The maps can also gauge solar energy at every other spot on the planet, and have already been used to help businesses to site solar panels in Morocco, for instance, or send text messages to tell sunbathers in Italy to put on more cream.
"We are trying to link up observations of the earth to benefit society," said Jose Achache, head of the 72-nation Group on Earth Observations which seeks practical spinoffs from scientific data, ranging from deep-ocean probes to satellites.
GEO member states will hold ministerial talks on Nov. 30 in Cape Town to review a 10-year project launched in 2005 which aims to join up the dots between research in areas such as climate change, health, agriculture and energy.
From satellite data collected over 22 years, NASA says the sun blazes down most fiercely on a patch of the Pacific Ocean on the equator south of Hawaii and east of Kiribati.
More practically for solar generation, on land the Sahara Desert region soaks up most energy with the very sunniest spot in southeast Niger, where one sun-baked landmark amid sand dunes is a ruined fort at Agadem.
"For some reason there are fewer clouds just there than elsewhere," in the Sahara, Paul Stackhouse, a senior scientist at NASA's Langley Research Center, told Reuters.
The area got a searing average of 6.78 kilowatt hours of solar energy per square metre per day from 1983-2005 -- roughly the amount of electricity used by a typical U.S. home in a day to heat water. The patch in the Pacific got 6.92 kilowatt hours.
The maps could help guide billions of dollars in solar investments for a world worried by climate change, widely blamed on burning fossil fuels that could mean more floods, droughts, heatwaves and rising seas.
Satellite pictures could also help site offshore wind farms - wind speeds can be inferred from wave heights and direction. Farmers might also be able to pick new crops, or estimate fertiliser demand, by knowing more about how much solar energy is reaching their land.
Using satellite data for Morocco, Portuguese company Net Plan worked out how many solar photovoltaic panels were needed to power a remote relay station for phone signals. It worked and a costly backup of diesel generators was removed a year ago.
"We're looking forward to install more units like this," said Iolanda Sousa, head of energy and environment at Net Plan. On top of this, she said the data from the freely available solar maps can be used to persuade banks to grant financing.
Among possibilities in Niger, the government is planning to award oil exploration permits for the Agadem block, which has been explored by Exxon Mobil and Malaysia's Petronas until the licence lapsed in 2006.
Anyone wanting to generate solar energy in Agadem - for instance to provide electricity for a workers' camp - would in theory need fewer solar panels than for anywhere else.
The world's environment ministers will meet in Bali, Indonesia, on Dec. 3-14 aiming to launch talks on a long-term pact to fight climate change, partly by shifting towards renewable energies such as solar power.
Among other uses of solar data, a Canadian school in northern Nunavut worked out that it was worth putting solar panels on the wall, after help from Canada's publicly run RETScreen International, which gives advice on solar energy.
And Swiss firm Enecolo monitors output from solar panels by checking the amount of solar energy reaching a spot as measured by satellites - if the panels generate less electricity than expected then the problem might be dust, or a loose wire.
"In some parts of Africa it could be economically interesting to use solar power rather than connect to a grid because of the lack of infrastructure," said Thierry Ranchin of the Ecole des Mines de Paris in France which leadsthe solar project with NASA.
"If you want to bring electricity to a small village in Africa it's often easier to do it with a standalone system than a grid with power lines," he said.
In Italy, a firm called Flyby monitors levels of ultraviolet radiation -- that can cause skin cancers -- and if it reaches critical levels sends out alerts by mobile phone to advise people to cover up.
"In the developed world we have good surface solar measurements. When you go elsewhere the data is much sparser -- that's where the satellites can help," said Richard Eckman, manager of the NASA programme at Langley.
"Our goal is to find more practical applications of NASA-derived satellite operations across a whole range, such as energy or agricultural efficiency," Eckman said.