The vast majority of energy is supplied via oil, coal or gas burnt at the point of use. In 2021, 82% of the USA’s end use energy consumption is still consumed directly via one of the following: heating buildings (primarily with diesel and natural gas), fuelling vehicles with oil, supplying high grade heat for industrial processes or another direct use of fossil fuels. Electricity provides just 18% of end use consumption.

In other words, in the Sankey diagram below, the boxes the left reading ‘source’ are primary energy. This is the total chemical energy in all the fuel we burn. Much of this is lost as waste heat, during the conversion of combustion heat to electricity. The yellow boxes on the right, reading ’end-use sector’ represent only the energy that we directly use.

The grey box on the bottom, reading ’electricity retail sales’ is just 18% of the final end use of energy.

U.S. Primary Energy Consumption by Source and Sector graphic. Shares by source in 2020: Petroleum 35%, Natural Gas 34%, Coal 9%, Renewable Energy 12%, Nuclear Electric Power 9%. Shares by sector: Transportation 35%, Industrial 36%, Residential and Commercial combined 29%

A simplified calculation thus shows that the electrical grid has to more than quintuple to supply energy to every use case throughout the economy. But happily, electrification of the economy will somewhat increase efficiency and push the energy demand down.

Here is it important to distinguish between two phenomena that are often confounding: 1. Renewables don’t need to replace the waste heat energy lost fossil energy used in generating electricity; 2. Electrifying the grid brings efficiencies.

We need to account for the fact that the primary energy figure from BP, IEA and EIA typically assumes that all the electricity was generated using a conversion efficiency of 40.625%. It lists the chemical energy of fossil fuel equivalent Joules to achieve that, not the end-use electrical demand. In other words the electrical energy demand is 40% of the primary energy numbers. In the diagram above, we can see that about 1/3 of primary energy is used to generate electricity. Therefore, when considering the demand that renewables and nuclear need to replace, we only need to be concerned with 40% of that 38%, i.e. Nuclear and renewables only need to replace 1/3 * 0.4 + 2/3 = 77% of primary energy supply to meet energy demand.

Whether you consider this to be ’efficiency’ depends on your definition of ‘using energy’.

We get efficiencies from fully electrifying the economy in two places: transport and heating.

The transport sector is currently fuelled almost exclusively by oil. In conventional energy reviews, such as the Monthly review by the US Energy Information Administration, the value of consumption for transport is inflated because in a combustion engine, 60% of the chemical energy is lost as waste heat, with only 40% being converted to useful kinetic energy which moves the vehicle, where Electrification could theoretically cut the energy demand in the oil fuelled vehicle segment of the transport sector by around 50%. In reality, this would not be as great due to the high embodied energy of electric vehicles and other new inefficiencies.

Further savings in electrification can be expected in heating through the use of heat-pumps. These operate at greater than 100% efficiency, by ‘stealing’ heat from either the air (in a conventional air-con unit run in reverse) or from the soil (via a network of pipes connected to a type of air-con unit).

There are other areas of savings and there are areas, such as aviation and the manufacture of plastics, cement and other which are very difficult to imagine decarbonizing. The need to generate carbon-neutral synthetic hydrocarbons or invest in carbon capture technology may significantly increase the energy demand in such sectors. And at this point, we also start to ask questions about the definition of electrification versus carbon neutrality.

It’s hard to find a good estimate in the literature for the total savings from electrification, so I asked on reddit and the most comprehensive answer turned out to be in a study by Marc Jacobson.

While electricity use increases with WWS (wind, water, and sunlight), conventional fuel use decreases to zero. The increase in electric energy is much less than the decrease in energy in the gas, liquid, and solid fuels that the electricity replaces for three major reasons:

1. The higher energy-to-work conversion efficiency of using electricity for heating, heat pumps, and electric motors, and using electrolytic hydrogen in hydrogen fuel cells for transportation, compared with using fossil fuels;

2. The elimination of energy needed to mine, transport, and refine coal, oil, gas, biofuels, bioenergy, and uranium;

3. Assumed modest additional policy-driven energy-efficiency measures beyond those under BAU (business-as-usual).

These factors decrease average demand ∼23.0%, 12.6%, and 6.9%, respectively, for a total of 42.5%. Thus, WWS not only replaces fossil-fuel electricity directly but is also an energy-efficiency measure, reducing demand.

― Mark Z. Jacobson et al, 100% Clean and Renewable Wind, Water, and Sunlight All-Sector Energy Roadmaps for 139 Countries of the World, Joule, Volume 1, Issue 1, 6 September 2017, Pages 108-121

In addition to this, a pro-renewable, financial think tank “Carbon Tracker” included the following claim in their report ‘The Sky is the Limit’.

The technical and economic potential of solar and wind is thousands of PWh a year whilst annual electricity demand is just 27 PWh, and annual energy demand in terms of electrical energy is 65 PWh.

― Carbon Tracker: Kingsmill Bond et al, The sky’s the limit

Considering that the IEA finds annual ‘Total Final Consumption’ to be 115PWh (9938 Mtoe), Carbon Tracker are also implying a demand reduction of approximately 43% in an all-electric scenario.

Carbon Tracker is openly pro-renewable and their report was extensively cited by one of their lead consultants, when he appeared on ‘The Energy Transition Show’, Episode 152, No Limits, one of the world’s most popular energy podcasts, to support his claim that the potential of solar far exceeds current consumption.

Marc Jacobson is also notoriously optimistic about the technical potential of renewables to entirely power our society. He gained some popularity for his anti-nuclear stance debate on “Does the world need nuclear energy?” with Stewart Brand back in 2010. In 2015, he published his 50 States, 100% renewable Plan which was comprehensively rebutted in the same journal two years later as “economically unfeasible”. He came back in 2017 with the report I cited above which lays out a global plan for renewable-energy.

This is to say, given the renewable-activist backgrounds of these reports, I am confident that the 42.5% demand reduction in final energy consumption constitutes a best-case electrification scenario.