Review of energy system flexibility measures to enable high levels of variable renewable electricity

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Abstract

The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.

Introduction

Energy systems need flexibility to match with the energy demand which varies over time. This requirement is pronounced in electric energy systems in which demand and supply need to match at each time point. In a traditional power system, this requirement is handled through a portfolio of different kind of power plants, which together are able to provide the necessary flexibility in an aggregated way. Once variable renewable electricity is introduced in large amounts to the power system, new kind of flexibility measures are needed to balance the supply/demand mismatches, but issues may also arise in different parts of the energy system such as in the distribution and transmission networks [1], [2].

Large-scale schemes of renewable electricity, noticeably wind and solar power, are under way in several countries. Denmark plans to cover 100% of country’s energy demand with renewable energy (RE) [3], Germany has as a goal to meet 80% of the power demand through renewables by 2050 [4], and in several other countries increasing the RE share is under discussion or debate [5], [6], [7]. At the same time, the renewable electricity markets are growing fast, e.g. in the EU, wind and solar stood for more than half of all new power investments in 2013 [8]. On a longer term, by 2050, RE sources could stand for a major share of all global electricity production according to several studies and scenarios [9], [10], [11], [12]. Compared to today’s use of RE in power production, the variable RE power utilization (VRE) could increase an order of magnitude or even more by the middle of this century. The experiences from countries with a notable VRE share, such as Denmark, Ireland and Germany, clearly indicate challenges with the technical integration of VRE into the existing power system, but also problems with the market mechanisms associated. Therefore, improving the flexibility of the energy system in parallel with increasing the RE power share would be highly important.

There is a range of different approaches for increasing energy system flexibility, ranging from supply to demand side measures. Sometimes more flexibility could be accomplished through simply strengthening the power grid, enabling e.g. better spatial smoothing [13]. Recently, energy storage technologies have received much attention, in particular distributed and end-use side storage [14], [15], [16]. Storage would be useful with RE power [17], but it is often perceived somewhat optimistically as a generic solution to increasing flexibility, underestimating the scale in energy [18]. Different types of systemic innovations, e.g. considering the energy system as a whole and integrating power and thermal (heating/cooling) energy systems together, could considerably improve the integration of large-scale RE schemes [19], [20]. The concept Smart Grid involves a range of different energy technologies and ICT to better manage the power systems and increase their flexibility [21]. Many other options are available as well.

The purpose of this study is to present a broad review of available and future options to increase energy system flexibility measures to enable high levels of renewable energy. Several of these measures are applicable for any type of energy system or energy supply. We present solutions that are linked to the demand side, electricity network, power supply, and the electricity markets. The literature on individual measures or technologies for energy system flexibility is vast. Recently, a few reviews on the subject have been published [22], [23], [24], [25], [26], but with a more narrow scope, whereas here we strive for a broader coverage of the available options. In addition to presenting options for energy system flexibility, we also try to reflect these against large-scale RE utilization and integration whenever possible.

Section snippets

Defining flexibility

To operate properly, the power system needs to be in balance, i.e. power supply and demand in the electric grid has to match at each point of time. The electric system is built in such a way that it has up to a certain point a capability to cope with uncertainty and variability in both demand and supply of power. For example on the supply side, the kind of flexibility is accomplished through power plants with different response time. Introducing variable power generation such as wind and solar

Overview

Demand side management (DSM) comprises a broad set of means to affect the patterns and magnitude of end-use electricity consumption. It can be categorized to reducing (peak shaving, conservation) or increasing (valley filling, load growth) or rescheduling energy demand (load shifting), see Fig. 1 [30]. Load shifting requires some kind of an intermediate storage [31] and a utilization rate of less than 100% [32] as both an increase and a decrease of power demand need to be possible in this case.

Grid ancillary services

With increasing variable renewable power production, system stability issues will become more likely [22] which can be mitigated through grid ancillary services. These services are generic in nature, i.e. not necessarily bound to RE power use.

Grid ancillary services involve different time scales and requirements with regard to power and energy capacity. For example, a power quality service has to provide rapid response, but only for a short duration, making it a power-intensive service. On the

Energy storage

Energy storage is used to time-shift the delivery of power. This allows temporary mismatches between supply and demand of electricity, which makes it a valuable system tool. Energy storage has recently gained renewed interest due to advances in storage technology, increase in fossil fuel prices and increased penetration of renewable energy [150]. In previous chapters, the usefulness of storage for ancillary services was already mentioned. In this chapter, we will present different storage

Supply-side flexibility

The power balance of electric systems is normally handled by the supply side (e.g. power plants). With supply-side flexibility, we mean measures or technologies through which the output of power generation units can be modified to attain the power balance in the grid, e.g. when large amounts of variable RE power is in use.

Advanced technologies

In the next, we present future strategies for dealing with large-scale RE schemes in which surplus RE production is utilized for different purposes, i.e. combining new loads to the power systems such as heating or cooling demand, electric vehicles and power-to-gas schemes. In this way, wasting the electricity from curtailment of RE power could be reduced or even avoided.

Grid infrastructure

Sufficient transmission capability is essential for power system flexibility [67], [318]. Robust and well-designed grids with appropriate grid codes [258] can balance large local differences in supply and demand, offering strong spatial interconnections. Furthermore, well-functioning energy markets need well-functioning transmission lines. Three future developments in grid infrastructure, namely supergrids, smart grids, and microgrids will be discussed here.

Electricity markets

Though energy system flexibility is often perceived as a technological issue only, it has a strong link to the electricity market as well. For example, different power tariffs may enhance flexibility. On the other hand, fuel-less energy sources such as wind and solar power have a zero-marginal cost on the market, meaning that large-scale RE schemes would drop the average electricity price. Poor market design may limit access to technical flexibility in energy systems [258]. In the next, we will

Conclusions

The number of options to improve energy system flexibility when increasing the share of renewable power in electricity production is large. It is likely that this theme will draw even more interest in the years to come as the prospects for new renewable energy technologies [387], [388], [389], [390], [391] are positive and further price reductions are expected. Energy system flexibility is definitely a “hot topic” as demonstrated by the large number of references contained in this review (close

Acknowledgements

The financial support of the Academy of Finland (Grant 13269795) is gratefully acknowledged.

References (393)

  • P Denholm et al.

    Grid flexibility and storage required to achieve very high penetration of variable renewable electricity

    Energy Policy

    (2011)
  • M Paulus et al.

    The potential of demand-side management in energy-intensive industries for electricity markets in Germany

    Appl Energy

    (2011)
  • P Finn et al.

    Facilitation of renewable electricity using price based appliance control in Ireland’s electricity market

    Energy

    (2011)
  • J-H Kim et al.

    Common failures of demand response

    Energy

    (2011)
  • G Strbac

    Demand side management: benefits and challenges

    Energy Policy

    (2008)
  • MH Albadi et al.

    A summary of demand response in electricity markets

    Electr Power Syst Res

    (2008)
  • DS Callaway

    Tapping the energy storage potential in electric loads to deliver load following and regulation, with application to wind energy

    Energy Convers Manage

    (2009)
  • J Bushnell et al.

    When it comes to demand response, is FERC its own worst enemy?

    Electr J

    (2009)
  • MEH Dyson et al.

    Using smart meter data to estimate demand response potential, with application to solar energy integration

    Energy Policy

    (2014)
  • A Arteconi et al.

    State of the art of thermal storage for demand-side management

    Appl Energy

    (2012)
  • I Stadler

    Power grid balancing of energy systems with high renewable energy penetration by demand response

    Util Policy

    (2008)
  • K Schaber et al.

    Transmission grid extensions for the integration of variable renewable energies in Europe: who benefits where?

    Energy Policy

    (2012)
  • P Cappers et al.

    Demand response in U.S. electricity markets: empirical evidence

    Energy

    (2010)
  • M Räsänen et al.

    Customer level analysis of dynamic pricing experiments using consumption-pattern models

    Energy

    (1995)
  • A Middelberg et al.

    An optimal control model for load shifting – With application in the energy management of a colliery

    Appl Energy

    (2009)
  • S Ashok et al.

    Load-management applications for the industrial sector

    Appl Energy

    (2000)
  • S Ashok

    Peak-load management in steel plants

    Appl Energy

    (2006)
  • S Mitra et al.

    Optimal production planning under time-sensitive electricity prices for continuous power-intensive processes

    Comput Chem Eng

    (2012)
  • K Nilsson et al.

    Industrial applications of production planning with optimal electricity demand

    Appl Energy

    (1993)
  • M Ali et al.

    Combining the demand response of direct electric space heating and partial thermal storage using LP optimization

    Electr Power Syst Res

    (2014)
  • AJ Van Staden et al.

    A model predictive control strategy for load shifting in a water pumping scheme with maximum demand charges

    Appl Energy

    (2011)
  • S Cao et al.

    Analysis and solution for renewable energy load matching for a single-family house

    Energy Build

    (2013)
  • P Finn et al.

    Demand side management of a domestic dishwasher: wind energy gains, financial savings and peak-time load reduction

    Appl Energy

    (2013)
  • MAA Pedrasa et al.

    A novel energy service model and optimal scheduling algorithm for residential distributed energy resources

    Electr Power Syst Res

    (2011)
  • H Holttinen

    Wind integration: experience, issues, and challenges

    Wiley Interdiscip Rev Energy Environ

    (2012)
  • The Danish Government. The Danish Climate Policy Plan: towards a low carbon society;...
  • The Press and Information Office of the Federal Government. Switching to the electricity of the future. Arch Der...
  • A Morales

    Further Spanish energy reform could mean “nasty revenue cut” for renewable

    Renewable Energy World

    (2013)
  • O Milman

    Solar Council campaigns against Tony Abbott over renewable energy target

    Guard

    (2014)
  • United Press International. France begins “energy transition” debate

    (2012)
  • Wind in power: 2013 European statistics

    (2014)
  • Technology roadmap: solar photovoltaic energy

    (2014)
  • Technology roadmap: wind energy

    (2013)
  • EU Energy Policy to 2050: achieving 80–95% emissions reductions

    (2014)
  • Annual energy outlook 2013 with projections to 2040

    (2013)
  • J Montgomery

    The case for distributed energy storage

    Renewable Energy World

    (2013)
  • MG Molina

    Distributed energy storage systems for applications in future smart grids

    Transm Distrib Lat Am Conf Expo

    (2012)
  • JV Paatero et al.

    Effect of energy storage on variations in wind power

    Wind Energy

    (2005)
  • AO Converse

    Seasonal energy storage in a renewable energy system

    Proc IEEE

    (2012)
  • Q Zhang et al.

    An analysis methodology for integrating renewable and nuclear energy into future smart electricity systems

    Int J Energy Res

    (2012)
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