Remote - Winter 2013 - (Page 10)

Feature Article Approaches to Powering Telecom Sites Arthur D. Sams, President Polar Power, Inc. Reducing energy costs presents the largest opportunity in telecom for reducing operational costs. The same principles discussed here can be applied to remote monitoring, and SCADA / RTU sites. Running an AC generator 24/7 is the traditional but least efficient method of powering an off grid site. Maintenance and fuel costs are too high and the reliability is poor. 3 kW to 15 kW DC generators are now replacing 20 kVA to 40 kVA AC generators in off grid and backup applications. Larger AC generators are used because they have proven to last longer than smaller AC generators. Additional factors requiring over sizing the AC generator in relation to the load include: * AC generators less than 10 kVA are aimed at temporary construction and standby use. These applications require low cost and do not need long life. The 5 to 10 kVA AC generators typically last a year before requiring replacement in off grid and solar PV applications. * You cannot reliably operate an AC generator close to its rated capacity and maintain frequency, voltage regulation, and prevent the circuit breaker from tripping. * Air-conditioning starting current requirements * Providing the power capacity to recharge the batteries and power the load after a disruption in power Cycling for Both Off-Grid and On-Grid Applications with Poor Utility Service Field trials have shown fuel savings of more than 40 percent when using a cycling generator as opposed to a generator operating 24/7. Reliability is enhanced and maintenance is reduced using the cycling solution. A - AC Cycling: AC generators can be used with rectifiers / battery chargers and operated in a cycle charging fashion; this offers a fuel saving advantage over operating an AC generator 24/7. The disadvantages of the AC generator cycling are: * There is a power loss of 8 to 15 percent through the battery charger/rectifier; the generator is required to produce more power, consuming more fuel. * The AC generator is less efficient than the DC PM generator in converting the engine's power into electricity. The DC generator is about 20 percent more fuel efficient than the AC generator. * The AC generator has to be oversized because its power output cannot be regulated. An over current condition trips a circuit breaker, requiring a manual reset. Larger generators with larger engine displacements consume more fuel. * The AC generator is fixed speed; fuel consumption diminishes only slightly with decreasing loads as shown in the graph. * CAPEX costs are higher with the AC generator cycling in off grid systems. The system requires an AC generator, transfer switch, battery charger/rectifier and a system controller. * OPEX costs are higher with the AC cycling as the system consumes more fuel and requires maintenance. 10 www.RemoteMagazine.com B - DC Cycling: DC Cycling is 25 to 40 percent more fuel efficient than AC cycling. As shown in the graph below, the concept behind DC cycling is to allow the generator to operate at its peak efficiency and shut off during low load demand, letting the batteries power the load. This saves fuel and engine maintenance. Also shown in the graph is the DC generator's additional fuel reduction due to the variable speed feature of the DC generator. As the load decreases, so does the engine speed, allowing the engine to continuously operate at near its peak efficiency. The power output of a Polar DC generator is regulated so can operate closer to the ideal engine power curve (there are no circuit breakers to trip). This saves fuel because it makes use of smaller displacement engines. In the chart we show the DC generator operating at 80 percent of its rated power. Sizing Sizing an AC generator requires that its capacity be greater than the sum of all the loads that may operate at the same time. This would include the surges for air-conditioning startup. Typically the sizing of the DC generator into an application is based on the amount of energy required in a 24 hour period plus charging losses in the battery divided by the desired generator runtime within the same period. AC vs. DC Generator Field trials have shown the DC generator having a 70 percent and greater fuel reduction over the conventional AC generators operating 24/7. You can efficiently operate the DC generator at 100 percent of its power rating. In comparison, the AC generator is operating a larger engine at less than 50 percent of its rating. In the graph above, the red line representing the AC generator is consuming more fuel than the blue line for the DC generator. The AC generator running while the load is at a minimum power level represents a significant waste of fuel. Using the DC cycling approach, the DC generator is off and the load is powered by the battery. DC Hybrid Power Solution - Combining Renewable Energy and Fuel The Hybrid solution consists of a DC generator which charges the battery and powers the load at the same time. The DC generator is designed to shut down after the battery is charged and the load demand is low. The battery provides power to the load while the generator is shut down. This is an energy efficient alternative to an AC generator operating 24/7. The hybrid power solution allows the convenient integration of solar and wind for further fuel reduction and lower generator maintenance. Solar and wind can be added at any time and incrementally. For most telecom applications the use of 100 percent solar and wind http://www.RemoteMagazine.com

Table of Contents for the Digital Edition of Remote - Winter 2013

Editor’s Choice
Message Oriented Middleware - The Future of SCADA
Enhanced SCADA Access and Big Data Lead to New Analytics & Optimization Capabilities
Approaches to Powering Telecom Sites
Satellite Communications for Water Metering and Other Water Applications
Remote Magazine Launches Internet of Things North America
Geospatially Integrated Surveillance Systems
Tier 1 Operator Case Study: Intelligent Site Management
SCADA - The Brain of the Smart Grid
SCADA
Networking
Security
Onsite Power
Industry News

Remote - Winter 2013