Miscanthus, (or “Elephant Grass”) is a perennial grass originating from Asia. It is becoming popular as an energy crop as it can easily and quickly grow on poor quality land. It can be grown without fertilisers or very much intervention, making its cultivation relatively straightforward.

Miscanthus has a calorific value of 3.6–4kWh per kg and a weight of 70-90kg per M³. With a less dense make-up than grain, miscanthus will need slightly more space to store enough fuel to generate the same amount of heat.

To be used as fuel, Miscanthus has to be stored dry with sufficient ventilation and must not have a moisture content above 20%. It should also conform to the W20 fuel quality standard for air dried, chopped miscanthus or W30 for fuel which is suitable for storage and drying.

Miscanthus harvest

The fusion point of miscanthus ash is around 900°C, compared to 1,200°C for wood ash. There can be a tendency for miscanthus ash to bind together, or ‘clinker’, and build up in the firebox. The moving, self-cleaning step grate in the Guntamatic Powercorn and Powerchip biomass boilers is purpose designed to prevent clinker building up which would reduce heating efficiency.

It is therefore advisable to add approximately 0.3 – 0.5% by weight of slaked lime to the fuel before use in boilers up to 50kW and 0.5–0.8% for boilers with ratings over 50kW. This increases the calcium content of the fuel, thereby raising the ash fusion point and reducing the likelihood of clinker forming.

The table below shows a comparison between miscanthus and other types of heating fuel.

A table that lists volume, CO2 emissions and kilowatt hours per kilo of various different biomass fuels
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