CARBON IN ENERGY SOURCES

The popular view of how to reach carbon neutral buildings is to avoid fossil fuels altogether by using all-electric techniques and strategies. This is logical – as long as the source of the electric power does not require fossil fuels to generate that electricity. Currently, that is not yet the reality since about 60 percent of electrical generation in the United States is powered by natural gas and oil, although progress is being made to reduce that usage. In general, there are two approaches to achieving increased carbon-free electricity generation:

• Site-Generated Renewable Energy:
  This is appealing to design professionals because it is something that we can control as part of a total project design. It has also become financially appealing for building owners of all types (commercial, residential, institutional) due to significant cost reductions and the availability of income tax credits. In particular, this has caused a boom in the installation of solar-electric (i.e., photovoltaic (PV)) systems on buildings. Each building that has such a PV system incorporated into it then has its own carbon-free source of power generation to supply some, if not all, of the electricity needed. While this sounds ideal, the reality is that well over 90 percent of all such solar installations connect to the electric power grid. This means they are actually shedding or even “selling” electricity to the grid during peak sunlight periods and then buying the electricity they need during times without adequate sunlight, including evenings, night-time, and early morning. While some systems are “stand-alone” and not connected to the grid, those require significant additional investments in batteries and control equipment to work properly.
• Grid-Generated Renewable Energy:
  Virtually all buildings are connected to either a public or private utility company in order to meet their electricity needs, whether that building has any on-site generation or not. The electricity being delivered by that utility originates at any number of power generating plants and is controlled by a grid system that can pull electricity from various sources and route it to where it is needed. While the hope is that grid-supplied electricity will one day be 100 percent free of fossil fuels, the current reality (as of 2020) is that approximately 60 percent of all electrical power generation in the United States still comes from burning fossil fuels. Advocates of full electrification using non-polluting renewable energy predict that it will likely take over 20 years to realistically reach carbon-neutral goals based on current conditions.

  These realities provide some insight into alternative strategies to pursue to achieve carbon-neutral building design. The strategy of 100 percent onsite renewable energy production completely separate from the grid may be an option in some instances and should be pursued where feasible, but that is not currently a widespread solution. The next best thing is to have a grid-connected onsite renewable energy system that can meet all of the energy needs of the building by using and selling to the grid the equivalent amount being consumed (i.e., a net difference of zero). This, of course, is only fully carbon neutral currently if the building owner subscribes to purchasing only renewable energy-based electricity (i.e., non-fossil fuel-based energy) where that is available or practical. Otherwise, the grid-supplied electricity may still be a majority of fossil fuel-based energy.

Photo courtesy of PERC

Site-generated renewable energy has the potential to provide as much energy from a carbon-free source as is consumed by a building.

A Hybrid Approach

There is another approach for bridging the gap between current energy production processes and the goal of full net zero emissions that has been implemented in some places around the country. This is a hybrid approach that combines on-site solar or other renewable energy with a low-emission “clean energy” fuel to meet combined heat and power needs. Just as hybrid vehicles have been used over the past 20 years to pave the way for cars and trucks to move to fully electric, such hybrid approaches to building design can help buildings move toward fully emission-free energy in the next 20 years.

Photo and image courtesy of PERC

Renewable propane made from the camelina plant has a substantially lower carbon intensity compared to the electric grid and other common fuel sources.

Architect Mary Ann Schicketanz, the principal architect at Studio Schicketanz in Carmel, California, is a good example of someone who has incorporated this hybrid approach. She strives to make all the custom homes she designs energy neutral as part of her firm’s focus on sustainability. The large, luxury homes she designs in Big Sur and on the California coast are built to be healthy for the occupant, for the surrounding ecology, and for the climate. But it’s also a necessity since many of the homes she builds in the remote region are off the electric grid, necessitating that energy-neutral approach.

Like most designers and architects, Schicketanz, relies on solar photovoltaic (PV) panels and battery storage as a source of renewable power. But despite the common perception that zero net energy means all-electric, Schicketanz has learned that it isn’t yet practical to rely on electricity alone. Instead, she finds that specifying an alternative fuel for energy-intensive systems such as space heating and water heating yields a particularly effective formula for zero net energy homes. The fuel of choice in this case is propane delivered and stored on site. Such propane-powered systems offer ongoing utility bill savings but also the improved comfort of gas heating and the performance of luxury amenities like gas cooking.

Why propane? It turns out that it is a better choice than almost any other fuel in terms of carbon emissions. The Energy Policy Act of 1992 lists propane as an acceptable “alternative fuel” along with biodiesel and liquified natural gas. Propane, sometimes known as liquefied petroleum gas, or LPG, is a gas normally compressed and stored as a liquid. It is nontoxic, colorless, and virtually odorless, although an identifying odor is normally added, so it can be detected. Propane is commonly used for space and water heating, for cooking, and as fuel for engine applications such as forklifts, farm irrigation engines, fleet vehicles, and buses. It is primarily a byproduct of domestic natural gas processing, though some propane is produced from crude oil refinement. U.S. propane supplies are becoming increasingly abundant due in large part to increased supplies of natural gas. Substituting propane for other fuels such as fuel oil and diesel fuel is an economical and viable step to reduce, albeit not eliminate, the greenhouse gas carbon dioxide and air pollutants like carbon monoxide and nitrogen oxide. The U.S. Energy Information Administration lists propane fuel as one of the lowest sources of carbon dioxide at only 12.68 pounds per gallon of fuel or 138.63 pounds per million Btu. (https://www.eia.gov/environment/emissions/co2_vol_mass.php)

Renewable Propane

After years of research and development, the propane industry now has another option available in the form of renewable propane. Unlike conventional propane, renewable propane can be made from a variety of renewable feedstocks. The most common form of renewable propane is a byproduct of renewable diesel and sustainable aviation fuel made primarily from plant and vegetable oils, animal fats, or used cooking oil. As such, renewable propane’s carbon intensity (i.e., the carbon emitted for every unit of energy it produces) is lower than conventional propane because it’s produced from bio-based or renewable sources.

An increasing amount of renewable propane is being generated from the seed oil of the camelina plant. It is worth noting that renewable propane made from camelina oil has a lower carbon intensity (CI) score than the electric grid in 49 out of 50 states (Measured on a scale of 0-300, only Vermont with a CI score of 2 is lower than renewable propane’s score of 7.). Camelina, also known as camelina sativa or false flax, is a member of the mustard family and a relative of cabbage, kale, and cauliflower, but is not a food crop, nor does it compete with food production. Camelina is grown in cooler regions of the U.S. and will likely expand to the south, as producers are experimenting with varieties that can thrive in warmer climates. Camelina is drought and pest-tolerant and is a pollinator for bees. This cover crop is completely waste-free as the seed produces 40% oil, twice the amount of soybean. The remaining meal is FDA-approved for cow and chicken feed, and the husks are used for mulch. It is beneficial for farmers because it enriches the soil, prevents erosion when fields are fallow, and provides additional income without the need for new equipment.