Is a natural gas ban an ‘antidote to climate change’?
By Anthony R Kovscek
As governments in California increasingly consider limiting new residential natural gas connections, it is important to question whether banning natural gas is an “antidote to climate change.”
Californians can take great pride in our nation-leading increases in the fraction of renewables used to generate electricity. The total renewable fraction in 2018 is about 40%, including hydroelectricity. This is twice what it was a decade earlier. On a sunny summer day, California’s solar farms, rooftop installations, and wind provide roughly 50% of the electrical energy consumed at noon, but at midnight the fraction of electricity provided by renewables drops to about 20%. With the setting of the sun, solar electricity is replaced principally by natural gas fired electricity. The flexibility and fast response of natural gas power plants has enabled the rise in renewables, of which we are rightly proud, by providing the necessary backup and power to stabilize our grid.
The importance of decarbonizing the energy system is indisputable, but the daily transition from significant renewable electricity to mostly natural gasgenerated electricity seems unlikely to change in the foreseeable future. There are no largescale energy storage solutions for daily and seasonal variations that are currently economic and environmentally acceptable. Community Choice Aggregation programs with a large fraction of renewable electricity do not overcome the time of day problem because electricity produced from various resources, including natural gas, is comingled on the grid. Over the long term, and if the costs of storage decline substantially, some of this evening and early morning demand could be met by storage, but we are a long way from that.
Before deciding that it would be good for the environment to ban access to natural gas, consider the carbon dioxide emissions associated with a shower outside of hours of substantial sunlight (typically 7 p.m. to 7 a.m.). A natural gas water heater produces about 0.1 pounds of carbon dioxide per gallon of water heated. The exact value depends on the efficiency of the heater. Instead, if we use an electric water heater, there is a very good chance we use electricity from a natural gas power plant. We need to consider the carbon implications of the energy transformations taking place before water is ultimately heated in our homes. The fleet of natural gas power plants supplying California is about 40% efficient. For a conventional electric hot water heater that uses electricity directly for heating, about 0.3 pounds of carbon dioxide are created per gallon of water heated. Thus, making electricity from natural gas and then using electricity to heat water for an early morning shower produces roughly three times as much CO2 as using natural gas directly. Importantly, most natural gas water heaters are immune from electricity shut-offs and outages.
Advanced hybrid electric hot water heaters dramatically reduce electricity consumption. Under real-world conditions, such systems deliver twice as much hot water per unit of electricity as compared to conventional hot water heaters, but they still result in about 25% greater emissions than a natural gas hot water heater, if used outside of the hours of substantial sunlight. Time of day thermal storage may provide a means to reduce emissions, but current hybrid hot water heaters already cost at least twice their conventional counterparts. Among other concerns, leakage of natural gas during distribution is problematic because methane is a potent greenhouse gas. Rates of leakage, however, are quite low in newly developed residential areas whereas they are greater in older cities. Available evidence suggests reasonably low rates in California and continued monitoring is wise.
Without belaboring the point, analysis of many components of residential energy consumption including space heating and clothes drying suggests that consideration of the time of day is important to understand the carbon implications of the choice of heating. We need to question critically whether banning new natural gas hookups actually reduces carbon dioxide emissions as natural gas will continue to be used — just in a more inefficient way. Anthony R. Kovscek is a professor of energy resources engineering at Stanford University and a senior fellow at Stanford’s Precourt Institute for Energy.
DAI SUGANO — BAY AREA NEWS GROUP
San Jose Mayor Sam Liccardo voted in favor of the city becoming the largest city in the United States to create an ordinance barring natural gas in new singlefamily homes, low-rise multifamily buildings and detached granny flats beginning next year.