Along with firewood, wood chips and briquettes, pellets are a wood fuel. Whereas firewood and chips are burned as they are, pellets are a densified fuel that is obtained by compacting small scraps of wood. The same goes for briquettes, which are about the same size as logs, whereas pellets look like small cylinders.
In this article we will talk about pellets, before explaining how to make your own homemade pellets to power your biomass stove or boiler.
What are pellets (home-made or purchased)?
Pellets are a fuel manufactured from sawdust or wood shavings which are compressed under very high pressure into small cylinders thanks to the binding agent lignin, which is present in the wood. Pellets don’t contain glues—they are prohibited—with the exception of natural substances such as starches or vegetable flours.
Do you have a lot of scrap wood lying around? For example, do you prune the trees and shrubs in your garden? Do you tidy your vineyard, orchard or olive grove in spring with a chainsaw or pruner, leaving piles of pruning waste? Do you trim hedges or clear the edges of ditches in the countryside with a brushcutter? Do you collect dead wood and branches from fallen trees in woodland? Do you have lots of untreated waste wood that you don’t know what to do with? If so, why not make the most of it by making your own pellets?
Nowadays making homemade pellets is a good way to keep the household budget down, given the skyrocketing prices of fuel (methane, LPG, heating oil, wood and of course pellets themselves). In addition to saving on fuel costs, by making pellets at home you can repurpose wood into a useful resource and, what's more, you have an extra guarantee that the raw material is safe.
Some experts suggest making pellets by adding sawdust, grass clippings, straw, nutshells and husks, paper/cardboard and other materials to the wood. To obtain quality homemade pellets, however, we advise using only wood and, at most, a small percentage of sawdust. Only wood gives you a pellet with a good calorific value—similar to that of firewood—and good cohesiveness, so it won’t crumble when transported or be crushed under its own weight when packaged and stacked.
Which wood is best for pellets? Commercially available pellets are most commonly made from beech, oak or fir. Although a distinction is commonly made between hardwoods (such as broadleaved woods, which should give off more heat) and softwoods (such as coniferous woods, which apparently have a lower energy yield), given the same unit weight and moisture content, the calorific value of wood varies little from species to species.
To obtain do-it-yourself pellets, the wood must first be ground and then compressed: there are commercially available machines for domestic use that can do this. Before investing in one, carefully weight up its technical characteristics against your needs. It will pay for itself within a few years. Alternatively, you can split the expense with neighbours or relatives, or hire a machine instead.
The ideal raw material for pellets is pruning waste. Pruning is far from simple work: it requires both expertise, the right techniques and suitable equipment. Here is how to prune a tree, how to perform winter pruning and avoid the most common pruning mistakes, how to limb, section and buck trees and when to cut firewood, plus our guide to the various pruning tools.
How to make your own wood pellets
Besides, pruning waste, scrap wood and plenty of space, here’s what you need to produce homemade pellets:
Chipper, bioshredder or biochipper
Protective clothing: ear defenders (the machines are quite noisy), protective glasses and gloves
The wood for making your homemade pellets must first be chopped into small pieces (chips), before being passed back through the machine to grind the chips down to a size of 8–10 mm. Chippers, bioshredders and biochippers produce similar results but work differently depending on the various blade, hammer and sieve systems. Bear in mind that waste wood used for pellets must not be treated, glued or painted, to prevent it from releasing harmful substances when burned.
At this point the chips should be dried out, simply by leaving them in the sun for a day. Similar to wood, moist pellets generate less heat because they have a lower calorific value. Use the hygrometer to check the moisture content. A certain amount of moisture is needed to compact the pellets: the water content of the wood chips should be around 10–15%. If they are too dry, before placing them in the hopper of the pellet mill, put them in a bucket, spray them with water and stir so that they are evenly moistened.
Now the wood chips are ready to become homemade pellets. That's what the pellet mill (or pellet press) is for: it compresses the chips into small cylinders a couple of centimetres long by means of rollers and a heated die. To make your homemade pellets more compact, you can use a certain amount of resinous wood, i.e. from conifers such as pines and firs. Alternatively, you can add commercially available pellet glues in the recommended doses, based on the type of wood you are pelletising. The pellets will be hot when they come out of the die, so they should be left to cool down and dry out.
Store your DIY pellets in bags in a sheltered, dry and ventilated place: humidity reduces their compactness and calorific value (the water content of the pellets should be around 8–12%).