Rising electricity rates and plentiful sunshine made solar power an ideal solution for the Las Gallinas Valley Sanitary District’s wastewater treatment facility. However, the project faced a number of challenges. The only available site was a mile from the facility and had unstable ground issues. Moreover, it was considered as an environmentally sensitive area.
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Photo: Tim Holmes, Kenwood Energy |
| The installation produces over 1 million kWh per year. |
Overcoming the drawbacks required some creative engineering (provided by San Rafael, CA-based EI solutions) and persistence from the project’s backers. Was it worth it? Considering the fact that the district will get 20 years of free electricity, going solar looks to be well worth the effort.
Just north of San Francisco, CA, Las Gallinas Valley Sanitary District sits on the shores of San Pablo Bay, providing services to more than 32,000 residents of Marin County. On an average day, the district pumps roughly 3.56 million gallons of wastewater through its irrigation system and settling ponds. Marin County’s wastewater demand wasn’t getting any smaller in 2004 when district board member Megan Clark floated the idea of going solar.
According to Clark, the environmental benefits looked attractive, but the key to selling the district lay in demonstrating a persuasive financial gain. District members talked first to a variety of solar panel sales representatives and thought the numbers looked good. But, after a review with an independent energy management consultant, district members were surprised to find that putting together a PV solar generation involved much more than just buying the panels.
Energy Efficiency Audits Can Lower System Costs
Consultant Tim Holmes, president of Kenwood Energy, wasn’t surprised by the results of his analysis, or the reaction he received. “Typically what happens is that somebody is interested in solar electricity, but they don’t know much about it,” says Holmes. “It’s a hot item, so there are a lot of people out there selling it. Salespeople come by offering their version of the information, but they always want to sell something.”
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Photo: Tim Holmes, Kenwood Energy |
| Drought’s silver lining: more sunshine and higher electricity production |
The proposals from those salespeople were designed to offset 100% of the facility’s energy use, but that approach would have ignored opportunities to boost efficiency and reduce the cost of the initial investment. The first step for Holmes was an energy usage audit—a process that typically takes about 30 to 60 days and is required, to qualify for renewable energy rebates from the state of California.
“We looked at energy efficiency opportunities and reduced the energy requirements by about 40%,” recalls Holmes. “We specified the installation of variable frequency pump drives and switched the time of day that they did their pumping, so they could take advantage of lower utility rates.”
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Photo: Tim Holmes, Kenwood Energy |
| By installing variable frequency pump drives, Las Gallinas can take advantage of lower utility rates. |
On the first phase of the project, the original proposals specified a 140-kW system. Holmes’ analysis brought it down to 92 kW—a reduction of around 38%. “The district was surprised by the amount of energy they were wasting,” says Holmes. “Solar is very glamorous, whereas energy efficiency is viewed as almost at a level of operations and maintenance. I do a lot of energy audits, and, in this case, we cut their use in half for a net savings of $175,000.”
Net Metering Rules Can Favor the Utilities
After construction of the second phase, the total output would rise to 588 kW, and offset 90% of the district’s historical energy use. Holmes considers 90% to be an aggressive ratio, because such systems typically peak a 70% to 80%, when designed for wastewater treatment plants. But in this case, a number of factors influenced the decision, starting with future expansion plans and ending with California’s net metering rules. Holmes knew that the district planned to add more treatment capacity to the facility, so the ratio would eventually fall closer to the 70% to 80% range.
Additionally, it was in the district’s best interests not to generate more energy than it consumed, because the excess would become free energy for the utility. “You don’t want to create that scenario, because it’s a lost investment where you create value for the utility at your expense,” says Holmes.
Rain or Shine, the Power Meter Swings 30%
The area’s weather was also a consideration in designing the system. Energy use at wastewater treatment plants typically peaks with rainfall. Dry weather and drought have the opposite effect, and usage at Las Gallinas has dropped as much as 30% during dry seasons. Not surprisingly, with below-average rainfall for 2006–07, the pumps at Las Gallinas have consumed about 30% less power.
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Photo: Tim Holmes, Kenwood Energy |
| The area’s weather can have a direct impact on onsite solar power generation. |
Less rainfall also means more sunshine, another factor that pushed the electricity production from the panels to exceed 100% of the plant’s usage. “The situation created more energy than needed, but, of course, next year everything could change,” says Holmes. “In hindsight, we would not have done anything different, because we could have had a wet year and been under our estimates. However, if the facility did not have to expand we would have created a smaller system.”
Ultimately, historical usage has to be included in the analysis. If the project is an office that has been occupied consistently over the years and it’s known that the energy use is more predictable than the weather, the design could reasonably target up to 90%.
Building a system capable of 588 kW required 2,940 Sharp ND-200UI PV panels and, of course, an area to locate these. The only choice was beside San Pablo Bay on man-made bay fill. The location came with significant challenges because of its distance from the pumping facility, plus muddy, unstable ground composition and environmental impact considerations. At this point, EI Solutions was responsible for the unique design and construction of large-scale solar systems. Linscott Engineering Contractors, also based in San Rafael, handled construction of the panel array and the special foundation to support it.
High Stepping the Transmission Line Route
The long distance between the array and the actual plant required a unique solution for the power transmission. The system uses a step up transformer that raises the voltage from 482 V to 12,000 V from the source. The power travels at the higher voltage until it reaches the pump site, where another transformer returns it to 482 V.
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Photo: Tim Holmes, Kenwood Energy |
| The stability of the system was tested during the winter storm season. |
“The benefit is that higher voltages can be transported with fewer losses,” explains Holmes. “It’s an efficiency solution, and there are some losses associated with stepping up and down, but, when comparing them to the loss in transmitting the power over a mile, we found it had the highest efficiency. And that included factoring in the cost of the transformer equipment.”
The shoreline of San Pablo Bay is composed of what is called bay mud, which has a history of residual runoff from the days when gold was mined from the area’s mountains, causing it to still be settling and, therefore, unstable. EI Solutions had a civil engineer study the area, and, instead of using conventional concrete piers planted vertically down to bedrock, the system sits on a concrete foundation that supports the array with a horizontal structure. Essentially, it floats on the ground while supporting the array. If there’s uneven settling, the array remains stable.
That stability of the concept had its first test during the winter months of construction when storms dumped enough rain to put the construction site under a foot of water. Then wind gusts hit 100 miles per hour and blew apart some of the unmounted units, but those that were mounted survived without damage.
The array’s layout accommodates some open space, as dictated by an environmental impact report requiring the retention of a wetlands area for wildlife. The district took environmental concerns a step further by burying the new transmission lines from the array to the pumping facility, and removing old towers and lines installed by Pacific Gas and Electric Co.
From the district’s point of view, the process was well worth the effort, according to Al Petrie, the former district manager that teamed with Clark, to guide the project from inception to completion. Petri notes that beyond the construction complications, much of his concern was focused on the role of EI Solutions.
“Seventy percent of the total cost of the project is in the panels,” says Petrie.
“The district went through a selection process with six or seven companies bidding and making presentations. The board wanted to be sure that we had a very good panel, since it was the dominant part of the project.”
Petrie defines quality as a good service life with strict performance criteria. The district’s contract specified that the panels could not degrade more than one fourth of 1% per year, in terms of generation efficiency.
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Photo: Tim Holmes, Kenwood Energy |
| As of November, the system produces 100% of the facility’s power. |
Further specifications included having all panels tested in advance, and EI Solutions had to put up a $250,000 bond to guarantee performance. Over the course of the first five years, EI Solutions has to demonstrate that the efficiency of the system has not degraded greater than one fourth of 1%. If it does, the company has to pay the district for the lost performance and erect additional panels to bring the performance back up to the contract’s levels.
From an annual perspective, that performance is meeting and exceeding the contract’s levels. The installation produces over 1 million kWh annually, with cash savings of more than $156,000 in its first year of operation. In fact, Mark Williams, the water district’s current manager, reports that the system was producing 100% of the facility’s power in November 2008. According to Clark, that’s cause for celebration.
Does 100% Power Mean Profit or Loss?
“Some people perceive that we’re losing money, because the system is currently supplying 100% of our power,” says Clark. “But that isn’t totally true, because our energy needs are going to surpass what we’re using now when we make a tertiary water treatment addition. So, our energy needs will increase, and the many improvements to the system with variable speed pumps accounts for the fact that we’re making so much money now.”
Moreover, there are different ways to view the financial impact. Such as from a cash flow perspective. “You always see the term payback, but that’s totally different from a positive cash flow,” notes Clark. “Yet many people don’t understand that you don’t have to wait for 10 years to see the cash benefits. Depending on the loan, you can get a positive cash flow immediately. In our case, because we had a ‘double A’ credit rating, we received a very good interest rate.
“Of course, the bureaucracy involved in getting a solar loan and rebate can be daunting, but, if the city can’t figure it out, there are entrepreneurs out there that will buy the system and lease it back to the city,” she adds. “So if a private enterprise is willing to do that, doesn’t it tell you something about the economics?”
Holmes agrees and points to performance data that shows the system is on target in terms of energy output. “The output plus costs and rebates were slightly different than what we anticipated, but our internal rate of return was almost identical to our original estimates and calculation,” he says. “The goal was about a 10% internal rate of return.” He adds that the numbers were at 9.5, which was very close to the original financial objectives.
With the dry weather, Clark says the district expects to hit its break-even point early. Original estimates were for 11 to 12 years, but if rainfall remains below average, the payback will come earlier. Then comes 20 years of free electricity, plus an environmental showcase for the residents of Marin County.