A	Availability, kW, Area, m2
At	Tube cross-sectional area, m2
Af	Amortization factor, 1/y
AAC	Absorption Air Conditioning
C	Thermo-economic cost stream, USD/kJ
Cp	Specific heat capacity, kJ/kg °C @ constant pressure
COP	Coefficient of Performance
D	Diameter, m
Denv	Collector glass envelope diameter, m
E	Exergy stream, kW
ETC	Evacuated Tube Collector
f	Function
FHP	Fan power, kW
H, h	Height, m, Enthalpy, kJ/kg
Hdish	Dish parabola height, m
Is	Solar intensity, W/m2
i	Interest rate, %
L	Length, m
Lm	Module length, m
LMT	Logarithmic Mean Temperature, °C
LPC	Levelized Power Cost, USD/kWh
LTp	Plant life time, y
M	Mass flow rate, kg/s
NOT	Number of Tubes
NOC	Number of Collectors
NOL	Number of Loops
P	Power, or Pressure, bar
ΔP	Pressure, bar
Q	Thermal power, kW
RPR	Relative Performance Ratio
Re	Raynold’s Number
S, s	Entropy, kJ/kg °C
SHX	Solution Heat Exchanger
T	Temperature, °C
U	Overall heat transfer coefficient, W/m2 °C
V, Vol	Volume, cm3
v	Velocity, m/s
W	Power, Work, kW
Wc	Collector width, m
X	Concentration percentage, %
Z	Hourly cost, USD/h
Subscripts
a, abs	Absorber
air	Air
amb	Ambient
a-hex	From absorber to heat exchanger stream
c	Condenser
c-evp	From condenser to evaporator stream
col	Collector
cw	Cooling water
e	Evaporator
etc	Evacuated tube collector
e-abs	From evaporator to absorber stream
f	Liquid phase
fan	Fan
fsh	Flashing tank
fst	Flashing steam
g	Generator, vapor phase
g-hex	From generator to heat exchanger stream
i	Inlet
loop	Loop
o	Out
p	Pump
ptc	Parabolic trough collector
pi,o	Pump inlet and outlet
q	Heat
r	Refrigerant
s	Steam
st	Steam
str	Strong
t	Turbine, total
w	Water
wk	Weak solution
Greek
η	Efficiency, %
ρ	Density, kg/m3
µ	Dynamic viscosity, Pa.s