Photovoltaic solar systems (solar cells) are generating electricity from sunlight. The most common kinds of solar cells are the ones based on silicon (Si). But there are also other kinds of solar cells that are currently being evaluated  that are based on other elements and therefore slightly different technologies. In tghe end there is always a surface of a certain size that can generate a certain amount of electricity. The more solar cells we have the bigger the surface has to be. Not all solar cells have the same amount of efficiency. Which means that efficient solar cells can produce more electricity on 1 square meter than less efficient ones. Of course, a sunray (or sunlight in general) only contains a certain amount of energy. But efficient solar cells can "catch" more of that energy than less efficient ones. Current cells based on silicon have an efficiency of up to 22%. Which means that 22% of the sunlights energy can be transformed into electricity. 

High efficiency is important when it comes to solar cells. Currently scientists are trying to develop new kinds of solar cells that top 40% efficiency. Which means that (current cells being around 20%) for the same amount of electricity we would only need half the surface. Or - the other way round - with the same sized roof on a house we could produce twice as much electricity. At the Fraunhofer ISE in Germany they broke the record with 47.6% efficiency. 

But as long as there are tons of roofs out there without solar pannels yet and other unused (wasted) space, it is probably more important to install solar cells at all. Some peolpe don't like the look of it in nature. Or sometimes they dont't like the look of it even on roofs. For that problem Tesla has already invented their solar tiles which look exactly like "normal" tiles and are supposed to be even stronger and longer lasting. Immagine how much more green electricity we would have if every house in every city in the world would have a solar roof. 

But even if each roof had solar cells already, there is plenty of other unused surfaces where solar cells would not disturb or even improve its original purpose. One example is solar cells over water canals. It helps to fix two things at once. It reduces the evaporation of precious drinking water and uses all those unused square meters for placing solar cells. And since California is a rather dry and sunny state, those canals offer potential for a lot of electricity production. Even better, The coolness of the water is cooling the solar cells and makes them even more efficient than without that free cooling.

Other place, similar principle. Fortunately in Switzerland we have more than enough drinking water thanks to many naturally formed rivers and lakes. And more than enough rain and snowfall over the year to keep the rivers flowing. That's why in connection with the mountains (difference in height) a considerable amount of green electricity can be produced with hydroelectric power plants. But still, we are far away from being a net zero country. But we don't just have a lot of mountains and rain. Like pretty much any other country on the world we also have a lot of... streets. Or more precisely; Highways.

It might be fun once in a while to drive in a convertible car and enjoy the wind and the sky while driving from A to B. But in like 99.9% of cases the Swiss "Autobahn" is just a means to get to another place as fast as possible. Because the air is usually smelly, there are usually way too many other cars (traffic jams are frequent), it's either too cold or too wet most of the year and even if we could enjoy the landscape and the nice weather we have to focus on the driving anyway. So: Immagine how much green electricity we could generate if all of the motorway was covered with solar pannels. Probably enough for everyone to drive and charge his electric car and even heat most if not all houses. That's pretty much what Laurent Jospin from Energypier was thinking. They are going to build the first mile or 1.6 kilometer of solar roof as a pilot in one of the sunniest regions of Switzerland. Which is supposed to deliver enough electricity for 12.000 households. So let' s say they would cover 60% of the Swiss Highway (which has a total length of 1600 km). That would deliver electricity for nearly twice as many housholds as there are. For 7.2 million housholds (while there are about 4 million households in total). So as I wrote before; There would probably be enough green energy to cover all our needs. Especially in connection with the green electricity we are already producing. To solve the climate crisis - especially in wealthy countries -  could be so easy. We just have to do it.

Another very promising spot for solar cells is railways. More precisely: between the two rails on the ground. The new Swiss company Sun-Ways is about to install the first 100 meters as a trial. Switzerland with a polulation of nearly 9 million people and a land area of 40'000 km2 has a total railway net of 7000 km (4300 miles). If the whole net was covered with those solar pannels, 30% of total energy consumption for public transport could be supplied. The company is currently working on a system so the solar pannels can be automatically installed on the railways. There's basically just a train loaded up with solar pannels that drives along the rails and is installing the solar pannels instantly while driving. This would be extremely cost effective. But that's also necessary so the pannels can easily be removed and reinstalled for maintenance work every couple years. If everything works out as planned one can immagine how easy it would be to scale it up and let that solar pannel train install those pannels all across Europe and the rest of the world. I can highly recommend Sun-Ways' visualization on their website. I think their vision is just genius. They would install the pannels at night wehn no train is scheduled so they would not even have to close the railway while they are installing it. What's also genius is the fact that the distance between the two rails by nature has just the right size for standard solar pannels. There are also other companies who made similar trials. But what's new with Sun-Ways is their patented system to install and remove them super quickly.