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The world’s resources of petroleum originated as algae. For several years, small US start-ups have been pushing these simple organisms as the best replacement for fossil diesel. Shell’s investment in Cellana looks like the first major validation of the large amounts of VC money that have gone into algae.

There are many, many different types of algae. The percentage of oil varies enormously by type. Specialists expect that we will use specially bred forms that yield about 50% oil by weight. When the algae is harvested the oil can be extracted by drying the organism and then compressing it. When the technology is mature, processing costs will be lower than other potential sources of biodiesel oil.

Yields of algae will be high. Estimates of the eventual maximum output per hectare vary enormously, but few doubt that algae will perform several times better than any conventional plant. Some estimates suggest that algae may eventually produce oils at a rate per hectare more than ten times better than oilseeds.

Algae are good at photosynthesis and probably produce over three quarters of all atmospheric oxygen. (Algae also use mechanisms other than photosynthesis as routes for turning CO2 into free oxygen.) Their ability to absorb CO2 has encouraged entrepreneurs into examining their ability to scrub CO2 from power station smokestacks. Small pilot plants now extract flue gas and run it across algae beds. The signs look good but it will be several years before we can be confident that algae will provide a cost-effective form of carbon capture. If they are successful as some of the proponents expect, algae will enable us to produce ‘carbon negative’ diesel.

In any list of the most interesting approaches to reducing fossil fuel dependency, and cheaply sequestering carbon, algae deserve a high ranking.

The UK government has announced an intention to allow offshore wind farm development around most of the UK. John Hutton suggested that about 33 GW capacity could be added by 2020. This would provide about 25% of current UK electricity demand (which is itself rising by 1 to 2% per year).

Simple calculations suggest that this change may add about 15-25% to UK electricity bills. Offshore wind is more expensive to construct and operate than onshore wind farms. The announcement may suggest that the government believes that offshore wind can be pushed through but that onshore farms are likely to be successfully opposed. The big push for offshore wind seems to mean that the government is losing faith in nuclear.

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The UK continental shelf is a good place to build wind farms. Wind speeds are high and the UK’s oil and gas industry has given us the capacity to work in harsh regimes. After a period of experimentation with smaller offshore wind projects, the 300-turbine London Array, shortly to be constructed, will become the largest marine wind farm in the world.

The government has given increasingly clear signs that it viewed offshore wind as a renewable technology of choice. It increased the proposed support from one ROC (currently worth about £45) to one and a half in the 2007 Energy White Paper. It now seems also to be willing to over-ride the Ministry of Defence’s concerns about the impact of wind farms on military radar. The worries over the turbines dicing small wading birds have been pushed aside.

The basic numbers
The government wants another 25 GW on top of the current 8 GW in various stages of planning. These figures refer to the maximum output of the turbines on a windy day. The actual output is likely to be between 30 and 35% of this figure. (Data from Scroby Sands, an early offshore farm, suggests a lower figure, but the turbines have suffered from reliability problems which have depressed the output.)

33 GW of offshore wind capacity will provide about 100-110 TWh, or perhaps 25% of total UK demand. This approximately equates to the electricity demand from households today.

When the wind is blowing hard, the total offshore capacity envisaged by Mr Hutton will almost match the minimum total demand during a winter’s day.

Total UK electricity demand (MW) in the 24-hour period to noon on Tuesday 11 December 2007

This chart is copied from National Grid real-time data. The y axis is MW. A GW is 1,000 MW. So the minimum demand on 11 December 2007 was reached at about 5am with a total demand of about 35 GW, about 10% more than would be generated on a very windy night all around the coasts.

If – and this is a very big if – the existing value of ROCs is maintained, then the possible subsidy from all electricity users to offshore wind if all 33 GW capacity is built is about £7bn. Over a year, this would raise the price of each kilowatt hour of electricity by about 1.8p, compared to the current retail price of about 10p. In addition, there will have to be substantial payments to other generators to incentivise them to build and hold ready gas-fired capacity for use when the wind isn’t blowing.

Offshore wind is expensive because its construction cost is high. The British Wind Energy Association mentions a figure of £2m per MW of capacity, compared to less than £1m for onshore wind. The total investment required to build 33 GW might therefore be as much as £64bn, about 6% of UK GNP. The BWEA figure looks a little high to me and the actual cost might be somewhat lower at perhaps £50bn.

The problems
The government’s announcement was broadly supported by the other main political parties. It is the easiest source of renewable energy to back, even though it is expensive. The ROC subsidy system disguises the true cost of switching to wind and other sources, so politicians must assume that the extremely heavy expense of wind will not be obvious enough to be politically dangerous.

The problems for offshore energy lie elsewhere:

• Turbine supply: only a small number of suppliers make marine-ready turbines. Vestas and Siemens, both based in Denmark, have made most of the ones already supplied. The worldwide shortage of top quality turbines is likely to persist for some years. New manufacturers will be enticed into the market if government support looks robust, but this could take the best part of a decade. Some of the existing turbines have severe problems with gearboxes (as at Scroby Sands) but we can expect these issues to be overcome eventually.
• Grid connections: powerful arrays of turbines must be located close to points on the high voltage transmission network. It is no good putting a hundred turbines 50km from the nearest point of interconnection unless you can be sure to get planning permission for the National Grid to run pylons. (I think I am right in saying that the substation to handle the electricity coming onshore from the London Array was the last part of the infrastructure to get planning permission.)
• Skills: the UK has offshore skills as good as most other countries, but getting 7,000 turbines built by 2020 is an extremely challenging task.
• Intermittency: offshore wind is reasonably predictable and strong. Below is the wind map from the BBC on the afternoon of Tuesday 11 December 2007:
  
  
  
  In the southern portion of the UK coastline, wind speeds will be low because of the prevailing cyclonic weather. But further north, the west coast is seeing reasonable wind speeds. Days of real quiet are surprisingly infrequent. Nevertheless, if we are to generate 25% of our electricity from offshore, we will need substantial back-up capacity. Very approximately, the UK has about 8 GW spare capacity. By ‘spare’ I mean unused generating capacity above what is likely to be the peak on a very cold December day at about 5.30pm. We will need to have much more when we have 33 GW of offshore power. I haven’t yet seen an estimate, but I suspect that it will be at least 12 GW more than we have at the moment. The capital cost of the gas plant to deliver this is likely to be over £4bn.
• The interaction with nuclear: it hasn’t been picked up by the press, but a 25% target for offshore wind is not easily compatible with a large nuclear industry. Nuclear needs to run all the time as baseload. If the wind is blowing strongly when demand is lowest (about 5am on a summer’s day) then the UK will run the risk of having too much electricity supply. Either nuclear or wind would have to be disconnected or the UK would have to invest in more of what is called ‘pumped storage’. Surplus electricity is used to push water uphill into reservoirs. The reservoir can be discharged later, turning hydro-electric turbines when demand is higher. It is difficult to encourage large amounts of both nuclear and wind, and the government’s new wind policy must mean that it is losing interest in nuclear.

The conclusion
Offshore wind is expensive and still somewhat untried. The government’s apparent decision to allow rapid development around a large portion of the UK coast is path-breaking. Most observers think that getting to 33 GW is an extremely optimistic target for 2020. However, industry people think that it may be possible to get as high as 20 GW, probably generating over 15% of UK power.

The carbon savings from these batteries are not large. My calculation is that they might save 10kg of CO2 a year in a household full of portable devices. But they will, of course, reduce the waste going into landfill.

The company that makes the batteries has won some important awards for its innovation. More importantly, it also has some extremely interesting views on the evolution of home electricity demand. It correctly points out that a larger and larger fraction of home energy is used in 12V, not 240V appliances. We waste a lot of energy switching 240V AC down to 12V DC. Its next products include a box that will allow all DC devices (phones, handheld consoles, laptops) to be efficiently charged. Eventually, it will be possible to use cheap(-ish) solar power collectors to charge all the battery DC devices in the home. The savings in carbon would be worthwhile (but probably outweighed by the purchase of one extra TV).

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These elegant batteries are sold by Moixa, a UK company that specialises in innovations that reduce home energy consumption. They are now widely available in UK stores. People in the UK throw away 600 million batteries a year (10 per person) so the market is large enough. This means 22,000 tonnes of toxic metal is disposed of every year.

The typical UK household has about 25 devices using batteries, ranging from remote controls, torches and games consoles. Some of the batteries are barely used and last for years, others fade within a few hours of heavy use.

Conventional rechargeable batteries have never really succeeded. They need a separate recharging device, and the performance of the batteries tends to disappoint. Moixa told me that the average rechargeable battery is only actually charged 8 times before it is lost, accidentally thrown away or the recharger is broken.

Moixa reckons its USBCell batteries can be recharged 500 times and that the ease of plugging the battery into a USB connection will mean that users cherish the product. They believe that each battery, which has a power equivalent to a disposable battery of the same size, will be reused at least 50 times. This means that the cost of around £11 for two batteries will turn out to be less than 25p each time it is recharged.

The electricity cost of recharging a battery is a fraction of a penny, and doesn’t really affect the economics. A laptop is a very good converter of 240V AC into 12V DC and little energy is wasted. For heavy battery users, it clearly makes sense to switch to the new USBCells.

What are the carbon implications? Moixa told me that an Australian study had shown that a USBCell reused 50 times would save 7kg of CO2. A house throwing away 25 batteries a year would therefore only save 3.5kg a year from buying USBcell AA batteries for all of its appliances. In the context of five or six tonnes of emissions yearly from a typical house, this is a tiny fraction of the total carbon footprint.

But the company was eager to explain the broader strategy. Thirty years ago, the only devices in the house using low-voltage electricity might have been a torch and a 12V children’s train set. Now the average house has scores of little devices, though all with quite low power use. Phone chargers, powered toothbrushes, iPods, laptops, and portable lights are all growing users of home electricity.

When the electricity supply system was coming into being in the 1880s in the US, Edison’s direct current system lost out to Nikola Tesla’s alternating current. AC was far better for long distance transmission. All our major appliances are designed around 240V or 110V AC. But most new appliances don’t need much power and operate at safe and cheap 12V DC. The AC power is still probably better for appliances with large motors, such as the washing machine, but for many other home devices it would be better if the supply was 12V DC.

Moixa’s next device, which it expects to start selling in late 2008, is a box that allows tens of devices all to be charged from it. It centralises the 12V transformer, reducing energy losses to a very low level. Importantly, this box could run from the mains, or could easily be powered by a small solar panel left in daylight. The savings aren’t likely to be huge, perhaps 200 kWh a year, but the new box could be a relatively cheap way of saving 5% of the electricity bill.

Eventually, all lighting will be switched to 12V. A large fraction of the lighting in new houses is already run at low voltage, with the power to each light going through an AC to DC transformer. It would be better to run a single 12V lighting circuit with a single, and very efficient, transformer. Moixa is working on this now.