Why A Solar Economy?
Solar and Geothermal Energy are the most direct forms of renewable energy. Other forms, such as biomass, wind or wave energy are ultimately powered by the sun. Since energy flows from the Earth’s interior are just 0.03% of incoming solar radiation, solar energy potential dwarfs all other forms. Studies indicate the total harvestable energy potential of wind is 5 times global energy demand. Solar’s potential is far higher. Indeed, more solar energy is incident on the earth in an hour than humanity consumes in a year.
Another reason to favour solar over wind is its lack of moving parts. Consequently, solar panels last longer than expected (up to 40 years) while wind turbines wear out sooner than expected ( full report here ). While wind turbines are getting bigger and bigger, solar panels remain compact as they get cheaper, more durable and more efficient.
These are sound reasons to believe the future belongs to a solar economy and not wind.
The main aim of renewable energy is to minimize cumulative atmospheric CO2 levels in 30-70 years time. CO2 levels next year, or even in 5 years, are unimportant. Only cumulative CO2 emissions over the next 30 to 70 years matter. If wind power is a dead end technology, we should concentrate economic resources on pushing solar down the learning curve as rapidly as possible. Indeed, even today, some solar projects are producing some of the cheapest energy in the world.
The argument “we need an energy mix” is a false one designed to humour obstinate people obsessed with pet dead-end technologies. We don’t need an energy mix. We just need a solar economy. This is the problems with a blind carbon price. In the long run, solar energy will clearly become the cheapest renewable, but, in order “to be fair”, we pay the same price for all carbon free energy. The result of a blind carbon price, compared to focusing funding on scaling up the solar economy as rapidly as possible, will likely cost hundreds of billions, if not trillions more to reach the exact same cumulative CO2 emissions in 30 years time.
A Solar Economy with Gas: A Winning Combination
Methane can be manufactured from electricity, water and carbon dioxide through the Sabatier reaction. The concept of using gas to store energy generated by renewables is known as Power To Gas. While the cycling efficiency of power to gas (Electricity -> gas -> Electricity) is only about 38%, existing gas infrastructure, like pipelines and LNG shipping, could transmit solar energy across the globe. The factor 2 difference in irradiance between countries with high and low solar energy potential also compensates for the 40% cycling efficiency of power to gas.
We don’t need a giant global HVDC grid. Power to gas enables the existing gas infrastructure to store and transmit solar electricity across the world. HVDC grids can’t store energy. Existing gas networks can store months of gas reserves. Pumped storage, hydroelectric dams and battery banks with cycling efficiencies of 90%+ could complement P2G for short term troughs in solar output – although high cycling efficiency storage is too expensive to store more than a few days worth of consumption.
An inventory of batteries kept in swapping stations for electric cars could serve a dual purpose of absorbing surplus renewable production as well as rapid EV charging.
Electric vehicles may not necessarily require more energy to be transmitted through the grid to cover transportation, as well as household, energy needs. If batteries banks located next to gas plants and solar panel field are charged up there and then physically transported to swapping stations, it might be possible to power a fleet of electric vehicles without upgrading the grid.
Importance of CO2 Sequestration
The Sabatier reaction requires high CO2 concentrations. It is, thus, important to sequester the carbon dioxide produced from burning gas, both to produce methane with solar power and to prevent climate change. If the solar energy is produced in a different location from where the gas is burnt, the CO2 will have to be piped back to the sunny region to be reconverted into methane. Existing gas infrastructure, that already transports large quantities of natural gas around the world, can also transport CO2. In other words, we will need CO2 pipelines as well as methane pipelines.
A solar economy with power to gas storage, will have a much lower CO2 inventory than a scenario without solar. Instead of storing decades, perhaps centuries of CO2 emissions, we need only store months of CO2 emissions, so there is less to fear from a leak in the system, as only a relatively small quantity of CO2 would escape.
Furthermore, concentrated CO2 will have a fundamental economic value to solar power plant operators. This will enable carbon sequestration companies to be profitable irrespective of carbon prices or government policy.
Space Heating
Combined heat and power, is a very favourable option for a solar powered economy with power to gas storage. Especially if burnt CO2 must be compressed and sequestered. During winter months when there is less sun, gas would be imported from warmer climes and burnt for electricity. Heating requirements will tend to be highest when sunshine is lowest.
Heat pumps could supply any further heating requirements. Electricity’s 18% share of total worldwide energy use is intimidating, given renewables currently only produce a fraction of the world’s electricity. However, for space heating at least, we can take solace in knowing that a little electricity goes a long way. A heat pump can transport about 4 joules of ground heat with just 1 joule of electricity. The number of joules of heat 1 joule of electricity can transport is its coefficient of performance. This is typically 3 or 4 for modest temperature differentials between the inside and outside.
Manufacturing
The gas, which power to gas produces, can be used in manufacturing directly. Additionally, the high temperatures produced by concentrated solar power have applications in a wide variety of manufacturing processes.
James May featured a group of scientists using CSP to manufacture gasoline out of water and CO2.
Shipping
The most credible alternative to fossil fuels for shipping are nuclear reactors. Aircraft carriers already use nuclear reactors so this is clearly feasible. Indeed, a nuclear powered merchant ship, the NS Savanah was built back in 1959 and, in 1969, became the first nuclear powered ship to dock in New York City for the festival “Nuclear Week In New York”
Maritime shipping accounts for 2.2% of CO2 emissions. Nuclear energy currently produce 6% of global energy and existing uranium reserves are sufficient for 135 years at our current rate of use. This implies that nuclear energy could power all maritime shipping for 405 years. Plenty of time to develop breeder reactors or beam driven fusion systems (which are more compact and cheaper than fusion systems designed to produce energy) to breed nuclear fuel from fertile materials as well as process long lived waste.
The only other fossil fuel free alternative is biomass but this is land intensive.
Either that or we go back to sailing boats which would require a significant reduction in ship size and speed with correspondingly lower cargo volumes and longer journey times.
Aircraft
The aviation industry is also responsible for 2% of CO2 emissions.
There are five possibilities for reducing aircraft emissions:
- Biofuels
- Replace with Maglev
- Metal Powder
- Radioisotopes
- Beam Powered Propulsion
As with shipping, aircraft cannot sequester CO2. But while biofuels emit CO2, the growth of biofuels absorbs atmospheric CO2. Biofuels, however, do take up a lot of land and there are even some claims that biofuels are not carbon neutral due to their effect on land use.
Alternatively, high speed trains could replace air travel. Maglev trains have reached record speeds of 375mph, two thirds of the cruising speed of an aircraft. Air travel would still be needed over the oceans, but Maglev trains could reduce aircraft biofuel requirements.
Metal powder combustion is another interesting candidate. The energy density of iron powder combustion exceeds that of gasoline so it maybe a credible power source for aircraft. Furthermore, iron oxide is a solid and so is much easier for a compact system like an airplane or a ship to sequester.
Nuclear reactors are not feasible for aircraft as the required neutron shielding is too heavy. However, many radioisotopes decay by emitting alpha or beta particles. This radiation is easily shielded yet very energy dense. Indeed, one intended use of radioisotope is to power pacemakers. One could envisage hot pellets with a radioisotope in the centre and shielding material around the outside. These hot pellets could heat air entering the jet engine to provide CO2-free thrust. However, radioisotopes can’t be turned off and would require constant cooling. One option is to only load hot pellets onto the aircraft just prior to launch and transfer them from the aircraft into a cooling facility immediately after landing. Getting this system to operate reliably to ensure public safety could be quite challenging. A small, beam-background powered fusion reactor could generate the radioisotopes used to manufacture the hot pellets. Fusion reactors could be relatively cheap to construct so long as they don’t need to generate net energy. Solar energy would ultimately power the atoms beams for these fusion systems.
Alternatively, the aircraft could be remotely powered by an energy beam of microwaves or a laser. The main challenge with powering aircrafts is storing the large quantities of energy required to propel them at high speeds without adding too much weight. Remotely beaming energy to the aircraft from a beam generator on the ground would bypass this problem entirely. This would require very high accuracy. Leik Myrabo is currently experimenting with laser power to propel a prototype lightcraft.
Summary
With appropriate infrastructure to store and transmit it, solar power could power our entire industrial economy. Although it currently only provides a miniscule portion of our total energy, solar capacity has exploded since 2010 going up 20 fold in some places. If the 27% annual compound growth can be maintained, solar could power our entire economy in the next 20 or 30 years. Maintaining that ~30% exponential growth will, however, require a strong political will, not just to install solar, but ensure a that suitable infrastructure of power to gas will exist to store the surplus energy.
John
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