Le centrali nucleari sono superate, ma continuano a tenere in piedi progetti per construirle: ma sono proprio convenienti?
una centrale tradizionale consuma una tonnellata di uranio all'anno, se fosse al carbone ne consumerebbe milioni di tonnellate di carbone, molto più economico ma molto più dannoso, alla salute ed al pianeta, perchè produce anidride carbonica. Però, Le risorse di uranio, al consumo attuale (non calcolando nuove centrali) saranno esaurite in 45 anni. Le centrali saranno sicure, ma l'energia recuperabile è poca rispetto a quella che va dispersa (acqua di raffreddamento), le scorie radiattive che vengono prodotte (ogni atomo di uranio da' vita ad isotopi di stronzio ed elementi intermedi pericolosi).
Esisono centrali nucleari su navi, portaerei e sottomarini, come mai sono più controllabili? probabilmente perchè non devono produrre grandi quantità di energia, e le reazioni partono da quantità minime di uranio, più controllabili
Ed il Torio? Reattori nucleari ad amplificazione di energia affiancato da una sorgente esterna di protoni (sistema noto in inglese come Accelerator-Driven System o ADS), necessaria ad alimentare la reazione nucleare nel nucleo del reattore in sé. Questo, infatti, ha la caratteristica di essere un reattore subcritico, incapace di sostenere autonomamente una reazione a catena e, dunque, di dar luogo a una reazione incontrollata. Per innescare la reazione a catena, esso ha bisogno di essere irraggiato da un potente fascio di particelle proveniente da un acceleratore di particelle (sincrotrone): una volta acceso, il nucleo del reattore rilascia sufficiente energia termica da poter essere trasformata in energia elettrica che servirà ad alimentare l'acceleratore di particelle e a fornire un surplus di energia elettrica destinato all'immissione nella rete elettrica
il torio non dà problemi di scarti radiattivi, e il nocciolo non è soggeto alla fissione incontrollata
le centrali al torio sono costruibili in pochissimi anni, tre-cinque, i prodotti della reazione sono più cisuri, meno instabili.... e costa molto meno dell'uranio, Nobel nel 1984, Carlo Rubbia, da anni propone di ricavare energia dal Torio, un elemento che non si autoinduce nella fissione nucleare come invece fa l'uranio
è circa dieci volte più abbondante dell'uranio ed è circa comune quanto il piombo; ne serve 1/1000 rispetto all'uranio che invece va arricchito: ....
un altro aspetto favorevole è a produzione di energia rilasciata lentamente, secondo i consumi e le necessità locali: potrebbe essere abbinato ad un impianto di produzione di idrogeno (idrogeno verde a partire da acqua), in uno scaling up che è limitato dalle dimensioni dei polimeri su cui avvengono le reazioni
tengo a precisare che le auto elettriche, e ciò che viene prodotto partire da altre energie non verdi , non è sostenibile: consumiamo un eccesso di energie tradizionali per alimentare la rete elettrica, quando dovremmo produrre sorgenti di energia pulita. Questo si traduce nella classificazione dell'idrogeno, H2, che se prodotto a partire da carbone, petrolio o centrali tradizionali, viene chiamato idrogeno blu, mentre dobbiamo puntare su idrogeno verde, produzione in cui le reazioni che permettono l'elettrolisi dell'acqua sono alimentate da energie rinnovabili.
ma... queste tecnologie per produrre idrogeno verde ha bisogno di uno scale up industriale, e di abbassare il costo a valle. Finchè sarà venduto a 17 euro/litro, le auto ad idrogeno per fare un pieno in Italia devono arrivare all'unico distributore presente, nel Trentino, e compiere con quel pieno 350/400 km. In Germania esistono almeno una ventina di distributori.
Oltre all'impiego di idrogeno nelle batterie (fuel cells) con efficenza dell'80%, è stato messo a punto da Toyota un motore a indrogeno, motori prodoti dall'azienda Acquarius, basato su un cilindro in cui i pistoni si muovono tra due capi del motore
per la produzione indusriale su larga scala di idrogeno, sono necessarie strategie di superfici esese catalizzanti, come i polimeri per membrane elettrolitiche del progetto REPHYNE II
in the Rephyne II project, there are products such as the world largest polymer electrolyte membrane, or PEM, electrolyser to produce green hydrogen at scale, a technology at level readiness near realization state
l'idrogeno verde costa attualmente 17 euro per litro, al consumo, ma potrebbe essere una fonte di energia di stoccaggio, prodotto quando se ne produce tanta, e usato quando la richiesta di energia aumenta.... un pò come le batterie che stoccano energia
un sistema innovativo per lo stoccaggio del surplus di energia solare abbinato a impianti fotovoltaici, è una batteria che utilizza anidride carbonica, fatta passare tra un stato liquido a uno gassoso, conserva temporaneamente l' energia mediante cycling del CO2 da gas a liquido
adopt different innovative hydrogen production technologies of water electrolysis, generate hydrogen by photovoltaic power, and then store hydrogen through suitable hydrogen storage and metal alloy storage, and then generate hydrogen through fuel cells Electricity and heat or other industrial applications, especially to provide low-cost green hydrogen power generation and heating products and services for off grid households and enterprises
Un altro approccio può venire dall'utilizzo di cellette ad alveare basate su composti di nickel
Research paperHierarchical and self-supporting honeycomb LaNi5 alloy on nickel foam for overall water splitting in alkaline media
Thorium, Th 90
named for the Norse god of thunder, is much more abundant than uranium and has 200 times that metal’s energy potential. Thorium is also a more efficient fuel source — unlike natural uranium, which must be highly refined before it can be used in nuclear reactors, all thorium is potentially usable as fuel. Thorium could be used as an energy amplifier in next-generation nuclear power plants. Known as an accelerator-driven system, it would use a particle accelerator to produce a proton beam and aim it at lump of heavy metal, producing excess neutrons. Thorium is a good choice because it has a high neutron yield per neutron absorbed. Thorium nuclei would absorb the excess neutrons, resulting in uranium-233, a fissile isotope that is not found in nature. Moderated neutrons would produce fissioned U-233, which releases enough energy to power the particle accelerator, plus an excess that can drive a power plant. A network of tiny underground nuclear reactors, maybe producing about 600 MW each....
The Innovation 2, 100180, November 28, 2021
Technologies and perspectives for achieving carbon neutrality
Solar thermal technologies rely on photothermal conversion to achieve heat, steam, and electricity production for C-neutral operations, unlike photovoltaic techniques. When solar thermal technologies, such as concentrated solar power systems, are employed in commercial and residential sectors to replace natural gas as a source of energy, an obvious reduction in both energy consumption of fossil fuels and CO2 emissions has been observed.51,52 Besides photovoltaic and solar thermal technologies, some strategies to convert solar radiation into stable chemical fuels also provide feasible ways for large-scale utilization and storage of solar energy toward energy decarbonization. For instance, great efforts have been made on solar hydrogen production, demonstrating an extremely attractive route to produce hydrogen fuel by adopting renewable solar energy or solar-derived power to electrolyze water.53,54 Note that hydrogen fuel is an ideal clean energy source to deliver C-free emissions, showing a great potential to reduce GHG emissions. Recently, a new concept of liquid sunshine has been proposed for combining solar energy with captured CO2 and water to generate green liquid fuels, such as methanol and alcohol, which may deliver an ecologically balanced cycle between generation and utilization of CO2 in global production systems.55
Solar energy represents an ideal solution tomeet the energy demands in a low-C and C-free society. Owing to the low-operating costs, a series of useful measures based on solar energy techniques are good candidates to reduce C emissions and utilize CO2 to form clean energy storage, thereby playing an irreplaceable role in the realization of C neutrality. The next decades will require accelerated development of advanced energy conversion/storage technologies and large-scale deployment of solar energy combined with clean resources to promote integrated pathways to C-neutral energy systems.
Wind energy
Wind results from the motion of air due to uneven heating of the Earth’s surface by the Sun. This means that wind power could be regarded as indirect solar energy.56 Like solar energy, wind energy will play a critical role in realizing "C peak and C neutrality."
The Earth has abundant wind resources, which are mainly distributed in grasslands, deserts, coastal areas, and islands.57 The site location has a significant impact on the economy, technicality, and implementation of wind energy.
The world attaches great importance to and vigorously supports the development of wind power. However, one of the issues that hinders wind energy utilization is the noise generated by wind turbines. Strategies to reduce or minimize the noise produced by wind turbines and further utilize wind sources sensibly are urgently needed. Another concern with wind energy production is that wind turbines may have an adverse effect on birds via collisions, disruptions, or habitat destruction if they are located inappropriately.
Although the wind resource on Earth is abundant, the uneven distribution of wind resources across the landscape poses a challenge to the transport of electrical energy produced by wind turbines. And the unpredictable nature of winds in terms of speed and direction will result in a variable and unstable phase, amplitude, and frequency for the generation of electricity, which may make it difficult to be integrated into the grid, resulting in a waste of wind energy. The cost of installing awind turbine is currently quite high,which also hinders the widespread adoption of this technology. It is necessary to devote more efforts to exploring and developing wind energy technology to meet the needs of energy users.
Ocean energy
Ocean energy refers to the energy contained in thewater body in the ocean and is both renewable and clean. The ocean energy reserve is enormous globally and is enough to power the entire world. There are typically five different energy forms: tidal energy, wave energy, ocean current energy, thermal energy, and osmotic energy. The tidal, wave, and current energies are mechanical energy. The research of exploiting ocean energy was started a few decades ago. The geographical distribution varies broadly for different energy forms, and the harnessing technologies are also quite different.
Tidal energy is the energy contained in the tide, including the potential energy related to the water level and the kinetic energy of the tidal current. The tide originates from the gravitational interaction of sea water with the Moon or the Sun. Tidal energy is estimated to be about 1,200 TWh per year,which is relatively low among all ocean energy forms58 due to limited locations from where tidal energy can be harvested. The tidal barrage is adopted to harvest the potential energy of tides, which is relatively technologically mature. Early tidal barrages started to operate in the 1960s, and tidal energy now has the largest share of ocean energy being exploited (Khare et al., 2019). Harnessing tidal current power mainly relies on turbines, although other types of devices are also under development.
Wave energy is the kinetic and potential energy in water waves, which is widely distributed. It essentially comes from wind, which transmits part of its kinetic energy to the water at the ocean surface. The potential of wave energy globally is 29,500 TWh per year.59 The technology for harvesting wave energy is less mature than that for tidal energy, and many different types of devices are being tested on a small scale toward commercialization.
The major device forms include point absorber, attenuator, oscillating water column devices, and overtopping devices. Besides traditional large devices using electromagnetic generators, new technologies based on triboelectric nanogenerator networks are also being developed toward effective harvesting of wave energy economically.60
Ocean current energy is reserved in the large circulations of sea water globally. It is the kinetic energy in the water flow. The supply of this source of energy is stable with little fluctuation. It can be extracted using turbines.
The device needs to be deployed in deep sea and far from the shore; thus, less effort has been devoted to harnessing this type of energy.
Thermal energy originates from the Sun’s irradiation, which heats the upper layer of the sea water, making its temperature different from the water in the deep sea. Such temperature differences can be exploited for electricity generation mainly based on thermal cycles. Due to the high-temperature difference required for improved efficiency, this form of energy ismainly distributed in the tropical region. The potential for this energy is estimated to be 44,000 TWh per year.61 The utilization of this form of energy is still at the research stage by universities and research institutes.
Osmotic energy, also called salinity gradient energy, is the energy that exists between water bodies with different salt concentrations. The salinity of sea water is not homogenous globally; for example, a salinity gradient is formed in estuaries where fresh water meets salt water. The harness of such energy relies on high-performance membranes that are robust in sea water. Twomain technologies are being tested at present: pressure-retarded osmosis and reversed electrodialysis.59 Osmotic energy is still a conceptual energy source and is not ready for commercialization.
The ocean energy reserve is enormous globally and is enough to power the entire world. Technologies to harvest tidal and wave energy are on the verge of commercialization. Technologies for harvesting ocean current energy, thermal energy, and osmotic energy are still in their early development stage. Major challenges of exploiting ocean energy lie in the economic costcompetitiveness and technological reliability in severe ocean environments. By overcoming these challenges, ocean energy will provide the world with abundant clean energy.
Bioenergy
Biomass is a renewable source of energy that originates fromplants. The most important sources of biomass are agricultural and forestry residues, biogenic materials in municipal solid waste, animal waste, human sewage, and industrial wastes. Biomass provides 13%–14% of the annual global energy consumption.62 Various processes are used to convert biomass into energy, including the following.
Thermochemical conversion of biomass includes gasification, pyrolysis, and combustion. Combustion produces approximately 90% of the total renewable energy obtained from biomass.63 Pyrolysis can convert biomass into solid, liquid, or gaseous products by thermal decomposition at temperatures around 400C–1,000C in the absence of oxygen, producing components such as acids, esters, and alcohols.64 Gasification converts carbonaceousmaterials into combustible or synthetic gas by reacting the air, oxygen, or vapor at a temperature of over 500C, preferably over 700 oC, yielding gases such as H2, CO, and CH4.64,65
Chemical conversion converts vegetable oils and animal fats into fatty acid esters through esterification or/and transesterification to produce biodiesel.
The transesterification process is necessary since raw materials are composed of triglycerides, which are not a useable fuel. Triglycerides are converted into methyl or ethyl esters (biodiesel) using amostly alkaline catalyst in the presence of methyl or ethyl alcohol, respectively. Rapeseed oil (accounting for 80%–85%) and sunflower oil (accounting for 10%–15%) are major vegetable oils used for biodiesel production.63
Biochemical conversion converts biomass into liquid fuels (e.g., alcohols and alkanes), natural gas (e.g., hydrogen and methane), different types of bio-products (e.g., carotenoids, omega-3 and omega-6 fatty acids), as well as other chemical building blocks (e.g., acetic acid and lactic acid) using microbes and enzymes as the catalyst.66 The most popular biological conversions are fermentation and anaerobic digestion.
The most common biomass feedstock used for biological conversion is lignocellulosic biomass, such as agricultural and forestry residues. Lignocellulosic biomass is the most abundant and widely available renewable resource in theworld,mainly composed of three heterogeneous biopolymers, namely cellulose, hemicellulose, and lignin. Threemajor steps are involved in cellulosic bioethanol production: (1) pre-treatment, (2) enzymatic hydrolysis, and (3) fermentation. Pre-treatment uses physical, chemical, or physicochemical
methods to improve biomass accessibility by enzymes. Enzymatic hydrolysis splits cellulose and hemicellulose into monomer sugars, such as glucose, xylose, and mannose. The conversion of biomass-derived sugars into ethanol by Saccharomyces cerevisiae has received most research and development efforts. Another method for producing butanol is through fermentation, specifically through an acetone/butanol/ethanol process that
is predominantly carried out by Clostridia strains.67 Anaerobic digestion consists of hydrolysis, acidogenesis, acetogenesis, and methanogenesis. These reactions break down the macromolecules in the biomass into simpler molecules with the generation of biogas in an anaerobic environment. One of the advantages of anaerobic digestion lies in the potential of the biogas to be used directly in ignition gas engines and gas turbines.
Despite the presence of abundant biomass resources, there is still a need for work on the use of biomass to produce energy, withmain efforts needed to increase productivity and reduce costs to further expand the share of such renewable energy in the total energy consumption.68 Some of the issues that need to be resolved are the high cost of transporting the biomass to the site for bioenergy production through various conversion processes and the sustainability of the production of bioenergy feedstocks.
H2 energy
Hydrogen has been a necessity for industrial use over the past two hundred years. The demand for hydrogen (currently >80 Mt per annum) has grown more than three times since 1975 and continues to rise. Up to now, H2 is almost entirely produced from fossil fuels, consuming around 6% of global natural gas and 2% of global coal, resulting in emissions of around 830 Mt of CO2 per year.69 Recently, hydrogen energy has drawn a great deal of interest because it can be used to establish a fully renewable energy system similar to an electricity grid, providing the sector integration needed for energy system transition and decarbonize energy end uses.70
Hydrogen production using renewable energy has a strong likelihood of both technological and economic viability in the near future. The decreasing costs of renewable energy and the increase in variable renewable power supplies’ market share have put significant roadblocks in the way of cheap water electrolysis.71 With the fast development of artificial intelligence, deployment and learning-by-doing are expected to reduce electrolyzer costs and supply chain logistics. After H2 production via electrolysis, safe and low-cost hydrogen storage and transportation technology need to be developed.
Hydrogen can be stored in gas, liquid, and solid states.72,73 As of now, none of these technologies are mature for establishing a hydrogen economy. In addition, hydrogen offers the lowest cost option for long-termenergy storage, such as inter-seasonal; however, the ability to store large quantities of hydrogen at low costs with a high safety is still a challenge. Underground H2 storage in large salt caverns and hydrogen transport via existing and refurbished gas pipelines are available at low cost to support long-term energy storage and sector coupling. However, equipment standards need to be adjusted and are also limited by geographical conditions.74,75
Hydrogen fuel cell technologies have developed rapidly and are ready for commercialization, to the point that we now see commercial sales of hydrogen-powered passenger cars, such as Mirai, Clarity, and Nexo, and heavy-duty vehicles, trains, and ships. The main issue now is to reduce the cost whilemaintaining an acceptable level of durability and efficiency.76 Other opportunities that pay more attention to the handling of energy-intensive commodities producedwith hydrogen—synthetic organicmaterials/pharmaceuticals, iron and steelmaking, building/marine bunkers or feedstock to produce ammonia/methanol, and so on—seem to be prime markets. We now need to develop scale-up technologies, increase energy use/conversion efficiencies, optimize the upgrade of H2 industrial structures, and lower costs to enable widespread use of H2 energy. There needs a long-term devotion to fundamental understanding and development of new strategy/technology and infrastructure.
