renewable energy

How do photovoltaic (PV) cells work

1. Sunlight hits silicon

2. Photons knock electrons loose

3. Electrons flow → electricity

Silicon is like an electron hallway.
Sunlight “pushes” electrons from one side to the other

Where is solar best?

Dry, sunny places:

• Southwest US

• Middle East

• Mexico

• Australia

• Deserts

Cloudy regions still use solar, just less efficiently.

Concentrated solar power (CSP)

Uses mirrors to direct sunlight to a tower → heats fluid → makes steam → runs turbine.

Benefits:

• Can store heat at night

• Provides “on-demand” solar

Challenges:

• Needs lots of land

• Uses water

• High cost

• Can harm birds

What causes wind?

Wind = moving air caused by temperature and pressure differences.

Warm air rises → cool air rushes in to replace it = wind.

Best places for wind

• Open plains

• Mountain passes

• Offshore (VERY strong and steady)

• Coasts

At night, wind is often strong — the opposite of solar → GREAT combo.

Hydroelectric Storage dams

Big reservoirs (Hoover Dam)

driven by gravity

Hydrokinetic ex Run-of-river

• No big reservoir → lower impact.

• Hydrokinetic is less dep. on storage and gravity

Hydrokinetic

Uses river flow or tides (no dam).

Environmental impacts of hydropower

• Blocks fish migration

• Floods huge areas

• Sediment trapped behind dams

• Alters water temperature

• Displaces communities

solutions for hydropower issues

• Fish ladders

• Fish elevators

• Dam removal

• Retrofitting existing dams

• Micro-hydro systems

GEOTHERMAL ENERGY 2 types

Electricity generation

Ground-source heat pumps

Electricity generation

Requires underground hot rocks → mainly in volcanic areas.

Ground-source heat pumps

Uses 55°F earth temperature for heating/cooling homes.