Editor’s Note: This blog was originally written by Zachary Davies Boren for Greenpeace UK.

Solar has always been the renewable energy sector’s prodigal son, with the potential to become the world’s largest resource. In the last few years it has become cheaper to generate from solar than coal or gas in many regions.

Yet despite that — and huge growth — solar still only accounts for around 1% of the global power market.

Most of these megawatts come from silicon-based solar panels that have been installed on roofs, in gardens, or as their own kind of energy farms.

As this sort of conventional solar energy has developed and improved, so have a number of new ideas emerged. If solar goes on to take a chunk of the remaining 99%, it may well look very different.

Here is a list of seven solar technologies you should know about.

Tofu Solar

As one of the major alternatives to silicon, thin-film cadmium telluride cells represent 5% of PV production — they’re a lot cheaper to make, but also a lot less efficient (they convert less sunlight to power) and have struggled to compete with silicon on overall cost.

That’s why this year a UK scientist Professor Jon Major went in search of an alternative to cadmium: tofu.

Well, it’s not really tofu. Magnesium chloride, a coagulate in the making of tofu, works just as well as cadmium chloride for a fraction of the cost. Where cadmium chloride costs about 30p per gram, magnesium chloride goes for less than a penny – it can even be bought off the shelf.

And not only it is cheaper, tofu solar is cleaner.

Producing tofu solar is all a bit Blue Peter. You require a spray-coater, the solution for which you mix in magnesium chloride, to apply it to solar cells before they go into the (high spec) oven.

You can bake your tofu cake and eat it too (warning: do not eat solar cell cake).

 Solar Freakin’ Roadways

According to the obnoxious promotional video for its kickstarter campaign, solar roadways will do everything short of stopping ageing.

Despite some financial support from the Federal Highway Administration, and donations from excitable folks on the internet, the ambitious Solar Roadways project will face challenges — many urban roads, for example, are largely shaded.

But solar roads are actually happening in the Netherlands — albeit on a far smaller scale.

While I too want to want the world to look like Tron, with green glowy grounds, maybe someone should mention that traffic lights are already often solar powered and cats’ eyes just use mirrors.

High Efficiency Solar

The average commercial solar cell is between 11 and 15% efficient, which means that more than 80% of the sunlight which falls upon it is not converted into energy.

If there’s anything holding solar back from taking over the energy world, it’s this.

There are a number of projects looking to improve that efficiency, and solar labs across the world have reached performances north of 40%.

One of these high efficiency solar cells is called ‘triple junction,’ the brainchild of Professor Keith Barnham from Imperial College University, London.

Barnham’s baby, which is based on gallium arsenide, produces three times the energy as conventional PV, the only problem: it’s expensive. So the trick isn’t about replacing silicon, as much as working where conventional solar doesn’t.

Triple junction cells can be chemically altered and optimized to make the most of any type of sunlight.

Barnham’s go-to example is a smart transparent window blind which tracks the sun, captures its light and uses luminescent light-pipes that guide it to the high-efficiency cells in the window frame. Clever.

The solar energy generated from this method, he said, also allows natural light into the room but no heat. That’ll allow Americans to cut on their air conditioning bill.

And for the UK, where summer sun is less intense and grey skies are more perpetual, there’s a different specialized solar cell.

It may only have an efficiency of 10 to 13%, but the grey cloud solar cells in development at the National Physical Laboratory are promising — thin, flexible ‘organic photovoltaic’ that performs better out of direct sunlight.

Space Solar

Solar panels in space is an idea that is at once completely logical and utterly absurd.

Over 30 years ago, NASA and the US Department of Energy thought it worthwhile to invest and investigate this future energy tech.

While their involvement may have dropped off (though they’re still doing stuff) emerging economies India and China are going ahead with their own space solar plans.

And Japan wants a whole solar farm up there in fewer than 25 years.

Mark Hopkins, CEO of America’s National Space Society, said: “There are two advantages to space solar: sunlight in space is more intense per unit area so it requires a smaller area of PV cells to get the same amount of energy.

“And when you get down to earth you have a day-night cycle. So you can only use solar cells during the day, but with space solar power the satellite is virtually always in sunlight.”

NSS sees the tech like so: highly efficient solar panels are equipped to fleet of space satellites the world already has orbiting the earth.

These solar satellites would beam the energy down to receptacles on the Earth using wireless power transmission (which works but over which questions of efficiency remain).

It really is like something out of sci-fi, but don’t hold your breath, space solar is ages away.

 

Floating Solar

Over 70% of the Earth’s surface is water, but currently it’s an inhospitable place to put a solar panel.

Floating solar farms were envisioned as a remedy to the complaints of those, like UK Environment Secretary Liz Truss, who claim solar panels are a blight which interfere with agricultural operations.

French firm Ciel et Terre has developed a smart agriculture system of which a floating solar farm is the Pièce de résistance.

Hydrelio can actually generate more energy than their land-bound counterparts which become less efficient as they heat up. The tech also both naturally purifies the water and limits its evaporation.

Ciel et Terre has a load of projects in France, a couple of large ones in Japan, and even one in Berkshire, England.

And this is not the only floating tech in town. India is trying out floating solar on its many canals, recently contracting Vikram Solar to get on with that.

And parts of the US are also embracing water-based solar, most notably in the California wineries.

See-Through Solar

There have been a number of sort-of see-through solar projects, none of which were able to convert the sunlight into energy without putting some wild colorful filter on it. Nobody wants that.

Earlier this summer you may have seen the picture of Michigan State University’s solar glass doing the rounds on the internet. It’s real, though there is a pretty major caveat – it barely produces any energy.

The product’s boring name is a ‘transparent luminescent solar concentrator,’ and it works this way because it’s only absorbing non-visible sunlight.

Small organic molecules developed and altered in the lab by engineer Richard Lunt are applied to any clear surface. There they capture ultraviolet light ultraviolet which they then luminesce into a infrared wavelength that can be guided towards thin strips of PV cells at the object’s border.

But as it’s a harder to harvest these non-visible types of light, efficiency is minuscule – only 1%. Lunt hopes to develop the technology to reach 5%, but even that falls far short of the 7% colored luminescent solar cells he hopes to replace.

 Spray On Solar

(aka Perovskite Solar Cells)

In 2013, Science magazine listed perovskite solar cells as one of the year’s 10 biggest breakthroughs, despite being first developed four years prior.

Though less energy intensive to make than silicon solar, perovskite had been up until that point inefficient, expensive and lacking in versatility. But in just 18 months, perovskite efficiency jumped to 16% — a milestone it had taken silicon scientists decades to reach.

The cell’s development has only accelerated since making the technology relatively cheap, versatile efficient and easy to scale up.

What does all this have to do with spray-on?

That method, demonstrated at Sheffield University earlier this year, is one of the first ways in which perovskite solar is leaving the lab.

Their hefty spraying machine can apply a thin uniform layer of perovskite, making any sort of surface capable of absorbing light. How about a solar powered smartphone? Or a car with a coat of solar powering coat of paint?

But, at around 11% efficiency, we’re still a ways off from a fully realized, completely viable spray-on solar.