4. Integrating Models of the European Gas
4.2 The Soft-Link Approach: Coupling EGN model and the CGEN model
A soft link methodology was used to integrate the European gas network model (EGN) and the combined gas and electricity network model (CGEN). The structure of the integrated model is shown in Figure 4.1. The EGN is depicted in the upper section of Figure 4.1. The model was developed to analyse natural gas supply across 37 countries in Europe. The key model inputs include each European country’s gas demand, domestic production as well as aggregated capacities of storage and LNG facilities. The non-linear relationship between pressure and gas flow through pipelines is not represented in this model.
Figure 4.1 Structure of the integrated EGN- CGEN model
The CGEN model is shown in the lower section of the Figure 4.1. The CGEN model is depicted in the lower section of Figure 4.1. The model includes a detailed representation of the GB gas and electricity networks. The key inputs of the model include gas terminal capacities, gas transmission pipelines parameters
European Gas demand (country level) EU Gas supply capacities (domestic
production & Import) Interconnectors, storage & LNG
capacities Costs
European gas network (EGN) model
Linear optimisation model
ü Operational cost üGas flow on interconnectors üGas storage utilisation, gas supply
volume
üUnserved gas demand
Gas demand in power generation +
Non-electric gas demand
Net gas flow on cross-border interconnectors btw GB and European countries and their supply
prices
GB non-electric gas demand Gas supply terminal capacities, Electricity demand
Generation technologies, transmission capacities Costs
GB Combined gas and electricity network model
(CGEN) Non- linear optimisation model
üSystem operational cost, üStorage utilisation, gas supply
volume
üPower generation output, unserved gas demand
üUnserved electrical energy
INPUT MODEL OUTPUT
Soft-link input/Output Model Input/Output
57
(comprising diameters, lengths and pressures), operational characteristics of compressor stations and storage facilities, electricity generation technologies and electricity transmission lines. Model outputs include volume of gas supplied at terminals, storage utilisation, change in linepack and power generation output.
The soft link methodology involved an exchange of a set of variables between the models in an iterative process. The variables taken from the EGN are gas flow on
cross-border interconnectors between GB and continental Europe and their corresponding gas supply prices. Three cross-border interconnectors link GB to the
rest of Europe namely; Norway to GB interconnector (NO-GB), Netherland to GB interconnector (NL-GB) and the bi-directional interconnector between GB and Belgium (GB-BE).
The total GB gas demand is a variable obtained from the CGEN model. The total GB gas demand was calculated as the sum of the non-electric gas demand and the amount gas used by gas-fired generators for power generation. The non-electric demand is an exogenous input while the amount of gas used by gas-fired generation for power generation is endogenously determined in the CGEN model. The CGEN model calculates the gas used for electricity generation based on the price of natural gas relative to the cost of generating electricity using alternative generation technologies such as coal. Hence, gas used for power generation decreases when gas prices are high and vice versa.
4.2.1
Description of the CGEN model
The CGEN model was modified to include the individual cross-border pipelines between GB gas network and neighbouring European countries. Figure 4.2 shows a schematic diagram of the GB gas network coupled by cross-border pipelines at Norway, Netherland and Belgium to the rest of the European gas network. GB gas terminals receive gas from offshore production fields, LNG import and cross-border pipelines with Continental Europe.
58
Figure 4.2 Linkages between GB gas network and the European gas network
In this study, Continental Europe refers to all EU countries, Bosnia, Macedonia and Serbia. It excludes GB and Republic of Ireland.
The Objective Function
The objective function of the CGEN model is to minimise the combined operational cost of gas and electricity networks whilst meeting gas and electricity demand. The operational cost includes costs of gas supplies, gas storage operation, change in linepack, electricity generation, unserved gas demand and electrical energy as expressed in Equation 4.1. The general formulation and description of the CGEN model is presented in Appendix D.
59 Minimise total operational cost (£) =
∑ 𝑡𝑠 𝑡 × { ∑ 𝐶𝑎,𝑡𝑔𝑎𝑠𝑄𝑎,𝑡𝑠𝑢𝑝𝑝 𝑎 ⏟ 𝑔𝑎𝑠 𝑠𝑢𝑝𝑝𝑙𝑖𝑒𝑠 + ∑(𝐶𝑠,𝑡𝑤𝑑 𝑄𝑠,𝑡𝑤𝑑− 𝐶𝑠,𝑡𝑖𝑛𝑗𝑄𝑠,𝑡𝑖𝑛𝑗) 𝑠 ⏟ 𝑠𝑡𝑜𝑟𝑎𝑔𝑒 𝑜𝑝𝑒𝑟𝑎𝑡𝑖𝑜𝑛 + ∑ 𝐶𝑡𝑠𝑝𝜕𝐿𝑃ℎ,𝑡 ℎ ⏟ 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑙𝑖𝑛𝑒𝑝𝑎𝑐𝑘 + ∑ 𝐶𝑔𝑔𝑒𝑛 𝑔 𝑃𝑔,𝑡 ⏟ 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑖𝑡𝑦 𝑔𝑒𝑛𝑒𝑟𝑎𝑡𝑖𝑜𝑛 + ∑ 𝐶𝑔𝑎𝑠𝑠ℎ𝑒𝑑 𝑖 𝑄𝑖,𝑡𝑔𝑎𝑠𝑠ℎ𝑒𝑑 ⏟ 𝑢𝑛𝑠𝑒𝑟𝑣𝑒𝑑 𝑔𝑎𝑠 𝑑𝑒𝑚𝑎𝑛𝑑 + ∑ 𝐶𝑒𝑙𝑒𝑐𝑠ℎ𝑒𝑑 𝑏 𝑄𝑏,𝑡𝑒𝑙𝑒𝑐𝑠ℎ𝑒𝑑 ⏟ 𝑢𝑛𝑠𝑒𝑟𝑣𝑒𝑑 𝑒𝑙𝑒𝑐𝑡𝑟𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦 } 4.1 where :
𝐶𝑎,𝑡 gas cost from terminal 𝑎 at time 𝑡 (£/m3) 𝑄𝑎,𝑡𝑠𝑢𝑝𝑝 gas supplied from terminal 𝑎 at time 𝑡 (m3/d)
𝐶𝑠,𝑡𝑤𝑑 cost of gas withdrawn from storage facility 𝑠 at time 𝑡 (£/m3) 𝑄𝑠,𝑡𝑤𝑑 volume of gas withdrawn from storage facility 𝑠 at time 𝑡 (m3/d) 𝐶𝑠,𝑡𝑖𝑛𝑗 cost of storage injection into storage facility 𝑠 and time 𝑡 (£/m3)
𝑄𝑠,𝑡𝑖𝑛𝑗 volume of gas injected in storage facility 𝑠 at time 𝑡 (m3/d)
𝐶𝑡𝑠𝑝 spot gas price at time 𝑡 (£/m3)
𝜕𝐿𝑃ℎ,𝑡 changes in linepack of pipe ℎ at time 𝑡 (m3/d) 𝐶𝑔𝑔𝑒𝑛 generation cost of generator 𝑔 (£/MWh)
𝑃𝑔,𝑡 power output from generator 𝑔 at time 𝑡 (MW)
𝐶𝑔𝑎𝑠𝑠ℎ𝑒𝑑 cost of unserved gas demand (£/m3)
𝑄𝑖,𝑡𝑔𝑎𝑠𝑠ℎ𝑒𝑑 volume of unserved gas energy at node 𝑖 and time 𝑡 (m3/d)
𝐶𝑒𝑙𝑒𝑐𝑠ℎ𝑒𝑑 cost of unserved electrical energy (£/MWh) 𝑄𝑏,𝑡𝑒𝑙𝑒𝑐𝑠ℎ𝑒𝑑 unserved electric power at bus 𝑏 and time 𝑡 (MW)
4.2.2
Stages Involved in the Soft-Link Approach
The coupling of the CGEN and EGN models is described in the following steps below:
Step 1: The EGN model received gas demand, domestic production and storage
60
Step 2: The EGN model was run to obtain gas flow on the European interconnectors
linked to the GB gas network and their corresponding gas supply prices.
Step 3: The gas supply prices and cross-border gas flow profiles calculated in the EGN
were used as input in the CGEN model.
Step 4: The CGEN model was run to obtain the amount of gas consumed in electricity
generation.
Step 5: The gas demand in electricity generation was used to calculate the total GB
gas demand profile which was updated in the next run of the EGN model.
Step 6: Steps 3, 4 and 5 were iterated (repeated sequentially) until the gas flow on the
interconnectors linked to the GB network and total GB gas demand profile reaches the convergence criterion or after four iterative cycles. The convergence criterion was given by Eq.3.2.
𝑁
𝑘− 𝑁
𝑘−1𝑁
𝑘≤ 0.05
4.2where
𝑁
is the GB gas demand data exchanged between the EGN and CGEN models,𝑘
is the iteration number.Once the models converged and a solution was reached, the loss of Ukraine transit capacity was applied in the EGN. The resulting cross border gas flows on the interconnectors connecting GB to Europe were imported into CGEN model to examine the impact of the supply disruption on gas dispatch in GB gas and electricity networks.