Marx, Musk and Moore
Not many will associate Karl Marx with energy but a close reading of his
‘Capital: A Critique of Political Economy’ which was first published in 1867 shows that Marx understood energy better than many do today. He observed that the energy sources powering industrialisation had to be ‘dependable, urban and completely under the control of man’. Dismissing the ‘horse’ as the worst form of energy he observed that the horse had a head of its own, was costly to maintain and was limited in factory applications. He also dismissed wind because it was ‘
inconsistent and uncontrollable’. He had more charitable views on the kinetic energy of flowing water but he noted that ‘it could not be controlled at will, failed at certain seasons and was essentially local’.
Marx’s vote was for coal (with water in the steam turbine of Watt) which he said was ‘
entirely under the control of man, mobile and a means of locomotion, and also urban unlike wind and water that were scattered up and down the countryside’. Marx did not dwell on the nature of energy but his observations on characteristics of energy such as ‘certainty’ ‘mobility’ and ‘controllability’ that would make certain sources of energy indispensable for industrialisation were accurate. Energy sources now have to be clean and green apart from being urban, mobile and completely under the control of man. The pursuit of ‘clean and green’ values in energy sources has taken us back to wind and sun that were dismissed by Marx as ‘uncontrollable and undependable’.
Powerwall battery system developed by Elon Musk’s Tesla is expected to overcome the ‘undependable and uncontrollable’ characterises of wind and solar power and ‘fundamentally change the way the world uses energy’ as Musk put it at the
launch of Powerwall in January 2015. Solar energy is already urban (as opposed to being scattered up and down the countryside) because photovoltaic panels can convert sunlight into electricity from urban roof tops. The hope is that Musk’s lithium-ion battery (LIB) will take care of not just the ‘uncertain and uncontrollable’ nature of solar energy but also make it mobile. Uncertain solar energy will be stored in Musk’s efficient batteries and allow people to draw energy whenever they want for whatever they want to do (use electrical appliances or move around in a vehicle) even when the sun is not shining.
Gordon Moore, co-founder of Intel famously said in 1965 that the circuit density of semiconductors (made of high-grade silicon) will
double every eighteen months. Moore’s law as it has come to be known has proved to be true in the micro chip industry. The number of transistors on a circuit has doubled almost every two years and the cost has fallen dramatically. If Moore’s law holds for PV (photovoltaic) panels (made from solar-grade silicon) and storage batteries that dependable and controllable electricity from these systems will be cheaper than grid-based electricity (derived from fossil fuels) in a matter of few years.
Efficiency gains in solar modules
PV modules and the inverters required to convert the DC power output from PV systems to AC power are commodity products that are traded internationally. The cost of PV modules has fallen from about
US$105/watt (w) in 1975 to about US$D 0.20/watt in 2020 which is over 12 percent annual average fall over the 45-year period. This is impressive but nowhere near a Moore-scale decline. Most of the cost declines are traced to
lower input material cost (solar grade silicon), increased the scale of production (economies of scale), lower labour costs through manufacturing automation and lower waste from efficient processing. In other words, the cost declines of PV modules are the result of
production experience and not changes in fundamental physics that is required for Moore’s law to work.
In the last fifty years, the power of a given-sized microchip has increased by a
factor of over a billion but the power output of a solar panel has merely doubled. This is not because of insufficient investment in research and development of solar technology. The United States poured money into solar technology in the late 1940s when
domestic reserves of oil began to decline. It increased support for research on alternative energy technologies after the
oil crises of the 1970s. Though the enthusiasm for alternative energy sources generally waned when oil prices fell, ideas such as peak oil,
the oil weapon (in the hands of oil producers) etc have kept up the support for alternative energy sources. Despite this, solar has not managed to make a breakthrough on the scale of microchips because of fundamental technical limitations of crystalline silicon.
In pure materials, electrons can only reside in certain discrete
energy bands. The electronic properties of materials are dependent on the profile of these energy bands and gaps between these energy bands. In semiconductors such as crystalline silicon, the band gap is somewhere between the high band gap of insulators (materials that do not conduct electricity) and
overlapping bands of conductors (materials that conduct electricity). To be precise, the band gap of semiconductors such as silicon is too large for it to
conduct electricity (allow movement of electrons from one band to another) in their normal state (in the absence of additional energy in the form of light/heat) but small enough for it to conduct electricity when additional energy from sunlight is available for absorption. A solar cell can only
absorb photons (light) with an energy gap greater than the band gap. The band gap energy is the maximum energy that can be extracted as electrical energy from each photon that is absorbed by the solar cell. One fundamental limitation
of crystalline silicon is its indirect band gap (which involves a change in energy and a change in momentum) which leads to weak light absorption and consequently makes thick wafers a necessity. This translates into higher capital costs, low power-to-weight ratios and constraints on module flexibility and design.
Alternatives to silicon wafers such as
gallium arsenide, a compound with a direct band the gap (only involves a change in energy) are being investigated but those in the field do not see commercially viable alternatives to silicon emerging within the next decade. Thin film PV technologies that are made by additive fabrication process reduce material usage and capital expenditure
accounting for 10 percent of global PV production capacity. Commercial thin films use hydrogenated amorphous silicon (non-crystalline silicon), cadmium telluride and
copper indium gallium Diselenide. These materials absorb light 10-100 times more efficiently than silicon. This property reduces the thickness of material required for light absorption to just a layer of film coated on a support material such as glass. Cadmium telluride is the leading thin PV technology on account of its ability to harvest solar energy with a direct band gap of
1.45 electron volt (eV) compared to the indirect band gap of 1.12 eV for crystalline silicon. Thin film PV technologies use
10 to 1000 times less material than crystalline silicon, reducing cell weight per unit area and increasing power output per unit weight.
Perovskite solar cells are thin-film devices that have demonstrated higher efficiencies with potential for further improvement, but their stability is limited compared to leading PV technologies. A key disadvantage of commercial thin-film technologies is their
low average efficiency compared to crystalline silicon. Another key problem with thin film technologies is that they often require scarce elements that cannot be replaced easily. This puts a limit on scaling up solar capacity that is dependent on thin films. Irrespective of which material is used, improvements in the efficiency of industrial processes are likely to bring down costs significantly in the future.
Efficiency Gains in Storage Technologies
Variability and imperfect predictability of solar PV systems, qualities that allowed energy sources such as wind and water to be displaced by coal-based steam generation during the first industrial revolution is a challenge that battery storage is expected to address. The higher energy density and specific energy of
Lithium-ion batteries (LIBs) have allowed the technology to replace nickel cadmium and nickel metal hydride batteries in grid storage applications. LIBs can maintain cell voltage levels approximately
3 times greater than alternatives.
Coulombic efficiency (faradaic efficiency or current efficiency), the ratio of the total charge extracted from the battery to the total charge put into the battery over a full cycle which measures the efficiency of batteries is highest for LIBs among rechargeable batteries. It offers an efficiency that exceeds
99 percent when charged at a moderate current and at cool temperatures. Most improvements in the efficiency of LIBs can be traced to engineering gains in active material capacity and cell or electrode optimization. These improvements have slowed in recent years, posing a significant challenge for battery storage. The cost can increase
two to four times when LIB cells are assembled into battery packs along with an increase in safety risks. If the industry manages to achieve
US$200/kWh (kilowatt hour) battery cost, then US$200 trillion worth of batteries (10 times US GDP in 2020) can only provide 2 weeks’ worth of storage, which is not sufficient to heat homes in the winter. In 2022, the levelized cost of storage (LCOS) in Musk’s Powerwall was put at
US$0.30/kWh which at current exchange rates is over INR 24/kWh. This is nowhere close to the tariff of grid-based electricity but the hope is that the cost of power from solar panels and batteries will decline rapidly and out-compete grid-based electricity.
Fire safety and
recycling of batteries are emerging challenges that require greater attention. Besides safety and economic concerns, the mineral intensity of producing solar panels and LIBs creates a tough problem for climate strategies. Mineral mining, solar panel and LIB production produce
substantial amounts of CO2, and are discarded in landfills or oceans upon retirement, generating large amounts of waste plastic and heavy metals that pose serious threats to the environment.
Like Marx’s ‘horse’, solar energy continues to have a head of its own, is costly to maintain and limited in applications even when saddled with battery storage. As there are doubts over making solar energy consistent and controllable, policy effort is also being devoted to making consumers consistent and controllable through incentives and penalties (price) for using energy at the right and wrong times. Likewise, if expected cost declines in solar PV plus battery storage do not materialise, the price for carbon or a tax on carbon will make fossil-fuel derived energy more expensive which in turn will make solar plus battery relatively inexpensive. Either way, life as we know it will come to an end.
Source: International Energy Agency
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