SunCache Solar Water Heating System Demonstration

This page updated April 30, 2008

Davis Energy Group

SunCache Solar Water Heating System Demonstration

Technology and Innovation

SunCache is a solar water heating system designed to preheat water entering a conventional water heater in residential applications.  The heart of SunCache is a rotationally-molded polyethylene panel that contains 50 gallons of water.  The water serves as a thermal storage and heat transfer fluid, requiring a top-off only every 5 years.  Submerged in the panel is a serpentine copper heat exchanger that contains the pressurized domestic hot water.  An optional thermoformed acrylic glazing improves performance.  SunCache has an attractive appearance that is flush with the roof surface and looks similar to a skylight.  SunCache is made entirely in California.

SunCache is an integral collector/storage (ICS) type solar water heating (SHW) system.  SunCache is made mostly from plastics (although all potable water is contained in copper) with high-quality stainless steel mounting equipment.  SunCache is sold as a kit including all plumbing and installation hardware to lower installation cost and ensure that all code requirements are met.  SunCache is approved for installation with PEX tubing, reducing installation cost and drastically improving freeze-resistance over copper piping. Installation is simple, fast and reliable. Installers with basic plumbing and construction experience can be trained to install SunCache systems in one day.  A typical retrofit installation requires one installer-day, compared to 4 (or more) installer-days for conventional systems. 

SunCache costs less than half as much (installed) as the current lowest-priced, code-approved and industry-certified solar water heating system. By making SHW more affordable, SunCache can have a major impact on the nearly stagnant SHW market in California, which currently installs about 1000 systems per year, compared to 150,000 new homes built per year.  Prices of conventional systems are rising due to their high copper and aluminum content.  Prices for conventional residential solar water heating system are about $7000* in Sacramento.  SunCache will cost homeowners about $3000* in 2008, when formal market introduction is expected.  Within two years, prices are expected to drop to below $2000 for subdivision-scale installations in new construction.  ICS systems are viable throughout the U.S. Sunbelt region, including all of California except the Sierra Nevada foothills.  With its greater freeze resistance than typical ICS systems, SunCache can be installed across the U.S. South and Northwest, although performance will suffer in milder climates (outside of California). 

Emission Benefit

Emissions reductions for SunCache installations will vary based on the backup water heating source.  For this project, we will target residential installations with conventional storage-type natural gas water heaters.  Based on prior field testing of SunCache prototypes, we project CO2 emission reductions of about 0.45 metric tons per year for each installation.  We expect to install about 80 SunCache systems in this project, resulting in CO2 emission reductions of 45 metric tons per year.  (When used with electric storage water heaters the CO2 savings will be about 0.55 metric tons/year.)

 Storage gas water heaters are also significant sources of NOX emissions.  Based on NOX emissions of 30 nanograms/joule for gas storage water heaters, we project a reduction in NOX emissions of 253.2 grams per year for each SunCache installation.  For the proposed 80-unit project, NOX emissions will be reduced by 25.3 kilograms per year. 

Project Description

The primary technical goal of this project is to increase the number of installed SunCache systems from 50 to 130.  This demonstration project will roll-out about 80 systems of the final production-spec SunCache in Southern California (SCG/SDGE territory) in preparation of formal market introduction in 2008.  This will work out any remaining production and reliability issues and generate confidence necessary for the investment required for high-volume production.  All R&D efforts will be completed prior start of the ICAT project, meaning that ICAT funds will not be used for any R&D activities.  Funding from DEG and other project partners will be used toward prototype fabrication and installation, as well toward administration, reporting, and training solar thermal installers. 

Installations will occur on single-family housing, primarily in retrofit applications.  To ensure sufficient carbon-free energy generation, installations will be limited to households with three or more full-time occupants and an unshaded south or west facing roof.  Installation sites will be recruited using a combination of SCG/SDGE bill inserts, public service announcements, and established solar thermal installers.  Prototypes will be produced using an established supply chain, with all production outsourced to vendors already tooled-up to produce SunCache.  All installations will be performed by established and reputable solar thermal installers.  This project will familiarize these installers with the benefits of the SunCache system

Funding Source

Funding Amount




$ 60,064



Partners $100,000

ICAT Funded Projects