RESEARCH PAPER SERIES, 2020-21   20 JuLY 2020

Australian electricity options: photovoltaics

Professor Andrew Blakers and Dr Matthew Stocks
Australian National University

1 Executive summary

• Solar energy supply is dilute, but vast, widespread and indefinitely sustainable. Its utilisation for electricity generation typically has minimal environmental, social and security impacts over unlimited time scales. Photovoltaics (PV) are currently the leading energy generation technology in terms of annual net global deployment rates. Intermittency of supply can be offset by energy storage systems such as Pumped Hydro Energy Storage systems and strengthening the connectivity of the grid.

Australian electricity options are short briefings on the principal energy sources and storage options being debated in Australia, including: coal, natural gas, wind, nuclear, photovoltaics (PV) and pumped hydro energy storage (PHES).

The global COVID-19 pandemic and its economic consequences mean that statements and projections about future demand and pricing of energy options may no longer be reliable. Readers should note that some figures quoted in these briefings may pre-date the pandemic.

Photovoltaic technology

PV is an elegant technology for the direct production of electricity from sunlight without moving parts. Sunlight is absorbed by the solar cell and the solar power is converted to electrical power with a typical conversion efficiency of around 20% (the remaining solar power (80%) is either reflected or becomes heat and is discarded). This process of conversion is called photovoltaics (photo=light, voltaics=voltage).

A solar cell is typically made from a square wafer of silicon (156 millimetres square and about one-sixth of a millimetre thick). Sunshine absorbed by the silicon detaches electrons from their host silicon atoms. Near the sunward surface is a ‘one-way membrane’ called a pn-junction. The pn-junction is formed by diffusing tiny quantities of phosphorus into the wafer to a depth of about one micrometre. When a free electron crosses this junction it cannot easily return, causing a negative voltage to appear on the sunward surface (and a positive voltage on the rear surface). Metal electrodes are printed on both surfaces of the solar cell. The sunward and rear electrodes are connected via an external circuit to extract current, voltage and power from the solar cell.

Solar cells are packaged into a solar module, also known as a PV panel, to protect them from the environment. Modules typically comprise 60-72 silicon solar cells contained within transparent plastic behind thick glass to form a durable PV module. The package usually includes aluminium edge-frames to help with module mounting in the field or on a rooftop. A junction box is added to the rear to house the electrical terminals.

This package is extremely reliable with PV modules now warranted for up to 30 years. PV modules have high reliability and low maintenance cost due to the lack of moving parts. Deterioration of PV modules can be caused by physical destruction caused by human action or violent hailstorms, slow chemical changes leading to yellowing of transparent encapsulation materials and ingress of moisture causing corrosion of metallic components.

A 20% efficient PV module will yield 200 watts of power per square metre of module at noon on a sunny day. On a sunny day where the amount of solar energy received is equivalent to 5 hours of noon-equivalent sunshine, the module would produce 1000 watt-hours of energy per square metre, which is one kilowatt-hour (kWh) per square metre.

Electricity produced in the PV module is conducted to a power conditioning unit that optimises voltages, converts the direct current produced by the solar cells to the alternating current used in electrical grids, transforms the voltage to match that of the local grid, and manages interfacing with the local grid.

Most (95%) of the world’s PV market is serviced by crystalline silicon solar cells. This is because silicon has important advantages over other potential PV materials, including abundance (silicon is the second most abundant element in the Earth’s crust), low cost, non-toxicity, high efficiency, device performance stability, the highly advanced state of knowledge of silicon material and technology, and the advantages of incumbency. The latter comprises extensive and sophisticated supply chains, large-scale investment in mass production facilities, deep understanding of silicon PV technology and markets, and the presence of thousands of highly trained silicon specialists—scientists, engineers and technicians.

Despite producing zero-emission electricity, photovoltaics can create some relatively small environmental impacts in their broader lifecycle, including during the extraction of some mineral inputs, their manufacture, and at end-of-life. The International Renewable Energy Agency has projected that PV panels could account for 78 million tonnes of annual waste by 2050 and has looked at opportunities for recycling or repurposing these products. This is far less than the waste associated with fossil and nuclear energy.

Figure 1: Royalla 20 MW solar farm near Canberra showing thousands of PV modules mounted on support frames. The aluminium frame surrounding each module can also be seen, as well as the 72 cells packed into each module.

Source: A. Blakers

PV systems

Large numbers of PV modules can be used to create PV systems. Some PV systems are mounted on fixed support structures that are tilted up to face the equator, with a tilt equal to the angle of latitude. Increasingly, large scale PV systems use sun-trackers to maximise annual output.

Alternatively, PV systems can be mounted on the roofs of houses and commercial buildings. A typical ground-mounted PV system has a peak power output of 100–1,000 Megawatts (MW). A typical new domestic PV system has a power capacity of 5–10 kilowatts (kW), while a commercial building might host a multi-Megawatt system.

Australia has the highest uptake of rooftop solar in the world. By mid-2019, there were more than two million PV systems registered with the Clean Energy Regulator in Australia with a combined capacity of more than 9,000 MW.

PV is unusual in that the unit cost of energy is similar for large (MW) and small (kW) systems—large systems have lower capital costs but higher financing costs and vice versa. Virtually all other energy sources have strong diseconomies of scale with small size. This confers a major advantage on PV, since it has markets at every scale from watts to gigawatts for the same basic product—the silicon solar cell.

The versatility of PV has contributed to its history of sustained growth. The average annual growth rate over the past 25 years has been 37% per year. PV has now emerged as the world’s fastest growing generation technology in terms of annual net new generation capacity, as shown in Figure 2. PV is approaching half of net new generation capacity installed each year, with coal, oil, gas, nuclear, wind, hydro and other renewables providing the balance. The fundamental reason is low and falling PV prices.

Figure 2: New global generation capacity added in 2015-2019 by technology type. PV is growing rapidly whilst the other generation technologies have negligible growth in annual net new deployment.

Source: REN21 2015, UNEP 2014, IRENA 2016

In earlier decades, PV found widespread use in niche markets such as consumer electronics, remote area power supplies and satellites. Throughout the world, remote area energy solutions are based upon various combinations of PV, wind, diesel and batteries. In recent decades the industry has expanded and costs have declined very rapidly.

PV module prices have been falling rapidly for decades. This is caused by steadily improving technology and the benefits of mass production. The PV learning curve illustrates the module price reduction achieved for each doubling of global cumulative production. All learning curves eventually flatten out as the technology matures and reaches the bottom of its cost curve. However, it is clear that PV is far from reaching the bottom of its price curve. The cost of silicon PV modules is likely to continue to decline for many more years.

The US investment bank Lazard has published a report showing current global PV costs can be as low as US$36/MWh, depending upon the scale of the installation, solar intensity, financial parameters and local factors. This is lower than competing new-build fossil, nuclear and renewable technologies in most parts of the world, and prices continue to fall.

Australia is experiencing a remarkable renewable energy transition. Over the three years 2018-20, about 17 Gigawatts (GW) of new wind and solar PV electricity generation systems are being completed, most of it in the National Electricity Market (NEM). For perspective, the average and peak electricity generation in the NEM is about 23 and 35 GW respectively. This 17 GW equates to 200-250 Watts of new renewable energy per person per year compared with about 50 Watts per person per year for the European Union (EU), Japan, China and the USA (see Figure 3).

Figure 3: Annual per capita renewables deployment rate for countries and regions.

Sources: Data for Australia (2018 and 2019) is from the Clean Energy Regulator and data for other countries/regions (2018) is from IRENA.

Curtailment of global greenhouse gas emissions

Use of coal, oil and gas for energy generation causes about 80% of greenhouse gas emissions, with agriculture contributing most of the rest. To curtail global warming, fossil fuel use needs to be replaced. PV is the leading contender for such replacement in electricity generation because of the following attributes:

• The solar resource is very large and ubiquitous. Sunlight will be available for billions of years to come. Most of the world’s population lives at low latitudes (less than 35°), where sunlight is abundant and varies little between seasons. A large proportion of PV systems are installed on rooftops and in arid regions, thus minimising competition with food production and ecosystems.

• PV has minimal greenhouse gas emissions and other environmental impacts and does not need water to operate.

• PV utilises abundant raw materials effectively in unlimited supply—silicon, oxygen, hydrogen, carbon, aluminium, glass, steel and small amounts of other common materials.

• There are minimal security concerns in respect of warfare, terrorism and accidents. More widely distributed PV generation across the world could reduce the risk of wide-scale electricity generation infrastructure disruption from natural disasters, war and terrorism.

• PV is already low cost and in mass production.

• Wind energy is an important adjunct to PV. However, other clean energy technologies can realistically play only a minor supporting role. Solar thermal and nuclear generators are being deployed at far smaller rates than the fast-growing PV industry (because of higher costs), and extravagant growth rates would be required to achieve the same new capacity installation rates as PV. Hydro power, geothermal, wave and tidal energy are only significant prospects in some regions, and biomass has very low solar conversion efficiency which means that severe conflict will arise with food production and ecosystems for land and water if used on a large scale.

Issues with PV

The first is the intermittency of supply—electricity isn’t generated when the sun isn’t shining, either at night or in bad weather, with the associated challenge of matching the generated PV power to meet energy demand where the two do not coincide. There are three main solutions to the ‘intermittency problem’: rapidly dispatchable power from energy storage systems such as pumped hydro (see separate article); power from systems that can rapidly come online such as gas powered turbines, or creating a more interconnected grid that has the flexibility to balance supply and demand from a wider area by smoothing out localised weather events. Sufficient storage or other generation technologies are required to meet electricity demand at night.

Second, there is a need to maintain frequency stability in the grid in the face of significant changes to production and demand, which is generally done by the heavy rotating machinery of base-load power stations. This frequency stabilisation can be performed by other paired technologies that can respond to fluctuations within seconds, such as large batteries (as the Tesla battery has done at Hornsdale in South Australia), by hydroelectric systems or even hydrogen electrolysis generators.

Emerging technologies

Silicon solar cells are by far the largest generation technology in terms of annual net global capacity additions. A promising development in PV is perovskites in solar cells instead of, or as well as, silicon. Perovskite refers to a class of lab-grown, crystalline materials that mimic the structure of the naturally occurring mineral perovskite. They could be relatively cheap, are highly efficient at converting sunlight to electricity, can be used in a thin-film format and offer other potential benefits. However, there are serious concerns about performance stability, and they are not yet in commercial production.

References and further reading

A Blakers, B Lu and M Stocks, ’100% renewable electricity in Australia’, Energy, Volume 133, pp. 471-482, August 2017.

Clean Energy Council, Clean Energy Australia report 2020.

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