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4.7. System calculation
4.7 System calculation
Most calculations are done in the respective component modules as
described in chapter 3, but calculations concerning more than one
component (or just very simple components - merely consisting of an
efficiency) have been places in the main system file. These calculations
will be described in the following sections.
Inverter
The power produced by the SOFC (Ẇ SOFC ) is delivered by direct current
(DC), but for many applications alternating current (AC) is more desirable.
It is assumed that the other components in the system (blower, fan and
pumps) are driven by AC power.
An inverter converts DC to AC which introduces a power loss. The
efficiency of the inverter is specified by η inver t which is estimated to 95%.
4.7.1 Efficiencies
When looking at the system it is convenient to know how much energy
that is available in each point of the gas stream (fuel, air and exhaust gas).
For this the ”energy flow rate”, ∆Ḣ, is used 13 . It is defined as how much
enthalpy the gas contains in a given point relative to when it is totally
combusted at the reference temperature (T re f = 25 ◦ C, in non-condensed
state):
∆Ḣ j = Ḣ j − Ḣ f ull y combusted at Tre f
(4.5)
∆Ḣ is calculated in point 0 to 24 (figure 4.1 page 80). The sum of all
incoming gases to the system (point 0, 1 and 11) is called ∆Ḣ i .
SOFC
The gross AC and the net AC power delivered by the SOFC stack (without
deductions for ABS pump or cooling tower fan) is calculated respectively
13 Caution! This has another reference than the normal enthalpy flow rate Ḣ as
defined in equation 3.1 page 43
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