off-grid power SYSTEMS


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Our stand-alone Solar Power Systems (SPS Series) are at the heart of our lighting, communications, and remote microgrid power solutions. By incorporating photovoltaics, generators, and other energy production technologies with batteries and state of the art controls, our SPS products enable customers to increase reliability while reducing operating costs and environmental impacts. Developed from more than three decades of industry experience and designed to operate in any location, regardless of climate, altitude or site accessibility, the SPS product line has been designed to be a reliable power supply for multiple applications in any environment. Furthermore every system can be further modified as required. The SPS Series incorporates the most recent advances in photovoltaic (PV) manufacturing, electronic controls, and power management, and can be configured to provide a broad range of DC or AC power outputs.


SPS Hybrid Overview


Northern Reliability’s SPS Hybrid line of power systems are high reliability, low maintenance systems that incorporate multiple sources of power generation deployed in a cycle-charge mode of operation. In most cases, the SPS Hybrid System incorporates two or more of the following power generation sources to produce energy:

  • Solar Energy from the Photovoltaic (PV) Array 

  • On-Demand Energy from a Fossil Fuel generator


A fossil fuel power generation device is normally one of the sources employed in our SPS Hybrid products. The generator provides on-demand power to supplement the more variable renewable sources such as solar or wind. Northern Reliability incorporates the most appropriate generator for the particular application, choosing from among:


  • Diesel Genset 

  • Propane or Natural Gas Genset 

  • Fuel Cell

SPS Hybrid systems are equipped with “on-demand” fossil fuel generator(s) to make up for any deficiencies in solar or wind resources. For most systems, Northern Reliability sizes the PV array so that during the best case solar months (typically July and August in the Northern Hemisphere) all solar energy produced will be consumed by the load. (The same is true if wind is used.) The system is designed so it will not waste any free energy during best-case conditions. As a result, during the poorer solar or wind months, the PV or wind will not generate sufficient energy to fully service the load. This is when the fossil fuel generator(s) come into play.


The System Controller continually monitors system conditions and will command the genset on or off as required. The key parameter to determine when the genset is run is the system’s battery bank State of Charge (SOC). Northern Reliability typically configures SPS Hybrid systems for genset start when the battery SOC reaches 40% (although the system can be programmed for genset start at any time).


Above is a graphic representation of a typical SPS Plus Hybrid (PV) cycle charge operation. In the summer, when most sites have very good solar resources, the energy produced by the PV array will be directly consumed by the load, or used to charge the battery. Every night, the battery bank discharges to support the load. The process repeats itself the next day. As indicated in the graph, even during summertime operation, a SPS Hybrid PV array can be insufficient to fully support the load. In these situations, the battery’s SOC reaches its prescribed set point, the System Controller will start the genset. Once on-line, the genset will charge the battery back up (while providing additional energy to the load). When the battery reaches a high SOC set point, the System Controller will shut down the genset and the cycle starts again.



Northern Reliability, Inc. 

81 Demeritt Place

Waterbury, VT 05676

T: (802) 496-2955

F: (802) 329-2096

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