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.

Our first kiln firing

Well we finally managed to fire the kiln after waiting for a suitable sunny day, this was no easy thing with the poor weather we have been having this summer. Here are some photos of the work just after opening the kiln the next morning once it had cooled off. The models are my wife's work and the bowls and cups are mainly mine.

Pieces waiting to be removed from the kiln after firing

Pieces safely removed and ready for decoration / glazing

The day we chose turned out not to be quite as sunny as forecast! - well it is England in the summer so we shouldn't have expected unbroken sunshine :-) Despite this we only used about 50p of electricity whilst the kiln was being fired and some of this was down to boiling the kettle and running other household appliances so the actual cost of running the kiln was a bit less than 50p which was pleasing.

We have since done another couple of bisque firings with similar results, we are still waiting for the elusive sunny days of summer when we might fire the kiln for almost nothing!

The next firing will be a stoneware glaze firing which requires a higher temperature to be reached, 1240C rather than 950C. This will use more electricity as the kiln will need to run at full power for at least a couple of hours to reach 1240C and then this temperature needs to be held for a 20 minute "soak" to allow the glaze to melt evenly. I will report back on how this went, we are excited to see the first finished pieces that we made in our own kiln.

Solar powered ceramics

We have been doing ceramics evening classes for the last three years and had been considering getting a small kiln for some time so that we could fire work at home. We had been put off by both the start up cost and the potential running costs. Some research revealed that we could get a hobby kiln that would run from a standard household 13amp socket and had a peak rating of 3kW. I did some calculations about firing schedules and realised that on sunny days between April and September it would be possible to fire the kiln pretty much entirely from the solar power. It would need the kiln to be started first thing in the morning so that the peak load coincided with peak output of the solar panels. Our system generates more than 3.5kW during the middle of the day at this time of year (if it is sunny) which is more than enough.With the summer months coming up we decided to go for it and have now purchased the kiln below.

Our shiny new kiln !

The next step is to do a test firing of the kiln, the only problem is it hasn't stopped raining for the last three weeks and the few sunny days have been during the week.  I did give the kiln a very short run up to check that everything was in working order, the picture below shows the kiln controller in action.

The kiln controller during a short test

We are busy making some work so that we have something to fire once the test firing has been done. The test firing is recommended for the new kiln as the elements will burn off their protective coating and the kiln will have had a "burn in". The test firing involves heating the kiln up at  a rate of 150C/hour until it reaches a temperature of 600C at this point it will be heated up at full power until it reaches the target temperature of 1050C. The test firing should take around 6 hours so I am planning to start the kiln at around 8am one morning as soon as we get a suitable sunny day.

The longest firing we will are likely to need is when we glaze stoneware which requires a top temperature of 1240C, this requires an initial rate of 180c/hour until it reaches 500C and then at full power until the target temperature. This should take somewhere between 6 and 7 hours to complete so the 8am start should still be fine. I might have to start the kiln a little earlier when the days get shorter in late August and September.

I will post some more reports once we have had a chance to fire the kiln for real, this should be in the next couple of weeks. I am going to check how much power we draw from the grid during the firing by taking meter readings before and after the firing, hopefully it won't be much.

We need to work hard now to create some work to be fired but that is the fun bit !