📚 Year 10 CAIE Engineering: A Case Study in Structural Design for a Solar Charging Canopy | Year 10 CAIE 工程：太阳能充电棚结构设计案例分析
Engineering is not just about knowing theories; it is about applying them to solve real-world problems. This case study walks you through the systematic design of a small-scale solar charging canopy intended for a school courtyard. By examining each stage—from identifying the need to final testing—you will see how engineering principles guide every decision, ensuring the final structure is safe, functional, and sustainable.
工程学不仅是了解理论，更是将理论应用于解决实际问题。本篇案例分析将带领你系统地设计一座用于学校庭院的小型太阳能充电棚。通过研究从需求识别到最终测试的每一个阶段，你将看到工程原理如何指导每一项决策，确保最终结构安全、实用且可持续。
1. Identifying the Need | 识别需求
Our school has a high usage of mobile devices among students, yet there are limited outdoor charging points. The school council noticed that students often gather near the canteen wall sockets, causing congestion and potential trip hazards. A survey confirmed that 78% of students would use a sheltered outdoor charging station if available, especially during break times. Furthermore, the school is committed to reducing its carbon footprint and aims to showcase renewable energy to students.
我们学校的学生大量使用移动设备，但户外充电点非常有限。学生会发现，学生经常聚集在食堂墙壁插座附近，造成拥挤和潜在的绊倒风险。一项调查证实，如果有带遮蔽的户外充电站，78% 的学生会使用，特别是在休息时间。此外，学校致力于减少碳足迹，并希望向学生展示可再生能源。
The engineering challenge was therefore defined: design a weather-resistant, self-contained structure that harvests solar energy to charge up to 10 USB devices simultaneously, without relying on mains electricity. The structure must be safe for public use, visually blend into the school environment, and withstand local wind and rain conditions.
因此，工程挑战被定义为：设计一个耐候的、自给自足的结构，利用太阳能同时为多达10个 USB 设备充电，且不依赖市电。该结构必须对公众使用安全，与校园环境视觉融合，并能承受当地的风雨条件。
2. Design Brief and Specifications | 设计简报与规格
Before sketching any ideas, a clear design brief was written to focus the team. The core objective was to create a 'Solar Charging Canopy' providing sheltered seating with integrated photovoltaic panels. Key specifications derived from stakeholder discussions and site analysis included: capacity for 10 USB charging ports (5V, 2A each), a roof area of at least 4 m² to house the panels, a frame height of 2.5 m to allow standing, and a projected lifespan of 10 years with minimal maintenance.
在草拟任何想法之前，我们编写了一份清晰的设计简报以聚焦团队。核心目标是创建一个“太阳能充电棚”，提供带遮蔽的座位并集成光伏板。根据利益相关者讨论和场地分析得出的关键规格包括：10 个 USB 充电端口（5V, 2A每个）的容量，至少 4 平方米的屋顶面积以容纳太阳能板，2.5 米的框架高度以便站立，以及最少维护下10年的预期寿命。
Environmental conditions were also quantified: the site is exposed to wind speeds up to 28 m/s in storms, and annual rainfall is approximately 650 mm. The design must comply with the school’s safety policy, meaning no sharp edges, all electrical components must be IP65 rated, and the structure must have a safety factor of 1.5 against overturning.
环境条件也被量化：场地暴露于风暴时风速可达28 m/s，年降雨量约650 mm。设计必须符合学校的安全政策，这意味着没有锋利边缘，所有电气组件达到 IP65 防护等级，并且结构对抗倾覆的安全系数为1.5。
3. Conceptual Design Options | 概念设计方案
Three initial concepts were generated using design thinking techniques. Concept A was a single central pillar supporting a cantilevered canopy—lightweight but possibly unstable in high wind. Concept B was a four-legged pergola style with a pitched roof, offering excellent stability but requiring more ground space. Concept C was a dual A-frame structure with a tensioned fabric roof, which was aesthetically appealing but complex to waterproof around solar panels.
通过设计思维技巧，我们产生了三个初始概念。概念 A 是一根中央立柱支撑悬臂式顶棚——轻便但在强风中可能不稳定。概念 B 是四柱凉棚式，带有斜屋顶，提供优良的稳定性但需要更多地面空间。概念 C 是双 A 型框架配张拉膜屋顶，外观富有美感，但太阳能板周围的防水处理复杂。
A decision matrix was used to score concepts against the design criteria (safety, cost, ease of manufacture, aesthetics, and durability). Concept B scored highest due to its inherent rigidity and straightforward construction. The pitched roof also aids water runoff and allows optimal south-facing panel orientation for our latitude (31° N).
我们使用决策矩阵，根据设计标准（安全性、成本、制造简易性、美观性和耐久性）对各概念评分。概念 B 因其固有的刚性和简单的构造得分最高。斜屋顶还有助于雨水径流，并使得太阳能板能够按我们所在纬度（北纬31°）最佳朝南布置。
4. Detailed Design and Material Selection | 详细设计与材料选择
ncrete footings. Cross-bracing with 50 × 50 mm SHS provides lateral stiffness. The roof truss is fabricated from 40 × 40 mm aluminium angles to minimise weight while supporting the glass solar panels.
选定的概念被发展成一个详细的 CAD 模型。框架由四根 80 × 80 mm 方形空心型钢（SHS）立柱组成，锚固在混凝土基础上。利用 50 × 50 mm SHS 的交叉撑提供侧向刚度。屋顶桁架由 40 × 40 mm 铝角材制成，以在支撑玻璃太阳能板的同时减轻重量。
Material choices were driven by function and environment. Hot-dip galvanised steel was chosen for the legs and bracing to resist corrosion over the 10-year lifespan. Aluminium 6063-T6 was selected for the roof frame for its high strength-to-weight ratio and natural corrosion resistance. The solar panels are standard 300 W monocrystalline glass-faced panels, chosen for efficiency and durability. Polycarbonate sheeting was added on the north-facing side as a windbreak and to provide additional shelter.
材料选择根据功能与环境决定。立柱和撑杆选用热浸镀锌钢，以在10年寿命期内耐腐蚀。屋顶框架选用 6063-T6 铝材，因其高强度重量比和天然的耐腐蚀性。太阳能板采用标准的 300 W 单晶玻璃面板，因效率和耐久性入选。北侧添加了聚碳酸酯板作为挡风并增加遮蔽。
5. Structural Analysis: Gravitational Loads | 结构分析：重力荷载
nels (4 × 22.5 kg = 90 kg), polycarbonate sheeting (12 kg), and miscellaneous fixings (8 kg), giving a total dead load of 155 kg. A uniformly distributed load of 0.25 kN/m² was assumed across the roof area of 4.8 m².
工程师必须确保结构能安全承载所有预期荷载。首先计算恒载：屋顶铝框架（45 kg）、玻璃面板（4 × 22.5 kg = 90 kg）、聚碳酸酯板（12 kg）以及杂项连接件（8 kg），总恒载为 155 kg。假设屋顶面积 4.8 m² 上作用均布荷载 0.25 kN/m²。
um bending moment on a simply supported beam model of a single roof truss was found using M = wL²/8. For a truss span of 2.4 m under factored load of 0.95 kN/m, M = 0.95 × (2.4)² / 8 = 0.684 kN·m. The aluminium angle section modulus Z = 4.76 cm³ was checked, giving a bending stress σ = M/Z = (0.684 × 10⁶) / (4.76 × 10³) ≈ 143.7 N/mm². This was below the allowable stress of 160 N/mm² for 6063-T6, satisfying the factor of safety.
活荷载包括维护人员（单点 1 kN）和保守的雪荷载 0.5 kN/m² 以应对偶发事件。基于单榀屋顶桁架的简支梁模型，最大弯矩用 M = wL²/8 计算。跨度 2.4 m，在 0.95 kN/m 的系数设计荷载下，M = 0.95 × (2.4)² / 8 = 0.684 kN·m。检查铝角材的截面模量 Z = 4.76 cm³，得出弯曲应力 σ = M/Z = (0.684 × 10⁶) / (4.76 × 10³) ≈ 143.7 N/mm²。该值低于 6063-T6 的许用应力 160 N/mm²，满足安全系数。
6. Structural Analysis: Wind Load and Stability | 结构分析：风荷载与稳定性
. Thus q = 0.613 × (28)² = 0.613 × 784 ≈ 480.6 Pa. Considering pressure coefficients for a mono-pitch roof (+0.8 on windward face, -0.5 on leeward), the net pressure coefficient was 1.3. The design wind force on the roof surface of area 4.8 m² was F = q × Cnet × Area = 480.6 × 1.3 × 4.8 ≈ 3000 N (3 kN).
风荷载往往是轻质屋顶结构的控制因素。基本风压 q 由 q = 0.613 × V² 计算，V = 28 m/s（3秒阵风）。因此 q = 0.613 × (28)² = 0.613 × 784 ≈ 480.6 Pa。考虑到单坡屋顶的压力系数（迎风面 +0.8，背风面 -0.5），净压力系数为 1.3。作用于 4.8 m² 屋顶面的设计风力为 F = q × Cnet × Area = 480.6 × 1.3 × 4.8 ≈ 3000 N（3 kN）。
This horizontal force creates an overturning moment about the leeward base. Overturning moment Mot 3 m³ × 24 kN/m³ = 7.2 kN per footing, total 4 footings = 28.8 kN) was calculated. Total weight = 1.52 + 28.8 = 30.32 kN. Restoring moment Mres = 30.32 × (2.4/2) = 30.32 × 1.2 = 36.38 kN·m. The factor of safety against overturning = Mres / Mot = 36.38 / 7.5 ≈ 4.85, well above the required 1.5.
该水平力对背风侧基础产生倾覆力矩。倾覆力矩 Mot = F × H = 3 kN × 2.5 m = 7.5 kN·m。抵抗倾覆的恢复力矩来自结构自重（恒载 = 155 kg ≈ 1.52 kN）加混凝土基础重量（每个 0.3 m³ × 24 kN/m³ = 7.2 kN 每基础，共4个基础 = 28.8 kN）。计算得总重 = 1.52 + 28.8 = 30.32 kN。恢复力矩 Mres = 总重 × (基底宽度/2) = 30.32 × (2.4/2) = 30.32 × 1.2 = 36.38 kN·m。抗倾覆安全系数 = Mres / Mot = 36.38 / 7.5 ≈ 4.85，远高于要求的 1.5。
7. Manufacturing Process | 制造工艺
Once the design was verified, a production plan was drawn up. Steel legs and bracing were cut to length using a cold saw and then drilled for bolt connections using a pillar drill and jig to ensure accuracy. All steel components were sent for hot-dip galvanising to a minimum coating thickness of 85 microns. Meanwhile, the aluminium roof frame was TIG welded in segments, then bolted together on site to allow transport.
设计验证通过后，便制定了生产计划。钢立柱和撑杆用冷锯按尺寸切割，然后使用台钻和夹具钻孔以螺栓连接，确保精度。所有钢构件送去热浸镀锌，最小镀层厚度 85 微米。同时，铝屋顶框架分段进行 TIG 焊接，然后现场栓接以便运输。
pection of weld penetration using dye penetrant testing, and galvanising thickness measurement with a coating gauge. Each USB charging module was pre-assembled in a workshop, integrating the voltage regulator, fuses, and connectors inside an IP65 enclosure.
质量控制检查包括依据 CAD 图纸进行尺寸验证，公差 ±1 mm，使用染料渗透探伤检查焊缝熔深，以及用涂层测厚仪测量镀锌厚度。每个 USB 充电模块在车间预组装，将电压调节器、保险丝和连接器集成在 IP65 外壳内。
8. Assembly and Installation | 装配与安装
Assembly began with concrete footing excavation. Four holes 0.6 m deep were dug, and formwork was placed. Each footing was reinforced with a steel cage, and M20 anchor bolts were cast in situ. After 7 days of curing, the steel legs were erected and temporarily braced. The cross-bracing was then bolted into place, and the aluminium roof frame was lifted and secured. Care was taken to align the frame with true south using a compass and inclinometer to achieve a 15° pitch.
装配从挖掘混凝土基础开始。挖了四个 0.6 m 深的坑，放置模板。每个基础用钢筋笼加固，并预埋了 M20 地脚螺栓。养护7天后，竖起钢立柱并加临时支撑。随后交叉撑被栓接到位，铝屋顶框架吊装并固定。使用指南针和倾角仪仔细将框架对准正南，实现 15° 倾角。
Solar panels were mounted using aluminium rails and clamps, with each panel’s junction box connected to a central combiner box. The batteries (two 12V 100Ah sealed lead-acid) were installed in a ventilated steel cabinet at the base. All wiring was run through flexible conduits and secured with UV-resistant cable ties. A final safety check verified earthing resistance was below 10 ohms.
太阳能板用铝轨道和夹具安装，每个面板的接线盒连接到中央汇流箱。蓄电池（两个 12V 100Ah 密封铅酸）安装于基座处的通风钢柜内。所有线缆穿过柔性导管，并用抗紫外线扎带固定。最后的安全检查确认接地电阻低于 10 欧姆。
9. Testing and Evaluation | 测试与评估
ere distributed across the roof for 24 hours, and no permanent deflection was observed. The USB output was measured under full artificial load (10 devices drawing 2A each), and the solar charge controller maintained a stable 5.0 V ± 0.2 V.
安装完毕后，系统经历了一系列测试。通过施加静载测试结构完整性：将总重 200 kg 的沙袋均匀分布在屋顶上持续24小时，没有观察到永久变形。在满人工负载（10个设备各抽取 2A）下测量 USB 输出，太阳能充电控制器保持稳定的 5.0 V ± 0.2 V。
User feedback was collected via a simple questionnaire. 92% of students found the canopy comfortable and visually appealing. However, a few noted that the seating area became too warm in direct midday sun, suggesting the addition of an awning. The energy audit showed that on an average sunny day, the 1200 Wp system generated 4.8 kWh, enough to fully charge over 100 smartphones.
通过简单的问卷收集了用户反馈。92% 的学生认为充电棚舒适且美观。然而，少数学生指出在正午直射下座位区过热，建议增加遮阳篷。能源审计显示，在普通晴天，1200 Wp 的系统发电 4.8 kWh，足够为超过 100 部智能手机充满电。
10. Sustainability and Cost Analysis | 可持续性与成本分析
The total project cost was £2,850, broken down as follows: materials (steel, aluminium, panels, electronics) £1,920; galvanising and welding services £410; concrete and fixings £180; and contingency £340. Compared to hiring commercial charging stations for 3 years, the payback period is approximately 2.5 years, after which the school saves on electricity and rental costs.
项目总成本为 2850 英镑，细分为：材料（钢材、铝材、面板、电子器件）1920 英镑；镀锌和焊接服务 410 英镑；混凝土和紧固件 180 英镑；应急储备 340 英镑。与租用商用充电站 3 年相比，投资回收期约为 2.5 年，之后学校可节省电费和租赁费。
From an environmental standpoint, the structure avoids an estimated 320 kg of CO₂ emissions annually by replacing grid electricity. The steel and aluminium are fully recyclable at end-of-life. To further enhance sustainability, the design incorporated a green roof option on the north side, using sedum plants to reduce heat island effect and improve biodiversity.
从环境角度看，该结构通过替代市电，每年可避免约 320 kg 二氧化碳排放。钢材和铝材在使用寿命终止时可完全回收。为进一步增强可持续性，设计在北侧引入了绿色屋顶选项，利用景天植物减少热岛效应并提升生物多样性。
11. Lessons Learned and Future Improvements | 经验教训与未来改进
Several valuable lessons emerged from this project. The initial design underestimated the time required for foundation curing and bolt alignment, delaying the project by 4 days. Communication between the electrical and structural teams could have been improved, as the cable routing originally clashed with a cross-brace. This highlighted the importance of regular interdisciplinary design reviews.
该项目总结出若干宝贵经验。最初设计低估了基础养护和螺栓对位所需的时间，导致项目延期 4 天。电气团队和结构团队之间的沟通本可改进，因为最初的电缆走向与一根交叉撑发生冲突。这突显了定期跨专业设计评审的重要性。
Future iterations will replace lead-acid batteries with lithium iron phosphate (LiFePO₄) for longer life and higher energy density. A smartphone app for monitoring energy production and consumption in real time is also planned, adding an educational dimension. Finally, we are exploring a parametric design tool to quickly optimise roof pitch and panel layout for different school sites.
未来的迭代将用磷酸铁锂电池 (LiFePO₄) 取代铅酸电池，以获得更长寿命和更高能量密度。我们还计划开发一款智能手机应用，用于实时监测能源生产与消耗，增加教育维度。最后，我们正探索一种参数化设计工具，可针对不同校址快速优化屋顶倾角和面板布局。
Published by TutorHao | Engineering Revision Series | aleveler.com
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