Appendix A

I dokument Hybrid Power System for Green Telecom Sites (sidor 65-72)

“Renogy,” 10th March 2021. [Online]. Available: https://www.renogy.com/blog/solar-charge-controller-sizing-and-how-to-choose-one-/.

7 Appendix A

The results for the Dittenheim site are shown in detail here.

In the first case, only 6pv panels with no batteries were considered. Table 14 illustrates all the main results of the iteration. The PV production covers 16% of the total yearly load and produces an annual savings of 639€. The payback period is calculated both with and without considering the time value of money, with a 5% of interest rate. The investment is recovered respectively in 13 and 9 years.

Table 14 - Main results for the case with 6 pv panels and no storage

Yearly PV production 3489 kWh

PV coverage of total load 16 %

Yearly Electricity demand 22134 kWh Electricity cost if 100% grid 4020 € Demand covered by grid only 18644 kWh

Cost from grid 3381 €

Savings 639 €

Capex 5538 €

Opex 55 €

Payback Period 10 Years

Discounted Payback Period

(5% interest rate) 14 Years

Other aspects of interest are shown in the following pictures. Figure 54 shows the electricity mix of the site, underlining the percentage of the load that is covered by solar energy. When only 6 panels are used, the renewable contribution to the total load is relatively low. Figure 55 shows the hourly production for the month of April.

66 Figure 54 - Monthly electricity mix and load

Figure 55 - Hourly profile of PV output for the month of April calculated from the tool

Then, the case with storage was analysed. The storage is utilized for peak shaving, the batteries are recharged with the grid during the lowest price hours and discharged during high price hours to save money. A solver was used to find the two optimum price limits to start charging and recharging, to minimize the annual purchasing cost from the grid. It was found that, the battery should be charged during the three lowest price hours in the early morning, when the electricity fee is below 0,14€/kWh and then cover the load in the evening when the price goes above 0,21€/kWh. Firstly, only one 100Ah battery was picked, with a total energy capacity of 4800 Wh. The battery is charged and discharged only from 20% to 90% of capacity, to increase its lifetime. The results for this case are shown in Table 15. Despite the higher Capital investment compared to the previous case, due to the purchasing of a storage device, the payback period stays the same, while the discounted payback period is even reduced by one year, because of the larger annual savings, resulting from the demand side management of storing electricity when the price is lower and releasing that energy during higher price hours.

1499 1167 736

53 0 105 0 247 513

1168 1358 1591

0 500 1000 1500 2000 2500

DG/Grid Wind PV (kWh) Load [kWh]

Energy Mix kWh/Month

0 500 1000 1500 2000

1 19 37 55 73 91 109 127 145 163 181 199 217 235 253 271 289 307 325 343 361 379 397 415 433 451 469 487 505 523 541 559 577 595 613 631 649 667 685 703

Hourly PV Output in April [W]

67 Table 15 – Main results for the case with 6 pv panels and one battery of 100Ah

Yearly PV production 3489 kWh

PV coverage of total load 16 % Yearly Electricity demand 22134 kWh Electricity cost if 100% grid 4020 €

Figure 56 illustrates the energy produced by the PV and the energy coming from the grid, in blue and grey bars, the battery state of charge and the electricity prices, red and yellow graphs, for every hour of the 2nd of January, as representative of the worst case. The total storage capacity is not enough to cover the whole peak evening demand, but only part of it.

Figure 56 - Hourly energy from grid, PV, battery state of charge and electricity prices for the 2nd of january

0

6Pv+1Battery on the 2nd of January

PV Grid BESS Load Grid Price

68 Next, a case with 6 panels and 3 batteries is analysed. The main results are shown in Table 16. Here, the savings are higher than before, because more energy can be stored in the morning to cover the evening peak. However, the high costs related to the replacement of the batteries every 10 years, result in a higher payback period.

Table 16 - Main results for the case with 6 PV panels and 3 batteries

Yearly PV production 3489 kWh

PV coverage of total load 16 %

Yearly Electricity demand 22134 kWh Electricity cost if 100% grid 4020 € Demand covered by grid only 18644 kWh

Cost from grid 3090 €

Figure 57 shows the energy produced by the PV, the energy coming from the grid, the battery state of charge and the electricity prices, for every hour of the 2nd of January. In this case, the peak shaving is achieved by charging the batteries with the grid from 2 to 6 am, when the prices are the lowest and discharging the batteries from 7 to 9 pm to completely cover the load when the prices are the highest. However, if the value of money is discounted by 5%

every year, the system is not economically feasible, since it does not recover the expenses within its lifetime.

Figure 57 - Hourly energy from grid, PV, battery state of charge and electricity prices for the 2nd of january

0

69 Then, 12 PV panels and 3 batteries. The main results are shown in Table 1. The larger number of pv panels helps achieving over 30% of total contribution from renewable energy, increasing also the savings from not using the grid. As a consequence, the payback period has significantlly improved from the previous case. Having 12 panels means that a peak power of 6 kW can be reached, which is far higher than the average load (2,5 kW). Therefore, in this case, there can be situations in which the battery should be used to store excess pv generation, rather than storing energy from the grid when is cheaper and releasing it when it is more expensive. A rough calculation based on the maximum radiation value for each month was made to split the year in two period. From April to August included, the batteries are used exclusively to store excess of pv, whereas, from September to March, the demand side management based on the electricity price that was done in the cases before was performed. This allowed to maintain the amount of dumped energy from the PV array fairly low and reduce waste.

Table 17 - Main results for the case with 12 PV panels and 3 batteries

Yearly PV production 6929 kWh

PV coverage of total load 31 %

Yearly Electricity demand 22134 kWh Electricity cost if 100% grid 4020 € Demand covered by grid only 15205 kWh

Cost from grid 2570 €

Savings 1450 €

Capex 10 815 €

Opex 108 €

Payback Period 11 Years

Discounted Payback Period

(5% interest rate) 14 Years

Excess of PV/Total PV 1 %

To better illustrate these different system behaviour, the hourly profile of PV production, Load, Battery capacity for two different days are shown in Figure 58 and Figure 59, for the 2nd of January and the 1st of July. The main difference it can be noticed is that, in winter, the batteries are charged with the grid and used for price peak shaving, whereas in summer, no grid energy is stored in the batteries, but it is left room to store solar energy during the day and realising it in the evening.

70 Figure 58 - Hourly energy from grid, PV, battery state of charge and electricity prices for the 2nd of january

Figure 59 - Hourly energy from grid, PV, battery state of charge and electricity prices for the 1st of July

Next, 18 PV panels and 3 batteries were picked. Despite the higher capital cost, the payback period keeps improving as the number of panels are increased, due to the higher renewable energy produced, which helps avoiding paying the grid, Table 18.

0

Grid PV Excess PV BESS Load Grid Price

71 Table 18 - Main results for the case with 18 PV and 3 Batteries

Yearly PV production 9466 kWh

PV coverage of total load 43 %

Yearly Electricity demand 22134 kWh Electricity cost if 100% grid 4020 € Demand covered by grid only 12668 kWh

Cost from grid 2136 €

In this case, from March to October the batteries are used only to store the energy coming from the PV array, while in the rest of the year, the demand side strategy is applied. Figure 60 shows the hourly profile for the 1st of July. A difference compared to the previous cases is that the excess of PV is much more noticeable (green bar chart), due to the oversizing of the panels. Nevertheless, the techno-economic performance are much better than the case with 12 panels only.

Figure 60 - Hourly energy from grid, PV, battery state of charge and electricity prices for the 1st of July 0

Grid PV Excess PV BESS Load Grid Price

72

I dokument Hybrid Power System for Green Telecom Sites (sidor 65-72)