Although 18,000 miles is actually the minimum distance that counts (of 24,900 miles equator length), and I assume their trip may be a tad longer than this, the enterprise hardly seems like an energy efficiency drive; at 360 miles per tank and assuming an 8 gallon tank, this is 45 mpg! The couple plus crew trailing in two cars behind wish to travel day and night for up to 14 hours and 620 miles per day, but even on a 60-day journey (they are stopping off at their daughter's wedding in Melbourne, Australia, for example), this means that they only need to average 300 miles per day at 30mph with 5 hours' driving each.
The Taylors apparently already hold 34 awards for fuel economy driving, and are thus described in one report as 'arguably the world’s most fuel-efficient drivers'. While some are of the opinion that it is a worthy effort to perform an inefficient process as efficiently as is then possible, I would argue that part of the task should be to find the best process. If everything one needs is in the car(s) behind (or to benefit from slipstreaming even in front), including, I imagine, quite a bit of the fuel, then heck, I could even argue the case for travelling round the world on the end of a crew-car tow-rope and claiming no energy use at all.
This highlights the need for looking at the overall process and total energy used for performing a task. When I argue the case for using light electric vehicles, which can have a consumption equivalent in the vehicle of over 280 mpg (10 kWh for 100 kilometres), some people then try an opposing position by asking "ah, yes, but where does the electricity come from: the energy waste is just moved to the power station, isn't it?" I try to answer with the following points:
1. by moving the (heat) inefficiency out of the car, I at least get a chance to generate the electricity somewhere where I can use the heat and do something on a larger scale with the emissions, a simpler and lighter electrically-powered vehicle still achieves some 90 mpg, even assuming inefficient generation and transport of electricity;
2.whenever the batteries are charged, there is the opportunity for using renewably-generated electricity directly when it is available; this reduces the need for providing less easily available bio-fuels as an alternative to an oil-sourced fuel.
This last point is interesting in terms of the 'energy harvest'. Energy efficiency is often seen as being a case of using less energy and fossil fuel when performing a task, but when using renewable energy it is also important to maximise a harvest by investing as little energy (and land) as possible for a given annual output. Only recently has it started to dawn within environmental circles that fuel crops (which have the advantage of being easily storable), have the disadvantage of needing a huge amount of land to grow on, whereas wind power takes very little land away from agricultural use, but has a very high rate of return on the energy investment. My personal calculation for the ratio of output to input from a wind turbine is lower than generally publicised figures, but is still an impressive 20:1 or more over a forecast 20-year turbine lifetime. If this energy return were money, we would say that the money was being invested at an interest rate of at least 100 per cent (as one can get back enough energy after one year to add a new turbine, two after two etc.). Were one really to pump back the energy used to build one turbine into building more, this would theoretically lead to having over a million turbines after 20 years just spawned from the first one, which is neither desirable nor necessary.
Just how many wind turbines we should really aim to have in a sensibly designed energy supply system will depend on how much energy we will actually be using in the future and on the question of how much of our energy is required to be held 'in storage' for use whenever we need it, and where that energy ultimately comes from. Current energy use should not be the base criterion because in the electric vehicle example I can get similar mobility in many many instances for just one sixth of the fossil fuel energy consumption. If I want to eat an apple, I don't pick or buy six and throw five away, and yet in terms of energy use for mobility we do just that and worse on a daily basis. We really can become very much more efficient individually and as a society; we need to sacrifice the inefficiency of many of our actions, not necessarily the actions themselves.
And back to the Taylors: try travelling around the world with a sixth of the energy ration which you're aiming for this time and it'll be the energy equivalent of travelling just 50 miles a day in a normal car. There are enough people around who use this amount of energy daily and only get to the office and back; in two months you'd be able to get round the planet. Oh, I forgot: you are going to get round the planet, just not very efficiently.