San Francisco's 399 Fremont St, owned by UDR and MetLife, now features the world’s tallest solar water heating project.

The rooftop installation completed by California Solar Integrators (Cal Solar) will make the 42-story luxury apartment building more energy efficient by reducing the gas needed to heat the building’s water.

Cal Solar VP Sean Neman says the system will reduce gas heating of the building's water supply by more than 30%. In total, heating the water with energy drawn from solar panels will save 12,000 therms/year when compared to older methods.

Cal Solar worked with Swinerton Builders to ensure the installation on the roof of the 400-foot building was on schedule and without incident.

The cost was originally estimated to run upwards of $500k. Cal Solar obtained a $250k cash rebate from the California Solar Initiative Thermal Program. The incentive is paid for by customers of PG&E, SCE, SoCalGas and SDG&E and administered by the California Public Utilities Commission.

San Francisco recently enacted a law that stipulates projects with 10 stories or fewer use 15% of their rooftop space for solar installations. While 399 Fremont was not affected by the measure, UDR and MetLife chose to proceed with the plan to lower operating costs and act as environmentally conscious corporate citizens, a statement said.