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Why Variable Speed? — Some History

Dunlite, formerly a private South Australian company, manufactured wind generators from 12 and 32 volt up to 2kW range storing energy in wet lead acid battery banks. Although appliance manfacturers did make some12/32 volt DC appliances, the range was limited. Once the small 240 volt AC diesel generators appeared on the scene however, more and more  appliances started to appear.

These were not without  problems — with light flicker on smaller sets, difficulty playing records on turntables due to the variable speed from the change in engine speeds (caused by variable loads and frequency fluctuation) — not to mention exhaust and noise pollution.

With the advent of electronics in the late 1980’s, the inverter has become the mainstay of rural and remote power generation. This, in combination with wind and solar photovoltaic arrays and improved battery storage systems, good quality AC power is now available in remote areas.

The amount of available power has generally been subject to the allocated budget, with a diesel generator still required for back up should insufficient sun or wind be available, or demand exceeds supply. (This is almost always the case with high power demands from appliances such as reverse cycle air conditioning and clother dryers.)

The cost of hybrid wind and solar systems is often expensive. It should be noted that significant levels of pollution are created in the manufacturing of batteries and solar panels. Capital costs may also not be recoverable with these systems, or recoverable only over significant periods of time.

In real terms, although effective, energy created by solar and wind generally comes at a high cost.

Since the mid 1980’s, much research has gone into developing systems that are more efficient and more cost effective. Combined heat and power (CHP) provides maximum efficiency when comparing input energy versus output. This holds especially true in cold climates where demand for thermal energy is high and/or there is a connection to the mains grid, where excess electrical energy can be exported and sold  back to the mains grid system.

The reason for this is due to the CHP system’s utilisation of a synchronous generator operating at a fixed speed. The generator is most efficient at approximately 80% of full load. This load however, is really only required for short periods. So most of the time, 20% of the generator capacity is required 80% of the time.In some instances, an additional smaller capacity generator could be installed to operate during low load periods.