Marin County, CA, has consistently led the way in pioneering environmentally pro-active actions. Located on the north side of the Golden Gate Bridge, the county is home to 250,000 people and 11 incorporated towns within its 520 square miles, with San Rafael and Novato the largest towns in the county. On Earth Day 2002, the Marin County Board of Supervisors adopted a resolution, committing the county to install 600 solar energy systems by 2010.

“Our solar activities began late in October 2001 as a response to the energy crisis,” says Gwen Johnson, solar projects coordinator for the county. “The Board of Supervisors set some money aside for the community development agency to create an energy program. Simultaneously, they brought me on to study the feasibility of putting solar on one of their facilities with the Public Works Department. Also, we’ve been operating under a grant from the US Department of Energy to do solar outreach and education, where we provide technical assistance to residents, businesses, and public agencies in Marin that are interested in looking at solar. We help them compare bids, do site surveys and economic analysis. Another thing we’re doing is we’re mapping solar energy resources using geographic information systems, parcel data, and aerial photographs to find out just how many rooftops in Marin County could be developed with solar.”

The county began by conducting a feasibility study of 10 of its buildings to determine which one would be the most appropriate candidate for solar. “There were four buildings that were good and two that were excellent,” states Johnson. “We ended up choosing this one [the General Services Building] because of a couple of factors. It was located on the Frank Lloyd Wright Civic Center campus, so it had great visibility and high traffic. As outreach education, it was a really good site and was visible from Highway 101. It had just recently been reroofed so we knew that that would mean we wouldn’t have to take the system down after 10 years and do some reroofing. It also had enough open unobstructed roof space that you could put enough solar panels to meet about 100% of the building’s energy needs on an annual basis. In every way, it ended up being the best choice for the demonstration project.”

Once the building was selected, it was necessary to develop a request for proposal (RFP) that would allow the county to analyze and compare the various options. “It’s a fairly simple RFP,” states Johnson. The biggest challenge, she says, was trying to develop a format that would standardize the information so that it could be compared. “We were looking for an open, design-built solution,” she states. “We said, ‘Here’s the roof, here’s how much energy this building uses, come up with a solution.’ We knew we were going to get a lot of proposals that were all completely different so that makes the evaluation of the proposals fairly interesting. We had to come up with some metrics to measure the proposals or to compare the proposals together even though they were entirely different.”

The process of developing the proposal drew on other RFPs for guidance as well as discussions with the county’s capital projects group regarding expectations and desired outcomes. In the end, the scope of work included the following objectives:

• Maximize the power and energy output, without exceeding the facility’s requirements
• Ensure that roof penetrations don’t void roof warrantees or result in any leakage for the life of the roof
• Allow the county to obtain state and utility loans and rebates
• Create the greatest value as compared to the original investment
• Display real time energy and power output information in a public area of the Civic Center, overlooking the photovoltaic (PV) installation

On November 5, 2002, the Marin County Department of Public Works released a request for proposals for its first PV installation on the 15,000-square-foot General Services Building. Proposals were due Friday, December 6, 2002. “That process actually took a while from the development of the RFP to the selection of the contractor,” states Johnson. “There was so much of a learning curve in-house. We did an RFP, which is not something that the capital projects group ever does. What they always do is design one construction project and then they bid that project. Everyone comes in with a bid and they choose it based on low bid. We didn’t want to do that with the photovoltaic system. Most solar companies do design and installation. It’s a young industry but there weren’t really many places we could have designed it because the systems out there are so different.”

Because of the design-and-build nature of the RFP, one of the key stakeholders who had to become comfortable with the process was the County Counsel. “Our County Counsel thought, ‘What are you doing? We do low bid—we don’t know why you’re doing it differently,’ ” recalled Johnson. “We had to track down the California government code that allows you to full-source a renewable energy project or to do an RFP. We had to find that and get that OK’d with County Counsel, so there were all of these little pieces that we had to address along the way before we could actually award a contract.”

And the Winner Is…
The county’s process resulted in proposals from six submitters. As a result of the selection process, the county chose the proposal submitted jointly by RWE Schott Solar of Rocklin, CA, and Prevalent Power (now EI Solutions) of Novato.

RWE Schott Solar, while less than two years old in name, is the result of nearly two decades of mergers and alliances in the solar industry. “We’re the fifth largest manufacturer worldwide of solar energy equipment,” states Mark Bettis, project sales manager. “RWE Schott Solar is owned jointly by RWE, a large German corporation, and Schott Glass, a large German industrial glass maker. We’re a joint venture of those two companies and our main focus is manufacturing and distributing solar electric equipment worldwide.”

The other team member, Prevalent Power, was founded at the end of 2001. “We really were born out of the kind of revolution that is happening in California’s solar market,” says Arno Harris, CEO of Prevalent Power and now general manager of EI Solutions. “The founders of the company come out of the technology industry. The company’s main focus is on providing 100% solar energy to commercial, institutional, and government clients throughout the entire state of California. California really represents about 80% of the solar market. Our goal is focused on that medium- to large-size, grid-connected market. The stage the market is in right now requires sort of a broad set of skills that encompass everything from engineering and system design, financing through to project management and construction.”

One of the principal reasons that the RWE Schott Solar system was selected had to do with the concerns related to the flat roof on the GSA building. “One of the specific needs was to be able to install on the flat roof without penetrating the roof,” stated Bettis. “This building has a PVC membrane roof. If you put conventional solar racks up there, where you have to put a bunch of holes in the roof you lose the roof warranty. You open up a lot of potential for roof problems as time goes on, so the county was pretty clear about wanting a penetration-free system. That was one of the significant reasons that they chose our system. Another had to do with the performance. These solar modules can either be flat on the roof or they can be tilted. The tilted module provides better performance because it’s facing the sun more directly. By tilting the modules at five degrees, our system produces more energy output per kilowatt of capacity than a flat array.”

The ability to inspect and perform any maintenance on the roof was an additional factor in the selection. “Our system allows for easy access to the roof membrane for inspection, maintenance, and repair,” says Bettis. “Between every row of modules is a walkway space so access to the roof is not limited. The bottom line was that it was just the best economic proposal. We came in with the best dollar-per-watt of solar that met the technical requirements of not penetrating the roof and producing the amount of power that they wanted to produce.”

Part of the economic analysis and design of the system involved conducting a detailed analysis of the energy consumption pattern of the facility. “The place where we started was to first say how much their energy is costing them,” says Harris. “Looking at their energy usage in detail, they are basically on a seasonal rate plan where they are paying a higher rate in the summer and a lower rate in the winter. The average rate they were paying during the summer was $0.19 per kilowatt-hour and $0.12 per kilowatt-hour in the winter. Even though their actual usage stayed pretty steady throughout the year, the cost in the summer was almost 50% higher. Solar is going to generate the most amount of energy during the summer, so we are saving energy when it costs the most. If you are net metering you can typically take advantage of the fact that if you export during those higher cost periods you get credit at the higher cost but you can then pull down during the winter when the system isn’t generating all your power needs. There is an opportunity when you see a pattern like that to be able to actually zero the energy bills but only replace 90% of their actual energy usage.”

Physical limitations of the site also had to be considered as part of the design process. “The first is the site assessment which has to do with the applicability of the site to a solar installation,” states Bettis. “Some of the issues are the orientation of the building, which direction it is facing, whether there are significant obstructions that could shade the roof. Shade drastically reduces the output of the solar power systems, so if there’s a lot of trees to the south or big hills or other buildings, we look for that. What’s the weather at the site? Out here in the Bay Area, there are a lot of microclimates. The other thing we look at is the building itself and the roof. Some of the things that make a good location would be a roof that is largely unobstructed, that doesn’t have a lot of equipment on it. For instance, you go to many roofs that are covered with air conditioning equipment, conduits or rails scattered around the roof, or high parapets. This building happened to have basically an unobstructed, large, flat roof making it an excellent location.”

One of the trade-offs in the design of the system involved the angle of the solar arrays. The system was designed to have a five-degree tilt, which allowed a greater power generation than a flat-mounted system, but still doesn’t maximize the output for each array. “A five-degree tilt angle does not give the maximum output for each solar module that could be realized,” states Bettis. “You actually need to tilt it pretty close to latitude. In this area, it’s about 30 degrees and would give us more power per kilowatt of installed capacity we put on the roof. However, there are some disadvantages to tilting the modules up that high. One is that when you tilt them up that high, you create wind-load that requires the modules be bolted to the roof. Another that’s very significant is that as you tip modules up higher you can put less solar on the roof because as the modules tip up, they create a longer shade path behind them. Consequently the next row of modules needs to be set back significantly further. If we were to have tilted the modules at ‘optimum’ angle, we would have not produced enough power to zero out the building’s bill.”

Putting the System Together
The installation consists of 540 modules on a trademark system of stainless steel and aluminum jacks that support a series of rails on which the modules are installed. Every 12 modules are brought into a “combiner” box to form an individual circuit; this resulted in 45 individual circuits. Ultimately, these 45 circuits are combined into four circuits prior to connection to the inverters. “Those four circuits will feed into two DC disconnects, one for each inverter,” says Bettis. “The DC disconnect switches simply combine those last four circuits into one circuit per inverter and also allow the system to be disconnected at that point for servicing the inverter—so that you can shut off the DC power to the inverters in order to service the inverters.”

Two Xantrex inverters were used in this project, one 45-kW and one 30-kW inverter for a total AC capacity of 75 kW. “As part of the final contract negotiations we evaluated the potential for using a single 100-kW inverter,” stated Bettis. “This would have given the advantage of adding a little bit of capacity but there is a 30-kW inverter, a 45-kW inverter, and then it jumps to a 100-kW. This has two downsides. One, it was more expensive for additional installation, but secondly, there’s potential that the inverter isn’t going to be operating at its maximum efficiency window as often as if the inverters are sized right to the size of the array. So, rather than putting in over capacity, we chose to use the two smaller inverters.

From the inverters, the AC power feeds through the AC-disconnects, which allow the inverters to be isolated from the grid side. The power goes to a meter that is used in a monitoring system to measure the actual output of each inverter. From there, the two inverter circuits go to the main power panel and connect to the main bus of the building. A meter at the service entrance is designed to run both forward and backward. “The power comes in and services the load of the building primarily and, if it’s generating more than the building is using, the power is then fed backwards into the grid and runs the meter backwards,” says Bettis.

Because of the public educational aspect of the project, a monitoring system that is tied into the county’s Web site was included in the installation. “We did put in a state-of-the-art system-monitoring package that includes an Internet-based real-time display,” states Bettis. “From any Internet computer you can actually click and see what the system is doing at any given time. There’s a weather station so it tracks sunlight, wind speed, air temperature, and AC output of the system. Additionally, all that data is downloaded and stored so that the information is always available so that we can monitor how the system is performing. It also is a public relations benefit to Marin County that they can publicize their system and show off what the solar power system is doing.”

The county has been very satisfied with the performance of the system and the reaction of the community. “So far, it’s been entirely positive,” reports Johnson. “It’s within 5% of the projection based on historic weather data. In terms of the Board of Supervisors, they were the ones initially pushing this to happen. We couldn’t make it happen fast enough for them. In terms of public reaction, I would use the dedication ceremony in March 2004 as an example. We ended up getting our local Fox news station, had our local cable channel, and we had 70 people from the general public. We had elected officials and public works directors throughout Marin show up, so there was a lot of interest.”

LYNN MERRILL is director of public services for the City of San Bernardino, CA.

DE - May/June 2005