Rising electricity costs make renewable energy an area of great potential for higher performance and lower costs.
The search for the most efficient use of water often includes finding improvements to infrastructure, and as this water district in northern California discovered, rising electricity costs make renewable energy an area of great potential for higher performance and lower costs.
Water usage and technology were much simpler when the South San Joaquin Irrigation District (SSJID) began serving agricultural interests in 1909, but, by 2005, the district found that much of the agricultural lands had given way to urban growth. The district now provides 40 million gallons per day to 155,000 residents and has expanded into providing domestic water service to the cities of Tracy, Lathrop, Manteca, and other parts of San Joaquin County. The growth required a state-of-the-art membrane filtration water treatment plant, and along with the plant came some staggering utility bills.
“After the water treatment plant came online in 2005, the electricity for that system was costing about $400,000 per year,” recalls Don Battles, utility systems director at SSJID. “It was a good idea to integrate a solar project on some property that was right next to the plant, so we could serve our own needs and sell excess into the Pacific Gas and Electric [PG&E] system.”
Selling the excess power had its advantages for the district to opt for a time-of-use rate schedule that looks anything but beneficial—during summer peak hours, rates are about 43 cents per kilowatt-hour.
“It’s a high rate, but actually works out better for the district, because it’s also the rate that PG&E pays us for any excess power we put back on the system,” says Battles. “In good weather during our peak hours, we are putting more into the system than we are taking.”
The off-peak rate averages closer to 10 cents per kilowatt-hour, and the district should break even on the $400,000 cost on an annual basis. Long-term payback on the capital expenditure is estimated at 15 years, and that includes the incentives of $6 million from the California Solar Initiative Program.
The high peak hour rates and power usage played a critical role in getting the project going, according to David Vincent, project developer at Conergy Projects Group. Based in Denver, CO, Conergy designs, manufactures, installs, and finances solar photovoltaic solutions for commercial and residential customers.
“Typically, the first thing to look at is the number of large power users, and their water treatment facility was pulling 3.5 to 4,000,000 kilowatt-hours per year, so they had a large demand for energy,” says Vincent.
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Photo: Conergy
Thin film modules on tilting axis mounts |
In fact, the demand was large enough to justify a 2-MW project, but California regulations wouldn’t allow it, and the district had to improvise.
“We actually started out with the idea of a two-megawatts project, but scaled it down to 1.6 megawatts and, ultimately, constructed two projects,” explains Battles. “The first project is 1,176 kilowatts of crystalline PV [photovoltaic] panels on single-axis trackers.
“We knew that wasn’t going to meet all of our needs, but, in California, you can only put up to one megawatt per rebate,” he adds. “So the second project required a different meter.”
It also required a high level of perseverance for all parties involved in the project.
To start, San Joaquin experienced a fairly rainy winter and muddy conditions slowed down the construction of the first phase. Then, a key team member left the project, and, as bad luck would have it, 15 PV panels were stolen right off of their mountings.
“Ultimately, we had to get very much more involved than we had anticipated, and none of us had been involved in solar before this,” recalls Battles. “So it was a learning experience, but we dug in and prevailed.”
For Vincent’s team, engineers had to properly split the load to each meter, so the project became a two-phase process with the first phase at 1,176 kW, and the second phase at 417 kW. The second phase required a whole new set of switchgear, and Conergy had to change the type of interconnection.
“We couldn’t do just a straight interconnection to their main meter box,” says Vincent. “And, we had to install quite a bit of different equipment just to get the interconnection approvals. That was both a physical challenge as far as the interconnection was concerned, and also a legal challenge, to make sure that everything was done right for the net metering rules that apply.”
Both phases are mounted on single axis tracking systems. Conergy estimates a 25–35% performance boost by having the panels follow the sun rather than remain stationary. Vincent notes that it was a challenge to minimize the number of drive motors for the tracking system, in order to reduce long-term maintenance demands. Each of the system’s 2-horsepower motors drives over 60,000 pounds of modules and steel to follow the trajectory of the sun. The solution uses a 30-ton screw jack and counter balance mechanism.
Although splitting the project into two phases more than tested everyone’s patience, it created the opportunity to do a second project with thin-film technology.
“They wanted to compare crystalline and thin-film side-by-side, both on trackers, to get a better understanding of the output and benefits of both,” says Battles. “We were sold on the idea of using thin-film, because we have some cloudy days during winter, and we were told that thin-film can take better advantage of the ultraviolet rays that make it through the atmosphere. We also have a lot of summertime days when temperatures exceed 100°F, and thin-film can utilize heat better than crystalline.”
One point was evident without much comparison. Although the thin-film modules had a lower price per watt than the crystalline units, the modules have a power capacity of 72.5 W per panel, so they required nearly double the number of modules, as compared to the higher capacity 175-W crystalline modules in Phase One. The result was more labor costs for installation that may have eliminated any savings over the crystalline option.
However, the district will be able to confirm performance differences, thanks to a monitoring system in the Direct Current (DC) to Alternating Current (AC) inverters. The power output data appears online at a monitoring and reporting company’s Web site: http://www.fatspaniel.com/log-in. Clicking on the “private site” option and typing in the username, “southsanadm,” will provide the visitor with access to information on performance.
As of June 2009, performance of the systems shows about 2% to 3% more energy from the crystalline panels. Vincent expects the thin film to catch up as the temperatures go up, and also on hazy or foggy days.
“We also have issues with dust,” he adds. “When you put a fine layer of dust over a PV panel, you’re decreasing the amount of light. This thin-film product can deal with what we call ‘soiling’ in the industry, much better than its crystalline counterpart.”
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Photo: Conergy
Robert O. Shultz solar farm phases 1 and 2. Darker panels are thin film modules. |
The comparison between the two technologies is an added bonus, and both Vincent and Battles say the project can stand on its own, based upon the success on its financial merits. Then too, there’s some valuable learning experience for other districts looking to try solar.
“I think you're going to encounter different things in different locations,” says Battles. “The regulatory climate is rather frustrating, because you're dealing with rules that don’t seem to make much sense, such as a limit of one megawatt maximum per meter. There’s no technical reason for that, and it’s really cumbersome to install additional infrastructure way beyond what you need.”
Vincent notes that it’s wise to be prepared throughout a project of this nature.
“One of the challenges in California in general is that we have many sites that could handle more than one megawatt of solar, but, because of net energy metering rules, a lot of those customers are limited as to what they can put in,” says Vincent. “Obviously, there are the typical construction issues, but the greatest impact here was the price of the additional equipment.”
From Battles’ point of view, keeping a positive attitude can overcome some of the more frustrating situations when it’s time to dig in and persevere. In fact, he’s already considering the district’s next project.
“For the future, California has some interesting new laws coming into effect regarding solar energy, and we have some more land out there, so we can add to our system,” he says. “We will probably work in the area of fees and tariffs, by taking the energy we produce and utilizing it to offset the cost of pumping water from other locations.”