Compare the resource basis, scalability, and limitations of solar, wind, hydroelectric, geothermal, and biomass energy, including the intermittency challenge.
Each renewable source has a distinct resource basis and trade-offs. Solar photovoltaic panels convert sunlight directly into electricity, with strength varying by latitude and cloud cover; costs have fallen dramatically over the past two decades. Wind turbines work best in consistently windy corridors or offshore sites, and their land-use footprint is mostly limited to the tower base, often allowing farming to continue around them; documented concerns include bird and bat mortality (studies generally find turbine strikes are a real but relatively small source of bird mortality compared to other human-linked causes such as window strikes and outdoor cats) and noise or visual concerns raised by nearby residents. Hydroelectric dams have large existing global capacity but can disrupt river ecosystems and fish migration and are not available everywhere a suitable river exists. Geothermal energy taps Earth's internal heat for a steady, constant output unlike solar or wind, but is geographically limited to regions with accessible heat, such as Iceland or parts of the western United States. Biomass can be close to carbon-neutral if regrown at the rate it is consumed, but raises land-use and food-versus-fuel competition concerns, as with corn ethanol.
Solar and wind share one central limitation: intermittency -- the sun does not always shine and the wind does not always blow -- which requires backup generation, long-distance transmission, or energy storage (batteries, pumped hydro storage) to keep the electric grid reliable at all times. This is a real, current engineering and economic challenge, not a reason to dismiss these sources, and it is an excellent return to the systems thinking from Week 2: matching a variable supply to a variable demand curve is exactly a stocks-and-flows problem.
Mastery looks like: They can match each renewable source to its best-suited geography, explain intermittency and which sources it affects, and use given comparative figures to reason about the relative scale of a documented environmental concern.
Common stumbles: Treating all renewables as interchangeable rather than recognizing their distinct geographic and technical trade-offs; assuming intermittency means a source cannot be relied on at all, rather than a challenge with known partial engineering solutions.