In order to achieve the primary goal of the 2015 Paris Agreement [1
] to limit the average global warming to less than 1.5 °C, Switzerland and many other countries follow a strategy to mitigate greenhouse gas (GHG) emissions and global warming by a transition from a fossil-based to a renewables-based energy system [2
]. In particular, the substitution of fossil fuels by alternatives based on electricity from renewables is an oft-cited option [3
In Switzerland, currently about 60% of all fossil CO2
emissions occur in the sectors of mobility and buildings [7
]. Therefore, a substitution of fossil energy carriers in these two sectors by electricity-based technologies seems to be most effective. With respect to buildings, it is primarily the substitution of fossil heaters and boilers operated on heating oil and natural gas by heat pumps [8
]. With regard to mobility, it is primarily the substitution of internal combustion engines (ICE) running on fossil gasoline and diesel fuels by battery electric vehicles (BEV) [10
While these electricity-based technologies do not directly emit CO2
during their operation, their actual (life cycle) CO2
emissions highly depend on the CO2
intensity of the used electricity [13
]. Especially in winter, when electricity demand is high, while in Switzerland the contribution of renewables is lower due to their seasonal and volatile nature, imports are needed. If electricity-based technologies are fed with highly CO2
intensive imports such as from coal or oil-fired power plants, their overall global warming impact may even be higher than their fossil counterparts. Moreover, due to their additional electricity consumption, electricity-based technologies pose several new challenges for the electricity system. These challenges encompass the additional total amount of electricity itself as well as the additional power needed to cope with increased demand and production peaks.
The “Swiss Energy Strategy 2050” (ES2050) of Prognos [2
] is based on a fixed overall socio-economic scenario regarding population (9 million), GDP growth (+1.1% p.a) and living floor area (+20%) by 2050. There are three demand scenarios (a conservative “Business As Usual” (BAU), a low-demand “New Energy Policy” (NEP) and a regulations-driven “Political Measures” (POM) scenario) along with two supply variants (“C” and “E” and a combination thereof “C&E”). The demand scenarios differ in their assumptions on efficiency gains, new regulations such as higher CO2
taxes, guidelines for heating, appliances, and vehicle drivetrains, etc., and social activity and behavioral changes such as less person-kilometers-per-year [14
]. The two supply scenarios both feature a phase-out of nuclear power plants (NPP), yet variant “C” stipulates new centralized Swiss “Combined Cycle Gas Turbine” (CCGT) power plants to avoid imports and no extra promotion of renewables, while variant “E” stipulates a substantial promotion of renewables such as photovoltaics (PV), wind, biomass and geothermal along with (partially) more imports, yet no CCGT.
With the renewable variant “E”, demand and supply challenges are in particular great as the expansion of renewables will most likely occur with volatile electricity produced by PV [15
], while simultaneously base-load electricity from NPP is discarded [16
]. Moreover, without load shifting strategies, also the electricity demand will become more volatile, partly because of additional demand peaks due to heat pumps and BEV, but also due to peer-to-peer trades in a liberalized electricity market causing non-grid friendly impacts without corresponding regulations and controls [18
In literature, the additional electricity demand by a substantial electrification of the Swiss energy system is discussed inconsistently [14
]. While Barmettler et al. [19
] and Andersson et al. [20
]—depending on their chosen scenario—report a rise from currently about 60 TWh to about 70–90 TWh per year, other studies [21
] assume that the additional electricity demand of about 10 TWh per year of heat pumps and BEV is just about offset by an overall reduction of the electricity consumption.
In existing studies, typically bottom-up energy system (optimization) models are used to investigate the future Swiss energy system based on given targets in the ES2050 [16
]. These models rely on forecasts and fixed scenarios of the whole energy system and use cost optimization to generate cost-optimal energy scenarios under technological, resource, environmental, and/or policy constraints [23
]. For the Swiss energy system, there are models with a high (mostly hourly) temporal resolution, but only in the electricity sector [24
]; and models with a distinction between the electricity, heat and mobility sector, but only at a coarse (weekly, monthly) temporal resolution [25
] or only with typical (averaged) days per season [27
]. While electricity-only models also (indirectly) incorporate the penetration of BEV and heat pumps by taking annual demand values (e.g., from “POM”, which implicitly also includes additional BEV and heat pumps) and linearly scaling them to historic (hourly) load profiles [16
], they are still not capable of representing additional and/or shifted demand peaks due to BEV and heat pumps. On the other hand, models that explicitly include the heat and mobility sector [25
] typically do not have input data at an adequately high temporal resolution. Therefore, they need to estimate the energy demand in these sectors on a coarser time scale and by the aid of surrogates such as heating degree days (HDD), etc., [25
] or, in the mobility sector, by not explicitly accounting for the time of recharging/fueling [30
]. Also, the translation of heat demand to an actual electricity demand (by heat pumps) is generally not modelled with time-dependent ambient temperature data, etc., but with yearly constant values [26
]. Moreover, these studies do not incorporate, if any, time-dependent CO2
emissions of the used electricity [27
For these reasons, this study investigates the impacts and challenges of a large electrification and simultaneous denuclearization of the Swiss energy system by means of a dynamic and data-driven approach. With this approach, there is no more need for predictions or forecasts on the evolution of the future energy system. This offers the benefit that large uncertainties and ambiguities such as on population growth, GDP growth, penetration of new technologies, social and behavioral changes, etc., do not need to be taken into account explicitly. In turn, the energy system is taken as it is and strategic measures (of the ES2050) are added or subtracted based on actual measurements and data of the electricity, heat and mobility sectors along with meteorological data and state-of-the-art specifications on the employed technologies (e.g., heat pumps, BEV, etc.). In particular, the high temporal resolution of the used data in all energy sectors (electricity, heat and mobility) allows for a dynamic analysis of the impacts of strategic measures also in the light of short-term effects such as additional and higher peak power demands, intermittent surpluses and deficits as well as momentary fluctuations of CO2 intensities in the electricity grid, etc.
The scope of this study is to primarily investigate technological and physical aspects of this large electrification and denuclearization of the energy system on the national scale of Switzerland. Socio-economic aspects, although also of high relevance to this topic, are out of the scope of this study. On a global scale such socio-economic aspects have already been investigated by Jacobson et al. [31
The organisation of this study is as follows: In Section 2
, the methodology and data to obtain hourly profiles of a highly electrified Swiss energy system in the heat and mobility sector as well as a simultaneous substitution of NPP by PV is presented. In Section 3
, results from these profiles on the additional electricity and power demand as well as the impacts on the overall electricity system in terms of total load, surpluses/deficits and CO2
mitigation are discussed. Section 4
summaries the conclusions of this study and provides an outlook for further study.
This study investigates a large electrification of the Swiss heat and mobility and shows the implications of this, taking into account the already decided phasing out of nuclear power and a large penetration of PV, by means of a dynamic and data-driven scenario analysis.
With an estimated substitution of fossil energy in the mobility and heating sector by 20% BEV and 75% heat pumps, there is an additional electricity demand of 13.7 TWh, of which 10 TWh and 3.7 TWh are for heat pumps and BEV, respectively. This is an increase of the current electricity (end-use) demand by 23%. Moreover, most of this additional demand is in winter, when domestic electricity production is lowest and more CO2 intensive electricity imports or new Swiss CCGT power plants are needed.
In terms of maximum power demand, an additional 5.9 GWh/h (hourly average power) is required. This is also a major challenge for the electricity system as capacities and flexibilities in the Swiss electricity production are limited and de facto only available from (pumped-hydro) storage power plants.
In a highly electrified Swiss energy system with a large share of PV and no base-load nuclear power, there are large amounts of electricity deficits (mostly in winter and at night) and surpluses (mostly in summer and at noon), which can only partially be offset by short-term (e.g., batteries, pumped-hydro storage) and long-term (e.g., power-to-gas) storage.
Depending on the reference scenario (with or without nuclear power) and assumption on the key parameters (e.g., extend of building retrofit, CO2 intensity of imports, heat pump and BEV penetration, etc.), CO2 savings of an electrified energy system vary and may even be offset by an increase of CO2 intensive imports in winter. Therefore, the most crucial parameter for a successful electrification of the energy system in terms of CO2 mitigation is a low CO2 intensity of electricity imports in winter. Moreover, for an effective CO2 mitigation, energy systems should be regarded integrally with focus and mitigation steps on all energy sources (also fossil ones) and technologies.
As neighbouring countries such as Germany and France are faced with similar challenges to decarbonize their energy system, renewable electricity imports from these countries are more challenging (and costly) to obtain. Therefore, a Swiss energy strategy and decarbonisation, which heavily relies on (renewable) electricity imports is economically and technically more and more dependent on the schedule of the European energy system decarbonisation.
Results show that an electrification cannot be the sole solution of an energy transition to less CO2. Nonetheless, the electrification of heat and mobility will play an important role in the future energy system, not least for reasons other than CO2 reduction (e.g., local air pollution and noise mitigation, etc.). It seems important that the expansion of renewable sources, be it electricity or other sources of energy, is matched to the additional consumption of the respective energy sources in a timely and quantitative manner.
With respect to further studies, in particular the following investigations should be conducted:
Investigations on the effective potentials to manage hydro and pumped-hydro storage in the various scenarios and along with other storage technologies (e.g., batteries, etc.)
Investigations on the impacts of varying nuclear phase-out scenarios (in time and intensity) on CO2 mitigation and electricity supply
Investigations on tangible building flexibility options such as local and district heat storage, storage options on both sides of heat pumps (electricity or heat), etc.
Investigations on tangible demand side control strategies for mobility (e.g., recharging scheduling, vehicle-to-grid, etc.)
Last but not least, also costs associated with all options in this and further studies are a crucial factor to investigate. Therefore, a cost estimation of different approaches for CO2 mitigation, for example with respect to infrastructure adaption, etc., should also be conducted.