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Zero energy homes generate as much energy as they use over the course of a year. Typically, these homes reduce energy use through carefully designed energy-efficiency measures, and then satisfy the remaining need through on-site solar panels. Of course, solar panels generate only electricity, so most zero energy homes consume only electricity.

While it is possible to have a true zero energy home that uses natural gas for space heating, water heating or cooking, this is seldom the case. There are four main reasons for this.

Methane Generates Carbon

Natural gas is essentially methane, a fossil fuel that is often associated with petroleum fields. Like petroleum, natural gas is pumped from the earth and transported in pipelines from the extraction point to homes and other buildings. Burning natural gas releases carbon dioxide and water, just like burning other fossil fuels. The big advantage of burning natural gas is that 30% to 50% less carbon is generated when compared to other fossil fuels like coal or petroleum products. Burning natural gas is definitely an improvement over burning fuel oil or coal. However, it still creates carbon dioxide. Solar panel generated electricity produces zero carbon.

Methane is a Greenhouse Gas

Methane doesn’t have to be burned to affect the climate. The chemical itself is a potent greenhouse gas with a global warming potential (GWP) 28 to 36 times that of CO2 before it is burned. Of the natural gas used for electricity generation about 2.4% leaks from extraction sites, transmission pipelines, and equipment. It’s not known how much gas leaks from distribution lines as it travels to homes, businesses, and factories for direct combustion. However, in cities where The Environmental Defense Fund looks for natural gas leaks, they are commonly found. By contributing to greenhouse gases released into our Earth’s atmosphere, natural gas proves to be even more damaging when it isn’t burned.

Net Metering Discourages Combustion Fuels

The typical home in an urban area uses energy in two forms: electricity and natural gas. Some areas still use fuel oil or propane, but the issues below still apply. One of the most important features of zero energy buildings is that they are usually grid-tied and have the ability to receive credit for unused electricity. Through a process called net metering, electric utilities either purchase excess energy directly from consumers or bank credits to be applied to future utility bills. Net metering policies vary widely among utilities and state regulators, but most policies limit credits to the amount used in the building. Whether the cap is applied monthly or annually, it discourages the building owner from installing an on-site solar system that generates more electricity than is used in the building. Now imagine that your building uses a fossil fuel for space and water heating. It would be easy to calculate the amount of energy consumed for these purposes and generate extra solar electricity to balance it out, so the home would be net zero in theory. However, under the vast majority of net-metering policies, you would not be paid for that extra production. In other words, you would purchase fossil fuel from one supplier, but not be able to recoup the cost from the electric company to whom you have sent your solar produced electricity.

Electric is More Efficient

While the purchase price of natural gas is cheaper than electricity almost everywhere, the story doesn’t end there. Another important factor that must be considered is end-use efficiency. Natural gas is burned on-site in furnaces, ranges, and water heaters with an efficiency topping out around 96%. That’s certainly good, but not nearly as efficient as electric heat pumps for space and water heating, which range between 300% and 400%. Electric induction cooktops have been shown to be more efficient and just as capable as gas ranges. In the end, electricity’s greater efficiency more than compensates for its higher fuel cost.

Post-Carbon Economy

Natural gas may still play an important role as an industrial-scale energy source in the transition from a fossil fuel-based economy to a clean-energy economy. But the four factors mentioned above will ultimately drive zero energy homes and buildings to use clean, site-generated electricity as the fuel of choice.