renewable energy conversion,transmission and storage

[...]... the net energy input, E = JQ,in — JQ,out + Jm (win − wout ) (2.12) The magnitude of the currents is given by (2.9), and their conventional signs may be inferred from Fig 2.2 The specific energy content of the incoming mass flow, win, and of the outgoing mass flow, wout, are the sums of potential energy, kinetic energy and enthalpy The significance of the enthalpy to represent the thermodynamic energy. .. changes, hin = Pin / ρin, hout = Pout / ρout, (8.4) where the internal energy term U in H, assumed constant, has been left out, and the specific volume has been expressed in terms of the fluid densities ρin and ρout at input and output If a linear model of the Onsager type (2.10) is adopted for Jm and Jθ and these equations are solved for Jm and Fθ, one obtains Jm = Lmθ Jθ / Lθθ + (Lmm − LmθLθm / Lθθ) Fm,... free energy, or maximum work, is found by considering a reversible process between the initial state and the equilibrium It equals the difference between the initial internal energy, Uinit = U + Uref, and the final internal energy, Ueq, or it may be written (all in terms of initial state variables) as G = U — Tref S + Pref V, (2.6) plus terms of the form Σµi,refni if chemical reactions are involved, and. .. the heat and mass flow into the device is converted to power is, in analogy to (2.4), η= E , J Q ,in + J m w in (2.19) where the expression (2.16) may be inserted for E This efficiency is sometimes referred to as the “first law” efficiency, because it only deals with the amounts of energy input and output in the desired form and not with the “quality” of the energy input related to that of the energy. .. cycle) Closer to the Carnot ideal is the Stirling cycle, involving two isochores (12 and 3-4) and two isotherms The Ericsson cycle has been developed with the purpose of using hot air as the working fluid It consists of two isochores (2-3 and 4-1) and two curves somewhere between isotherms and adiabates (cf e.g Meinel and Meinel, 1976) 14 3 THERMODYNAMIC ENGINE CYCLES The last cycle depicted in Fig 3.1... Rankine cycle in Fig 3.1) may be less than the energy input to the compressor, thus further reducing the COP and the second law efficiency, relative to the primary source of high-quality energy I GENERAL PRINCIPLES 15 4 DIRECT THERMOELECTRIC CONVERSION CHAPTER 4 DIRECT THERMOELECTRIC CONVERSION If the high-quality energy form desired is electricity, and the initial energy is in the form of heat, there is... where the superscript g stands for the gas performing the thermodynamic cycle, f stands for the fluid leading heat to the heating chamber heat exchanger, and x increases from zero at the entrance to the heating chamber to a maximum value at the exit Cp is a constant-pressure heat capacity per unit mass, and Jm is a mass flow rate Both these and h’, the heat exchange rate II HEAT ENERGY CONVERSION PROCESSES... variables are the mass flow rate, Jm (2.9), and the generalised force Fm given in (2.18) The specific energy contents win and wout are of the form (2.13), corresponding to e.g the geopotential energy of a given water head, pot w in = g ∆ z , pot w out = 0 , (8.2) the kinetic energy of the working fluid, kin 2 w in = ½ u in , kin 2 w out = ½ u out , (8.3) and the enthalpy connected with the pressure... up reversibility and accept a finite amount of energy dissipation and an efficiency that is smaller than the ideal one (2.4) 2.3 Efficiency of an energy conversion device A schematic picture of an energy conversion device is shown in Fig 2.2, sufficiently general to cover most types of converters in practical use (Angrist, 1976; Osterle, 1964) There is a mass flow into the device and another one out... reversibility (Onsager, 1931) Considering FQ and Jq (Carnot factor and electric current) as the “controllable” variables, one may solve for Fq and JQ, obtaining Fq in the form (2.24) with FQ = FQ,in and Lqq = (Rint) -1; LqQ = LQq = α T/Rint The equation for JQ takes the form JQ = CTFQ + α T Jq, where the conductance C is given by C = (LQQLqq − LQqLqQ)/(LqqT) Using (4.2) and (4.3), the dissipation may be written . amounts of energy input and output in the desired form and not with the “quality” of the energy input related to that of the energy output. In order to include reference to the energy quality,. (thermochemical) cal 4.184 J energy British thermal unit Btu 1055.06 J energy Q Q 10 18 Btu (exact) energy quad q 10 15 Btu (exact) energy tons oil equivalent toe 4.19 × 10 10 J energy barrels oil. 5.74 × 10 9 J energy tons coal equivalent tce 2.93 × 10 10 J energy m 3 of natural gas 3.4 × 10 7 J energy kg of methane 6.13 × 10 7 J energy m 3 of biogas 2.3 × 10 7 J energy litre