Lecture 5 Energy Systems and Energy Conversion Technologies

Gang He

February 24, 2025

Energy systems

Resources vs reserves

Energy and their conversions

Global energy flow

U.S. energy flow

Energy by supply

Energy end-use by sector

Matching supply and demand

It operates like “magic”
But relies on massive infrastructure, markets, and regulations

• Deliver service at the right time, location, and price
  
• Meet safety, reliability, and environmental standards
  
• Increasingly disrupted by political economy and climate change

Solution is usually location and temporal based

Electrify eveything, where are we now

Electrify eveything, net zero

Energy efficiency

Electric efficiency vs fossil efficiency

Milestones for long-term energy transition

NYS Climate Leadership and Community Protection Act

35%-40% of the benefits of NY CLCPA investments must flow to disadvantaged communities

U.S. shale gas revolution

Renewable revolution: achieving grid parity

Renewable revolution: solar and wind taking off

Sample analytic questions

• How much coal can be saved/emissions can be mitigated if China’s average coal power efficiency increased by 1 percentage point?
  
• Why combined heat and power saves energy?

Thermodynamics

• Thermodynamic efficiency
  
• Comparing different technologies
  
• Thermodynamics provides physic limits

Heat engine

Heat -> Mechanical energy (work)

Laws of thermodynamics

• Zeroth law
  “If two systems are each in thermal equilibrium with a third, they are also in thermal equilibrium with each other.”

• First law
  “In a process without transfer of matter, the change in internal energy, \(\Delta U\), of a thermodynamic system is equal to the energy gained as heat, \(Q\), less the thermodynamic work, \(W\), done by the system on its surroundings.”

• Second law
  “Heat does not spontaneously flow from a colder body to a hotter body.”

• Third law
  “As the temperature of a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.”

Three efficiencies

• 1st law: actual, thermal efficiency;
  \(\eta_1 =\frac{W_{net}}{Q_{in}}=\frac{Q_{high}-Q_{low}}{Q_{high}}=1-\frac{Q_{low}}{Q_{high}}\)
• Carnot: maximum possible efficiency;
  \(\eta_c =\frac{W_{net}}{Q_{high}}=\frac{T_{high}-T_{low}}{T_{high}}=1-\frac{T_{low}}{T_{high}}\) (Kelvin)
  
• 2nd law: comparing 1st and Carnot;
  \(\eta_2 =\frac{\eta_1}{\eta_c}\)

A gas turbine engine

A steam coal plant

Brayton cycle vs. Rankine cycle

Jet engine, gas turbine

Steam engine, steam turbine

Brayton cycle vs. Rankine cycle

Brayton Cycle	Rankine Cycle
Jet, Gas turbine	Steam turbine
Open	Open/closed circuits
Working fluid in gaseous phase	Working fluid phase change

Largest coal plant in the U.S.

Georgia Power plant Scherer (3,720 MW)

Can you identify the components

• Coal storage
  
• Generating unit
  
• Cooling stack
  
• Bottom ash landfill
  
• Sub-station
  
• Transimission lines
  
• Waste/pollution management
  

Combined cycle

CCGT Diagram

Defining a Rosenfeld Plant

• 500 MW
• c.f.: 70%
• T&D losss: 7%

Results:

• 3 TWh/year
  

• 3 MtCO2/year

• NYC electricity use: ~4 TWh/year

Solar

Solar spectrum

Solar constant: 1.361 kW/m2

Harvesting the sun

Heqing Solar Cooker Project in Zhangye

Young NaDEET students in Namibia learning to use a parabolic solar cooker

Silicon

P and N type

P-N Junction

How solar works

Solar irradiance

• Direct normal irradiance (DNI)
  
• Diffuse horizontal irradiance (DHI)
• Ground reflected irradiance (GRI)
  
• Global horizontal irradiance (GHI)
  
• Plane-of-array irradiance (POA)

GHI=DNI+DHI+GRI

POA = GHI \(\times \cos \theta\)

Key corrections

• Solar position at any time of day: altitude angle, latitude, zaimuth angle, hour angle
  
• Radiation: direct beam, diffusion, reflected
  
• Tracking: fixed, 1-axis, 2-axis

The quest for efficiency

Global and U.S. distribution

Air pollution and dust

Climate change impact

Prioritize solar installation

Solar thermal: CSP

Pros and Cons

Pros	Cons
Renewables	Variable & integration
Low emissions	Land use
Low costs	Distribution

Wind

\(P=\frac{1}{2}\rho \pi r^2 v^3\)

Where,
\(\rho\) = Air Density (\(kg/m^3\))
\(A\) = Swept Area (m2) = \(\pi r^2\)
\(v\) = Wind Speed (m/s)
\(P\) = Power (W)

Betz’s law: 59.3%

Average power

Rayleigh (a special type of Weibull) distribution

\(f(v)=\frac{2v}{c^2}\exp [-(\frac{v}{c})^2]\)

\(\bar{P}=\frac{6}{\pi}\cdot \frac{1}{2}\rho \pi r^2 (\bar{v})^3=1.91P\)

Use average power when dealing with average wind speed

Power curve

Important corrections

• Temperature: \(\rho = \frac{P\times M.W. \times 10^{-3}}{RT}=\frac{1 atm\times 28.97 g/mol \times 10^{-3}kg/g}{8.2056\times 10^{-5}m^3\cdot atm/(K\cdot mol)\times(273.15+T)K}\)
  
• Altitude: \(P=P_0 e^{-1.185\times 10^{-4}H}\) (H is elevation in meters)
  
• Tower height: \(\frac{v}{v_0}=(\frac{H}{H_0})^\alpha\) (\(\alpha\) is the friction coefficient)

Class of wind resources

Class	10 m (33 ft)		50 m (164 ft)
	Wind power density (W/m2)	Speed m/s (mph)	Wind power density (W/m2)	Speed m/s (mph)
1	0 - 100	0 - 4.4 (0 - 9.8)	0 - 200	0 - 5.6 (0 - 12.5)
2	100 - 150	4.4 - 5.1 (9.8 - 11.5)	200 - 300	5.6 - 6.4 (12.5 - 14.3)
3	150 - 200	5.1 - 5.6 (11.5 - 12.5)	300 - 400	6.4 - 7.0 (14.3 - 15.7)
4	200 - 250	5.6 - 6.0 (12.5 - 13.4)	400 - 500	7.0 - 7.5 (15.7 - 16.8)
5	250 - 300	6.0 - 6.4 (13.4 - 14.3)	500 - 600	7.5 - 8.0 (16.8 - 17.9)
6	300 - 400	6.4 - 7.0 (14.3 - 15.7)	600 - 800	8.0 - 8.8 (17.9 - 19.7)
7	400 - 1000	7.0 - 9.4 (15.7 - 21.1)	800 - 2000	8.8 - 11.9 (19.7 - 26.6)

Global wind power density map

Higher and bigger

Offshore wind

Challenges

Low speed wind

Smaller generator. \(\rightarrow\) Decreased generator weight and cost.

Operating at higher capacity in lower wind speeds. \(\rightarrow\) Greater generator efficiency.

Decreased tower head mass. \(\rightarrow\) Decreased foundation and tower costs.

Decreased PE system rating. \(\rightarrow\) Decreased PE system costs

Pros and Cons

Pros	Cons
Renewables	Variable & integration
Low emissions	Land use/NIMBY
Low costs	Distribution

Unexpected benefits

Hybrid power systems

References

Bergin, Mike H, Chinmay Ghoroi, Deepa Dixit, James J Schauer, and Drew T Shindell. 2017. “Large Reductions in Solar Energy Production Due to Dust and Particulate Air Pollution.” Environmental Science & Technology Letters 4 (8): 339–44.

BMWi. 2015. “An Electricity Market for Germany’s Energy Transition: White Paper by the Federal Ministry for Economic Affairs and Energy.” Federal Ministry for Economic Affairs; Energy. https://www.bmwk.de/Redaktion/EN/Publikationen/whitepaper-electricity-market.html.

Chen, Shi, Xi Lu, Chris P. Nielsen, Michael B. McElroy, Gang He, Shaohui Zhang, Kebin He, Xiu Yang, Fang Zhang, and Jimin Hao. 2023. “Deploying Solar Photovoltaic Energy First in Carbon-Intensive Regions Brings Gigatons More Carbon Mitigations to 2060.” Communications Earth & Environment 4 (October): 369. https://doi.org/10.1038/s43247-023-01006-x.

IEA. 2021. “Net Zero by 2050.” International Energy Agency. https://www.iea.org/reports/net-zero-by-2050.

Koomey, Jonathan, Hashem Akbari, Carl Blumstein, Marilyn Brown, Richard Brown, Chris Calwell, Sheryl Carter, et al. 2010. “Defining a Standard Metric for Electricity Savings.” Environmental Research Letters 5 (1): 014017. https://iopscience.iop.org/article/10.1088/1748-9326/5/1/014017.

Liu, Laibao, Gang He, Mengxi Wu, Gang Liu, Haoran Zhang, Ying Chen, Jiashu Shen, and Shuangcheng Li. 2023. “Climate Change Impacts on Planned Supply–Demand Match in Global Wind and Solar Energy Systems.” Nature Energy 8 (8): 870–80. https://doi.org/10.1038/s41560-023-01304-w.

Masters, Gilbert M. 2013. Renewable and Efficient Electric Power Systems. John Wiley & Sons.

Smil, Vaclav. 2017. Energy: A Beginner’s Guide. Simon; Schuster. https://vaclavsmil.com/2017/02/21/energy-a-beginners-guide-beginners-guides-2nd-edition/.