2. Why do we need renewables?

‘Why do we need renewables?’ describes the dangers of fossil fuels and explains the importance of renewable energy as an alternative. It shows that the use of fossil fuels causes global warming and climate change, leading to widespread concern, and also to a growing realization of the harm caused by the air pollution from coal burning and from internal combustion engines in cars and lorries. These threats are causing a switch away from fossil fuels to renewables that is gaining impetus from the growing awareness of the increased intensity and frequency of extreme weather seen in recent years. This transition is also being aided by the falling price of clean energy from renewables, in particular, solar and wind farms, which will become the dominant sources. The area of land or sea required for these farms is readily available, as are the back-ups required to handle their variability. Alternative supplies of low-carbon energy are examined. In the Paris Agreement in 2015, it was recognized that carbon dioxide emissions must reach net-zero by 2050 to avoid dangerous climate change.

1. What are renewables?

‘What are renewables?’ defines renewable energy and provides a brief history of its use. It focuses on energy generated by solar, wind, and hydropower. These energy sources are renewable, in the sense that they are naturally replenished within days to decades. Only a few years ago, giving up our reliance on fossil fuels to tackle global warming would have been very difficult, as they are so enmeshed in our society and any alternative was very expensive. Nearly all of the sources of energy up to the 18th century were from renewables, after which time the world increasingly used fossil fuels. They powered the industrial revolution around the globe, and now provide most of our energy. But this dependence is unsustainable, because their use causes global warming, climate change, and pollution. Other than hydropower, which grew steadily during the 20th century and now provides almost a sixth of the world’s electricity demand, renewable energy was a neglected resource for power production for most of this period, being economically uncompetitive. But now, renewables are competitive, particularly through the support of feed-in tariffs and mass production, and governments are starting to pay more attention to clean energy, as the threat of climate change draws closer. Moving away from fossil fuels to renewables to supply both heat and electricity sustainably has become essential.

9. The transition to renewables

‘The transition to renewables’ discusses the need for a large-scale transition to renewable energy. This transition is now urgent. We need to respond to the recent International Panel on Climate Change (IPCC) report on the impacts of 1.5 oC of global warming. This rise in temperature must be the limit to significantly reduce the dangers from extreme weather events and the probability of irreversible damage occurring. For this to be met, emissions must be net-zero by 2050. The transition to predominantly renewable electricity generation, aided by ever improving costs and the increasing role of digital technology, is happening, but not quickly enough. Reducing the consumption and demand for energy are now vitally important, as they will result in a decrease of the rate required for decarbonizing the power supply. Above all, we need to stop burning fossil fuels as quickly as possible, and we need a carbon price. But our reliance on fossil fuels will make the transition to renewables a huge task that governments, states, cities, and individuals must all take on with urgency.

7. Renewable electricity and energy storage

‘Renewable electricity and energy storage’ addresses the transmission of electricity using high voltage alternating or direct current (HVAC or HVDC), the effect of the variability of renewable energy supplies, and the importance of energy storage. Solar and wind farms are now providing an increasing proportion of electricity on many electricity grids. This is changing the requirements on power plants, requiring fast-reacting generators, interconnectors to other grids, demand response, smart grids, and energy storage. There is a cost in accommodating the variability in supply of electricity from wind and solar farms, and surplus supply can lower revenues and give rise to a ‘missing money problem’. Lithium-ion batteries are increasingly important in providing storage for the grid and for electric vehicles. Other storage options are explored, including pumped and compressed air storage, flow batteries, and using electricity to heat or cool water or to generate a combustible fuel (power-to-gas), such as hydrogen, which can be used to provide heat sustainably.

8. Decarbonizing heat and transport

‘Decarbonizing heat and transport’ describes methods for decarbonizing heat and transport. Using renewable electricity directly to produce heat, as in an electric oven, is currently more expensive than burning gas, or other fossil fuels, to generate heat. Capturing the carbon dioxide emissions from existing industrial processes is difficult, and the chapter addresses the challenges of meeting the large heat demand with renewable electricity, particularly for industrial processes that require high temperatures, such as in the manufacture of steel and cement. There, using electricity to produce combustible fuels (power-to-gas), such as hydrogen, could be effective. For heating buildings, electrically driven heat pumps are promising. Transportation also presents challenges. While the performance of electric cars is good, currently the main hurdle to switching is their cost. However, battery costs are falling fast, and new and traditional car manufacturers are already investing a considerable amount of money in developing electric cars. For heavy transport, fuel cells and power from ammonia are being considered.

6. Other low-carbon technologies

‘Other low-carbon technologies’ examines other low-carbon technologies, and sees how they fare against those already discussed in previous chapters. These are the renewables: tidal, wave, and geothermal power; and the low-carbon technologies of nuclear power and carbon capture. The contribution from tidal and wave power is small, with only a few tidal stream and underwater wave devices under development, and that the power from geothermal sources is potentially large, but difficult to extract. The deployment of nuclear power has been affected by concerns over its safety, the disposal of its waste, and its cost. By 2050, the total generation from all renewables and nuclear power could be close to 90 per cent of current global demand. While capture at fossil-fuel power plants looks uncompetitive, air capture through reforestation and through using chemical absorbers might remove 10 per cent of the emissions of carbon dioxide and help the world to be on target to achieve net-zero emissions.

5. Solar photovoltaics

‘Solar photovoltaics’ considers developments in solar technology and their potential contribution to global energy generation. Since the invention of silicon solar cells, it has taken some sixty years for their efficiency to increase to over 20 per cent, and for their cost to fall by several hundred times, to the point where the electricity generated by silicon photovoltaic cells can now be cost competitive with that generated by fossil fuels. It has required considerable development and mass production to achieve this, as the processing of silicon to form a solar cell is complex. Silicon cells now account for about 95 per cent of all solar cells; under development are higher efficiency silicon-perovskite tandem cells. In operation, solar photovoltaic power produces no pollutants, no greenhouse gases, and is a safe way of generating electricity. There are no moving parts, which reduces maintenance, and in Europe, it takes only between one and two and a half years, dependent on location, to generate the same amount of energy as was used in making the solar panels. New generators are increasingly photovoltaic, and distributed generation in residential systems is improving access to electricity across the globe. With massive investment, solar photovoltaics could provide about 40 per cent of the world’s energy demand by 2050.

4. Wind power

‘Wind power’ focuses on wind-based power and its potential as a renewable energy source. Single wind turbines, both large and small, can be used to provide power to homes or a community. Wind turbines for large power generation are usually deployed in wind farms, which are arrays of turbines. These are located in regions where the wind conditions are good, such as exposed ridges, high-altitude plains, mountain passes, coastal areas, and out at sea. Wind power produces essentially no global warming nor any pollution; only a small amount of associated carbon dioxide emissions from the fossil fuels used in the construction and operation of the wind farms. And it takes less than a year for a wind farm to generate the same amount of energy used in its manufacture. The sharp fall in the cost of electricity from wind farms, corresponding to a 20 per cent learning rate over the last decade, is such that onshore wind farms have now achieved cost competitiveness (grid-parity) with fossil-fuel-fired generators. By 2050, it is estimated that about a seventh of the world’s energy demand could be met by wind power.

3. Biomass, solar heat, and hydropower

‘Biomass, solar heat, and hydropower’ discusses three forms of renewable energy: biomass, solar heat, and hydropower. Biomass and biofuels provide energy via heat generation and food consumption. But with the rising global population, land resources are being drastically depleted, and using biomass for energy can clash with growing plants for food, and cause serious home air pollution. Solar heating for homes and industry is facing competition from electrically driven systems, but the chapter shows that the outlook for concentrated solar power is encouraging, as its cost is falling, and the availability of supply after sunset offered by concentrated solar power plants with thermal storage can be a significant advantage over solar photovoltaic farms. In a hydropower plant, the energy in water falling from a height is converted to electrical energy using a turbine. Although hydropower plants can provide large amounts of low-cost, low-carbon electricity, and provide useful energy storage through pumped storage plants, serious social and environmental issues need to be considered when deciding whether the construction of a new hydroelectric scheme is appropriate.