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Northwest Energy Storage

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10418 Hwy. 95 N. Sandpoint, ID 83864 Voice 208-263-6142 Fax 208-265-3677

Four Kffl© Ffe Station

Fourmile Fire Station

Rich Hunter our Mile Fire Station, a volunteer organization started in 1984 to provide fire and ambulance services for 69 square miles of Teller County and ambulance service for 235 square miles of Park County in central Colorado, has recently completed construction of their new building. Located over a mile from the nearest utility lines, the volunteers decided on solar to provide their electric power. The site houses emergency equipment and is used for meetings and training as well as serving as the command center when the volunteers are called to duty.

Tackling the Bureaucracy

With a clear picture of what was needed and almost limitless energy, Andy McKee, Four Mile Area Fire Chief and project engineer for the construction project, set about defining and financing the photovoltaic portion of the construction effort in early 1995. Helped by Marc Roper of the Colorado Office of Energy Conservation, Hal Post of Sandia National Laboratories and others, he developed a comprehensive design specification with clearly identified objectives for performance. Armed with this tool, Andy went the rounds of financial institutions and funding sources for several months, finally securing financing assistance from Sandia, Public Service of Colorado and local volunteers.

Contract Awarded to Local Firm

Discover Solar Engineering, located in Divide, Colorado was one of several firms selected to receive a request for quotation for the "I photovoltaic system installation.

Andy and his team reviewed the bids and awarded the contract to Discover Solar Engineering in ©1997 Rich Hunter September 1995. Very competitive pricing and near-by location were keys to the selection. The system design phase was greatly simplified due to the completeness of the specifications. With computer design assistance from Solar Electric Specialties of Santa Barbara, CA, Discover Solar was able to precisely calculate the best fit of panels, inverter and batteries to match the needs for the fire services' building. During evaluation of bids, it was decided to go with Pacific Chloride 2 volt deep cycle batteries for extended life. These batteries, along with the other major components, Siemens PC-4JF 75 watt panels, Trace 4024 4000 watt true sine wave inverter and the Ananda APT power center, were all selected with the intent of providing a highly reliable, long lasting system, designed for years of trouble free operation.

A complete written contract was prepared and agreed upon before beginning work. Materials, expected performance, system design, labor provided, and warranties, were spelled out in advance. Knowing who is going to do what and what the finished system will deliver before you start is the best way to assure satisfaction.

Above: The PV combiner box contains fuses for each 24 Volt pair, a circuit breaker, and an APT lightning arrestor.

Right: The eighteen Siemens modules were racked and bolted directly to the station's metal roof.

As part of the contract, agreement was made to cooperate on the installation labor. Volunteers helped on a variety of tasks such as mounting the arrays on the roof, building a battery enclosure, assisting in pulling cable and many other tasks. The installation cost was kept to a minimum by the outstanding effort of several volunteers.

Working with a crew of dedicated assistants, installation was started in October before the really cold weather and snows arrived. We met on a weekday morning and determined how we would proceed with the help and scheduling availability of the volunteers. First, Andy and his team built the battery enclosure and installed the wall support for the inverter and APT Power Center. Then, we all worked together for several days securing the roof mounts to the metal-roofed building. Since we were going to install solar heat collectors to aid in heating the building, in addition to the photovoltaic panels, space on the south facing roof was at a premium. The PV panels were firmly secured on the lower portion of the roof with Andy crawling under the rafters and atop the previously installed sprayed insulation inside the building while Sandy Knox, another dedicated volunteer, and I drilled holes and fed the mounting screws down to him from the outside. In all, the volunteers contributed about 140 hours of effort. The installation was completed by the first week in November.

PV System Components

The system was designed to be completely automatic and provide sufficient electric power to meet the

Above: The PV combiner box contains fuses for each 24 Volt pair, a circuit breaker, and an APT lightning arrestor.

expected part-time operation needs of the volunteer organization.

18 Siemens PC-4JF 75 watt panels were mounted, 3 panels per mount, on the south facing roof above the office area. These panels operate especially well in cold weather and typically output the rated 4.4 amps per module in a full sun condition. The current output is the key determinant in evaluating actual output power. The nine pairs of panels deliver a total of over 40 amps on clear sunny days. At 25 volts nominal, and an average 6 hour sun day, this results in 6000 watts hours of energy stored each day. This is considerably less than the 75 watts of rated power per panel times 6 hours per day, but is well above the amount needed to meet the system requirements.

Two panels were wired in series to create 24 volt sets. Pairs of 12 gauge wires from each set were individually run from the panels to an array combiner box located on the western wall of the equipment bay building. The array combiner consists of individual fuses for each panel pair, a main 60 amp DC rated circuit breaker, a negative lead bus bar and a lightning arrestor all mounted in a weatherproof plastic enclosure. The wire size was determined by calculating the acceptable 2% maximum loss allowable over the total distance from the farthest panel pair to the array combiner assembly.

The power was fed from the panels to a 60 amp charge controller installed in the APT control center which was located in the first bay of the equipment area. 6 gauge THHN wire was used for this run. The size again being determined by calculating for a maximum of 2% loss

Above: The power wall with Ananda Power Center, Trace 4 Kilowatt inverter, and step up transformer.

from the array combiner to the control panel. By paying careful attention to wire sizing and minimizing lengths of cable runs, we managed to conform to all building codes and keep system wiring losses to well under 5% for the total system.

The batteries, 12 Pacific Chloride 2 volt deep cycle batteries with a combined storage capacity of 1270 AH, were considerably more expensive than some other commonly used residential batteries (e.g. the L-16 6 volt 350 AH units), but should provide a much longer life time. They are very heavy, each cell of the 85CB-25 weighs about 150 LB, but the more lead, the more power and the longer the battery life.

The DC power was converted to 120 volt ac through a Trace 4024 true sine wave inverter. Requirements for the emergency services operation includes using a small computer for record keeping and battery charging to charge their portable phones. It was felt that the sine wave inverter would best handle these types of loads. In addition, it is planned to use this inverter to control a standby propane fired generator for additional power generation in the near future. This sine wave inverter is rapidly becoming a standard for residential PV systems. It offers plenty of power for most applications, and the programming features, internal metering and high charging capability are all features valuable to the user.

An APT control center houses safety fuses, charge controller, and system metering. A 60 amp charge controller was selected to allow room for expansion should more panels be added in the future. The charge controller circuitry has a normal setting for regular operation and an equalize setting to allow "overcharging" of the batteries from the PV panels on a periodic basis. The APT metering consists of a "smart light" meter to allow casual monitoring of battery condition and a Vista-3 digital read-out meter. By selecting the proper function, the Vista-3 displays battery voltage, input current and output "load" current.

A Trace T-220 transformer completes the system. This unit "steps-up" the 120vac from the sine wave inverter to 240 vac for running large loads.

System Size Calculations

The average estimated daily energy requirement for the building is 3.7kw and the peak power is 4.8kw. With rigid load management, the maximum load will stay below 4kw. Worst month output from the panels was calculated to be 4.2kw per day in January based on the siting and the geographical location.

The PV panel output was calculated using insolation data for Eagle Colorado, a latitude of 39.65 degrees north, a longitude of 106.92 degrees west, and a tilt angle of 65 degrees. Average output per month is shown below.

Average KilloWatt Hours Per Day from a 1350 Watt PV Array

Average KilloWatt Hours Per Day from a 1350 Watt PV Array

System Costs

The system was awarded to Discover Solar Engineering as a result of a competitive bid, with price being a key element in the selection process. As such, Discover Solar and its supplier, Solar Electric Specialties, pushed the limit to offer the lowest possible price. A lot of labor was "volunteered" by Discover Solar and a lot more labor was "volunteered" by members of the Emergency Services team. Total out of pocket cost to the Emergency Services Organization was $18,920.

Building Codes

No job is complete until it has been inspected. In Teller County, our county electrical Inspector travels to each and every installation, no matter how small or remote

System Component Cost




PV Panels, Supports, Combiner



Inverter and Controls









Installation material, wire, conduit



Total Cost


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