Something quietly remarkable happened in Germany recently. As the country enjoyed a sunny May day, its extensive solar power installations recorded their best ever performance. Solar power hit a new international record of 22GW, equivalent to 20 nuclear power stations. At one point on Saturday, Germany was almost 50% solar powered.
There’s lots I could say about Germany’s power strategy, both positive and negative, but what I wanted to highlight was the way that renewable energy was accommodated in the system. Averaged over a year, solar power only accounts for 3.5% or so of Germany’s electricity generation, yet at the end of May there were days when solar power was providing ten times that. So far, the national grid has proved it is perfectly capable of handling these extremes.
This illustrated one of the big challenges to renewable energy: they are intermittent energy sources. A coal power station can run as long as you have coal to shovel into its furnaces. Wind power only operates when the wind blows, and solar photovoltaics need cloudless skies to reach their full capacity. Surely, say the critics, too much renewable energy puts us at the mercy of the elements? The greater the percentage of wind or solar in our energy mix, the more likely we are to end up with rolling blackouts. It’s a logical question, but there are solutions.
The first and biggest answer to this problem is the grid. Power stations feed into a national grid that balances inputs and outputs across the whole country. When demand rises, new capacity is brought online. At night, demand drops off and supply drops accordingly. It’s a highly versatile system, able to handle massive spikes in demand. The famous example is half-time during big football matches. The whistle blows, and everyone goes into the kitchen to switch on their kettles for a cup of tea, or opens their fridge for another beer. The National Grid refers to these as ‘tv-pickups’ and plans ahead for them so that the lights don’t go out.
It’s easy to take functioning power infrastructure for granted. If you’ve lived off-grid or in a developing country, you’ll know the luxury of not having to think about it. When I lived in Madagascar, the power levels dropped so low at night that we couldn’t switch on the TV. If you wanted to watch something that night, you had to remember to turn it on at about five o’clock and leave it on standby. By the time it had got dark and everyone had turned on their lights, there would be enough power to run it but not to turn it on. By day, you had to holler if you were going to boil the kettle. If you forgot, there would be wails from the office as someone lost their homework as the computer blinked off.
Those sorts of eccentricities don’t happen in Britain. At least not any more. The idea of balancing power supplies across the country goes back to 1926, and today the grid incorporates 181 major power stations and thousands of smaller installations. This infrastructure allows us to plug in a variety of variable energy sources, and the broader the network, the easier it becomes.
You can broaden the network beyond our own borders too. Interconnectors already link our grid with France, Ireland and the Netherlands. There are plans to build links to Norway and Belgium too, and a feasibility study was launched last month to see if we could connect to Denmark. Iceland has far more geothermal capacity than it can use itself, and is investigating ways to export it to Britain.
None of this infrastructure is cheap, but the fact that we already have three international links proves that it isn’t prohibitively expensive either. Whether we can afford a Europe wide grid with links to North Africa is another matter, but you can see the advantages of spreading the net as wide as possible. If the sun isn’t shining here right now, it might be in Devon. It might be a calm day in London, but the wind is blowing in Scotland. Expand that principle South to Spain and north to Sweden, and you’ve got a wide variety of conditions.
I’ve already mentioned the issue of peaks in demand. Some of these are unusual, like football matches. Others are regular, when people get up and make breakfast, or get home from work in the evening and turn on their lights and cook their supper. Coal power is one of the easiest ways to deal with these large peaks, as they can be switched on quickly. There are renewable energy equivalents, using biomass and incineration (or see hydropower below), but a better approach would be to avoid the extremes in the first place.
That be done through more efficient technologies – if everyone is switching on low-energy light bulbs at twilight, that’s a much lower step in demand than everyone switching on an incandescent. Another way of stabilising demand is through smart appliances that can read demand and respond accordingly. Fridges don’t run constantly, but maintain a steady temperature by switching the cooling mechanism on when needed. A smart fridge would time its cooling cycles to periods of low demand. A smart washing machine would automatically run off-peak when energy prices are cheapest. Samsung, LG and others already offer appliances with this kind of technology.
Those living off-grid with their own solar or wind power rely on batteries to make sure that they capture energy when its there, and can use it later. That would be pretty useful in the national grid too, if we could store the solar energy from a sunny day to use it at night. Currently there’s no form of battery big enough to do that, but there are a few other options. One is pumped storage hydropower. When energy is cheap, water is pumped uphill to fill a reservoir. When needed, gates can be opened and it runs back downhill through turbines, generating electricity. This is the renewable energy way of dealing with demand spikes, and also a way of storing intermittent sources. Dinorwig power station is housed underground inside a Welsh mountain, and can bring 1.8GW of power online in 12 seconds.
If you haven’t got a suitable lake, the same thing could be achieved with rail cars, according to a California company. They’re developing a model where surplus energy is used to haul heavy rail cars uphill when wind or solar power is running at full capacity. When it drops off, the cars are released to roll back downhill, generating electricity on the way.
You can also ‘bank’ energy in the ocean, taking advantage of the pressure of the deep sea. A team at MIT suggest that large hollow concrete spheres could be sunk on the seabed near offshore wind turbines. Excess energy would be used to pump out the spheres. When the wind dropped, water would rush back in through a turbine.
Another form of energy storage is solar thermal. I’ve written about it before so I won’t go into detail here, but it essentially stores heat in molten salt, and allows solar power stations to carry on generating electricity through the night. This turns solar energy into a form of constant renewable energy.
Constant renewable energy
Speaking of which, wind and sunshine are intermittent, but there are other natural forces that are much more predictable. Hydropower is one such source, using the steady flow of rivers. There are countries in the world that generate all their electricity from hydropower, and are thus enjoying 100% renewable energy. Hydropower is often overlooked because while it is renewable and clean, it isn’t always environmentally benign and has large capital costs. Large dams are often hugely destructive and displace entire communities. But there is good hydropower too, and I may have to dedicate a separate post to it.
There’s also a whole lot of energy to be sourced from the sea. Harnessing wave power is one approach, but doesn’t count as a constant renewable source because waves are variable. Tidal power does count however, as there’s always a tide. So far, tidal power requires a barrage across a suitable estuary. Like dams on land, dams across estuaries are just as controversial – see the running debate about the Severn Barrage. But there are simpler and smaller ways to harness tidal power too, placing turbines on the sea bed, or using the vertical movement of the tides rather than the vertical. Ecotricity are trialling a hybrid sea technology that uses sea swells to pump water onshore, which is a lot simpler than generating the electricity out on the open sea.
Geothermal provides another source of constant renewable energy. Britain has limited geothermal capacity, and is more useful for providing heat than electricity, but there is still untapped potential. The main reason that geothermal hasn’t been pursued in Britain is that it hasn’t been economical so far, but as the price of energy rises, it is becoming more viable. The Eden Project is pioneering a geothermal plant in Cornwall, the first of what it hopes will be a fairly substantial contribution from Cornwall’s ‘hot rocks’.
Biomass and anaerobic digestion (biogas) are two more renewable energy sources that are often overlooked. Biomass is best reserved for smaller and more localised energy generation, and the current practice of co-firing biomass with coal is a short term option. Biogas is generated from waste, so it doubles up as a useful way of dealing with rubbish otherwise destined for landfill, and its main waste product is a liquid that can be used as fertiliser.
Lowering energy use
Even with these various technologies and techniques, renewable energy can never be a direct swap for fossil fuels. Coal, oil and gas are very dense forms of energy, and deliver a high energy return for energy invested. Renewable energy cannot match it, and if we are to rely on renewable energy more in the future, we will have to reduce our energy use. That’s entirely possible, given how inefficient our houses are, how much electricity is lost in transmission and how low our standards are for appliances.
Quite how far we need to reduce our energy use is debateable, but those assuming we can expand it or carry on as usual aren’t paying attention. The Zero Carbon Britain report, which aims for 100% renewable energy by 2030, assumes a 55% reduction.
In summary, there are ways of managing the intermittent output of certain renewable energy sources. It is a challenge, but it is not an insurmountable obstacle.
- For more, see the detailed and unsentimental accounts of renewable energy capacity in George Monbiot’s Heat, and David MacKay’s Sustainable Energy Without the Hot Air.