The first phase of our arithmetic journey confirmed the staggering challenge: affluent Britain currently demands 125 kWh/d per person of primary energy input. Our strategic shift to sustainability requires aggressively reducing this demand through efficiency measures—electrifying transport and heating—resulting in a monumental reliance on clean delivered electricity: 48 kWh/d per person (120 GW nationally), nearly a tripling of current consumption.

The next step—quantifying indigenous sustainable production (the “green stack”)—revealed a severe limitation: due to inevitable public opposition, the realistic maximum attainable output from Britain’s own renewable resources is constrained by a social ceiling of approximately 18 kWh/d per person.

Energy gap: 30 kWh/d/p shortfall between 48 kWh/d demand and 18 kWh/d UK renewables

This shortfall compels us to search for high-density, high-output energy sources beyond the physical and social boundaries of the British Isles. Sunlight, the most pervasive energy source of all, presents the greatest opportunity, provided we are willing to leverage its full potential, whether by highly efficient conversion of thermal energy locally or by importing massive amounts of electrical power from sunnier climes.

I. The Local Solar Equation: Constraints of British Sunniness

Solar power is often discussed in two distinct forms: passive collection of thermal energy (heat) and active conversion into electricity (photovoltaics or PV). In the UK, both face constraints dictated by latitude and climate.

1. Solar Thermal: The Efficient Collector

Solar thermal panels, often referred to as solar hot water (SHW) systems, are the most effective local application of solar energy in Britain. They function by capturing sunlight and transferring the resulting heat to water flowing through pipes, providing domestic hot water. They are highly efficient at energy capture.

The massive potential of thermal capture significantly outweighs the electrical output from localized photovoltaics. A large commitment to solar thermal systems—installing panels on a south-facing roof area of 10 m² per person—could theoretically deliver approximately 13 kWh/d per person of thermal energy.

In the blueprint for a sustainable future, solar hot water plays a crucial role in reducing the overall heat burden, estimated to contribute a realistic 1 kWh/d per person toward the nation’s domestic hot water load.

2. Solar Photovoltaics (PV): The Power-to-Efficiency Confusion

Photovoltaic panels convert solar radiation directly into electricity. While panel technology is advancing rapidly, becoming “ever cheaper,” the maximum delivered power in the UK remains limited by the density of solar radiation (sunniness).

The critical distinction is that efficiency must not be confused with delivered power. While expensive solar cells can achieve efficiencies of 20%, the average power density of sunlight in the UK is simply lower than in sunnier parts of the world.

UK solar PV limit: 5 kWh/d/p from 10 m²/person rooftop panels

  • Rooftop PV limits: Assuming the installation of high-efficiency (20%) PV panels across a substantial rooftop area of 10 m² per person, the maximum electrical energy yield in the UK is only about 5 kWh/d per person.
  • The myth of the energy payback: It is false that manufacturing a solar panel consumes more energy than it will ever deliver. The energy yield ratio for a roof-mounted, grid-connected solar system in central northern Europe is 4, assuming a 20-year lifespan.

This modest realistic output confirms that local solar PV cannot, on its own, meet the future electrical demand of 48 kWh/d/p.

II. Scaling Solar: The Desert Calculus

If Britain cannot sustain itself on its own renewables due to physical and social constraints, the logical strategy is to tap into areas rich in solar power and import the energy. Many large, area-rich countries, such as Saudi Arabia, Libya, Algeria, and Kazakhstan, have population densities far lower than Britain’s and possess vast deserts.

In these sunnier regions, the most promising technology is concentrating solar power (CSP), which uses mirrors or lenses to focus sunlight.

1. Concentrating Solar Power (CSP) Technology

CSP plants operate by concentrating solar heat, which drives a conventional thermodynamic engine (like a steam turbine or Stirling engine) to generate electricity. They come in various configurations, such as parabolic troughs or power towers.

CSP power density: 15–20 W/m²—10× higher than UK onshore wind

  • High power density: CSP facilities typically deliver average powers per unit area in the ballpark of 15 W/m² to 20 W/m².
  • Thermal storage: A significant advantage of CSP thermal systems over PV is the potential for heat storage. Energy absorbed by the mirrors can be stored in materials like molten salt, allowing the power plant to keep generating electricity during the night or during periods of cloudiness.

2. The Scale of the Desert Resource (The “Blob”)

The immense scale required to generate enough power for entire continents can be visualized using the concept of energy “squares” or “blobs.”

A massive square of 600 km by 600 km located in Africa or Saudi Arabia, completely filled with concentrating solar power facilities, would theoretically provide enough power for the entire world’s energy needs.

For a more practical visualization relevant to Europe, the Desertec plan proposes generating solar power in sunnier Mediterranean countries.

  • The blobs: A “blob” is defined as a circular area of 1500 km², which, if one-third-filled with solar power facilities operating at 15 W/m², would generate 10 GW average power.
  • To supply all one billion people in Europe and North Africa with 16 kWh/d per person, 65 such blobs would be required.

3. The Grand Engineering Challenge: HVDC Transmission

Importing massive amounts of power over vast distances (1000 km or more) necessitates high-voltage direct-current (HVDC) transmission lines. HVDC technology has been in use since 1954 and is employed for long-distance transmission in countries like China, Canada, and Brazil.

HVDC transmission losses: 15% over 3500 km lines for desert solar imports

  • Transmission losses: HVDC is efficient, but losses are unavoidable. For a 3500 km-long HVDC line, total losses (including conversion from AC to DC and back) are estimated to be about 15%.
  • Scaling up: The NIMBY plan for Britain, which avoids major domestic renewable industrialization, relies heavily on this importation strategy. This plan requires sourcing 20 kWh/d per person (50 GW) from distant deserts. This necessitates a 25-fold increase in the capacity of the current electricity connection from the continent.

This immense engineering commitment is the inevitable consequence of choosing to source energy from distant, sunnier locations.

III. Complementary Solar Technologies

While large-scale CSP and PV are the main contenders for massive deployment, other solar technologies exist but often face limitations.

1. Concentrating Photovoltaics (CPV)

CPV systems place high-quality solar cells at the focus of cheap lenses or mirrors.

  • Cost and location: CPV systems are argued to be “completely cost-competitive with fossil fuel” in sunnier desert states, often without the need for subsidy.
  • Power output: The average power density of high-concentration CPV systems in the desert is comparable to CSP thermal systems.

2. Solar Chimneys (Updraft Towers)

Solar chimneys are geo-engineering projects where the sun heats a massive area of air, and the resulting updraft drives turbines placed at the base of a very tall chimney.

  • Efficiency limits: Despite the vast scale of construction required, these devices have demonstrated extremely low efficiency, often achieving only about 1% conversion efficiency. Given the acute need for efficiency in all energy solutions, such low conversion rates make them unviable for large-scale production goals.

IV. The Verdict on Solar: Necessity of Scale

Solar energy, particularly when harvested in optimal locations, has the big output potential required to meet Britain’s future electrical demand of 48 kWh/d per person.

The solar resource is necessary both locally (via highly efficient solar hot water systems for heat conservation) and internationally (via massive concentrating solar power imports).

However, reliance on importing vast amounts of solar power introduces major political and security challenges, specifically dependence on foreign sources and the complex infrastructure of HVDC lines. Furthermore, the domestic contribution from PV is limited by geography, yielding only a modest 5 kWh/d/p even with generous assumptions about land use.

To maintain flexibility and energy security, policy planners must consider reliable, centralized, high-density power sources that are independent of fluctuating weather and foreign supply, leading inevitably to the discussion of nuclear power and sustainable fossil fuels.