Energy for All

District Energy System

Sharing a Sustainable Future

In Tucson and other western cities, there's plenty of energy to keep buildings comfortable. But most of it goes unused. Photovoltaic solar panels are a step in the right direction, but since today's grid doesn't have much storage capacity, we still burn fossil fuels to provide energy at night and on days when there is a lot of demand for energy.

SunBlock changes that by generating carbon-neutral thermal energy and storing it near where it will be used. Our goal is to condition buildings and provide hot water for buildings in SunBlock communities using carbon-neutral energy. SunBlock can do this at a lower economic and environmental cost than using gas or electricity from the grid.

While SunBlock relies on technical solutions, equity is at the heart of the SunBlock concept. Sharing energy allows everyone in our community to reach a greater potential.

The problem: different types of buildings have different energy needs at different times.

Office Buildings

Lights, computers, and people mean that many commercial buildings typically needs some cooling at most times of year.


Schools need big mechanical systems to keep students and teachers comfortable, but those systems sit idle when school's out.

Homes and Apartments

Many homes in Tucson's climate can need heating and cooling on the same day. Utility bills can be difficult for some in our community to afford.

The SunBlock solution: generate carbon-neutral thermal energy and share it with the neighborhood.

The SunBlock system connects existing buildings, existing technologies, and new buildings to serve the community.

1. Make electricity

Standard photovoltaic, or PV, panels make carbon-neutral electricity—often more than can be used on-site. Typically, surplus electricity goes straight into the grid, where it can stress the existing infrastructure.

2. Make thermal energy

Air-to-water heat pumps, like this exceptionally efficient one made by Chiltrix, warm or chill water depending on the time of year and the needs of neighborhood buildings. In essence, this makes solar energy useful at any time of the day or night, while keeping surplus electricity from stressing the grid.

3. Store thermal energy

Thermal energy generated by air-to-water heat pumps or other building uses is stored in tanks like this one. The tanks can also be used to collect rainwater to be used for irrigation.

4. Share thermal energy

Pipes buried in Tucson's extensive network of utility easements move the energy from where it's generated to where it's needed.

5. Connect existing buildings

With modified or new equipment, existing buildings can join the SunBlock. These buildings can use or share thermal energy that would otherwise go to waste.

6. Connect new buildings

By using best practices and passive building principles to set energy targets, new or substantially retrofit buildings can generate more energy than they consume. The SunBlock system lets these buildings share surplus energy with the community.

Move discussion of grid benefits here (duck curve, peak shifting.)

SunBlock uses this approach to share energy at the neighborhood scale.

In 2020, students in The University of Arizona's Solar Decathlon Design Challenge studio teams explored the SunBlock concept in Tucson's Myers neighborhood. Dashed lines show the potential route for the district loop in existing utility easements. In 2019, students designed a loop system to serve Tucson's Garden District neighborhood located near Grant and Alvernon.

SunBlock puts public goods to good use.

SunBlock makes Tucson's network of utility easements key to a climate-positive city.

Many utility easements in Tucson are disconnected, neglected spaces without enough connection to feel safe. SunBlock turns these neighborhood liabilities into assets.

SunBlock uses buried pipes to share thermal energy. Other utilities can be placed underground to make more roof for people. While some easements, like this one, can add connectivity to make our auto-oriented city more bikeable and walkable, others can be designed to create habitat for pollinators and other urban wildlife.

SunBlock allows existing PV arrays at neighborhood schools to share energy with the community.

Many existing schools in Tucson have large PV arrays that generate electricity. Feeding this electricity back into the grid can cause grid stress on days when there's not enough demand.

By using electricity to generate thermal energy, which can safely and easily be stored in water, the SunBlock system lets locally-generated energy benefit the entire community.

SunBlock is a systemic approach to address difficult-to-solve problems.


While Tucson may have ample solar energy, many in our community struggle to pay utility bills. In a climate like ours, where summer temperatures regularly exceed 100° F, cooling is not a luxury—it is a necessity to sustain life. In a SunBlock community, everyone has access to an affordable, carbon-neutral source of energy for home conditioning. And the SunBlock subscription model means monthly utility costs include routine maintenance and unexpected repairs, significantly reducing the financial burden imposed by unexpected expenses.

Before: $200

(Citywide Average)

After: $100

(Projected Cost)
Thousands of gallons of rainwater—even in the desert.

Water Scarcity

Did you know that a 2,000 square foot roof can capture 14,000 gallons of water per year? Since the thermal storage requirements for a SunBlock house can be satisfied with only one or two thousand gallons of water, the surplus water can be used for irrigation. Using rainwater for irrigation helps to reduce Tucson's reliance on energy-intensive water moved across the state by the Central Arizona Project.

Refrigerant Use

Air conditioning units may look inert, but a menace lurks inside. Refrigerant, even R410a, which is marketed as a green alternative to Freon, has an immense global warming potential. Residential air conditioners can use 10 to 20 pounds of refrigerant, or even more, and commercial refrigerators, such as those in grocery stores, can use hundreds of pounds. Unfortunately, even well-maintained systems leak, and a small amount of leakage has a big impact on climate change.

SunBlock reduces the amount of refrigerant needed to provide comfort by using water instead of refrigerant to move thermal energy. Two SunBlock projects, SunBlock Elementary and Barrio 2.0 investigated the use of night sky cooling and radiative cooling, a way to keep buildings comfortable without any refrigerant at all!

Refrigerant's significant global warming potential means we should use as little of it as possible.
Energy production and consumption are not aligned in time.

Grid Stress

Unfortunately, we have the most solar energy when it is least needed. Peak production is mid day, when energy usage is lowest. Our current grid isn't able to store this energy for later use. When people come home from work in the afternoon energy use ramps up quickly. This makes it difficult for utilities to provide a steady supply of power. This phenomenon, illustrated in the graph to the left, is called the "duck curve."

SunBlock takes advantage of the mid day drop in usage, converting solar energy to thermal energy during this time of surplus. SunBlock lowers the peak of energy usage by providing thermal energy to condition homes. This helps flatten the duck curve, reducing grid stress.

Community Resilience

The whole of SunBlock is more than the sum of its parts. SunBlock provides comfortable homes, reduces utility costs, increases rainwater storage, reduces the urban heat island effect, reduces stress on the utility grid, and puts spaces and assets owned by the public to work for the community.

SunBlock is ready for the next step.