Wood pellet fuel management - the DIY option

Those who have never used wood pellets, and those who supply wood-pellet systems, commonly underestimate the challenge of manually managing the fuel to minimise the cost whilst ensuring that you don't run out.

Visual estimation of the fuel level in your wood-pellet store

Even if you have a clear view of the contents of your fuel-store, the store is not a regular shape and the pellets are not going down evenly. Most people have difficulty estimating the volume of an uneven pile of pellets in a space with sloping floors or a bag that is changing shape as the pellets go down.

In practice, you won't have a clear view. The best you're likely to have is a viewing port or two.

When the pellets are above a certain level, they'll cover the viewing port and you won't be able to tell the level behind (remembering that the pellets won't be going down evenly).

When the pellets are below that level, the viewing port will be covered in dust and the light inside the store will be so limited that you probably won't be able to see a thing - all you'll know is that there are no longer pellets in the window, but you won't know how far down they are.

Converting a visual guesstimate to tonnes of wood pellets

Once you've guessed the volume, you've got to convert it into weight, because what you see is measured in cubic metres, but what you order is measured in tonnes. It's an easy mistake to get the conversion wrong, and an expensive one.

How long will your guesstimated tonnage of wood pellets last?

Once you've guesstimated the tonnage remaining in your store, you're not done. Now you've got to guess how long that quantity will last. Do you know how fast your boiler will get through that quantity of pellets? To get the best value, you want to time it about right, so you haven't got too much left at the next delivery. But if you get it wrong, you go cold.

The rate of usage can change for all sorts of reasons - most obviously the weather, but also behavioural factors. Are all your heat-users behaving predictably?

You could do with an accurate representation of the historic trend, but all you've got is a few guesstimates. Can you really tell the difference accurately between the quantity of pellets in the store from one day to the next?

Converting heat output to tonnes of wood pellets

Maybe you'll work it out from your boiler's heat output, but you've got to allow for conversion efficiency. Is the system as efficient in reality as the manufacturer's claimed performance, measured under ideal conditions? What about other losses outside the boiler?

Do you know the density of the pellets? Do you know the Calorific Value (CV, i.e. energy content)? Your supplier's specification tells you the minimum (if you've used a reputable supplier), but it doesn't tell you the actual figures.

You need to know these figures accurately, if you are going to convert heat output to the fuel-level in the store. Discrepancies in these figures accumulate to make any assumptions about fuel usage unreliable.

Proximity sensors - one inaccurate snapshot

Or you may have a proximity sensor that is supposed to tell you when the pellets fall below a certain level. If it's working (and we see plenty that don't), all this tells you is a single point in time in each load - the point at which the pellets fall below that level on that side of the store.

If the pellets bridge on that side of the store, you'll get no warning. If they sit deeper elsewhere in the store, it will make you think you are emptier than you really are.

At best, this gives you an unrepresentative snapshot, without any ability to judge the rate at which you are using the pellets and how much is left before or after the moment that the proximity sensor alarms.

The only way to really know how you are getting through the fuel is regularly to measure the amount in the store.

Allowing for wood-pellet suppliers' changing lead times

And that's not the end of your guesswork. You've guessed the rate you're getting through the pellets and how much longer they will last, based on visual estimates of the content in the store from time to time and guesses about the weather and your users' behaviour. But you've also got to guess what the lead-time for delivery will be. It's no good working out that you've got a week's worth of fuel left, only to find out that your suppliers can't deliver for two weeks.

How do you know what your supplier's lead-time will be? You should kick any supplier out of the door who tells you that their lead-time is constant, or even predictable. They are lying.

Changes in the weather, in levels of commercial activity, in patterns of usage of different types of building (schools, universities, hotels, leisure centres, homes, etc), and so on will result in large and unpredictable swings in the combined level of demand. But supply capacity is limited - you can't conjure specialist pellet-blower trucks out of thin air. Increased demand has to result in extended lead-times or the use of unsuitable equipment to provide extra capacity.

That's assuming that everything always runs smoothly on the supply side. In reality, equipment breaks and skilled staff get ill from time to time. If the trucks aren't dedicated to wood pellets (e.g. animal-feed trucks), changes in demand for the alternative uses will affect the availability of the trucks for supplying wood pellets. These restrictions won't always happen conveniently so that the supply constraints coincide with periods of low demand. When they coincide with high demand, lead-times will get stretched further.

That's true even for us, and we have a big enough fleet of dedicated wood-pellet delivery trucks, network of depots, and stock of pellets that individual failures reduce our capacity by only a few percent. For our competitors, one or two of these constraints could decimate their ability to supply.

The solution: inclusive wood-pellet supply contract from Forever Fuels

You have no way of knowing how your pellet supplier's lead-time may change. But if you're responsible for managing your fuel level, it's still your problem. You'll have to guess. Get it wrong, and you could be cold for a while.

There's one simple solution: Forever Fuels' fixed-price, inclusive fuel-supply contract, including remote monitoring with a DELOX level-sensor.