B	dimensionless activation energy of adsorption for lumped equilibrium constant
B ’	dimensionless heat of adsorption for lumped equilibrium constant
C p	specific heat capacity (kJ/(mol K))
d M	thickness of membrane (m)
E	activation energy (J/mol)
E x	exergy (kJ/mol)
HHV	molar higher heating value (kJ/mol)
ΔH	enthalpy change (kJ/mol)
$\Delta h^{\prime }$	lumped heat of adsorption (kJ/mol)
J	hydrogen permeation flux (mol/m2/s)
K	equilibrium constant of the MCH dehydrogenation reaction
K ’	lumped equilibrium constant at reaction temperature
K r ’	lumped equilibrium constant at reference temperature
K A	adsorption equilibrium constant of MCH (bar−1)
K B	adsorption equilibrium constant of TOL (bar−1)
K C	adsorption equilibrium constant of hydrogen (bar−1)
k d	apparent short-term deactivation constant (day−1)
k	rate constant at the reaction temperature (mol/g/s)
k r	rate constant at the reference temperature (mol/g/s)
P	pressure (bar)
P 0	atmosphere pressure (bar)
P r	reaction pressure (bar)
p A	partial pressure of MCH (bar)
p B	partial pressure of TOL (bar)
p C	partial pressure of hydrogen (bar)
Q preheat	solar thermal energy input for raising the temperature of reactant (kJ)
Q enthalpy	solar thermal energy input for enthalpy change (kJ)
Q sh	thermal energy contained in gases after reaction (kJ)
R	universal gas constant (J/(mol K))
R in	inner radius (cm)
R o	outer radius (cm)
r	kinetic rate of the reaction (mol/g/s)
T 0	room temperature (K)
T H	reaction temperature (K)
T r	reference temperature (K)
T sun	surface temperature of sun (K)
t d	online reaction deactivation time (day)
$W_{\mathrm{p},\mathrm{vacuum}}$	exergy consumed by vacuum pump to separate hydrogen (kJ)
$W_{\mathrm{p},\mathrm{compressor}}$	exergy consumed by compressor to feed MCH into reactor (kJ)
q coal	heating value of standard coal (kJ/kg)
Greek symbols
μ	mass ratio of carbon dioxide emission from standard coal combustion (–)
α	conversion rate of methane (–)
η c →e	conversion efficiency from standard coal to electricity (–)
η c →h	conversion efficiency from standard coal to heat (–)
η HHV	First-law of thermodynamic efficiency with separation exergy (–)
η HHV,real	First-law of thermodynamic efficiency with real separation energy (–)
η s →f	Solar-to-fuel efficiency with separation exergy (–)
η s →f,real	Solar-to-fuel efficiency with real separation energy (–)
η ex	exergy efficiency (–)
η abs	absorption efficiency (–)
η opt	optical efficiency (–)
${\eta }_{{\mathrm{p}}_1}$	vacuum pump efficiency (–)
${\eta }_{{\mathrm{p}}_2}$	compressor mechanical efficiency (–)
η s →e	Solar-to-electricity efficiency (–)
Superscript
$\ominus$	standard state
*	active sites of catalyst
Subscripts
d	day
in	input, inside
init	initial
opt	optical
out	output, outside
p	vacuum pump/compressor
res	residual gas