Renewable Energy

Renewable energy definition

any form of energy that is renewed continually or annually

Sustainable energy definition

rate of renewal vs rate of consumption is balanced

Hydro energy

mechanical energy, electrical power

Wind energy

kinetic and mechanical energy, electrical power

Solar energy

heating, electrical power

Geothermal energy

passive heating, electrical power

Bioenergy

direct heating, electrical power, biomass, biofuels, biogas

ocean/water energy

electrical power, wave, ridal, salinity, ocean thermal energy conversion (OTEC)

U.S. Fuel mix over time

annual energy consumption: petroleum > natural gas > renewables = nuclear = coal

Percentage of renewable energy in U.S. overall fuel mix

9.2%

Percentage of nuclear in U.S. fuel mix

8.5%

Biggest source of U.S. renewable enrgy consumption

bioenergy (biofuels)

Ranking of U.S. renewable energy consumption by source

biofuels > wood > wind > solar/pv > hydroelectric > waste > geothermal

Cause of growth in biofuels

mandates

Hydropower energy consumption 2023

0.82 quads

Requirement for hydroelectric power

height differences and large volumes of water

Country with most hydropower

Norway

Largest Dam in the world

Three Gorges Dam (China)

Purposes of dams

flood control, water storage, irrigation, recreation, navigation

Benefits of hydroelectric power

• mechanical (potential) to electrical conversion

• reliable

• very efficient (89%)

• quick start-up/turn-off times

• low emissions during generation

• black start rated (can turn it on even when power is out)

Drawbacks of hydroelectric power

• displaced populations

• disturbs ecosystems

• creates evaporation from lakes

• ½ of national capacity is already built (built between 1930s-1970s)

• silting can limit lifetimes to 100 years

• source of GHGs (CO2 and CH4 from decaying vegetation)

• end-of-life planning not built into project development

• susceptible to drought

Potential of hydro in U.S.

small hysro and adding powerhouses to unpowered dams (expand capacity by 12 GW)

Summary of U.S. hydropower

• adding powerhouses to dams that already exist for flood control and irrigation

• pumped hydro

• micordrams

• dam end-of-life and removal planning

• data centers as potential customers to reinvest in dams

Wind energy consumption 2023

1.5 quads

Most critical factor of power generation from wind turbines

highly dependent on wind speed

Betz’ Law

an ideal wind turbine can convert as most 59% of the kinetic energy in the wind to mechanical power

States that generate over hald of the wind energy generation

Texas > Iowa > Oklahoma > Kansas > Illinois

Benefits of wind energy

• mechanical to electrical conversion

• no emissions

• fuel is free

• inexhaustible, renewable supply

Capacity Factor

actual output over theoretical output

Variables for capacity factor

prime mover, fuel, operational intent

Drawbacks of wind energy

• wind cuts out at low and very high speeds

• wind is where people aren’t

• land intensive

• needs critical minerals and rare earth materials

• noise

• looming concerns about impacts on birds/bats

• maintenance challenges

Continental Wind

• 25-35% capacity factor

• mismatched with summer peak demand in warm climates

Coastal Wind

• 40-50% capacity factor

• better alignemnt with summer peak in warm climates

Country with greatest installed wind power capacity

China (Texas would be 5th if they were a country)

Three key trends of wind turbines

• more installations

• larger turbines

• offshore

Solar energy consumption 2023

0.89 quads

Solar Photovoltaic (PV)

direct electrical production, utility scale and distributed PV (radiant to electrical)

Solar Thermal

space and water heating (radiant to thermal)

Concentrating Solar Power (CSP)

• to create steam-generated electricity (radiant to thermal to mechanical to electrical)

• Largest CSP: Ivanpah CSP Plant (California)

Benefits of solar

• cheap capacity

• fuel is free

• clean at point of generation

• renewable

• inexhaustible

• matches well with peak demand

Drawbacks of solar

• variable (14-33% capacity factor)

• lower efficienct than thermal power plants (from 10-20% to 30-60%)

• benchtop efficiency >40%

• much of sun is where people aren’t

• land intensive

• needs rare earth materials

Impacts of cold weather on solar

• less power is produced because there is not as much sun

• panels become covered with snow

• panels can get extra power from sunlight reflected off nearby snow

• panel efficiency is better in low temperatures

Country with greatest cumulative installed pv power

China

Future of solar pv

• integrated into building materials

• plug-in

• flexible panels

• thinner layers

• carbon based

Geothermal energy consumption 2023

0.12 quads

Forms of geothermal

• vents of steam exist

• naturally hot water underground

• stable ground temperatures

Variables of naturally occuring geothermal systems

heat, permeability, fluid

Advantages of geothermal

• Earth does heating for us

• dsitributed throughout the world

• can be used for dispatchable power (can turn it on and off)

• no direct emissions of GHGs or pollutants

Drawbacks of geothermal

• might not be sustainable at a local scale

• limited geological understanding

• low efficiencies

• typically smaller-scale power plants

• higher costs

Best locations for geothermal resources

• easier to reach near active faults

• Iceland

• U.S. mountain west

Current U.S. geothermal generation

16,000 GWh (16 TWh)

Country with most installed geothermal power capacity

U.S.

Country with greates geothermal heat generation

Iceland

Dry Steam Cycle

use steam straight from the earth to spin a turbine (oldest type)

Flash Steam Cycle

take hot water from the earth, turn it into steam, use it , return it (most common)

Binary Cycle

use geothermal fluid to turn a secondary fluid into steam that powers a turbine

Enhanced Geothermal System

use hydraulic fracturing to make a man-made heat reservoir (increase heat access and requires less pipe/drilling)

Advanced Geothermal System

• uses closed-loop systems (don’t lose water)

• Simplifies fluid handling

• avoids hydraulic fracturing

Geothermal as passive heating and cooling

• ground source heat pumps

• use the Earth’s constant 50-60 F temperature for heating in the winter and cooling in the summer

• already cost-effective

• can reduce heating/cooling neefds by 65-70%

Bioenergy consumption 2023

5 quads

Sources of bioenergy

biofuels, wood, waster

Biomass

renewable organic material that comes from plants and animals

When is Biomass considered carbon-neutral?

when the rate of consumption is less than the rate of replenishment (takes CO2 out during growth phase)

When is biomass considered carbon-negative?

when carbon capture is added

Is wood carbon-neutral as fuel?

• treated as carbon-neutral because CO2 emissions at point of combustion are offset by the growth of trees

• mismatch in rates between carbon emissions (seconds) vs. carbon uptake (decades)

Combustion of Biomass

solid biomass to heat/electricity

Fermentation of Biomass

Solid biomass to biofuels

Anaerobic digestion/gasification of biomass

solid biomass to biogas

Dominant sector for bioenergy consumption

Industrial (heat and electricity)

Potential supply of bioenergy resources

over 1 billion tons by 2040 that can be sustainably used (from forestry resources, agricultural residues, waste resources, and energy crops)

Most popular form of biomass

wood pellets

Municipal Solid Waste (MSW)

• waste incinerators (direct generation of electricity)

• waste-to-energy or energy recovery

• unpopular in U.S. (concerns about emissions)

• popular in Europe (because of land constraints)

• small part of overall fuel mix

Per Capita MSW Generation

5 pounds/person/day

Total MSW Generation

300 million tons (recycle 1/2)

Dominant materials of MSW Generation

energ-dense fibers and plastics

Decompostion of organic waste

• Aerobically: to CO2

• Anaerobically: to CH4

Organic Waste Streams

• Landfill Gas: mining for biogas from anaerobic digestion of MSW (indirect use)

• Municipal Wastewater: anaerobic digestion of sludge

• Agricultural Operations: anaerobic digestion of manure

• Cow Power: agricultural manure to biogas through anaerobic digestion

Advantages of Bioenergy

• usually cheap

• most people live within walking distance of biomass

• can be carbon neutral or carbon negative

• solid forms are easy to store

Drawbacks of Bioenergy

• land-intensive

• water-intensive

• concerns about indirect land use changes (deforestation) in other parts of the world

• invites moral dilemma of food vs. fuel

• inefficient use of photons

• emissions and pollution

Benefits of Ocean Energy

• scale of resource base

• clean, renewable, inexhaustible, free fuel

• avoids NIMBYism

• much of the world’s population lives near oceans

• long-lived infrastructure

Drawbacks of Ocean Energy

• diffuse resource intensity (takes a lot to get energy)

• large-scale engineering and thermodynamics challenges

• hostile, corrosive, environment

• unknown environmental impacts

Ocean Thermal Energy Conversion (OTEC)

• temperature differences of the ocean surface (15-25 C) and depths (5 C) drive a power cycle

• maximum carnot efficiency: 3.5-6.7%

• good fit for tropical island communities that use expensive diesel for power

Salinity Gradients and Osmotic Power

• uses pressure difference between fresh and salt water at river/ocean interface

• technical potential: 30,000 TWh

• economic/recoverable potential: 1500-5000 billion kWh (TWh)

Advantages of Salinity Gradients and Osmotic Power

• round the clock power generation

• similarily scaled/sited infrastructure as hydroelectric

• does not need a reservoir

Disadvantages of salinity gradients and osmotic power

• cost

• supply chain immaturity for specialty membranes

• lingering questions about ecosystem impacts

Tidal Energy

need good separation between low and high tide

Advantages of tidal energy

• can be forecasted

• 40% capacity factor

Disadvantages of tidal energy

• limited site suitability globally

• expensive offshore infrastructure

• can be impactful on coastal ecosystems

Biggest tidal power project

Sihwa Lake, South Korea (254 MW)

Advantages of Nuclear

• supreme energy density

• minimal waste generation per kWh

• excellent capacity factor, maintenance and safety records

• domestic or friendly sources of uranium

• possible source for electricity for hydrogen production for transportation fuel

Drawbacks of Nuclear

• waste is radioactive and long-lived

• public safety

• concerns about weapons proliferation

• some facilites are difficult to ramp (don’t follow load)

• new plant construction costs

• water needs for cooling

How long did it take for the first nuclear weapon to be tested after nuclear fission was discovered

6 years

How long did it take to create electricity from a nuclear reactor since the first weapon

6 years (1952)

What made nuclear more desirable

oil shocks

Causes for nuclear build-out slowing down

• environmentalist opposition, high interest rates, peace movements

• energy conservation in response to 1970s oil shocks

• accidents and near-misses catch

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Three major nuclear reactor accidents

• Chernobyl

• Fukushima

• Windscale Piles

Percentage of U.S. energy consumption that is nuclear

9%

Percentage of U.S. electricity generation from Nuclear

18%

Nuclear energy consumption in 2023

8.1 quads

Nuclear Fission

nuclear decay where a nucleus splits into at least two new nuclei, usually of different masses (excess mass released as kinetic energy)