You are not permitted to download, save or email this image. Visit image gallery to purchase the image.
The new wood pellet boilers heating many of Dunedin's schools are costing more than three times as much to run as their older coal-fired equivalents, which has left one school principal regretting the decision to move to wood pellets. Reporter John Lewis talks to several Dunedin schools about why they have, or have not, converted to the new technology.
In years gone by, Dunedin schools were prominent in the community not only for their output of high achieving pupils, but for the clouds of blue smoke that billowed across the city from their coal boilers.
Since the cleaner-burning wood pellet boiler technology was introduced to many Dunedin schools in 2008, the air around the city has been considerably cleaner.
But, as with most things in life, there has been a cost.
Otago Boys' High School rector Clive Rennie said his school was one of the first to convert to a wood pellet-burning boiler about five years ago.
It was a decision the school had regretted.
He said the school's old coal-fired boiler was not expected to meet new Otago Regional Council air quality resource consent requirements, so the school spent about $30,000 in 2008 to have its boiler converted to burn wood pellets.
''The outcome has been that in 2008, our coal bill was $32,000. Last year, our wood pellet bill was $114,000.
''If we'd actually not been able to recoup that from the Ministry of Education, we wouldn't have gone there.''
Mr Rennie said there was a difference in the heat from coal-fired boilers compared with wood pellet boilers.
A coal-fired boiler took a while to warm up, but it had a lot of residual heat at the end of the day, he said, whereas the heat from pellet boilers ''died'' as soon as they were turned off.
''If we had purpose-built school boilers for pellets, I think we would feel that we had more control over what happens.
''We're now stuck with a system that is not totally fit for purpose.''
If the school could make the decision again, it would stick with the coal boiler, he said.
''Wood is cleaner to burn, there's no doubt about that, but if your [coal] boiler is in good condition, and fine-tuned, it doesn't put out much smoke, and I don't think we would have breached the rules for ORC consent.''
For Logan Park High School deputy principal Peter Hills, there was no question the new technology was worth every cent.
Like many other schools around Dunedin, Logan Park decided to convert to wood pellets because its two 1MW coal boilers would no longer gain resource consent from the ORC.
''Half of Dunedin knows you could see Logan Park in the morning, chucking blue smoke down the valley towards town, and now people go past and you can't tell if anything is coming out of our chimney.
''It's a good outcome in terms of the emissions.''
The cost of a new boiler at the time was about $500,000, whereas a conversion of the boiler to wood pellets was only about $100,000 over three or four years, and the Energy Efficiency and Conservation Authority (EECA) funded half of the cost.
''So it was quite an attractive proposition to shift,'' Mr Hills said.
''The cost was a huge motivator to change, but also Logan Park High School is green and environmentally friendly - [coal] was just not the right look for us.''
The school paid $120,000 for pellets in 2011, but the cost had decreased to about $93,000 last year because the wood pellet market had become more competitive and lower prices could be negotiated, he said. The school had also found ways to maximise its boiler's efficiency.
Kaikorai Valley College executive officer Brian Lee said the school was about to replace its 40-year-old coal boiler, but it had no plans to change to wood pellets.
The school had investigated a change to wood pellets, but based on anecdotal evidence from other schools that had already made the change, Mr Lee estimated it would cost about three times more to run than the coal boiler.
The school spent about $30,000 a year on coal for its boiler, and for that reason, it had opted to stay with the status quo, he said.
''We spent a considerable amount of money last year installing a sophisticated filtration system in our boiler house, which filters out all the particles and soot, and what that means is that we have a resource consent from the ORC to continue to burn coal for another 35 years.
''That extended the life of the boiler. If we couldn't get that, the other option was wood pellet, wood chips or lpg.
''Just the capital cost of converting to one of those was quite horrendous - and then the expendables costs on top of that was also horrendous.''
The largest distributer of wood pellets for commercial boilers in Dunedin is A.J. Allen.
Manager Kevin Sullivan confirmed the cost of wood pellets had not decreased over the past five years, and was not expected to drop in the future.
Rather, he believed consumers had become more efficient in their usage and better at negotiating cheaper prices for buying in bulk.
He could not divulge the cost per tonne because it was commercially sensitive.
''It's a green trend. Wood is taking over from coal. The price hasn't really come into it.''