The Kaohsiung Arena MRT Station is fed with electricity generated from fossil fuels, the purpose is to know how many piezoelectric tiles would be necessary to replace the thermal generation.
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To make the analysis is required to know the amount of power that Pavegen tiles can generate per day. In total, and according to the Republic of China calendar, in the year 107, Kaohsiung Arena Station had 5,205,631 passengers going into the station, and 5,366,932 passengers going out from the station, through the whole year (Appendix 1), considering that a year has 365 days, in average the passengers going into the station was 14,262 passengers per day, and passengers going out from the station 14,703.92, it means around 29,000 people transit the station per day.
Figure 27.Pavegen working model. (Boby, 2014)
Figure 27 shows the representation of the working model of Pavegen tiles, to generate energy the person must give a step on the tile, then the energy can be stored or consume immediately depending on the requirements of the company.
According to Pavegen, a single tile can generate 5 joules or what is the same 5 watts per step, to generate this energy a person should have an average weight of 60 to 70 kg, and we assumed the electrical consume of the station is 9,000 kWh per day, and this information along with the number of pedestrians, allow us to calculate the number of required tiles to supply the electric consume of the station.
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First of all, we will convert kWh into Joules using the next formula.
1 𝑘𝑊ℎ = 3,412 𝐵𝑇𝑈, 𝑤ℎ𝑒𝑟𝑒, 1 𝐵𝑇𝑈 = 1,055 𝐽𝑜𝑢𝑙𝑒𝑠.
1 𝑘𝑊ℎ = 3,412 ∗ 1,055 = 3,600,000 𝐽𝑜𝑢𝑙𝑒𝑠 𝐸𝐽 =9,000 kWh day * 3,600,000 = 32,400,000.000 Joules
The electric consumption of the station per day reaches 32,400,000,000 Joules. And also, as we said above, one tile can generate 5 Joules.
32,400,000,000 Joules / 5 Joules= 6,480,000,000 Joules per tile
We know that Kaohsiung Arena MRT Station holds an average of 29,000 pedestrians per day, with this information we can calculate the footsteps required to power the station.
6,480,000,000 Joules per tile / 29,000 Pedestrian = 223,448.28 footsteps
To generate 6,480,000,000 joules, are required about 223,449 footsteps of each pedestrian per day in order to supply the electric consumption with piezoelectricity.
Assuming every pedestrian hits 30 times the piezoelectric tiles, and that there are 7,000 tiles arranged in the station where each tile costs about $78 USD, under these conditions the energy produced would cover the electric consumption of the station per year. However, the cost per square meter is $620 USD, which indicates that the final value of the tiles will reach roughly
$546,000 USD, and the fact that it is impossible to get the maximum power of each tile, it is non-viable condition.
Considering the place where the tiles will be located, the ticketing gates, and the chances to hit them 30 times, it makes of it, an impossible situation to set a big amount of tiles. It means
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that using piezoelectricity to replace thermal energy by itself is not an option, on one hand, because of the high cost of the tiles and on the other hand because to produce electricity through piezoelectric requires and external factor, it is kinetic energy.
Despite this technology is not suitable to supply the total consumption of the station, it might be a good complement source to produce electrical energy to reduce the electric consumption of the station. Given the location of the ticket gates, the objective is to place 1.5 square meters of the tiles on each gate, just as it is shown in Figure 28.
Figure 28. Location of the Tiles on each ticketing gate.
In the station there are ten gates, so, in total there will be fifteen square meters of Pavegen tiles, it means one-half square meter per ticketing gate. The proposal mat of Pavegen tiles for each ticketing gate is 300 cm x 50 cm in order to make it fit on the floor.
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There are two scenarios, the first one is with the price of $620 US dollars per square meter of Pavegen tiles and the second one, with a price of $125 US dollars per square meter.
Below it is shown the key data considering the first scenario, in table 5 we can observe the cost of the piezoelectric tiles along with the amount of energy that will produce in the proposed scenario.
Table 5. Cost and generation of electricity using Piezoelectric-Scenario 1.
Number of tiles arrangement (1.5sqr meter) 10 Price of one-half sqr meter of tiles [USD] $930
Steps on the tiles 15
Average Users per Day 29,000
Total Steps Users 435,000
Energy per Step [Joules] 6
Total Energy per Day [Joules] 2,610,000
Total Energy per Day [kWh] 0.73
Total Energy per Year [kWh] 264.63 Total Energy 20 Years [kWh] 5,292.50 Price of kWh in a lifetime [USD] $1.17
As we can see in table 5, the total energy produced during the lifetime of the tiles (20 years) is 5,292.5 kWh, which means, the price of a kilowatt-hour using piezoelectric will be $1.17 USD.
Now, the Taiwan electricity price of thermal energy, in 2019 for business or industries was $0.129 USD per kWh (Global Petrol Prices, 2019), which implies a big difference on the electricity price using piezoelectric tiles.
Table 6. Electricity price thermal energy in Kaohsiung Arena MRT Station-Scenario 1.
Electrical Consume of the Station per day 8,340.94 kWh Price of kWh Thermal Energy, 2019 [USD] $ 0.129
Price per kWh on a day [USD] $ 1,075.98
Price of electricity in one year (2019) [USD] $392,733.3 Electricity Bill in 20 years kWh [increasing 3% per year] $ 11,992,811.5
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In Table 6, we have the electric consumption of Kaohsiung Arena MRT Station per day, the price of a kilowatt-hour from Thermal Energy in 2019, the price of electricity that Metro Company pays per day and per year, and finally considering that Metro Company claims the electricity bill increases in average 3%, the projection of the electricity bill in 20 years, all the price units in US dollars.
Table 7. Electricity Saves using piezoelectric in Kaohsiung Arena MRT Station- Scenario 1.
Electricity generated in the Station per day [kWh] 0.73 kWh
Saves in [USD] per day $0.093525
Saves in a year [USD] $34.14
Saves in 20 years [USD] $1,042.42
Cost per kWh of the tiles [USD per kWh] $1.75
In Table 7, it shows the electricity generated per day from the tile and the saves generated with the piezoelectric tiles in Kaohsiung Arena MRT Station, where the saves in 20 years will be
$1,042.42 US dollars. In the first scenario, we can observe that the price of kilowatt-hour from thermal energy is $0.129 US dollar and from piezoelectric tiles is $1.75 US dollars, where the last one is 13.62 times more expensive. We can see that there is a big difference when comparing the prices of one and another technology.
Now we will consider the second scenario, with a price of $125 US dollars per square meter of Pavegen tiles.
Table 8.Cost and generation of electricity using Piezoelectric-Scenario 2.
Number of tiles arrangement (1.5 sqr mt) 10 Price of an sqr meter of tiles [USD] $187
Steps on the tiles 15
Average Users per Day 29,000
Total Steps Users 435,000
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Energy per Step [Joules] 6
Total Energy per Day [Joules] 2,610,000 Total Energy per Day [kWh] 0.73 Total Energy per Year [kWh] 264.63 Total Energy 20 Years [kWh] 5,292.50 Price of kWh in a lifetime [USD] $0.35
Table 8 is shown the same information as Table 7, but here the difference is about costs, the price of the tiles is different, and also the cost of a kilowatt-hour in the lifetime of the tiles.
Due to, we already know the key data about the price of thermal energy that was generated in Table 6, we will continue with the saves using piezoelectric in the second scenario.
Table 9.Electricity Saves using piezoelectric in Kaohsiung Arena MRT Station- Scenario 2.
Electricity generated in the Station per day [kWh] 0.73 kWh
Saves in [USD] per day $0.093525
Saves in a year [USD] $34.14
Saves in 20 years [USD] 1,042.42
Cost per kWh of the tiles [USD per kWh] $0.3533
With the second scenario, we can notice the difference between the price of thermal energy and piezoelectricity, given that here, the cost per kWh of tiles comes to $0.3533 US dollars, however, it is still more expensive than thermal energy about 2.73 times.
Table 10.The unit cost of electric generation.
Source of Energy Scenario 1 Scenario 2 Thermal $0.129 $0.129 Piezoelectric $1.75 $0.3533
Relation 13.57 2.74
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In Table 10, we can see in summary what was found concerning the cost per unit of electrical generation, where clearly shows that piezoelectric is more expensive than thermal energy.