January-February 2006

Alpha Technologies Powers a Remote Repeater Station

A cost-saving option for many operations far from power sources

On a lonely stretch of highway in southeastern Arizona between Sierra Vista and Bisbee, a new cell repeater station is quietly breaking new ground in distributed energy, even if in a small way. Rick Holz, solar applications engineer for Alpha Technologies, believes the new system has possibilities for many unique and remote settings throughout the world.

This repeater station, like others, is an integral part of the cell phone network. If a cell tower is in a remote location and too distant from any power supply, such as grid power, that tower would almost by default have to be powered by either a generator or renewable energy.

The site was originally set up to receive power from the traditional power grid. Unknown at the time was when the grid would actually reach this desolate location. In the meantime, the company that operated the site had a need for a different type of power solution for its repeating station. Initially a standard 10-kW Onan propane generator served as the power source to run the station. “This unit sat there, chugging along, 24-7,” says Holz. “Basically this mode of operation simply runs that kind of generator into the ground, and even though the load is pretty small, they just chew up fuel. ‘Prime mover’ generators are generally not available in that small a size—less than 5 kilowatts.”

The cell tower operator, one of Alpha Technologies’ customers, was incurring yearly costs of more than $10,000 to power this 250-W continuous load at the site. After a year of running the setup with the continuously running generator, the cell tower operator decided to find a better system to meet its needs. “The technician that was servicing this site was going crazy,” says Holz. “Their technicians just don’t have the time to be traveling out to service these generators all the time, especially when they have many other sites they are maintaining.”

After being contacted by the cell tower operator, Alpha Technologies came up with a hybrid power system (HPS), consisting of a 900-W photovoltaic (PV) array, a 1,500-amp-hour battery bank, and a 6-kW generator. All of these components, and the control/switchgear cabinet, were mounted on a steel platform. The steel platform with all the major parts—generator, battery enclosures, wiring, and control enclosures—was delivered to the site on a flatbed trailer and set into place by a crane. The PV array had to be stowed away during transport, and the batteries arrived in a tightly packed steel cage. Setup consisted of craning the battery cage onto the platform, erecting the PV array on a pole in the middle of the platform, completing the PV and battery wiring, and piping propane to the generator. Setup took two trained persons approximately one full day.

“Since the entire unit is on its own skid, you don’t have to prep the ground very much,” says Holz. “It depends on the site, though. You don’t want a lot of weeds growing up through the system, and even in Arizona, the opportunistic weeds can be prolific and must be kept back to protect against fire hazard.”

The original generator was removed and this hybrid system was set up in its place. The new smaller Kohler generator (6-kW) that Alpha Technologies deployed was plumbed into the propane tank already onsite. Next the PV array was put into place, the batteries were loaded, and the system was ready to go. In a hybrid system such as this, because the batteries are charged from solar energy during the day to cover the nighttime demands, this system could go a week to two weeks in the sunnier times of the year before the batteries discharge enough to trigger the start of the generator. Generator starting is done automatically and is based on the battery state of charge and voltage. The batteries also provided the necessary ballast to keep the PV array—acting as a large sail in high winds—from toppling over.

The PV on this setup provides approximately 75% of the energy consumed by the repeater. In combination with the battery bank, this system reduced the generator runtime from 8,760 hours per year to less than 200 hours per year. This same system installed in another area, with a less abundant solar resource, might result in an increase in generator hours of 100 to 200 a year.

Since this type of generator needs servicing every 100 hours, this means the Arizona site’s generator will be getting an oil change about twice each year. “Before our system was put into place, maintenance on the generator was done every couple of weeks,” says Holz. “Eventually the generators had to be replaced. They were simply running it into the ground. It wasn’t that this was a question of a poor-quality generator, but that this was the wrong application for such a generator.”

The new generator that Alpha Technologies is running at this site is designed to be in place for many years. As long as it is oiled and the air filters are kept clean, it is very easily maintained. The entire system has been up and running successfully now for approximately three years. This HPS paid for itself in less than two years of operation.

Basically what these types of systems do is fill a niche where the grid is not readily available along the stretches of highway where there is not much cell phone call capacity. Solar power is reasonable for an application such as this, which involves lower power. In a city setting, where calls per minute may be in the thousands, the regular power grid would be more cost-effective.

“Alpha Technologies has been around since the mid-1970s making power supplies for large cable and telecommunications customers,” says Holz. “Through our network of salespeople in contact with such companies, we were alerted to the need and ready with a solar solution.”

The two types of systems that Alpha Technologies currently offers are the HPS, primarily a PV battery generator system, and the solar power system (SPS), which is a PV battery with no generator. SPSs are used for such things as traffic lights and security cameras, where there is an isolated load of some sort that runs off DC power (AC power can be provided, but DC is more efficient when solar power is concerned), and can be placed on a pole or side of a building. Both SPSs and the HPSs include the most recent PV-manufacturing advances. Their controls include battery regulation, load disconnect, complete input and output circuit protection, and temperature compensation. The PV modules have 20- to 25-year performance warranties, and the entire system includes a limited one-year warranty that may be increased to three years at the customer’s request.

Alpha Technologies’ SPSs are designed for a minimum of one week of load autonomy. These particular systems typically require no maintenance or routine operation costs. Mounting may be on poles, walls, or a pad. These state-of-the-art, fully integrated systems provide virtually zero loss of load.

An interesting offshoot of the SPS is Alpha’s remote camera system. These systems incorporate the latest security camera, wireless transmitter, and solar technology so that customers may place security cameras without ever giving a thought to running wires to the unit. These systems take advantage of tailoring the loads to the solar power source. “The smaller you make your load and consequently the PV module, the more feasible the whole system becomes to many users,” says Holz. “We are working with cell repeater, security camera, and various other manufacturers to encourage them to strip all the AC components away and get down to the DC parts. Then they’ll have made a much better product to match our product.”

HPSs best serve applications involving slightly larger electric loads or requiring higher reliability, and those in areas with highly variable solar resources. HPSs incorporate an auxiliary engine generator that typically meets 25% to 50% of the load energy. The PV solar array supplies the balance of the systems’ load energy.

“We are a solar solutions provider,” says Holz. “People come to us for answers for their applications. We figure things out through engineering, and then integrate and supply the hardware to offer them a complete turnkey solution. It does not always necessarily have to be a solar solution, although solar is definitely our core business currently.” The company does try to call itself more of an alternative energy provider to cover other energy sources, like fuel cells or wind turbines. Every project it handles is a DC bus–based system, working to keep the batteries charged and providing power to the loads.

As with other solar projects, one drawback is the cost. Generators are fairly inexpensive up front. But fuel and maintenance costs can be high. With solar power the costs are simply reversed. The cost up front is high, but maintenance costs are fairly low. “For a lot of people, that initial cost can be a problem if the system is not being financed,” says Holz. “But if the costs are bundled together, in many cases the hybrid system will beat the sole generator system on a life-cycle basis. Of course, if someone is going to use a system for only a couple years, they may be inclined to go with burning fuel for the few years of operation and saving money in the short term.” This was clearly not the case in Arizona.

The Arizona system cost about $20,000. But in approximately one-and-a-half to two years, this system has paid for itself. “Typically, when people start looking at five-year or more paybacks, that’s when they start wondering if solar systems are for them,” says Holz. “Overall though, they are easy to operate, fully automatic, less labor intensive, quieter, and cleaner. We feel that a hybrid system such as this—involving solar energy—is not something that is very ‘run of the mill’ right now, but that will be changing soon.”

Alpha Technologies also has another HPS for the same customer near Amarillo, TX. This system is located on another remote stretch of highway, about 20 miles northeast of this Texas panhandle city. Its system has dual generators. With its large energy requirements—1 kW continuously or approximately 24 kWh per day—and about the same budget as the Arizona project, the system would have to be much more dependent on its generator power.

By having two alternating generators coupled with a 1,050-W PV array and a 1,500-amp-hour battery bank, the company was able to reduce maintenance visits to a reasonable level—approximately one visit every month or so. The relatively small solar contribution still allowed for less overall trips to fill the fuel tank. The system with two generators is used when the PV array supplies less than 50% of the load energy requirement. Those generators require maintenance about every 100 hours of runtime. Battery electrolyte is checked during the same generator-maintenance visits. This HPS setup contains a sophisticated system controller that detects any faults in the generators. If a fault is detected in a generator, the controller will defer to an alternate generator. This controller is user-friendly and accessible with screens easily viewed on any laptop computer. The controller also includes the capability to notify someone in case the battery voltage gets too high or too low. The battery low-voltage alarm is typically a result of both generators failing to start—a very improbable occurrence.

The HPS24-1050/1500-2GEN used in the Amarillo site is very dependable, especially because of its alternating generator topology. This particular system is operated and sized such that each of the generators runs every other day for approximately six hours, accumulating roughly 90 run hours every month. The monthly consumption of combined liquid propane is about 160 gallons. With this HPS, the 1,050-W PV array adds about 17% of the total load energy needed. A 1,500-amp-hour bank of batteries gives one-and-a-half days of load autonomy, making this HPS totally automatic in its operation.

Alpha Technologies has also just delivered several hybrid systems to the military. The project involves radio communications, and uses the same basic concept as the Arizona and Texas projects. Each HPS powers a radio tower located in rugged, remote terrain. Radios work over a limited distance, and several towers had to be installed to fully cover the area of interest.

Alpha Technologies installed several systems near the radio towers. Since, the regular power grid wasn’t anywhere nearby, this was the only alternative for power. “In some locations—especially extremely remote places—solar is the only way to go,” says Holz. “Sure you can stick a generator out there, but sometimes that’s hardly plausible. During the winter at the military installation we worked on, the mud makes travel virtually impossible and you simply cannot get a fuel truck in to the site to keep a generator going. Everyone has been extremely positive in their feedback about these systems. Customers have been very satisfied with their performance overall.”

As various sites are studied by Alpha Technologies, accessibility is studied so that judgments may be made on the advisability of using one of its solar-only or solar-hybrid systems. As ease of access increases, the impetus for using such a solar setup decreases. If the regular power grid is readily available or if the project is short term, where servicing a generator from reliable roads is feasible, a solar array may not be the most cost-effective solution at that site.

Worldwide, there are many situations where Alpha Technologies’ solar or solar hybrid systems may find a use. These include secluded island, coastal, mountaintop, or desert locations. “There are plenty of places in the United States where this system would be applicable, but for the world at large it is often an even better fit,” says Holz. “The only thing that is stopping us is getting the word out, educating potential users, and actually finding those who may have such a need. Though there hasn’t been that much change in the area of generators or photovoltaic modules in recent years, with hybrid systems, there are many options still out there to be explored.

“The market is there for these systems,” says Holz. “Also, a great deal depends on economics and fuel costs, which all drive whether things are a viable option for a company or not. As fuel costs continue to rise, the life-cycle cost of this item continues to look better.”

Alpha Technologies is currently looking at all new technologies in order to stay ahead in the market, and to better meet the needs of its customers by providing more efficient loads. “The key to using solar power is to find those devices—such as repeaters, cameras, lights, or radios—that really run on DC power,” says Holz. “We live in an AC world. Many electronic devices today take AC power and convert it to DC, with a resulting conversion loss. Our solar systems are all DC. If we have to put an inverter in this system, you’re really double-dipping, or going through two unnecessary conversions. From a solar point of view, we want to see a DC world again.”

AC power is useful in transmitting large amounts of power long distances, and can transform it into different voltages, but it’s not necessarily beneficial on a system using something such as solar power. For solar applications where you are not transmitting large amounts of power long distances, AC is not really necessary. AC power can also create noise. “If you keep everything DC at a small project site, it’s better for everybody,” says Holz. “And because you’re not going through those double power losses, you can more adequately size the solar equipment or reduce the size of it—overall reducing the cost of the entire system. If the devices we are powering remain AC, then that’s a major impediment to putting more solar out there. A lot of electronic devices these days rely on AC power, simply because we live in an AC world.”

Holz says that in the years when Thomas Edison started out, there were actually DC power plants in the US as well as a DC power grid in New York and other parts of the country. Eventually, AC won out. With AC, by working with the magnetics in transformers, a very high voltage and low current could be reached, which greatly lowered the cost of transmission. “DC is the power of choice in my world; it’s something to strive for,” says Holz. “I work mainly with solar power. DC is also used in small-scale wind turbines, but not in many of the larger wind systems, which do use AC. In some ways it’s like living in a world where cars are all ‘gas guzzlers’—because gas is (or was) cheap. In the AC world, electricity is cheap so everyone uses AC-to-DC power supplies. We’ve got to get rid of those unnecessary conversions to make the best use of solar power.”