9.5 Green technology

Green technology offers solutions to environmental challenges by reducing emissions, conserving resources, and minimizing pollution. It encompasses renewable energy, energy efficiency, sustainable transportation, and waste management. These innovations aim to mitigate climate change and promote sustainability.

Adopting green tech brings economic benefits like job creation and reduced energy costs. However, challenges include high upfront costs, lack of awareness, and infrastructure gaps. Despite obstacles, green technology continues to advance, promising a cleaner, more sustainable future.

Benefits of green technology

• Green technology offers numerous environmental benefits, such as reducing greenhouse gas emissions, conserving natural resources, and minimizing pollution, which contribute to mitigating climate change and preserving ecosystems
• Adopting green technologies can lead to economic advantages, including job creation in renewable energy sectors, reduced energy costs for consumers and businesses, and increased energy security by reducing dependence on finite fossil fuels
• Green technologies promote social well-being by improving air and water quality, which can positively impact public health, particularly in communities disproportionately affected by pollution

Challenges in green tech adoption

• High upfront costs associated with implementing green technologies can be a significant barrier for individuals, businesses, and governments, despite the long-term economic benefits
• Lack of awareness and understanding about the benefits and functionality of green technologies among consumers and decision-makers can hinder widespread adoption
• Insufficient infrastructure and supply chains to support the deployment and maintenance of green technologies can limit their accessibility and reliability
• Resistance from established industries and lobbying groups with vested interests in traditional energy sources can create political and regulatory obstacles to green tech adoption

Solar energy technologies

Photovoltaic (PV) systems

• PV systems directly convert sunlight into electricity using solar panels made of photovoltaic cells, which are typically made from silicon or other semiconductor materials
• PV systems can be installed on rooftops, integrated into building facades (building-integrated photovoltaics or BIPV), or deployed in large-scale solar farms
• Advances in PV technology have led to increased efficiency and reduced costs, making solar power more accessible and cost-competitive with traditional energy sources
• PV systems can be connected to the grid (grid-tied) or used in off-grid applications, providing electricity to remote areas or during power outages

Concentrated solar power (CSP)

• CSP systems use mirrors or lenses to concentrate sunlight onto a receiver, which heats a fluid to generate steam that drives a turbine to produce electricity
• There are four main types of CSP technologies: parabolic troughs, solar power towers, linear Fresnel reflectors, and dish Stirling engines
• CSP plants can store thermal energy using molten salt or other heat storage media, allowing them to generate electricity even when the sun is not shining
• CSP is particularly suitable for large-scale, utility-scale power generation in regions with high levels of direct solar radiation (deserts)

Solar water heating

• Solar water heating systems use solar collectors to absorb heat from the sun and transfer it to water, which is then stored in a tank for later use
• There are two main types of solar water heating systems: active systems, which use pumps to circulate water or a heat-transfer fluid, and passive systems, which rely on natural convection
• Solar water heating can significantly reduce energy consumption and costs associated with heating water for residential, commercial, and industrial applications
• Solar water heating systems are most effective in regions with abundant sunshine and can be used in combination with conventional water heaters for backup during periods of low solar radiation

Wind power technologies

Onshore wind turbines

• Onshore wind turbines harness the kinetic energy of moving air to generate electricity, with blades that rotate a shaft connected to a generator
• Modern onshore wind turbines can have hub heights exceeding 100 meters and blade lengths over 50 meters, allowing them to capture stronger and more consistent winds at higher altitudes
• Onshore wind farms can be developed on agricultural land, grazing land, or other open spaces, with minimal impact on existing land uses
• Advances in wind turbine design, materials, and control systems have increased the efficiency, reliability, and cost-effectiveness of onshore wind power

Offshore wind farms

• Offshore wind farms are constructed in bodies of water, typically in coastal areas with shallow water depths and strong, consistent winds
• Offshore wind turbines are generally larger than onshore turbines, with higher rated capacities and longer blades to capture the greater wind resources available offshore
• Offshore wind farms face unique challenges, such as the need for specialized foundations (monopiles, jackets, or floating platforms), submarine cables for power transmission, and resistance to harsh marine environments
• Offshore wind development has grown rapidly in recent years, particularly in Europe and Asia, with increasing interest in the United States and other regions with significant offshore wind resources

Hydroelectric power

Conventional hydropower

• Conventional hydropower plants generate electricity by harnessing the energy of falling or flowing water, which is used to spin turbines connected to generators
• Hydropower plants typically involve the construction of dams to create reservoirs, which store water and provide a controlled release for power generation
• Large-scale hydropower projects can provide significant amounts of electricity, with some of the world's largest plants having capacities exceeding 10 GW (Three Gorges Dam, China)
• While hydropower is a renewable energy source, the construction of dams can have significant environmental and social impacts, such as altering river ecosystems, displacing local communities, and affecting fish populations

Pumped storage hydroelectricity

• Pumped storage hydroelectricity (PSH) is a form of energy storage that uses two water reservoirs at different elevations to store and generate electricity
• During periods of low electricity demand, water is pumped from the lower reservoir to the upper reservoir, effectively storing energy in the form of gravitational potential energy
• When electricity demand is high, water is released from the upper reservoir, flowing through turbines to generate electricity before being collected in the lower reservoir
• PSH is the most widely used form of large-scale energy storage, providing a means to balance the variability of renewable energy sources like wind and solar power

Tidal and wave energy

• Tidal energy harnesses the kinetic energy of tidal currents, which are driven by the gravitational pull of the moon and sun, to generate electricity using underwater turbines
• Wave energy converts the kinetic and potential energy of ocean waves into electricity using various technologies, such as oscillating water columns, point absorbers, or overtopping devices
• Tidal and wave energy resources are predictable and consistent, offering a reliable source of renewable energy for coastal communities
• However, tidal and wave energy technologies are still in the early stages of development, with challenges related to cost, scalability, and potential environmental impacts on marine ecosystems

Geothermal energy systems

Geothermal heat pumps

• Geothermal heat pumps, also known as ground-source heat pumps, use the relatively constant temperature of the earth to provide heating, cooling, and hot water for buildings
• Heat pumps circulate a fluid through underground pipes, absorbing heat from the ground in winter to warm buildings and transferring heat from buildings into the ground in summer for cooling
• Geothermal heat pumps are highly efficient, with coefficients of performance (COP) typically ranging from 3 to 5, meaning they provide 3 to 5 units of heat for every unit of electricity consumed
• While geothermal heat pumps have higher upfront costs compared to conventional HVAC systems, they can significantly reduce energy consumption and operating costs over their lifetime

Geothermal power plants

• Geothermal power plants generate electricity by harnessing heat from underground hot water or steam reservoirs, which are accessed through wells drilled into the earth
• There are three main types of geothermal power plants: dry steam plants, which use steam directly from a geothermal reservoir; flash steam plants, which convert high-temperature water into steam; and binary cycle plants, which use a secondary fluid with a lower boiling point to generate steam
• Geothermal power plants provide baseload electricity, as they are not dependent on variable weather conditions like wind or solar power
• Geothermal resources are location-specific, with the most suitable sites located in regions with high heat flow and favorable geological conditions, such as near tectonic plate boundaries or volcanic areas

Bioenergy and biomass

Biofuels vs fossil fuels

• Biofuels are liquid or gaseous fuels produced from biomass, such as plants, agricultural waste, or organic matter, while fossil fuels are derived from ancient fossilized remains of plants and animals
• The two main types of biofuels are bioethanol, produced from sugar or starch crops (corn, sugarcane), and biodiesel, produced from vegetable oils or animal fats
• Biofuels are considered renewable because the biomass feedstocks can be replenished relatively quickly, while fossil fuels take millions of years to form
• However, the sustainability of biofuels depends on factors such as land use, water consumption, and the energy balance of production processes, with some biofuels having lower net greenhouse gas emissions than others

Biomass for electricity generation

• Biomass can be used to generate electricity through direct combustion in power plants, co-firing with coal, or gasification to produce syngas for use in gas turbines
• Common biomass feedstocks for electricity generation include wood and wood waste, agricultural residues (straw, corn stover), and dedicated energy crops (switchgrass, miscanthus)
• Biomass power plants can provide baseload electricity and offer a means to dispose of waste materials, such as municipal solid waste or forestry residues
• However, biomass combustion can still produce air pollutants and greenhouse gases, and the sustainability of biomass energy depends on factors such as land use, biodiversity impacts, and carbon balance over the life cycle of the feedstocks

Green building design

Energy-efficient construction materials

• Energy-efficient construction materials help reduce the energy consumption and environmental impact of buildings by improving thermal insulation, reducing air leakage, and minimizing embodied energy
• Examples of energy-efficient materials include high-performance insulation (aerogel, vacuum insulated panels), low-emissivity windows, cool roofs, and recycled or renewable materials (bamboo, hemp, sheep's wool)
• Advanced framing techniques, such as optimum value engineering (OVE), can reduce the amount of lumber used in construction while maintaining structural integrity and improving insulation
• The use of local and sustainable materials, such as earth-based materials (rammed earth, straw bale) or certified wood products, can further reduce the environmental footprint of buildings

Passive solar design principles

• Passive solar design is an approach to building design that uses the sun's energy for heating and cooling, minimizing the need for mechanical systems and reducing energy consumption
• Key principles of passive solar design include proper orientation of the building to maximize solar gain in winter and minimize it in summer, use of thermal mass to store and release heat, and strategic shading to control solar heat gain
• Passive solar heating strategies include direct gain (sunlight entering through south-facing windows), indirect gain (using a thermal storage wall or Trombe wall), and isolated gain (using a sunspace or greenhouse)
• Passive cooling strategies include natural ventilation, night-flush cooling, and the use of shading devices (overhangs, deciduous trees) to block summer sun

Green roofs and walls

• Green roofs are rooftops partially or completely covered with vegetation, growing in a lightweight growing medium over a waterproofing membrane and drainage layer
• Green roofs provide numerous environmental benefits, such as reducing urban heat island effect, improving air quality, managing stormwater runoff, and creating habitat for wildlife
• There are two main types of green roofs: extensive green roofs, which have a shallow growing medium (2-6 inches) and support low-growing, drought-tolerant plants; and intensive green roofs, which have a deeper growing medium (6 inches or more) and can support a wider variety of plants, including shrubs and small trees
• Green walls, also known as living walls or vertical gardens, are walls partially or completely covered with vegetation, using either a growing medium (soil-based) or hydroponic systems (soil-less)
• Green walls can be used indoors or outdoors and offer similar benefits to green roofs, as well as improving thermal insulation and acoustic performance of building facades

Sustainable transportation solutions

Electric vehicles (EVs)

• Electric vehicles are powered by electric motors and batteries, emitting no tailpipe emissions and offering a cleaner alternative to conventional internal combustion engine vehicles
• There are three main types of EVs: battery electric vehicles (BEVs), which run solely on electricity stored in rechargeable batteries; plug-in hybrid electric vehicles (PHEVs), which have both an electric motor and an internal combustion engine; and fuel cell electric vehicles (FCEVs), which use hydrogen fuel cells to generate electricity
• EVs have lower operating costs compared to conventional vehicles due to the higher efficiency of electric motors and lower cost of electricity compared to gasoline
• The environmental benefits of EVs depend on the sources of electricity used to charge them, with greater reductions in greenhouse gas emissions achieved when using renewable energy sources

Hybrid cars vs conventional vehicles

• Hybrid cars combine an internal combustion engine with an electric motor and battery, allowing them to switch between the two power sources to optimize fuel efficiency
• There are two main types of hybrid systems: parallel hybrids, where both the engine and electric motor can directly power the wheels; and series hybrids, where the engine is used to generate electricity for the motor, which powers the wheels
• Hybrid cars typically have higher fuel economy compared to conventional vehicles, particularly in city driving conditions with frequent stops and starts
• Regenerative braking systems in hybrid cars capture the kinetic energy that would otherwise be lost during braking and use it to recharge the battery, further improving efficiency

Biofuel-powered vehicles

• Biofuel-powered vehicles run on liquid fuels produced from biomass, such as bioethanol or biodiesel, which can be used in conventional internal combustion engines with little or no modifications
• Flex-fuel vehicles (FFVs) are designed to run on gasoline, E85 (a blend of 85% ethanol and 15% gasoline), or any combination of the two, providing flexibility in fuel choice
• Biodiesel can be used in compression-ignition (diesel) engines, either in pure form (B100) or blended with petroleum diesel (B20, B5), reducing emissions of some air pollutants
• The sustainability of biofuel-powered vehicles depends on the production methods and feedstocks used for the biofuels, with some biofuels having lower net greenhouse gas emissions and environmental impacts than others

Waste-to-energy technologies

Anaerobic digestion

• Anaerobic digestion is a process that breaks down organic waste in the absence of oxygen, producing biogas (a mixture of methane and carbon dioxide) and digestate (a nutrient-rich residue)
• Organic waste materials suitable for anaerobic digestion include food waste, animal manure, sewage sludge, and agricultural residues
• Biogas produced through anaerobic digestion can be used for heating, electricity generation, or upgraded to biomethane for use as a vehicle fuel or injection into natural gas pipelines
• Anaerobic digestion helps reduce greenhouse gas emissions by capturing methane that would otherwise be released into the atmosphere during the decomposition of organic waste in landfills

Incineration with energy recovery

• Incineration with energy recovery involves the controlled combustion of waste materials, with the heat generated used to produce steam for electricity generation or district heating
• Modern waste-to-energy incinerators are equipped with advanced air pollution control systems to minimize emissions of harmful substances, such as dioxins, furans, and heavy metals
• Incineration can significantly reduce the volume of waste (up to 90%), extending the life of landfills and recovering energy from materials that cannot be recycled
• However, incineration still produces greenhouse gas emissions and ash residues that require proper management, and the energy recovery efficiency can vary depending on the composition and moisture content of the waste

Smart grids and energy storage

Distributed renewable energy integration

• Distributed renewable energy systems, such as rooftop solar PV or small-scale wind turbines, generate electricity at or near the point of consumption, reducing transmission losses and increasing grid resilience
• Smart grids use advanced communication, monitoring, and control technologies to integrate distributed energy resources (DERs) and optimize the balance between electricity supply and demand
• Advanced inverters and microgrids can help manage the variability of renewable energy generation and provide grid services, such as voltage regulation and frequency control
• Virtual power plants (VPPs) aggregate multiple DERs, such as solar PV systems, battery storage, and demand response, to create a single controllable entity that can participate in electricity markets and provide grid support

Battery storage systems

• Battery storage systems store electrical energy in chemical form, allowing it to be released when needed to provide power during periods of high demand or low renewable energy generation
• Lithium-ion batteries are the most common type of battery storage technology, offering high energy density, efficiency, and cycle life
• Battery storage can be deployed at various scales, from small residential systems to large utility-scale installations, providing benefits such as peak shaving, frequency regulation, and renewable energy time-shifting
• The declining costs of battery storage, driven by advances in technology and economies of scale, are making it increasingly cost-effective for both grid-scale and behind-the-meter applications

Green technology policies and incentives

Government regulations and standards

• Government regulations and standards play a crucial role in driving the adoption of green technologies by setting minimum performance requirements, mandating the use of renewable energy, or limiting emissions from various sectors
• Examples of green technology regulations include renewable portfolio standards (RPS), which require a certain percentage of electricity to be generated from renewable sources; energy efficiency standards for appliances and buildings; and fuel economy standards for vehicles
• Building codes and green building certification systems, such as LEED (Leadership in Energy and Environmental Design) or BREEAM (Building Research Establishment Environmental Assessment Method), promote the use of energy-efficient and sustainable design practices in the construction industry
• Emissions trading schemes, such as cap-and-trade programs or carbon taxes, create financial incentives for companies to reduce their greenhouse gas emissions and invest in cleaner technologies

Tax credits and rebates

• Tax credits and rebates are financial incentives offered by governments to encourage the adoption of green technologies by reducing the upfront costs for consumers and businesses
• Examples of tax credits for green technologies include the Investment Tax Credit (ITC) for solar energy systems, the Production Tax Credit (PTC)