Solar Energy
In one hour the sun sends the Earth more energy than humankind uses in a whole year.
No energy source is as mighty and as democratic as the sun. It shines on every roof, every field and every desert, no matter who owns the land. Almost all other forms of energy are only detours of the sun: wind, water, plants, even coal and oil. All the more astonishing how long we took to use its light directly.
A bit of history
That sunlight brings warmth was known to every culture that oriented its houses toward the south. But electricity from light is young. In 1839 the physicist Alexandre Becquerel discovered the photoelectric effect, and in 1954 the Bell Labs built the first usable silicon solar cell. At first it was astronomically expensive and flew mainly on satellites into space. Only in the last twenty years did the price fall so dramatically that solar electricity is today, in many places, the cheapest energy of all.1
Two paths: electricity and heat
We use solar energy in two fundamentally different ways. Photovoltaics turns light directly into electric current, those are the bluish shimmering modules on the roofs. Solar thermal, by contrast, simply captures the heat: collectors heat water for shower and heating, and on a large scale mirrors concentrate the light so strongly that the resulting steam drives a turbine.
Both are astonishingly simple to operate, since they have hardly any moving parts, use no fuel and make no noise. A solar module on the roof works away uncomplainingly for twenty, thirty years.
Between these two poles there are many further ways to capture the sun, and they show how versatile the light is. The simplest is passive solar use: a large south-facing window, a dark stone wall that stores heat during the day and gives it off at night, a greenhouse that warms up by itself in spring, entirely without technology. A step further goes the solar cooker, which with a simple mirror concentrates enough heat to boil water, in many sun-rich countries a small revolution against expensive firewood. On a large scale, solar thermal power plants do the same: hundreds of mirrors direct the light onto one point and generate so much heat that whole turbines run, and the stored heat even delivers electricity in the evening. And finally agrivoltaics combines two uses on one field: above, the modules harvest electricity, below, vegetables or pasture grass keep growing in the half-shade. Seen this way, "solar energy" is not a single device but a whole family of ways to tap the same sun.
Today
Photovoltaics has become the driving force of the energy transition. Worldwide more solar capacity is now being added than any other kind of power plant, because it is so cheap and so quick to erect. You find it on single-family houses as well as on huge open spaces, and even on the balcony railing as a plug-in solar device with which tenants can harvest a few kilowatt-hours themselves. Precisely in this lies its emancipatory streak: it turns consumers into producers and takes a piece of control away from the big corporations.
Advantages
The strengths are obvious. The fuel is free and inexhaustible, in operation there are no exhaust fumes and no CO₂, and the technology is divisible down to a single roof. It can be set up almost anywhere, from the garage driveway to the desert, and it delivers most when demand is high: on bright, hot days when air conditioners are running.
Disadvantages and the honest catch
As clear as the benefit, so clear is also the problem: the sun does not always shine. At night photovoltaics delivers nothing at all, in winter little, and a thick cloud can make the output collapse within seconds. Solar electricity is therefore fluctuating, and that calls for storage (batteries, pumped storage, later hydrogen) and for smart grids that carry the surplus to where it is needed.
The manufacture of the modules, too, costs energy and raw materials, and the cells need space. Both are often exaggerated: a module produces the energy needed for its fabrication back within one to two years and then works for decades in the plus. And there is enough space if you use roofs, car parks and already sealed-over areas instead of sacrificing valuable farmland. Here the critical look pays off in both directions: one should neither play down the problems nor let oneself be intimidated by panic figures.
The critical look
Around solar energy many half-truths circulate, from both sides. Opponents claim that modules "never pay back energetically" or that the electricity is "in truth expensive," which the numbers long ago refuted. Proponents, for their part, sometimes talk as if all it took were enough panels and everything else would follow by itself, and pass over the unsolved storage problem.
Whoever wants to judge in a self-determined way therefore asks concretely: how much does an installation deliver over the year, not just at the midday peak? Where does the electricity come from at night? And who ultimately owns the installation, the household or a distant investor? For the decisive question with the sun is rarely the technology, but the distribution: it could place energy in many hands, if we let it. The sunlight itself sends no bill. Everything that comes after is a political decision.