erik Straser, Nanosolar board member and general partner at Mohr Davidow Ventures, in a statement.

Other solar thin-film CIGS startups that have replaced and lost CEOs of in recent years include MiaSole, SoloPower and HelioVolt. Solyndra got a new CEO in mid-2010, and a year later it went bankrupt.

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Verizon discovered a few things about the service in the months it has been widely available, as well as via the months it was been available as a pilot service. First, Verizon Director of Product Development, Home Monitoring and Control Ann Shaub said Verizon’s standalone energy products haven’t been as attractive as the whole smart home package that includes cameras, door sensors, and door locks.

That’s not so surprising, as security and media management are clearly a lot more attractive to customers across the board compared to products used for reducing home energy consumption. Verizon also says it doesn’t make claims about saving energy for its home energy products, so it’s not actively marketing them as energy efficiency tools.

Verizon is currently working with Ingersoll Rand for its security products, and Aeon Labs for its thermostats and energy reader, which attaches to a circuit breaker and appliance switches. Shaub also told me Verizon is actively looking to add more smart home tools over the coming months.

Verizon says it has seen 95 percent of its smart home customers install their own devices. That could be a good sign for Nest, the smart learning thermostat startup, which is selling thermostats straight to consumers.

Verizon wouldn’t give me any information about the numbers it’s getting for its smart home tools at this point. Shaub would only say the division is here to stay, and it’s seeing significant growth.

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It was also the year that direct current (DC) took a back seat to alternating current (AC) after Niagara Falls Power Company chose AC transmission for its power plant.

Although we live in an AC-dominated world, DC seems poised for a comeback, particularly in data centers. Facebook adopted a DC architecture in its Prineville, Ore., data center. SAP spent $128,000 retrofitting a data center at its offices in Palo Alto, Calif., to rely on DC power. In 2010 it cut SAP’s energy bills by $24,000 per year.

ABB, the Swiss-Swedish conglomerate, bought a controlling interest last year in Validus DC Systems, which specializes in DC data center equipment. ABB also opened a factory in North Carolina to produce HVDC (high voltage DC) equipment for delivering power from solar and offshore wind farms to the grid. The Tres Amigas “superstation” will rely heavily on HVDC.

General Electric, meanwhile, bought Lineage Power, which produces DC equipment, and it has talked about using DC to power mining shovels and other heavy-duty equipment.

Nextek Power Systems and the EMmerge Alliance are also promoting DC as a way to cut power in buildings.

Behind the DC drive

What’s driving it? Although AC became the standard for electronic transmission, DC didn’t disappear. It just hid. Servers, large numbers of electric motors, batteries, even ships and airplanes run on DC. Solar panels produce DC power. Wind turbines can produce AC or DC power, but the extreme variability of wind power means that electricity generated by turbines has to pass through battery banks before it gets to the grid. As a result, wind farms are effectively DC.

The landline telephone system runs on DC too, notes Brian Fortenberry, a program manager at the Electric Power Research Institute.

To solve the mismatch, a whole industry of AC-DC converters has been developed. National Semiconductor sells billions of dollars’ worth of chips to convert power. Inverters in the solar industry exist to convert DC from solar panels to AC that can run on the wires in your home.

In data centers, the AC-DC gymnastics top the charts. Typically, AC from the grid has to be stepped down in voltage so it can be routed safely in building equipment. Lower-voltage AC then gets converted to DC so it can go to an uninterruptable power supply (UPS). DC power from the UPS then gets converted to AC so it can go over the wires in the building. Then it gets converted back to DC. Usually five conversions, or steps, downward take place.

By converting grid AC at the door of a data center to medium-voltage DC or converting stepped-down AC to DC at the last possible moment, a data center can cut utility bills by 10 to 20 percent or more, according to Trent Waterhouse, the VP of marketing for power electronics at General Electric.

Validus and others have also eliminated some of the technological hurdles involved in transmitting via DC, namely the monster-sized copper cables.

The same dynamics work in buildings. In a retail establishment, DC power from solar panels could go directly to DC-powered LED lights with not-intermediate conversions that sap energy, according to Nextek. Perhaps not coincidentally, Redwood Systems, the lighting networking company, touts that its technology is actually an example of DC networking.

More savings comes in real estate. DC data centers require 25 percent to 40 percent less square footage than their AC counterparts, largely because computer equipment can connect directly to backup batteries.

In a hypothetical example, a 2.5-megawatt data center power module in the AC world might need 7,295 square feet, Ronald Ranaldi, the VP of sales at Validus, told me last year. An equivalent DC power module might occupy only 5,102 square feet, a savings of 2,193 square feet. What’s more, a single data center might consist of several 2.5-megawatt modules.

“Real estate is often greater than the energy savings,” says Ranaldi. “In large, green field data centers, you are literally eliminating buildings.”

DC won’t take over the world. And not everyone is sold. Google is not taking DC for its data centers in part because of the cost that would be involved in retrofitting their existing architecture. But it seems that an idea that was current when Grover Cleveland was in the White House and Japan was just adopting the Gregorian calendar could make a comeback.

Image courtesy of The Planet

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The new service from Time Warner Cable, called IntelligentHome, will provide customers with connected home management services, like security, with remote home-video viewing and window and door sensors, as well as wireless management of home heating, cooling and lighting. The service is already available in upstate New York and Southern California. (I will add pricing details when they send it to me).

IControl has worked with cable companies before: It is the company behind Comcast’s similar smart home service that was launched last summer. Comcast is also an investor in iControl. IControl provides the software layer while the cable companies provide the broadband connection, and third-party hardware providers make the dashboards and security gadgets. IControl has long had the strategy to white label its service and to avoid getting into the hardware market itself.

Cable operators as well as telcos are increasingly beginning to offer home management services as a way to try to avoid becoming a dumb pipe and also as a way to reduce churn and add extra subscription revenues. Verizon launched a similar service about a year ago, which included home security control and monitoring as well as energy reading devices, smart thermostats and smart appliance control devices, among other applications. Verizon worked with Motorola’s 4Home(a startup that it acquired a couple of years ago) as well as Ingersoll-Rand for the security applications.

At CES the big-box retailers Lowe’s and Best Buy are also both looking to have a presence and push new smart home devices and services. Lowe’s is working with UK smart energy company AlertMe, while Best Buy is selling a variety of devices like the smart thermostat Nest.

Connected devices that control home energy consumption can make homes more energy-efficient. The Nest smart thermostat can reduce home energy consumption by 20 to 30 percent.

IControl is backed by Comcast, Kleiner Perkins Caufield & Byers, Charles River Ventures, Intel Capital, Cisco, GE and security firm ADT.

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1. Smart energy homes. Quite a few companies will be showing off their smart energy home gadgets and services, including the largest big-box retailers. Lowe’s will be kicking off a major home energy push with partner AlertMe at CES, and Best Buy will also be touting its home energy plans, launched a few months ago.

The telcos and their partners will probably have a decent-sized showing. Nest and its learning thermostat will be there taking meetings in the Hilton. Newcomers Wireless Glue and Allure Energy also showed off new devices.

Power and utility company Reliant and NRG Energy will have an updated version of its smart energy home on wheels at the show, and we’ll be chatting with them later this week. Chip company Marvell is also showing off how its wireless chips can be the silicon connector for the smart energy home.

2. Electric cars. Ford dominated the electric car news at CES 2011, and it will probably be the same in 2012. Ford also has the Detroit Auto show going on, so there will be a lot of news this week from them. On Sunday night at the Detroit Auto Show, Ford unveiled the plug-in Fusion Energi, which has 100MPGe and can drive on electric for 20 miles before the gas engine kicks in. Ford President and CEO Alan Mulally will be speaking at some point at CES. Read more on Ford’s digital dreams here.

Also at CES, there’s the Go Electric Drive Test Zone, which includes retailer Best Buy, electric charging company Coulomb Technologies, Mitsubishi Motors North America, Qualcomm and Siemens. In addition, Kia Motors plans to show off a new electric vehicle.

Solar iPod apps

3. Solar-powered gadget cases. Over the past couple of years, a variety of products have emerged that have embedded small solar strips on the back of cases that can top off gadgets with a small amount of solar electricity. Much of the value-add of these cases is often times an additional lithium-ion battery, as the amount of the power provided by the solar strips can be pretty weak. VentureBeat has some of the first shots of a case for a solar-powered Kindle, made by Taiwanese company SolarFocus, which says will make the Kindle battery last three times the normal duration. The cost is $80.

4. Sustainable Planet Section. CES has a sustainable section every year, which usually features a couple dozen vendors making gear like smart plugs and batteries; it’s pretty lame. But at the 2o12 CES, I was interested to see trash giant Waste Management has a booth in the Sustainable Planet Section. While Waste Management has a very interesting investment startup strategy, I’m looking forward to see what’s the connection with gadgets — e-cycling?

5. Cars in the cloud. The digital car isn’t always about sustainability, but car data, infotainment and digital systems are becoming a hot topic at all gadget events, and CES 2012 will be no different. And sometimes the digital car does lead to a more sustainable car. One of the first announcements to come out of CES 2012 is that GM’s Onstar has given the greenlight to third party applications, and one of the first will be from car sharing company RelayRides. Woot!

6. One Laptop Per Child. One Laptop Per Child is showing off its long-awaited XO-3 tablet at CES, and TechCrunch has some of the first pics of it. Is it eco-friendly? Not really, but it’s planet-friendly, and there’s so little green content this year at CES that I added one that’s only half-green.

Updated: 7. Cool lighting: Switch, the startup that makes a liquid-cooled LED bulb, is showing off its SWITCH75 LED light bulb at CES — it’s one of the first times the bulbs are being showed off to the public. The company is backed by VantagePoint Capital Partners.

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So with that in mind, the company has signed a deal with Ericson to upgrade 250 of its diesel powered cell stations with solar generation in an attempt to go green and also to access a stable off grid power source. I’m seeing more of this sort of approach, of co-building renewable energy generation next to critical infrastructure.

Texas based WindData has planned a five data center facility in Pfugerville, Texas with wind power generation locked into the plan so that the data center has good visibility on what its long term electricity pricing will be. As the world trudges toward large scale utilities offering reliable renewable energy sourcing, these sorts of smaller-scale energy projects for businesses with power needs could be an important medium term trend.

Check out GigaOM Pro’s Green IT section (subscription required) to read all of my reports and research notes on. Inside you can read up on:

• Opportunities for the future of batteries
• Green IT 2012: looking for bright spots amid the clouds
• The economics of peer-to-peer car sharing

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Boston-based Satcon makes inverters that convert direct current from solar cells to alternating current to feed to the grid. Inverters play a critical role in solar power generation, and startups that aim to improve inverters’ performance have attracted some big investments from venture capitalists.

Satcon’s decision to close its factory in Ontario and cut about 140 employees worldwide reflects a trend that took hold last year when solar companies – mostly solar cell and panel makers – began announcing layoffs, factory closures and bankruptcies. A pileup of solar energy equipment and the corresponding fall in prices have caused not only declining profits but a trade complaint against Chinese silicon solar cell and panel makers.

The complaint contends Chinese manufacturers have received unfair government help to boost their production and sell their products at below-market prices. The U.S. International Trade Commission and the Department of Commerce are reviewing the complaint, which seeks to impose duties on Chinese imports.

The global inverter market saw a 20-percent decline in revenue during the third quarter of 2011, said IMS Research last month. Although prices stopped falling quickly in the third quarter, they were still 15 percent lower on average than in 2010.

Meanwhile, San Jose, Calif.-based GlobalWatt said it will ditch a plan to build a $177 million silicon solar panel factory in Michigan. The company apparently had started production on a small scale at what was to be a larger factory in Saginaw, Mich., and NBC has reported  Michigan officials are saying GlobalWatt presented false information when it tried to line up government incentives for the factory.

Here’s our list of solar companies that have gone out of business or shrunk their operations in light of the tough market:

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CoolPlanet BioFuels makes what the company calls negative carbon fuels, using a technology it calls biomass fractionator. The technology essentially takes nonfood biomass (plant waste, energy crops, etc.) and turns it into a drop-in replacement for gas and diesel. That process sounds similar to what biofuel company KiOR is doing.

KiOR uses a catalyst to carbonize biomass (called its Biomass Catalytic Cracking Process), which was originally developed to help the oil industry break down heavy crude oil into more-easily refined products for the oil industry. Drop-in replacements for gas and diesel will be more attractive to the oil industry, because they can use the current infrastructure for transport and use.

BP has invested in a variety of biofuel companies including Verdezyne, which engineers yeast that eats plant sugars and excretes biofuel and biochemicals, and Synthetic Genomics, Craig Venter’s firm that is using genetics to tweak algae to produce fuel. BP also has a joint development agreement with Martek Biosciences to work on making microbial oils for biofuels, and earlier this year BP spent $98 million acquiring the biofuel arm of Verenium, a startup that makes enzymes that break down cellulosic biomass into sugars.

While there are dozens (likely hundreds) of next-gen biofuel companies, almost none of them have produced biofuels at any scale. The Environmental Protection Agency said this week that once again, only a tiny fraction of the biofuels required by the U.S. mandate will come from next-gen cellulosic biofuels: less than one-tenth of 1 percent, according to the Wall Street Journal. The mandate was for 3 percent.

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The article about the hog waste project, which was published in the Los Angeles Times, says Google invested part of the $1.2 million it cost to build the project that uses bacteria to digest hog poop, burn methane to produce electricity and convert ammonia into nitrogen for fertilizer. Duke University and the farmer Loyd Bryant were the other financiers of the system.

The article notes Google has a data center nearby, and Google will earn carbon offset credits from the system. Like some of Google’s other clean power micro investments, the project could be a way for Google to investigate ways to tap into distributed power in local regions, for either its data centers or offices. (There’s no indication this one in North Carolina will be powering anything Google related).

Remember Google was the first customer for Bloom Energy’s fuel cell, which can use biofuel, as well as natural gas and biogas, to produce electricity. Google used the Bloom Energy fuel cells to provide power in a data center test lab. Distributed energy production could be a way for Google to manage and control power costs.

Back when Google invested in CoolPlanetBiofuels, Google Ventures’ Managing Partner, Bill Maris, told me this:

As a company, Google is interested in reducing all aspects of its environmental footprint. As a firm, Google Ventures is interested in contributing to this effort both on Google’s behalf and for the benefit of positive global impact. While petroleum does not constitute a large percentage of Google’s emission profile, we are enthusiastic about supporting technologies that can help us economically reduce our carbon footprint while simultaneously contributing to our domestic energy security.

How do you think Google could use biomass and biofuel projects for its business?

Image courtesy of eutrofication&hypoxia.

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So starting with No. 10 and running through to No. 1, here are our top 10 green GigaOM stories of the year:

10. 25 battery breakthroughs for gadgets, electric cars & the grid. Innovation for batteries is struggling when compared to the progress of innovation in IT, which is a big bummer, because batteries are the pain point for mobile devices, wireless computing, and electric cars. These are 25 researchers and startups that are trying — hard!

9. Google to switch on seawater-cooled data center this fall. Google, you so crazy. The search engine giant built a data center that’s being cooled by the sea in Finland, and I reported that it planned to switch it on in the fall of 2011. It’s not very economical, but super energy-efficient — and pretty awesome.

8. Why Cyber Monday is greener than Black Friday. This post got a lot of attention because it was a headline on Google News and it irritated a lot of people. Sometimes being hated is better than being loved.

7. Photos: Inside Tesla’s Model S Alpha workshop. While Tesla came out with its Beta Model S sedans recently, we got an exclusive sneak peek of the cars when they were in the Alpha phase, and we brought you these pics.

6. The ultimate startup lesson: Knowing what matters. Marcus Tallhamn, CEO of Otelic.com, won readers over with his candid look at the lessons he learned by running energy software company Hug Energy. The gist: Identify your value system, and figure out what matters to you.

5. Cloud computing could lead to billions in energy savings. GigaOM readers are craving info on the energy efficiency of the cloud. This story was just a little news post about a report, but I guess it had a good headline enough to turn it into No. 5.

4. Solyndra to file for bankruptcy, lay off 1,100. Yeah, the sad tale of Solyndra comes in at No. 4. I don’t need to explain this one to y’all, but actually, I’m happy it wasn’t No. 1. (I thought it might be before I checked.)

3. 4 reasons why cloud computing is efficient. Computing power expert Jonathan Koomey penned this piece on why cloud computing is more energy-efficient than companies running their own IT and servers.

2. How Apple could revolutionize solar. I wrote this piece because I wanted Apple to add some kind of solar power to its devices, which I think could be a major game changer for solar companies. Soon after, news leaked of Apple’s solar array at one of its data centers, but not much official on any micro solar for gadgets (except for way “out there” patents).

1.. Introducing a thermostat Steve Jobs would love: Nest. Readers couldn’t get enough of the Nest learning thermostat, which was created by Tony Fadell, the former chief architect at Apple, who led the development of the iPod and the first three versions of the iPhone. Can it do for the boring old thermostats what the iPhone has done for cell phones? Well, it has enough buzz that the device is sold out until well in 2012.

Image courtesy of WoodleyWonderWorks.

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Last week, as soon as I put tidal power into a box labeled “waste of time,” I received some deserved howls of protest. I saw it coming, and had built in words to soften the “waste of time” label. But it was a poor choice from the start. A better set of labels is “abundant,” “potent,” and “niche.” The last could also be thought of as “boutique,” in that it is cute, perhaps decorative, may serve some function, but will never be a heavy lifter. The “potent” label—formerly “useful”— is meant to indicate a source that could supply a healthy fraction (say over a quarter) of our global demand if fully exploited. We will never fully exploit any resource, so the numbers at least need to support ¼-scale before we can believe that it may play a major role.

I should also point out that all along, my approach is to pretend that our goal is to keep up our current energy standards in a post-fossil-fuel world. In the process, we will see just how hard that will be to do. It is by no means impossible, but it’s much more difficult and compromised than most people realize.

In the end, it is not clear that we will maintain our current global rate of energy usage: the future is unwritten. On the plus side, some of the approaches I cast into the “niche” box may become “potent” in a scaled-down world. Firewood was once abundant, then moved to potent, and is now a niche. But a reversal of fortunes could change all that.

Hydro Basics

I may be starting to sound like a broken record, covering the basic physics of hydroelectricity now in several posts. But we learn by repetition, right? So in the spirit of self-containment, here we go…

Hydroelectric dams exploit storage of gravitational potential energy. A mass, m, raised a height, h against gravity, g = 10 m/s², is given a potential energy E = mgh. The result will be in Joules if the input is expressed in meters, kilograms, and seconds (MKS, or SI units). Water has a density of ρ = 1000 kg/m³, so if we know how many cubic meters of water flow through the dam each second (F), the power available to the dam will be P = ηρFgh. We have inserted η to represent the efficiency of the dam—usually around 90% (η≈0.90).

The height of the water behind the dam is the relevant height for the potential energy calculation, even if a given parcel of water is collected at the bottom of the dam. This is because the pressure of the water above provides the motive force. In the absence of turbines or other restrictions, the water would emerge from the penstock at a velocity of v = sqrt(2gh) so that a flow, F, would require an area A = F/v. For example, Hoover Dam, at 222 m high (in the days when Lake Mead was full!) would eject water at a stunning 67 m/s (150 m.p.h.) if a big hole opened up in the bottom. At the nominal flow rate of 1000 m³/s, this corresponds to a hole about 4 m in diameter. I think we should do it.

Now, it is the job of the turbine(s) to extract some of the kinetic energy this water would have if it were allowed to shoot out of the bottom of the dam. As a consequence, it comes out at a much more sedate pace. Some of the 10 percent inefficiency in hydroelectric dams is due to generator inefficiency, but some is because you can’t take all of the kinetic energy out of the water or it would stop flowing and stall the flow of the next batch. But nature is kind here, since kinetic energy goes as the square of the velocity. The velocity of the energy-sapped water is therefore sqrt(1 − η). So if we pull 96 percent of the energy out of the water, its flow velocity is 20 percent of the free-flow value (13 m/s in the foregoing example). Or we can grab 99 percent at a 10 percent exit speed (7 m/s, or 15 m.p.h.). This sounds much more reasonable—and seems like a good bargain. The area needed now expands accordingly, but that’s what large turbines/penstocks are for.

Hydroelectricity in Practice

The U.S. has 78 GW of hydroelectric capacity installed. In a year, these plants produce 272 TWh. Divide by 8766 hours in a year, and we find 0.031 TW (31 GW) of average power. This implies a 40 percent capacity factor. I was surprised by this: I thought dams churned along at a steady rate all the live-long day. Seasonal variations are apparently much larger than I appreciated—snow-melt being one factor. The following table lists all hydroelectric facilities in the U.S. bigger than 1 GW—representing 30 percent of total installed capacity in just 11 dams. The table shows each dam’s nameplate (peak) capacity, height, implied flow at peak generation capacity (after which spillways must be activated; assumes 90 percent efficiency), and capacity factor.

Eight of the eleven dams in the table are in the Pacific Northwest. Of possible interest is the fact that the power-capacity-weighted heights of these dams is 113 m, while for the entire U.S. fleet, it is 88 m (much higher than I thought).  For reference, the newly completed Three Gorges dam in China is rated at 20.3 GW, has a nominal head height of 81 m, an implied flow of 28,500 m³/s, and a capacity factor of 0.45.

Current Contribution

What fraction of our energy currently comes from hydroelectricity? Such a simple question deserves a simple answer. Yet numbers range all over. The hard answer is that 272 TWh of annually delivered electricity in the U.S. corresponds to 0.9 percent of the primary energy use, or 2.3 percent of primary energy associated with electricity. Of the delivered electricity, it’s 7.3 percent.

Much of the variation is due to an apples-to-oranges comparison of efficient hydroelectricity to heat engines that convert only 35 percent of their primary energy into useful energy. For instance, the Department of Energy’s Annual Energy Review (whose numbers are well-depicted in the LLNL graphic) artificially inflates the contribution from hydro to put it on the same footing as the fossil fuel inputs. But however you want to slice it, hydro is on the small side.

Global Hydro Potential

Now the fun part. How much hydro power is theoretically achievable? Hydroelectricity is cashing in on residual potential energy provided by the rain cycle. A look at the Earth’s energy budget shows that a whopping 23 percent of the solar budget goes into evaporating water!  The water cycle is a big deal.

Each gram of water takes 2250 J of energy to vaporize. It takes additional potential energy to lift the water into the atmosphere. Hoisting a gram of water 10,000 m high (to the top of the troposphere) takes a comparatively small 100 J. Since all water caught by the land and used for hydroelectricity had to first be evaporated, we can say that if all the water got lifted to 10 km (it doesn’t, but bear with me for easy math), then 1 percent of the solar budget goes into lifting water. I love it when numbers like 2250 J align so neatly with 23 percent of the solar budget!

The lower atmosphere contains far more water than the upper atmosphere — largely because air gets cooler with altitude, and can hold less water. But clouds represent condensed water and can clearly contain significant amounts of water all the way up to 10 km. If water were evenly distributed in the troposphere, the average height of water within it would be about 5 km. Considering the non-uniform profile, I’ll use an average height of 2 km. Therefore, we adjust our hoist factor to 0.2 percent of the incident solar energy.

Then it rains. And most of that stored energy is wasted as the drops fall irresponsibly through the sky—without a thought to our needs. When water hits the ground, the average height of the land is—I’m guessing—500 m. Since potential energy is linear with height, we can use a simple average in this way.  If we could capture all that remains of the potential energy as we return the water to the sea, we get 0.05 percent of the solar potential. But this only works on land, which is 28 percent of the Earth’s surface. Now we’re down to 0.014 percent.

Don’t despair yet. The solar potential is huge. These percentages all relate to the incident energy at the top of the atmosphere: 1370 W/m² over πR² square meters turns into 175,000 TW. So our 0.014 percent is 25 TW. Our global energy diet is about 13 TW, so we’re in the game.

We can pursue an alternate approach to check that we’re on the right track. If annual rainfall averages 0.5 m (20 inches) on land globally, and typically falls on land 500 m above sea level, we can total up the potential energy and divide by the number of seconds in a year to get a power. I calculate 11 TW by this method, so yes—we’re making sense. My guess of 0.5 m of rain per year may be a little low, but perhaps this compensates a bit for the fact that low areas tend to get more rain than high areas.

Now, nature provides a convenient water collection system, concentrating the water that falls on land into streams and rivers and lakes. This natural concentration is what makes such a diffuse power source usable at all, and is why hydroelectric was the vanguard of modern renewable energy (I’m skipping over firewood as non-modern).

But as convenient as this collection system is, much of the energy is lost en-route to the rivers. Think about the journey a water drop that lands in your yard or on a mountain slope must make before finding a body of water large enough to profitably dam up. Obviously there is friction in the collection process, or water would be screaming along at 100 m/s (220 m.p.h.) at the bottom of a 500 m slope. In the end, we must accept heights of static water collected behind dams: no kinetic harvesting, practically speaking.

I’ll make a rough guess and knock off a factor of two for the energy lost in the collection process leading up to the river/stream. My gut says that I’m probably being generous here. In any case, we’re dealing with something in the neighborhood of 6–12 TW of global potential. For the U.S., with 7 percent of the world’s land area, this turns into 0.4–0.8 TW.

At present, the U.S. has 78 GW of installed hydro power (out of which we get 31 GW, averaged annually). The world has about 1 TW installed, likely realizing 400 GW on an annual average. The realized capacity therefore undershoots our crude estimate of global potential by a factor of 10 or more. Does this mean we could go nuts and expand hydro to amazing new levels? Should I ask for water skis for Christmas?

Realistic Assessments

I don’t want to discount the top-down approach we did here. After all, if anyone tried to tell me that hydro could deliver much more than 25 TW of power, I would know that the basic physics of the planet does not allow it. But at the same time, the upper limit we established does not account for a whole host of practical considerations, like actual rivers with known flow rates and geographic potential for damming. So I turn to a study that has put some more time into the question than I can afford personally, outside of my day job. Specifically, a report by the Eurelectric group assessed global hydro potential in four cascading steps:

1. Gross potential if all runoff is developed to sea level with no loss;
2. Technical potential, ignoring economic limitations;
3. Economically viable potential, cost competitive with other sources;
4. Exploitable potential, considering environmental and other restrictions.

For the first step, they come away with 5.8 TW — not far at all from my estimate (I’m not cheating I swear: I did not look at any estimates prior to writing the above sections). Other assessments get 4.4 TW, 4.6 TW, and 5.1 TW.

For technical feasibility, these same sources estimate 1.6–2.3 TW globally. Economic feasibility (in today’s economic climate) drops this to 1.0–1.4 TW. Environmental restrictions (in today’s climate) reduce this number further. Thus, having developed 0.4 TW worldwide (using average annual output for proper comparison to studies), the world may be able to expand by a factor of 2–5.  This is a large range: a factor of two isn’t that much, while a factor of 5 is a pretty big jump. Where is it, really?

For the U.S., the Idaho National Laboratory estimates a gross potential of 0.3 TW, and a technical potential of 0.17 TW. The latter was determined after a study of 500,000 potential sites, out of which 130,000 made the cut. It is also estimated that existing dams with no hydroelectric capacity could add 0.013 TW (13 GW).

So here in the U.S., we could expand by a factor of 5 according to this report—ignoring economic and environmental barriers. Such a boost would bring hydro up to 5 percent of our gross energy, or 12 percent if we correct for the heat-engine effect (40 percent of our electricity). I have seen other reports less optimistic about our expansion potential, coming in closer to a doubling of current capacity—likely factoring in economic and environmental considerations, and consistent with the lower end of the range estimated for global potential.

Which Box?

At a global potential of approximately 10 percent of our current energy scale, my initial reaction is to throw hydro into the “niche” box with tidal, since my criterion is that a resource be theoretically able to meet a quarter of our demand to be labeled “potent” — which incidentally is in line with what oil, natural gas, and coal each deliver to us today: all are momentarily “potent” sources by this reckoning.

If we consider that thermodynamic losses in conventional electricity production do not apply to hydro, we might be tempted to boost it into the “potent” category. But I didn’t need to do this for wind, and certainly not for solar. And even this boost does not put it over the top in the U.S. (at 12 percent), even if entertaining a 5× increase in hydro development. So I think I’ll leave it in the niche box. It’s a borderline call (and meaningless, really). Hydro beats the pants off of tidal, and is currently used to good effect the world over. But it’s a real stretch to make it a big player in the energy game at today’s rates of usage.

Almost all renewable resources are dilute, and face substantial environmental hurdles for being adopted. Dams are not without controversy. They radically change the landscape and natural ecosystem. They silt up and lose capacity over time. And they can cause long-term threats to settlements downstream in the case of failure (and all dams will someday fail—they really haven’t been around that long).

When push comes to shove, we may be willing to ignore aesthetic and environmental concerns. I might rather hike through Glen Canyon than listen to jet skis on Lake Powell (in the fossil fuel crunch, maybe I won’t have to), but weighed against the hardship of energy decline, will we collectively make that choice?

Lake Powell already offers one answer.  Of course dams require tremendous up-front (energy) investment, and therefore are susceptible to The Energy Trap. So in crunch time, I’m not sure I can predict what we’ll do, or if our choices will be at all rational.

In hydroelectric power, we again face the problem that the impending fossil fuel shortage is not fundamentally an electricity shortage problem. So most of the “solutions” I’ve hit so far do not address the fundamental and most immediate crisis in liquid fuels. Overall, I’m a fan of hydro power, and I’m glad nature does most of the work for us. Nonetheless, my mind is not much eased by the joint facts that it falls far short of our current demand and that it’s yet another way to make electricity. It’s a gift from nature, but much like getting yet another tie for Christmas to add to the pile, I’m not getting excited about the prospect of more dams.

Thomas Tu contributed research on hydroelectric installations for the table, and rounded up assessments of global hydro potential from a variety of sources.

This post originally appeared on Tom Murphy’s blog, Do the Math: Using physics and estimation to assess energy, growth, options.

Tom Murphy is an associate professor of physics at the University of California, San Diego. An amateur astronomer in high school, physics major at Georgia Tech, and Ph.D. student in physics at Caltech, Murphy has spent decades reveling in the study of astrophysics. He currently leads a project to test general relativity by bouncing laser pulses off the reflectors left on the moon by the Apollo astronauts, achieving one-millimeter-range precision. Murphy’s keen interest in energy topics began with his teaching a course on energy and the environment for nonscience majors at UCSD. Motivated by the unprecedented challenges we face, he has applied his instrumentation skills to exploring alternative energy and associated measurement schemes. Following his natural instincts to educate, Murphy is eager to get people thinking about the quantitatively convincing case that our pursuit of an ever-bigger scale of life faces gigantic challenges and carries significant risks.

Image courtesy of Lingaraj, 123 Chroma Pictures, Kyle Monahan, Mano Ranjan, Yuya Tamai, grungepunk 2010.

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