On a calm night at sea, Captain Erwann Le Rouzic is not just paying attention to the wind and currents, twin tools sailors have used for centuries in nautical navigation. Rather, he is looking at predictions for sunlight: areas in the surrounding ocean where rays are the strongest for longest need to be calculated into his route for the next few days. It was the PlanetSolar captain and his crew who received a warm welcome last week as they landed their completely solar-powered boat the Turanor PlanetSolar - the largest in the world - in Hong Kong for a stop on their inaugural world tour. But it would be impossible for the captain to navigate without his weather team back in Toulouse, France. They provide accurate weather information, telling him where to best recharge his boat's batteries by monitoring solar activity and communicating the information to him via a solar map in the cockpit of his boat. Darker, red areas indicate cloud coverage, places he wants to avoid; the lighter yellow or white areas are the sunny regions. For this solar nautical adventure, bad weather is no longer just something to avoid in fear of chaos at sea, but something that could literally cause their journey to stop. In 2014, a plane will attempt to do what the boat has been doing so far: travelling around the world powered by the sun alone. The pilot, CEO and co-founder of the Solar Impulse project Andre Borschberg, seems like an invincible figure. He has been training himself to keep awake and alert for journey legs of up to two days and nights at a time, because such a light plane is only large enough to fit one person. But even he cannot do without the weathermen on the ground. They can see high into the upper reaches of the atmosphere, and tell him how to proceed. Last month, Borschberg succeeded in a test flight in Europe that went for 26 hours straight. The whole time, he was communicating via the plane's satellite system to their weather partners at Meteo-France. They've got a separate back-up satellite system, just in case - because a lack of communication could mean not just disaster in terms of traffic control, but in the supply of power for the vehicle itself. If Borschberg finds himself flying in the morning without having navigated to the right spot during the night, there won't be enough sunlight to recharge his batteries. 'That would be a difficult situation for the airplane,' he says. 'You could land away from your destination. But if you are over the ocean ...' So he needs the teams of people on the ground who tell him where to go: the ones who man the machines that crunch out data for energy essentials like solar radiation, and make sense of it all. They can calculate the actual energy of the sun received after you take away the clouds, aerosols, or other moving, absorbent materials in the atmosphere. These people give the sailors and pilots not only the raw weather information, but information about how to move forward in a way that is best for their long-term goals. Bertrand Piccard, Borschberg's partner in the Solar Impulse project, shared a story at a technology conference two summers ago. It was about something a weatherman told him that he never forgot: up in the air on a pioneering hot-air balloon flight, with a limited supply of fuel (there was no solar energy for him then), Piccard's weatherman one day asked him to fly very low to the ground and slow. Thinking he wouldn't make it around the world going so slowly, Piccard decided to rebel and find the jet stream - a much faster layer of air - further up in the atmosphere. The weatherman was the one who told him that if he kept going that way, he would be lifted to the North Pole. Piccard recalled him asking: 'Do you want to go very fast in the wrong direction, or slowly in the right direction?' That same weatherman is chief meteorologist at the Solar Impulse Project today. 'Our chief meteorologist is a very critical person, as you can imagine, because we are very close to the limit,' Borschberg said. But weathermen's new roles are certainly not limited to pioneering travel adventures. Energy companies have long worked with weather bureaus to figure out how much energy they need to provide to meet demand in a certain area, depending on how cold the winter is or how hot the summer. (Imagine the air-conditioning energy costs for a few degrees of temperature difference in buildings across Hong Kong.) Yet the combination of meteorology with renewable energies is just emerging, says Dr Alberto Troccoli, a climate scientist who is convening the first ever International Energy and Meteorology Conference in Australia in November. 'I could feel there was a need for a conference to gather experts around this area of meteorology and energy,' he said. 'Now there are also requests from people looking at wind and solar-energy forecasting and other things. So things are only going to grow because of the expansion of renewable sources of energy.' Indeed, solar-energy scientists and advocates have been using solar-radiation data to see which sites are best suited for the use of the energy and the building of solar panels. 'Based on that weather data, we can estimate how much electricity or energy we can get out of solar,' says Professor Michael Leung of the School of Energy and Environment at the City University of Hong Kong. 'We want to work out the payback period of a solar energy system. How much energy can be produced in one year, and how many years does it take to be paid back?' That way, the scientists can apply the data to see if solar energy will be sustainable. This human application and manipulation of meteorological data comes at a time when meteorology itself is changing to become more automated. Despite the romantic notion of meteorologists sitting in an office looking at maps and communicating their findings to an unknowing audience, modern-day meteorologists are no longer the pretty-picture analysers of the past, according to Troccoli, the energy-and-meteorology conference organiser. For most jobs in the field, extensive computer-programming skills are needed, as well as maths- and physics-modelling knowledge. Today's meteorologists are often the ones writing code and testing algorithms to figure out better ways for modelling the weather. 'What is done is that you collect a lot of observations from satellites and from the ground, so there are millions of pieces of information every day coming in. 'This information is processed through a data-simulation method that combines observations with the numerical models that describe the physics of the system, put the things together and produce forecasts,' Troccoli said. Meteorologists can predict temperature even 10 days in advance, with only a few degrees of fluctuation. But why is precipitation so hard to predict and so likely to fluctuate? Troccoli said it was because with the precipitation model, technology was not good enough to observe every phenomenon yet, although new technologies might be on the horizon. The highest resolution that precipitation can be studied in is in weather cells of 10 by 10 kilometres, meaning that the data comes in from a large area and is then analysed over that whole space. Consequently, the subtle evolutions of weather in the area under study are often invisible. 'In principle, if you could observe every millimetre, then you could probably predict precipitation very well,' Troccoli said. Yet part of the adventure for Borschberg in his solar plane is the unpredictability of the journey, even with his reliable meteorologists at hand. 'You have to fly with nature and not against nature,' he says, as he flies against convention.