LOAD-SHARING HYBRID SYSTEMS 33


In the solar hybrid example below, the factory runs one small genset overnight at 62% of its capacity, providing 100% of the load for security lighting etc., while the second larger genset is at rest.


generator(s) set in Frequency


Control mode to automatically provide the remainder of the power. Output from the renewable


energy source will inevitably fluctuate up to the pre-set limit through changing weather conditions caused by climatic or seasonal changes etc., and so the load on the generator(s) would also fluctuate, automatically taking a smaller share of the load in favourable weather conditions. However, be aware - the


system will become unstable if the load on the generator falls below a specific kW loading, leading to the generator shutting down. This can be as much as 30% of the genset capacity. All generators have different


minimum load requirements affecting reliability, running efficiency, emissions etc. Manufacturers’ specifications must be checked to determine this requirement.


Energising the bus If the bus is not energised by


a source other than the inverter, the inverter cannot produce any power, so the generator is used to keep the bus live.


www.gmp.uk.com


An effective way to deal with


this issue is to use a multi-set load sharing system with generators of different sizes so that when changes to the load occur or power from the inverter changes, individual generators within the system are automatically started and brought on line or powered down. Looking for an alternative


way to energise the bus can lead to massive investment into such as large batteries, which on top of the cost has a poor carbon footprint and life span. So the choice of system components must be carefully considered and balanced against the needs of reliability and efficiency.


Consider the example at the


top of the page: a 24-hour period in a solar hybrid installation The factory’s main hours of


operation are between the hours of 7am and 7pm with minimum power needed overnight for maintenance and security equipment. During daylight hours solar provides up to 70% of their energy requirements. In the solar hybrid example cited, the factory runs one small genset


overnight at 62% of its capacity, providing 100% of the load for security lighting etc., while the second larger genset is at rest. In the morning the DSEM870 starts up the second genset and they run in parallel ready for the factory start-up. When solar power becomes


available, the dependency on the gensets is reduced accordingly, but never falls below 30% of their capacities ensuring maximum use of the Renewable source while maintaining stability of the system. The gensets continue in Load Demand Scheme mode, a built in feature of the DSE control module. The smaller set is shut down once the factory is at full load and the inverter output is sufficient, but can be easily brought on line if or when required. The DSEGenset controller


best suited to load sharing applications as described above is the DSE8610MKII.


Reverse power If all of the above steps


are taken to ensure the system is running as described, the following situation should never occur, but is something to be aware of.


It is essential to ensure the


load does not fall below the output level of the inverter to avoid the genset(s) being driven into reverse power, leading to a trip and subsequent black out. In this scenario if the load were to drop, the DSEM870 is capable of reducing the amount of solar power being produced to an appropriate level or issuing instructions to switch the load entirely to the genset if necessary. The sophistication of the


DSEM870 and the DSE genset control modules enable total automation of the hybrid system, explains the manufacturer. Sunny climates where solar


energy is reasonably predictable lends itself very well to this type of application and is fast becoming popular, but hydro, wind and other Renewables can also achieve good results. For more information please


refer to the DSE website: www.deepseaplc.com


8610 MKII


Worldwide Independent Power June 2018


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