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Some renewables are now cheaper than conventional sources, even when the cost of providing backup to deal with their variability is included.

When the health costs associated with using conventional energy sources is also included, the comparison is even more favourable: air pollution from burning fossil fuel is a killer.

If the longer term global social, economic and health impacts of climate change are also added in, then most renewables win out across the board, although some may have local impacts, such as visual intrusion, and for some there will be potential land-use conflicts.

We need to decide on priorities, and on issues of scale, although most of these local impacts can be avoided or limited, as I illustrate in my new book Green Energy Futures. That also looks at how the variability of some renewables can be dealt with at low cost, an issue I will focus on here. It often seen as the Achilles heal of renewables.

Harnessing variability

Can variability really be dealt with and at low cost? Actually we already do it. Grid systems already cope with quite large variations in supply and demand, mainly by ramping the output of some power plants up and down.

With renewables on the grid, they will have to do that a bit more often, reducing the cost and carbon savings from not using fossil fuel very slightly. We don’t have to build new plants for this extra back up – they already exist. As they age, new, better, ones will have to be built, for example flexible gas turbines using low net carbon biogas as a fuel, produced from farm and home wastes.

As renewables begin to dominate we will need further balancing measures. Energy storage systems, including pumped (hydro reservoir) storage and advanced battery technologiescan offer part of the solution, as can other newly developing storage options like liquid air storage.

There are some clever new ideas emerging too, such as the ‘Power to Gas’ (P2G) approach being pioneered in Germany, which offer extra flexibility. With P2G, surplus electricity from wind and PV generation, produced when demand for power is low, is converted by the electrolysis of water into hydrogen gas.

That can be stored ready to use as a fuel when demand for electricity is higher. Or it can be converted to methane gas, using carbon dioxide captured from the air or from power plant exhaust, and used as a fuel for power generation, heating or in vehicles.

The grid re-empowered

Or again, it can be converted into ammonia: an energy rich gas that’s already manufactured in huge volumes as the feedstock for the nitrogen fertiliser industry. Most ammonia today is made  by burning natural gas……….

So far from being a problem, dealing with the variability of renewables may thus in fact offer some economic benefits, once we redesign and upgrade the power system.

Matching demand for power to the available supply

There are other approaches. Smart grid demand management can help us delay demand peaks, by interrupting supply to devices that can cope without power for an hour or so. So some demand is shifted in time.

For example, domestic and commercial freezer units can coast for a while with no ill effects. That might also be done when supply from renewables was low. This dynamic ‘demand response’ could be achieved automatically, by smart grid signals that, with consumers’ agreement, disconnect selected devices briefly, perhaps in return for a lower tariff.

Or consumers could simply elect to shut devices themselves at times of high demand, in response to smart meter price signals. Since the result would be that demand peaks were reduced, less supply and backup capacity would be need, thus saving money…….

100% of electricity? Or 100% of all energy?

How far can this take us? Optimists claim that, given proper attention to energy saving to reduce demand, renewables can supply up to near 100% of electricity globally, with no major supply, balancing or cost problems – and there are scenarios illustrating this for many countries……

Going further, to make 100% of our energy renewable, not just electricity, may be more daunting. But there are many scenarios suggesting that this can be done. And in terms of cost – when the local and global environmental costs of fossil fuels are taken into account, along with the risks and costs of nuclear power – this seems like a wise target.

The book: ‘Green Energy Futures A Big Change for the Good‘ by Dave Elliott is published by Palgrave. http://www.theecologist.org/essays/2986169/a_clean_green_energy_future_beckons.html