These days more and more people seem to be railing against renewable energy—in the media, on the internet and down the pub. Here are some recent examples:

• Wind farms ‘will never keep the lights on’: Study claims turbines are ‘expensive and deeply inefficient’ (Daily Mail, 27 October 2014). [Poulter, 2014]
• Green energy costs ‘far higher than ministers admit’—report claims renewable energy is ‘the most expensive domestic policy disaster in modern British history’ (Daily Telegraph, 18 March 2015). [Gosden, 2015]
• The windfarm delusion—The government has finally seen through the wind-farm scam – but why did it take them so long? (The Spectator, 3 March 2012). [Ridley, 2012]

This kind of stuff is common in the mainstream media, as the above examples testify. It often contains emotive terms like ‘disaster’ and ‘scam’, as the above examples also testify. The regular drip feed of it seems to be turning ‘Middle England’ against renewables and the government is responding by rolling back the measures it had in place to encourage them. However, I’ve yet to see a fact-based critique of these arguments anywhere. Here’s my attempt fill the gap.

As far as I can see, anti-renewables campaigners usually make one or more of the following claims about renewable energy:

1. The available resource is too small to supply our needs.
2. It’s inefficient.
3. It’s intermittent and consequently needs a lot of fossil-fired back up capacity to keep the lights on.
4. It’s expensive.
5. It’s subsidised, and the subsidies are
   1. intrinsically bad, by definition,
   2. a transfer of wealth from the poor to the rich and
   3. a way for politcians to siphon public money to their friends.
6. We don’t need it to stop climate change, we could do it all with energy efficiency, nuclear and carbon capture and storage.
7. It has environmental and social impacts of its own, which are worse than its claimed benefits.
8. It takes more energy to build than it produces in its lifetime.
9. It will not be ready in time—enough capacity can’t be built before either a) the UK’s ageing conventional power stations have to close and/or b) climate change goes beyond the point of no return.
10. If China doesn’t reduce its emissions, there’s no point in a little country like the UK (or even the EU as a whole) doing so. Taking unilateral action, when our industrial competitors don’t, simply exports jobs while achieving a negligible reduction in global emissions, or even an overall increase because the outsourced production is less energy efficient than it would be if it had remained here.

Some of these are true and some are false. Some matter and some don’t. This is the first of a series of articles that will examine these claims one at a time. It looks at claim number one on the list—that our renewable resource is too small.

Part 1: the size of the resource

Claim

Renewables can’t supply all our energy because there just isn’t enough of it out there.

Facts

Haven’t you always wanted to know whether we could live entirely on renewables if we really wanted to? By this I mean whether the quantity of energy available in the UK over the course of a year is more or less than the amount we consume over the course of a year? This doesn’t necessarily mean that we could consume it all. It might be too expensive or it might not be available when we need it. These are different questions and are dealt with in subsequent articles in this series. This post just looks at the quantity available.

Over the years the level of ambition in this area has increased dramatically. For example in 1994 the Department of Trade and Industry stated (in rather peculiar English) that ‘…a plausible figure for the upper band of what is feasible by 2025 under severe pressures of need and economics would be … 60TWh/y …’ [Department of Trade and Industry, 1994]. In 2014 renewables supplied 109TWh, of which 64TWh was in the form of electricity.

To answer this question we need to find out the size of our renewable resource and the size of our energy demand and compare them. First, lets look at the size of our renewable resources.

Renewable resources

This is a difficult question to answer because the studies that have been published on it over the years give a wide range of different answers. This is to be expected because such calculations involve many quantities that are basically a matter of guesswork judgement, such as how much of our land area we could cover with wind turbines before nimbies stage a coup (1%, 5%, 10%?). The size of our renewable resource is like the number of clothes you can cram into your suitcase before you go on holiday, you can always stuff a few more in if you push hard enough and so the result is rather elastic. In fact, renewable resource estimation is more of an art than a science.

I have surveyed the available studies that attempt to quantify the UK’s renewable resource. The details can be found here. As mentioned in the preceding paragraph, the results that these studies present are all over the place. For some technologies there is more than a factor of ten between the lowest and highest estimates. To get round this, I have discarded the highest and lowest estimates and presented the 2nd highest and 2nd lowest, and in some cases the 3rd highest and 3rd lowest, as the upper and lower ends of a range. Table 1 below lists the results of this exercise.

Table 1: Estimates of the UK’s renewable resource.

Technology	Lower estimate (TWh/y)	Upper estimate (TWh/y)
Offshore wind	200	663
Onshore wind	127	470
Solar	84	140
Bioenergy	53	210
Wave	50	100
Tidal range	33	38
Tidal stream	16	42
Hydro	7.5	7.5
Total	570.5	1670.5
Total (excl. bioenergy)	517.5	1460.5

The upper end of this range is still nearly three times bigger than the lower end. Because of the inherently rough and subjective nature of all estimates of renewables potential, I think we should round these numbers pretty drastically. The total including biomass is:

550 to 1700TWh/y

and the total excluding biomass is:

500 to 1500TWh/y

Now let’s find out how this comapres with our energy demand.

The next few sections are a bit of a slog. If you just want to find out the answer, feel free to skip to the conclusions section.

Energy demand

First, a note about decimal places, significant figures and rounding. The numbers presented here are subject to considerable uncertainty and only justify a small number of significant figures, certainly no more than two. However, to avoid rounding errors being magnified through multiple stages of calculation, I have chosen to apply rounding only at the very end of the calculation, and to present intermediate numbers with more precision than they deserve.

Table 2 below presents numbers from the most recent edition of the Digest of UK Energy Statistics (DUKES). Although the 2015 edition contains data for the year 2014, I’m going to use the numbers for 2013 instead. This is because not all of the data we need from other publications is available for 2014 yet.

Table 2: UK energy consumption in 2013 (TWh/y), from DUKES 2015 Table 1.2

	Coal	Manufactured fuel	Petroleum products	Natural gas	Bioenergy & waste	Electricity	Heat sold	Total
Industry	16.63	6.90	50.28	93.01	6.66	97.67	10.71	281.86
Transport	0.11		605.86		12.70	4.27		622.94
Domestic	5.63	2.56	33.36	342.50	20.33	113.44	0.60	518.44
Public administration	0.18		4.03	44.42	1.21	18.82	4.47	73.13
Commercial	0.04		5.31	57.79	0.62	78.90	0.17	142.83
Agriculture			4.56	1.10	2.61	3.87		12.15
Miscellaneous	0.06		3.40	12.07				15.52
Non energy use		1.63	82.89	5.60				90.12
Total	22.65	11.10	789.70	556.48	44.13	316.98	15.96	1756.99

The bottom line total is almost exactly the same as the upper end of the range of estimates that we have found for our renewables potential. We can’t just compare them as they are, however. We first need to make some assumptions about the technologies that would supply and use the energy. This is for the following reasons:

1. There are some uses of energy that are currently not able to make use of renewables. These include aviation and some high-temperature industrial processes such as virgin steel manufacture. We will just have to accept that these cannot be decarbonised at the moment and hope that they are not too big. Maybe in the longer term ways will be found to decarbonse them.

2. There are some uses of fuels that are categorised as ‘non-energy uses’. This refers to petroleum that is used as a chemical feedstock, such as in the manufacture of various plastics, petrochemicals, lubricants, road surfacing materials and solvents. The carbon contained in this feedstock does not end up in the atmosphere and so does not contribute to golbal warming. Consequently, these uses do not need to be decarbonsied and can be ignored.

3. All renewable energy technologies apart from biomass produce electricity directly. This means that if renewables are going to supply space heating, industrial process heating and transport it will be necessary to:

   1. decide how much biomass we are willing to use and then
   2. electrify the remaining heat demand.

For the purpose of this analysis I’m going to assume that bioenergy does not play a part in the UK’s long term energy mix. This is for the following reasons:

1. The calculations are easier that way.

2. I don’t feel comfortable with the idea of growing energy crops on land that is needed for food production and housing. The era of food mountains and wine lakes is over and there is no such thing as ‘surplus land’ any more. Farmers struggling to make a profit from food production may disagree but that is because of short term market fluctuations and distortions, not long term fundamentals. If we want to avoid contributing to world hunger we should avoid energy crops. This also applies to ground-mounted PV arrays.

3. Production of combustible waste and landfill gas is likely to decline over the coming decades due to increasingly rigorous application of the waste hierarchy. Energy from waste and landfill gas are therefore unlikely to be available in the long term, though we should obviously use them while we have them. Anaerobic digestion of sewage sludge, farm slurries and food industry waste will be available long term but are too small to have a noticeable impact on the numbers in this analysis.

Bioenergy currently supplies 61% of our delivered renewable energy so it would appear to be a big deal to do without it. However, its share of our renewable potenial is smaller than its share of current production, which is underdeveloped across all technologies, so it isn’t such a big deal as this would suggest.

If we are to do entirely without biomass it will be necessary to electrify space heating, some types of industrial process heating and transport. The amount of energy that the electrified versions of these activities will need is different from the amount of fossil energy that they currently consume and will depend on the technologies used to convert the electricity into heat or motive power.

For heating there are four alternatives:

• resistive heating;
• microwave heating;
• induction heating;
• heat pumps.

Resistive heating is the old-fashioned type of electric heating as used in electric kettles. 1kWh of electrical energy is converted into 1kWh of heat, so if we are replacing a fossil heater with a resistive electric heater we need to replace every kWh of fossil energy by 1kWh of electrical energy.

Microwave and induction heating also convert 1kWh of electrical energy into 1kWh of heat energy but are able to deliver the energy much more precisely and don’t heat the surrounding air and materials quite as much. This means that in practice they are more efficient than fossil fired heating.

Heat pumps are capable of supplying several times as much heat energy as they consume in electrical energy, the additional heat being sucked out of the surrounding air or ground. A heat pump’s heat output divided by its electricity input is called its ‘coefficient of performance’ (COP) or ‘seasonal performance factor’ (SPF), which is just the COP measured in a standardized test. COP is strongly influenced by a large number of factors so it is important to use a realistic figure derived from actual measurments in the UK. Fortunately DECC has recently carried out a number of field trials. These found a wide spread of COPs ranging from 0.5 to 4.5 with a peak at 2.5 (promotional literature typically claims 3 to 4). Consequently, for this exercise, I’m going to assume a value of 2.5.

Some people regard heat pumps as a source of renewable heat but that is wrong. The correct way to think of a heat pump is as a device that creates a temperature difference through the expenditure of mechanical work. A heat pump heats a building above ambient temperature by cooling some other place, usually the surrounding air or ground, below ambient temperature. The mechanical work required to do this comes from a power station where it was produced by harnessing a flow of heat, released by the combustion of fuel, as it ‘falls’ from a high temperature, in the furnace of a boiler, to a low temperature, in the water of a cooling tower. A small quantity of heat flowing through a large temperature difference is equivalent to a large quantity of heat flowing through a small temperature difference. The temperature to which we heat our buildings is very much less than the temperature produced by the combustion of fuel in a power station, so the quantity of heat delivered by a heat pump is greater than the quantity of heat from which its electrical input was generated.

It is this inverse relationship between heat-quantity and temperature-difference that explains the ‘extra’ heat delivered by a heat pump, not the existence of a source of renewable heat that augments the heat pump’s energy input. This is also the reason why heat pumps are, theoretically at least, better than CHP.

Proponents of the ‘heat pumps are renewable’ view may say that the heat extracted from the surroundings is replenished by heat from the sun or, more fancifully, by ‘geothermal’ heat, but it would be more accurate to say that the initially localised cold spot diffuses away into the wider environment where it is diluted beyond recognition by the enormous heat capacity of the Earth’s atmosphere and crust. In any case, all of the heat inside a building heated by a heat pump eventually finds its way back into the surroundings and is more than sufficient to replenish the heat that was pumped out of those surroundings in the first place.

Another reason for not counting heat pumps as renewable is that they cannot operate without an external source of energy. If every heat demand in the country were supplied by heat pumps we would still require around 40% of external electricity. If a heat pump used electricity from a wind turbine it would be valid to call its output renewable provided that the electrical output of the turbine wasn’t counted toward the renewable total. If, on the other hand, the heat pump uses non-renewablre power then none of it should be counted. The fact that the European Commission allows member states to count a portion of the heat delivered by heat pumps towards their targets under the Renewable Energy Directive is a political fact, not a scientific one.

I do think that heat pumps should be encouraged, but not by calling them renewable.

That’s enough ranting. Back to the topic under discussion. Resistive, microwave and induction heaters are capable of heating their targets to very high temperatures, whereas heat pumps can, practically, only achieve a temperature of about 50°C. This means that we can use heat pumps for some applications, such as space heating and some low temperature processes, but not for others, such as high temperature processes. To work out how much heat we can supply from each of these technologies we need to look at how energy is consumed in more detail in industry, transport and buildings.

Industry

DECC’s publication ‘Energy Consumption in the UK’ [ECUK, 2015] gives more detail on how our energy is consumed. Table 3 below shows data from ECUK’s Table 4.07, which shows how industrial energy consumption in 2013 is broken down by type of process.

Table 3: Breakdown of industrial energy consumption by type of process in 2013 (TWh/y), (from Energy Consumption in the UK 2015, Table 4.07: Industrial final energy consumption by end use (different processes))

	Electricity	Natural Gas	Oil	Solid Fuel	Total fossil	Total energy
High temperature process	10.92	21.21	2.11	13.13	36.45	47.38
Low Temperature Process	17.33	36.23	5.39	23.27	64.89	82.23
Drying / Separation	6.40	12.19	1.85	10.99	25.02	31.42
Motors	35.53	0.00	0.00	0.00	0.00	35.53
Compressed Air	10.00	0.00	0.00	0.00	0.00	10.00
Lighting	2.81	0.00	0.00	0.00	0.00	2.81
Refrigeration	5.61	0.00	0.00	0.00	0.00	5.61
Space Heating	7.86	9.99	2.41	8.78	21.18	29.04
Other	4.94	10.49	1.50	7.67	19.66	24.60
Total	101.40	90.12	13.26	63.84	167.21	268.61

The total in Table 3 is less than the total of Industry in Table 2, which is because the former doesn’t include ‘heat sold’ and ‘bioenergy and waste’. Taking these into account brings the numbers closer; 281.86 – 10.71 – 6.66 = 264.49, which is 4.12TWh/y short of the total of Table 3. This appears to be a genuine discrepancy between DUKES and ECUK, but is too small to be worth bothering about for this analysis.

ECUK defines the processes listed in Table 3 as follows:

High temperature processes

High temperature processing dominates energy consumption in the iron and steel, non-ferrous metal, bricks, cement, glass and potteries industries. This includes coke ovens, blast furnaces and other furnaces, kilns and glass tanks.

Low temperature processes

Low temperature processes are the largest end use of energy for the food, drink and tobacco industry. This includes process heating and distillation in the chemicals sector; baking and separation processes in food and drink; pressing and drying processes, in paper manufacture; and washing, scouring, dyeing and drying in the textiles industry.

Drying/separation

Drying and separation is important in paper-making while motor processes are used more in the manufacture of chemicals and chemical products than in any other individual industry.

It doesn’t, however, define the temperature that marks the transition between ‘high’ and ‘low’ temperature processes. The above definitions suggest it is somewhere between 1000°C and 2000°C. This means that some of the processes officially listed under ‘low temperature’ will also be too hot to be supplied by heat pumps. These would include some food manufacturing processes, for example. These processes would, however, be amenable to the other forms of electric heating.

Our task is to work out what numbers should go in the ‘Total fossil’ column if those applications were electrified. To do this we make the following assumptions:

1. heat pumps are used everywhere that heat pumps can be used;
2. induction and/or microwave heating are used everywhere that they can be used that isn’t alrerady supplied by a heat pump;
3. resistive heating supplies the rest;
4. all high temperature processes that are capable of being heated electrically are already heated electrically and that the remaining ones will continue to use fossil fuels.

I am also going to apply the concept of ‘COP’, which is normally only used in the context of heat pumps, to the other types of electric heating, so the calculation can be done in the same way for all of them. I’m going to arbirarily assume the values of ‘COP’ shown in Table 4, because they seem reasonable.

Table 4: assumed COPs for electric heating.

Technology	‘COP’
Resistive heating	1.0
Inductive and/or microwave	1.2
Heat pumps	2.5

Table 5 below translates the above assumptions into numbers and also sets out the calculation of the amount of electricity required.

Table 5: Calculation of industry sector electricity consumption after electrification.

	Existing electricity	Existing fossil	Resistive	Inductive or microwave	Heat pump	Average ‘COP’	Electricity that repl- aces existing fossil	Total electricity
‘COP’	–	–	1.0	1.2	2.5	–	–	–
Low temperature processes	17.33	64.89	33%	33%	34%	1.576	64.89 ÷ 1.576 = 41.174	58.504
Drying and separation	6.40	25.02	0%	0%	100%	2.5	25.02 ÷ 2.5 = 10.008	16.408
Space heating	7.86	21.18	0%	0%	100%	2.5	21.18 ÷ 2.5 = 8.472	16.332
Other	4.94	19.29	33%	33%	34%	1.576	19.29 ÷ 1.576 = 12.240	17.180
Total	36.53	130.38	–	–	–	–	71.894	108.420

It can be seen that 130TWh/y of fossil fuel has been replaced by 72TWh of delivered electricity, which is susbtantially less than one-to-one.

We can now put these numbers back into Table 3 to give the energy consumption of the ‘Industry’ sector under an electrified scenario. This is shown in Table 6 below.

Table 6: Total industry sector energy consumptuon under electrified scenario.

	Electricity	Fossil	Total energy
High temperature process	10.92	36.45	47.38
Low Temperature Process	58.504	0	58.504
Drying / Separation	16.408	0	16.408
Motors	35.53	0	35.53
Compressed Air	10.00	0	10.00
Lighting	2.81	0	2.81
Refrigeration	5.61	0	5.61
Space Heating	16.332	0	16.332
Other	17.180	0	17.180
Total	173.294	36.45	209.754

So in this ‘almost all electric’ scenario, the industry sector consumes 210TWh/y of delivered energy compared with 269TWh under the current situation. This is not an enormous reduction.

The 36.45TWh/y that remains fossilized represents 2% of the total delivered energy consumption of 1756.99TWh/y reported in Table 2.

Residential sector

Energy statistics annoyingly use the word ‘domestic’ for this sector thereby inviting confusion with that word’s other meaning, which is ‘of one’s home country’ as in ‘gross domestic product’. ‘Residential’ is better because it is unambiguous.

Table 7 below gives a breakdown of residential energy consumption in 2013 by end use and fuel, from Energy Consumption in the UK.

Table 7: Residential energy consumption by end use and fuel in 2013

	Solid fuel	Gas	Electricity	Oil	Heat sold	Bioenergy and Waste	Total
Space heating	7.67	264.38	24.98	27.89	0.6	15.67	341.19
Hot water	0.52	70.98	7.59	5.47	0	4.66	89.23
Cooking	0	7.14	5.7	0	0	0	12.84
Lighting and Appliances	0	0	75.17	0	0	0	75.17
Total	8.19	342.5	113.44	33.36	0.6	20.33	518.44

Assume that space heating and hot water are supplied by heat pumps with a COP of 2.5 and cooking is supplied by resistive electric heating with ‘COP’ of 1.

Table 8: Residential energy consumption after electrification, derived from data for 2013

	Existing electricity	Electrcity that replaces fossil fuel	Total
Space heating	24.98	(7.67 + 264.38 + 27.89 + 0.6 + 15.67) / 2.5 = 126.48	151.46
Hot water	7.59	(0.52 + 70.98 + 5.47 + 0 + 4.66) / 2.5 = 32.652	40.242
Cooking	5.7	7.14	12.84
Lighting and Appliances	75.17	0	75.17
Total	113.44	166.27	279.71

Commercial and public buildings

The sectors that DUKES calls ‘Public administration’, ‘Commercial’ and ‘Agriculture’, Energy Consumption in the UK lumps together and calls ‘services’. Table 9 below lists the energy consumption of this sector by end use and fuel. As with the industry sector there’s a slight discrepancy between this and DUKES but the difference is too small to bother about.

Table 9: Service sector final energy consumption by end use and fuel 2013, TWh/y (from Table 5.17 of Energy Consumption in the UK, June 2015)

	Electricity	Natural Gas	Oil	Solid fuel	Heat Sold	Bioenergy and Waste	Total fossil	Total
Catering	13.05	9.56	0.47		0.29	0.01	10.34	23.39
Computing	5.90							5.90
Cooling and Ventilation	8.69	0.39					0.39	9.08
Hot Water	3.45	16.76	1.16	0.04	0.66	0.24	18.86	22.32
Heating	13.95	85.75	10.96	0.24	3.61	1.58	102.14	116.09
Lighting	39.84							39.84
Other	12.84	1.82	0.14		0.08		2.03	14.87
Total	97.72	114.28	12.73	0.28	4.64	1.83	133.76	231.48

Table 10 below applies the same methodology as for the preceding sectors. ‘Catering’, which I assume means cooking, is converted to resistive heating, while space heating and hot water are assumed to be done by heat pumps with a COP of 2.5.

Table 10: Service sector final energy consumption under electrified scenario, TWh/y (from Table 5.17 of Energy Consumption in the UK, June 2015)

	Existing electricity	Existing fossil	“COP”	Electricity that replaces existing fossil	Total electricity
Catering	13.05	10.34	1.00	10.34	23.39
Computing	5.90		n/a		5.90
Cooling and Ventilation	8.69	0.39	1.00	0.39	9.08
Hot Water	3.45	18.86	2.50	7.55	11.00
Heating	13.95	102.14	2.50	40.86	54.81
Lighting	39.84		n/a		39.84
Other	12.84	2.03	1.00	2.03	14.87
Total	97.72	133.76		61.16	158.88

Planes, cars, lorries, trains and some boats

Table 11 below gives a more detailed breakdowm of transport energy consumption.

Table 11: UK transport energy consumption in 2013, from DUKES 2015 Table 1.2

	Coal	Petroleum products	Bioenergy & waste	Electricity	Total
Air	0.00	144.60	0.00	0.00	144.60
Rail	0.11	7.62	0.00	4.24	11.97
Road	0.00	444.00	12.70	0.03	456.73
National navigation	0.00	9.64	0.00	0.00	9.64
Total	0.11	605.86	12.70	4.27	622.94

‘National navigation’ is defined as follows:

Fuel oil and gas/diesel oil delivered, other than under international bunker contracts, for fishing vessels, UK oil and gas exploration and production, coastal and inland shipping and for use in ports and harbours.

It is difficult to envisage boats being powered by electrcity. The size of national navigation, 9.64TWh/y, is a bit less than the current use of biofuels in transport. So, although I said that I was going to do without biofuels for this exercise, I’m going to backtrack a bit and reallocate to sea transport some of the biofuels currently used in road transport. This will still require less than are currently used and certainly won’t entail an increase in biofuel production.

Planes

According to Table 11 deliveries of fuel to aviation activities in the UK amounts to 144TWh/y. This is a surprisingly large 8% of our total energy consumption. It includes fuel for planes setting off on international journeys though it doesn’t include, obviously, their return journeys. Possibly a better measure would be the fuel attributable to flights taken by UK citizens anywhere in the world but I’m pretty sure there are no data on this.

Steam trains

Table 11 includes 0.11TWh of coal under the heading of rail. The only thing this could possibly be is steam trains run by enthusiasts for recreational purposes. Obviously if these were converted to electrcity they wouldn’t be steam trains any more and it would be cruel to force these people to do that. Consequently this coal will have to be part of our energy demand that is unreachable by renewables.

This is the last of our incorrigibly fossilized activities. The total of high temperature industrial processes (36.45TWh/y), aviation (144TWh/y) and recreational steam train use (0.11TWh/y) is 180.56TWh/y or 10.3% of our 2013 total delivered energy consumption of 1756.99TWh/y as reported in Table 2.

Ordinary trains

Energy consumption data for many different kinds of UK trains is given in a 2001 report by Hobson and Smith [Hobson and Smith 2001]. This lists the energy consumption per km of a large number of different ‘classes’ of UK trains. All of the diesel trains listed are local service DMUs. Plotting energy consumption (kWh/km) against weight of the train (tonnes) and fitting a linear regression line through the origin suggests that these DMUs consume roughly 0.129kWh/km/te. The electric trains listed include several freight and inter city trains. Excluding these and performing the same regression on the remaining local service EMUs gives 0.055kWh/km/te. This means that an EMU requires roughly 42% of the delivered energy erequired by a DMU of the same weight.

Since 2012 the International Union of Railways (UIC in French) and the International Energy Agency (IEA) have produced an annual report surveying energy consumption and CO₂ emissions from railways in different countries and regions of the world. The 2012 edition of this report (International Union of Railways and International Energy Agency, 2012), though not subsequent ones, includes the chart shown in Figure 1 below. This shows energy concumption in kJ per passenger-km for diesel and electric versions of two different categories of train. These data were only presented as an image without any associated numbers, but measuring pixels on this image gives the ratio of electrical to diesel energy consumption as 40.3% for ‘regional’ and 31.2% for ‘inter city’.

Figure 1: Passenger specific consumption by service type and traction type, 2005 (kJ/pkm), [International Union of Railways and International Energy Agency (2012)]

Finally, a report by IFEU Heidelberg (from IFEU Heidelberg 2008), carried out as part of the EcoPassenger project (see http://ecopassenger.org/), included the table reporduced in Tables 12 and 13 below. In these tables the fuel consumption of the diesel trains is given in grammes. To convert this to Wh I have used a gross calorific value of 45.4GJ/tonne = 12.61Wh/g, which is the average of seven values reported in DUKES 2015 each referring to a different year; 1980, 1990, 2000, 2010, 2012, 2013 and 2014.

Table 12: Average values for specific energy consumption of European trains, passenger basis (IFEU Heidelberg, 2008)

	Electric (Wh/Pkm)			Diesel (g/Pkm)		Diesel (Wh/Pkm)
	Highspeed	Intercity	Regional/Suburban	Intercity	Regional/Suburban	Intercity	Regional/Suburban
Average	70	76	125	22	27	22 × 12.61 = 277.42	27 × 12.61 = 340.47

On a per passenger basis, inter city electric trains use 76 / 277.42 = 27.4% as much energy on average as a diesel powered inter city trains and electric ‘regional’ trains use 125 / 340.47 = 36.7% on average as much as their diesel powered equivalents.

Table 13: Average values for specific energy consumption of European trains, seat basis (from IFEU Heidelberg 2008)

	Electric (Wh/seatkm)			Diesel (g/seatkm)		Diesel (Wh/seatkm)
	Highspeed	Intercity	Regional/Suburban	Intercity	Regional/Suburban	Intercity	Regional/Suburban
Average	39	35	33	8.3	6.4	8.3 × 12.61 = 104.66	6.4 × 12.61 = 80.704

On a per seat basis, inter city electric trains use 35 / 104.66 = 33.4% as much energy on average as a diesel powered inter city trains and electric ‘regional’ trains use 33 / 80.704 = 40.9% on average as much as their diesel powered equivalents.

These three different data sources are roughly consistent, and based on them I’m going to assume that an electric train uses 40% as much delivered energy as a diesel powered one, so 1TWh of diesel fuel is replaced by 0.4TWh of electrcity.

The electricity required to replace the petroleum products used by not-yet-electrified trains is therefore 7.62 × 0.4 = 3.05TWh

Cars and lorries

There are many ways in which road transport could be electrified. For the purposes of this exercise, I’m going to assume that it will be done by electric vehicles that use batteries to store their energy—‘battery electric vehicles’ or BEVs.

The electricity that these vehicles consume will be less than the petrol and diesel that current vehicles use. We therefore need to calculate how much this will be.

We want the number of kWh of electricty that would replace one kWh of petroleum-derived road-fuel when a fossil-powered vehicle is replaced by an electric one. This is given by the ‘tank-to-wheel’ efficiency of the fossil vehicle divided by the ‘plug-to-wheel’ efficiency of the electric one.

Hill et al 2012 summarise data on engine efficiency for UK road vehicles. Their data are shown in Table 14 below.

Table 14: Summary of basic component efficiency assumptions used in the study analysis (Table 3.1 of Hill et al 2012)

Area	Category	Unit	2010	2020	2030	2040	2050	Source/Notes
Petrol ICE powertrain	All	%	22%	22%	22%	22%	22%	Indicative estimate
Diesel ICE powertrain	All	%	25%	25%	25%	25%	25%	Indicative estimate
DNG ICE	All	%	25%	25%	25%	25%	25%	As for heavy duty diesel
Electric motor	Best	%	92%	93%	94%	94%	95%	JEC (2011), AEA (2008)
	Low	%	92%	93%	93%	94%	94%	AEA indicative estimate
	High	%	92%	93%	94%	95%	96%	AEA indicative estimate
Electric powertrain	LDV	%	95%	95%	95%	95%	95%	Indicative estimate based
	HDV	%	95%	95%	95%	95%	95%	on IEA (2012
	Motorcycle	%	95%	95%	95%	95%	95%	forthcoming).
Battery + Charger	LDV	%	75%	79%	83%	86%	90%	Cenex (2012), AEA (2008)
	HDV	%	75%	79%	83%	86%	90%	As for LDVs
	Motorcycle	%	75%	79%	83%	86%	90%	As for LDVs

‘ICE’ is short for internal combustion engine. The efficiency values for ‘petrol ICE powertrain’ and ‘diesel ICE powertrain’ are described as ‘indicative estimate’s, by which I assume they mean that they are values commonly accepted in industry. I propose to assume that the efficiency of all fossil powered road vehicles is 25%, because I don’t know the ratio of pretrol to diesel mileage and it is better to overestimate the amount of electrcity needed than to underestimate it.

The efficiency for the complete electric drivetrain is the product of the efficiencies of the battery + charger, the motor and the transmission, which is what I assume the word ‘drivetrain’ refers to in Table 14. This gives:

0.92 × 0.95 × 0.75 = 0.65550 = 66%

so every TWh of fossil vehicle fuel is replaced by 25 / 66 = 0.38TWh of electricity.

Before applying this factor we first need to add the petroleum products (444.00TWh/y) to the ‘bioenergy & waste’ (12.70TWh/y) to give 456.7TWh. Multiplying this by 0.38 gives 173.55TWh/y.

Table 15 below gathers together the above results for the different modes of transport:

Table 15: Transport under electrified scenario

	Coal	Petroleum products	Bioenergy & waste	Existing electricity	Electricity that replaces petroleum	Total electricity	Total
Air	0.00	144.60	0.00	0.00	0.00	0.00	144.60
Rail	0.11	0.00	0.00	4.24	3.05	7.40	7.40
Road	0.00	0.00	0.00	0.03	173.55	173.58	173.58
National navigation	0.00	0.00	9.64	0.00	0.00	0.00	9.64
Total	0.11	144.60	9.64	4.27	176.60	180.87	335.22

Sub total

For renewables to supply our economy’s energy needs, excluding aviation, high temperature industrial processes, recreational steam-train use, we will need the quantity of energy shown in Table 16 below.

The figures in Table 16 represent final delivered energy, but electricity generation will have to be a bit bigger because of transmission and distribution losses, which for electricity are roughly 7%. When we have calculated our bottom line figure we’ll therefore need to scale up the electrcity requirement by a factor of $latex 1 / \left( 1 – \frac{7}{100} \right) = 1.075$ or 7.5% .

Table 16: Target electricity demand that an all-renewable UK will have to meet.

	Renewable electricity (TWh/y)	Bio-fuel (TWh/y)	Fossil fuel (TWh/y)	Total energy (TWh/y)
Industry	173.294	0	36.45	209.754
Transport	180.87	9.64	144.71	335.22
Residential	279.71	0	0	279.71
Services	158.88	0	0	158.88
Subtotal	792.754	9.64	181.16	983.554
Losses (7.5% of subtotal)	59.457	0.000	0.000	59.457
Total	852.211	9.640	181.160	1043.011

This is the point where we round to the nearest two significant figures. This means we need: 850TWh/y of renewable electricity, plus 10TWh/y of biofuel. We have also left 180TWh/y as continuing to use fossil fuel because these applications are technically too difficult to electrify.

The incorrigibly fossilised applications represent 10% of our current delivered energy consumption as set out in Table 2, but are 17% under the electrified scenario set out in Table 16. Aviation accounts for 80% of this residual fossil fuel.

Table 1 above found a range of 500TWh/y to 1500TWh/y for our renewable potential excluding biomass. This means that our energy demand is right in the middle of the range of estimates of our renewable resource, which means that it is probable that renewables could supply all of the demand that is technically capable of being electrified.

Imported goods

The UK is a post-industrial economy. Almost all of the physical ‘stuff’ we consume is imported and brings with it a large amount of ‘embedded’ emissions.

Given that we’ve lost most of our real industries to Germany, Japan, Korea and, more recently, China, we could leave it up to those countries to work out how to decarbonise them. But that would be perverse. Firstly, we want these industries back (well, I do, anyway), and when that happens they will emit CO₂ inside our borders. Secondly, it is rightly becoming the norm for governments to report their CO₂ emissions on a consumption basis, which means CO₂ emitted within a country’s borders plus that ‘embedded’ in imported goods (after netting off exports, for pedants, though that’s pretty academic in the case of the UK).

A number of studies have been published that estimate the UK’s CO₂ emissions on a consumption basis. Figure 2 below shows data from a report updated annually by Defra [Defra, 2015]

Figure 2: CO₂ emissions associated with UK consumption 1997 to 2012, from [Defra, 2015]

This shows that CO₂ emissions embedded in imported goods are roughly the same size as the in-country emissions, so it is likely that the energy used to make the imported goods is also roughly the same size as the energy consumed inside the UK. Therefore if we continue to be a post-industrial economy roughly half of our CO₂ emissions will be beyond our control. These figures don’t allow us to draw any more precise conclusions, however.

An interesting feature of Figure 2 is that CO₂ embedded in imported goods and services peaked in 2007, the year before the 2008 crash. It then declined steeply during the following two years before levelling off. The other categories of emissions, however, varied much less over the same period. That is, imported emissions respond strongly to economic growth while in-country emissions do not. This is a consequence of the UK’s massive trade deficit in physical goods, which means that the effect of economic growth is to suck in imports rather than to stimulate production at home.

The data graphed in Figure 2 are not exactly what we need, however. Firstly, they are in units of CO₂, which makes it impossible to work out how much corresponds to different uses and fuels. Secondly, we want to estimate of the quantity of energy that would be consumed inside our borders if we were to make everything we consume, or, more accurately, to make as much as we consume. This would have to exclude some parts of the production process, such as ore extraction, that will always have to occur overseas. It would therefore be far too difficult to derive an estimate for how much extra energy we would need to supply if we were lucky enough to stop being post-industrial. The best I can do is to give a hand-wavy answer and say that it would be a roughly the same size as our current energy consumption.

Conclusion

Renewables cannot supply 100% of our energy needs because there are some activities that cannot make use of them. These are principally aviation, high temperature industrial processes and recreational steam train use. Together these add up to 10% of our current delivered energy consumption. This means that however much renewable resource we have we can’t supply more than 90% of our current energy demand. Technological innovation may change this in the long run, however.

Of this 90%, the answer to the question of whether there is enough renewable energy in the UK to meet this demand is:

probably,

but if we were to stop being a post industrial economy and actually make as much as we consume then the answer would change from probably to almost certainly not. In that case, we would probably be able to meet roughly half of our energy demand.

The important question, however, is not whether we can be 100% renewable but whether renewables can make a significant contribution. It can certainly do that.

This article has only looked at our current energy demand. It will almost certainly be different in the future, however, because of two opposing forces—growth in demand and improvements in energy efficiency. It would be too speculative to try to predict how it will change in the future, however. Hopefully efficiency improvements will prevail and demand will go down.

The next post in this series is going to be looking at the concept of efficiency and what it means when applied to renewables and conventional energy.

References