Friday, 7 September 2012

Solar powered kiln update

Items that have just been glaze fired

We have used the kiln several times over the course of the summer for both bisque and glaze firing and have been very pleased with the results so far. The biggest challenge has been finding reliable sunny days to fire the kiln so we can stick to our green agenda. With careful timing of the firing it has been possible to have the main part of the firing (when the kiln runs at full power) happen when the solar panels are generating maximum power so that it runs entirely from solar power.

A typical glaze firing has been started at around 7:30am and the kiln runs at 180C/hour until it reaches 600C, usually around 10:45. At this point the kiln goes to full power until it reaches the target temperature which is 1240-1260C, it then holds this temperature for 10-20 minutes to allow the glaze to melt evenly. The firing usually completes some time between 1:30pm and 2pm. As our solar panels face south east we generate maximum power from mid morning to early afternoon which covers the maximum demand from the kiln nicely.

During the early part of the firing when the kiln is gradually warming up to 600C it uses a "duty cycle" which means the elements are turned on for a few seconds at a time. The kiln controller turns the elements on for long enough each minute to meet the meet the requested temperature rise needed, in this case 180C/hour. This is in fact quite gradual, much slower than a normal domestic oven. The down side is that when the elements are on they will draw full power (3kW) which is more than our solar panels will be generating at that time. However when you calculate the power used during this period it is small compared to the amount used in the second part of the firing when the kiln runs at 3kW for more than 3 hours continuously. Our solar panels gradually increase output during the first part of the firing so quit a lot of the energy required will still be supplied by the solar panels. Each firing is in practice costing is very little, just a few pence at most.

The challenge as we head into autumn is to find enough time to cover the kiln firing as the peak power from the panels gradually reduces from 3.6kW we get during the summer. Judging from the measurements I took last year the latest that we will have enough of a window to cover the main part of the kiln firing is probably around mid October. Our plan is to put the kiln somewhere dry for storage over the winter and not fire it again until the spring. At the moment the kiln is in the middle of the garage and we want to put the car in there during the winter months so that is another reason not to fire it during the winter.

We will be busy getting some more work through the kiln over the next few weeks whilst we can, I will post some more photos of work fired in the kiln soon.


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