Adding Solar Photovoltaic Capacity at Galena Alaska: Initial Assessment and Recommendations
This 2014 report explores the potential for adding additional solar photovoltaic (PV) arrays on Galena’s grid. It considers the current electricity generation infrastructure and makes suggestions for future infrastructure upgrades.
The City of Galena is located on the Yukon River in the Alaska Interior. Electricity is supplied to Galena mainly by diesel electric generators, and since the city is not accessible by road, all diesel fuel is shipped in on the Yukon River. Consequently, the cost of fuel is high and so are the environmental risks associated with shipping. In recent years, Galena and private entities have installed solar PV electric generators totaling approximately 30 kW of capacity distributed over several arrays. The Alaska Interior receives a fair amount of solar radiation between March and September, and Galena has expressed interest in adding additional solar PV capacity. However, due to the intermittent nature of solar resources, it is important to understand the limitations of the islanded diesel microgrid in accommodating additional solar PV capacity without compromising grid stability.
The Galena powerhouse was heavily damaged in a May 2013 flood and may be replaced in the future. This project, therefore, explored possible options for adding solar PV capacity under several scenarios, both with existing equipment and one in which the existing equipment would be replaced. As of this assessment, Galena is generating electricity using 450 kW and 800 kW diesel electric generator units. Based on monthly pre-flood data, the average load is 685 kW, ranging from 493 kW in June to 898 kW in January.
This project explored the maximum amount of solar PV generation that could be added to the system without risking under-loading conditions on the diesel generators. Under
loading diesel generators for prolonged periods of time can lead to incomplete combustion and low exhaust gas temperatures, damaging both the engine and the exhaust
system, respectively. A simple model based only on available generation assets was employed, assuming that the minimum optimal loading levels for the given generators is 30% and that the spinning reserve capacity required in the system is 75 kW at all times.
All PV arrays in Galena are currently “uncontrolled PV arrays,” meaning that the installations cannot be controlled by the powerhouse and cannot be automatically adjusted
to meet optimal criteria for grid stability and generator loading. This project found that to allow for minimum optimal loading levels to be guaranteed at all times, the total
amount of solar PV on the Galena grid may not exceed 135 kW, with 110 kW as a prudent maximum target for total capacity installed in the current situation.
However, if the output of distributed PV arrays were known to the powerhouse and if a dynamic and automatic diesel scheduling system existed, spinning reserve requirements could be varied in time, depending on PV output. The current system in Galena does not allow this approach, but if this level of dynamic control were implemented for PV and diesel, the maximum allowable solar PV capacity would potentially increase to 205 kW.
Should the City of Galena decide to pursue the integration of large amounts of PV power in the future, it is recommended that data collection efforts regarding electricity
and heat usage begin as soon as possible and that a grid assessment be performed with the goal of identifying needed improvements to accommodate distributed PV arrays. The powerhouse replacement should be designed with accommodation of significant solar PV generation in mind, and it is recommended that distributed residential solar PV installations be required to grid-tie with inverters that have communications and remote control capabilities. Adding further solar PV capacity will require significant engineering, and if a larger amount of PV capacity is intended to co-generate with diesel generators, a small energy storage system may be required to maintain power stability.
Photo 1: Flooding in Galena in May 2013. Photo Courtesy Alaska Dispatch News, www.alaskadispatch.com.
Photo 2: Galena, Alaska. Courtesy of www.akbeb.com.
Photo 3: PV System Installed at the Ambler W&S Treatment Facilities. Photo credit: Robert Bensin with Bearing Straits Native Corporation.