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Austin's Pecan Street Project. Pecan Street Inc.

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

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.

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Earth Day Tips From the EcoWatch Team

At EcoWatch, every day is Earth Day. We don't just report news about the environment—we aim to make the world a better place through our own actions. From conserving water to cutting waste, here are some tips and tricks from our team on living mindfully and sustainably.

Lorraine Chow, reporter

Favorite Product: Dr. Bronner's Castile soap

It's Earth-friendly, lasts for months and can be used as soap, shampoo, all-purpose cleaner and even mouthwash (but I wouldn't recommend that).

Essential Tool: Blender

It has paid for itself in homemade smoothies, soups, sauces and dips. It also means I don't have to buy those individual foods in unnecessary plastic containers. Blending scraps helps your compost, too!

Earth Day Tip: Skip the straw

If you feel weird about saying "no straw" at restaurants, just tell the waiter that you're allergic to plastic.

Olivia Rosane, reporter

Favorite Product: Seventh Generation products

Their household cleaning and personal care products are a great way to take care of yourself and your home in a way that is safe both for your health and the planet. Plus, their packaging is made from recycled materials and is designed to be recycled again.

Essential Tool: My portable thermos

I bring it with me when I order coffee or tea to go. That way I don't have to use paper cups, which are not actually recyclable, and some coffee shops even offer me a discount for bringing my own container!

Earth Day Tip: Get involved

In 2012, researcher Brad Werner ran a computer model and found our best shot at combating climate change was for people to form a mass social movement to demand it. So if you're worried about the environment, reach out to other people in your community and talk about what you can do together to make a difference!

Tara Bracco, managing editor

Favorite Product: Collapsible water bottle

Whether you're traveling or running errands, a reusable water bottle that's light and compact will help keep you hydrated and keep you from buying bottled water.

Essential Tool: Backpack

It's great for carrying your groceries home from the store, and you won't have to use plastic bags. If you have a long shopping list, try a rolling suitcase.

Earth Day Tip: Don't waste water

Turn off the water while you brush your teeth. It can save eight gallons of water a day!

Chris McDermott, news editor

Favorite Product: Clothes from Patagonia

Patagonia makes a wide range of inspired products and their environmental policies are world class. They use only organic cotton in their clothes, and they even offer trade-ins, recycling and repairs at any time.

Essential Tool: RIVER mobile power station and solar generator

This powerful piece of mind is always ready regardless of storms and travel, for as long as one can tap the sun.

Earth Day Tip: Savor something vegan

There's no nutritional substitute for fresh, unprocessed food, but food science has revolutionized the taste and texture of vegan alternatives. For the pure delight of it, celebrate with Miyoko's Kitchen vegan cheese, Tofurky Italian sausage (30 grams of protein per serving!) and SoDelicious non-dairy dark chocolate truffle frozen dessert made with cashew milk.

Irma Omerhodzic, associate editor

Favorite Product: Living Libations's Everybody Loves the Sunshine

Unlike sunscreen, this skin product works with the sun and helps absorb the nutrients from the sun's rays while giving skin protection at the same time.

"Rather than being afraid of the sun, harmonize with it," Living Libations says. Love it!

Essential Tool: My bike

Not only is this an emission-free way to get around town, but it also gives my body the activity it needs.

Earth Day Tip: Start small

Your one "small" action isn't small at all.

Jordan Simmons, social media coordinator

Favorite Product: Sustainable clothing by Amanda Sage Collection

Designer Lana Gurevich uses patterns from Amanda's transformative paintings to create an ethically and environmentally conscious clothing line. While supporting local businesses and an eco-friendly printing method, the fabrics are made from 100 percent recycled plastic bottles.

Essential Tool: My paintbrush and set of mineral paints

I found the all natural, biodegradable mineral paints at a local farmers' market in the Sacred Valley of Peru. I used to favor working with acrylic paints until I learned about their high carbon footprint and harmful substances.

Earth Day Tip: Honor Mother Earth

Gather some of Mother Nature's gifts such as stones, beautiful dried leaves and feathers. Set them in a special place in your home to create a unique "altar" to remind you to honor your Mother each and every day. Find peace and blessings in loving our home—the earth.

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