Santa Rosa must spend millions to achieve local and state mandated greenhouse gas emissions targets, but if managed properly the cost savings from lower energy use should create a net long-term savings for City Hall.

That's the conclusion of a report outlining ways Santa Rosa can "cost-effectively and efficiently" reduce greenhouse gas emissions from city operations.

"In a nutshell, energy efficiency pays for itself," said Tim Holmes, an energy consultant who worked on the city's Municipal Climate Action Plan.

The plan, released this month, is open for public comment until June 30.

It explains that city government operations, from lighting streets to running buses to treating wastewater, make up about 2 percent of the 1.3 million metric tons of carbon dioxide equivalents produced by the community annually.

City Council members pledged in 2005 to reduce emissions from city operations to 20 percent below 2000 levels by 2010, an aggressive goal did not meet. By 2010, a combination of green energy projects and staff reductions due to the recession had reduced municipal emissions to about 27,100 metric tons of carbon dioxide equivalents, or 5 percent below 2000 levels.

But the city must squeeze an additional 4,335 metric tons from its annual operations to meet the goal, and far more to meet state goals of an 80 percent reduction below 1990 levels by 2050.

So the city reviewed more than 100 possible emission reducing projects, analyzed them for cost-effectiveness, and arranged them in order of priority. The highest priority was given to projects in progress and expected to have a high return on investment.

These "no brainers" including upgrading to more efficient methane cogeneration system at the city's wastewater treatment plant and replacing streetlights with more efficient models, Holmes said.

Such projects would cost about $1.2 million, but would pay for themselves in two years, and over 20 years could save the city $12 million, according to the report.

Bigger ticket items, such as a $6.6 million one-megawatt floating solar array or $9.2 million for new hybrid buses, would take a longer to recoup the investment but are worth pursuing, the report found. Some, like the $14 million ultraviolet disinfection system at the sewage treatment plant were given the lowest priority because of their long payback time, in that case 22 years.

Many of the projects identified are at the city's wastewater treatment plant on Llano Road, a around-the-clock operation that accounts for 46 percent of the city's emissions.

Dell Tredinnick, project development manager for the city's utilities department, said the report shows that the investments can pay huge dividends.

"If we strategically use the money, we can lower our GHG and we can save money and stabilize our rates in the long-term by having cleaner energy and making energy efficiency improvements," said "That's a pretty good business model."

While much of the report analyzes the relative merits of capital improvements projects, it also stresses the importance of buying cleaner power.

Without getting into the politically polarizing issue of whether the cleaner power should come from PG&E or some other provider like the nascent Sonoma Clean Power agency being developed by the County of Sonoma, the report concludes buying cleaner power, defined as 50 percent renewable, is the only option available that keeps the city on track to meet the 2050 goals.

Tredinnick said the report intentionally sidestepped who would provide greener power because city staff didn't want the paper to read "like an advocacy paper for Sonoma Clean Power." But it's clear buying cleaner power goes a long way toward helping the city achieve its emission goals.

"If you can start at the source, it's the most efficient way to get from A to B," Tredinnick said.

You can reach Staff Writer Kevin McCallum at 521-5207 or kevin.mccallum@pressdemocrat.com. OnTwitter@citybeater