Faculté des Sciences appliquées
Faculté des Sciences appliquées

Development of an energy model to study the relevance of long-term energy storage in electricity zones powered with 100% renewables

Argilés Sánchez, Carmen ULiège
Promotor(s) : Léonard, Grégoire ULiège
Date of defense : 26-Jun-2019/27-Jun-2019 • Permalink :
Title : Development of an energy model to study the relevance of long-term energy storage in electricity zones powered with 100% renewables
Translated title : [en] Development of an energy model to study the impact of long-term energy storage in electricity zones with 100% Renewable energy sources: comparison between Belgian and Spanish cases.
Author : Argilés Sánchez, Carmen ULiège
Date of defense  : 26-Jun-2019/27-Jun-2019
Advisor(s) : Léonard, Grégoire ULiège
Committee's member(s) : Ernst, Damien ULiège
Dewallef, Pierre ULiège
Marenne, Daniel 
Language : English
Number of pages : 100
Keywords : [en] RES
[en] power-to-fuel
Discipline(s) : Engineering, computing & technology > Energy
Target public : Researchers
Professionals of domain
General public
Institution(s) : Université de Liège, Liège, Belgique
Degree: Cours supplémentaires destinés aux étudiants d'échange (Erasmus, ...)
Faculty: Master thesis of the Faculté des Sciences appliquées


[en] For the present project, six simplified models of an electricity zone with
100% renewables are developed. The approach is applied to three different
hypothetical scenarios: (i) a combination of wind energy and methanol storage,
(ii) a combination of PV solar energy and methanol storage, (iii) a combination of
wind energy with PV solar energy and methanol storage. Those are developed for
two European countries with a very different distribution of renewables energies
and electrical network: Belgium and Spain.
These three scenarios are not entirely realistic as in reality, wind and solar
will be complemented by other sources such as hydro or biomass. However, the
idea is to study the impact of having large shares of variable renewable sources
with different variability profiles on the electricity grid.
The purpose of this study is to minimize the energy cost (euros/kWh) by
determining the optimal combination of energy generators (windmills, solar
panels or both) and long-term storage based on methanol production (power-to-fuel).
This combination must respect two constraints, a period of LOLH (lost of load
hours) lower than 0.25h during the period (5.8 years for Belgium and 4 years for
Spain), and preserve the same storage level (amount of methanol stored) at the
beginning and the end of the period. This condition ensures the match between
installed capacities and system requirements.
Then, this model determines the viability of power-to-fuel storage technology.
One significant advantage of power-to-fuel methanol is the fact that the storage
is very very cheap (storing a liquid at ambient T and P) so that the marginal cost
of storage itself is neglected.
Another assumption is that curtailed energy occurs when wind and/or solar
generation surpasses both the demand and the storage capacity without incurring
on detrimental consequences to the grid stability. Furthermore, all the models
consider a system optimum rather than an agent-based approach. So, it is
assumed that the energy that is stored is free as a result of a zero cost for the
storage units. Also, market competitiveness, other applications for methanol or
oxygen (electrolysis by-product), and grid limitations and control costs are not
The grid of both of the countries considered in this job is different. In Belgium,
natural gas and nuclear energies are much more exploited. However, in Spain,
the coal is the second energy source more used, but the demand supplied by
renewables energies is 15% higher in this region. Consequently, the actual
emissions of CO2 per kWh are much higher in Spain than in Belgium, being
243.23 gCO2/kWh and 175.91 gCO2/kWh, respectively. The average capacity
factor for wind is similar in both countries (0.277 Belgium, 0.240 Spain) but,
for solar it is almost double in Spain (0.111 Belgium, 0.217 Spain). Finally, the
average load during the sample period in Belgium is 8.89 GW and in Spain 28.70
The first system proposed is the 100% wind energy system. In Belgium, the
optimum is found for 9119 windmills with 45.6 GW installed and 58250 storage
units with 14.56 GW installed. Wind directly energy served is 72.7% of the total
energy served between windmills and power-to-fuel units. In Spain, the resulting
grid has 28965 windmills with 145 GW installed and 182295 storage units with
45.57 GW installed. In this country, the energy served by windmills is higher than
in Belgium, 81.80%. The final electricity price is 88.3 euros/MWh for Belgium
and 85.9 euros/MWh for Spain. The CO2 emissions savings compared to the
actual grid are more significant for Spain, with 94.24%; 92.04% in Belgium.
For the 100% PV solar energy system scenario, the installed capacity needed
is enormous due to the low capacity factor. Therefore, these are not realistic
systems. In Belgium the resulting grid has 2520 millions of PV panels with 760
GW installed, 405159 power-to-fuel units with 101.29 GW and a 48% of the
total energy served by PV cells. In Spain, the optimum cost is obtained for 70430
millions of PV cells with 2112 GW installed, 479565 storage units with 120 GW
installed, and 81.42% of energy demand supplied by PV cells (almost double
than in Belgium). The energy cost is 951.6 euros/MWh in Belgium and 753.9
euros/MWh in Spain. As said before, neither the system or the energy cost is
realistic. The CO2 emissions are reduced by 74.42% in Belgium and 81.50% in
Finally, the lowest price is found for a 100% wind and PV solar energy system.
In this scenario, the Belgian grid is composed by 8007 windmills with 40 GW
installed, 29.92 millions of PV panels with 9 GW installed, and 51256 storage
units with 12.81 GW installed. With 76.14% of the total energy served by wind
and PV solar. On the other hand, the Spanish grid is formed by 15413 windmills
with 70.07 GW installed, 237.56 millions of PV panels with 71.23 GW installed,
and 139891 power-to-fuel units with 35 GW installed. In this case, the energy
served by windmills and PV panels is 82.62% of the total. The final energy cost
is 86.2 euros/MWh in Belgium and 71.10 euros/MWh in Spain. This last one
experiences a more considerable decrease on the final price with the combination
of both energy sources. That and the larger cost of storage units electricity in
Spain for a 100% wind energy system shows that the harmony between the peak
load periods and energy generation by renewable sources periods reduces the cost
of power-to-fuel energy and, consequently, the final electricity cost. However,
for this scenario, the percentage of CO2 emissions savings is slightly larger in
Belgium (88.80%) than in Spain (88.11%).
So, for all the scenarios considered, the final energy cost is larger in Belgium
than in Spain, and the overcapacity is necessary for the full energy demand
supply. Nevertheless, for both cases, due to the lower installed capacity required,
energy cost, and energy curtailed, the most efficient system is the 100% wind
and PV solar energy system. With this energy grid, the energy cost in Belgium is
less than twice the actual one and, in Spain, around 65% larger. Still, the CO2
emissions savings are larger for the scenario 100% wind energy system.
In conclusion, to achieve the European Commission objectives assuring the
energy supply, and a reasonable energy cost, a 100% RES system combined with
power-to-fuel storage is a realistic alternative to the actual grid system.



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  • Argilés Sánchez, Carmen ULiège Université de Liège > conv. Erasmus en sc. appl.


Committee's member(s)

  • Ernst, Damien ULiège Université de Liège - ULiège > Dép. d'électric., électron. et informat. (Inst.Montefiore) > Smart grids
    ORBi View his publications on ORBi
  • Dewallef, Pierre ULiège Université de Liège - ULiège > Département d'aérospatiale et mécanique > Systèmes de conversion d'énergie pour un dévelop.durable
    ORBi View his publications on ORBi
  • Marenne, Daniel
  • Total number of views 39
  • Total number of downloads 357

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