1 Introduction

Power is the use of energy over time. Work is force applied over distance. Mechanized society requires considerable energy to accomplish useful work. Competition and growth demand working faster, or across greater distances, requiring more power. Accelerating food production results in more population, who require more energy in a self-stoking cycle. The failure of humankind to curb greenhouse gas emissions in the decade or more since global climate change has been well established suggests a Malthusian endpoint to civilization. Humankind urgently needs power sources that are globally abundant, environmentally clean, sustainable across generations, and low in cost so that nearly everyone can afford the basics of survival in the modern world.

To solve all of the world’s energy problems for once and forever requires such solutions in three areas: (1) large-scale, baseload ("always on") dispatchable power for cities and industrial parks; (2) distributed, local, small-scale power for rural villages or remote outposts; and (3) mobile and portable power for vehicles and hand-held electronics. Renewable energy generation from wind and ground-based solar are intermittent and cannot be dispatched as needed to follow demand. Renewable sources such as geothermal, wave, and tidal power are geographically limited. One proposed solution is a world-wide energy grid because there is always sunshine and wind somewhere on Earth [1]. Another approach is to pair wind and solar with energy storage such as compressed air energy storage and pumped storage hydro. These "grid-scale" solutions are lower in cost than batteries, but are also geographically limited.

Existing baseload power sources include nuclear power plants, coal-fired power plants, natural gas-fired power plants, and site-specific technologies such as geothermal power, wave power, and tidal power. Renewable energy such as wind and solar are intermittent, and require grid-scale energy storage to provide dispatchable, baseload power needed by metropolitan statistical districts (MSD), large factories, and data centers.

Presented here for the first time is a comprehensive, integrated solution suitable for all of human activity with minimal environmental impact. Area (1) above is served by power satellites (powersats) in orbit beaming energy wirelessly to ground-based receivers. Area (2) is served by biomass conversion using locally-available feedstock to produce energy, chemicals, fuel, and heat. Area (3) is served by low-energy hydrogen storage based on earth-abundant sorbents, using hydrogen from electrolysis of water via area (1) and hydrogen from syngas via area (2). This whole-of-Earth approach can serve all energy and power requirements based on sunlight, water, and soil, for all time to come.

2 Methods

The Paris Climate Accords, adopted in 2015, call for global average temperature to be limited to two degrees centigrade above pre-industrial levels. Global emissions declined during the COVID-19 global pandemic, but have since returned to the "business as usual" trajectory [2]. The sixth report of the Intergovernmental Panel on Climate Change makes abundantly clear the anthropogenic nature of climate change, and projects that our current civilization is likely to pass through the 2 degree limit without appreciably slowing [3]. Greenhouse gases are persistent, and the warming from existing emissions has not yet manifested. Even if civilization collapsed entirely this year, the Earth will continue to increase in temperature for a decade or more. Carbon removal from the atmosphere is theoretically possible, but challenging in practice, and energy-intensive. For the current global economic environment and interconnected activity to persist, a clear vision and pathway is needed for a rapid shift to low-emissions energy and power solutions.

First envisioned in a science fiction novel in the 1940s, and first patented in the US in the 1960s, solar power from space has the potential to serve area (1) of baseload power. For satellites in high orbits, the shadow of the Earth occludes the sun only briefly at the Spring and Autumnal Equinoxes, but is otherwise available without interruption or decline. Very large powersats with millions of solar panels generate DC power from sunlight. This power is converted to radio frequency (RF) using solid-state electronic devices and is then fed into an antenna array ("spacetenna"). Using the same frequency as cellular telephones, the spacetenna directs a low-density power beam to a rectifying receiving antenna ("rectenna") on the surface of the Earth (Fig. 1). The rectenna converts RF back to DC, which is then delivered to a nearby city or industrial park. Inverters and transformers condition the power so that existing appliances and machinery can operate without modification.

2.1 Space solar power

Fig. 1
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One possible powersat configuration for beaming baseload power to terrestrial customers

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There are many engineering challenges to space solar power (SSP), but the primary obstacle is cost. Launching hardware into orbit is expensive, and consumes a great deal of energy. For a space system intended to supply energy to terrestrial customers, one must question the energy returned on energy invested (EROEI). A superior solution is to use materials that are already in orbit. A factory delivered to the Moon can extract silicon [4, 5] and produce solar panels [6].

Delivering solar panels from the lunar surface to orbit requires significantly less energy than launching from Earth (Fig. 2). This requires considerable infrastructure development on the Moon [7] but, once established, can dramatically reduce the cost of electricity delivered to terrestrial utilities [8]. Space resource utilization is in its infancy, and may require a community of nations to establish the necessary components [9].

Fig. 2
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Lunar factory for extraction of silicon and aluminum from soil (regolith)

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2.2 Indirectly-heated pyrolytic gasification

Agriculture requires open land, so population density is low in rural regions. Power transmission lines can be built to serve few customers widely spaced, but this is expensive to install and prone to disruption. In the United States, president Harry Truman signed the Rural Electricifation Act into law in 1936, which dramatically aided farm communities in that country. Many other countries have spotty or irregular power, if any. Fortunately, growing food produces non-edible biomass such as rice husks and corn stover. These feedstocks, plus woody waste, and even non-halogenated plastics, can be gasified to produce "syngas"—a mixture of hydrogen and carbon monoxide (CO). A high-temperature, indirectly-heated gasifier improves on the traditional gasification methods by eliminating tars in the reaction vessel [10]. Syngas can be converted to electricity and heat either by a fuel cell (solid-oxide type) or a spark-ignited internal combustion engine driving a dynamo. For rural, remote villages, the electricity can be used for education, communication, and light industry, while the heat can be circulated through domiciles to provide smoke-free cooking hearths [11]. When the feedstock moisture content is below 20%, there is a surplus of pure carbon, called biochar, which can be tilled into dirt as a soil augmentation [12]. This approach can reverse desertification around rural villages, and is the only proven method of carbon sequestration [13].

Fig. 3
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Indirectly-heated pyrolytic gasifier (I-HPG) for biomass conversion

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The mineral ash remaining after gasification includes silicates drawn up from the soil by the growing plant. When heated to 1800 C in a reducing atmosphere in the presence of biochar, the oxygen will be scavenged from the \(SiO_{2}\), leaving relatively pure silicon metal [14]. With suitable treatment, this silicon can be used as a solid-state hydrogen storage media, as described in the next subsection [15]. Using a proton-conducting membrane, a stream of pure hydrogen can be extracted from the syngas, while leaving sufficient energy in the remaining gas to self-power the indirectly-heated pyrolytic gasification (I-HPG) system shown in Fig. 3 [16].

2.3 Catalytically-modified porous silicon

Hydrogen can be reversibly stored on the internal surfaces of porous silicon [17, 18] provided there is a catalyst to mediate between gaseous hydrogen (\(H_2\)) and molecular hydrogen [19] that is sorbed onto the silicon surface via spillover [20,21,22]. Figure 4 shows palladium nanoparticles dispersed on a grain of porous silicon, although studies have indicated the potential for transition metals to be sufficient [23].

Fig. 4
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Porous silicon with deposited catalyst clusters (white)

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A hydrogen storage vessel based on catalytically-modified porous silicon can recharge at 8 atmospheres in 3.5 min [24, 25]. Cycles can easily exceed 10,000 with hydrogen of sufficient purity (e.g. 99.9999%) [26], at a very low cost, when made using silicon extracted from, for example, rice husks. Being granular, this storage media can scale from robotic insects to railroad tanker cars. This technology can serve the mobile and portable power needs for when wires are impractical.

3 Scaling up renewable energy

In 2021, renewable sources accounted for 12.9% of global electricity generation [27]. Apologists for the status quo claim that renewable sources cannot scale sufficiently quickly to address the climate crisis. Their counter-arguments favor geoengineering such as iron seeding of the oceans, sulfur oxide aerosols in the upper atmosphere, induced volcanism, or adjustable mirrors in space to modulate insolation. The renewable methods described in the prior section must come with a plan to scale-up in a superlinear, or even exponential, manner.

3.1 Viral rural growth

A village with an I-HPG system can coordinate specializations with nearby villages to form a manufacturing hub that produces more I-HPG units. With low-cost labor and modest shipping costs, these new biomass conversion systems can be provided to villages that may have lacked the resources to get an initial installation. With the benefits of electricity, heat, biochar, and perhaps fuels, this growing population can participate in a larger economy in a sustainable manner. As the second round of villages form their own hubs, the production of I-HPG units can increase geometrically.

3.2 Cheap, earth-abundant silicon

All non-food biomass contains silica \(SiO_2\). Two of the worlds primary grain crops generate silicon-rich residues. Rice harvesting produces 142 million metric tons (MMT) of rice husks, and maize/corn produces 603 MMT of stover each year. Rice husks are approximately 20% silica, and corn stover is about 6%, so the annual potential yield from these two crops is 30 MMT of silicon metal (\(Si)\), which is 3.5 times the current production rate of mined and refined silicon (statista). Although growing plants selectively take up silica, they also incorporate phosphorus and potassium. The mineral ash from I-HPG will need to be acid leached (e.g. acetic) to obtain pure silica, which can then be combined with the pure carbon biochar produced by I-HPG to produce purified silicon [28]. The silica and biochar then become an item of commerce for the villages mentioned above [29]. Eventually, local resources and equipment could produce fungible silicon metal as an even more valuable byproduct, all derived from non-food crop waste.

Silicon produced from agricultural residues can be produced for as little as 0.0037 USD/kg (marginal cost) assuming 40 USD/MT of labor or cost to gather the feedstock. This source could "flood" the global silicon market, and effect a price reduction and capacity increase of photovoltaic-grade silicon for making more solar panels. There will still be ample quantities to also make hydrogen storage material, such as catalytically-modified porous silicon. Processing into hydrogen storage tanks will need to be performed at centralized facilities because of the use of strong acids and the need for anoxic synthesis conditions (Fig. 5). Still, farmers could barter their silicon for hydrogen storage tanks that can then be refilled using hydrogen extracted on-site from the syngas produced by I-HPG.

Fig. 5
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Cost of silicon derived from agricultural residues

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Hydrogen can be used as a fuel in suitably-modified internal combustion engines, of which there are approximately 1.4 billion extant. A cottage industry for such conversions could quickly accelerate adoption of clean-burning hydrogen in motor vehicles. For greater efficiency, hydrogen can be used in fuel cells. Fuel cells suitable for mobile use generally require expensive catalysts such as platinum. As lunar operations expand, the isotope separation technology used for metals extraction can be carried to asteroids, some of which have abundant platinum. Retrieval of platinum group metals from space can eventually help reduce the cost of fuel cells, thereby accelerating their adoption.

3.3 Exponential manufacturing in space

In 2021 the global electricity generation was 28,466 terawatt-hours, 61% of which derived from fossil fuels [27]. Assuming energy storage at 95% efficiency for portable and mobile uses, the required number of SSP powersats delivering 5 gigawatts (GW) of baseload power is 417 units, this being sufficient to replace electricity from coal, oil, and natural gas. The minimum time to establish a lunar base for solar panel production is three years, with three more years needed to produce sufficient photovoltaics, structure, and wiring for a single 5 GW powersat [30]. On-orbit assembly of a single powersat will require about three years [31, 32], largely overlapping with material delivery [33]. Still, as with most other proposed low-carbon solutions, rapid scale-up is a significant challenge if addressed in a linear, sequential fashion. A superior approach is exponential manufacturing, also called self-replicating assembly, in which the original machines first make more of themselves from in situ materials, and then the ensemble converts to build more complex machines. The first powersat delivery is delayed somewhat but subsequent items arrive more rapidly. As each additional unit is produced, it carries a smaller fraction of the cost burden of the infrastructure creation, so that the cost to produce new 5 GW powersats decreases with increased volume. This economy of scale, together with an expected learning curve in technology maturation will rapidly reduce the marginal cost [34].

4 Conclusion

Human civilization on Earth requires a rapid shift to low-carbon sources of energy for cities and factories, for vehicles and electronics, and for the rural food-growing regions of our planet. These can be served by a trio of interconnected technologies, each with the potential for the exponential growth required to avert the worsening of climate-related disasters. Each technology is founded upon existing US patents, plus detailed analysis published in technical venues as reflected in References section. The overall concept of this paper can be viewed as a universal framework that need not rely on these specific technologies. Resistance to these disruptive energy technologies are likely to be raised by those who profit from the existing system [35]. As climate-related impacts become increasingly severe, there will reach a point when the will and finances, talent and cooperation needed to bring this vision to reality will converge. Together, then, we can solve all the world’s energy problems for once and forever.