Spent the weekend building and filling a #SolarKiln ... which is a thing for rapidly drying firewood without any additional fuel.
In Scotland, it can take a year or more to season wood. The idea here is to accelerate that process by increasing the temperature.
I knackered my back about a month ago loading pallets into our car. They were sodden, and weighed about 30kg each.
Anyway, I reckon the temperature in there will get up to ~35-40ºC this week, given our weather forecast.
I'll measure actual temperatures over the coming days and record them here.
Meanwhile, here's what the contraption looks like (trigger warning: it looks like a £30 Lidl greenhouse, 3 pallets, and half a tonne of wood.)
It's a #prototype, I suppose.We'll see how it goes.
The frame is tethered to the pallets and half a tonne of wood, and also guyed to the fence behind.
So it should withstand anything but the worst winter storm.
Worst thing that can happen is I have half a tonne of damp wood ¯\_(ツ)_/¯
Day 1. Observed temperatures peaked at 22°C here.
Inside the woodstack the peak was 28°. That’s measured in the middle of the pile, 2 or 3 layers from the top. So well out of direct sunlight.
On the surface the temperature peaked at 39°C. Again I chose a spot out of direct sunlight.
Here's a graph of the data so far for today.
I am, obviously, not going to update this 24/7.
I *could* force the temperature higher by keeping the vents and door closed. But I need some ventilation to maintain airflow and give the moisture somewhere to go.
So the vents at the side are partially open, and the zippers either side of the door opened to the height of the pallets to draw air up and through it.
I'm measuring the temperature using one of these: https://www.ikea.com/gb/en/p/fantast-meat-thermometer-timer-digital-black-20103016/
Means I can stick the probe into the stack but keep the readout visible simply by opening the south vent.
So I don't lose too much heat making observations.
23 º at 11pm. Dark now, sun has long gone.
That's a result. It's actually quite chilly now in the garden, mostly because of the breeze.
But we are still cooking wood.
At this rate, a couple of months will be enough. Don't want it to be too dry or it will just be kindling.
I'm going to bed now, and have no desire to hack an IKEA thermometer to send me data over SMS or whatever overnight.
We'll just have to infer what's going on between now and then.
No power. It needs to do the job itself.
#SolarKiln week 4: https://docs.google.com/spreadsheets/d/e/2PACX-1vSzBovgfOQXnE8DmAmNJb-NXycvQFiokGuL214XBjnN6OYd5iuUswN_UhIiRDpN-CCeSbMnOvBU1GX2/pubchart?oid=283420095&format=interactive
Solar kiln week 5:
Solar kiln week 6:
#SolarKiln week 7: https://docs.google.com/spreadsheets/d/e/2PACX-1vSzBovgfOQXnE8DmAmNJb-NXycvQFiokGuL214XBjnN6OYd5iuUswN_UhIiRDpN-CCeSbMnOvBU1GX2/pubchart?oid=193885569&format=interactive
#SolarKiln week 8: https://docs.google.com/spreadsheets/d/e/2PACX-1vSzBovgfOQXnE8DmAmNJb-NXycvQFiokGuL214XBjnN6OYd5iuUswN_UhIiRDpN-CCeSbMnOvBU1GX2/pubchart?oid=1678904204&format=interactive
#SolarKiln week 9: https://docs.google.com/spreadsheets/d/e/2PACX-1vSzBovgfOQXnE8DmAmNJb-NXycvQFiokGuL214XBjnN6OYd5iuUswN_UhIiRDpN-CCeSbMnOvBU1GX2/pubchart?oid=1710744269&format=interactive
So. Experiment over.
What, if any conclusions can I draw?
I consolidated all the data into one chart.
Interactive version here: https://docs.google.com/spreadsheets/d/e/2PACX-1vSzBovgfOQXnE8DmAmNJb-NXycvQFiokGuL214XBjnN6OYd5iuUswN_UhIiRDpN-CCeSbMnOvBU1GX2/pubchart?oid=196703998&format=interactive
The maximum internal temperature in the kiln was consistently above the daytime max.
So, we're definitely not making things worse, but better.
There were only 2 days in the 63 days of the study when the kiln failed to improve on daytime max.
The biggest difference was +8ºC. On average it was +3.72ºC.
On 13/63 days, the mean temperature inside the kiln was lower than the daytime high.
Which means, obviously, that on 50 days it was higher.
On average, the mean temperature inside the kiln was 1.41ºC higher than the daytime maximum.
It's not really a solution. Very few people have a a garden like ours. Or access to a local tree surgeon, whose wood is mostly from trimming rather than felling.
It cost >£3k to install a woodburner, and we already had a chimney.
Our stove gets us through the shoulder months, but we still rely on gas in the winter.
I am unlikely to forget those.
A note on the design of this: the cover is not taut enough over the roof section to prevent pooling when it rains heavily.
The weight of the water can get to a point where it causes the frame to sag.
I solved this using a sheet of 2mm perspex between the frame and the cover. It gives just enough rigidity to ensure the rain is drained away efficiently.
When it's empty I will add some timber to support the frame at the back.
David O'Brien
Craig Mcgee
Ciara
Colin Haynes
Dan Hoover