For more than 200 years, modern society has been built on the back of cheap energy taken from the ground. That energy has been used to deliver improved life expectancy, better health care, personal mobility, intellectual opportunity, universal access to information and egalitarianism. In the meantime, and perhaps because of it, we have become dependent on motor vehicles and round-the-clock electricity.
It took the Earth millions of years to develop those stores of high energy density fossil fuels (coal, oil and gas). In the last 150 years, big holes have been made in those fuel stores. For oil, at least, production may soon peak and start to fall. Gas may be in short supply this century and, eventually, coal will meet the same fate. All this at a time of growing energy demand from countries like China and India.
As if this were not concern enough, we are now told that these high carbon fuels are damaging the atmosphere and warming the planet and we need to quickly replace them with other forms of energy. Further, to avoid the same problem happening again, we need these energy sources to be low-carbon and sustainable. This is a Herculean task. We are trying to do in a few decades what the earth took millions of years to do.
All energy sources come from the sun, directly or indirectly. Before man started digging huge quantities of coal out of the ground, energy use was largely sustainable. Populations were much smaller and people burned wood and peat for heating and cooking and there was no mass production. There was some mechanisation in the form of windmills and water wheels and animals or humans to pull ploughs and carts but all these devices sourced their energy indirectly from the sun.
Renewables - wind, moving water, geothermal hot water, solar heating and biomass (burning woody material) - have been sources of energy for millennia. Now we need to leave our fossil fuels behind and go back to renewable energy - from renewables to renewables in 15 generations.
Motor vehicles provide challenges when it comes to sustainable energy. Biofuels (like ethanol and biodiesel) made from plants, are renewable energy that can power motor vehicles. Currently, biofuels provide 1 per cent of all transport fuels and use 1 per cent of all the available arable land worldwide. Even at this relatively low level, they are already blamed for food shortages and are generally recognised as not sustainable.
Hydrogen is another renewable energy that can be used in vehicles but it must be made from low-carbon electricity if it is to reduce greenhouse gas emissions.
A third alternative is electric cars. Whether the vehicles are powered by hydrogen from electricity or electricity directly, replacing oil for transport will significantly increase the demand for electricity. The average family with two cars recharged at home will increase their electricity use by 50 per cent.
Renewable electricity is key to a sustainable energy future. Innovations have proceeded over the last 150 years. In the 19th century, electricity was generated from wind and moving water (hydropower). Electricity from natural geothermal steam was first generated in the early 20th century. In the early 1950s, the photovoltaic (PV) solar cell was developed to generate electricity directly from sun light. Engineered geothermal systems (EGS), sometimes called hot dry rocks, were developed in the 1970s and electricity from concentrated solar power (CSP) using solar thermal energy began commercial generation in the 1980s. Electrical energy has also been harnessed from tides.
These renewable energy sources all have natural cycles varying from decades (geothermal) to seasons (hydropower, biomass) to daily (wind, solar thermal) to hours and minutes (wind, solar PV). Some of these cycles are more predictable than others. We can have a reasonable level of confidence when a dam will have sufficient water to produce hydroelectricity but we cannot be so confident about when the wind will be blowing. This variability makes them less than ideal for every day, round-the-clock electricity supply. The Earth’s fossil fuels provide a huge store of energy that is continuously available and, apart from the occasional power plant breakdown, we can be confident about the amount of electricity we can generate at any one time. Until the fuel runs out of course.
Electricity cannot easily be stored in large quantities. This means it has to be generated at the same time as it’s used. Mass production has led to 24 hours a day factories that demand large quantities of electricity continuously. We want to turn on the lights or watch TV anytime of day or night. This means that the electricity supply companies have to generate electricity at a certain level, 24 hours a day. In Australia, the minimum supply needed round-the-clock (sometimes referred to as baseload) is about two thirds of the total electricity demand.
How are we to supply this round-the-clock demand using renewable sources that have natural cycles that, in most cases, preclude continuous supply?
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