nZEB – Evergreen

From Installed Capacity to Available Flexibility: What 636 Days of V2G Operation Taught Us

Introduction System Evergreen AG has published EVERGREEN® Technical Note No. 2, From Installed Capacity to Available Flexibility: A Practical Comparison of Smart Charging, V2H, V2G and Dedicated Battery Energy Storage in Zero-Energy Buildings. The paper compares the main flexibility options available to a highly electrified residential building and tests its assumptions against 636 days of measured operation of an electric vehicle connected to a bidirectional (V2G) charger in one of our condominiums, as part of the Swiss-European GLOCALFLEX project.

The Question Behind the Paper

Electric vehicles carry large batteries, so it is tempting to treat every parked car as extra storage for the building. But a car battery is first of all a mobility asset. Whether it can help the building depends on whether the car is parked, how much charge it has when it comes home, how much the driver needs for the next trip, and whether the owner is fairly compensated. The paper therefore asks a more practical question:

Not “Can an EV battery provide flexibility?”
But “When does using an EV battery add value to a building that already has its own stationary battery?”

The Valleverde Pilot Site

The measurements come from the Valleverde pilot site, a condominium of 12 flats whose electricity demand also covers heating and cooling. The site includes:

A 27 kWp photovoltaic array.
A 44 kWh building battery.
A 10 kW bidirectional V2G charger.
A Nissan Leaf with a 62 kWh battery, monitored from 1 January 2025 to 28 September 2026.

Over the period the car travelled 34,738 km. Its presence, state of charge, charging energy and the energy it returned to the building were recorded continuously.

A Clear Hierarchy for Building Flexibility

The paper proposes an operating order for zero-energy buildings with stationary storage:

1. Use solar energy directly in the building.
2. Store the surplus in the building battery.
3. Charge electric vehicles smartly, choosing when they charge.
4. Use V2H/V2G discharge only as a supplementary, contracted resource.

In this view, the EV is first a flexible heavy user of the building’s energy system and only secondarily a battery for it.

Key Results

Charging flexibility is abundant

On 99.8% of the days the car was at home, it stayed plugged in longer than it needed to recover its driving energy.
The median margin was 19.1 hours, and on 450 days it exceeded 12 hours.
Presence was highest overnight: the car was at the building on roughly three nights in four.

In practice, charging almost never has to start the moment the car arrives. It can wait for solar surplus, cheaper hours or energy stored in the building battery, without discharging the car at all.

Discharge flexibility is limited

The car usually came home with 40–50% state of charge, leaving little energy above a reasonable mobility reserve.
Only 60 days in 2025 met the paper’s reference V2G eligibility rule (evening presence and at least 50% charge on arrival).
On those days, about 16.5 kWh was available on average, less than half of what fleet models typically assume.
The car returned 2.04 MWh to the building in 2025 and 4.02 MWh over the whole period, mostly between April and September.

The solar surplus is real, but its timing is the problem

From April to September 2025, the building battery was full while solar energy was still being exported on most days.
At the same time, 44% of the car’s charging energy still came from the grid, largely because the car is often away at midday and charges after sunset.

What It Means Economically

Using the paper’s reference prices and the measured utilisation:

V2G yields a gross operating return on its incremental investment of about 2% (about 4% under the more optimistic fleet assumption).
A dedicated building battery reaches 15–24% under the same price assumptions.
With the illustrative financing structure, V2G’s return on equity stays negative, while the dedicated battery remains positive in every scenario.

This is not a general verdict on V2G. It shows that, in this configuration and for this vehicle, routine discharge does not justify the extra infrastructure compared with smart charging and dedicated storage.

Next Step: The Figino Pilot

The results point to a different next experiment. Instead of discharging cars more often, the building battery can act as a buffer between daytime solar production and night-time EV charging:

Store the solar surplus in the building battery during the day.
Reserve what the flats need for the night, using a day-ahead solar and load forecast.
Charge the parked car overnight with the remaining energy, at a local tariff between the export price and the retail price.
Free the building battery for the next solar day.

System Evergreen AG proposes to test this forecast-constrained battery-to-EV charging strategy at the Figino pilot site, measuring how much export it avoids, what it saves the EV owner, and whether the building’s own supply is always protected. Read the Full Paper The complete Technical Note, with methods, figures and the full economic comparison, is available here: EVERGREEN® Technical Note No. 2 (PDF) Learn more about the project at www.glocalflex.eu

Giuseppe Macario

CEO & Senior Executive Project Director at System Evergreen AG

Miro Rava

Data Science, AI and Energy Engineer at System Evergreen AG

Enhancing Energy Flexibility: How Evergreen is Paving the Way to a Low-Carbon Future

Innovative Solutions and Strategic Collaborations for Sustainable and Resilient Energy Systems

As the world moves towards a low-carbon future, the need for energy flexibility in buildings becomes increasingly critical. At Evergreen, we are dedicated to advancing sustainable building technologies that not only meet current energy efficiency standards but also adapt to the dynamic needs of the energy market. Recently, we had the opportunity to address these issues in a panel at the Energy Flexibility Forum: Advancing Building and Community Management Solutions in Prague. This panel, organized as part of the GLocalFlex project, focused on demonstrating grid balancing mechanisms through cross-sectoral interconnected and integrated energy ecosystems enabling automatic flexibility trading. In this blog post, we will explore the ten key questions discussed during the panel, highlighting how Evergreen’s innovative projects, like the Figino Resort, are at the forefront of this transformative movement.

Q1. How can building energy flexibility contribute to a low-carbon future energy system? Building energy flexibility plays a crucial role in a low-carbon future by allowing buildings to adapt their energy demand in response to supply conditions. This adaptability enhances the integration of renewable energy sources by aligning energy consumption with periods of high renewable energy generation, thus reducing reliance on carbon-intensive power sources. At Evergreen®, our focus on advanced solar technology and hydrogen as an energy vector in projects like the Figino Resort demonstrates our commitment to such flexibility, ensuring our projects contribute to a sustainable and low-carbon energy ecosystem.

Q2. How can energy flexibility be quantified? Energy flexibility can be quantified through indicators such as the Demand Response Potential (DRP), which measures a building’s ability to adjust its electricity load in response to external signals. Other metrics include the Shiftability Index and the Load Shifting Potential, which assess the capacity to shift energy usage across different time periods. These quantitative assessments help in designing systems that optimize energy consumption patterns in line with renewable availability, a strategy Evergreen® employs to maximize the efficiency of our energy-efficient building solutions.

Q3. How can energy flexibility be harnessed? Energy flexibility can be harnessed through technologies such as smart grids, advanced metering infrastructure, and energy management systems that enable real-time monitoring and control of energy usage. By integrating these technologies into buildings, like in our Figino Resort project, Evergreen® enables automated adjustments to energy consumption based on grid demands and renewable supply, thereby optimizing energy use and reducing operational costs.

Q4. How do multicarrier energy systems contribute to energy flexibility? Multicarrier energy systems, which utilize multiple energy sources and carriers (e.g., electricity, heat, gas, hydrogen), enhance energy flexibility by providing various options for energy generation, storage, and consumption. These systems allow for better balancing between supply and demand, facilitating the integration of intermittent renewable energy sources. Evergreen® leverages multicarrier systems to ensure our projects are versatile and adaptable to different energy inputs and market conditions.

Q5. Can energy flexible buildings contribute to energy system resilience? Yes, energy flexible buildings can significantly enhance energy system resilience by reducing peak load pressures on the grid and providing backup options during outages or fluctuations. Buildings with the ability to modulate their energy demand and supply can act as micro energy hubs that support grid stability. Evergreen® designs buildings with these capabilities, ensuring they not only meet energy efficiency standards but also contribute to the broader resilience of the energy infrastructure.

Q6. Who are the stakeholders involved in energy flexibility? Stakeholders in energy flexibility include building owners, tenants, utility companies, energy service providers, local governments, and regulatory bodies. Each plays a role in implementing and benefiting from flexible energy solutions. Evergreen® actively collaborates with these stakeholders to tailor our engineering solutions, ensuring alignment with local regulations and community needs while maximizing energy efficiency.

Q7. What new approaches to the design of energy flexibility solutions can increase user engagement? Innovative design approaches such as gamified energy management systems, real-time energy consumption feedback, and personalized energy saving tips can significantly increase user engagement. By making energy usage data accessible and understandable, users are more likely to adjust their behavior to save energy. Evergreen® incorporates these user-centric designs into our projects, fostering a culture of proactive energy management.

Q8. How should energy performance standards and requirements be adapted to support building energy flexibility? Energy performance standards should evolve to not only mandate minimum energy efficiency levels but also reward flexibility capabilities that align energy usage with grid needs and renewable energy availability. Standards like these would encourage the adoption of advanced technologies and designs that Evergreen® specializes in, promoting broader implementation of flexible and sustainable building solutions.

Q9. What business models can successfully develop and utilize energy flexibility? Business models such as Energy-as-a-Service (EaaS), where customers pay for energy services rather than the energy itself, can drive the adoption of energy flexibility. This model encourages the use of energy-saving and flexible technologies without upfront costs to the user. Evergreen® supports such models by offering consultancy and engineering solutions that facilitate the transition to innovative and flexible energy usage practices.

Q10. How can policy evolution support the future deployment of energy flexibility? Policy evolution can support energy flexibility by incentivizing investments in smart energy technologies, revising building codes to require or reward flexible energy capabilities, and supporting pilot projects that demonstrate the benefits of energy flexibility. Such policies would align with Evergreen®’s strategic objectives, enabling us to contribute more effectively to the development of sustainable, flexible energy solutions in the markets we serve.

Conclusion

Building energy flexibility is a cornerstone of the transition to a sustainable and resilient energy system. By incorporating advanced technologies such as smart grids, multicarrier energy systems, and user-centric energy management designs, we can create buildings that not only minimize their carbon footprint but also actively contribute to grid stability and resilience. The insights shared during the Energy Flexibility Forum in Prague, organized under the GLocalFlex project, emphasized the importance of these innovations. At Evergreen®, we collaborate with a diverse range of stakeholders to develop tailored solutions that meet local regulations and community needs, promoting a proactive culture of energy management. As policies evolve to support energy flexibility and innovative business models like Energy-as-a-Service gain traction, the future deployment of flexible energy solutions will become increasingly viable. Through our commitment to cutting-edge engineering and sustainable practices, Evergreen® is proud to lead the way in creating the flexible, low-carbon buildings of tomorrow.

Giuseppe Macario

CEO & Senior Executive Project Director at System Evergreen AG