Variable Renewables Research Articles

On the Way to Integrate Increasing Shares of Variable Renewables in China: Experience from Flexibility Modification and Deep Peak Regulation Ancillary Service Market Based on MILP-UC Programming

China has declared ambitious carbon emission reduction targets and will integrate increasing shares of variable renewables for the next decades. The implementation for flexibility modification of thermal power units and deep peak regulation ancillary service market alleviates the contradiction between rapid capacity growth and limited system flexibility. This paper establishes three flexibility modification schemes and two price rules for simulation and proposes an analysis framework for unit commitment problem based on mixed-integer linear programming to evaluate the policy mix effects. Results confirm the promoting effects of flexibility modification on integrating variable renewables and illustrate diverse scheme selections under different renewables curtailment. Particularly, there is no need for selecting expensive schemes which contain more modified units and more developed flexibility, unless the curtailment decrement is compulsorily stipulated or worth for added modification cost. Similarly, results also prove the revenue loss compensation effect of deep peak regulation ancillary service market and illustrate diverse price rule selections under different curtailment intervals. Price rule with more subdivided load intervals and bigger price differences among them is more effective, especially under the higher requirement for curtailment rate. Therefore, the government should further enlarge flexibility modification via but not limited to more targeted compensation price, while generators should further consider a demand-based investment.

Impact of high solar and wind penetrations and different reliability targets on dynamic operating reserves in electricity generation expansion planning

Wind and solar are increasingly cost-competitive as well as environmentally less harmful alternatives to the fossil-fuel generation that dominates most electricity industries. However, their highly variable and somewhat unpredictable output still requires high levels of dispatchable plants to ensure demand can be met at times of low renewables availability. While this capacity overhead has associated costs, it does offer potentially useful outcomes for dynamic operating reserves. We present a method for assessing these potential outcomes in electricity industry planning. We use an evolutionary programming-based capacity expansion model, NEMO, that solves least-cost generation mixes through full operational dispatch of candidate solutions, using high-temporal resolution demand and wind and solar profiles, over a year or more. We apply our method through a case study of the Java-Bali grid, considering future scenarios both with and without variable renewables, and under different carbon pricing scenarios, reliability targets, and minimum operating reserves requirements. Our study suggests that not only might high renewable penetrations reduce industry costs and emissions, their inclusion provides significantly higher operating reserves over most of the year, hence the ability to cover unexpected plant failures and other disruptions. Lower reliability targets reduce this capacity overhang but still see improved operating reserves.

On the Way to Integrate Increasing Shares of Variable Renewables in China: Activating Nearby Accommodation Potential under New Provincial Renewable Portfolio Standard

More than 1.2 billion kW wind and solar power generation will be integrated in China by 2030. The new provincial renewable portfolio standard, officially implemented in 2020, establishes an efficient bridge between rapid capacity growth and limited accommodation capability. A data-driven prospect analysis framework was proposed to evaluate the activated potential under two kinds of nearby accommodation approaches and to explore the completion prospect of this new obligated quota from provincial levels. Empirical results illustrate diverse prospects across regions. Particularly, it is hard for two kinds of provinces to complete their obligated quotas merely via the single nearby accommodation approach: The first one is close to renewable energy resources but lacks flexible peak regulation capability in Northeast and Northwest China, and the other is close to the nationwide load center but lacks nearby integration from renewables in Southeast, North, and Middle China. Therefore, the pathway for the former is to activate more provincial accommodation potential either via releasing system flexibility or by substituting generation right, and the pathway for the latter is to introduce trans-regional or trans-provincial accommodation and import more renewable energy power.

Large-scale integration of offshore wind into the Japanese power grid

Offshore wind power attracts intensive attention for decarbonizing power supply in Japan, because Japan has 1600 GW of offshore wind potential in contrast with 300 GW of onshore wind. Offshore wind availability in Japan, however, is significantly constrained by seacoast geography where very deep ocean is close to its coastal line, and eventually, nearly 80% of offshore wind resource is found in an ocean depth deeper than 50 m. Therefore, power system planning should consider both the location of available offshore wind resource and the constraint of power grid integration. This paper analyzes the impact of power grid integration of renewable resources including offshore wind power by considering the detailed location of offshore wind resource and the detailed topology of power grid. The study is performed by an optimal power generation mix model, highlighted by detailed spatial resolution derived from 383 nodes and 472 bulk power transmission lines with hourly temporal resolution through a year. The model identifies the optimal integration of power generation from variable renewables, including offshore wind, given those predetermined capacities. The results imply that, together with extensive solar PV integration, total 33 GW of offshore wind, composed of 20 GW of fixed foundation offshore wind and 13 GW of floating offshore wind could contribute to achieve 50% of renewable penetration in the power supply of Japan, and that scale of offshore wind integration provides a technically feasible picture of large-scale renewable integration in the Japanese power sector.

Long-term scenario pathways to assess the potential of best available technologies and cost reduction of avoided carbon emissions in an existing 100% renewable regional power system: A case study of Gilgit-Baltistan (GB), Pakistan

The long-term power planning at the regional level has recently gained significance due to the economic and efficiency competitiveness of a decentralized energy system. In Pakistan, the power sector faces the challenge of exceptionally increasing electricity demand in metropolitan areas and the urgency of reliable power access in rural areas. In this paper, a regional power-generation system of GB is developed using the LEAP (Long-range Energy Alternative Planning) model from 2016 to 2050, to explore future clean pathways to understand the planning and operational implications of futuristic variable renewables (VRE) and best available technologies (BAT). The regional power system model is further expanded by using the end-user and econometric approaches to construct five scenarios which include Business-As-Usual (BAU), BAU-OPT (BAU-optimization), Demand Side Management (DSM), DSM-OPT, and National Energy Mix (NEM). The model estimates the electricity demand projection of 3.2 TWh in 2050, at an annual average growth rate of 3.19%, and suggests that hydropower is the most dominant variable renewable source in GB’s electric power system. The adoption of the BAT would avoid 1.34 TWh or about 41% of the projected electricity consumption, which shows the maximum potential of energy efficiency measures in GB. Moreover, the results indicate that: i) home appliances and lighting account for nearly halved of the reduction potential; while lighting and cooking are the most cost effective measures in terms of energy saving at regional level; ii) least cost constraint displays the transition towards large scale renewable projects; iii) the penetration of small scale renewable project is nearly doubled under least cost constraint by the introduction of demand side measures; and iv) higher emission penalties aggressively shift energy mix toward renewables with the cost of annual environmental externalities reducing in long-term. Overall, these findings can provide a scientific basis for the sustainable development of regional power-generation systems, as well as co-benefits of penetration of VRE and BAT in low-carbon electric power regions.

Will dispatchability be a main driver to the European Union cooperation mechanisms for concentrated solar power?

ABSTRACT The use of the European Union cooperation mechanisms for concentrated solar power (CSP) projects could kill two birds with one stone. First, CSP electricity can cover demand when variable renewables cannot generate. Second, CSP projects deployed under the cooperation mechanisms could contribute to a European-wide optimization of resource use and grid management. This paper analyzes whether the dispatchable nature of CSP is a main driver to the use of the cooperation mechanism for this technology. Based on an expert elicitation and a survey to different types of stakeholders, our results show that, indeed, dispatchability will be the main driver to the use of the cooperation mechanisms for CSP projects in the future. The findings suggest that two types of policy interventions will be required to encourage the use of these mechanisms for CSP. Some policy measures should be directed at the technology itself, whereas other policies should target the cooperation mechanisms.

Enabling Technology Maturation in Carbon Capture: The Role of a University Based Power Plant as a Test Facility

The Abbott Power Plant at the University of Illinois at Urbana-Champaign (UIUC) provides a unique facility for testing carbon capture, utilization, and energy storage technologies. This combined heat and power (CHP) facility supplies power and electricity for the needs of the UIUC campus. Despite being an operational plant, Abbott Power Plant is actively engaged in a variety of projects. These projects range in technology readiness level (TRL) and demonstrate the ability of the plant to couple field research with operational excellence. While the plant is a fossil asset (e.g., coal and natural gas boilers), it is connected through the campus grid to renewables. This connectivity provides the ability to evaluate how new technologies (e.g., capture, utilization, and energy storage) respond to variations in the grid due to the increased penetration of variable renewables. Because the plant is located on the UIUC campus, it is also engaged in educational activities at both the undergraduate and graduate level. The ability of the plant to couple operational excellence with research and development (R&D) and education makes it an important asset for the evaluation of new technologies.

Optimal Combination of Solar and Wind Power Generation and Energy Storage Systems to Realize Baseload Electricity Supplies with 100% Variable Renewable Energy

Optimal Combination of Solar and Wind Power Generation and Energy Storage Systems to Realize Baseload Electricity Supplies with 100% Variable Renewable Energy

An autopilot for energy models – Automatic generation of renewable supply curves, hourly capacity factors and hourly synthetic electricity demand for arbitrary world regions

Energy system models are increasingly being used to explore scenarios with large shares of variable renewables. This requires input data of high spatial and temporal resolution and places a considerable preprocessing burden on the modeling team. Here we present a new code set with an open source license for automatic generation of input data for large-scale energy system models for arbitrary regions of the world, including sub-national regions, along with an associated generic capacity expansion model of the electricity system. We use ECMWF ERA5 global reanalysis data along with other public geospatial datasets to generate detailed supply curves and hourly capacity factors for solar photovoltaic power, concentrated solar power, onshore and offshore wind power, and existing and future hydropower. Further, we use a machine learning approach to generate synthetic hourly electricity demand series that describe current demand, which we extend to future years using regional SSP scenarios. Finally, our code set automatically generates costs and losses for HVDC interconnections between neighboring regions. The usefulness of our approach is demonstrated by several different case studies based on input data generated by our code. We show that our model runs of a future European electricity system with high share of renewables are in line with results from more detailed models, despite our use of global datasets and synthetic demand.

Using electricity storage to reduce greenhouse gas emissions

While energy storage is key to increasing the penetration of variable renewables, the near-term effects of storage on greenhouse gas emissions are uncertain. Several studies have shown that storage operation can increase emissions even if the storage has 100% turnaround efficiency. Furthermore, previous studies have relied on national-level data and given very little attention to the impacts of storage on emissions at local scales. This is an important omission, as carbon intensities can vary very significantly at sub-national scales. We introduce a novel approach to calculating regional marginal emissions factors, based on a validated power system model and regression analysis. The techniques are used to investigate the impacts of storage operation on CO2 emissions in Great Britain in 2019, under a range of operating scenarios. It is found that there are significant regional differences in storage emissions factors, with storage tending to increase emissions when used for wind balancing in areas with little wind curtailment. In contrast, the greatest emissions reductions are achieved when charging storage with otherwise-curtailed renewables and discharging to reduce peak demands in areas consuming high volumes of fossil fuel power. Over all regions and operating modes studied, the difference between the highest reduction in emissions and the highest increase in emissions is considerable, at 741 gCO2 per kWh discharged. We conclude that power system regulators should pay increased attention to the impact of storage operation on system CO2 emissions.

A systematic review of the costs and impacts of integrating variable renewables into power grids

The impact of variable renewable energy (VRE) sources on an electricity system depends on technological characteristics, demand, regulatory practices and renewable resources. The costs of integrating wind or solar power into electricity networks have been debated for decades yet remain controversial and often misunderstood. Here we undertake a systematic review of the international evidence on the cost and impact of integrating wind and solar to provide policymakers with evidence to inform strategic choices about which technologies to support. We find a wide range of costs across the literature that depend largely on the price and availability of flexible system operation. Costs are small at low penetrations of VRE and can even be negative. Data are scarce at high penetrations, but show that the range widens. Nonetheless, VRE sources can be a key part of a least-cost route to decarbonization.

A Review and Categorization of Grid-Interactive Efficient Building Technologies for Building Performance Simulation

Abstract Buildings of the future are expected to not only be energy efficient but also able to offer grid services through implementation of demand-side management strategies by utilizing existing and new technologies that enhance electrical load flexibility. With the high penetration of variable renewables, grid operators have to balance between variable supply with controllable and adaptable demand. This article reviews the current literature on grid-interactive efficient buildings (GEBs) that can provide grid services. In particular, the review identifies categories and examples of measures and technologies that are suitable for GEBs using various criteria. These criteria include demand-side management strategies, potential to provide grid services, technology maturity, as well as ability to model the technologies to perform detailed analyses and assessments in whole-building simulation software.

On current and future economics of electricity storage

AbstractIncreasing electricity generation from variable renewable energy sources, such as wind and solar, has led to interest in additional short‐term and long‐term storage capacities. The core objective of this paper is to investigate the costs and the future market prospects of different electricity storage options, such as short‐term battery storage and long‐term storage as pumped hydro storage, as well as hydrogen and methane from power‐to‐gas conversion technologies. The method of approach is based on a formal economic framework with a dynamic component to derive scenarios up to 2040.The major conclusion is that the economic prospects of storage are not very bright. For all market‐based storage technologies it will become hard to compete in the wholesale electricity markets and for decentralized (battery) systems it will be hard to compete with the end users’ electricity price. The core problem of virtually all categories of storage are low full‐load hours (for market‐based systems) and low full charge/discharge cycles (for decentralized batteries). However, any new storage capacity should be constructed only in a coordinated way and if there is a clear sign for new excess production, in this case from variable renewables. In addition, for hydrogen and methane there could be better economic prospects in the transport sector due to both, higher energy price levels as well as a general lack of low carbon fuel alternatives. © 2020 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons, Ltd.

Heating with wind: Economics of heat pumps and variable renewables

Abstract With the growth of wind and solar energy in electricity supply, the electrification of space and water heating is becoming a promising decarbonization option. In turn, such electrification may help the power system integration of variable renewables, for two reasons: thermal storage could provide low-cost flexibility, and heat demand is seasonally correlated with wind power. However, temporal fluctuations in heat demand may also imply new challenges for the power system. This study assesses the economic characteristics of electric heat pumps and wind energy and studies their interaction on wholesale electricity markets. Using a numerical electricity market model, we estimate the economic value of wind energy and the economic cost of powering heat pumps. We find that, just as expanding wind energy depresses its €/MWhel value, adopting heat pumps increases their €/MWhel cost. This rise can be mitigated by synergistic effects with wind power, “system-friendly” heat pump technology, and thermal storage. Furthermore, heat pumps raise the wind market value, but this effect vanishes if accounting for the additional wind energy needed to serve the heat pump load. Thermal storage facilitates the system integration of wind power but competes with other flexibility options. For an efficient adoption of heat pumps and thermal storage, we argue that retail tariffs for heat pump customers should reflect their underlying economic cost.

Profit-Sharing Mechanism for Aggregation of Wind Farms and Concentrating Solar Power

Concentrating solar power (CSP) has been advocated as a promising technology to mitigate the uncertainty in variable renewables generation due to its thermal storage capability. In deregulated markets, however, it remains an open question as to how to identify different CSP plants’ contributions to uncertainty mitigation, and incentivize their participation in joint offering with variable renewable generation. In this article, we propose a profit-sharing mechanism to incentivize the joint offering of CSP and wind power aggregation. The joint offering strategy is formulated as a two-stage stochastic optimization model, aimed at maximizing the day-ahead market revenues, considering real-time imbalance settlement. A Nash bargaining (NB)-based market mechanism is designed to allocate the surplus from the joint offering. In contrast to symmetric NB with equal bargaining power (BP), we develop a novel BP evaluation method by precisely quantifying the market contributions of different producers in the joint offering. To preserve the autonomy of each producer, a decentralized solution framework is presented. Case studies show that the joint offering of wind power and CSP aggregation can effectively mitigate real-time imbalance. The proposed profit-sharing mechanism can identify market participants’ contributions in both the day-ahead and balancing markets.

Economies of Scope for Electricity Storage and Variable Renewables

In this paper, we investigate whether and under which conditions jointly owning a variable renewable source of electricity (VRES) and an electricity storage generates economies of scope in competitive electricity markets. Using a simple stochastic optimization model that assumes frictionless markets, we analytically show that no economic benefit arises from combining the two assets. This finding is in contradiction to large parts of the literature, which claim that it is in the economic interest of owners of VRES to additionally own electricity storage. We also identify circumstances where our argument does not hold and the combination of storage and VRES could theoretically make economic sense on the level of individual agents. In the last part of the paper, we demonstrate in a numerical case study of the German market that even in cases where our theoretical results do not hold, tying together storage and VRES may produce suboptimal results.

A case study of Australia's emissions reduction policies - An electricity planner's perspective

Australia offers an interesting case study of climate policy effectiveness as Australia has ‘tried’ a wide range of policies to mixed effect. Given that more than half of Australia's greenhouse gas emissions typically come from stationary energy generation, most climate policy in Australia has focussed on electricity sector reform, particularly the uptake of variable renewable energy and the decrease of thermal power generation. Electricity supply in Australia has undergone substantial change over recent years, substantially due to these policies, and needs to continue changing in the future to meet climate change mitigation targets and ensure stable, cost-effective electricity supply. This paper is therefore written from the perspective of an electricity planner and seeks to learn from the experiences of climate policies tried over recent decades. We start by reviewing the history of Australian energy policy and a description of how the Australian electricity network is structured to operate. We examine the theory and effects of different policies tried, which range from renewable energy targets, carbon pricing schemes, subsidies for renewable energy and research and development initiatives. We make three key observations from the case analysis: (1) that there has been substantial expense and effort effectively wasted through duplicate effects of different policy mechanisms by both federal and state governments; (2) as various mechanisms enable variable renewable energy generation to increase, the market becomes distorted, increasing total system costs and decreasing system robustness and resilience; and (3) the narrowed focus of climate policy mechanisms on certain variable renewables, such as solar photovoltaic and wind generation, omitted the opportunity for uptake of scale-able low carbon, firm generation options, like nuclear power and carbon capture and storage.

Managing variable renewables with biomass in the European electricity system: Emission targets and investment preferences

Biomass can help reaching climate goals in many sectors. In electricity generation it can complement variable renewables or, if coupled with carbon capture and storage (CCS), also provide negative emissions. This paper adds to the existing literature by focusing on the cost-efficiency of balancing variable renewables with biomass and by providing an indication on acceptance of these technologies. A dynamic optimization model is used to analyse the role of biomass in the European electricity system pending different emission targets for 2050. The results are compared with survey data on investment preferences for biomass technologies, and wind and solar power. The formulation of the emission target greatly influences the cost-efficient use of biomass, with more concentrated use observed, if bioenergy with CCS is allowed. This indicates that a Europe-wide emission target could be more cost-efficient than separate national targets. Both governmental and nongovernmental actors tend to be negative towards investing in biomass technologies, although with greater variation if combined with CCS, indicating possible challenges for implementation. Their attitudes towards wind and solar power are much more positive in all countries, supporting the continuation of the existing trend of an increasing share of variable renewables in the European electricity system.

Increasing the integration of variable renewable energy in coal-based energy system using power to heat technologies: The case of Kosovo

The goal of this work is to identify the influence which utilization of district heating systems coupled with the power-to-heat technologies based on the flexible operation of coal-based thermal power plants and limited electricity system interconnections can have on the maximum integration of variable renewables. An hourly deterministic tool EnergyPLAN was used for modelling and simulation of Kosovo energy system. Results revealed that Wind and PV power plant capacities of 450 MW and 300 MW respectively can be installed in the actual Kosovo energy system, when operating in an isolated mode. Additional capacities around 800 MW for wind and 385 MW for PV can be integrated into this isolated energy system with the contribution of power-to-heat technologies coupled with thermal energy storage in district heating with a fixed capacity. Furthermore, it was found that separate integration of wind can contribute to decease total primary energy supply and CO2 emissions for 3.34 TWh/year and 1.08 Mt compared to the referent scenario. Total primary energy supply and CO2 emission savings for separate integration of PV power plant compared with the referent scenario were estimated 2.74 TWh/year and 0.5 Mt respectively. Finally, the combined integration of variable renewable energy sources (1MWW+1MWPV) contributed to 3.29 TWh/year total primary energy supply and 1.02 Mt CO2 emissions savings.

A Penalty Scheme for Mitigating Uninstructed Deviation of Generation Outputs From Variable Renewables in a Distribution Market

With rapid growth of distributed renewable generation, the establishment of electricity distribution markets has attracted widespread concerns. Different from existing transmission grid-scale electricity markets, an electricity distribution market is featured by numerous small-scale prosumers, and zero marginal cost and intermittency of renewable generation units. Against this background, this paper first extends an average pricing market (APM) mechanism for pricing renewable generation outputs with zero marginal cost in the distribution network concerned. Then, to mitigate the uninstructed volatility of renewable generation outputs and power demand, a penalty scheme is proposed for deviations between the real-time demand/output and market cleared bid/offer, with frequency regulation service (FRS) from energy storage systems (ESSs) considered. It is proved that the market volatility can be well controlled within an expected limit through properly setting the penalty prices for load demand and generation output fluctuations. Also, with this mechanism a non-negative market surplus could always be attained. Case studies are carried out to demonstrate the feasibility and efficiency of the proposed distribution market mechanism and penalty scheme.