Can 'green' natural gas work as a transition fuel for home heating?
By John Loukidelis and Thomas Cassidy
Published November 23, 2020
In "Wrestling the GHG Emissions Monster to the Ground, One Building at a Time" we showed how Thomas Cassidy reduced the greenhouse gas (GHG) emissions associated with heating his home by 94 percent.
Thomas replaced his gas-fired furnace with an air source heat pump that uses electricity from Ontario's relatively clean grid to provide space heating for Thomas's home. Thomas went from emitting about 5,000 kg of CO2 to about 320 kg annually for heating.
John took a different approach. About six years ago, John started buying "green" natural gas (aka "renewable" natural gas, or "biomethane") from Bullfrog Power. Bullfrog collects biogas from landfills then cleans it and injects it as green natural gas into our pipeline system. By "using" this gas to heat his home John has reduced his GHG emissions by about the same amount as Thomas.
Conventionally-sourced natural gas is a non-renewable gas composed mainly of methane (CH4). Ancient animals and plants captured CO2 from the atmosphere, and when they died their remains decomposed without releasing carbon back into the atmosphere. This matter decomposed under high heat and pressure over millenia to produce, among other things, natural gas that remained trapped underground.
Natural gas, when it is extracted, processed, transported and burned by humans, releases this captured carbon back into the atmosphere in the form of methane and CO2. The release of these GHGs has increased the concentration of CO2 and methane in Earth's atmosphere dramatically over the last 200 years.
The increased concentration of these GHGs has caused global warming and will continue to do so for centuries to come.
Green natural gas is refined from biogas, a material that is about 50 percent methane by volume and results from the decay of organic material in the absence of oxygen. The most significant sources are food waste, livestock, sewage and wastewater treatment, and agricultural residues.
The carbon in biogas, and thus green natural gas, was captured from the atmosphere by the plants and animals that produced the organic material from which the gases were derived. The plants and animals lived only a few years before their organic material breaks down to biogas.
As a result, burning green natual gas, while it releases CO2, simply returns the same mass of carbon to the atmosphere that was captured by the organic material. Burning green natural gas does not add any "new" GHGs to the atmosphere, in theory, and so it does not contribute to additional warming beyond those GHGs necessary to build the insfrastructure then collect, refine and deliver the gas.
For various practical reasons, green natural gas is not a perfectly renewable and carbon neutral fuel source. John significantly reduced the emissions associated with heating his home by buying green natural gas, but he did not eliminate them.
Methane, the key component of natural gas, is a potent GHG. A single methane molecule creates warming at a rate about 130 times that of CO2. One often hears that the global warming potential (GWP) of methane is about 34 times that of CO2, but that is its effect measured over 100 years. Here is how the GWP trend of methane looks over time:
Chart: Methan GWP by year
The rapid decay of GWP over time is because methane, when it is in the atmosphere and exposed to oxygen, oxidizes to produce CO2. It does this at a rate of about 6 percent per year so the warming impact is felt most intensely at the start before it has broken down. The half-life is about ten years, so every ten years the amount of methane remaining is cut in half:
Equation: rapid decay of GWP over time
Why does this matter? Some of the damage and change caused by global warming is irreversible. Global warming causes "state changes". For example, the melting of the polar ice will be permanent from our perspective: the ice, once it is gone, will not reappear for millenia. Similarly, if warming causes a species to go extinct, that species will never reappear.
Seen this way, the fact that the damage caused by CO2 and methane measured over, say, 1,000 years is nearly identical, does not matter if the extra warming of methane emissions over a shorter timespan causes damage or change that cannot be repaired or reversed.
To avoid the damage from warming caused by methane, we need to keep it out of the atmosphere. Unfortunately, this is easier said than done.
Let's ignore the truly horrifying prospect that we have already heated the atmosphere so much that the permafrost covering much of northern Russia and Canada will inevitably release a large amount of methane that we will be powerless to stop.
And don't even think about methane hydrates. Let's focus instead on the problems we create with using methane as a fuel.
Some sing the praises of natural gas as a "transition fuel". Burning natural gas, as such, emits only about one-half of the GHGs as coal for the same amount of energy. Replacing a coal-burning power plant with a gas-fired plant of the same size (as measured by power output) would seem to be a climate win on the path to net zero emissions by 2050.
However, some climate scientists and investors are less optimistic about the benefits of natural gas. Ignore for the moment whether we should be building any new natural gas infrastructure on the path to net zero by 2050 (hint: we shouldn't). Is natural gas really so beneficial from a climate perspective?
The extraction and transport of both coal and natural gas generate GHG emissions even before they are burned. The problem with natural gas is that it leaks into the atmosphere at every stage of the process from extraction to combustion.
Gases are, by their nature, more difficult to handle safely and without leakage than are solids. Because natural gas (methane) is a powerful GHG, its so-called benefits from a climate perspective could disappear, compared to coal, when these "fugitive emissions" are taken into account.
"Fugitive emisssions" come from all points of the natural gas lifecycle. Methane leaks when natural gas is extracted, when it is transported, when it is processed, and when it is used.
The amount of methane that leaks is controversial. The US Environmental Protection Agency (EPA) uses a leakage figure of 1.4 percent of the amount that is actually burned. Some anecdotal evidence suggests that the problem is worse than that.
For example, a power plant in Los Angeles was found to have been leaking over 280 cubic metres of natural gas per hour for a couple years! According to the Sierra Club, this represented the same warming over the course of a year as would have been caused by 30,000 cars.
A recent study that modelled the use of gas plants compared to coal used 3 percent for one of its scenarios based on more recent research into fugitive emissions. The study found that, when the 3 percent figure is used, gas plants are no better than their coal-fired cousins.
Peter Kalmus, the climate scientist, believes that 5 percent is a more realistic figure, which makes natural gas worse than coal in the short term (Peter Kalmus, Being the Change (2017), 154ff).
As has been noted already, landfills are a major source of biogas and thus methane. In many landfills, that methane simply leaks into the atmosphere where it causes warming.
In Ontario, some landfills are required to "flare" biogas before it leaks into the atmosphere. To flare this gas, it is collected using vertical or horizontal wells (or some combination of them) that are connected to a blower or a kind of vacuum. The wells collect landfill gas that is drawn to a wellhead where the gas can be "flared" or burned.
Burning the gas prevents landfill methane from leaking into the atmosphere. The burning combusts the methane so that CO2 is released instead. The result is a release of GHGs with a significantly lower GWP.
The Essex-Windsor regional landfill undertook a landfill gas capture and flaring project so that it could sell GHG offsets. The project, by flaring its 2009 "vintage" methane, avoided the emission of 47,264 tonnes of CO2e.
The Ontario regulations that require landfill flaring don't apply to legacy landfills or landfills below a certain size. As a result, many Ontario landfills simply leak methane into the atmosphere.
The annual GHG emissions (in tonnes) of some local landfills stuck out:
|Niagara Road 12 Landfill||844||21,108|
|Park Road Landfill||452||11,293|
|Elm Street Landfill||591||14,775|
That's a lot of methane. The database shows that Ontario has 34 landfill sites that emit more than 100 tonnes of methane per year. In the US, landfills contribute the third-largest share of the country's total anthropogenic methane emissions.
One tonne of methane at normal temperature and pressure is the equivalent of about 1,500 cubic metres of natural gas. John's home, in a typical year, burns about 3,000 cubic metres, or about 2 tonnes, of natural gas for space and hot water heating.
If the methane from the landfills listed in the table above could be captured and burned in homes instead, then it could provide heat for over 7,000 homes like John's. About 14,224 fewer tonnes of natural gas would be needed from conventional sources and 355,621 fewer tonnes of CO2e would be emitted from the landfills.
Of course, this is exactly what Bullfrog does when it sells green natural gas to consumers like John. It undertakes projects that collect biogas from landfills and wastewater treatment plants. The biogas collected is processed to remove moisture and impurities before the resulting biomethane is injected into the "natural" gas distribution network.
Bullfrog promises its customers that it will inject an amount of biomethane into the distribution network that is at least equal to the amount for which the customers pay. Of course, customers pay extra for this gas. Currently, John pays $0.15 per cubic metre extra (including tax). This is on top of the roughly $0.25 per cubic metre fully loaded cost that John pays to Enbridge to supply natural gas to his home.
Per our last article, burning a cubic metre of conventional natural gas produces about 1.95 kg of CO2e of direct emissions from combustion plus about 0.25 kg of CO2e from upstream emissions related to production, refinining and transport. This works out to about 2.2 kg of CO2e per cubic metre.
Since John burns about 3,000 cubic metres per year in his house, his emissions from burning conventional natural gas would be about 6,600 kg of CO2e per year.
The savings from using green natural gas depend on how much methane from the landfill is captured and burned for heating compared to what would have been flared or simply allowed to escape into the atmosphere.
In the case where the biogas from the landfill would have been flared anyway, John's emissions from using green natural gas would be just the carbon cost of capturing and refining the biogas and then transporting the resulting green natural gas to his home.
Let's assume the emissions from those processes are the same as their counterparts for conventional gas. We estimate those carbon costs to be 0.25 kg per cubic metre. In that case, the emissions to provide heating and hot water for John's home would be 0.25 kg of CO2e per cubic metre burned, and so John's total emissions would be about 750 kg of CO2e per year (0.25×3,000).
As a result, John would be avoiding emissions of about 5,850 kg of CO2e, which amounts to almost a 90 percent reduction. The cost per tonne of CO2e avoided would be about $77, calculated as follows:
Equation: cost per tonne of CO2 emissions avoided
John's emissions reductions would be much more impressive in the case where the landfill biogas would have otherwise escaped into the atmosphere. In that case, the net emissions reduction from capturing the methane should also be added.
A cubic metre of natural gas has a mass of about 0.7 kg and a 100-year GWP of 34 so the savings are therefore an additional 0.7×34 = 23.8 kg per cubic metre over a 100-year timeframe. Under these assumptions, and looking forward 100 years, John would avoid emissions of 77,250 kg of CO2e per year from buying and using biomethane or green natural gas, and the cost per tonne avoided would be about $6, calculated as follows:
Equation: CO2 emissions avoided
It's hard to say what would otherwise happen to the landfill biogas, and so the true value probably lies somewhere near the middle of these two extremes. You can follow along with the calculations here or with a Bullfrog-commissioned report here (pdf link) to see more on calculating the environmental benefits.
Moreover, it's critical to understand that John's savings are dependent on the existence of landfills.
What would happen if we did a much better job of reducing food waste and composting so that we didn't need the extra capacity to handle that waste and the waste never had the chance to produce biogas? In that case, there would not be so much biogas escaping from landfills and adding to global warming, which in turn would reduce or eliminate the savings to be gained by capturing and burning green natural gas.
This Enbridge site claims that "if we consider greenhouse gases as countries, food waste would be the third biggest emitter in the world".
Chart: If food waste was a country
In other words, in the world in which we live - in which we waste food and dump a lot of organic material in landfills where it turns into biogas - it is possible to reduce your carbon footprint by at least 90 percent at a cost below $77 per tonne by buying and burning green natural gas.
In a world that needs to be at net zero emissions by 2050, however, the use of biomethane could be seen as nothing more than a stop gap. Should John try to reduce his emissions in other ways?
For example, John might consider buying a high-efficiency boiler to replace his current model. John's current boiler runs at about 65 percent efficiency and uses about 2,300 cubic metres of natural gas per year (the other 700 cubic metres are assumed to be for water heating). The gas burned costs $575 per year (2,300 cubic metres × $0.25 per cubic metre) and creates 5,060 kg of CO2e (2,300 cubic metres × 2.2 kg CO2e per cubic metre).
Let's say he replaces his boiler with a new 95 percent efficient unit for $6,000, which he expects will last for 25 years. His annual fuel consumption will drop to 1,574 cubic metres per year, which saves 726 cubic metres per year, and he will pay $393 per year in fuel costs.
The amortized cost of the boiler will be PMT(0.04,25,-6000)=$384 per year and as a result, the total cost to operate the new boiler would be $777 per year ($393+$384), which operations would produce 3,462 kg of CO2e annually (1,574 cubic metres × 2.2 kg CO2e per cubic metre).
Compared to John's current setup, this works out to $202 more, 1,598 fewer kg of CO2e, and a price of $126 per tonne of CO2e saved:
Equation: $126 per tonne of CO2 saved
If John keeps his existing unit, he can use $202 to buy green natural gas while still matching the annual operating cost he would have paid after upgrading.
Under this option, he would not need to decommission the existing boiler, there would be no emissions created by buying a new boiler and no landfill waste associated with scrapping the old one, no inconvenience associated with choosing and installing a new unit, and he could preserve cash, all while achieving lower emissions than upgrading. He would also not be locking himself into using natural gas for another 25 years.
Another option would be to fuel switch by installing a heat pump, as discussed in our last article. The calculations are here on the 'retire or keep boiler' tab. The calculations show that fuel switching would cost John about $90 per tonne of emissions reduced when compared to keeping his existing boiler. Switching for John, while his boiler works, would again be more costly, more cash intensive and more work than simply buying green natural gas until his existing boiler reaches end of life.
As is shown above, John's use of biogas depends on other practices and infrastructure that have harmful effects. In particular, that we generate so much food waste and thus, indirectly, natural gas should not be excused through its use for home heating. Instead, we should re-think how we handle food and manage our landfills.
Even when our wasteful practices make landfill biogas relatively abundant, green natural gas is still relatively expensive. John spends an extra $460 per year on his home heating by using Bullfrog. That's a price that not everyone can afford. Perverse federal policy does not help: John still pays the carbon tax on his "regular" gas bill despite reducing his carbon emissions significantly by buying green natural gas!
He has imposed a carbon tax on himself, in effect, to reduce emissions, which the carbon tax is supposed to encourage, but he pays the carbon tax on his gas bill anyway. The current carbon price per cubic metre of natural gas is $0.0587. If John were to receive a carbon tax credit for buying green natural gas, the net cost for the Bullfrog green natural gas would fall almost 40 percent. At a carbon price of $76.66 per tonne the Bullfrog gas would cost the same as a regular cubic metre of natural gas.
In any case, even if more homeowners decided to pay extra for green natural gas, it can't come close to heating all of Canada's homes, never mind its other buildings. The Canadian Biogas Association estimates that biogas can supply at most 3 percent of our current demand for natural gas, enough to supply about one million homes if we only used gas at home.
According to 2016 Census data, Canada has 14,072,079 occupied private dwellings.
Moreover, perhaps biogas should be seen as a valuable resource that we could use for other purposes. Green natural gas can be used in industrial processes and as a chemical feedstock. Biogas could be directly burned to generate electricity. When used for that purpose, biogas requires less processing, which makes it cheaper and less energy-intensive to produce. It would be even more efficient to use biogas in cogeneration facilities that find creative uses for the waste process heat.
For now, John will continue to use Bullfrog because it is the right stopgap for him at this time. He is planning to fuel switch eventually by installing a heat pump, but for him now green natural gas is the right transition fuel for heating his home.
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