Hydroelectricity, wind, biomass and waste biogas, and solar photovoltaics (solar PV) account for more than 90 percent of the electricity generated by renewables. These technologies are maturing, and will dominate renewable energy electricity generation for the foreseeable future.
Hydroelectricity accounts for nearly 70 percent of the world’s renewable energy electricity supply, with more than 150 countries producing hydroelectricity. China, Canada, Brazil, the USA, Russia, India, Norway, and Japan are the leading hydroelectricity producers.[i] Hydroelectricity typically provides bulk power for supplying base load grid electricity (i.e., supplying the minimum level of grid electricity demand), and offers 24/7 flexibility in its supply.[ii]
On a smaller scale, run-of-the-river hydroelectric systems are also used to generate electricity. These systems capture the kinetic energy in rivers without the use of river blocking dams or reservoirs. Small hydroelectric projects (<10 megawatts) and micro-hydroelectric projects (10–100s kilowatts)[iii] are used for supplying electricity to small industries and communities.[iv]
Small-scale hydropower lends itself well to countries rich in river water resources, while avoiding significant environmental damage associated with new river-blocking hydroelectricity dams. Hydroelectricity generation on this scale can be paired in a complimentary way with other renewable energy sources (wind, solar PV, biomass, etc.) to achieve off-grid or decentralized energy supply.
Wind power has grown over the last two decades to supply more than half of non-hydroelectric renewable energy,[v] and nearly one hundred countries use wind power.[vi] Wind turbine technology has advanced significantly, making wind power competitive for grid electricity supply.[vii]
A modern wind power plant can have up to 200 turbines, each with three-megawatt output, with rotor diameters exceeding 100 meters. Such wind plants are comparable in capacity to conventional power plants.[viii]
Wind power innovation has centered on taller towers, longer blades, and the use of advanced, lighter construction materials, as well as the use of intelligent communications and remote wind sensing. This all helps to increase the energy output and improves its utility in lower wind conditions, enabling wind turbines to be installed on all continents and coastlines.[ix]
Offshore wind permits the use of larger wind turbines and blades compared with land turbines because large ships can be used to install them. Offshore locations provide greater and more constant wind speeds,[x] making offshore wind useful for supplying coastal cities with decentralized electricity supply.
Solar PV converts sunlight into electricity through the photoelectric effect using silicon semiconductors.[xi] In 2016, solar PV accounted for one-sixth of the global supply of non-hydroelectric renewable electricity.[xii]
Solar PV is already an economically attractive option for all scales of market use. Enhanced integration systems and weather forecasting will help make solar PV more competitive with large-scale grid suppliers.[xiii] Solar PV is also the most important renewable energy technology for home use (see Chapter 12).
The other important large-scale solar technology is concentrating solar power. This technology offers utility company-scale supply, with heat storage capability that allows electricity supply to be extended beyond sunlight hours.[xiv]
Geothermal energy taps reservoirs of steam or hot water from beneath the earth’s surface to generate electricity.[xv] Geothermal power plants can operate 24/7, and are used to provide base load electricity,[xvi] as well as grid balancing of electricity supply when large quantities of renewable energy are integrated into the grid.[xvii] The US, the Philippines, Indonesia, New Zealand, Mexico, Italy, and Iceland are world leaders in geothermal energy supply.[xviii]
Geothermal, or ground source, heat pumps utilize the outer crust of the earth as a heat source for heat exchange.[xix] This type of renewable energy system represents a major source of renewable energy capacity for heating and cooling buildings. A heat pump and ground-coupled heat exchanger are used to move heat energy into the earth (cooling by day) and out of the earth (warming by night). These heat exchange systems are a key component of energy efficient homes, buildings, and greenhouse designs (see Chapter 12),[xx] providing free sustainable heat and cooling once the energy system is installed.
Biogas recovery is a proven technology and potentially a large source of renewable energy. Biogas recovery from biomass waste is a process widely used in food processing, the processing of farm and municipal wastewater, and also for processing agroforestry residues.[xxi],[xxii],[xxiii] Biogas is generated from biomass using anaerobic digestion processes. It is then converted into electricity, heat, and transport fuels.[xxiv],[xxv] The European Union is a market leader in biogas generation, with biogas already contributing about one-twelfth of the EU’s renewable energy supply.[xxvi]
Global agriculture and the food distribution system waste more than one-third of the food that is produced. This waste offers the opportunity for biogas production on the farm, or via larger-scale farming cooperative or commercial ventures.[xxvii] Agriculture also generates massive quantities of biomass, such as forestry byproducts and crop residues, offering farmers a source of renewable energy to offset their energy needs or to provide an additional revenue stream.[xxviii],[xxix],[xxx],[xxxi] Biomass recovery from food distribution hubs and retailers, and city-generated biomass and municipal waste, are sources of plentiful (and renewable) biomass waste for the production of biogas.[xxxii],[xxxiii],[xxxiv],[xxxv],[xxxvi],[xxxvii],[xxxviii]
Without technology, fossil fuels, and renewable energy, how will humans keep warm and cook? Yes, that’s right, the same way they did for tens of thousands of years: with firewood and fire.
Planting trees today makes good sense for future generations, who will need the wood for fuel[xxxix],[xl],[xli],[xlii],[xliii],[xliv] when oil and gas have run out or are being withheld by governments and corporate entities during a global energy or climate crisis.
The electricity grid refers to a network of overhead and underground transmission lines, substations, and transformers that deliver electricity from a network of power plants to homes and industries.[xlv],[xlvi] In many countries, the existing transmission and distribution infrastructure for electricity is aging and being stretched to its limits, necessitating the upgrading of national and regional electricity grids.[xlvii],[xlviii]
Without upgrading the existing electricity grids and switching to two-way electricity metering, renewable energy will not meet its potential for switching the world’s energy system, or permit the decentralized supply of electricity.[xlix],[l]
Integration of more than one-third of renewable energy supply into an electric grid at any one time is achievable with most grid systems and with advanced management methods. To accommodate a large-scale renewable energy switch, transmission and distribution networks will need to handle a much larger supply of renewable energy from a larger network of suppliers, and spread over a much wider geographical area than traditional bulk electricity suppliers.[li],[lii]
Smart grids are part of the solution to the above quite complex challenge. Smart grids manage the direct interaction and communication between energy consumers and suppliers, and enable the integration of vast amounts of renewable energy into the electricity grid. These smart grids provide a more resilient and flexible grid supply, and are able to accommodate a large number of suppliers and consumers. Smart grids will be integral to a future renewable energy power system.[liii],[liv],[lv]
Storing energy at times of low prices provides additional grid flexibility to cope with peak electricity demand, or for use in emergency situations.[lvi],[lvii] The ability to store half a day of energy is considered the sweet spot for large-scale grid suppliers.
Pumped-storage hydropower involves pumping water uphill into reservoirs at times of low price and low electricity demand, and then when the demand and price are higher the energy is “harvested.” Pumped-storage hydropower offers large-scale, low-tech grid storage of energy, which helps to make electric grids more resilient.[lviii] Battery storage of energy at a gigawatt-scale will also be possible in the future,[lix] and will further enable smart grids by helping ensure the resilience of the electricity supply when grid supply is unable to meet demand.[lx],[lxi],[lxii]
High voltage direct current (HVDC) transmission systems are used for transporting bulk electricity over long distances from power plants to local substations or large consumers and markets,[lxiii],[lxiv] including transit of bulk electricity underwater.[lxv] These HVDC transmission systems are an enabler of smart grids and regional super-grids and represent the best solution for long distance transmission of bulk renewable energy.
As the switch to renewable energy accelerates, supply agreements and transmission links, operating to harmonized standards, will be needed in all parts of the world. This will permit regional networks of interconnected countries with complementary renewable resources to transmit electricity to distant markets and across different time zones. These collective arrangements will also permit the pooling of electricity resources to improve the resilience of electricity supply across multiple countries, when electricity supply in one country is unable to meet market demands.
These regional electricity grids are referred to as wide area synchronous grids or super-grids,[lxvi] and already operate in regions like the EU,[lxvii] North America,[lxviii] Russia, China, other parts of Asia, and North Africa.
Decentralized energy, or distributed energy, is generated at or near the point of use, and is connected to a local smart grid. Decentralized energy supply using renewable sources is also readily scalable.[lxix],[lxx],[lxxi],[lxxii] This type of decentralized electricity supply represents the best energy supply strategy for homes and urban areas, for mitigating the risks of a tightening global energy supply, and in an international energy or climate crisis.
[i] Data: US Energy Information Administration: World electricity generation data by category and country were obtained from the International Energy Statistics data portal. https://bit.ly/2J8TJ0t.
[ii] US Department of Energy. Office of Energy Efficiency & Renewable Energy. Hydropower Vision. A New Chapter for America’s. Renewable Electricity Source. https://www.energy.gov/sites/prod/files/2018/02/f49/Hydropower-Vision-021518.pdf.
[iii] Microhydropower Systems. https://www.energy.gov/energysaver/buying-and-making-electricity/microhydropower-systems.
[iv] Run of River Power. http://www.energybc.ca/runofriver.html.
[v] U.S. Energy Information Administration. International Energy Statistics. Generation of Electricity Billion Kwh. https://bit.ly/2JtfawJ. Last Accessed June 01 2018.
[vi] US Energy Information Administration: World electricity generation data by category and country were obtained from the International Energy Statistics data portal. https://bit.ly/2J8TJ0t.
[vii] Camila Stark et al., “Renewable Electricity: Insights for the Coming Decade.” Joint Institute for Strategic Energy Analysis. Technical Report NREL/TP-6A50-63604. February 2015.
[viii] Camila Stark et al., “Renewable Electricity: Insights for the Coming Decade.” Joint Institute for Strategic Energy Analysis. Technical Report NREL/TP-6A50-63604. February 2015.
[ix] Camila Stark et al., “Renewable Electricity: Insights for the Coming Decade.” Joint Institute for Strategic Energy Analysis. Technical Report NREL/TP-6A50-63604. February 2015.
[x] Camila Stark et al., “Renewable Electricity: Insights for the Coming Decade.” Joint Institute for Strategic Energy Analysis. Technical Report NREL/TP-6A50-63604. February 2015.
[xi] US Department of energy. Solar Energy Technologies Office. Photovoltaics. Photovoltaics fact sheet. https://www.energy.gov/sites/prod/files/2016/02/f29/PV%20Fact%20Sheet-508web.pdf.
[xii] US Energy Information Administration: World electricity generation data by category and country were obtained from the International Energy Statistics data portal. https://bit.ly/2J8TJ0t.
[xiii] Camila Stark et al., “Renewable Electricity: Insights for the Coming Decade.” Joint Institute for Strategic Energy Analysis. Technical Report NREL/TP-6A50-63604. February 2015.
[xiv] U.S. Department of Energy Solar Energy Technologies Office. Concentrating Solar Power. https://www.energy.gov/eere/solar/concentrating-solar-power.
[xv] Geothermal energy and Engineered Geothermal System. https://setis.ec.europa.eu/technologies/geothermal-energy.
[xvi] EGEC Geothermal. The Voice of Geothermal in Europe. https://www.egec.org/about/#aboutgeot.
[xvii] U.S. Department of Energy. Office of Energy Efficiency & Renewable Energy. Geothermal Technologies Office. Geothermal. https://www.energy.gov/eere/geothermal/geothermal-energy-us-department-energy.
[xviii] US Energy Information Administration: World electricity generation data by category and country were obtained from the International Energy Statistics data portal. https://bit.ly/2J8TJ0t.
[xix] EGEC Geothermal. The Voice of Geothermal in Europe. https://www.egec.org/about/#aboutgeot.
[xx] https://www.energy.gov/eere/buildings/building-technologies-office, https://www.energy.gov/energysaver/choosing-and-installing-geothermal-heat-pumps.
[xxi] European Commission Study Report. Optimal use of biogas from waste streams. An assessment of the potential of biogas from digestion in the EU beyond 2020. Study Authors. CE Delft: Bettina Kampman, et al. December 2016.
[xxii] United States Environmental Protection Agency. Learn About Biogas Recovery. https://www.epa.gov/agstar/learn-about-biogas-recovery.
[xxiii] United States Environmental Protection Agency. Recovering Value from Waste. Anaerobic Digester System Basics. December 2011. https://www.epa.gov/sites/production/files/2014-12/documents/recovering_value_from_waste.pdf.
[xxiv] United States Environmental Protection Agency. Learn About Biogas Recovery. https://www.epa.gov/agstar/learn-about-biogas-recovery.
[xxv] United States Environmental Protection Agency. Recovering Value from Waste. Anaerobic Digester System Basics. December 2011. https://www.epa.gov/sites/production/files/2014-12/documents/recovering_value_from_waste.pdf.
[xxvi] European Commission Study Report. Optimal use of biogas from waste streams. An assessment of the potential of biogas from digestion in the EU beyond 2020. Study Authors. CE Delft: Bettina Kampman, et al. December 2016.
[xxvii] M.E. Brown et al., 2015, “Climate Change, Global Food Security, and the U.S. Food System.” http://www.usda.gov/oce/climate_change/FoodSecurity2015Assessment/FullAssessment.pdf.
[xxviii] European Commission. Biomass. https://ec.europa.eu/energy/en/topics/renewable-energy/biomass.
[xxix] https://www.epa.gov/agstar/agstar-data-and-trend. This page provides national market data and trends related to these biogas recovery systems, exemplified by anaerobic digesters operating on livestock farms across the United States.
[xxxi] Renewable Energy Production on Farms. https://ag.umass.edu/crops-dairy-livestock-equine/fact-sheets/renewable-energy-production-on-farms.
[xxxii] Opportunities for Combined Heat and Power at Wastewater Treatment Facilities: Market Analysis and Lessons from the Field. October 2011. Report prepared by: Eastern Research Group, Inc. (ERG) and Resource Dynamics Corporation (RDC) for the U.S. Environmental Protection Agency, and Combined Heat and Power Partnership, October 2011.
[xxxiii] D. Panepinto et al., “Energy from Biomass for Sustainable Cities.” IOP Conf. Series: Earth and Environmental Science 72 (2017) 012021 doi:10.1088/1755-1315/72/1/012021.
[xxxiv] Turning Food Waste into Energy to Power Homes. https://www.biogasworld.com/news/turning-food-waste-into-energy-to-power-homes/.
[xxxv] Smart City Sweden. http://smartcitysweden.com/focus-areas/bio-energy/
[xxxvi] Asia Biomass Office. https://www.asiabiomass.jp/english/topics/1612_02.html.
[xxxvii] Energy from municipal solid waste. https://www.eia.gov/energyexplained/?page=biomass_waste_to_energy.
[xxxviii] Using biogas technologies to reduce methane emissions from waste https://www.biogas.org.nz/.
[xxxix] Forestry New Zealand. Planting one billion trees. https://www.mpi.govt.nz/funding-and-programmes/forestry/planting-one-billion-trees/.
[xl] Australian Government. Department of the Environment and Energy. 20 million Trees by 2020. http://www.environment.gov.au/land/20-million-trees.
[xli] The Billion Tree Campaign. https://www.plant-for-the-planet.org/en/treecounter/billion-tree-campaign-2.
[xlii] The Great Green Wall in Africa (Sahel). http://www.greatgreenwall.org/great-green-wall/#great-green-wall-internal.
[xliii] Andrés Viña et al., “Effects of conservation policy on China’s forest recovery.” Science Advances 18 Mar 2016: Volume 2, no. 3, e1500965. DOI: 10.1126/sciadv.1500965.
[xliv] The Power of Trees. http://trees.org/.
[xlv] National Grid. Electricity in New Zealand – Electricity Authority. https://www.ea.govt.nz/dmsdocument/20410.
[xlvi] European Network of Transmission System Operators. ENTSO-E Transmission System Map. https://www.entsoe.eu/data/map/.
[xlvii] Department of Energy. Office of Electricity. Grid Modernization and the Smart Grid. https://www.energy.gov/oe/activities/technology-development/grid-modernization-and-smart-grid.
[xlviii] European Network of Transmission System Operators for Electricity. E-Highway2050. Unveiling the Electricity Highways Project Results: “Europe’s Future Secure and Sustainable Electricity Infrastructure”. https://www.entsoe.eu/outlooks/ehighways-2050/.
[xlix] European Commission. Smart-grid: from innovation to deployment. Communication from the commission to the European Parliament, The council, The European Economic and Social committee and the Committee of the Regions. Smart-grid: from innovation to deployment /* COM/2011/0202 final */ http://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1409145686999&uri=CELEX:52011DC0202.
[l] Department of Energy. Office of Electricity. Grid Modernization and the Smart Grid. https://www.energy.gov/oe/activities/technology-development/grid-modernization-and-smart-grid.
[li] Camila Stark et al., “Renewable Electricity: Insights for the Coming Decade.” Joint Institute for Strategic Energy Analysis. Technical Report NREL/TP-6A50-63604. 2015. https://www.nrel.gov/docs/fy15osti/63604.pdf.
[lii] Katrin Schaber et al., “Parametric study of variable renewable energy integration in Europe: Advantages and costs of transmission grid extensions.” Energy Policy, Volume 42, 2012, 498-508, https://doi.org/10.1016/j.enpol.2011.12.016.
[liii] Department of Energy’s Office of Electricity Delivery and Energy Reliability. What is the Smart Grid? https://www.smartgrid.gov/the_smart_grid/index.html.
[liv] European Commission. Smart-grid: from innovation to deployment. Communication from the commission to the European Parliament, The council, The European Economic and Social committee and the Committee of the Regions. http://eur-lex.europa.eu/legal-content/EN/TXT/?qid=1409145686999&uri=CELEX:52011DC0202.
[lv] European Commission. Smart-grid and meters. https://ec.europa.eu/energy/en/topics/markets-and-consumers/smart-grids-and-meters.
[lvi] Department of Electricity. Office of Electricity. https://www.energy.gov/oe/activities/technology-development/grid-modernization-and-smart-grid.
[lvii] European Commission. Energy storage. https://ec.europa.eu/energy/en/topics/technology-and-innovation/energy-storage.
[lviii] Department of Energy’s Office of Electricity Delivery and Energy Reliability. Pumped-storage hydropower. https://www.energy.gov/eere/articles/5-promising-water-power-technologies.
[lix] Energy Storage Association. White Paper, 35×25: A Vision for Energy Storage. http://energystorage.org/vision2025.
[lx] Department of Energy. Energy Storage. https://www.energy.gov/science-innovation/electric-power/storage.
[lxi] National Renewable Energy Laboratory. Valuing the Resilience Provided by Solar and Battery Energy Storage Systems. https://www.energy.gov/sites/prod/files/2018/03/f49/Valuing-Resilience.pdf.
[lxii] Energy Storage Association. Energy Storage Technologies. http://energystorage.org/energy-storage/energy-storage-technologies.
[lxiii] W. Breuer et al., Siemens AG, Energy Sector, Power Transmission Division, Germany. “Highly Efficient Solutions for Smart and Bulk Power Transmission of “Green Energy”.” Presented at 21TH World Energy Congress, Montreal, Canada. September 12–16, 2010. Updated Version, July 2011.
[lxiv] Alexandre Oudalov et al., “A Method for a Comparison of Bulk Energy Transport Systems.” Environ. Sci. Technol., 2009, 43 (20), 7619–7625. DOI: 10.1021/es900687e.
[lxv] European Commission. EU Science Hub. Report. The European Commission’s science and knowledge service. “HVDC Submarine Power Cables in the World: State-of-the-Art Knowledge.” https://ec.europa.eu/jrc/en/publication/hvdc-submarine-power-cables-world-state-art-knowledge.
[lxvi] P. Kuhn et al., “Challenges and opportunities of power systems from smart homes to super-grids.” Ambio (2016) 45(Supplement 1): 50. https://doi.org/10.1007/s13280-015-0733-x.
[lxvii] European Commission. Smart-grid Task Force. https://ec.europa.eu/energy/en/topics/markets-and-consumers/smart-grids-and-meters/smart-grids-task-force.
[lxviii] US Department of Energy. Office of Electricity Delivery and Energy Reliability. What is the Smart Grid? https://www.smartgrid.gov/the_smart_grid/smart_grid.html.
[lxix] European Commission. European Parliament – Europa EU. Directorate General for Internal Policies. Policy Department A: Economic and Scientific Policy. Industry Research and Energy. Decentralized Energy Systems. Decentralized Energy Production. IP/A/ITRE/ST/2009-16 JUNE 2010. PE 440.280. www.europarl.europa.eu/document/activities/cont/…/20110629ATT22897EN.pdf.
[lxx] US Department of Energy. Office of Energy Efficiency & Renewable Energy. How Distributed Wind Works. https://www.energy.gov/eere/wind/how-distributed-wind-works.
[lxxi] World Alliance for Decentralized Energy. http://www.localpower.org/abt_mission.html.
[lxxii] Peter Alstone et al., “Decentralized energy systems for clean electricity access.” Nature Climate Change Volume 5, 305–314 (2015).