📚 Energy Production | 能源生产
Modern civilisation depends on a continuous supply of usable energy. In IB Physics, the topic of energy production examines primary energy sources—both renewable and non‑renewable—their conversion processes, efficiency, and environmental impacts. This article covers the essential physical principles, Sankey diagrams, energy density, and the mechanisms of generation from fossil fuels, nuclear reactions, solar radiation, wind, water, and geothermal heat.
现代文明依赖持续可用的能源供应。在IB物理中，能源生产这一主题探讨一次能源（包括可再生能源与不可再生能源）、它们的转换过程、效率及环境影响。本文涵盖基本的物理原理、桑基图、能量密度，以及来自化石燃料、核反应、太阳辐射、风、水和地热的发电机制。
1. Primary Energy Sources and Demand | 一次能源与需求
(1 EJ = 10¹⁸ J) and continues to rise, driven by population growth and industrialisation.
一次能源是指在任何转换之前自然界中存在的能源。它们包括化石燃料（煤、石油、天然气）、核燃料（铀）以及可再生能源，如太阳能、风能、水力、潮汐能、波浪能、地热能和生物质能。全球能源需求以艾焦（1 EJ = 10¹⁸ J）计量，受人口增长和工业化推动而持续上升。
the rate of energy transfer is power (P = ΔE/Δt), measured in watts. When discussing large‑ just the raw resource available but also the power output, reliability, and cost per kWh.
用物理术语说，能量传递的速率是功率（P = ΔE/Δt），单位为瓦特。讨论大规模发电时，我们使用兆瓦（MW）和吉瓦（GW）。选择能源不仅要考虑可用的原始资源，还要计及功率输出、可靠性和每千瓦时的成本。
2. Fossil Fuels | 化石燃料
atter. In a thermal power station, the fuel is burned to release heat, which produces high‑ thermal energy → kinetic energy of steam → kinetic energy of turbine → electrical energy.
化石燃料储存来自远古有机物的化学能。在火力发电站中，燃料燃烧释放热量，产生高压蒸汽。蒸汽驱动与发电机相连的汽轮机。总能量转换为：化学能 → 热能 → 蒸汽的动能 → 汽轮机的动能 → 电能。
theoretical efficiency of any heat engine is given by the Carnot efficiency: η_carnot = 1 – Tcold / Thot, where temperatures are in kelvin. Real fossil‑fuel plants achieve around 35–45% efficiency, with the rest lost as waste heat.
任何热机的最大理论效率由卡诺效率给出：η_carnot = 1 – Tcold / Thot，其中温度为开尔文。实际的化石燃料电厂效率约为35–45%，其余能量以废热形式散失。
Burning fossil fuels emits CO₂, SO₂, and NOₓ, contributing to the enhanced greenhouse effect and acid rain. The specific energy of coal is about 30 MJ kg⁻¹, oil 42 MJ kg⁻¹, and natural gas 55 MJ kg⁻¹, but their CO₂ intensity per unit of energy released varies.
燃烧化石燃料会排放CO₂、SO₂和NOₓ，导致增强的温室效应和酸雨。煤的比能量约为30 MJ kg⁻¹，石油42 MJ kg⁻¹，天然气55 MJ kg⁻¹，但它们每单位释放能量的CO₂强度各不相同。
3. Nuclear Fission | 核裂变
Nuclear fission involves splitting a heavy nucleus, typically uranium‑235, after absorbing a neutron. A common reaction is:
²³⁵U + ¹n → ¹⁴¹Ba + ⁹²Kr + 3¹n + energy
核裂变是指重核（通常是铀‑235）吸收一个中子后分裂。常见的反应为：
²³⁵U + ¹n → ¹⁴¹Ba + ⁹²Kr + 3¹n + energy
nergy released per fission is about 200 MeV, translating to a specific energy of roughly 80 million MJ kg⁻¹—millions of times greater than fossil fuels.
产物的总质量略小于反应物的质量；这一质量亏损Δm按照E = Δm c²转换为能量。每次裂变释放约200 MeV的能量，相当于约8千万 MJ kg⁻¹ 的比能量——比化石燃料高数百万倍。
In a nuclear reactor, the chain reaction is controlled by control rods (absorbing neutrons) and a moderator (slowing neutrons). The heat produced generates steam to drive turbines, leaving radioactive waste that must be stored securely for thousands of years. Safety and waste disposal remain the biggest challenges.
在核反应堆中，链式反应由控制棒（吸收中子）和慢化剂（减慢中子）来控制。产生的热量生成蒸汽驱动汽轮机，留下的放射性废物必须安全储存数千年。安全和废物处置仍是最大的挑战。
4. Nuclear Fusion | 核聚变
Nuclear fusion joins light nuclei, such as isotopes of hydrogen, to form a heavier nucleus. The most promising reaction for future reactors is deuterium–tritium fusion:
²H + ³H → ⁴He + ¹n + 17.6 MeV
核聚变是将轻核（如氢的同位素）结合成较重的核。未来反应堆最有前景的反应是氘‑氚聚变：
²H + ³H → ⁴He + ¹n + 17.6 MeV
Fusion releases even more energy per unit mass than fission, with virtually unlimited fuel from seawater and lithium. However, the nuclei must overcome the Coulomb barrier, requiring temperatures above 100 million K to create a plasma. Magnetic confinement (tokamaks) and inertial confinement are being researched, but a sustained net energy gain has only recently been demonstrated in experimental settings.
聚变单位质量释放的能量比裂变更大，且燃料几乎无限，来自海水和锂。但是，核子必须克服库仑势垒，需要超过1亿K的温度才能产生等离子体。磁约束（托卡马克）和惯性约束正在研究中，但持续净能量增益仅在实验环境中最近才得以证明。
If commercialised, fusion would produce no long‑lived radioactive waste and only a modest amount of short‑lived activation products, making it a transformative energy source.
一旦实现商业化，聚变将不会产生长寿命放射性废物，仅产生少量短寿命活化产物，从而成为一种变革性的能源。
5. Solar Power | 太阳能
Solar energy can be harnessed either as heat (solar thermal) or directly as electricity using photovoltaic (PV) cells. A PV cell is a p‑n junction semiconductor: incident photons with energy greater than the band gap create electron–hole pairs, generating a direct current.
太阳能可以通过热利用（太阳能热发电）或直接用光伏（PV）电池转化为电能来获取。PV电池是一种p‑n结半导体：能量大于带隙的入射光子产生电子‑空穴对，从而产生直流电。
The solar constant is approximately 1361 W m⁻² at the top of the atmosphere, but after absorption and scattering, the peak irradiance at Earth’s surface is around 1000 W m⁻². Practical efficiencies of commercial silicon cells are 15–22%, though multi‑junction cells exceed 40% in laboratories.
太阳常数在大气层顶部约为1361 W m⁻²，但经过吸收和散射后，地球表面的峰值辐照度约为1000 W m⁻²。商用硅电池的实际效率为15–22%，尽管多结电池在实验室中已超过40%。
Solar power is intermittent and has a low capacity factor (typically 10–25%), so energy storage or grid backup is essential. Despite this, the levelised cost of solar electricity has fallen dramatically, making it one of the cheapest new generation sources in many regions.
太阳能是间歇性的，容量因子较低（通常10–25%），因此储能或电网备用至关重要。尽管如此，太阳能的平准化电力成本已大幅下降，使其在许多地区成为最便宜的新建电源之一。
6. Hydroelectric Power | 水力发电
ere ρ is the water density, g is gravitational field strength, Q is the volume flow rate, and h is the effective height of the water column.
水力发电将储存在大坝后面的水的重力势能转化为电能。可用功率为P = ρ g Q h，其中ρ为水密度，g为重力场强度，Q为体积流量，h为水柱的有效高度。
Large‑scale hydro can achieve efficiencies above 90%, a capacity factor of 40–60%, and has a very rapid response to demand changes. Pumped‑storage schemes, which pump water to a higher reservoir when electricity is cheap and release it at peak demand, are the most mature form of grid‑scale energy storage.
大型水电可实现90%以上的效率，容量因子为40–60%，并对需求变化响应极快。抽水蓄能方案在电价低时将水抽到高处水库，在高峰需求时释放，是最成熟的大规模储能形式。
However, dam construction can cause significant ecological disruption, displace communities, and, in tropical regions, decaying submerged vegetation can emit methane, partially offsetting the carbon‑neutral status.
然而，大坝建设可能造成严重的生态破坏、社区搬迁，并且在热带地区，腐烂的淹没植被会释放甲烷，部分抵消其碳中和地位。
7. Wind Power | 风能
theoretical fraction of the wind’s kinetic energy that can be captured is 16/27 (about 59% er output of a turbine is P = ½ ρ A v³, where A is the swept area and v is the wind speed.
风力发电机从流动的空气中提取动能。根据贝茨定律，可捕获风动能的最大理论比为16/27（约59%）。风机的功率输出为P = ½ ρ A v³，其中A为扫风面积，v为风速。
Because power scales with the cube of wind speed, a small increase in wind velocity causes a large rise in output. This also makes wind power highly variable; capacity factors typically range from 20% to 40% depending on location. Modern turbines can reach rated capacities of 15 MW and blade lengths exceeding 100 metres.
由于功率与风速的三次方成正比，风速的微小增加会导致输出大幅上升。这也使风能变化很大；容量因子通常在20%到40%之间，具体取决于地点。现代风机额定功率可达15 MW，叶片长度超过100米。
Onshore wind is one of the lowest‑cost electricity sources, while offshore wind benefits from stronger, steadier winds but has higher installation and maintenance costs. Environmental concerns include noise, visual impact, and bird mortality.
陆上风电是成本最低的电源之一，而海上风电得益于更强、更稳定的风，但安装和维护成本较高。环境问题包括噪音、视觉影响和鸟类死亡。
8. Wave and Tidal Power | 波浪能与潮汐能
Wave power harnesses the motion of ocean surface waves, which arises from wind transferring energy to water. The power per unit width of wave crest is proportional to the square of the wave height and the period of the wave. Devices such as oscillating water columns and point absorbers convert this irregular kinetic and potential energy into electricity.
波浪能利用海洋表面波浪的运动，波浪源于风将能量传递给水体。单位波峰宽度的功率与波高的平方和波浪周期成正比。振荡水柱和点吸收器等装置将这种不规则的动能和势能转化为电能。
barrages trap water at high tide and release it through turbines at low tide, much like a low‑ e basin area, h the tidal range, and T the tidal period. Tidal streams, which harness fast‑ te on the same aerodynamic principles as wind turbines but with much higher fluid density.
潮汐能源于月球和太阳的引力。潮汐堰坝在涨潮时截留水体，在退潮时通过水轮机释放，就像低水头水坝。理论功率为P = ½ ρ g A h² / T，其中A为盆地区域面积，h为潮差，T为潮汐周期。潮汐流利用快速流动的水流，其工作原理与风力发电机相同，但流体密度大得多。
Both wave and tidal energy are highly predictable but have high capital costs and challenging marine engineering. Tidal barrages can alter coastal ecosystems significantly.
波浪能和潮汐能都具有高度可预测性，但资本成本高、海洋工程挑战大。潮汐堰坝可能显著改变沿岸生态系统。
9. Geothermal Energy | 地热能
Geothermal energy taps heat from the Earth’s interior, originating from radioactive decay and residual formation heat. In regions with high geothermal gradients, hot water or steam is extracted from deep wells. Dry‑steam and flash‑steam plants use steam directly to turn turbines; binary‑cycle plants transfer heat to a secondary fluid with a lower boiling point.
地热能利用来自地球内部的热量，这些热量源于放射性衰变和残余形成热。在地温梯度高的地区，从深井中提取热水或蒸汽。干蒸汽和闪蒸发电厂直接使用蒸汽驱动汽轮机；双循环发电厂则将热量传递给沸点较低的二次流体。
The power output depends on the mass flow rate and the temperature drop of the geothermal fluid. Typical efficiencies are 10–20%, lower than fossil‑fuel plants because of the relatively low source temperature. However, the capacity factor can exceed 90%, providing reliable baseload electricity.
功率输出取决于地热流体的质量流量和温降。典型效率为10–20%，低于化石燃料电厂，因为热源温度相对较低。然而，容量因子可超过90%，提供可靠的基荷电力。
Enhanced geothermal systems (EGS) aim to extend potential by fracturing hot dry rock, but induced seismicity is a concern. Direct uses of geothermal heat include district heating, greenhouses, and industrial processes.
增强型地热系统（EGS）旨在通过压裂干热岩扩大潜力，但诱发地震活动备受关注。地热直接利用包括区域供暖、温室和工业过程。
10. Biomass | 生物质能
Biomass is organic material—wood, crop residues, algae, organic waste—that stores solar energy via photosynthesis. It can be burned directly for heat and power, or converted into biofuels such as ethanol (fermentation) and biodiesel (transesterification). In a combustion plant, the carbon released was recently captured from the atmosphere, so biomass is considered carbon‑neutral in principle, provided replanting occurs.
生物质是通过光合作用储存太阳能的有机物质——木材、作物残余物、藻类、有机废弃物。它可以直接燃烧用于供热和发电，或转化为生物燃料，如乙醇（发酵）和生物柴油（酯交换）。在燃烧装置中，释放的碳是近期从大气中捕获的，因此只要有再种植，生物质原则上被视为碳中和。
The specific energy of dry wood is about 15–20 MJ kg⁻¹, lower than coal, and its energy density per volume is poor, making transport costly. Biogas, rich in methane, can be produced by anaerobic digestion of waste, offering a flexible fuel for heating, electricity, or transport.
干木材的比能量约为15–20 MJ kg⁻¹，低于煤，其单位体积能量密度较低，导致运输成本高。通过废弃物的厌氧消化可产生富含甲烷的沼气，为供暖、发电或交通提供一种灵活的燃料。
Large‑scale biomass energy raises concerns over land‑use change, food‑versus‑fuel competition, and real net carbon savings, which must be analysed through full life‑cycle assessment.
大规模生物质能源引发了对土地利用变化、粮食与燃料之争以及真实净碳节约的关切，这些必须通过全生命周期评估来分析。
11. Energy Density and Specific Energy | 能量密度与比能量
Specific energy is the energy liberated per unit mass of fuel (J kg⁻¹); energy density is the energy per unit volume (J m⁻³). These quantities determine the size and mass of fuel storage for transportation and the practical viability of a fuel. Hydrogen has an extraordinarily high specific energy (142 MJ kg⁻¹) but a very low energy density as a gas, necessitating compression or liquefaction.
比能量是单位质量燃料释放的能量（J kg⁻¹）；能量密度是单位体积的能量（J m⁻³）。这些量决定了交通领域燃料存储的尺寸和质量，以及燃料的实用可行性。氢的比能量极高（142 MJ kg⁻¹），但作为气体时能量密度很低，必须压缩或液化。
For comparison:
| Fuel | Specific energy (MJ kg⁻¹) | Energy density (MJ L⁻¹) |
|---|---|---|
| Uranium‑235 (fission) | ~80 000 000 | ~1.5 × 10⁹ |
| Hydrogen (gaseous, 700 bar) | 142 | ~4.7 |
| Natural gas | ~55 | ~0.036 (gas) |
| Diesel | ~42 | ~36 |
| Lithium‑ion battery | ~0.5–1.0 | ~1.5–2.5 |
对比：
| 燃料 | 比能量 (MJ kg⁻¹) | 能量密度 (MJ L⁻¹) |
|---|---|---|
| 铀‑235（裂变） | ~80 000 000 | ~1.5 × 10⁹ |
| 氢（气态，700 bar） | 142 | ~4.7 |
| 天然气 | ~55 | ~0.036（气体） |
| 柴油 | ~42 | ~36 |
| 锂离子电池 | ~0.5–1.0 | ~1.5–2.5 |
Nuclear fuels have by far the highest specific energy, which is why they are attractive for baseload electricity and naval propulsion. The low specific energy of batteries explains the difficulty of electrifying long‑haul aviation.
核燃料的比能量遥遥领先，这就是它们对基荷电力和海军推进具有吸引力的原因。电池的低比能量解释了长途航空电气化的困难。
12. Sankey Diagrams and Efficiency | 桑基图与效率
A Sankey diagram is a flow diagram where the width of the arrows is proportional to the quantity of energy. It makes energy losses immediately visible. For any energy converter, the efficiency η is:
η = useful power output / total power input
桑基图是一种流量图，其箭头的宽度与能量数量成正比。它使能量损失一目了然。对于任何能量转换器，效率η为：
η = 有用功率输出 / 总功率输入
In a thermal power station, the largest arrow is usually the waste heat rejected to the environment (e.g., via cooling towers or a river). A combined heat and power (CHP) plant achieves higher overall efficiency by using that waste heat for district heating, raising the total useful output to 80% or more.
在火力发电站中，最大的箭头通常是排向环境（例如通过冷却塔或河流）的废热。热电联产（CHP）工厂通过将废热用于区域供暖，提高了总效率，使总有用输出达到80%或更高。
Sankey diagrams can be drawn for national energy systems, showing primary energy inputs, conversion losses, and the final energy delivered to transport, industry, domestic, and other sectors. They are a powerful tool for identifying where efficiency improvements can make the largest impact.
桑基图可用于国家能源系统，显示一次能源输入、转换损耗以及输送到交通、工业、家庭等部门的最终能源。它们是确定效率改进可在何处产生最大影响的有力工具。
In the context of renewable energy, the ‘efficiency’ of a wind turbine is often reported as its capacity factor or the power coefficient, while for a solar cell it is the ratio of electrical power output to the incident solar power. All such metrics are vital for comparing the technical performance of different technologies.
在可再生能源领域，风力发电机的“效率”通常以其容量因子或功率系数来表述，而太阳能电池则是其电功率输出与入射太阳能功率之比。所有这些指标对于比较不同技术的技术性能至关重要。
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