Quantcast

Rooftop Solar and EVs Save Water and Cut Pollution: Better Use of Data Will Optimize the Benefits

Austin's Pecan Street Project. Pecan Street Inc.

By Beia Spiller

Thanks to improvements in technology, it's easier than ever to be green.

Solar panels and electric vehicles (EVs) are two prime examples of technologies that can help people minimize their environmental footprint, without sacrificing comfort or having to radically change their daily behavior. But the question still remains: How much of an environmental benefit do these technologies actually produce? And, are there actions that owners of these technologies can take to minimize their pollution footprint even more?


A new paper by my colleagues and me, recently published in Energy Economics, attempts to answer these two questions for households in Austin, Texas. These homes are part of Pecan Street Inc., a living smart-grid laboratory with the largest customer energy-use database on the planet. Using detailed household-level data from 2013-2015, we were able to track solar panel performance and EV use and charging patterns, and match these actions to two important environmental impacts: water use and greenhouse gas (GHG) emissions.

Our paper confirms that, in Texas, using residential solar panels consumes less water and pollutes the air less than using the central-grid power (based on its electricity sources during those years), and driving an EV instead of a gasoline vehicle generally reduces the household's water and emission footprint, even though EVs charge from the grid. Moreover, our analysis demonstrates how carefully examining energy-use data can help us make sure we're maximizing clean energy's benefits.

Energy-water connection

People may know that burning fossil fuels—whether to create electricity or drive gasoline vehicles—emits gases that pollute the air. But you may ask, how do the central electric grid and cars use water?

Water is used to produce many forms of energy, including both fossil-fuel based electricity and gasoline. For electricity generation in a natural gas or coal plant, large quantities of water are used for process-related needs, as well as to cool the power plant. The production and refinement of gasoline also uses a lot of water; in fact, we calculate that it takes about four gallons of water to produce one gallon of gasoline.

Wind and solar PV, on the other hand, need virtually no water to create power, and they do not emit GHGs or other pollutants in the process.

The solar findings

Because solar panels consume no water and emit no pollution, installing a solar panel allows a household to reduce both the water use and air pollution associated with grid electricity.

In fact, we find that solar panels in Texas have a very large and positive impact on both water and GHG emissions, reducing a household's combined footprint by about 75 percent (a previous Pecan Street study also found solar panels reduce homes' water-intensity by approximately 79 percent).

In Texas during the day when the sun shines, the main power sources are natural gas and coal. So, if you're getting some or all of your power from your own solar panels, you're avoiding using that high-GHG emitting, thirsty electricity from the grid.

Importantly, we find that a household can improve its environmental footprint even further by facing its solar panels south, capturing more sun throughout the day. However, this can conflict with local electric system attempts to maximize production during periods of peak demand, generally in the afternoon when people are getting home from school and work. For example, Pecan Street provided subsidies for solar owners in their community who face their panels west, thereby generating more electricity during that afternoon period, but less overall over the course of the day. Less electricity from the solar panels overall means more water use and emissions from the central grid.

This contradiction highlights the importance of analyzing data. A better understanding of hourly energy usage and emissions can inform electric system policies and pricing that lead to a reduction in total costs, including those related to the environment.

The EV findings

Understanding electric vehicles' environmental impact by these measurements is a bit trickier, because EVs avoid gasoline (thereby reducing water use and GHGs), but they also charge using the grid, which in Texas is largely powered by fossil fuels (thereby increasing both water use and GHG emissions).

Our paper therefore tested whether, on net, EVs are good for the environment—in this case by reducing water use and GHGs—in Texas.

To be able to quantify the environmental benefits of EVs, we needed to think about what vehicle the household would have driven had it not purchased an EV. Vehicle owners have many choices in the marketplace, and fuel efficiency is not the only deciding factor. For example, a family with many children or someone who needs to haul a trailer may not be willing to trade off vehicle size or horsepower in favor of a more compact EV. On the other hand, a person who likes small cars may place greater weight on fuel efficiency; this person's alternative to an EV is more likely to be a hybrid, whereas the large family's alternative vehicle is more likely to be a minivan.

Understanding what the alternative choice would have been is key in measuring the environmental impact of an EV: the less fuel-efficient the alternative vehicle, the better the EV is for the environment. For example, if you switch from driving a gas-guzzler to an EV, that's more beneficial than someone switching from a hybrid. In fact, we find that if the household's alternative-choice vehicle is a hybrid, using an EV can actually increase its net water use—the reduction in gasoline use is very small due to the high efficiency of the hybrid, and the EV is charged with thirsty grid electricity.

That said, we find that EVs always reduce GHG emissions, on net, regardless of the alternative vehicle. Although the benefits do vary largely with the efficiency of the alternative vehicle, they would always increase the cleaner the grid becomes.

Our findings related to EVs suggest three distinct policy solutions:

  1. Ensure that vehicles such as SUVs and trucks have electric offerings, which manufacturers like Tesla and Volvo are already working on. This will help steer those who require larger sized vehicles towards choosing an electric option, thereby drastically reducing their environmental footprint.
  2. When people purchase a new EV, a well-designed rebate program that pays them to surrender their inefficient vehicle to be destroyed (such as an improved "Cash-for-Clunkers" program from 2009) could lead to even greater reductions in the environmental impacts of driving.
  3. Ensure more grid electricity comes from solar and wind, thereby further improving the water- and emission-intensity of EVs. Especially as EV adoption increases, having a clean grid will help us achieve a more environmentally-friendly transportation sector.

Solar panels and electric vehicles will help pave the way to a cleaner future, but we must dig into the details to ensure we maximize the environmental benefits. The more data we have and examine, the better that decision-makers can design energy programs and incentives to improve our environmental footprint.

Sponsored
by [D.Jiang] / Moment / Getty Images

By Alena Kharlamenko

Tofu is a staple in vegetarian and vegan diets.

Read More Show Less
KarinaKnyspel / iStock / Getty Images

2018 saw a number of studies pointing to the outsized climate impact of meat consumption. Beef has long been singled out as particularly unsustainable: Cows both release the greenhouse gas methane into the atmosphere because of their digestive processes and require a lot of land area to raise. But for those unwilling to give up the taste and texture of a steak or burger, could lab-grown meat be a climate-friendly alternative? In a first-of-its-kind study, researchers from the Oxford Martin School set out to answer that question.

Read More Show Less
Sponsored
Three scissor-tailed flycatcher fledglings in a mesquite tree in Texas. Texas Eagle / CC BY-NC 2.0

By Gary Paul Nabhan

President Trump has declared a national emergency to fund a wall along our nation's southern border. The border wall issue has bitterly divided people across the U.S., becoming a vivid symbol of political deadlock.

Read More Show Less
PeopleImages / E+ / Getty Images

By Daniel Ross

Hurricane Florence, which battered the U.S. East Coast last September, left a trail of ruin and destruction estimated to cost between $17 billion and $22 billion. Some of the damage was all too visible—smashed homes and livelihoods. But other damage was less so, like the long-term environmental impacts in North Carolina from hog waste that spilled out over large open-air lagoons saturated in the rains.

Hog waste can contain potentially dangerous pathogens, pharmaceuticals and chemicals. According to the state's Department of Environmental Quality, as of early October nearly 100 such lagoons were damaged, breached or were very close to being so, the effluent from which can seep into waterways and drinking water supplies.

Read More Show Less
This picture taken on May 21, 2018 shows discarded climbing equipment and rubbish scattered around Camp 4 of Mount Everest. Decades of commercial mountaineering have turned Mount Everest into the world's highest rubbish dump as an increasing number of big-spending climbers pay little attention to the ugly footprint they leave behind. DOMA SHERPA / AFP / Getty Images

China has closed its Everest base camp to tourists because of a buildup of trash on the world's tallest mountain.

Read More Show Less