separate wind and PV generation profiles for Winter and Spring are provided in Figure5.4and for Summer and Autumn in Figure5.5.
Figure 5.4: Wind and solar PV generation profiles in a typical day of Winter and Spring.
Figure 5.5: Wind and solar PV generation profiles in a typical day of Summer and Autumn.
As expected, PV production is highest during Summer, followed by Spring and Autumn, being at its lowest point during Winter. Meanwhile, wind generation is highest during Winter, followed by Autumn, Spring and finally Summer.
for each energy resource are provided in Table5.2. The values of these bids are based upon the ones presented in [130] and in [168].
Table 5.2: BAU: Energy resources bids andH2prices.
Energy Resource Price External supplier 0.100 m.u./pu
CHP 0.020 m.u./pu
Wind Farm 0.0 m.u./pu
Solar PV 0.0 m.u./pu
BESS Charge 0.030 m.u./pu
Discharge 0.040 m.u./pu
H2PP
Electrolyser 0.0 m.u./pu Fuel cell 0.0 m.u./pu
CHP 0.0 m.u./kg
Forklift fleet 0.0 m.u./kg Tube trailer 0.0 m.u./kg
After the simulation is executed, a single day of each season is analysed, more concretely, the first day of each season. The results, such as the daily operating cost, exchanges with the SU (i.e., energy imported from and exported to the 33 kV grid) and the total amount of energy bought from all three CHP are given in Table5.3.
Table 5.3: BAU - Simulation results for a day of each season.
Result Winter day Spring day Summer day Autumn day
Operating cost [m.u.] 2.3065 0.9270 1.8274 1.9504
SUimport[pu] 19.542 5.7083 14.055 15.343
SUexport[pu] 11.253 23.029 20.002 9.1971
CHP [pu] 17.019 17.213 20.501 20.214
ELEC [pu] 0.0 0.0 0.0 0.0
ELEC [kg] 0.0 0.0 0.0 0.0
FC [pu] 0.0 0.0 0.0 0.0
CHP [kg] 0.0 0.0 0.0 0.0
FL [kg] 0.0 0.0 0.0 0.0
TRSP [kg] 0.0 0.0 0.0 0.0
According to these results, the costs are at their highest in Winter, reaching 2.3065 m.u., and at their lowest for Spring days, at 0.9270 m.u. Even though wind generation is at its peak during the Winter, a low PV production, combined with a high load, leads to the need to import more expensive energy from the SU and also to the necessity of acquiring energy from the CHP. From the generation and load diagram of a Winter day, given in Figure5.6, most of the energy bought from the SU is imported during the evening peak hours, after PV production is no longer available.
In the meantime, from 5h to 15h, there is an energy surplus in the distribution grid, meaning the VPP is able to export energy to the SU.
Figure 5.6: BAU - Generation and load diagram during a Winter day.
Meanwhile, on a Spring day, as seen in Figure5.7, even if wind production is lower, the load is smaller and PV generation is significantly higher, resulting in less imported energy from the SU and in lower operating costs. Also, the energy exported to the SU from 6h to 17h greatly surpasses the imports during the evening peak hours.
Figure 5.7: BAU - Generation and load diagram during a Spring day.
The difference between Summer and Autumn days, whose generation and load diagrams are presented in Figures 5.8 and5.9, is not very sharp in this simulation. Daily operating costs for a Summer day stay at around 1.8274 m.u. and reach 1.9504 m.u. on the Autumn day. The cost
is marginally smaller during Summer, and imports from the SU are very similar, same with the energy bought from CHP. The main difference is in the value of exported energy, which is much higher in Summer, at 20.003 pu, than in Autumn, at 9.1917 pu. However, since it was assumed that the exported energy is acquired by the SU at 0 m.u./MWh, this factor has neither a positive nor a negative effect on daily operating costs. Still, it can be thought of as a waste of cheap and renewable energy, which is undesirable and higher in Autumn.
Figure 5.8: BAU - Generation and load diagram during a Summer day.
Figure 5.9: BAU - Generation and load diagram during an Autumn day.
In all four seasons, energy surpluses take place during the morning and the first hours of the afternoon, meaning that this is the period when the electrolyser is expected to turn on and produce
H2in the next scenarios. Meanwhile, the fuel cell is expected to turn on during the hours when expensive energy is bought from the SU, to minimize operating costs.
5.2.2 Case 1: Base case with the H2PP
In this case, theH2PP is added to the grid on bus 14. Similarly to the BAU case, this is also a reference case to which other scenarios evolving theH2PP will be compared to. The bid prices for each energy resource are given in Table5.4, along with the prices that eachH2customer is willing to pay per kilogram of this gas.
Table 5.4: Case 1: Energy resources bids andH2prices.
Energy Resource Price External supplier 0.100 m.u./pu
CHP 0.020 m.u./pu
Wind Farm 0.0 m.u./pu
Solar PV 0.0 m.u./pu
BESS Charge 0.030 m.u./pu
Discharge 0.040 m.u./pu
H2PP
Electrolyser 0.010 m.u./pu Fuel cell 0.043 m.u./pu CHP 0.00084 m.u./kg Forklift fleet 0.00088 m.u./kg Tube trailer 0.00087 m.u./kg
The bid price of the electrolyser is set to a value small enough to guarantee that it only pur-chases energy and operates when there is only renewable energy being generated in the distribution grid. In other words, theH2PP does not acquire energy from the SU or from any of the CHP. The results in the production of greenH2only. Regarding the bids for each service, the bid price of the fuel cell is given by Equation5.1. The Return On Investment (ROI) multiple is set to 1.5. The bid prices for the CHP, forklift fleet and transportation tube trailer are given in Equations5.2,5.3and 5.4, respectively.
πFC= πeB ηELEC·ηFC
·ROImult= 0.01
0.7·0.5·1.5=0.043m.u./pu (5.1)
πHCHP2 = πeB ηELEC
·HHVH2·ROImult=0.01 0.7 · 39.4
1000·1.5=0.00084m.u./kg (5.2)
πHFL2 =
"
πeB ηELEC
·HHVH2+πeB·PCPFL
#
·ROImult=
=
"
0.01 0.7 · 39.4
1000+0.01· 2.7 1000
#
·1.5=0.00088m.u./kg
(5.3)
πHT RSP2 =
"
πeB ηELEC
·HHVH2+πeB·PCPT RSP
#
·ROImult=
=
"
0.01 0.7 ·39.4
1000+0.01· 1.7 1000
#
·1.5=0.00087m.u./kg
(5.4)
Using those bid prices, the first day of each season is once again simulated and analysed, with the results related to the operation of the grid andH2PP being detailed in Table5.5.
Table 5.5: Case 1 - Simulation results for a day of each season.
Result Winter day Spring day Summer day Autumn day
Operating cost1[m.u.] 2.1254 0.8203 1.6405 1.7724
Electricity cost2[m.u.] 2.1613 0.8897 1.7030 1.7736
SUimport[pu] 17.131 4.2859 11.715 12.825
SUexport [pu] 0.7394 10.869 8.5579 1.0902
CHP [pu] 16.567 16.189 20.258 19.908
ELEC [pu] 10.499 12.514 11.444 8.1019
ELEC [kg] 186.53 222.32 203.32 143.94
FC [pu] 2.8504 2.7822 2.5701 2.8101
CHP [kg] 0.0 8.5549 5.3197 0.0
FL [kg] 41.838 72.538 67.538 1.2990
TRSP [kg] 0.0 0.0 0.0 0.0
1Operating cost includes expenses with electricity and revenue fromH2sale
2Electricity cost only includes expenses with electricity
In this case, compared to the BAU, daily operating costs are lower in all seasons, and, again, the Spring day leads to the lowest and the Winter day leads to the highest cost. Electricity costs, i.e., the expenses associated with buying electricity while ignoring the revenue from H2 sales, are provided in this table and are lower than the daily operating costs of the BAU case, which only included electricity costs as well. This result means that, with the addition of theH2PP, the operator not only benefits fromH2commercialization but can also reduce electricity costs.
In the simulated Winter day, compared to the BAU case, the amount of energy imported from the SU is slightly smaller, dropping from around 19.542 pu to 17.131 pu, but the main difference is in the exported energy, which fell from around 11.253 pu to only 0.7394 pu. This happens due to the presence of theH2PP, which allows the operator to store a substantial amount of energy during the hours when there is a surplus. This energy is injected into the grid using the FC during the evening peak and also during the very first hours of the day when it is necessary to import energy from the SU, as displayed in Figure 5.10. During Winter, it was only possible to sellH2 to the forklift fleet operator.
During Spring, the energy imported from the SU is lower than in the same season in the BAU case, falling from 5.7083 pu to 4.2859 pu. Meanwhile, exported energy suffered a significant drop, from 23.029 pu to 10.869 pu due to the additionH2PP, which allows the energy surplus to be stored and used for the advantage of the grid operator, instead of being supplied to the SU at
Figure 5.10: Case 1 - Generation and load diagram during a Winter day.
no profit. Again, the FC is mostly used during the first hours of the day and during the evening, as shown in Figure5.11. Compared to the Winter day, in Spring there is a more substantial amount ofH2being supplied to customers, including the CHP and the forklift fleet. Again, the tube trailer is not supplied, even if this is the season with the largest dailyH2production, at 222.32 kg.
Regarding the Summer day, whose diagram is presented in Figure5.12, once more the acqui-sition of theH2PP led to a reduction in imported energy, from 14.055 pu to 11.715 pu, and to a reduction in exported energy, from 20.002 pu to 8.5579 pu. It is still possible to supplyH2to the CHP and to the forklift fleet, but in a lower quantity than during Spring, asH2production is not as high, around 203.32 kg.
Figure 5.11: Case 1 - Generation and load diagram during a Spring day.
Figure 5.12: Case 1 - Generation and load diagram during a Summer day.
At last, on the Autumn day, one can see that the imported energy falls from 15.343 pu to 12.825 pu, and the exported energy falls from 9.1971 pu to 1.0902 pu. Its load diagram is given in Figure5.13. NoH2is supplied to the CHP microturbine or to the tube trailer and only a negligible amount ofH2is to be provided to the forklift fleet.
Figure 5.13: Case 1 - Generation and load diagram during an Autumn day.
In all four seasons, as expected considering the bids detailed in Table5.4, the production ofH2 is done only during the hours when the renewable generation exceeds the load on the distribution grid. The presence of theH2PP conducts in a reduction in energy imported and exported to the grid, due to theH2 storage capability. It is also possible to supply multipleH2 customers, but, under the envisioned scenarios, theH2was mostly used by the fuel cell to avoid the purchase of
expensive energy from the SU rather than sold to the customers for other end-uses. In none of the seasons was possible to fill the tube trailer, as the amount of generatedH2is too low in all periods to completely fill a trailer with 300 kg ofH2.
5.2.3 Case 2: H2PP single service (Fuel Cell)
In this scenario, it is assumed that theH2PP loses all of its customers, meaning that H2, if produced, can only be used in the fuel cell. The bid prices are provided in Table5.6and the results obtained for a day of each season are given in Table5.7.
Table 5.6: Case 2: Energy resources bids andH2prices.
Energy Resource Price External supplier 0.100 m.u./pu
CHP 0.020 m.u./pu
Wind Farm 0.0 m.u./pu
Solar PV 0.0 m.u./pu
BESS Charge 0.030 m.u./pu
Discharge 0.040 m.u./pu
H2PP
Electrolyser 0.010 m.u./pu Fuel cell 0.043 m.u./pu
CHP 0.0 m.u./kg
Forklift fleet 0.0 m.u./kg Tube trailer 0.0 m.u./kg
In this case, there is no differentiation between operating costs and electricity costs, because, without theH2customers, all costs are already associated with electricity.
Table 5.7: Case 2 - Simulation results for a day of each season.
Result Winter day Spring day Summer day Autumn day
Operating cost [m.u.] 2.1424 0.8377 1.6620 1.7728
SUimport[pu] 17.131 4.2859 11.715 12.825
SUexport [pu] 2.7506 15.851 12.602 1.1339
CHP [pu] 16.567 16.186 20.258 19.908
ELEC [pu] 8.6117 7.3431 7.3431 8.0289
ELEC [kg] 153.00 130.46 130.46 142.65
FC [pu] 3.0141 2.5701 2.5701 2.8101
CHP [kg] 0.0 0.0 0.0 0.0
FL [kg] 0.0 0.0 0.0 0.0
TRSP [kg] 0.0 0.0 0.0 0.0
Once again, costs are the lowest during Spring and highest during Winter. Even with the loss of theH2customers, the daily operating costs are still lower than in the BAU case, but higher than in Case 1. The energy imported from the SU is the same as in Case 1 in all seasons. This is a result that could be anticipated because the loss ofH2 customers should not have a major effect on electricity consumption and production, since the total installed power in the grid, renewable generation and the daily load are not affected by this change. In other words, the loss of those customers does not have a significant impact on most electrical-related quantities. This conclusion is also supported by the fact that the energy acquired from the CHP plants is also the same as in Case 1. Nevertheless, energy exportation is higher in this case, because theH2PP does not produce as muchH2as before when it had the possibility to supply external customers.
5.2.4 Case 3: H2PP operates without the Fuel Cell
In this case, it is assumed that theH2PP operates without the fuel cell, but allH2customers are available. Again, bids are provided in Table5.8and the results obtained for a day of each season are given in Table5.9.
Table 5.8: Case 3: Energy resources bids andH2prices.
Energy Resource Price External supplier 0.100 m.u./pu
CHP 0.020 m.u./pu
Wind Farm 0.0 m.u./pu
Solar PV 0.0 m.u./pu
BESS Charge 0.030 m.u./pu
Discharge 0.040 m.u./pu
H2PP
Electrolyser 0.010 m.u./pu Fuel cell 0.0 m.u./pu CHP 0.00084 m.u./kg Forklift fleet 0.00088 m.u./kg Tube trailer 0.00087 m.u./kg
Due to the loss of the fuel cell, operating and electricity costs are higher than in Case 1. More precisely, it can be noted that, in this case, electricity costs are equal to the operating costs achieved in the BAU case. This is due to the fact that there is no fuel cell to generate and replace the energy bought from the SU or from the CHP. In other words, even though theH2PP is still fitted with a storage tank, the P2G process is interrupted. This means that, from an electrical point of view, the H2PP is no longer a storage unit, but a mere electrical load.
The operating costs resulting from the removal of the fuel cell are also higher than the oper-ating costs of Case 2, when theH2 customers were lost. This means that, under the conditions of this case study, the fuel cell is a more valuable asset to theH2PP than the external customers.
Also, as costs were lower in Case 3 than in Case 2, grid operation benefits more from the fuel cell and the G2P process than fromH2trading (i.e., sellingH2to these three customers).
Table 5.9: Case 3 - Simulation results for a day of each season.
Result Winter day Spring day Summer day Autumn day
Operating cost [m.u.] 2.2645 0.8850 1.7871 1.9101
Electricity cost [m.u.] 2.3065 0.9270 1.8274 1.9504
SUimport[pu] 19.542 5.7083 14.055 15.343
SUexport [pu] 3.1545 14.985 12.239 1.4189
CHP [pu] 17.019 17.212 20.501 20.214
ELEC [pu] 8.0688 8.0688 7.7396 7.7396
ELEC [kg] 143.35 143.35 137.51 137.51
FC [pu] 0.0 0.0 0.0 0.0
CHP [kg] 23.354 23.354 19.505 19.505
FL [kg] 120.00 120.00 118.00 118.00
TRSP [kg] 0.0 0.0 0.0 0.0
5.2.5 Case 4: Increased Capacity Factor for wind power
In this case, the CF values mentioned in 5.1 are raised by 50 % in all seasons. The main purpose of this increase is to analyse the impact that massive RES have onH2PP behaviour. Hence, it may enable the participation of the tube trailer in theH2trade, and, as such, its biding price is slightly increased when compared to other customers (the value of ROImult for this customer is increased to 1.7 and kept at 1.5 for the CHP and forklift fleet). Notwithstanding, it should be noted how this is a more optimistic scenario than all the previous ones, with substantially higher availability of renewable generation, meaning that a direct comparison is not entirely fair. Like before, bids are given in Table5.10and the results of the simulations are provided in Table5.11.
Table 5.10: Case 4: Energy resources bids andH2prices.
Energy Resource Price External supplier 0.100 m.u./pu
CHP 0.020 m.u./pu
Wind Farm 0.0 m.u./pu
Solar PV 0.0 m.u./pu
BESS Charge 0.030 m.u./pu
Discharge 0.040 m.u./pu
H2PP
Electrolyser 0.010 m.u./pu Fuel cell 0.043 m.u./pu CHP 0.00084 m.u./kg Forklift fleet 0.00088 m.u./kg Tube trailer 0.00099 m.u./kg
It can be seen how the increase in the CF has a deep impact on theH2PP and the operation of the grid. First, the operating costs are now negative in all seasons except in Summer, meaning the operator is having a net profit. Spring days are still the most beneficial, but they are now followed by Autumn, Winter and Summer days, which had the lowest initial CF and thus benefit less from the increase of this factor.
Table 5.11: Case 4 - Simulation results for a day of each season.
Result Winter day Spring day Summer day Autumn day
Operating cost [m.u.] -0.0289 -0.1248 0.0085 -0.0608
SUimport[pu] 0.0 0.0 0.1134 0.0
SUexport[pu] 39.199 47.388 28.512 26.444
CHP [pu] 3.8874 0.0 3.922 1.7946
ELEC [pu] 25.528 26.843 21.083 23.734
ELEC [kg] 453.54 476.91 374.57 421.67
FC [pu] 1.4400 1.2000 1.4683 1.4400
CHP [kg] 0.0 13.088 0.0 0.0
FL [kg] 80.443 102.89 0.0331 48.569
TRSP [kg] 300.00 300.00 300.00 300.00
Furthermore, in all but the Summer day, the distribution grid can be said to be self-sufficient, without importing any energy. Still, it needs the SU to receive energy surpluses, which is quite high, as seen in the great amount of exported energy in all seasons. Some energy is also bought from the CHP, except on the Spring day when it can even be asserted that the grid is not only self-sufficient but also 100 % based on RES.
As expected with the increase in wind generation, the production of H2 is now higher than ever, surpassing 476.91 kg on the Spring day and still reaching 374.57 kg in Summer. As a result, theH2PP is now able to supply 300 kg ofH2to the tube trailer across all days. The remainingH2 is consumed by the FC or supplied to the forklifts. Only on the Spring day, there is enough gas to partially supply the CHP.
5.2.6 Case 5: Limited line capacity with H2PP disconnected from the grid
This case and the next follow a different methodology than the previous ones. Now, the main intent of the simulations is to analyse the impact of theH2PP in grid constraints, namely voltage levels and lines congestion. For that, the maximum capacity of the power lines, which was initially set to 20 MVA, was reduced to 4 MVA. The operation of the grid is simulated under these new conditions both with and without theH2PP.
Starting with the operation without the H2PP, bid prices are the same as in the BAU case, reproduced in Table5.12. Since it would be unfeasible to analyse the voltage profile for all hours within a day, for all the seasons, only one hour is presented and analysed. It was decided to study the 21sthour of the Winter day when the load is at its peak. Results are given in Table5.13.
Table 5.12: Case 5: Energy resources bids andH2prices.
Energy Resource Price External supplier 0.100 m.u./pu
CHP 0.020 m.u./pu
Wind Farm 0.0 m.u./pu
Solar PV 0.0 m.u./pu
BESS Charge 0.030 m.u./pu
Discharge 0.040 m.u./pu
H2PP
Electrolyser 0.0 m.u./pu Fuel cell 0.0 m.u./pu
CHP 0.0 m.u./kg
Forklift fleet 0.0 m.u./kg Tube trailer 0.0 m.u./kg
Due to the lower capacity of the power lines, grid operation is much more limited, and thus operating costs are now higher than in any of the previous cases, reaching 3.1846 m.u. in the simulated season, Winter. Furthermore, and as expected, the operator had to import more energy from the SU, export more and acquire more energy from the CHP than in the BAU case.
Regarding voltage levels and lines congestion at the 21sthour of the day, those are pictured in Figure5.14, while Table5.14provides information concerning the average, minimum and maxi-mum voltages in all buses and power flows through all lines, in percentage.
Figure 5.14: Case 5 - Voltage levels and line capacity at 21 h in Winter.
The most overloaded lines are the ones between buses 1-27, 2-4 and 13-14. The high current in line 2-4 is due to the existence of a wind farm in bus 4. Similarly, the high current in line 13-14
Table 5.13: Case 5 - Simulation results for a Winter day.
Result Winter day
Operating cost [m.u.] 3.1846
SUimport [pu] 21.059
SUexport [pu] 15.311
CHP [pu] 19.902
ELEC [pu] 0.0
ELEC [kg] 0.0
FC [pu] 0.0
CHP [kg] 0.0
FL [kg] 0.0
TRSP [kg] 0.0
is a consequence of the presence of theH2PP, a CHP, a wind farm and a PV installation in bus 14.
The high power flow through line 1-27 is due to the fact that this line supplies more loads than any of the other lines connected to bus 1, and there are not many DER between buses 27 and 37, apart from the PV installations.
Table 5.14: Case 5 - Average bus voltage and power line utilization.
Result Winter day V¯i[pu] 1.032 Vimin[pu] 1.021 Vimax[pu] 1.050 S¯i,j [%] 28.76 Smini,j [%] 5.206 Smaxi,j [%] 88.55
The average voltage stays around 1.032 pu, with its maximum value reaching 1.05 pu, which is the maximum admissible value. On average, power lines are at around 28.76 % of their capacity (4 MVA), with the most overload line reaching 88.55 %.
5.2.7 Case 6: Limited line capacity with H2PP connected to the grid
In this case, which is similar to Case 5, line capacity is again limited to 4 MVA. The only difference is that theH2PP is back to the grid, being connected once more at bus 14. Bid prices for each energy resource are given in Table5.15, along with the prices that eachH2 customer is prepared to pay per unit of mass. The results for a Winter day are given in Table5.13.
With theH2, it is possible to reduce operating costs in comparison to Case 5. However, costs are still higher than in both the BAU case and in Case 1.