This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
I think a useful indicator of the uselessness of a Green technology is whether the Greenies themselves snub it.
One example would be the plug-in electric car. In the UK there have only been 2,149 electric cars sold since 2006. Only 1,082 electric cars were sold in 2011 despite a £5K subsidy and the Nissan Leaf being manufactured in the UK. Clearly the Greenies don't buy the product they want to impose on the rest of us.
In the case of towing kites the obvious strong candidate to buy one or more of these things would be Greenpeace. Greenpeace operate a fleet of about half a dozen ships, but as far as I can see they do not use these kites to save fuel. If they did I'm pretty sure it would be mentioned on Greenpeace's webpages about the ships or on Skysail's website.
It looks like Greenpeace also snub the modern version of a sailing ship pioneered by Jacques Cousteau, which is to use Flettner rotors or 'turbosails'. Greenpeace has one sailing ship in its fleet, the Rainbow Warrior III (launched last year), but it uses the traditional design of sails mounted on masts. I suspect the sails come down and they switch the engines on as soon as nobody is looking.
Lord Cochrane had a try with kites during the Napoleonic wars and decided against trying anything further.
The modern versions have long been touted (hyped?) as the answer to all our prayers but unless it is government you ask, getting anyone to invest serious money is a problem.
In a similar vein, we once had some wind turbine manufacturing in this country.
Then the business took off with the greenies in ecstasy. But by the time the big offshore win farms came to be built we had none left and our wind turbines were being fabricated in China. Then when they arrived they were found to be flawed and they flew in Chinese welders to fix the problem.
Nothing in it for the UK workers but proof that if all this greenieism was creating "green jobs" it was in China.
Next came the news that Sheerness had been designated a CORE area (I think that is the acronym for something about Centre something or other Renewable Energy) and Vestas, with lots of our money I assume, were going to build a factory there.
The trouble is, Vestas has been in financial trouble for some time and with the cut in subsidies saw the writing on the wall. There have been a lot of cases of solar panel manufacturers going belly up in Germany and elsewhere and, that other recipient of tax payers money, US taxpayers in this case, electric car manufacturing is also in trouble in the US with one company suddenly going bankrupt along with its battery manufacturer.
It gives one a warm cosy feeling to see so many greenie inspired projects crashing about their ears only slightly tinged by the fact that a lot of tax payers money has gone west with them. Still, cheap at half the price. If they were all to survive they'd be leaching money out of the taxpayer for generations to come.