Gas network
- Introduction
- User interface
- Results
- Modelling approach
- Financial
When looking at future energy systems the following questions are relevant in the discussions about the gas-infrastructure:
- When building a new neighbourhood: should we invest in gas infrastructure?
- For existing neighbourhoods: should we keep investing in the existing infrastructure? (e.g. in the case of other heating options (e.g. areas with all-electric houses, heat networks)).
- How big are the investments in the electricity network that we can prevent if we keep the current gas network operational? And what would that cost?
- What is the capacity for feeding locally produced gas (hydrogen, biogas) back into the network?
- What losses are associated with feeding in locally produced and upgraded gas? What happens when there is insufficient capacity or demand at the pressure level where the gas is fed in?
The gas section in ETMoses was added to help answer these questions. This section first covers the user interface in ETMoses related to the gas network, after which the possible results are discussed. The modelling approach and assumptions related to the gas network are explained at the end of this section.
When editing a LES, the user is shown the following gas asset list:
The user can select the assets at each pressure level and adjust their properties, such as the type and quantity. The system operator is the default stakeholder. The building year (together with the costs) is used to calculate the equity value of the gas assets. Together with the lifetime of assets this determines when re-investment is needed.
The default parameters for these assets are derived from the total national gas assets scaled down to the number of gas connections in the LES. The research behind this is documented in this spreadsheet. With the 'Rescale assets to gas connections'-button, the user can re-initialise the gas asset list using the current number of gas connection in the LES as a multiplier. This resets all fields to their default values for the current number of gas connections.
Note: lifetime, initial investment cost and O&M costs are attributes of the assets and are based on internal research from Alliander. Because for several types of pipe, technical lifetimes are unknown we have used economic lifetimes for default values. Currently, the user cannot change these attributes in the front-end.
There are two charts visible below the gas asset list showing:
- Equity value: the remaining value of an asset assuming linear depreciation (value = investment * (1 - age/lifetime) )
- Cumulative investment: the sum of investments needed to renew the current assets after their lifetime has passed
The charts are updated when the user saves the page or presses 'Apply':
These charts can help the user to get a feeling for when would be a good moment to abandon a gas infrastructure and switch to district heating or an all-electric situation.
The acronyms used in the gas asset table are explained below:
- pe_lp: a gas pipe at 125 mbar made out of PE
- pvc_lp: a gas pipe at 125 mbar made out of PVC
- steel_lp: a gas pipe at 125 mbar made out of steel
These three are the most common used materials at the 125 mbar level.
- pe_hp: a gas pipe at 4 or 8 bar made out of PE
- ductile_iron_hp: a gas pipe at 4 or 8 bar made out of ductile iron
- steel_hp: a gas pipe at 4 or 8 bar made out of steel
These are the most common used materials for gas pipes at 4 and 8 bar.
Connectors are (buildings with) installations that reduce the pressure level of the gas. The following table indicates at which pressure levels the various connectors operate:
| Abbreviation | Name | Connection |
|---|---|---|
| GOS | Gas Transfer Station | 40 bar --> 8 bar |
| Gas Overslag Station | ||
| OS | Transfer Station | 8 bar --> 4 bar |
| Overslag Station | ||
| DRS | District Control Station | 4+ bar --> 100 mbar |
| District Regel Station | ||
| HAS | Main Delivery Station | Small Consumers (Kleinverbruikers) |
| Hoofd Aflever Station | ||
| AS | Delivery Station | Bulk Consumers (Grootverbruikers) |
| Aflever Station |
The costs attributes for connectors between pressure levels are summarised in the table below:
Asset| Investment [EUR]| Yearly O&M costs [EUR/y]| Lifetime [y]| |---|---|---|---|---| |GOS *| 100| 3850| - | |OS| 35000| 730| 30| |DRS| 35000| 730| 30| |AS| 7600| 210| 30| |HAS| 7600| 210| 30|
* The equipment is owned by the TSO, the building and surrounding area is owned and maintained by the DSO
Locally produced gas can be fed into the gas network at the lowest pressure level (125 mbar) (see below for details). If this production exceeds the consumption at this level, the gas needs to be compressed before it can be transported to the 4 bar level. The same is true for this 4 bar level and for the 8 bar level.
In order to compress the gas, a compressor needs to be added to the gas asset list. This compressor needs to be connected to the lower pressure level, i.e. if you want a compressor between the 125 mbar and the 4 bar pressure levels, the compressor needs to be connected to the 125 mbar level.
Compressors come in a wide range of capacities and are usually tailored to very specific pressure levels. We found that the specifications that are relevant for ETMoses do not differ that much for these specific pressure levels and decided to base all compressors on the compressor that has been researched within the context of the Energy Transition Model. The compressors used have a capacity of 8.9 MW and an efficiency of 93.1%. This research can be found here.
In the market model, the user can add transactions based on gas-consumption and connections. More on this can be found in the section market models and the [modelling approach] (https://github.com/quintel/etmoses/wiki/Gas-network#measuring-gas-consumption) below.
Two separate charts provide insight in the loads on and flows through the gas network. Both can be found under the Gas load tab.
The 'Load on the gas network' chart shows the net load per 15 minutes on all pressure levels for a selected week. The net load is defined as the net flow per time and expressed in Watts W, where net flow is defined as consumption minus production of gas. For higher pressure levels than 125 mbar, this means that the load is defined by how much gas is transported through that level. NOTE: the curves only show different behaviour, if losses occur or the capacity of compressors is insufficient (when feeding in from low levels).
The yearly gas flow chart shows the aggregated net flows throughout the entire year between two pressure levels (Endpoints <-> 0.125 bar, 0.125 bar <-> 4 bar, 4 bar <-> 8 bar and 8 bar <-> 40 bar).
The Yearly gas flow chart shows the following aspects of the gas network:
- Losses: moving gas from lower pressure levels to higher ones costs energy, which is modelled as a loss. We assume that connectors are lossless, i.e. gas flows from higher to lower pressure levels without losses.
- Feed-in: gas is fed-in at the 125 mbar pressure level; if not all of this gas is consumed at this level, it will be compressed and moved to a higher pressure level if a compressor is installed in the net. The feed-in bar shows how much of this fed-in gas is flowing between the two pressure levels
- Consumption: gas is consumed at the end-points of the gas network. If this gas cannot be produced locally, it is sourced from higher pressure levels. This item shows how much consumed gas is flowing through the connector between the two pressure levels.
- Deficit: if the local production of gas is not sufficient to meet the consumption, gas needs to be sourced from higher pressure levels; if the capacity of the connector is limited, it might happen that not all this gas can be sourced, leading to deficits. For now we assume that the capacity of all connectors is infinite, so the deficit will be zero.
- Surplus: locally produced gas can be fed into the 125 mbar pressure level. If not all this gas is consumed at this level, it is compressed and moved to a higher pressure level if a compressor is installed in the net. If the capacity of the compressor is not sufficient to compress all gas, the remaining gas is counted as surplus. This item shows how much gas would be needed to be 'flared' at the interface between two pressure levels.
The costs related to the gas network assets and technologies are included in the general business case, just as the gas transactions that you have included in your market models.
In this section we explain how the gas system is modelled: the network and the flow of gas, consumption and production, related costs and benefits.
The topology of the gas-network is very much circular/meshed:
Many routes can be taken from one point in the network to another. This suggests the following simplifying assumption: we describe the gas network primarily by its different pressure-levels. We use 125 mbar throughout the the application to indicate the lowest pressure levels (between 100 and 200 mbar).
ETMoses determines the consumption/production of gas per 15 minutes. This consumption is based on the demand for space heating and hot water, the chosen technologies for space heating and hot water and the demand profiles for the space heating and hot water consumption.
Gas can currently only be consumed at the end-points of the electricity topology (where all technologies and demands are connected). At the moment endpoints are always connected to the 125 mbar pressure level.
Gas can be produced locally by power-to-gas (P2G). We assume that this gas is fed in at the 125 mbar pressure level. If this local production of gas is not sufficient to meet the consumption, gas needs to be sourced from higher pressure levels (4 bar, 8 bar and 40 bar). This gas flows from higher pressure levels to lower pressure levels through a connector.
If the local production of gas exceeds the demand, this gas has to flow 'upwards' to higher pressure levels. In order to do this, the gas needs to be compressed, for which a compressor needs to be added between these pressure levels. The capacities of connectors and compressors might be limited and could therefore limit the flow of gas from higher to lower and lower to higher pressure levels respectively, resulting in deficits and flaring respectively. For now, however, we assume that the capacity of all connectors is infinite, so the deficit will be zero. Finally, compressing gas comes at a loss while flow from high to low pressure levels is assumed to be lossless.
In order to calculate the potential for storing gas and the losses associated with feeding-in of locally produced gas, the following attributes have to be known for each pressure level:
- capacity for extraction (consumption) [kW]: The capacity of extraction is assumed to be unlimited
- capacity for feed-in [kW]: The capacity for feed-in after consumption has been subtracted, which is limited by the installed capacity of compressors
- losses for compression of feed-in [kW]: Losses occur every time net feed-in of gas occurs and applies to each crossing from a pressure level to the next. Losses are assumed to be 7% per compression-step
Contrary to the load calculation for electricity, there is no flexible network topology but rather a static 'stack' of buffers which communicate with each other. The gas topology can be visualised as follows:
The levels, and the connectors have the same structure and functionality at all levels (8 and 40 bar). The attributes included in the above image are variable and are directly determined by the choices the user makes in the asset page.
The calculation steps are (for each time-step):
- start at lowest gas level and add/subtract all load of connected gas-technologies.
- check sign of load:
- if net consumption, import from higher level and go to step 4,
- if net production, pressurise gas constrained by compressor capacity and subtract losses.
- keep track of the size of the flow and the losses and store them.
- go to the next level.
In this section we describe how the consumption of gas as a commodity by stakeholders is taken into account. To do this we need to explain how:
- Gas-consumption is associated with a stakeholder
- Gas-consumption is measured
- Gas-consumption is taken into account in market models and business cases
Consumption takes place at the lowest (125 millibar) pressure level of the gas network. An end-point of the electricity network topology is 'connected' to the gas network if there is at least one gas-technology attached to that end-point. The number of gas-connections is determined similarly to the number of connections for the electricity network: the number of base-load technologies is used as a proxy. More information on the number of gas connections can be found [here] (https://github.com/quintel/etmoses/wiki/Networks#number-of-gas-connections).
The user can add transactions in the Market Model based on gas-consumption by adding a new line and selecting gas-consumption as a measure:
The gas consumption is measured for all the end-nodes in the electricity topology that are also gas-connections (see previous section) and belong to the stakeholder that has been selected under "measured at stakeholder".
Gas-consumption transactions between stakeholders can be based on the following tariffs:
- Fixed price
- Price profile
- Merit-order price (note that this is the electricity Merit-Order price!)
Local production of gas can be fed into the network at the lowest (125 millibar) level by using a power to gas (P2G) installation. Power to gas produces hydrogen. For now, it is assumed that this hydrogen can be fed into the gas network directly. We treat hydrogen (and other gas) purely energetically at this moment. The mixing fraction, Wobbe index etc. are not taken into account. In reality hydrogen cannot be directly fed back into the grid. Extra upgrading or mixing with natural gas is needed, as the network can only accommodate gas within certain limits / composition.
Similar to the consumption of gas, production of gas (by any stakeholder associated with an end-point of the topology where gas is fed into the network) can be used in market model transactions.
Gas-production transactions between stakeholders can be based on the following tariffs:
- Fixed price
- Price profile
- Merit-order price (note that this is the electricity Merit-Order price!)
An important aspect of the business cases are the yearly costs due to depreciation and fixed yearly operation and maintenance. Similar to the yearly costs of other technologies and assets, the yearly costs for gas infrastructure are calculated as:
yearly_costs = depreciation_costs + om_costs_per_year
Where the om_costs_per_year are the annual fixed operation and maintenance costs. The depreciation costs are defined as
depreciation_costs = initial_investment / technical_lifetime
where the technical_lifetime has been chosen to represent the time-scale over which an asset will be depreciated. Contrary to using the more subjective economic_lifetime, the chosen approach results in a physically motivated and unambiguous estimate of the depreciation costs.
The total yearly costs are added to the business cases for the stakeholder(s) which own(s) (part of) the gas network. The stakeholder can be chosen per asset in the gas asset list.
The total yearly costs per stakeholder are shown on the diagonal of the business case matrix:
NOTE: technical_lifetime, initial_investment and om_costs_per_year are attributes of the assets and are based on internal research from Alliander. Alliander has provided economic lifetimes for several types of gasassets. As the precise technical lifetimes are unknown, we have used economic lifetimes for default values. Currently, the user cannot change these attributes in the front-end.
The cost attributes for different types of pipes are summarised in the table below:
| Attribute | Investment [EUR/m] | Yearly O&M costs [EUR/y/m] | Lifetime [y] | Pressure level(s) [bar] |
|---|---|---|---|---|
| PE-hp | 210 | 1 | 55 | 4, 8 |
| steel-hp | 290 | 1 | 55 | 4, 8 |
| ductile-iron-hp | ? | 1 | 55 | 4, 8 |
| PE-lp | 130 | 1 | 45 | 0.1 |
| PVC-lp | 120 | 0.5 | 45 | 0.1 |
| steel-lp | ? | 0.5 | 45 | 0.1 |
