Energy conversion/Description: Difference between revisions

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{{ComponentSubDescriptionTemplate
|Status=Publishable
|Reference=Hoogwijk, 2004;
|Description=<h2>Electric power model</h2>
In our description, we concentrate on the most complex model first. Next, we indicate how the hydrogen model is derived from this. The figure on the right shows the electricity model. The main assumptions, inputs and outputs of the module are shown as well as the route from inputs to outputs. It illustrates the diversity of technologies that can be used to produce electricity as well as the two stages for arriving at the output demand for primary energy carriers – the investment strategy and the operational strategy.
===Total demand for new capacity===
Investment decisions in the electricity model are made in response to expected electricity demand and to changes in relative generation costs (see also Hoogwijk, 2004). The demand for capacity is derived from the forecast for the simultaneous maximum demand plus a reserve margin of about 10%. A challenge in the simulation of electricity production in an aggregated integrated assessment model is that in reality, often much more detailed consideration play a role. Our model uses a simplified approach in which the simultaneous maximum demand is calculated on the basis of the gross electricity demand: net electricity demand plus electricity trade and transmission losses. The model determines a monthly load duration curve for each region. The form of the Load Duration Curve has been preset by expected changes in region-specific factors such as heating and cooling degree days, daylight and assumed patterns of appliance use. In general, this results in a monthly variation with a maximum value of 20-30% above the average value and a minimum value 40% below the average value. The demand for new capacity equals the difference between required capacity and existing capacity, plus replacement of plants at the end of their life (the lifetime of plants varies, depending on the technology, from 30 to 50 years).


===Decisions to invest in specific options===
Next, a decision is made to invest in different technologies on the basis of their total costs. For this a multinomial logit equation is used, assigning the largest market share to the lowest costs options. The cost of each plant is broken down into a number of categories: i.e. investment costs, fuel costs, operational and maintenance costs and other costs (see further). Notably, an exception is made for hydropower. The capacity for hydropower is exogenously prescribed, given the fact that in the construction of large hydropower plants often other considerations than electricity production (for instance flood control) play a role. In the equations, some exceptions are added to account for limitations in supply (e.g. restriction in bio-mass availability).
INV =INVTOT *  (LCOE+PREF)<sup>-labda</sup>/SIGMA(LCOE+PREF)<sup>-labda</sup>
With investments equal to the new investments into specific technology i, LCOE the levelized costs of electricity generation of technology i, preference the additional costs assigned to technology i based on preferences and labda the logit parameter determining the sensitivity to price differences.
===Operational strategy===
For the operational strategy, power plants are basically used based on operational costs (the lowest costs options are used most). This implies that capital-intensive plants with low operational costs, such as renewables and nuclear energy, will therefore in principle operate as many hours as possible. To some degree this is also true for other plants with low operational costs (e.g. coal). Therefore, the operational decision is represented by the following steps:
# first intermittent renewable sources (PV and wind) are assigned, followed by hydropower as these options have the lowest operational costs;
# in the next step, the peak load capacity is assigned on the basis of operational costs and the ability of options to function as peak load capacity.
# In the final step, base load is assigned on the basis of the remaining capacity, operational costs and the ability of options to function as base load capacity.;
In reality, the merit order strategy is more complex, given the many additional requirements that exist with respect to reliability and start-up times.
===Fossil fuel and bio-energy of power plants===
A total of 20 different plant types generating electricity from fossil fuels and bio-energy are modeled (in additional to PV, wind, hydro and nuclear power). These plant types represent different combinations of
# conventional technology;
# gasification and combined cycle technology;
# combined-heat-and-power and,
# carbon-capture and storage (see also Hendriks et al., 2004). The efficiency and capital requirement of these plant types are determined by exogenous assumptions that describe technological progress of typical components of these plants (the characteristics of the total set are derived from these typical components).
* For conventional plants, the coal-based plant is defined in terms of overall efficiency and investment costs, which are broken down into fuel handling, plant and fuel gas cleaning and operational costs. The requirements for all other conventional plants (oil, natural gas and bio-energy) are derived by indicating differences for investments for a) desulphurization, b) fuel handling and c) efficiency.
* For Combined Cycle plants, the natural gas combined cycle plant is set as standard. Other plants are defined by indicating additional capital costs for gasification, efficiency losses due to gasification and operation and maintenance (O & M) costs for fuel handling.
* Carbon capture and storage plants are assumed to be Combined Cycle plants with corrections (as a function of the carbon content of the fuel) for efficiency, investment costs, O&M costs (for capture) and storage costs.
* CHP plants can be based on Combined Cycle plants or on conventional plants (the model selects the lowest cost option). In both cases a small increase in capital costs is assumed in combination with a lower efficiency for electric conversion and an added factor for heat efficiency (in other words, the model only includes large-scale CHP).
The total costs of these plants are:
LCOE = 1/ LoadFactor* Cap * Ann + OM + 1/Eff * (FuelCost + CO2Emis* StorCost) * kWhtoGJ
Renewable energy.
Apart from fossil-fuel and bio-energy fired plants, the model distinguishes hydropower, solar power, wind power and nuclear power. The costs of technologies are described in terms of learning and depletion dynamics.
LCOE = 1/ LoadFactor* (Cap*Ann * Depl * LearnFactor) + OM + SystemIntegration
For renewable energy sources with an intermittent character (wind and solar power), additional costs are borne for discarded electricity (if production exceeds demand), back-up capacity, additional required spinning reserve (the two last ones to avoid loss of power if supply of wind or solar power suddenly drops; spinning reserve is formed by power stations operating below maximum capacity, which can be scaled up in a relatively short time) and depletion (see also Hoogwijk, 2004).
* To determine discarded electricity for each load fraction a comparison is made between supply and demand. It is assumed that wind power can be either fully in phase or fully out-of-phase with electricity demand: both situations are calculated and the average is used. For PV, it is assumed that supply mainly occurs during the hours at which demand is highest. If supply exceeds demand (calculated for each individual month based on available data on monthly variation in supply), the electricity produced is assumed to be discarded, reducing the effective load factor of wind and solar electricity (and thus increasing their costs).
* Depletion is modeled as a function of built-capacity. The costs decrease via the depletion factor. The underlying assumptions are described in the supply chapter.
* Back-up capacity is added to account for the low capacity credit (meaning the contribution of a plant to a reliable supply of electricity at any moment in time) of the intermittent sources. For the first 5% penetration of the intermittent capacity, the capacity credit equals the load factor of the wind turbines. If the penetration of intermittent sources increases further, the capacity credit decreases. The costs of back-up power (for which capacity with a high capacity credit but low capital costs is used) are allocated to the intermittent source (system integration factor).
* The required spinning reserve is assumed to be 3.5% of the installed capacity of the conventional park. If wind and solar photo-voltaic cells (PV) penetrate the market, the additional required spinning reserve equals 15% of the intermittent capacity, but only after the existing 3.5% in exceeded. These costs are allocated to the intermittent source (system integration factor).
===Nuclear power===
The costs equation of nuclear power is a combination of that the of the fossil fuel and renewable energy plants:
LCOE = 1/ LoadFactor* (Cap*Ann * LearnFactor) + OM + 1/Eff * (FuelCost) * kWhtoGJ
Similar to the renewable options, learning for nuclear power is prescribed via learning curves. For nuclear power, depletion, however, occurs via increasing fuel costs. The fuel costs are determined on the basis of depletion uranium and thorium resources (as described in the chapter on energy resources).
===Hydrogen===
The hydrogen model follows a similar structure as the electric power model. There are, however, some important differences:
* In total, the hydrogen model distinguishes between 11 supply options: 1-4) H2 production plants on the basis of coal, oil, natural gas and bio-energy, 5-8) Similar to 2-5 but in combination with CCS, 9) Bio-energy production from electrolysis, 10) direct bio-energy production from solar thermal processes and 11) 1) Small methane reform plants.
* For simplification, no description of preferences for different power plants is accounted for in the operational strategy. In other words, the load factor for each option equals the total production divided by the capacity for each region.
* Hydrogen can be traded. Therefore, a trade model is added, similar to the fuel trade models for fossil fuels (See Chapter on Resources).
* Intermittency does not play an important role as hydrogen can be stored to some degree. Therefore there are no equations simulation the role of system integration included.
|Flowchart=FlowDiagramElectrictyModel.png
|AltText=Flow diagram for the electricity model in TIMER
|CaptionText=Flow diagram for the electricity model in TIMER
}}

Revision as of 11:25, 18 November 2013

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