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School study fuels wood energy debate

Wood energy can bring many benefits to schools, writes
Greg Visser, business general manager at the Energy Efficiency
and Conservation Authority.

The merits of wood versus coal-fired boilers have
recently come under scrutiny in Otago.

It’s great to see energy choices being debated locally.

The Energy Efficiency and Conservation Authority (EECA) has
supported wood energy projects – in schools and industry – as
a carbon-neutral, low-emission, renewable heat source.

In our view, wood energy has numerous benefits – economic,
social and environmental. But like any fuel, there are pros
and cons.

If the sole criteria is fuel cost, then wood is unlikely to
stack up against coal, which is almost always cheaper to buy.

Looking at the bigger picture however, wood can be more
cost-effective. Between 2007 and 2010, EECA helped fund 31
schools to switch from coal to wood energy, under the
Renewable Heating in Schools pilot, with the Ministry of

The aim was to test the feasibility of wood energy in

It was acknowledged from the outset – including by the
schools – that the ongoing cost of wood fuel was higher than

So, schools were recruited only where it was clear that
continuing to burn coal was no longer feasible for them.

This was because the schools were faced with needing to
invest significantly in repairing or replacing their coal
boilers – either because boilers were at the end of their
life, or because resource consent was due to expire, and
gaining a new consent would require a costly upgrade to
reduce pollution.

The Ministry of Education agreed to fund the difference in
ongoing fuel costs, so there was no financial risk for the
schools involved.

In some schools, existing coal boilers were converted to run
on wood pellets; in others, brand new boilers were installed
– some running on wood chips and some on pellets.

The pilot results were extremely informative, and have helped
EECA and the industry get a clearer view of the costs and
benefits, as well as the best ways to manage these projects.

A key finding from the pilot was that wood chips are cheaper
than pellets.

Tahuna Intermediate in Dunedin and Dunstan High School in
Alexandra installed purpose-built chip boilers.

Often sourced from sawmillers, foresters or joineries, wood
chips are cheaper than pellets, and help these businesses
dispose of wood waste, a local win-win.

Another finding was that coal-to-wood-pellet boiler
conversions are always less efficient than purpose-built wood

A new wood boiler (especially wood chip) will have a higher
up-front cost but much lower operating cost due to its very
high efficiency (up to 90%).

EECA recommends any school considering wood should consider
the benefits of installing a new wood boiler alongside the
case for converting a coal boiler.

The true cost of energy is not just the cost of the fuel and
the operating costs. It includes the capital cost of the
equipment, such as replacement boilers, and any
emissions-control equipment needed to avoid air pollution and
meet regional air quality regulations.

In cities like Dunedin, emissions standards for new boilers
are stringent due to air-quality issues.

Emissions-control equipment on a coal boiler can cost as much
as the boiler itself.

Switching to wood was often a low-cost option when assessed
on a ”whole-of-life” economic basis – not just because it
didn’t need emissions control, but because ongoing
operations, maintenance, and labour costs were lower.

Modern wood energy technology can produce 80% less
particulate emissions than coal.

Some types of coal discharge heavy metals and/or sulphur to
the air – as well as other pollutants that worsen air quality
and can be harmful to human health.

Coal ash can be toxic, so needs careful disposal to prevent
soil contamination.

Wood produces only about a fifth of the volume of coal ash
and, as a natural fertiliser, can be simply spread on school

Many of our pilot schools commented positively on the
reduction in waste disposal costs, and found caretakers spent
far less time cleaning boilers.

Wood energy is sustainable when it comes from plantation
forests such as New Zealand’s.

It is carbon neutral so does not contribute to climate change
(the CO2 released when burning wood is the same as that
absorbed by the tree during its lifetime). Collectively, the
31 pilot schools are avoiding 3300 tonnes of CO2 emissions a

A desire to show environmental leadership is one of the
reasons schools in Southland, Otago, the Bay of Plenty and
elsewhere have opted for wood without funding from EECA.

If schools rule out wood energy solely on the basis of its
cost relative to coal, they may be overlooking a renewable
fuel that can deliver far greater benefits over the long term
– both to their school and their community.

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