A new way to look at efficiency

With all the discussion of renewable energy we hear these days, we repeatedly hear how inefficient many of these energy conversion processes are. The real question is how important are these numbers and should we be looking at efficiency in a different manner?

Let us consider the case of solar power. Our very own Dr. Webber commented, in a lecture on Renewable Power, that solar has “lower efficiency than power plants”. It is safe to assume that he is referring to the ability to convert the suns radiation to electricity via photovoltaic converters or concentrated solar power systems (not solar thermal energy conversion). And of course the statement is not inaccurate; the energy out of these systems divided by the incident energy is less than many other forms of energy conversion. But of what significance is this comparison? I would argue that efficiencies of these sorts have no relevance when comparing energy conversion processes of different types. To abuse an overused phrase, it is like comparing apples and oranges. The maximum theoretical efficiency that a photovoltaic conversion process can achieve (assuming a band-gap of 1.1 eV from the sun with incident radiation of 1000 W/m^2) is 43% (Da Rosa 2005). Does this mean that we should not consider solar power as a vital part to our future energy portfolio? I think not, instead it means that we should compare PV cells to the maximum theoretical efficiency. Simply stating that the solar to electrical is not as good as a traditional method is the argument not the correct argument.

So how should we compare energy conversion processes? That is a difficult question to answer because many of the effects of energy conversion are difficult to quantify. For example we can quantify the kWh per dollar, kWh per lb CO2, or kWh per square meter, but those don’t accurately describe the entire picture. In my opinion we must attempt to compare “Gala” to “Granny Smith” apples or at least oranges to tangerines. For example when comparing a natural gas fired Rankine cycle power plant to a natural gas driven Brayton cycle plant thermodynamic efficiencies, cost, and emissions output are an accurate ways to compare the systems. Renewable energy conversion processes should be compared to other process that require the same basic inputs, for example, wind and solar energy conversion. These two energy conversion processes both require large amount of land, so doesn’t it make since to compare them on that basis. We should evaluate the power output per unit area available as compared to the traditional efficiencies of these processes.

In conclusion I hope that as we encounter quoted efficiencies of energy conversion processes that we search for a more meaningful comparisons.

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Da Rosa, A.V. (2005). Fundamentals of Renewable Energy Processes. New York: Elsevier Academic Press.

Webber, M. (Speaker). (2009, February 12). Renewable Power. Austin: University of Texas at Austin.

If GE is so Green, Why Do They Put a Clock on Everything?

VAMPIRE POWER! Sounds scary huh? Well it is. "Vampire power" is a term used to describe electronics' continued energy use when in a powered-off state, also referred to as standby mode. Even though you may have taken your phone off the charger or hit the "off" button on your TV, those devices are likely continuing to draw a trickle of power that can add up over time on your electricity bill and carbon footprint.

As an example, here's a back-of-the-napkin type calculation. There are around 230million cell phone users in the US. If 10% of them leave their charger plugged in all the time, charges their phone 1hr/day, and the charger uses about 0.1W (see pg 87) when not in use, this adds up to over 19 million kWh of wasted electricity. If half that is from coal (~1 metric ton of CO2/MWh) and 15% from natural gas (~.5 tCO2/MWh), we're talking about roughly 15,500 tCO2 from wasted energy in cell phone chargers, and I think that I'm being conservative here. Now think about your microwave, TV, computer, etc. You get the idea.

Now before we get too worked up, standby power can be useful for features such as memory retention in your DVR or computer or to allow use of a remote control to turn devices on and off. However, I don't understand why charging devices should draw power when not in use (can a EE explain this to me?), and I personally see absolutely no reason why every kitchen appliance needs to have a clock, hence the title of this post. I've seen a coffee maker that uses an LCD display to show a digital image of an analog clock - this is absolutely ridiculous to me.

ENERGY STAR and the UK's Energy Savings Trust are fantastic market based mechanisms to give incentive to reduce standby energy consumption. The UK is even debating a ban on the standby option for electronics, though I am not sure this is reasonable.

What is reasonable, and necessary, is for consumers to change their behavior and product preferences regarding standby power use. If you had to get up to turn your TV on and off, would it be that big of a deal? You had to get up to walk to the couch anyway. If you wear a watch with a 3yr battery, do you really need 18 clocks in your kitchen? How about unplugging chargers when not in use (or plugging them all into a power strip that you can switch on and off)?

Behavior changes aren't always easy, but any move towards electricity conservation can help reduce CO2 emissions and your electricity bill. We don't need to wait on government programs and market economics to cut down on standby energy consumption, all we have to do is unplug.

What if ENERGY STAR Took Its Efforts a Bit Further?

Most of us have probably heard of the ENERGY STAR program, a joint venture by the DOE and EPA to promote energy efficient products and buildings. The public face of the program typically comes in the form of an ENERGY STAR logo sticker placed on products that meet the program's design requirements (see image below). I doubt that many people know the details behind ENERGY STAR ratings, so I primarily view the program as a way for consumers to feel better about the purchases they decide to make. This is definitely a good thing, though we have discussed in class that when energy efficiency is not coupled with high energy cost, total consumption may not decline.


So here's a thought. What if there was a similar program to label products that are have particularly BAD energy efficiency? Maybe it could use something like the graphic I created below? I bet that if the government mandated such a program, companies would scramble to make sure their product wasn't required to have a brown frowney face stuck to it.


I believe that ENERGY STAR is a good program for its simplicity, directness, and combined emphasis on the environmental and economic benefits of energy conservation. However, I feel that at least as much attention should be brought to products that ignore the energy and environmental crises that threaten our planet and our way of life.

Efficiency = More Consumption?

I recently read Robert Bryce's recent book, "Gusher of Lies," in which he describes one of the pitfalls of increased energy efficiency: more consumption.

Bryce refers to a 2004 report from the National Commission on Energy Policy which posits that even if CAFE standards were increased to 44 mpg (2007 standards were only 27.5 mpg), America's fuel consumption would sill increase by 3.7 million barrels per day by 2025.

The basic argument is summed up as he quotes authors Peter Huber and Mark Mills: "efficiency fails to curb demand because it lets more people do more, and do it faster-and more/more/faster invariably swamps all efficiency gains." (Peter W. Huber and Mark P. Wills, The Bottomless Well: The Twilight of Fuel, the Virtue of Waste, and Why We Will Never Run Out of Energy (New York: Basic Books, 2005), p. 109)

This seems like a compelling argument for more focus on conservation, as described in Dr. Webber's "Conservation Can be America's Oil Weapon" article, rather than efficiency gains, although both are important pieces of the pie.