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FIGURE 3 THE PROJECT MODEL SKETCH MAP the levelised cost of Xgas (LCOX)
represents the break-even selling price
EXCESS BIOGAS PLANT of the product RNG. For a particular
POWER plant of lifetime n, the LCOX, expressed
in RMB/Nm³ is defined by:
EXCESS POWER GRID
POWER CONNECTION CO2
1MW 50 NM3/H
ELECTROLYSER H2 METHANATION INJECTION STATION RNG GRID
ALKALINE 200 NM3/H BIOLOGICAL 50 NM3/H

O2 HEAT In this study, costs were separated
into CAPEX, O&M costs and input costs.
320 KW
Energy price data collection and
WASTE WATER TREATMENT assumptions
The electricity and gas prices are
considered to be the result of a totally
reaction. Common electrolysis multi-energy systems, such as marketised transaction.
technologies include alkaline hydrolysis electricity-gas-heat-cold, etc. Electricity prices
and proton exchange membrane (PEM) In the process of electricity-gas and Using power trading information
hydrolysis. Other water electrolysis gas-electricity conversion, heat is from the China Electricity Council,
methods are still in R&D stage, such usually generated and consumed. The the different electricity prices were
as solid oxide electrolysis cell (SOEC) reasonable collection and utilisation of collected (see Table 1).
technology. heat can improve the overall efficiency From this data, the lowest price was
Methanation is exothermic. of the energy centre. judged to be from water power, with a
Approaches include catalytic This is also a very attractive floor price of 0.2042 RMB/kWh. So, we
methanation and biological methanation. application scenario for PtG in China, can calculate the excess power price for
Alkaline hydrolysis is the most as it faces fewer constraints from the 2018 to be 204RMB/MWh.
mature of these, with the lowest political system and industry. The case As 150RMB/MWh is considered to be
cost. Future costs may also be lower. studied here is of this kind. the possible price of excess power by
Biological methanation commonly many experts for the moment, the price
needs only moderate reaction Case study and methodology for 2030 is conservatively assumed
conditions and has the potential to be of economic evaluation to be 90RMB/MWh. The intermediate
carried out on a large scale. The case Case study value of 120RMB/MWh) is set for the
studied in this paper is, therefore, On Chongming island, a small scale 2025 scenario.
composed of these two processes. (1MW input) power-to-methane plant Gas prices
is planned. For the aforementioned For the case study, the gas price in the
Coherence points with the Chinese reasons, the project is designed micro grid was set at 3.1RMB/Nm³.
energy internet according to the sketch map in Figure 3. This price was also used to compare
Considering the characteristics of the In this model, the renewable natural with the LCOX to evaluate the economic
Chinese energy internet and those gas (RNG) produced is injected into the feasibility of the system.
of PtG, several scenarios for PtG micro gas grid and the auxiliary products
application are proposed, including (O₂ and heat) are recovered and sent to a Results
four macro-integration scenarios and waste water treatment factory. With the general assumptions
one micro-integration scenario. mentioned above, the summary list is
In terms of macro-integration Methodology of economic evaluation as shown in Table 2.
scenarios, PtG plants can absorb a For a given power-to-Xgas case study, In terms of the input costs (of CO₂ and
large amount of surplus power created
by intermittent renewable energy
through the national power grid. This TABLE 1 SUMMARY OF VARIOUS POWER MARKET TRANSACTIONS OF LARGE POWER GENERATION GROUPS FOR 2018
is considered to be the most important
application scenario at the moment. Photovoltaic Nuclear
But PtG plants can also participate in Coal power Gas power Water power Wind power power power
the operation and optimisation of the
power system as part of the grid. On grid electricity 2443.10 86.10 645.10 184.20 32.80 267.50
Finally, it can offer ancillary services for quantity (billion kWh)
the power system with a suitable market Market transaction
mechanism. In addition, once the power- electricity quantity 1045.90 5.40 205.60 39.50 8.70 66.20
natural gas system is built, PtG will play (billion kWh)
an important role in the daily dispatch Marketisation rate of
and operation of the system. on-grid electricity 42.8% 6.3% 31.9% 21.4% 26.6% 24.8%
In terms of micro-integration
scenarios, a PtG plant can absorb Average price of
surplus renewable energy directly in market transaction 0.3383 0.5436 0.2245 0.4295 0.7731 0.3585
order to coordinate with and optimise electricity(yuan/kWh)

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