Carbon dioxide emissions effects of grid-scale electricity storage in a decarbonizing power system

Abstract

While grid-scale electricity storage (hereafter 'storage') could be crucial for deeply decarbonizing the electric power system, it would increase carbon dioxide (CO 2 ) emissions in current systems across the United States. To better understand how storage transitions from increasing to decreasing system CO 2 emissions, we quantify the effect of storage on operational CO 2 emissions as a power system decarbonizes under a moderate and strong CO 2 emission reduction target through 2045. Under each target, we compare the effect of storage on CO 2 emissions when storage participates in only energy, only reserve, and energy and reserve markets. We conduct our study in the Electricity Reliability Council of Texas (ERCOT) system and use a capacity expansion model to forecast generator fleet changes and a unit commitment and economic dispatch model to quantify system CO 2 emissions with and without storage. We find that storage would increase CO 2 emissions in the current ERCOT system, but would decrease CO 2 emissions in 2025 through 2045 under both decarbonization targets. Storage reduces CO 2 emissions primarily by enabling gas-fired generation to displace coal-fired generation, but also by reducing wind and solar curtailment. We further find that the market in which storage participates drives large differences in the magnitude, but not the direction, of the effect of storage on CO 2 emissions.

Effects on power system operations of potential changes in wind and solar generation potential under climate change

“…To co-optimize energy and reserves, we set regulation provision costs to $10, $6 and $4 ($ 2017 ) per megawatt-hour (MWh) for coal, NGCC and natural gas steam units, respectively. These costs capture variable operation and maintenance (VOM) and heat rate degradation costs incurred while providing reserves (Craig et al 2018b).…”

“…To ensure system reliability against variable wind and solar generation and unexpected generator and transmission outages, as well as to approximate current reserve classes in ERCOT (Electric Reliability Council of Texas 2013), the UCED model includes three reserve classes: regulation, flexibility and contingency reserves (table 1) (SI.1). To capture greater reserve requirements at high wind and solar penetrations modeled here, the three reserve classes vary with load and wind and solar generation (Craig et al 2018b, Lew et al 2013. All reserve classes procure positive or up reserves, i.e.…”

“…Since hydropower accounts for less than 1% of the fleet capacity, we subtract the estimated hourly generation by hydropower units from demand, then remove them from our fleet (SI.1). We augment the CDR generator fleet with carbon dioxide (CO 2 ) emission rates by fuel type (US Energy Information Administration 2017a); unit commitment parameters by plant and fuel type and capacity (Craig et al 2018b); VOM costs by fuel type (Craig et al 2018b); and latitudes and longitudes (US Environmental Protection Agency 2017) (SI.1). Based on 2017 data for Texas, we set coal, natural gas and nuclear fuel costs equal to $2.21, $3.26 and $0.65 per MMBtu ($ 2017 ) (US Energy Information Administration 2018), but test the sensitivity of our results to higher natural gas prices of $6 per MMBtu ($ 2017 ).…”

“…Since we conduct our analysis for 2041-2050 climate change conditions and given recent continued growth in Texas renewable penetrations, we add 15 GW wind and 30.5 GW solar to the CDR fleet (which originally contained 20 GW wind and 1 GW solar) to construct a high-renewable fleet with roughly 25% wind and 15% solar penetration by energy. We use greater wind than solar capacity to reflect results of studies on cost-optimal high-renewable generation fleets (Hand et al 2012, Craig et al 2018b. Given that adding renewables increases system reserve and flexibility requirements, we do not remove generators from the CDR fleet.…”

Economic drivers of wind and solar penetration in the US

“…Many existing studies of high wind and solar penetration assess the role of a couple of drivers in isolation or with a limited number of joint sensitivities (e.g. Fell and Linn 2013, Shearer et al 2014, Hirth 2015, MacDonald et al 2016, Craig et al 2018, Eshraghi et al 2018, Sepulveda et al 2018, as shown in SI appendix, table 1. Although these one-way sensitivities are valuable ceteris paribus experiments, they do not comprehensively assess the relative impact of a range of factors by jointly varying all drivers simultaneously.…”