Saturday, December 20, 2008

The FCX Clarity from Honda

Honda FCX Clarity

On this week's Top Gear, James May called the FCX Clarity "the most important car for 100 years".
[Photo courtesy of] It runs on hydrogen, which "will never run out", because it is "the most abundant element in the universe". And the only emissions are water.
What twaddle!
The programme took the time to point out that the electricity to power a Tesla electric car in Britain is produced at a fossil fuel power station. Why didn't they also discuss where the hydrogen comes from?
Top Gear loves to quantify accelerations, lap times, car prices, top speeds - why couldn't they quantify the energy requirements to run "the car of the future", the FCX Clarity? And compare it with the Tesla?
Here's the answers, according to chapter 20 of Sustainable Energy - without the hot air.
Energy consumption (in kWh per 100 person-km) versus typical speed
The energy consumption of the FCX Clarity is 69 kWh per 100 km. (Very similar to the consumption of an ordinary fossil fuel car.) That's assuming the hydrogen is produced in the standard way, using lots of methane and a bit of electricity, and counting one unit of chemical energy as having the same energy content as one unit of electricity. Meanwhile, the energy consumption of the Tesla (according to its manufacturers) is 15 kWh per 100 km. (Of electrical energy.) Even if we penalize electricity, saying "every 1 kWh of electricity costs 2.5 kWh of fossil fuels", the Tesla is still much better than the fuel-cell car, and better than the average fossil fuel car. (And in the future, we won't be getting electricity from fossil fuels, hopefully!)
So the hydrogen car is NOT a "solution" to our problem, if our fundamental problem is an energy problem.

Saturday, December 6, 2008

Why on-site renewables don't add up

Straight up, I want to say I love renewables, and I believe that we should have a massive increase in renewables as part of making a sustainable energy plan that adds up (as explained in my book Sustainable Energy - without the hot air, now available on paper).
This is an article about on-site renewables. Imagine a developer is making a new urban development. Offices or homes, perhaps. A three-floor building. Under some planning regulations, new buildings must get some fraction of their energy consumption from on-site renewables. Now, these regulations have some undeniable benefits: if it is expensive to install on-site renewables, the developer may modify the building so as to reduce its energy consumption, thus making it less costly to reach the required renewable fraction. Having local renewable energy production may also increase awareness about energy consumption among the building's users. And some local renewables are no-brainers - making hot water using solar panels, for example, makes complete sense, providing roughly half of the hot water consumption of an average home.
But here is the problem:

200 kWh per year per square metre = 23 W per square metre

On the left, 200 kWh per year per square metre is the typical total energy consumption of many homes and offices, expressed as energy per year per square metre of floor area. In terms of energy rating bands, 200 kWh/y/m2 is the boundary between bands F and G. Many government buildings use twice as much as this. (The Home Office uses 400 kWh/y/m2, for example.) The Passivhaus standard, at 120 kWh/y/m2, is not much better than this 200 kWh/y/m2 benchmark.
On the right, I've converted this quantity into watts per square metre, which are the unit in which I prefer to express renewable power production. Sadly, most renewables have powers per unit land area that are substantially less than 23 W per square metre. Wind farms generate 2 W/m2. Energy crops generate 0.5 W/m2. Solar photovoltaic panels generate 20 W/m2. And remember, we're imagining a three-floor building. So the power required per unit land area occupied by the building is not 23, but 3x23 = 69 W/m2.
On-site renewables are an interesting gesture, but if we are serious about renewables making a big contribution, they have to be big - they must occupy a land area much bigger than the land occupied by the buildings we are powering. If you want to completely power a three-floor 200 kWh/y/m2 building from energy crops and wood, for example, then the land area required for the energy crops and wood must be roughly 140 times as big as the land footprint of the building.
The response of an angry green campaigner to what I have just written can be predicted: "But we could make the buildings far more efficient!" Could we? I'd love us to build more-efficient buildings, but show me data. Not wishful thinking, but NUMBERS. The Elizabeth Fry building at UEA is often held up as an example of a state-of-the-art eco-friendly building. And here are the numbers for that building (from page 299 of my book). It consumes 96 kWh/y/m2, which is 11 W/m2, which is only about 50% better than the Energy-Rating-Band-F/G benchmark from which I started.
The bottom line: if you want to completely power a typical building, or even an amazing eco-building, from renewables, most of those renewables have to be offsite. There isn't room on-site! And it's probably a better use of resources to accept this fact up front, rather than force developers to squeeze uneconomic figleafs (such as micro-turbines) into their developments. We should modify the planning regulations for new buildings so that developers are still required to build renewables, but are encouraged to build new renewable capacity off-site.

Sunday, November 23, 2008

Petrol, diesel, miles per gallon, litres per 100 km, energy, and emissions

Too many units! Too many things to measure! In Europe they talk about "the one litre car" (using 1 litre of fuel per 100 km). In Britain, drivers of the Prius are happy to do "more than 50 miles per gallon". In the USA, gallons are different. Then there's emissions (does it emit less than 100 grams of CO2 per km?) and finally there's energy measures (for example, the average British car consumes 80 kWh per 100 km).

And, while we're dealing with all these different units, the most annoying detail of all is that petrol is different from diesel. Diesel has bigger energy per litre (roughly 10% more), and it has bigger carbon emissions per litre too.

I've put together a graph that makes it possible to compare and convert some of these measures of vehicle performance.

Some memorable anchors on this diagram:
  1. A 90 mpg petrol vehicle is roughly equivalent (in energy and emissions) to a 100 mpg diesel car. Both use an energy of about 30 kWh per 100 km and have emissions of about 75 g per km. People have sometimes lampooned the Prius for consuming more fuel than a BMW. If the Prius is using petrol and the BMW is using diesel, then it's not fair to compare the numbers of litres used.
  2. A 'one litre car' delivers 282 mpg, and uses about 10 kWh per 100 km. This is the energy consumption, incidentally, of quite a few prototype electric cars (measured at the socket).
  3. My 'average UK car today' uses 80 kWh per 100km and emits 200 g per km. Europeans would call it an 8-litre car.

For more about energy consumption of eletric vehicles and hydrogen vehicles, see Sustainable Energy - without the hot air.
Small print: 'mpg' means miles per imperial gallon. 'g' means grams of carbon dioxide.
Energy contents (high heat values) and emissions were assumed to be:
Petrol: 34.7 MJ per litre; 2344 g per litre.
Diesel: 37.9 MJ per litre; 2682 g per litre.

Sunday, October 19, 2008

How to boil water

A friend told me he'd been fighting with his kitchen-cohabitants over the question of whether to simply use the gas to make hot water for pasta, or whether to use the kettle, then put it in the pot.
To answer this question quantitatively, I did some experiments and I've written a new webpage, How much is inside HOT WATER? The page assumes that the motivation is to save energy. The conclusions apply to Britain today and to similar countries.

My conclusion is that using the gas hob is slightly better in energy terms than using the kettle; but my recommended behaviour depends on the time of year. In the winter, if you would like to have more heat in your kitchen, then using the gas hob alone is definitely best; in the heat of summer, using the kettle may be preferable.

Disclaimers, small print...
If your motivation is to save money then the answer will depend on your fuel prices. If your motivation is to cook the pasta as fast as possible then you should use neither method alone - you should use both the kettle and the hob, with roughly half in each.

Friday, September 26, 2008

Lights on cars in the daylight

According to the Dail Mail, crazy European legislation forcing car drivers to keep headlights on ALL day could inflate fuel costs by up to £160 a year.

What are the numbers? Well, this is one that I worked out earlier. It's in chapter 9 of Sustainable Energy - without the hot air, on page 58. Let's say the four bulbs for the running lights on a car use about 100 W. Allowing for the engine's and generator's inefficiencies, this 100 W of bulb power requires a petrol power of 730 W. For comparison, the petrol consumption of an average car running along at 50 km/h and consuming one litre per 12km is 42000 W. So having the lights on while driving requires 2% extra power.

If you drive 50km per day and fuel costs £1.20 per litre then you spend £5 per day on fuel. Putting the lights on is going to increase your costs by 2%, which is 10p per day. That's £37 pounds per year, for a typical driver. Obviously the answers come out differently if we change the vehicle to a Hummer, or if we replace the incandescent bulbs by modern LEDs.

I hope this helps!

Thursday, September 25, 2008

The book's finished!

I'm happy to announce that Sustainable Energy - without the hot air is finished.
It's got a publisher, a cover design, and a publication date of December 1st 2008.
All that remains is some frantic last minute editing and correcting; then an 8-week wait.
The book will remain free on my website.

Friday, July 25, 2008

Performance data for a GWiz in London

This article is by Kele Baker and David MacKay, based on data collected by Kele

The performance of the G-Wiz varies with driving conditions and the weather. The G-Wiz can be driven on 'high' or 'low' power. The lights may be on or off. And the efficiency of the battery appears to depend on the temperature. The graph shows data for 19 charging events: the distance travelled in miles is on the horizontal axis and the energy required from the grid to recharge the battery (measured at the socket with a Maplin meter) is on the vertical axis.

The best performance was 16 kWh per 100 km. The worst was 33 kWh per 100 km. The average was 21 kWh per 100 km. This number is roughly four times better than the energy consumption of an average petrol car doing 33 miles per gallon, which uses 80 kWh per 100 km. In money terms, the electricity cost of the G-Wiz is 2.1 pence per km (assuming 10 p per kWh).

Tuesday, July 22, 2008

Mysterious cheap electricity generated in Nevada

There is a strange violation of economics going on on the Nellis Solar Power Plant wikipedia page. It asserts that the US air force are paying 2.2 c per kWh for electricity from a solar PV farm that happens to be on their land. This sounds far too cheap. The article says the '14MW' farm cost $100M to build (that's 7 dollars per watt, peak) and will generate 25M kWh per year. That means it will generate an income of $0.55M per year for the owners of the farm (who paid $100M, remember). That corresponds to a pay-back time of 180 years. So what's going on? Is it a strange Nevada phenomenon? Did aliens subsidise the farm? Or did wikipedia get the numbers wrong?

Monday, June 23, 2008

I DO advocate switching off electrical gadgets on standby

Well, well, it's been an interesting few days... Since The Register posted an article about my draft book, I've received a flood of emails, and been shocked to observe the cacophony of people on blogs and bulletin boards all debating 'what the Professor said', plopping me in one camp or another of their running battles.

I'd like to make one suggestion to everyone: if you want to discuss what I said in the book, please read the book!.

Some readers seem to think that whatever the journalist wrote, I said. For example his introduction said that most people 'have no need to worry about the energy they use to power their electronics; it’s insignificant compared to the other things'. That was the journalist, not me! This attitude to standby power has provoked the mob to get out their flame-throwers, saying 'MacKay should know that 8% of all domestic electricity goes to power junk on standby!' Sigh!

For the record, here is my domestic electricity consumption for the last few years.
I started paying attention to my electricity consumption in 2007. I started switching off all my stereos, answering machines, cable modem, wireless, and so forth, in mid-2007. I am happy to confirm that switching off these vampires has reduced my domestic electricity consumption from roughly 4 kWh/d to below 2 kWh/d. This is an energy saving well worth making; I encourage everyone to bye-bye their standby, and read their meters to see the difference it makes.

Monday, June 2, 2008

The last thing we should talk about

Wallace Broecker has been promoting the idea that `artificial trees are the way to solve global warming'. Pushed for details, he says that `brilliant physicist Klaus Lackner has invented a method to capture CO2 from thin air, and it doesn't require very much energy'. Broecker imagines that the world will carry on burning fossil fuels at much the same rate as it does now, and 60 million CO2-scrubbers (each the size of an up-ended shipping container) will vacuum up the CO2.

I think it's a very good idea to discuss capturing CO2 from thin air, but I feel there is a problem with the way this carbon scrubbing technology is being discussed. The problem is energy: how much energy does Lackner's CO2-capture method require. `Not very much'? Come on, we need numbers, not adjectives.

Here are some of the numbers required for a coherent conversation about carbon capture. Grabbing CO2 from thin air and concentrating it into liquid CO2 requires energy. The laws of physics say that the energy required must be at least 0.24 kWh per kg of CO2. What does Lackner's process require? In June 2007 Lackner told me that his lab was achieving 1.3 kWh per kg. Let's imagine that further improvements could get the energy cost down to 0.7 kWh per kg of CO2.

Now, let's assume that we wish to neutralize a typical European's CO2 output of 11 tonnes per year, which is 30 kg per day per person. The energy required, assuming an exchange rate of 0.7 kWh per kg of CO2, is 21 kWh per person per day. For comparison, British electricity consumption is roughly 17 kWh per person per day.

So as a ballpark figure, the Broecker/Lackner plan requires an amount of energy equal to current electricity production.

When I call carbon capture from thin air `the last thing we should talk about', I don't mean that we shouldn't talk about it. I definitely think we should talk about it, in detail, to help drive us towards more radical action now, to reduce the need to create these mega-vacuum-cleaners.

P.S. What about trees?. Trees are carbon capturing systems; they suck CO2 out of thin air, and they don't violate any laws of physics. They capture carbon using energy obtained from sunlight. The fossil fuels that we burn were originally created by this process. So, the suggestion is, how about trying to do the opposite of fossil fuel burning? How about creating wood and burying it in a hole in the ground, while, next door, humanity continues digging up fossil wood and setting fire to it?
From the minutes of the Select Committee on Science and Technology, the best plants in Europe capture carbon at a rate of roughly 10 tonnes of dry wood per hectare per year. Or in equivalent CO2 terms, that's about 15 tonnes of CO2 captured per hectare per year.
So the area of forest per person required to fix a European output of 11 tonnes of CO2 per year is 7500 square metres per person. (And then you'd have to find somewhere to permanently store 7.5 tons of wood per year!) Taking Britain as an example European country, this required area, 7500 square metres per person, is twice the area of Britain.

Friday, March 21, 2008

Cost-effective ways to reduce your carbon footprint

I'd like to highlight Sandy Polak's
page on how to be green
. It is the best page I've read on this topic. The main thing I would have amplified more than Sandyis heat pumps: I bought a 'green' condensing boiler a few years ago, and now regret having done so - I wish I had looked into air-source heat pumps. Condensing boilers are not green: they use fossil fuels! I reckon that, even if electricity is produced from gas-fired power stations, air-source heat pumps are a good thing, environment-wise; and if and when the grid is decarbonised, heat pumps will get ever greener. Heat pumps have to be the future for domestic heating without carbon.

Sunday, March 9, 2008

Eco bollocks awards

An emailer pointed me to a great blog that features well-written explanations of the authors' occasional Eco bollocks awards. Two model recipients are:
Ken Livingstone, whose claim that London will cut carbon by 60% is given a thorough inspection, and the Windsave WS1000 wind turbine. "Come on, it’s time to admit that the roof-mounted wind turbine industry is a complete fiasco. Good money is being thrown at an invention that doesn’t work. This is the Sinclair C5 of the Noughties."

Mark Brinkley's writing style in this blog is eloquent and fun -- "The world has gone mad. This seems like some insane game about seeing who has got the greenest willy."

Saturday, February 2, 2008

Stuff dominates!

I used to summarise British energy consumption by saying "transport, heating, electricity".
However I just read Too Good To Be True? The UK's Climate Change Record,
(pdf) by Dieter Helm, Robin Smale and Jonathan Phillips, who estimate (based on the value of British imports from other countries, and those countries' carbon intensities) that the net carbon footprint of British imports and exports is 10 tonnes of CO2e per person! - this doubles the British carbon footprint at a stroke and implies that our energy consumption is not dominated by transport, heating, and electricity after all. Stuff is king!

Monday, January 7, 2008

How much hydro does it take to "power Glasgow"?

Whenever a renewable power facility is described they always say how many 'homes' it will power. Today's news says The 100MW Glendoe Hydro Scheme will be able to power around 250,000 homes – equivalent to a city the size of Glasgow.

I think this 'homes' description is really misleading, because I bet people confuse 'powering all the homes in Glasgow' with 'powering all Glasgow's electricity' or even 'powering all Glasgow's energy'.

Let's do a simple calculation.

The average expected power from Glendoe is 180 GWh per year [source]. Now
if we take 180 GWh per year and share it between a Glasgow of people
(616,000 people), we get 0.8 kWh/d per person.

OK; what is the average electricity consumption per person (including all forms of electricity, not just domestic)? Answer: 16 kWh/d per person. So Glendoe actually provides 5% of the electricity consumption of Glasgow.

So if people get the impression from the press releases that Glendoe will power Glasgow, they have been misled by a factor of twenty!

This is a bigger factor than the normal factor by which people are usually misled. The statement
that Glendoe (180 GWh/y) would power 250,000 homes implies that each 'home' uses just 720 kWh per year. But the normal assumption in press releases about wind or tide is to assume the average home uses 4000 kWh/y or 4700 kWh/y. What's going on? The ratio between 720 kWh and 4000 kWh (18%) is suspiciously similar to the ratio between the average power production of Glendoe (180 GWh/y) and its capacity (100 MW is equivalent to 877 GWh/y). Methinks that someone at Scottish and Southern must have screwed up (or deliberately misled the public) by pretending that Glendoe will produce 100MW 100% of the the time, whereas in fact it will have an average load factor of 20%.