Renewable energy Study Guide

📖 Core Concepts Renewable Energy – Energy from naturally replenished resources (solar, wind, hydro, bioenergy, geothermal). Variable vs Controllable – Variable (solar, wind) fluctuate with weather; controllable (dammed hydro, bioenergy, geothermal) can be dispatched on demand. Levelized Cost of Energy (LCOE) – Net‑present‑cost of electricity over a plant’s life; lower LCOE ⇒ more competitive. Technical Potential – Maximum electricity that could be generated if a resource were fully exploited (e.g., solar PV ≈ 5,800 PWh yr⁻¹). Intermittency – Mismatch between variable generation and demand; managed with storage, diversification, sector coupling. Net‑Zero Goal – IEA: ≈ 90 % of global electricity must be renewable by 2050 to hit net‑zero emissions. 📌 Must Remember Global Renewable Share 2024 – > 30 % of electricity; projected > 45 % by 2030. Solar PV Cost Trend – Swanson’s Law: ≈ 20 % cost drop every capacity doubling. LCOE ≈ $0.03 /kWh (2023). Wind Power Scaling – Output ∝ cube of wind speed; offshore wind speeds 90 % higher than on‑shore. LCOE ≈ $0.04 /kWh (on‑shore, 2023). Storage Dominance – Pumped‑hydro ≈ 85 % of grid‑scale storage; batteries dominate short‑term ancillary services. Technical Potentials – Solar ≈ 89×, Wind ≈ 14×, Combined Solar+Wind ≈ 100× current global energy demand. Investment Milestones – $2.7 trillion (2010‑2019) in renewables; $200 billion added in 2023 (+75 % YoY). Job Numbers – 12 million worldwide (2023); solar employs 5 million, wind 3 million. 🔄 Key Processes Photovoltaic Power Generation Sunlight → photon absorption → electron‑hole pairs (photoelectric effect) → DC electricity → inverter → AC grid. Wind Turbine Power Capture Wind kinetic energy → rotor blades (power ∝ v³) → gearbox (optional) → generator → electricity. Pumped‑Hydro Storage Cycle Low‑demand → pump water to upper reservoir; high‑demand → release water through turbine to generate power. Green Hydrogen Production Renewable electricity → electrolyzer → split water → H₂ + O₂; H₂ stored or used in fuel cells. Sector Coupling for Flexibility Excess renewable → charge EV batteries, run heat pumps, produce H₂ → demand‑side response smooths net load. 🔍 Key Comparisons Solar PV vs Solar‑Thermal PV: Direct electricity, 2/3 of solar capacity, faster cost declines. Thermal: Stores heat in water, can generate electricity via steam turbine, higher CAPEX. On‑shore vs Offshore Wind On‑shore: Lower CAPEX, lower capacity factor, more land‑use conflict. Offshore: Higher wind speeds (≈ 90 % higher), capacity factors > 50 %, higher CAPEX. Pumped‑Hydro vs Batteries Pumped‑Hydro: Bulk storage, > 90 % of grid‑scale capacity, long lifetime, geographic constraints. Batteries: Fast response, modular, declining costs, limited duration (hours). Bioenergy vs Fossil Fuels Bioenergy: CO₂ ≈ 39 g MJ⁻¹ vs 75 g MJ⁻¹ for fossil; can be carbon‑neutral if sustainably sourced. Fossil: Higher emissions, often cheaper without carbon pricing. ⚠️ Common Misunderstandings “Renewables are always cheap.” – LCOE is low in many regions, but integration costs (grid upgrades, storage) can add to total system cost. “Solar can run 24 h.” – Only with storage or complementary dispatchable sources; panels produce only during daylight. “Wind turbines don’t need water.” – Offshore wind may require water for cooling of power‑electronics; also, installation impacts marine ecosystems. “Hydropower is always renewable.” – Reservoirs can emit methane from decomposing biomass; ecological impacts can be significant. 🧠 Mental Models / Intuition “Energy‑flow pyramid” – Think of the grid as a pyramid: base = abundant, low‑cost, dispatchable sources (hydro, geothermal); middle = variable renewables (solar, wind) needing storage; tip = peak‑load demand managed by flexible resources (batteries, demand response). “Cube law for wind” – A 10 % increase in wind speed → 33 % more power → visualize wind speed as the lever that magnifies output. “Storage as a bathtub” – Inflows = excess generation; outflows = demand; level = stored energy; overflow = curtailment. 🚩 Exceptions & Edge Cases Geothermal – Viable only near tectonic plate boundaries or with enhanced geothermal systems (high CAPEX, pilot‑stage). Solar PV in high latitudes – Lower insolation but can still be cost‑effective with high‑efficiency panels and storage. Hydropower in drought years – Reduced water flow limits generation; climate‑resilient designs needed. 📍 When to Use Which Site selection High wind speeds & offshore access → offshore wind. High solar irradiance, limited land → rooftop/agrivoltaic PV. Reliable water flow → run‑of‑the‑river hydro. Technology choice for firm power Need baseload → geothermal or hydro with storage. Short‑term peak → battery storage or pumped‑hydro. Policy‑driven financing Feed‑in tariff → favors large‑scale PV or wind. Tax credit → encourages residential rooftop PV. 👀 Patterns to Recognize “Capacity factor ≈ (Actual output)/(Rated power)” – > 20 % for solar PV, > 30‑40 % for on‑shore wind, > 50 % for offshore wind. Cost‑trend “learning curve” – 20 % cost reduction per doubling of cumulative capacity (Swanson’s Law for PV, similar for wind). Emission‑gap correlation – Countries with > 30 % renewable electricity see 0.5 GtCO₂/yr reduction. Investment‑share feedback – Higher investment → faster cost declines → more competitive bids → even higher investment (positive feedback loop). 🗂️ Exam Traps Confusing “technical potential” with “economic potential.” – Technical potential is the physical limit; economic potential accounts for cost‑competitiveness. Assuming 100 % renewable penetration is always feasible. – Land, water, material, and grid constraints create practical ceilings; most studies highlight “modest” portions (e.g., 30‑50 % of land) as sufficient. Misreading growth rates – CAGR figures (15 % for solar/wind) apply to capacity, not to share of total electricity (which grows slower). Over‑estimating storage efficiency – Pumped‑hydro round‑trip ≈ 75‑80 %; batteries ≈ 90 % – not 100 %. Mix‑up of LCOE units – LCOE is expressed in $/kWh, not $/MWh; remember to convert when comparing. --- Use this guide to review core ideas, memorize high‑yield facts, and spot the patterns that will let you eliminate distractors on exam questions.