Solar power is the world's fastest growing source of energy, but obvious problems remain. New research suggests, if properly located, it could play a surprisingly large role in powering countries far from the equator during the winter.
Solar is now usually the cheapest way to generate electricity during daylight hours. It's also increasingly practical to store energy for night time use. Winter, however, remains more of a challenge. It's one thing to store electricity for 12 or even 16 hours, quite another to hold onto it for months of darkness.
According to Dr Annelen Kahl of the Ecole Polytechnique Federale de Lausanne, however, that may not be necessary, at least in places with high mountains. Kahl and colleagues have modeled the use of solar panels in Switzerland. In Proceedings of the National Academy of Sciences, they argue if panels are placed correctly we can “shift a significant amount of electricity generation from the summer to the winter months.”
The secret is to put the panels at high altitude and angle them closer to vertical than is usually done.
There's an obvious reason to put solar farms up mountains. The less atmosphere, particularly fog, between the panel and the Sun, the more light it collects. However, it's also cheaper to collect energy closer to where it will be needed, so panels usually get installed lower down slopes – often on the roofs of existing buildings.
That may make sense when only a small portion of our electricity comes from sunlight, but Kahl argues that as we move towards fully renewable grids, timing becomes as important as quantity of power. Using satellite data from thousands of locations across Switzerland, the authors show the differences between summer and winter sunlight shrink with elevation. Once you get above 2,500 meters (8,200 feet) there's more sunlight during winter than at lower elevation during summer – enough to keep the lights on.
Solar panels need to be angled to catch the Sun, which is lower in the sky in winter. Using a steeper angle means less electricity over the course of the year, but more in winter when a solar-dependent grid will need it most. This is particularly important for countries like Switzerland, where demand for electricity is higher in winter. Steeply angled panels also don't collect snow, and sunlight reflected off surrounding snowfields can increase yields by 10 percent.
Kahl's calculations are of little use for nations that are both far from the equator and close to sea level, but they show the places that need either fossil fuels or nuclear power are rarer than advocates for those sources claim.
Meanwhile, PV Magazine reports one development is setting out to prove solar alone can power homes all year round even in the most unexpected place – Sweden.
The municipal housing company for Vårgårda, Sweden, is building six buildings, containing 172 apartments between them, that will not be connected to the electricity grid. Instead, they will produce all their own power from solar panels. Rather than batteries, hydrogen will be used to store surplus energy from the summer. When burnt in winter the hydrogen will supply both heat and electricity.
One building is already in use. It's unlikely the hydrogen storage will prove cost-effective compared to connecting Sweden's grid, which has some of the lowest carbon emissions in the world anyway, but the buildings serve as a demonstration of what is possible.