The simplest way to ensure the swift attainment of an all renewable electricity supply is for countries to impose a 50 gCO2/kWh emission limit on all new electricity generation here and now.
There is general agreement world-wide that an a 100% renewably powered world would be a desirable objective, and that the renewable technologies are particularly well suited to provide the energy needed in the countries most vulnerable to climate change.
There is also a clear scientific consensus that renewable electricity generators emit the lowest greenhouse gases: at least nine times less than the lowest fossil fuel generators and in some cases 40 times less.
There are, however, powerful lobbies that argue that the renewables are too unreliable; expanding too slowly; and too expensive to supply the world's electricity needs. Without, that is, significant help from the technologies the lobbyists are paid to represent - be they fossil fuel or nuclear.
Here is the evidence, some of it new and unexpected, that the lobbyists' arguments at a variance with the realities. Two projects in Germany, under the collective name of Komikraftwerk (combined-power plant) have clearly demonstrated that the reliability objection is a myth.
Solar PV and wind power are complementary. Together they can supply around 80% of the electrical power needs of Germany. The only backup required is 17% biogas electricity and 5% storage power. Together they provide a renewable electricity supply that is reliable 24/7, summer through winter.
Recent evidence in a paper I wrote with the head of Kombikraftwerk and an Italian colleague in Nature Materials explodes the second myth. Wind and PV and wind power are expanding exponentially in many countries. The expansion is so fast in Germany that wind and PV could provide the foundation of an all-renewable electricity supply as early as 2020.
Had the savage cuts to the subsidies for PV and wind power in the UK not been implemented, wind and PV could likewise be on target to provide the backbone of an all-renewable electricity system just two years later, in 2022.
The third renewable objection, on cost, fails when one notes that, thanks to the expansion of wind and PV, the wholesale price of electricity in Germany has fallen 37% in the last three years. Good Energy, the all-renewable electricity company, points out that the wholesale electricity price in the UK started falling in 2014.
How to achieve all renewable electricity supplies
The conclusion to our study was that the fastest way to reduce carbon emissions is to ensure that all new electricity generators are renewable. Kombikraftwerk showed that PV, wind and biogas power, the three most established renewable technologies, provided the minimum requirements for an all-renewable electricity supply.
Many more renewable technologies can contribute. Some are established: large and small scale hydropower and geothermal power. Others are emerging: concentrating photovoltaics (CPV), concentrating solar power (CSP), wave, tidal stream and tidal lagoons.
Large scale hydropower and geothermal can back up PV and wind in a similar way to biogas, and to some extent so will tidal and CSP, the latter when it has a heat storage option that allows the sun's heat to be stored up during the day, and used to generate power on demand at night.
Most importantly, all these renewables have carbon footprints, or life-cycle greenhouse gas emissions below the 50 gCO2/kWh recommended by the UK Committee on Climate Change for 2030. The consensus in the peer-reviewed scientific journals is that the carbon footprint of nuclear power is above this limit. The lowest fossil fuel electricity generators are at least nine times higher.
So the simplest way to ensure the swift attainment of an all renewable electricity supply is for countries to impose a 50 gCO2/kWh emission limit on all new electricity generation here and now. I suggest we call this the 'Get it from the Sun' principle (wind is, after all, solar-powered).
The evidence in our paper shows that the renewables are expanding so fast that this is a safe and reliable option as well as producing the lowest cost electricity.
'Get it from the Sun' is already a grassroots movement
I am under no illusions that all governments will accept the idea of a carbon limit on new electricity generation - even though it would be politically popular as renewable electricity generation has a high approval rating with the electorate as a whole.
Indeed, an amendment to insert a carbon limit on electricity generation into the UK coalition government's Energy Bill came extremely close to passing in the last parliament. Most importantly, the 'Get it from the Sun' principle can be argued by environmentalists at local and individual levels, as a few examples will show.
The 'Keep it in the Ground' campaign has had some notable divestment successes in their attempts to limit fossil fuel supply. However, in the UK the fossil fuel industry has out-gunned them by successfully lobbying the new government to make a second 'dash for gas' the foundation of its energy policy.
In her statement of 18th November 2015, energy secretary Amber Rudd responded by giving natural gas electricity generation the highest priority to replace the PV and wind power that will be lost by the severe cuts to the renewables - even though it's far from clear right now where that gas is even going to come from
While lobbying Local Authorities to divest from fossil fuels, 'Keep it in the Ground' supporters should be encouraging them to set the 'Get it from the Sun' carbon emission limit on new electricity generators that come their way in planning applications - and so turn down the many applications to local authorities in Bristol, Manchester, Yeovil and St Albans and elsewhere to site small diesel and natural gas generators in urban areas.
The government has been so obsessed by its nuclear programme that it has ignored the pressing need for flexible power supplies to back up the exponentially rising (until subsidies were cut to the bone) wind and PV power on the grid. The fossil fuel companies claim to be responding to this demand.
For example, Bristol Council has received applications to build 48 diesel electricity generators. The council should turn this down on the basis of carbon emissions. While doing so they could point out that the ideal flexible electric power would come from a combined heat and power (CHP) generator sited near Bristol's award winning anaerobic digestion (AD) plant. This would produce electricity from the plant's bio-methane with a carbon footprint around 70 times lower than diesel. In return, waste heat from the electricity generation could speed up the AD.
In the past year, since completing The Burning Answer: a User's Guide to the Solar Revolution I have been fortunate to meet and talk with many community energy and Transition groups in the UK and the USA. They have for some time been enthusiastically applying the 'Get it from the Sun' limit in their efforts to generate their own electricity locally.
But they now have to face up to the UK government's hatchet jobs on PV and onshore wind and its vindictive removal of the tax relief that stimulated the financing of community energy schemes. These community groups are clearly motivated more by the wish to do something about global warming than by the hope of financial gain. I am confident that they will overcome these new hurdles as they have many others in the past.
The power versus energy confusion
Many people, particularly energy experts, are incredulous when I say that the data in our Nature Materials paper predicts that Germany and the UK (before the cuts) were on course to have the onshore PV and wind power contributions at the level required to achieve an all-renewable electricity supply by 2020 and 2022 respectively.
The operative word here is power. Most experts make their predictions in terms of energy rather than power, which is measured in units of energy per second. It is power, and the timing of the power, that matters where electricity is concerned: to keep the lights on the operators of the national grid have to balance the power supply and the power demand every second of the day.
Amazingly, on most days in Germany their electricity power demand rises up in the morning, peaks around noon and falls back in the afternoon - broadly matching the output from their large PV power supply. So the country's solar capacity helps the grid operators match power supply and demand - and helps to reduce wholesale electricity prices.
Wind power, however, is more intermittent. However it is also predictable (using weather forecasts), and is most productive around dawn and dusk, and during winter months - all of which make it a good fit with solar. It can also be backed up by flexible gas power which, in terms of both carbon emissions and monetary cost, should be provided ideally by biogas.
My co-author Kaspar Knorr and his Kombikraftwerk team matched the power of a number of PV, wind and biogas generators to the actual scaled down power demand of the German grid in real time throughout 2006. They were the first to show that the correlations between solar power and national demand, and the complementarity of wind and PV power, mean that 80% of German demand for elecrical power could be met by wind and PV alone.
Coincidentally in 2006, Massimo Mazzer, my other co-author, and I started publishing predictions for future wind and PV power supply based on cumulative installed power. As time passed, these predictions turned out either to be realistic or, in some cases, under-estimates, of the eventual achievements.
How wrong can you be using energy to make predictions?
DECC's 'Pathways to 2050' computer programme is based on energy rather than power. So it would suggest that, as only 3% of the German electrical energy in 2011 came from PV, it would make an insignificant contribution.
But in fact PV had reduced the peak wholesale price of electricity by 20% in the previous four years. This was because on many days PV power reaches its maximum around noon, near the time of peak daytime demand. PV then played an important part along with wind power in the subsequently reducing by 37% the overall wholesale price of electricity in Germany by 2014.
Similarly PV in the UK generated only 1% of UK electrical energy in 2014. However, it played (together with wind) an important role in reducing the wholesale electricity price in the UK through the so-called 'merit order effect', as reported by Good Energy. This works because when wind and solar power kick in, they push out the most expensive fossil fuel generation, and drop the price for everyone.
The observation that the decline in wholesale prices in the UK started at a lower PV contribution than in Germany reflects the fact that the summer / winter wind power variation is a better match to electricity demand in the UK.
A 1 GW nuclear reactor that runs 70% of the year will generate seven times more electrical energy than 1 GW of solar farms in the UK that only run 10% of the year. So 'Pathways to 2050', being based on energy, predicts that we need nuclear reactors. However it generates its power 24 hours a day, whether we need it or not, so much of its production is not actually meeting demand.
By modelling its power production against power demand minute by minute, therefore, we can say that by 2025, should EDF's first Hinkley Point C reactor be completed and operational, the power it produces will make a far less useful contribution than PV and wind power at that time, even if the cuts are not restored.
In addition, by 2025, there will be many times each week that wind and PV power together will exceed demand. That would mean that nuclear electricity will have to be sold abroad at a knockdown price, with British electricity consumers paying a huge surcharge under the government's Contract for Difference to guarantee EDF a price of £92.50 per megawatt hour (in inflation-indexed 2012 pounds).
The fastest, cheapest and safest way to reduce carbon emissions
On the basis of the evidence reported in our paper in Nature Materials we make the following suggestions to all participants and demonstrators at COP21:
- Countries should set a date when an environmental life-cycle limit of 50 g CO2/kWh will be imposed on all new electricity-generating technology.
- All fossil-fuel subsidies should be transferred to the renewables. They should be paid by taxation rather than a levy so that the fall in the wholesale electricity price due to the renewable expansion is reflected in the retail price per kWh.
- Kombikraftwerk power tests should be made on national and state electricity grids to determine the most appropriate mix of renewables from indigenous resources.
- Progress towards all-renewable goals should be measured on a frequent and regular basis.
Our data suggests that these three policies, taken together, will form the quickest, cheapest and safest approach to reduce the carbon emissions from electricity generation.
The paper: 'Recent progress towards all-renewable electricity supplies' is by Keith Barnham, Kaspar Knorr & Massimo Mazzer, and published in Nature Materials.
Keith Barnham is author of 'The Burning Answer: a user's guide to the solar revolution' and Emeritus Professor of Physics at Imperial College London.