Methanol synthesis
For the methanol synthesis a reactor with the same size of the Alkaline electrolyzer (10 MW) has been considered . In order to carry out the reaction, it is necessary to provide a certain quantity of hydrogen and carbon dioxide to obtain one kg of methanol. For this reactor, the consumptions are equal to the stechiometric ratios:
0.19 kgH2/kgMeOH and 1.38 kgCO2/kgMeOH. The values adopted in this section are provided by ENEA in the following source [26]. With a capacity of 10 MW the corresponding consume is equal to 1.23 ton of CO2/h; converting this value per unit of energy, the consumption is equal to 0.123 tonCO2/MWh. The methanol synthesis efficiency is considered to remain constant in the future at a fixed value of 75.5%
(MWhHHV-MeOH out/MWhHHV-H2 in).
Fuel Cell
Regarding the fuel cell technology, a Reformed Methanol Fuel Cell has been used due to the high efficiency and the advanced stage of development. Moreover it is suitable for large scale application and therefore it has been possible to assumed a 10 MW RMFC system. A value of efficiency of 70% has been considered because of a possible improvement of the technology by 2050 with an actual value of 60%[39].
Storage
In the present work, due to the relative ease of storing methanol at room temperature and due to the high availability of tanks, an infinite capacity of the storage has been considered [6].
3.2.2 Economical analysis
Definitions of the terminology
With the purpose of studying the economical influence of Power to Methanol tech-nology in the present work, it is necessary to make some assumptions. The total cost of this technology has been calculated with the sum of the costs of the sin-gle technologies involved in the process and projected by 2050. First of all, it is necessary to define some economical parameters defined in the study ”Potential of power-to-gas” conducted by ENEA in 2016: [26]
Total CAPEX = Installed CAPEX + Project CAPEX (3.1) With
Installed CAPEX = Factory gate cost + Additional costs (3.2) and
Alkaline electrolyzer
[26] As said previously, for the production of hydrogen the use of an alkaline elec-trolyzer with an electricity capacity of 10 MW and with a delivered pressurized hydrogen at 10 bar have been assumed. The total installed CAPEX estimated to be in 2050 (including balance of plant, transport, installation and commissioning) is 500 eur/kW assuming 50% decrease from the current cost (Equation: 3.4).
In order to obtain a hydrogen purity higher than 99.999%, it is necessary a pu-rification unit that generally represents from 10 to 20% of the factory gate of the electrolyzer (in the total installed CAPEX has been already assumed). The cost of the water, source of the hydrogen, has been neglected. The annual Fixed Op-erational and Maintenance has been considered equal to 1.5% of the CAPEX cost (Equation: 3.5). The lifetime of the electrolyzer has been assumed equal to 25 years with a discount rate of 7% [26]. Using the definitions previously explained:
Total CAPEX = 500 + 0.3 × 500 = 650 eur/kW (3.4) FO&M = 1.5% × 650 = 9.75 eur/(kW year) (3.5)
3.2.3 CO
2cost
The estimated price of CO2 in 2050 is very uncertain and for this reason three dif-ferent literature sources have been used .
In the first source [28] there are present several costs depending of the type of plants;
an average value of 40 euro/ton has been taken.
In the second source [27] an average cost of CO2 from high-purity sources equal to 26 $/ton has been taken, with a value varying between 3.9 and 74$/ton.
In the last source [26] the price of CO2 has been set at a price between 80 and 120 eur/ton assuming capture of CO2 from industrial and fossil power plants and including CO2 pressurization at 70 bar and transportation.
Considering a consumption of 8.6 ton of CO2 per hour in case of a power capacity of 10 MW [26], it corresponds to a consume of 0.123 ton of CO2 per MWh pro-ducted. The table below (TAB: 3.2) gives a summary of all the assumption and the computations:
Table 3.2. Table summarizing the assumption taken in different sources. [28] [27]
[26]
In the present model an average price of CO2 equal to 40 eur/ton (4.92 eur/MWh of energy stored) has been taken into consideration.
Methanol synthesis
Regarding the methanol synthesis, as said previously, a methanol reactor with power capacity of 10 MW has been considered. The source used for this technology [26]
estimates a specific factory gate cost of the methanol reactor in 2050 equal to 700 eur/kW (current value is equal to 1500 eur/kW). In addition to this value it is necessary to take into consideration the additional cost (eq: 3.6) of the methanol reactor and the project cost (eq: 3.8). Additional costs (transport, civil work, isntallation, balance of plant and commissioning costs) equal to 50% of the cost of the methanol reactor have been assumed. Using the definitions explained, the total CAPEX has been computed (eq: 3.9). Moreover it was necessary to consider a Fixed O&M cost of the reactor; it has been assumed equal to 7.5% (eq: 3.10).
The lifetime of the methanol reactor has been assumed equal to 20 years with a discount rate of 7%.
Additional cost = 50% × 700 = 350 eur/kW (3.6) Installed capacity = 350 + 700 = 1050 eur/kW (3.7) Project CAPEX = 0.3 × 1050 = 315 eur/kW (3.8) Total CAPEX = 1050 + 315 = 1365 eur/kW (3.9) FO&M = 1.5% × 650 = 9.75 eur/(kW year) (3.10) Fuel cell
As explained before, the conversion from the methanol stored to electricity has been done with a Reformed Methanol Fuel Cell. A projected CAPEX costs in 2050 equal to 500 eur/kW has been assumed for this technology (actual cost = 1000 eur/kW) with a Fixed O&M costs equal to 20 eur/kW for year. Regarding the lifetime, a value of 20 years with an annual discount rate of 7% have been assumed . [39]
Storage
Because of the relative ease of storing methanol and the investment much lower than the cost of converting electricity into fuel (and back), the cost of keeping energy stored over time has been considered as negligible, which is one of the great advantages of methanol storage. [6]
Table 3.3. Table summarizing the assumption in the different components
3.2.4 Model building
As cited before, power to methanol technology requires several components in order to convert electricity into fuel and then fuel into electricity. In the python model, this technology has been summarized in only one technology (such as a ”black box”) gathering together all the components.
The presence of a long-term storage guarantees several advantages in case of a sys-tem with high penetration of intermittent renewable energies. In order to implement Power to Methanol technology in the actual model it has been necessary to make assumptions.
The round trip efficiency has been multiplied directly in the conversion from electricity to methanol without having any losses during the process to convert the fuel into electricity.
When there is surplus/needs of electricity it has been decided to use P2F as last candidate to store/release energy; it means that the energy is stored/released in first step with a short term energy storage (PHES and battery) and then with this technology. This decision has been taken because of:
• High investment cost of the technology
• Low round trip efficiency
• Long term role in the energy system
In order to implement this technology in the python code, several parameters have been used. It is possible to divide them in three main categories:
1. TECHNICAL PARAMETERS
• Power capacity in absorbing and releasing electricity [p in max m] and [p out max m]
• Maximum and minimum energy capacity [st max m] and [st min m]
• Round Trip Efficiency [RTE m]
• CAPEX [capex st m, Fixed O&M [fixed om st b], Annuity factor [annu-ity cst st m].
• Life time [life st m]
2. CONTROL VARIABLES
• Energy level available in the storage [level m(t)]
• Initial energy level available [level m0 (equal to st max m/2 ]
• Quantity of stored energy including losses through RTE [st in m(t)]
• Quantity of served energy neglecting losses losses[serv st m(t)]
• LCOE cost [cost st m]
3. CONTROL VARIABLES
• Number of P2F units [n st m]