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Renewable Energy. David ElliottЧитать онлайн книгу.

Renewable Energy - David  Elliott


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plants, it may just be used to compensate for continued fossil fuel use. Carbon capture nevertheless might reduce the associated climate impacts, although there will be limits to the storage space for CO2. As with adaptation, it is not a long-term answer to climate change and the impacts of continued fossil fuel use. Avoiding emissions at source is a more fundamental, effective and sustainable approach (Schumacher 2019a).

      My aim in this book is to ask, how far can the use of renewable energy sources allow us to move in that direction? Can they help us to cut emissions substantially or even entirely, and, if so, when and at what cost?

       To set the scene, this chapter looks in outline at the key renewable options and systems, their potentials, costs and problems. It reviews the basic issues of choice at stake and also looks at how rapidly the options might be deployed.

      The renewable options

      Natural energy flows can be tapped and converted into mechanical power and then electrical energy, as in hydro projects, and by wind-, wave- and tide-driven devices. In addition, there are systems which use natural sources of heat, either directly for heating or indirectly to generate electrical energy, and finally there are devices which convert solar energy directly into electricity, using photovoltaic cells (PV solar).

      I have explored these options in some detail in a recent book (Elliott 2019a), so here I will simply present a brief summary of the state of play. The most developed option so far is hydroelectric power, with around 1.2 terawatts (TW) of capacity installed globally, supplying about 16% of the world’s electricity, producing it relatively cheaply. Indeed, although they are expensive to build, once in place hydro plants often offer some of the lowest-cost electricity on the grid in many countries.

      The same thing may be done with large cross-estuary tidal barrages. Tidal barrages capture a head of water behind a dam at high tide and this (along with any extra head created by pumped storage) can be used to generate electricity, as with hydro plants. Smaller artificial tidal lagoons, impounding areas of open water, are another option, and they too can be run in pumped storage mode. Although both these tidal-power generation systems are technically viable, and two medium-scale (250 MW) barrages have been built, large tidal barrages are expensive and are usually opposed by environmentalists as being too invasive (they block off entire estuaries), while as yet no tidal lagoons are in operation.

      While these new options are still mostly at the development stage, wind power, on- and offshore, has been the big new technology success, with costs falling dramatically and global capacity heading for 600 GW and 1 TW soon (IRENA 2019a). The rate of expansion in many parts of the world is staggering, in China especially but also in parts of the United States and much of Europe. Longer term, 5–10 TW or more may be possible, including increasing amounts offshore.

      It may be a wild card but the wind resource could be dramatically expanded if airborne devices prove to work well and safely. Mounting turbines on autogyro-like flying devices or giant drones, delivering electricity to the ground by cable or using the pull from tethered kites to drive ground-mounted generators is some way off, and there are many issues. However, systems like this, perhaps used in remote offshore areas away from aviation corridors, would give access to the much larger wind resource higher up in the atmosphere (Bown 2019).

      That is all very speculative. For the present, large floating offshore wind devices are the main breakthrough technology, able to operate in deep water far out to sea, where direct seabed-mounted supports would be prohibitively expensive or impossible. Systems are under test in the EU and Asia. Like offshore wind in general, they avoid the land-use and visual intrusion issues that have sometimes constrained onshore wind projects (Equinor 2019).

      Biomass, in its modern usage for electricity production, has faced even tougher land-use and eco-impact constraints, particularly in relation to the impact of the use of forest-derived biomass on carbon balances and carbon sinks: replacement growth can take time. There have also been major concerns over the land-use and eco-impacts of vehicle biofuel production. As I will be describing, views clearly differ on whether biomass can be relied on as a major source of heat, electricity and transport fuel, but, as noted in chapter 1, some look to the use of bio-wastes to avoid the eco-problems and extra land use.

      Direct solar heat use, for example via solar heat collectors on rooftops, or large ground-mounted arrays, has had far fewer problems and is heading for 500 GW (thermal) globally, with, in some cases, large heat stores offering a way to use summer solar heat in the winter, although at a price. Concentrated solar power (CSP) conversion of solar heat to power also has a large potential. It uses sun-tracking mirrors or parabolic focusing dishes or troughs to raise steam or other working vapours to drive a turbine generator. However, CSP has been less successful than PV solar so far, with only around 5.5 GW of CSP in use globally. That is despite the fact that CSP has a heat storage option (using tanks of molten salt), so that the power generators can run at night, enabling the plant to operate 24/7, unlike PV solar. This is a significant advantage, enabling CSP to deliver firm, continuous power, but it comes at a cost and with limits. Unlike non-focused PV, CSP needs direct, as opposed to diffuse, sunlight, so it is mostly used in desert areas and, although arid, deserts do have fragile ecosystems which CSP can disturb.


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