A Zero Energy Building (ZEB) Home and How It Pays For Itself

by Special Contributor November 15, 2024

Community, Cool Solutions, Energy, Inspiration

As we prepare for the Make a Plan Home Energy Workshops in 2025. Cool Davis invites community members to suggest their homes as tour sites and to participate in our workshops & tours to gain valuable insights into the electrification process. Take our Home Energy pre-survey here and sign up to participate in 2025.

In this piece, Bertrand Perroud shares his personal journey of upgrading his home to a Zero Energy Building (ZEB), providing insights into the steps, costs, and long-term benefits of transitioning to a more energy-efficient, sustainable home. His experience offers practical advice for homeowners looking to reduce their energy consumption, save on utility bills, and contribute to a greener future.

Zero Energy Building (ZEB) Home: What Is It and How Can It Pay for Itself?

How does one “Davisite” evaluate their yearly home energy balance?

How do you evaluate your home’s yearly energy balance? It’s easier than you think! For Davis residents, Pacific Gas and Electric (PGE) offers a handy tool that displays your energy usage over the last three years. By selecting “Energy Use,” “Year View,” and “Combined,” you can see both electricity (kWh) and gas (Therms) usage combined. Adding up the results from the past 12 months will show your total annual energy consumption. If your energy usage is negative, your home is generating more energy than it consumes – making it a Zero Energy Building (ZEB), as illustrated below for our home.

What Is a Zero Energy Building (ZEB)?

A Zero Energy Building (ZEB) is defined by the U.S. Department of Energy (DOE) as an energy-efficient home or building where, on a source energy basis, the annual delivered energy is less than or equal to the on-site renewable energy it exports. It’s important to note that a Nearly Zero Energy Building (nZEB), used in Europe, refers to a building that has both zero energy consumption and zero CO2 emissions.

In our case, our Davis home is not only a ZEB, but it also supports the charging of our electric vehicles (EVs). We’ve reduced our personal greenhouse gas (GHG) emissions significantly with our EVs, contributing to a more sustainable future.

How Did We Achieve Zero Energy at Home?

Our Davis home was built in the 1950s, with little insulation and single-pane windows — basically, a “thermal colander.” In the early 1990s, we remodeled our home to bring it up to code with added insulation and energy-efficient double-pane windows. We also installed a tankless gas water heater, and with a gas furnace and gas stove, our home became much more efficient, less polluting, and economical to operate. Back then, our monthly PGE bills were relatively low, in the two-digit range. At that time, climate change was still a concern for only a few scientists.

In the past 10 years, however, energy rates have steadily increased, and we began worrying about how energy costs might impact our retirement budget. This prompted us to install solar panels on our roof in order to gain more control over our energy bills. By then, climate change was a well-known issue, and we wanted to reduce our GHG emissions by relying on 100% renewable electricity.

We made further upgrades to our home, including replacing the gas furnace/AC and stove with an electric heat pump system and an induction stovetop. These appliances look like conventional models but consume significantly less energy, and they’re powered entirely by renewable energy from our solar system.

The only remaining gas use in our home is for our tankless water heater, which now uses just 47 therms annually, costing us about $62 per year before California’s gas climate credit. This modest gas consumption is easily offset by our excess solar generation, creating a net energy surplus as shown in the PGE graph above.

While a heat pump water heater or a solar water heater would be even greener, we chose to prioritize our EV purchase instead, as we believe this move offers a larger impact in reducing our GHG emissions. Replacing our gas tankless water heater with an electric system would require a costly upgrade to a 400-amp electrical service, which isn’t cost-effective for us at the moment. When our EV is paid off, we’ll reconsider this option.

How Much Did the Zero Energy Home Upgrade Cost?

The cost of transforming our home into a ZEB was substantial, but it will pay for itself over time. Here’s a breakdown of the costs:

Solar system: $25,000
Heat pump: $16,500
Induction stove and installation: $2,000

We opted for the PGE Time-of-Use (TOU) Rate Plan D, which has fewer peak hours (5–8 PM on weekdays), helping us save even more. We were advised that this was the most economical plan available. For reference, peak electricity rates can range from 40 to 60 cents per kWh, but with our solar system, we now save around $5,000 per year on energy costs compared to prior consumption.

Additionally, our EV has saved us about $2,000 annually in gas expenses. Overall, we’re saving about $7,000 per year. The investment will pay off in less than five years, excluding the EV purchase. After that, we’ll be enjoying free energy, saving for future equipment replacement (12–15 years down the line), all while reducing our GHG emissions and protecting ourselves from utility cost spikes as we approach retirement.

How Long Did It Take to Make the Transition?

While we began upgrading our home’s insulation, windows, and water heater over thirty years ago, the significant steps to achieving ZEB status took place over the last three years:

2021: Solar panel installation
2022: Heat pump HVAC system installation
2023: Induction stovetop installation

In just three years, we transformed our home to achieve the energy savings shown in the graph above, all while maintaining comfort. The new systems are more efficient and quieter than the aging equipment they replaced. Looking ahead, we plan to upgrade our home charging infrastructure in 2025 with a bidirectional charger (V2X), which will allow our EV to act as a battery backup during power outages. In 2026, we hope to purchase a solar-powered EV, but we’ll cover that in a future article.

Key Steps to Achieve ZEB at Home

Starting with insulation (walls, doors, and windows) is crucial for reducing thermal leaks. We understand that everyone’s situation is different, and what works for one home may not work for another. For example, electrical panel upgrades and service size are important considerations when transitioning to ZEB. In our case, we upgraded to a 200-amp electrical panel during our 1990s remodel — an upgrade that turned out to be essential for the ZEB transition.

Our experience demonstrates that it is technologically possible and cost-effective to upgrade an existing home to a Zero Energy Building. The key is to start by assessing your home now, so when an appliance breaks, you’ll know exactly what you need and avoid making hasty replacements.

We hope this article inspires others to assess their homes and consider making the transition to more sustainable living. To learn more about home energy transitions, check out this Make a Plan Workshop.

Sustainable Technology Is Here and Cost-Effective

With today’s advancements in sustainable technology, transitioning to a ZEB is not only possible but also cost-effective over the long term. It’s your turn to act and make a difference!

References:

“A Common Definition for Zero Energy Buildings,” U.S. Department of Energy, September 2015.
“Zero Energy Buildings: A Critical Look at the Definition,” P. Torcellini, S. Pless, M. Deru, National Renewable Energy Laboratory; D. Crawley, U.S. DOE.
Cool Davis Blog: Slow but Steady – The Transition to an All-Electric Home