This section describes the electricity component of the model used in this analysis. Primary data is provided by the Tunisian Company of Electricity and Gas (STEG), complemented with other sources and checked against the International Energy Agency’s world energy balances [13].
2.1. Structure of the Tunisian electricity system
The Tunisian power system is dominated by gas supply with increasing, albeit still low, levels of renewable energy technology (RET). The need for gas is met almost equally with imported gas (mainly from Algeria) and domestic gas resources. The use of electricity interconnections with neighbouring countries is limited [14]. Domestic resources of coal are scarce and not exploited. Domestic resources of oil are not anymore exploited either. The country has been struggling with a status of energy deficit in the past decade, mostly due to improvement of living conditions, increased final energy consumption and decline of domestic production. The deployment of renewables has been hampered by policies subsidising the final consumption of electricity [2].
The country’s strategies for the energy sector aim to achieve the Intended Nationally Determined Contributions submitted to UNFCCC in 2015 [15]. Main points in the mitigation goals are the increase of renewable penetration in electricity supply and the reduction of primary energy use through energy efficiency measures. The National Appropriate Mitigation Actions turn the above in feasible goals for the country [16]. The Tunisian Solar Plan (PST) further concretises the renewable targets and is the reference strategy for the development of renewables and energy efficiency measures in the country [4].
Unemployment in Tunisia has been increasing since 2014. The government has set objectives to create jobs and the energy efficiency and renewable sectors have a potential to create new jobs [17]. At the same time, the impacts on the economy of reduced use of gas need to be evaluated carefully. While reducing use of imported gas could have positive effects, reducing use of local gas and operation of local gas-fired power plants could cause loss of jobs.
Key features of the existing power system are summarised below and provided by STEG, when not indicated otherwise.
-
In 2017, 73 PJ of electricity was generated according to the IEA [13], almost entirely from gas-fired power plants and using around 160 PJ of gas to produce that in the process. Imports of electricity accounted for only around 2 PJ in the same year and were balanced out by exports.
-
Of the gas used in the entire economy, national production accounted for just under 40%. Imported gas just over 60%. The latter may fuel natural gas expansion.
-
Transmission and distribution losses amounted to 18% in 2017 and are expected to reduce to 11% by 2022.
-
Currently, there is 245MW of wind power, 30MW solar and 62MW of hydro in the power system. The remainder of the country’s ca 5 GW of installed capacity comprises gas fired power plants.
2.2. Model structure
Including the IO job multipliers allows for a very initial (and limited) level of integration between an IO and energy systems model. Below, we suggest further steps that might be considered to increase integration.
To do so, the aforementioned average job-gains and job-losses are added to the OSeMOSYS model and represented as ‘emissions’. CO2 emissions are also represented. By doing this, different configurations of the energy system are associated with a simple estimate of jobs lost and gained in a semi-dynamic fashion.
For job losses and gains, we do this specifically for: Combined Cycle Gas Power Plants, Open Cycle Gas Power Plants, Solar PV, Concentrating Solar Power, Wind onshore and offshore, Residential Energy Efficiency, Commercial Energy Efficiency and Industrial Energy Efficiency programmes, and Electricity import. This is a limited and cursory set of potential interventions. It is also a limited set of potential interactions between elements of the IO and systems model. Further, many elements of this analysis are static, but the ambition is to develop a clear and simple ‘first step’.
Similarly, CO2 emissions are tracked for the key fuel used for bulk power generation, namely natural gas. For simplicity, it is assumed that the bulk of the natural gas extracted (nationally) and imported for the power sector is used and burned in the power sector. Accordingly, gas heading for the power sector, and resulting emissions are tracked.
In the Reference Energy System (RES) in Fig. 2, boxes indicate groups of technology. Lines indicate flows. Coloured lines represent energy flows and trace energy movement from supply to power station operation to transmission and distributions to demand; lines in black track job-losses or gains as a function of the operation of the technology and CO2 emissions.
Elements of the real system were simplified for the purpose of this study to keep the representation intuitive, yet realistic. Coal and nuclear power plants are disregarded, as not officially accounted for in present strategies. Current gas fired power plants are included in the model separately and here grouped by type for sake of representation. Future gas fired power plants are represented as aggregated capacity, instead.
The model period covers the years from 2015 (for calibration with the IO model) to 2040.
Every year is divided in 108 parts, i.e. in 7 seasons, 2 day-types (workday and weekend) and 8 parts of the day, in the attempt to capture as much as possible the variations of the demand and of the availability of renewable sources. The global discount rate used in the model is 8%, equivalent to the one considered in the IO model. Table 1 summarises other overall characteristics of the study.
Table 1
Overall characteristics of the model.
Time period
|
2015–2040
|
Time resolution
|
108 parts in one year: 7 seasons * 2 day-types (weekday and weekend) * 8 parts in one day
|
Global discount rate
|
8%
|
Depreciation method
|
Straight-line
|
2.3. Job gains and losses as ‘emission factors’
As mentioned, the link between the IO model developed in part one of this paper and the energy investment model lies in the coefficients representing job gains and job losses. These coefficients are added to OSeMOSYS in the form of ‘emission coefficients’ for the aforementioned reasons. The methodology was previously developed and based on efforts applied in various peer reviewed studies4–7. Here a description of the main features of the link between the energy and the IO model is given:
• Emission factors are entered as a function of the activity of the selected technology.
• In the previous part of the paper, job impacts related to investments in energy efficiency measures and in new electricity generating capacity are computed. They vary over time, with changes during the construction or implementation and running of the energy efficiency, gas or renewable energy project. In OSeMOSYS, they are introduced as averages and as emission factors. To do so, we divide the total job-gains or job-losses by the number of years of the economic life of the power plant or energy efficiency measure operates.
• In the static IO analysis, we made the important assumption that we will decompose when using OSeMOSYS. This decomposition is done as OSeMOSYS is dynamic. Specifically this is around imports of natural gas:
- In the static analysis, it was assumed that an intervention would change the amount of gas-powered electricity generation. This was entered as exogenous assumption and can now be endogenised. Job-gains for domestic gas extraction as well as the building of new power plants are accounted for.
- For energy efficiency, this allows OSeMOSYS to endogenously calculate changes in the need to build and import gas, as lower electricity use will require less generation.
- For renewables investment, this allows OSeMOSYS to determine the level of gas fired generation displaced, and with that the proportion of imported gas used.
The job-loss and job-gain numbers calculated in part one of this paper are reported in Table 2, as thousands jobs per PJ and per year. They are computed for the whole national economy and they include both direct and indirect effects. This overcomes a limitation highlighted in Dhakouani et al. [2]. They are disaggregated by potential technology investments. The values refer to the first year of the time domain (2015). Those followed by a downward facing arrow decrease during the time domain of the study, due to the assumption of decreasing capital costs.
Table 2
Job-gains and job-losses per energy system element.
Technology*
|
Job creation coefficient (1000 jobs / PJ - year)
|
Job loss coefficient (1000 jobs / PJ - year)
|
450 MW new CC
|
0.32
|
0.58
|
300 MW new GT
|
0.40
|
0.82
|
Onshore wind
|
0.58
|
0.43
|
Offshore wind
|
1.20
|
0.87
|
Wind autoproduction
|
0.67
|
0.51
|
Solar PV utility scale
|
0.64↓
|
0.46↓
|
CSP (concentrating solar power)
|
1.30 ↓
|
1.02↓
|
Solar autoproduction
|
0.71↓
|
0.51↓
|
Energy Efficiency – Residential
|
0.41
|
0.26
|
Energy Efficiency – Commercial
|
0.37
|
0.21
|
Energy Efficiency - Industrial
|
0.52
|
0.24
|
Electricity import
|
0
|
0.71
|
While taking this approach is an advance as it allows a first analysis of its type for Tunisia, it has important limitations. While the limitations are not addressed in this work, the model(s), data and approach are deliberately developed to allow for advances and changes to be facilitated and easily made in future work.
The data in the table, derived from Part One of this paper, are subject to a range of assumptions. Those include costs, payback and local content. None of those are precise and they are also a function of policy. If targeted, for example, local content in the measures might be higher than those assumed.
The results are also impacted by assumptions made in the economy analysis. The economic analysis is based on the IO Table of Tunisia. In the table, the electricity sector is aggregated together with the gas and water sectors. Similarly, one average value for wages across sectors was used, in the absence of more aggregated information.
As job-gains and job-losses are entered as ‘emission factors’ in OSeMOSYS to allow for the integration, they represent average per-unit effects of the power plants and energy efficiency interventions. Those per unit averages are used in calculations when the intervention is actively producing or saving electricity use. Ideally, they would be split further. They should indicate the job impacts as a function of the capacity of the intervention as well as during production. This is because, especially in the case of very high RET (not examined here), there will be the need to increase investment in conventional power plants simply to provide extra reserves. Reserve capacity may operate for very limited periods during the year. Their investment will change economic flows in the system and impact jobs.
In future work, it is recommended that an extra equation is added to OSeMOSYS to allow for job gains and losses as a function of capacity, not just activity. That will allow for the representation of money flows (and job impacts) as a function relating to capital repayment and fixed operating and maintenance costs that are independent of the power plant’s load factor.
2.4. Demand projections
The electricity demand projection is assumed according to projections by STEG and is reported in Table 3. It excludes the ‘auto-production’, i.e. the estimated self-production by de-centralised rooftop PV and wind. The assumed self-production by the latter two, in terms of projected installed capacity, is given in Fig. 3. The demand projection includes, on the contrary, impacts of energy efficiency measures. The load profile is calculated from half-hourly electricity load data from STEG, for year 2017. It can however be customised for every year.
Table 3
Electricity demand growth assumed for Tunisia.
Year
|
2015
|
2019
|
2020
|
2025
|
2030
|
2035
|
2040
|
Demand (PJ)
|
56.4
|
71.3
|
66.8
|
86.9
|
106.2
|
124.4
|
142.4
|
2.5. Performance characteristics of power plants
Power plant techno-economic characteristics data is provided by the electricity and gas utility STEG for almost all power plant types. When not available through STEG, it is derived from literature as follows. The capital cost for Concentrating Solar Power (CSP) is derived from IRENA, assuming the technology of choice will be parabolic trough with a storage capacity of 4 to 8 hours, taking a lower end cost for 2018 [18] and assuming a trend of cost decrease by STEG. The capacity factor of CSP is assumed to be constant and suggested by STEG. Biomass power plants are assumed to be fed with agricultural waste and their characteristics are assumed as the averages for power plants in Europe as given by IRENA [18]. For offshore wind turbines, the capital cost for a 250 MW park to be built off the Sicilian coast by an independent developer (Copenhagen Offshore Partners) is assumed as representative and taken from online news [19]. Other data is derived from that of onshore wind turbines and a capacity factor constantly 7% higher than the one of onshore wind turbines is assumed. For energy efficiency measures, the capital costs are assumed by the authors, hypothesising a payback time of 5, 4 and 6 years (respectively, for commercial, industrial and residential measures) and an avoided electricity cost equal to the average electricity tariff in Tunisia as obtained from RES4MED [20]. All these are assumptions, developed by the authors in the absence of more precise data, and need to be tested and updated by analysts in the openly available model.
All key techno-economic assumptions are summarised in Table 4. For batteries, it must be noted that costs are all given per unit of energy stored. Where a downward facing arrow is provided next to the cost figure, it means that the given cost refers to the start of the modelling period and it is assumed to decrease through the years, according to trajectories developed by STEG.
Table 4
Techno-economic characteristics of power plants.
|
Capital Cost
|
VOM
|
FOM
|
Efficiency
|
Max CF
|
Availability
|
Lifetime
|
|
MUSD/GW
|
MUSD/PJ
|
MUSD/GW
|
%
|
%
|
%
|
Years
|
New CCGT
|
950
|
0.39
|
8.52
|
54%
|
100%
|
85%
|
30
|
Existing CCGT
|
-
|
0.40
|
8.99
|
48%
|
100%
|
86.3%
|
30
|
New OCGT
|
642
|
0.65
|
10.8
|
36%
|
100%
|
88.5%
|
30
|
Small OCGT
|
-
|
-
|
20
|
28.7%
|
100%
|
89.2%
|
30
|
Hydro
|
-
|
-
|
14.4
|
-
|
9.5%
|
100%
|
100
|
Pumped Storage
|
808
|
-
|
20
|
-
|
-
|
-
|
50
|
Solar PV farm
|
800↓
|
-
|
20↓
|
-
|
15% (average)
|
98%
|
25
|
Solar PV rooftop
|
880↓
|
-
|
22↓
|
-
|
15% (average)
|
98%
|
25
|
Concentrating Solar Power (CSP)
|
4700↓
|
1.39
|
141↓
|
-
|
45% (constant)
|
98%
|
30
|
Biomass
|
1250
|
1.39
|
62.5
|
30%
|
85% (constant)
|
100%
|
|
Batteries utility scale
|
83333↓ in MUSD/PJ
|
0.83 in MUSD/PJ
|
2500↓ in MUSD/PJ
|
90%
|
100%
|
100%
|
15
|
Steam Turbine
|
-
|
-
|
21
|
32.7%
|
100%
|
81.7
|
40
|
Wind onshore
|
1300
|
2.22
|
39
|
-
|
28.3% (average)
|
98%
|
25
|
Wind offshore
|
2964
|
2.22
|
88.9
|
-
|
35.3% (average)
|
98%
|
25
|
Commercial EE
|
2186
|
-
|
-
|
-
|
-
|
-
|
10
|
Industrial EE
|
2448
|
-
|
-
|
-
|
-
|
-
|
10
|
Residential EE
|
2623
|
-
|
-
|
-
|
-
|
-
|
10
|
2.6. Fuel prices
The current and projected price of natural gas is provided by STEG and it has been updated to take into account the decrease in international prices resulting from the COVID-19 pandemic. It is given in Fig. 4.
2.7. Test scenarios
Scenario development is undertaken in order to help unpack the insights potentially deriving from this methodological approach. For this purpose, we allow the cost optimisation to deviate from the strategies and decisions of the electricity utility and of the government. The latter are analysed in the case study paper linked to this publication. Here, we are first interested in historic trends to form a reference: what would happen if historic trends were continued - i.e. the future was frozen to limit potential decisions? This helps to create a basis against which policies, programmes and projects can be evaluated. We can then take other scenarios and compare the changes in costs, jobs and CO2 emissions to this scenario. It helps us to understand if any changes we make result in costs or benefits - and what the relation between the two are.
We use the Open Source energy Modelling System (OSeMOSYS) as it calculates dynamic changes to the system - but ensures that the system configuration is thermodynamically consistent (recall that this was a limitation in a standard IO model). In OSeMOSYS we determine levels of substitution and interactions that happen as RET replaces gas and EE changes electricity supply requirements. To do so we make assumptions about the relative roles that RET and EE might play in the economy. These are assumptions, based on studies and targets by STEG and the National Agency for Energy Management (ANME). Note that these can be adjusted as new information becomes available.
In summary we assume:
• Deployment of wind, solar and biomass aiming to reach 30% share of renewables in electricity generation, based on the Tunisian Solar Plan [4]. Here we assume the capacity of each technology is at least equal to what was planned in the Tunisian Solar Plan by 2030, but we allow it to be higher if cost-optimal.
• Potential energy efficiency deployment is allowed to penetrate, reducing electricity demand by 30% in 2030. This is an extrapolation of the INDC objective of reaching 30% reduction of primary energy demand in 2030 compared to reference. We assume a mix of energy efficiency measures in industrial, commercial and residential sector as follows:
- 11% by aggressive measures in the industrial sector
- 8% by aggressive measures in the commercial sector
- 10% by aggressive measures in the residential sector
Assumptions reflect commitments as well as results of studies on energy efficiency potentials. For instance, the NAMA of Tunisia highlights high potential for energy efficiency in the cement sector, the highest emitting industrial sector in Tunisia [16]; GIZ and ANME highlight potential in the buildings sector, for instance through roof insulation and energy-saving lamps [17].
Higher levels of RET penetration and EE reductions are possible. However, they will require structural adjustments that will incur non-trivial non-marginal changes to the system.
Based on these considerations we define four scenarios. The scenarios are limited as we are interested in tractability and exploring selected insight. In summary, those are:
-
‘Frozen Future’ (FF), which continues historic trends. Besides the already committed investments in renewable technologies scheduled until 2025, it invests only in gas to meet new demands.
-
‘Energy Efficiency’ (EE), that allows for the maximum energy efficiency penetration described above, totalling approximately a 30% reduction in demand by 2030, compared to baseline projections. For comparative purposes, all other aspects are kept as in the Frozen Future scenario.
-
‘Renewable Energy Technology (RET)’, that allows for investments in variable RET, aiming for RET to reach 30% of the total electricity generation by 2030 (including hydro) and potentially overshoot the target. For comparative purposes, all other aspects are kept constant. Investments in hydro power are not allowed and investments in biomass are allowed just up to the extent discussed in the Tunisian Solar Plan, since no higher potential is yet proven or discussed locally.
-
‘Clean Growth’ (CG), combining the assumptions of the EE and RET scenarios.