Storage plants – a solution to the residual load challenge of the power sector?

doi:10.1016/j.est.2020.101626

Journal of Energy Storage

Volume 31, October 2020, 101626

https://doi.org/10.1016/j.est.2020.101626 Get rights and content

Highlights

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Storage plants can provide highly flexible, firm and renewable power capacity to cover residual load in any electricity supply system world wide.
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Storage plants are based on available technology.
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Storage plants offer possibility to finalize global energy transition to renewables.
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Combination of thermal electricity storage and sustainable fuels provide firm and renewable power from thermal power plants.

Abstract

We formulate the concept of a multi-functional energy system, called storage plant, as a possible solution to cover the variable residual load that appears in most countries after introducing renewables in the power sector. A storage plant consists of a photovoltaic power plant, a heat storage system with electric heater to transform solar power, a steam power cycle to convert stored heat to dispatchable power, a backup heating unit for the storage based on the combustion of biomass or other renewable hydrocarbons, and a gas turbine with waste heat recovery for peak loads. After explaining the storage plant concept, the paper describes a simulation model of the German power sector and its transformation from the year 2020 with roughly 40% renewable electricity share to 2040 with a hypothetic 90% renewable electricity share. Multi-indicator benchmarking over that period shows that storage plants can have a key role to achieve emission goals and at the same time sustain full supply security within the German power sector.

Introduction

A key challenge of transforming the power sector from fossil fuel based to renewable energy based generation is the residual load curve, which is basically the result of subtracting fluctuating renewable power production from power demand, and tracking that difference over a specific period of time [2,10,16]. The residual load curve can vary greatly over time between a maximum, when no renewables are available, and zero, when renewables work at maximum supply [6]. The objective of the present paper is to introduce a novel energy conversion and storage concept that turns out to be affordable, flexible and secure and therefore appears to be suited as one solution for overcoming the residual-load problem.

Residual load requires covering the gaps left vacant by wind and solar power production providing highly flexible and at the same time renewable power [3,7,17]. In future, thermal power plants will still be needed to provide firm capacity, but at the same time they will face highly variable load and reduced utilization in terms of full load operating hours, both affecting their technical and economic performance. Another challenge is that in the long-term the residual load – left over by renewable power production – must be covered by renewable energy as well.

Up to now, thermal power plants using fossil and nuclear fuel have been the only available options to securely cover the adversely fluctuating residual load, and up to now it is controversially discussed if there is any other solution to that at all. On the other hand, the storage concept of Carnot Batteries [1,5,9,8,11,13], also referred to as pumped heat electricity storage (PHES) paves the ground for large-scale energy storage based on inexpensive thermal energy storage materials. In the present work we demonstrate how a combination of available power plant technologies and Carnot Battery concepts can be used to solve the residual-load problem.

The paper is organized as follows: In the following chapter we shall formulate our concept and explain its basic features. Chapter 3 presents the model instrument used for multi-indicator benchmarking the transformation of power supply systems. Chapter 4 is devoted to applying our concept to the specific case of the German power sector. We shall demonstrate, using available transformation scenarios, how the concept of the storage plant is capable of providing affordable coverage of the residual load. In chapter 5 we summarize our conclusions.

Section snippets

Storage plants for high supply flexibility

The following presents an innovative thermal power plant concept that could become a key to a fast transition towards renewable electricity supply world wide, as it solves the challenges related to the residual load curve. The storage plant proposed here uses photovoltaic power, solid biomass and biogas (or temporarily natural gas) as primary energy sources to supply renewable electricity just as required by the residual demand. Depending on availability, synthetic hydrocarbons and liquid

Power system simulation and multi-indicator benchmarking

The simulation tool ELCALC balances hourly time series of electricity demand and supply by renewable and conventional power stations, electricity storage and grid interconnections for selected model years for a selected country or region [14]. The tool allows for benchmarking selected indicators of the power supply system and tracking their change over a defined transformation period.

The simulation model ELCALC (Fig. 3) for electricity sector calculation makes use of an energy data base ENDAT

Role of storage plants in the German power sector

In the following we present a possible transition pathway of German electricity supply up to the year 2040. ELCALC simulates the installation of 70 GW storage plants until 2040, consisting of 21 GW steam turbines and 49 GW gas turbines, 105 GW photovoltaics and heat storage with 600 GWh_th storage capacity that is equivalent to about 12 hrs of maximum power output of the steam turbines. The storage plants are assumed to be part of the German national power supply system described in Table 2. The

Conclusions

Covering the increasingly fluctuating residual electrical load with renewable energy is a global challenge of energy transition that up to now has not been answered with satisfying solutions. The paper at hand sets the hypothesis that storage plants can take over this task using existing commercial technology.

Storage plants, as defined in this paper, consist of an energy source with fairly regular production cycles such as photovoltaics, a buffer storage, preferably a molten-salt heat storage,

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful to Norbert Jentsch and Thomas Hörtinger for fruitful discussions on the implementation of the storage plant concept.

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View full text

Storage plants – a solution to the residual load challenge of the power sector?

Highlights

Abstract

Introduction

Section snippets

Storage plants for high supply flexibility

Power system simulation and multi-indicator benchmarking

Role of storage plants in the German power sector

Conclusions

Declaration of Competing Interest

Acknowledgements

J Clean Prod

Solar Energy

Energy Policy

Structural change and plant repurposing in the Rhenish lignite mining area

Stromspeicher I-TESS: Studie zur Integration thermischer Stromspeicher in existierende Kraftwerksstandorte

Solarinstitut Jülich der FH Aachen

Dauer und Häufigkeit von Dunkelflauten in Deutschland

Energiewirtschaftliche Tagesfragen 69 Jg

Flexibility requirements of renewable energy based electricity systems – a review of research results and methodologies

Renewable and Sustainable Energy Reviews