Plant Energy
Every plant is a little power station fed with light. Almost everything that warms and nourishes us begins in a green leaf.
Plants seem quiet and harmless, yet they are the actual basis of almost all the energy we use. They do something none of our machines can: they capture sunlight and turn it into a substance you can eat, burn and store. Whoever grasps this sees a cornfield or a forest no longer merely as landscape, but as what it is: a gigantic, silent energy plant.
The green power station
The trick is called photosynthesis. From light, water and the carbon dioxide of the air, a plant builds sugar and from it everything else: starch, wood, fibres, oils. You can picture it like a charging-up. The plant stores solar energy in chemical bonds, just as a battery stores electricity. Later, when we eat or burn the plant, this energy is released again.
The remarkable thing about it: it is the only major route by which living energy enters the world at all. Animals cannot do it, humans cannot do it, no factory can do it on a large scale. All of them, from the deer to the corporation, ultimately live on what plants once captured. This dependence is easy to overlook, precisely because it is so complete.
Plants as food
Most directly we feel plant energy while eating. Bread, rice, potatoes, fruit: all of it is stored sun, measured in calories, which is nothing other than a unit for energy. When a muesli packet says "2000 kilocalories," it says, in essence, how much sunlight this field collected for us.
Meat, too, is only a detour via the plant. A cow eats grass and converts it into muscle, but at every step of this chain a large part of the energy is lost as heat. Roughly: only a fraction of the plant energy arrives in the end as meat on our plate. That is why a plate with a lot of meat needs far more arable land than a plate with vegetables and grain. This is not a moral wagging finger but a plain energy calculation, and it explains why the question of what we eat is always also a question of energy and land.
Plants as fuel
The oldest energy technology of humankind is fire, and its fuel is wood. A campfire releases exactly the solar energy that the tree stored over decades. To this day billions of people cook and heat with wood, charcoal or dried dung. Added to this are modern forms: wood pellets, biogas from manure and food scraps, biodiesel from rapeseed or bioethanol from maize and sugar cane, which is blended into petrol.
Such fuels from living matter are called biomass.1 They sound like the perfect solution, since renewable and, unlike coal, from the sun of today rather than the day before yesterday. But this is exactly where the critical look pays off.
The catch: land, plate and tank
Biomass has an uncomfortable price, and its name is land. Whoever grows maize for the car tank cannot grow grain for bread on the same field. In the years of the great biofuel boom, exactly this drove food prices up in some regions. The conflict was aptly named "plate or tank": should the field feed people or the car?
The label "climate-neutral," too, does not always keep what it promises. True, a renewable plant takes up again the CO₂ released when it burns. But if rainforest is cleared or moors drained for it, the bottom line is often more damage than benefit. And a tree we burn today has grown back only in many decades' time: the account only balances over long periods.
Plants are, moreover, astonishingly inefficient at storing sunlight. Only a tiny fraction of the incoming light ends up as usable biomass. A solar cell on the same area harvests many times the energy. So whoever believes the whole world could be run on biofuel underestimates how much land that would devour.
Why we should look closely
Plant energy is a prime example of the fact that no form of energy is only good or only bad. Wood from a sustainably managed forest in the region is something entirely different from palm oil for which primeval forest burns. Biogas from waste that arises anyway makes sense; energy crops grown specially for the purpose often do not.
The emancipatory lesson is simple: don't let yourself be lulled by green labels, but don't demonize the matter across the board either. Instead, ask where the biomass comes from, how much land it costs and who benefits from it in the end. Plants remind us that all energy ultimately comes from light, and that the truly scarce resource is not the sun but the soil on which we harvest it.