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Big Power Consumer Becomes Power Producer

Electricity bills were having a shocking effect on KTWR’s budget.

KTWR is operated by TWR, a global Christian media ministry, also known as Trans World Radio, on the Pacific island of Guam. The station has one 100kW transmitter and two 250kW transmitters. All three units are connected to six antennas via an antenna switch matrix, enabling them to beam signals toward Australia and New Zealand, northeast Asia, southeast Asia and south Asia.

Electricity bills were having a shocking effect on KTWR�s budget. Guam�s reliance on bunker oil and diesel fuel for its power generation makes for some rather high power rates. The rates are greatly affected by changes in the price of oil. Expensive power was making it difficult for KTWR to keep its costs down. In fact, electricity was easily the largest line item in the station�s budget.

In early 2014, KTWR started looking at alternative energy sources as a way to save money. Solar and wind quickly appeared as possible candidates for installation on the station�s property. However, wind was dropped from consideration due to its unreliability. Guam allows businesses to have grid-tie systems as large as 100kW. Having a wind system limited to 100kW might generate an average of only 25kW, so that option was deemed unfeasible.

We wanted to use a phased approach to avoid sinking a lot of money into something that might not work. Phase 1 was planned to have a capacity somewhat less than the power KTWR consumes during nonbroadcast times. This was due to our being unsure about how the power company�s net reading metering would work. This was new territory for them, too.

It took us quite a while to get the first 23kW system designed. The hardware arrived in June 2014. We hoped the system would be installed and operational by the end of the following month. Unfortunately, rainy season arrived and delayed the project completion until September. This photo shows the rack hardware being attached to the posts. The most difficult part of the entire project was to get the posts aligned and set in concrete. With that milestone passed, installation of the arms and rails that hold the solar panels progressed quickly. The installers really enjoyed how easily installation of the Schletter rack system went.�

After the racks were ready, installation of the 120 250-watt panels only took a few days. Proper alignment of the racks makes all the difference in the world.

Once the panels were completed, the inverter and wiring were installed. One problem we encountered involved the panel output voltage being too high for normal 660-volt wire. We needed 1,000-volt wire, but only 2,000-volt wire could be obtained. This made for a tight squeeze in the conduit. Fortunately, the inverter was designed to handle up to 1,000 volts. If we had a �do-over,� we would have made the array smaller to keep the voltage low enough for normal wire or made it larger to take more advantage of the expensive wire. Speaking of high voltages, it is very important that a decent fence is installed around the solar array. Otherwise, someone could easily get themselves electrocuted.�

One may have done the math and realized that we have enough panels to generate 30kW, but we have a 23kW system. That is because the 100kW legal limit is based on the inverter output. Having more panel capacity than the inverter rating allows for more power to be generated in off-peak times for a given system limit. By the time that KTWR has installed all of its planned 100kW system, the total panel capacity could be in the 110-to-120kW range.

Since Phase 1 was put online at the end of September 2014, KTWR�s power bills have been reduced by ~6 percent. This cost savings may be reduced as we enter another rainy season. Thick clouds do reduce panel output. Nevertheless, the system has shown itself to be quite helpful in keeping KTWR on the air.

Hardware for Phase 2, another 20kW system, is being shipped to Guam now. We hope it can be installed and operational by the end of September 2015. Once that phase is running, KTWR�s net reading meter will start to �run backward� during the day when we are not broadcasting. The power company will essentially become our battery. The credits generated will get used when the transmitters are on the air at night. The money saved will be used for other facets of TWR�s ministry.