The Transition to Renewables

While the ideal of designing all-electric, non-polluting, energy-efficient buildings is being enthusiastically supported in many parts of the United States, the reality is that the current system of generating and distributing electricity isn’t there yet. Utility scaled generation by renewable energy is growing, but so is electricity demand for buildings, electric cars, and industry. Perhaps the best way to describe the current situation is one of transition – moving away from coal and other fossil fuels as they are replaced by cleaner, renewable energy options with less environmental impact.

One tool used to measure the real impact of different energy sources is referred to as carbon intensity, which is the total carbon emissions (or total carbon footprint) embodied in an energy choice from the source to the point of use. The units for carbon intensity are typically expressed in kg/MMBtu (million BTU) or grams/Megajoule. Based on our prior discussion, it should not be surprising to realize now that the electrical grid still has a rather high carbon intensity compared to the goal of a much lower one approaching zero.

During this transition, a more realistic goal should ultimately be how to best reduce the carbon intensity of the energy being used in a building. Architects can and should consider on-site generation from solar or wind when possible since it reduces or eliminates the inefficiencies and energy loss found in the grid. However, many building situations aren’t conducive to solar or wind systems due to space limitations, solar access, or other factors. There may also be limitations related to the building owner or local regulatory requirements. In some cases, those can be overcome through the use of community solar systems or selecting renewable energy from public utilities where available. In many cases, though, there needs to be another option.

A number of architects have begun to incorporate a hybrid energy approach into their building designs as a viable solution. This typically includes providing some amount of on-site renewable energy, most commonly solar electric, with another source that has a low carbon intensity. This combination creates a hybrid system that can be used to achieve short-term environmental goals while the longer-term solution is still evolving. Perhaps automobiles are a good analogy: hybrid gasoline/ electric cars have been in use for several decades helping with the transition to all-electric vehicles with readily available charging stations. In the same way, hybrid energy solutions in buildings can help move us closer to more environmentally responsible results.

PROPANE AS AN ENERGY ALTERNATIVE

One option worthy of consideration for creating a hybrid building design is the use of propane energy. Why propane? While it is true that it is a hydrocarbon, propane has a comparatively low carbon intensity for each unit of energy produced. Part of that is based on its chemical makeup and part on the efficiency of its distribution. In fact, the Energy Policy Act of 1992 lists propane as an acceptable “alternative fuel” along with biodiesel and liquified natural gas. Further, plant-based renewable propane is coming to be available with even less carbon intensity.

Image courtesy of Propane Education & Research Council

Propane is produced at central locations, distributed across the country, and stored locally for on-site delivery to buildings.

Propane as a Fuel

Propane, or as it is technically known, Liquefied Petroleum Gas (LP-gas or LPG) is a byproduct of either crude oil refining or natural gas processing. Once it is refined, there’s little difference between LP gases processed from these sources. The resulting propane is nontoxic, colorless, and naturally odorless so an identifying odor is added so it can be readily detected. For a number of years, over 99 percent of the propane used in the U.S. has been produced in North America. In fact, the US has available for export more than twice as much as is used in this country. In recent years, 30 billion gallons have been produced with 10 billion gallons being used and 20 billion gallons available for export. Hence, there is an abundance available.

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, also known as camelina sativa or false flax. Camelina is a member of the mustard family and a relative of cabbage, kale, and cauliflower, but it 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 and prevents erosion when fields are fallow and provides additional income without the need for new equipment.

U.S. fuel processors are making renewable propane today, and the push for cleaner liquid fuels such as sustainable aviation fuel and renewable diesel fuel will lead to a sharp increase in renewable propane production. By 2050, renewable propane could meet half the world’s demand for propane, according to the World LP Gas Association. All of these efforts can help contribute to a more carbon-neutral world.

Propane Distribution

Part of the efficiency of distributing propane is that it can be stored and transported in either a liquefied state or as a gas. Propane producers use primary above-ground or below-ground storage systems to stockpile the available supply. From there it is shipped by pipeline, rail, or truck to thousands of secondary storage facilities throughout the United States. It is then accessed by propane retailers who are trained professionals located all over the country to provide propane service wherever there is a need.

At a specific building, propane is delivered, usually by truck, as a liquid and is pumped into an on-site storage tank which may be an above-ground or underground tank. If the tank is above ground, then the tank and any support system will be visible along with the needed valves, a pressure regulator, and a tank gauge. If it is underground, then typically the only visible portions are the cover which protects the shut-off valve, a regulator, a safety relief valve, and a tank gauge.

Using propane in the building is based on appliances and piping similar to using natural gas systems. Before leaving the on-site tank, the liquid changes to gas vapor and flows through a gas piping system to appliances inside and outside the home. The gas piping system commonly used in residential applications is pressure regulated at the tank with gas piping running underground to the home where further pressure regulation is usually needed to meet final appliance pressure requirements. The mounting of the regulator on the outside of the home must be planned with distance requirements from possible ignition sources.

Image courtesy of Propane Education & Research Council

A hybrid heat pump system includes coordinated components that work together to provide electric heat when that is the most efficient and propane-powered heat in colder temperatures when that is more efficient.