The definition of paralleling is: consisting of or having parts connected in parallel: a parallel circuit. In the case of generators, this translates to operation and connectivity of two or more generators to create a larger capacity.
There are three primary reasons for paralleling generators. Many clients want to know the benefits and potential drawbacks of paralleling.
- The load required is larger than any single engine can provide.
Today the largest single engine 1800RPM, 60Hz generator set rating is somewhere between 3200 and 4000 kilowatts. Conversely, by combining multiple generators in a paralleling system the KW capability is virtually endless. For example, if a facility requires 10,000KW of power, it will likely have to have multiple generators to accommodate the load. In this application, five 2000KW generators paralleled would be a typical design.
- Cost of the equipment and the cost per kilowatt.
In some instances, paralleling generators can increase the cost. These costs are tied to installation that is slightly higher for multiple generators versus a single engine configuration. Additionally, a multiple generator system might require more physical space than a single generator.
Conversely, in larger applications, the cost per KW is much higher when using a single engine as compared to paralleling. The reason is the engine represents 65% of the cost of a generator set. When we look at the economics of generator paralleling, the greatest benefits are those designed with diesel engines that are also used in heavy duty trucks. Likewise, when we look at the economics of generator paralleling for gaseous fueled applications, the greatest benefits are with systems designed with gas engines used in cars. This is because these engines are mass produced. Engines that are larger than these universal applications are very expensive since fewer are produced.
Diesel engine cost per KW increases significantly above 600KW because mass produced truck type engines used in generators typically produce less than 600KW. For example, a 1000KW generator will cost more than two 500KW generators in parallel. There is also a significant cost per KW increase for generators over 2000KW due to the increased engine cost. If a client requires 3200KW they would recognize savings by using two 1600KW or four 800KW generators.
Similarly, gaseous engine cost per KW increases above 150KW because automotive style engines used in generators typically produce less than 150KW. Above the 150KW range, heavy duty industrial diesel engines are modified for gaseous fuel applications. If a client requires a 300KW gaseous fueled generator, there will be substantial cost per KW savings by utilizing two 150KW generators.
- Systems requiring higher reliability or redundancy.
Imagine having an early morning airline departure, you jump in your vehicle to head to the airport and the battery is dead. If you have a second vehicle, no problem! Just switch vehicles and deal with the battery issue later. If you don’t have a second vehicle, then it would be time to panic. This same logic applies with multiple sets of parallel generators. Let’s again assume there is a 1200KW system that consists of three 400KW generators and the actual load is 240KW, but one of the generators has a dead battery. No problem! Two engines fire up and take the load. Now assume that there is a single engine 1200KW, and it has bad batteries and will not start. That is a total failure versus a partial failure on the parallel system.
In the same system with three 400KW generators (1200KW capacity) with a load of 1000KW, but only two engines start, 800KW is not enough to power the load. In this scenario, this is a big challenge, but if properly designed it is manageable by shedding some of the non-essential loads. Non-essential loads might be half of the lights, motors or temperature controls of the facility. This is typically planned during the design stage.
Critical systems such as data centers will typically be designed to accommodate the full load plus an additional generator for redundancy to assure reliability of operation. A back up power system that meets full load with an additional generator is represented as N+1. In the case of a system that meets full load plus two additional generators it is represented as N+2. So with the same scenario of a 1200KW with an N+1, this would take four 400KW generators for a total capacity of 1600KW, or for an N+2, it would take five 400KW generators for a total capacity of 2000KW.
Clifford Power is a proud distributor of Generac!
Generac’s MPS is an integrated approach to generator paralleling, and is cost competitive with large single gensets and traditional paralleling systems. Advantages are redundancy, flexibility and scalability in a modular type paralleling system.
Superior Reliability – Each genset backs up the others in the system, so critical loads get redundant protection. Built-in redundancy also allows individual units to be taken off-line for routine maintenance while retaining coverage for critical circuits.
Scalability – With MPS or the Gemini® Twin Pack, Generac customers can purchase the system they need today, and can add units quickly and easily as they are needed. There’s no need to replace the system if future power requirements exceed projections and no need to over-spend on a larger system that might never be fully utilized.
Flexibility – MPS gensets are small enough to fit into spaces that can’t accommodate large units, and they are light enough for rooftop applications. Since MPS modules don’t have to be physically located together, you can better utilize available space. In addition, the space required for switchgear and large external panel boards is eliminated.
Serviceability – By using consistently reliable, high volume engines, MPS units are easy to service by qualified engine technicians like those at Clifford Power Systems. Maintenance items and replacement parts are relatively inexpensive and readily available.