A factor with wood chips which needs careful consideration is your storage capacity.

There are three important questions you will need to ask yourself before committing yourself to choosing this type of biofuel for your biomass heating system.

  • How much space do you have for a store?
  • How much energy will that store contain?
  • and how long will that store go between refills?

How much space do I need?

Wood chip fuel is fairly bulky, 250kg per cubic metre.  So for every tonne of wood chip you are going to need up to 4 cubic metres of storage space.

To help you visualise – A typical 20 foot container has an internal volume of 30 cubic metres, space for around 7.5 tonnes of wood chips.

How much ‘Energy’ can fit into a certain space?

As discussed in one of my previous posts, the energy content of a tonne of wood chip is dependent on its moisture content (mc).

The dryer the chip the more energy it contains.  Typically…

  • A tonne of wood chip at 30% mc has an energy content of 3,500kWh.
  • Therefore your 20 foot container will hold 26,250kWh of energy.

Storage Capacity and your biomass boiler

Matching your storage capacity to your boiler is very important.  If your fuel store is too small you will need frequent deliveries.  Our example of a 20 foot container sized store would last a 50kW boiler for 525 hours (22 days) at full output, whereas the same sized store for a 100kW boiler, running at full output, would need refuelling every 11 days.

In reality of course the refuelling period will be less as you don’t want to be running your store down to almost empty before getting a refill.

Needless to say, I welcome any questions you may have and would love to help you out – please drop in a comment below or call on 01350 723 313.

Written by Stephen Gorton