Energy management on a stand-alone power system for the ...

<strong>Energy</strong> <strong>management</strong> on a stand-alone power system for the production of electrical
energy with hydrogen long term storage
3.4. Effect of key variables to the operation of the stand-alone power system
The study of the integrated system requires the analysis of the effect of the limit SOC min
as well as of the hydrogen constraint and diesel use. Table 1 shows that, reduction the
SOC min causes less hydrogen to produce and to consume but the total hydrogen is
higher. Furthermore, there was part of energy that was lost during the analysis of the 3 rd
strategy at 7.75, 3.15 and 2.62kWh for SOC min at 84, 80 and 76% respectively.
H 2 ,-Elec, Νm 3 H 2 -FC, Νm 3 H 2 –Tot, Νm 3
1 st Strategy 92.1 102.8 49.8
SOC min
84%
SOC min
80%
SOC min
76%
2 nd Strategy 106.7 144.4 22.8
3 rd Strategy 118 185.6 -7.2
1 st Strategy 75.2 53.9 81.8
2 nd Strategy 75.9 58.6 77.8
3 rd Strategy 74.6 61.5 73.6
1 st Strategy 71 38.3 93.2
2 nd Strategy 71.2 41.2 90.5
3 rd Strategy 69.3 42.3 87.5
Table 1: Results for the hydrogen production and consumption during a typical four
month period for various values of SOC min and of fuel cell output power
From the analysis of the three strategies, it was found that there were cases where the
demand for hydrogen was more than it was stored in the storage tanks. Especially for an
increase in the output power of the fuel cell the consumption was higher and the stored
hydrogen was less [5, 6]. This outcome resulted in the use of commercial hydrogen with
an additional cost in the system. For the next case study, a hydrogen constraint is used
in all algorithms. If the hydrogen stored is higher than the 95% of nominal capacity of
the storage tanks the excess of energy is used to charge the accumulator (until 100%)
and if excess energy still exists then it is lost (driven to the dump load). In case that
shortage of energy exists then the fuel cell meets the energy demand without taking into
consideration the SOC of the accumulator. Similarly, when the hydrogen stored is lower
than the 5% of the nominal capacity of the storage tanks and shortage of energy exists
(SOC