📚 1. Energy Sources | 1. 能源
Energy is the capacity to do work, and the choices we make about energy sources shape our environment, economies, and everyday lives. In this article, we explore the major primary energy sources, their physical principles, conversion efficiencies, and environmental implications, as required by the IB Physics syllabus.
能量是做功的能力，我们对能源的选择塑造了环境、经济和日常生活。本文依据IB物理课程要求，探讨主要的一次能源，涵盖其物理原理、转换效率和环境影响。
1. Introduction to Energy Sources | 能源介绍
A primary energy source is any naturally occurring form of energy that has not been subjected to any conversion or transformation process. Examples include sunlight, wind, fossil fuels, and nuclear fuels. The energy chain from primary source to end use often involves several conversion steps, and each step introduces efficiency losses that can be analysed using the concept of energy degradation.
一次能源指未经任何转换或转化过程的天然能量形式，例如阳光、风、化石燃料和核燃料。从一次能源到最终使用，能量链往往经过多个转换步骤，每步都带来效率损失，可用能量退降的概念进行分析。
The total power available from a source is often described by its energy density (energy per unit volume) or specific energy (energy per unit mass). These quantities allow quantitative comparison of different fuels and storage systems, and they are central to transport and stationary power applications.
描述一种能源的总可利用能时，常使用能量密度（单位体积的能量）或比能（单位质量的能量）。这些物理量便于定量比较不同燃料和储能系统，在交通和固定发电应用中至关重要。
2. Fossil Fuels | 化石燃料
Fossil fuels — coal, oil, and natural gas — be written using Unicode symbols: CₙH₂ₙ₊₂ + excess O₂ → nCO₂ + (n+1)H₂O + thermal energy.
化石燃料——煤、石油和天然气——由埋藏有机质经过数百万年的厌氧分解形成。它们将化学势能储存在碳氢键中，通过燃烧释放。典型烃类燃烧反应可用Unicode符号表示为：CₙH₂ₙ₊₂ + 过量 O₂ → nCO₂ + (n+1)H₂O + 热能。
The energy released per unit mass varies: coal about 24 MJ kg⁻¹, oil around 42 MJ kg⁻¹, and natural gas about 55 MJ kg⁻¹. In combined-cycle gas turbines, efficiencies can reach 60 %, but the overall life-cycle efficiency must account for extraction, transport, and pollution control.
单位质量释放的能量各不相同：煤约 24 MJ kg⁻¹，石油约 42 MJ kg⁻¹，天然气约 55 MJ kg⁻¹。在联合循环燃气轮机中，效率可达 60 %，但全生命周期效率还需考虑开采、运输和污染控制。
Burning fossil fuels releases greenhouse gases, especially CO₂, and particulates. The enhanced greenhouse effect links the increased atmospheric concentration of CO₂ to global temperature rise, an important topic in climate physics.
燃烧化石燃料释放温室气体，尤其是 CO₂ 和颗粒物。增强温室效应将大气 CO₂ 浓度升高与全球升温联系起来，是气候物理学的重要课题。
3. Nuclear Energy | 核能
nergy is released through nuclear fission or fusion. In a typical fission reactor, uranium‑ d per kilogram of uranium fuel is of the order 80 TJ kg⁻¹, vastly exceeding chemical fuels.
核能通过核裂变或核聚变释放。在典型裂变反应堆中，铀‑235 原子核吸收一个慢中子后分裂成较小的碎片，每次裂变释放约 200 MeV。质量亏损 Δm 按 E = mc² 转换为能量，每千克铀燃料释放的能量约为 80 TJ kg⁻¹，远超化学燃料。
The reactor core converts nuclear energy to thermal energy, which is transferred to a coolant and then to a steam turbine. The overall efficiency is usually 30–35 %. Safety concerns centre on meltdown risk, radioactive waste containment, and proliferation, while physics discussions often focus on the decay chains and half‑lives of fission products.
反应堆堆芯将核能转化为热能，传递给冷却剂，再驱动蒸汽轮机，总效率一般 30–35 %。安全问题集中在熔毁风险、放射性废物隔离和核扩散上，而物理讨论常涉及裂变产物的衰变链和半衰期。
fic energy with fuels like deuterium and tritium, but achieving the required temperature (∼ ion D + T → ⁴He + n + 17.6 MeV is the most accessible, discussed widely in plasma physics.
核聚变使用氘和氚等燃料，有更高的比能潜力，但实现所需温度（∼10⁸ K）和约束仍是巨大挑战。最易实现的反应 D + T → ⁴He + n + 17.6 MeV，在等离子体物理中广泛讨论。
4. Solar Energy | 太阳能
of about 3.85 × 10²⁶ W, and the solar constant (the power per unit area arriving at Earth' this is reduced to roughly 1000 W m⁻² under clear skies due to absorption and scattering.
太阳以约 3.85 × 10²⁶ W 的功率辐射能量，太阳常数（到达地球大气层上界的单位面积功率）约为 1361 W m⁻²。由于吸收和散射，晴朗天气下地表接收的功率降至约 1000 W m⁻²。
ower output) / (incident solar power). Monocrystalline silicon panels typically achieve 18–22 % efficiency, while multi‑junction cells can exceed 40 % in laboratory conditions.
光伏电池通过光电效应直接将太阳光转换为电能。光伏板效率 η 定义为 η =（最大电功率输出）/（入射太阳功率）。单晶硅板效率通常为 18–22 %，多结电池在实验室可达 40 % 以上。
where I is insolation and A is collector area. These systems can incorporate thermal storage, smoothing output variability.
太阳能热系统用镜子聚光加热流体，驱动涡轮机。单位面积收集的功率 P = I × A × ηₒₚₜ，其中 I 为日照强度，A 为集光面积。这些系统可结合储热，平滑出力波动。
5. Wind Energy | 风能
ng air. The power available in the wind is given by P = ½ ρ A v³, where ρ is air density (∼ v is the wind speed. The cubic dependence on v explains why site selection focuses on high‑wind locations.
风力机从流动的空气中提取动能。风能功率为 P = ½ ρ A v³，其中 ρ 为空气密度（海平面约 1.2 kg m⁻³），A 为风轮扫掠面积，v 为风速。功率对风速的三次方依赖解释了为什么选址集中于高风速地区。
According to Betz's law, the maximum theoretical efficiency of a wind turbine is 59.3 %. Modern horizontal‑axis turbines achieve power coefficients Cp of 0.40–0.50. The electrical output also depends on the generator and gearbox efficiencies, with overall plant efficiency around 35–45 %.
根据贝茨定律，风力机的最大理论效率为 59.3 %。现代水平轴风力机的功率系数 Cp 为 0.40–0.50。电输出还取决于发电机和齿轮箱效率，电站总效率约 35–45 %。
Wind energy is variable and intermittent; capacity factors typically range from 20–40 %. Integration into national grids requires energy storage or complementary sources to maintain supply reliability.
风能具有可变性和间歇性，容量因子通常为 20–40 %。接入国家电网需要储能或互补电源以维持供电可靠性。
6. Hydroelectric Power | 水力发电
0 kg m⁻³), g is 9.81 m s⁻², Q is the volume flow rate (m³ s⁻¹), and h is the effective head. Real efficiencies η often exceed 85 % for large turbines.
水力发电利用储存在高处水的重力势能。可用功率 P = η ρ g Q h，其中 ρ 为水密度（1000 kg m⁻³），g = 9.81 m s⁻²，Q 为体积流量（m³ s⁻¹），h 为有效水头。大型水轮机实际效率常超过 85 %。
Run‑of‑river schemes generate electricity without large reservoirs, reducing ecological disruption, but their power output fluctuates with seasonal river flow. Pumped‑storage systems smooth supply by pumping water uphill during low demand and releasing it during peak demand, acting as giant gravitational batteries.
径流式水电站无需大型水库即可发电，减少生态干扰，但其出力随季节性径流波动。抽水蓄能系统在低谷时抽水至高处，高峰时释放，充当巨大的重力电池来平滑供应。
7. Biomass and Biofuels | 生物质能与生物燃料
Biomass is organic material derived from recently living organisms, used as a renewable source of chemical energy. When burned directly, wood, crop residues, or biogas release thermal energy, with a typical specific energy of 15–20 MJ kg⁻¹ for dry wood. Because plants absorb CO₂ during growth, biomass can be carbon‑neutral if regrowth matches consumption.
生物质是来自近期活体生物的有机材料，可作为化学能的可再生来源。直接燃烧时，木材、作物残余物或沼气释放热能，干木比能一般为 15–20 MJ kg⁻¹。由于植物在生长时吸收 CO₂，若再生速度与消耗相匹配，生物质可实现碳中和。
Biofuels such as ethanol and biodiesel are produced by fermentation or transesterification. In IB Physics, one may calculate the energy output from a given mass of fuel and compare it with fossil alternatives. The overall energy balance must account for energy inputs in cultivation, fertilisers, and processing — the energy return on investment (EROI) is often modest.
乙醇和生物柴油等生物燃料通过发酵或酯交换生产。在IB物理中，可以计算给定质量燃料的能量输出，并与化石替代品进行比较。整体能量平衡需要考虑种植、化肥和加工中的能量投入——能量投资回报率（EROI）往往不高。
8. Geothermal Energy | 地热能
Geothermal energy taps the thermal energy stored in the Earth's crust. The temperature gradient is typically 25–30 °C per kilometre of depth in non‑volcanic regions; in geothermal hotspots, it is steeper. Wells extract steam or hot water to drive turbines directly or via a heat exchanger.
地热能利用地壳中储存的热能。非火山区地温梯度一般为每公里深度 25–30 °C；地热热点梯度更陡。钻井提取蒸汽或热水直接或通过换热器驱动涡轮机。
The steady thermal flux from the Earth's interior is about 0.06 W m⁻² on average, so a geothermal plant must concentrate energy over a large area. Enhanced geothermal systems (EGS) inject water into deep, hot, fractured rock to create artificial reservoirs, expanding potential sites.
地球内部稳定的热流平均约为 0.06 W m⁻²，因此地热电厂需要在很大面积上集中能量。增强型地热系统（EGS）将水注入深层高温裂隙岩石中形成人工热储，扩大了潜在选址范围。
9. Tidal and Wave Energy | 潮汐能与波浪能
is the tidal range and T is the tidal period. The La Rance plant in France has a capacity of 240 MW.
潮汐拦河坝利用由月亮和太阳引起的海面涨落的引力势能。面积为 A 的潮汐盆地理论功率为 P ≈ ½ ρ g A R² / T，其中 R 为潮差，T 为潮汐周期。法国朗斯电站装机容量 240 MW。
ve can be estimated by P = ½ ρ g a² v, where a is wave amplitude and v is wave speed. Real‑world devices show lower efficiencies due to energy spreading and mechanical losses.
波浪能转换装置从表层波浪中提取动能和势能。单位波峰长度的波功率可估算为 P = ½ ρ g a² v，其中 a 为波幅，v 为波速。实际装置的效率较低，因为能量扩散和机械损失。
10. Energy Density and Specific Energy | 能量密度与比能
Energy density is the energy stored per unit volume (J m⁻³), while specific energy is the energy per unit mass (J kg⁻¹). These parameters are critical for mobile applications. For example, lithium‑ion batteries have a specific energy of about 0.5–0.7 MJ kg⁻¹, kerosene about 43 MJ kg⁻¹, and uranium‑235 about 80,000,000 MJ kg⁻¹.
能量密度是单位体积储存的能量（J m⁻³），比能是单位质量的能量（J kg⁻¹）。这些参数对移动应用至关重要。例如，锂离子电池比能约为 0.5–0.7 MJ kg⁻¹，煤油约 43 MJ kg⁻¹，铀‑235 约 80,000,000 MJ kg⁻¹。
journey given the vehicle efficiency and distance, using energy = specific energy × mass.
IB物理数据手册中通常会给出这些数值。学生应能根据车辆效率和距离，利用能量 = 比能 × 质量，计算旅程所需燃料质量。
11. Environmental Impact and Sustainability | 环境影响与可持续性
Energy choices involve trade‑offs between power density, carbon footprint, land use, and waste. The levelized cost of energy (LCOE) combines capital, operation, and fuel costs, but does not always include externalities such as air pollution damage or climate impacts. A full life‑cycle assessment (LCA) accounts for greenhouse gas emissions per kWh, and shows that renewables like wind and nuclear have very low operational emissions compared to coal.
能源选择需要权衡功率密度、碳足迹、土地使用和废物。平准化能源成本（LCOE）综合了资本、运维和燃料成本，但并不总能涵盖空气污染损害或气候影响等外部因素。全生命周期评估（LCA）考虑每千瓦时的温室气体排放，表明风能、核能等可再生源运行排放远低于煤电。
The concept of renewability is linked to the timescale of resource regeneration. Fossil fuels are non‑renewable on human timescales; solar, wind, tidal, and biomass are considered renewable provided the rate of use does not exceed the rate of replenishment. Sustainability also depends on material availability for energy technologies, such as rare earth elements for wind turbine magnets.
可再生性与资源再生时间尺度有关。化石燃料在人类时间尺度上不可再生；太阳能、风能、潮汐能和生物质能在使用速率不超过再生速率时视为可再生。可持续性还取决于能源技术的材料可获得性，例如风力机磁体的稀土元素。
12. Comparison of Energy Sources | 能源比较
A useful framework for comparison includes power density, intermittency, carbon intensity, and scalability. The following table summarises representative values.
能源比较的有用框架包括功率密度、间歇性、碳强度和可扩展性。下表总结了一些有代表性的数值。
| Source | Specific Energy (MJ kg⁻¹) | Carbon Intensity (g CO₂e/kWh) | Intermittent? |
|---|---|---|---|
| Coal | 24 | 820 | No |
| Natural Gas | 55 | 490 | No |
| Uranium (fission) | 80,000,000 | 12 | No |
| Solar PV | — | 48 | Yes |
| Wind | — | 12 | Yes |
| Hydro | — | 24 | Somewhat |
No single energy source is ideal: decarbonisation strategies require a mix of low‑carbon sources, storage solutions, and demand‑side management to maintain grid stability and meet climate targets.
没有单一能源是十全十美的：脱碳策略需要组合各种低碳电源、储能方案和需求侧管理，以维持电网稳定并实现气候目标。
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