
\newcommand{\thistitle}{Lecture 2: Energy Balances}

\input{title.tex}


\section{Measuring Energy}




\begin{frame}
  \frametitle{Goal: Understand Energy Flow Through the Economy}

  Example: \alert{energy balance} for Germany in 2022 in Petajoule (PJ)

  \vspace{.2cm}
  \centering
  \includegraphics[height=6.8cm]{energiebilanzen-2022.png}


   \source{\hrefc{https://ag-energiebilanzen.de/en/data-and-facts/energy-flow-chart/}{AG Energiebilanzen, 2023}}

\end{frame}

\begin{frame}
  \frametitle{Example: Sankey diagram for US in 2022}

  \centering
  \includegraphics[height=7.5cm]{us-sankey-2022.png}

   \source{\hrefc{https://flowcharts.llnl.gov/sites/flowcharts/files/2023-10/US\%20Energy\%202022.pdf}{LLNL, 2023}}

\end{frame}


\begin{frame}
  \frametitle{Example: Useful energy (Nutzenergie) for Germany 2021}

  \centering
  \includegraphics[width=14cm]{nutzenergie-de-2021.png}

\source{\hrefc{https://ag-energiebilanzen.de/daten-und-fakten/nutzenergiebilanzen/}{AG Energiebilanzen, 2023}}
\end{frame}

\begin{frame}
  \frametitle{Energy conversion/transformation processes}
  \centering
  \includegraphics[width=14cm]{conversion_processes.png}

  \source{Zweifel, Praktiknjo \& Erdmann (2017)}

\end{frame}

\begin{frame}
  \frametitle{Definitions: Primary Versus Final Versus Useful Energy}


  {\small
  Definitions of energy are oriented towards conventional
  energy sources like coal, oil and gas.

  \begin{itemize}

  \item \alert{Primary energy} is energy as found in nature before it
  undergoes any transformation (crude oil, coal, gas, biomass,
  nuclear, wind, solar).

  \item \alert{Secondary energy} is energy after conversion processes,
  either chemical or physical (refined fuels like gasoline,
  electricity from a coal power plant).

  \item \alert{Final energy} is the energy  as it is sold to end users
  (electricity, refined fuels like gasoline, gas for building heating).

  \item \alert{Useful energy} is the energy after conversion by the
  consumer, available to be used (heat in a home, light, mechanical
  work).

  \item \alert{Energy services} is what the consumer actually wants: a warm
  home, transportation from A to B, manufactured goods, etc.
  \end{itemize}

  The two most commonly used definitions are \alert{primary} and
  \alert{final} energy, since they are \alert{easier to measure} in a fossil-fuelled world. With more focus on renewables and electrification, this \alert{may change}!
}

\end{frame}


\begin{frame}
  \frametitle{Classification of Energy Sources}

  \centering
  \includegraphics[height=7.5cm]{renewables_classification.png}


  \source{OECD/IEA Energy Statistics Manual, 2005}
\end{frame}

\begin{frame}
  \frametitle{Units of Energy: Joule and tonne of oil equivalent}

  \alert{Joule} (J) is the SI unit of energy.

  Conventional primary energy sources are often measured in units corresponding to their natural form: volume, mass etc.

  We can convert from measurements of mass [kg] and volume [m$^3$] to energy units using the \alert{calorific value} [J/kg, J/m$^3$], which measures the heat from combustion.

  Example: the unit \alert{tonne of oil equivalent} (toe) is the energy generated by burning one metric ton of oil. Since the calorific value of oil is 41.88 MJ/kg, we have
  \begin{equation*}
    1 \textrm{ toe} = 41.88 \textrm{ GJ}
  \end{equation*}

  \vspace{.4cm}
  [Reminder: k = kilo = 1e3, M = Mega = 1e6, G = Giga = 1e9, T = Tera = 1e12, P = Peta = 1e15, E = Exa = 1e18.]
\end{frame}
\begin{frame}
  \frametitle{Lower Heating Values of Energy Fuels}

  \centering
  \includegraphics[width=12cm]{fuel_lhv.png}

\end{frame}

\begin{frame}
  \frametitle{Higher and Lower Heating Values}


  \begin{itemize}
  \item \alert{Lower Heating Value (LHV)} is the maximum amount of usable heat from combustion without counting the condensation enthalpy of water vapor contained in the exhaust gas.
  \item \alert{Higher Heating Value (HHV)} includes the condensation enthalpy of water vapor contained in the exhaust gas. It is always higher than the LHV (e.g. 11\% higher for methane).
  \end{itemize}

  \vspace{.35cm}

  \centering
  \includegraphics[width=8cm]{Higher-and-lower-heating-values-for-various-fuels-22.png}

  \vspace{.35cm}


  \raggedright
 LHV is most commonly used in European statistics.
  HHV becomes relevant in e.g. condensing combined heat and power plants (CHP) where vapor is condensed.

\end{frame}


\begin{frame}
  \frametitle{Power: Flow of energy}

  \alert{Power} is the rate of consumption of energy.

  It is measured in \alert{Watts}:
  \begin{equation*}
     1 \textrm{ Watt } = 1 \textrm{ Joule per second }
  \end{equation*}
  The symbol for Watt is W, 1 W = 1 J/s.

  \centering
  1 kilo-Watt = 1 kW = 1,000 W

  1 mega-Watt = 1 MW = 1,000,000 W

  1 giga-Watt = 1 GW = 1,000,000,000 W

  1 tera-Watt = 1 TW = 1,000,000,000,000 W


\end{frame}



\begin{frame}
  \frametitle{Power: Examples of consumption}

  At full power, the following items consume:

  \ra{1.1}
  \begin{table}[!t]
    \begin{tabular}{lr}
      \toprule
      Item & Power\\
      \midrule
      New efficient lightbulb & 10 W \\
      Old-fashioned lightbulb & 70 W \\
      Single room air-conditioning & 1.5 kW \\
      Kettle & 2 kW \\
      Factory & $\sim$1-500 MW \\
      CERN & 200 MW \\
            Germany total demand & 35-80 GW \\
      \bottomrule
    \end{tabular}
  \end{table}

\end{frame}

\begin{frame}
  \frametitle{Power: Supplying world's energy with wind and solar}

  If all energy is electrified in 2050 and energy consumption
  equalises between nations, the average electricity consumption of
  the world would be around 12~TW.

  Suppose half is met with wind (capacity factor 33.3\%) and half is
  met with solar PV (capacity factor 16.6\%). [Capacity factor $=$ average
  generation $/$ capacity.] How much wind and solar capacity does the world need (assuming perfect lossless storage)?

  \pause

  \vspace{1cm}

  Wind: 6~TW / 0.333 $=$ 18~TW (around 900~GW was installed by 2022)

  Solar: 6~TW / 0.166 $=$ 36~TW (around 1050~GW was installed by 2022)

  \source{\hrefc{https://www.irena.org/Publications/2023/Mar/Renewable-capacity-statistics-2023}{IRENA Statistics 2023}}

\end{frame}

\begin{frame}
  \frametitle{Power: Supplying world's energy with wind and solar}

  If installed wind density on average is 10~MW/km$^2$ and solar is 72~MW/km$^2$, what percentage of world land (149 million km$^2$) is taken with each?
  \pause

  \vspace{.5cm}

  Wind: 18~TW/(10~MW/km$^2$) = 1.8 million km$^2$ (around 1.2\% of total land $=$ area of Indonesia)

  Solar: 36~TW/(72~MW/km$^2$) = 0.5 million km$^2$ (around 0.3\% of total land $=$ area of Spain)

  \vspace{.5cm}

  Nota Bene:
  \begin{itemize}
    \item Wind doesn't interfere with other land uses like agriculture; can also be built offshore
    \item 10~MW/km$^2$ is a \alert{local} maximum installation density for wind, but to allow wind replenishment over large areas 2~MW/km$^2$ is suitable as a \alert{wide-area} limit
      \item Solar can be rooftop or combined with agriculture = agrivoltaics
  \end{itemize}

\end{frame}


\begin{frame}
  \frametitle{Units of energy: Watt-hour}

  In the electricity sector, energy is usually measured in
  `Watt-hours', Wh.

  1 kWh = power consumption of 1 kW for one hour

  E.g. a 10 W lightbulb left on for two hours will consume

  10 W * 2 h = 20 Wh

  It is easy to convert this back to the SI unit for energy, Joules:

  1 kWh = (1000 W) * (1 h) = (1000 J/s)*(3600 s) = 3.6 MJ
\end{frame}





\begin{frame}
  \frametitle{Yearly energy to power}

  Germany consumes around 600 TWh per year, written 600 TWh/a.

  What is the \emph{average} power consumption in GW?

  \pause
  \begin{align*}
    600\textrm{ TWh/a} & = \frac{(600\textrm{ TW}) * (1\textrm{ h})}{(365*24 \textrm{ h})} \\
    & =  \frac{600}{8760} \textrm{ TW} \\
    & = 68.5 \textrm{ GW}
  \end{align*}

\end{frame}

\begin{frame}
  \frametitle{Tables for converting units}

  \centering
  \includegraphics[width=8cm]{conversion.jpg}

  \raggedright Units used in the United States:
  \begin{itemize}
  \item British thermal unit (Btu), 1 million Btu = MBtu (often written MMBtu) = 0.293 MWh
  \item Quad = 1e15 Btu = 293 TWh
  \end{itemize}
\end{frame}

\begin{frame}
  \frametitle{Energy conversion efficiency}

  \alert{Efficiency} of an energy conversion device (e.g. power plant, vehicle engine):
  \begin{equation*}
    \textrm{Efficiency, } \eta = \frac{\textrm{Useful energy output}}{\textrm{Energy input}}
  \end{equation*}


  Example: How much much natural gas is required for generating 100 MWh of
  electricity in a gas power plant with an efficiency of 50\%?

\end{frame}

\begin{frame}
  \frametitle{Measuring primary energy of renewables}

  How to value primary energy of carriers which do not have a calorific value,
  e.g. wind, solar PV, hydroelectricity?
  \begin{itemize}
    \item \alert{Fictive Efficiency Principle:} (also known as `Physical Energy Accounting Method' or `Direct Equivalent Method') (most common: used by IEA, OECD, Eurostat, IPCC) assume there is a 1-to-1 correspondence between primary energy and electricity for wind, solar, hydro (i.e. 100\% conversion efficiency)
  \item \alert{Substitution Principle:} (also know as the `Input-Equivalent Method') (used by BP) assume the conversion efficiency from primary energy to electricity is the same as in a thermal (fossil or nuclear) powerplant
  (e.g. 35-45\%)
  \item \alert{Efficiency Principle:} actual efficiency of respective technology
  (hydro 80-90\% gravitational potential energy of water to electricity, wind 30-55\% kinetic energy of air to electricity, solar 10-25\% radiation to electricity)
  \end{itemize}

\end{frame}


\begin{frame}
  \frametitle{Fictive Efficiency vs Substitution Principle for Electricity Generation}

\begin{columns}[T]
  \begin{column}{7cm}

  \centering
  \alert{Fictive Efficiency Principle}

  \vspace{.3cm}

  \begin{tikzpicture}[
    scale=1.1,
    demand/.style={blue, thick},
    supply/.style={red, thick},
    axis/.style={very thick, ->, >=stealth', line join=miter},
    important line/.style={thick}, dashed line/.style={dashed, thin},
    every node/.style={color=black},
    dot/.style={circle,fill=black,minimum size=4pt,inner sep=0pt,
      outer sep=-1pt},
  ]
  % axis
  \draw[axis,<->] (2.5,0) node(xline)[right] {} -|
  (0,2) node(yline)[above] {energy};

  \draw[draw=none,fill=black] (0.5,0) rectangle ++(0.3,1.8);
  \draw[draw=none,fill=black] (1.5,0) rectangle ++(0.3,0.72);
  \node[below] at (0.65,0) {primary};
  \node[below] at (1.65,0) {final};
  \node[above] at (1.2,1.7) {fossil};


  \begin{scope}[yshift=-3cm]
  % axis
  \draw[axis,<->] (2.5,0) node(xline)[right] {} -|
  (0,2) node(yline)[above] {energy};

  \draw[draw=none,fill=blue] (0.5,0) rectangle ++(0.3,0.72);
  \draw[draw=none,fill=blue] (1.5,0) rectangle ++(0.3,0.72);
  \node[below] at (0.65,0) {primary};
  \node[below] at (1.65,0) {final};
  \node[above] at (1.2,1.7) {wind};
  \end{scope}
  \end{tikzpicture}
  \end{column}
  \begin{column}{7cm}

  \centering
  \alert{Substitution Principle}

  \vspace{.3cm}

  \begin{tikzpicture}[
    scale=1.1,
    demand/.style={blue, thick},
    supply/.style={red, thick},
    axis/.style={very thick, ->, >=stealth', line join=miter},
    important line/.style={thick}, dashed line/.style={dashed, thin},
    every node/.style={color=black},
    dot/.style={circle,fill=black,minimum size=4pt,inner sep=0pt,
      outer sep=-1pt},
  ]
  % axis
  \draw[axis,<->] (2.5,0) node(xline)[right] {} -|
  (0,2) node(yline)[above] {energy};

  \draw[draw=none,fill=black] (0.5,0) rectangle ++(0.3,1.8);
  \draw[draw=none,fill=black] (1.5,0) rectangle ++(0.3,0.72);
  \node[below] at (0.65,0) {primary};
  \node[below] at (1.65,0) {final};
  \node[above] at (1.2,1.7) {fossil};


  \begin{scope}[yshift=-3cm]
  % axis
  \draw[axis,<->] (2.5,0) node(xline)[right] {} -|
  (0,2) node(yline)[above] {energy};

  \draw[draw=none,fill=blue] (0.5,0) rectangle ++(0.3,1.8);
  \draw[draw=none,fill=blue] (1.5,0) rectangle ++(0.3,0.72);
  \node[below] at (0.65,0) {primary};
  \node[below] at (1.65,0) {final};
  \node[above] at (1.2,1.7) {wind};
  \end{scope}
  \end{tikzpicture}
  \end{column}
\end{columns}



\end{frame}

\begin{frame}
  \frametitle{Beware: primary energy can underestimate renewables share}

  Suppose 50\% of electricity is provided by wind and solar, the rest by fossil plants with 33\% efficiency.

  What is the fraction of renewables in primary energy for electricity:
  \begin{enumerate}
  \item Using the Fictive Efficiency Principle
  \item Using the Substitution Principle
  \end{enumerate}

  \pause
  \begin{enumerate}
  \item $\frac{50}{50 + 50/0.33}\% = \frac{50}{50 + 150}\% = 25\%$
\item 50\% (since we assume renewables need as much primary energy for each unit of electricity as a thermal plant)
  \end{enumerate}

  Bad faith actors will often present renewable shares in terms of primary energy to make it look small.
\end{frame}



\begin{frame}
  \frametitle{Primary and final energy change with electrification}

  {\small Primary energy in grey and green; useful energy in blue.  NB: Also in \alert{industry}, \hrefc{https://doi.org/10.1088/1748-9326/abbd02}{electrification} of process heat can be more efficient since the heat can be focused better than e.g. burning gas.}

  \centering
  \includegraphics[height=6.5cm,trim=2.7cm 20cm 3.2cm 1.8cm,clip=true]{bmwi-whitepaper-figure_18.pdf}

  \source{\hrefc{https://www.bmwi.de/Redaktion/EN/Publikationen/whitepaper-electricity-market.html}{BMWi White Paper 2015}}
\end{frame}



\begin{frame}
  \frametitle{Primary and final energy change with renewables and electrification}

  Switching from thermal power plants to wind, solar and hydro leads to an \alert{automatic decline in primary energy} using the Fictive Efficiency Principle, since thermal losses are no longer counted.

  With electrification and efficiency, \alert{final energy also declines} (compare gasoline required for a car versus electricity need; similarly natural gas for boiler versus electricity for a heat pump).

  Both primary and final energy would decline! Primary by $\sim 50\%$, final by $\sim 33\%$.

  Expect roughly a \alert{doubling electricity demand} (assuming widespread
  electrification of end demands, indirect electrification with H2 and
  efficiency measures).

  Electricity would become the dominant final energy, primary energy becomes less relevant.

  Most important metrics become: fraction of electricity from non-emitting sources; efficiency of electricity meeting energy services.

\end{frame}

\section{Energy Balances}

\begin{frame}
  \frametitle{Energy Balances}

  Energy is always \alert{conserved} as it flows through the energy system.

  \alert{Energy balances} tabulate this energy conservation at
  each step of conversion from primary energy supply to primary energy
  consumption to final energy to energy services for consumers.

  At each interface, inputs and outputs \alert{balance}.


  \vspace{.2cm}
  \centering
  \includegraphics[height=4cm]{400px-Balanced_scales.svg.png}

  \source{\hrefc{https://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Balanced_scales.svg/400px-Balanced_scales.svg.png}{Wikimedia}}
\end{frame}

\begin{frame}
  \frametitle{Principles of Energy Flow}

  \vspace{.2cm}
  \centering
  \includegraphics[width=13.5cm]{energy_flow.png}

  \source{Zweifel, Praktiknjo \& Erdmann (2017)}

\end{frame}


\begin{frame}
  \frametitle{Energy Flow In Germany}

  Example: \alert{energy balance} for Germany in 2022 in Petajoule (PJ)

  \vspace{.2cm}
  \centering
  \includegraphics[height=6.8cm]{energiebilanzen-2022.png}


   \source{\hrefc{https://ag-energiebilanzen.de/en/data-and-facts/energy-flow-chart/}{AG Energiebilanzen, 2023}}


\end{frame}



\begin{frame}
  \frametitle{Energy Balance Structure (AGEB)}

  \centering
  \includegraphics[height=7.5cm]{balance_structure.png}



   \source{\hrefc{https://ag-energiebilanzen.de/}{AG Energiebilanzen}}
\end{frame}



\begin{frame}
  \frametitle{Simplified Energy Balance for EU28 in 2016}

\begin{columns}[T]
  \begin{column}{9cm}

  \centering
  \includegraphics[width=9.4cm]{eb-eu-2016.png}
  \end{column}
  \begin{column}{5cm}
    \begin{itemize}
    \item Gross inland consumption = Primary energy consumption = Production + Imports + Stock changes - Exports - Bunkers
    \item Bunkers is e.g. marine fuel stored at ports
    \item Around 330 Mtoe lost in transformation
    \item Final consumption = Final non-energy + Final energy consumption
    \end{itemize}
  \end{column}
\end{columns}
  \source{\hrefc{https://ec.europa.eu/eurostat/web/energy/data/energy-balances}{Eurostat Energy Balances}}

\end{frame}


\begin{frame}
  \frametitle{Questions}

  \begin{itemize}
  \item What is the average electrical efficiency of conventional power stations in the EU?
  \item What is the average electrical efficiency of nuclear power stations in the EU?
  \item What fraction of industry/transport/residential final energy consumption is electricity?
  \item What is non-energy consumption?
  \end{itemize}

\end{frame}


\begin{frame}
  \frametitle{Moving Beyond Energy Balances: JRC IDEES Database}

  Includes more granular estimates of useful energy, efficiency, CO$_2$ emissions, breakdown e.g. industry by process.

  From Joint Research Centre (JRC) of the European Commission.

 \urlc{https://data.jrc.ec.europa.eu/dataset/jrc-10110-10001}

  ``The `Integrated Database of the European Energy Sector' (JRC-IDEES) is a one-stop data-box that incorporates in a single database all information necessary for a deep understanding of the dynamics of the European energy system, so as to better analyse the past and to create a robust basis for future policy assessments. JRC-IDEES offers a consistent set of disaggregated energy-economy-environment data, compliant with the EUROSTAT energy balances, as well as widely acknowledged data on existing technologies. It provides a plausible decomposition of energy consumption, allocating it to specific processes and end-uses.''
\end{frame}

\begin{frame}
  \frametitle{JRC IDEES: Residential energy appliances}

\begin{columns}[T]
  \begin{column}{10.5cm}

  \centering
  \includegraphics[width=11cm]{res-spec.png}
  \end{column}
  \begin{column}{5cm}

    \begin{itemize}
      \item NB: Peak electricity consumption in Europe is around 500 GW.
      \item If all 1760 GW of appliances came on simultaneously, system would be overwhelmed.
      \item What do you notice about the ratio of total energy consumption to installed power?
    \end{itemize}


  \end{column}
\end{columns}


 \source{\hrefc{https://data.jrc.ec.europa.eu/dataset/jrc-10110-10001}{JRC IDEES}}

\end{frame}

\begin{frame}
  \frametitle{JRC IDEES: Residential heating efficiency}

\begin{columns}[T]
  \begin{column}{10.5cm}

  \centering
  \includegraphics[width=11cm]{res-eff.png}
  \end{column}
  \begin{column}{5cm}

    \begin{itemize}
      \item    Ratio of final energy to actual heating for space/water/cooking.
        \item Which fuel source is most efficient?
      \item Why is `air conditioning' efficiency greater than one?
\item Why is `advanced electric heating' efficiency greater than one?
    \end{itemize}


  \end{column}
\end{columns}

 \source{\hrefc{https://data.jrc.ec.europa.eu/dataset/jrc-10110-10001}{JRC IDEES}}

\end{frame}


\end{document}
