A PRACTICAL STUDY FOR A SUSTAINABLE WOOD-BASED ENERGYSUPPLY SYSTEM-Case example for Heating Greenhouse CropsMasanobu NAGANO, Yoshimasa TERADA, Masao NAGANO
Kochi University of Technology
ABSTRACT: This study was designed to construct a wood-based energy supply system that helps
sustainable development of a local community as well as environmental conservation. The system would
utilize local forests within a natural resource cycle and supply wood-based energy to heating greenhousecrops. To construct this system, we have been developing a combustion appliance which utilizes wood-basedenergy. In order to improve the combustion system, an experiment was conducted in 6a greenhouse. In thecombustion appliance, downdraft system was adopted and it can produce the generating power of 60,000kcal/h (if the moisture content is within 10%). In this experiment, we verified that the system was able toproduce a stable combustion effect as well as minimized smoke and ash emissions. Also, we found out thatthe moisture content in wood-chips was reduced as low as 25% if the wood-chips were dried in thegreenhouse. Meanwhile, a survey targeting local greenhouse farmers was conducted to determine thetargeting price of the wood-based fuel. According to the survey, the maximum value that the farmers canafford for the A type heavy oil under a certain circumstance is around 45 yen/l, which is same as the price of
21.27 yen/kg for the wood-based fuel. The result of the survey indicated that it is important to break down
the process flow from lumber to supply and make each process as efficient as possible in order to accomplish
this supply cost for the energy needs.

KEYWORDS: sustainable development, sustainable energy, natural resource cycle
Presuming that the global environment is conserved

1. INTRODUCTION

and sustained, we have to aim to construct a system
The purpose of this study is to develop a sustainable

that satisfies the following three conditions: (1) Use

wood-based

willwood-based biomass which can be reproduced

contribute to the sustainable development of a local

within a natural resource cycle (2) CO2 emissions

community as well as promote global environmental

within the limit of purification capacity in nature (3)and energy conservation. One of our objectives was

Lower cost than crude oil market prices. Basically,

to construct a model in which energy was produced

the important tasks are: establishing the lumber toand consumed in a local community.

Wesupply system that materially and economicallyexperimented with energy conversion to wood-based

functions; developing burners and machines thatenergy from crude oil, which is an energy source forenable us to effectively and efficiently convert plants

heating greenhouse crops.

into energy.

energysupplysystemthat

2. BACKGROUND AND PURPOSE OF THE

prices.

STUDY
Concentration of population in urban areas causes
thcentury, an increasing world

one-way labor absorption from local areas as well as

unboundedandcreates economic disparity and this has become atechnological progress helped our global economy

key factor in preventing sustainable development ingrow to incredible heights.

local communities.

In the late 20
populationandscientific

However, such progresshas come at a high cost as we have depleted ourFrom the global environmental

point view, this leads to the concentration of energy

natural resources and irreparably degraded our planet. consumption and creates an enormous emission of
At present, most energy is imported from abroad,environmental load substances. In the end, thealthough only a century ago, our life system wassituation worsens until the clean up capacity inmostly based on the wood-based energy source

nature is no longer effective enough.

produced from forests in Japan. We have suitableconditions required for tree growth such as sunshine,

While an upward trend on crude oil price is expected

precipitation67%

to continue in the future (Figure-1), sustainable(25,120,000ha) of the nation’s land is covered with

development of local communities and reduction offorests. The ratio of artificial forests and naturalenvironmental load are the fundamental challenges

forests are almost the same. The amount of theto our society.

andtemperature,

andforests is approximately 3.5 billion m3 1) and theyearly growth reaches up to 80 million m3 1).
However, as a result of continuous forestation, which
has been a state policy since the end of World War II,
forest devastation due to poor replant maintenancehas become a big problem.
bythedepreciationThis situation is caused

ofconverted

timbers,

disadvantaged business in forestry due to risingproduction costs, and a decrease in the labor
population due to an aging society coupled with aFigure 1 World oil price in three cases, 2980-2030

record low birthrate.

Source International Energy Outlook 2006, Energy
Information Administration, Japan, 32 p, 2006.

In agricultural production, the food self-sufficiency
ratio in Japan is approximately 40% (about 20% if

We experimented to construct the energy supply

include animal feed). This ratio is remarkably low

system for heating greenhouse crops in G village incompared to other developed countries. Most grains,

Kochi prefecture. G village is blessed with a mild

except rice, are imported from abroad and in recent

climate and lots of sunshine, and it is whereyears, even fresh food such as vegetables have been

greenhouse crops originated in Japan.

more and more imported.

If the situation continues,

young people working in agriculture may disappear
as it was in forestry because of the competition
between domestic production costs and import

3. SUSTAINABLE

ENERGYSCHEME IN G VILLAGE

SUPPLY3.1 An overview of G village

only value creation is small in the region, but also

G village is a small local community which faces thethe relationship between forests and agriculture is

Pacific Ocean and has a population of 4,206 in an

not reciprocally circulated.

area of 3,963ha.
By using wood-based energy produced from forests,
The forest area occupies 70% of the land, 2,813 ha,

CO2 in the region is circulated and neutralized.

and the rest of 30% is the flatland. The acreage under(Figure-2)

cultivation is only 6% of the land, which is 237 ha.
However, G village has the agricultural values ofRain

Temperature Rise

Artificial forest

Water Resource

Sunshineproduction (number of farm households: 332) ofmore than 3 billion yen and the values of production
per farm household reaches approximately 10
million yen. The values of production per 10a rank

Mountain Forest
Natural forest

Woods

Energyresource

in a high position in Japan. Especially, heating

Vaporization

greenhouse crops has made a great contribution toheat

the village above all other types of agriculture.

CO2

Even in winter, they are able to ship fresh vegetables

In the region

and flowers. The cultivated area of the heating

Chip

HeatingGreenhouse

Agricultural products

greenhouse crops in G village is 70 ha and there areabout 700 greenhouses. From the end of November

Plant

O2

pelletEnergyFossil fuelFigure 2 Intra-regional cycle

to March, about 7,000 kl of heavy oil (type A) isused. However, because of an increase in the price ofThe management cycle of artificial forests differs

crude oil since 2005, the benefit of the heatingfrom that of natural forests as shown in Figure-3, andgreenhouse has been reduced and furthermore, there

natural forests hardly require care by man.

has been a tendency for the greenhouse framers totimber

suffer their business due to the high production costs.
On the other hand, though there are 140 households

Artificial

who own local forests, no families actually maketheir living working in the forest. Therefore, thetaken care of and the densely planted trees need to begrowcare

Energythin

value of the forest production is much smaller
compared to agriculture. Planted trees have not been

thin

plant

resource
timberregenerate

Naturalthinned. Also, natural forests which are near town
are barely cared for and those far from town aregrowneglected.
Figure 3 Resource cycle of artificial forests and3.2 Intra-regional cyclical energy supply scheme
In the present system, in which fossil fuel is used,energy is imported from outside regions and crops
are exported to outer regions. Under this system, notnatural forests in the mountains

approximately 600 million kcal. As described in 3-3

3.3 Combustion and growth amountand 3-4, sustainable supply calories from theCombustion

40 years growthmountain forests in G village are 894 million kcal.

calorieAmountTherefore, it is physically feasible to supply energy(kcal/m3)(m3/ha)produced in the local mountain forests for heating

527

greenhouse crops.

490

4. TASKS TO BE SOLVED

Coniferous tree 1,550,000(Cedar)Broad leaf tree

2,050,000

Source: Forest biomass energy, National Forestry
One of the primary tasks in this paper is to reduce

Extension Association in Japan, 2001

the energy supply cost despite the type A heavy oil
market prices. Secondary, to develop an appliance

3.4 Timber cycleThe mountain forests in G village comprise 2,813 ha,which includes an area of coniferous tree forest of
1,285 ha, an area of broad leaf tree forest of 1,447 ha,
and a region of bamboo trees of 81 ha. Most of theconiferous trees are in artificial forests and 3,000 to
4,000 cedar trees and Japanese cypress per hectare
were planted there. Regarding the economic value ofthat burns trees efficiently is also an important task
to be solved. Finally, it is so important to gain
understanding from the public regarding this projectin which mountain trees are timbered and used forenergy, because there are some stereotyped opinions
in public that timbering trees can only lead toenvironmental destruction.

coniferous trees, Japanese cypress older than 100years and cedars older than 80 years are moremarketable. The ideal number of those older trees tobe timbered is 100 to 200 per hectare. By the timethose older trees are timbered, approximately 95% of
the whole trees need to be thinned. If we assume thattimbered cycle of coniferous trees is 40 years (1,285ha/40), we are able to acquire the trees from an areaof 32 ha yearly. On the other hand, it is known thatbroad leaf trees in this area can be recovered to its
original in 30 years after timbering. Assuming thatthe timbered cycle is 40 years (1,447

ha/40), we

can collect the broad leaf trees from an area of 36 hayearly. As for bamboo, since the growth of bamboo
is complete in 2 years, it is possible to be timbered ina 3 year cycle from an area of 27 ha yearly.

4.1 Supply costAccording to the survey of farmhouses conducted inMay 2006, most of the houses requested around 40
yen/l, which was the standard price in 2004, as thetype A heavy oil price to properly sustain theirgreenhouse crops. Moreover, an energy cost of 45-50
yen/l is the maximum value farmers can afford if it is
not expected that there will be an increase in theprice of the products. Presently, the market price of
70 yen/l has remained constant for two years and it isconsidered that there is only a little possibility of aprice reduction in the future. In addition, theyanswered the amount of money that they could
invest for the combustion appliance and it would beapproximately 500 thousand yen for a 10a sizedgreenhouse.

3.5 Necessary calorie and supply calorie
The amount of type A heavy oil (8600 kcal/l) usedby greenhouse farmers in this village is 7000 kl
yearly and the necessary combustion calories are

The amount of combustion energy is inversely
proportional to the moisture content of a combustible
body. The combustion energy of type A heavy oil /lis 8,600 kcal, and 2.15 kg of dried material with autilizing wood-based biomass have been promoted,

5% moisture is required in order to secure the same

focusing on biomass power generation, homeamount of energy by using wood-based energy.

heating, and the use of this energy in plants, with a

The supply cost of wood-based energy needed tonational objective to reduce CO2 emissions based on

satisfy the needs of farmers is 45 yen / 2.15 kg. In

the Kyoto Protocol.

other words, 21.27 yen/kg is the target price thatfew projects involving heating greenhouse crops.

Our case study is one of thesupply side should be aiming for.
In this study, involving farmhouses, the objectiveTo accomplish the supply cost for the energy needs,

was to improve the efficiency of the burner section

it is important to break down the process flow fromof a combustion boiler in order to provide anmountain forests that supply wood-based fuelefficient, inexpensive supply. To construct such an(Figure-4) and reduce the cost by striving to makeappliance, we stipulated some conditions for theeach process from (1) to (8) as efficient as possible.

appliance that the structure has to be simple, and it
would enable to maximize combustion efficiency

There are certain elements that promote efficiency

and minimize smoke and ash emissions at the same

such as improving workers’ skills, utilizing naturaltime.

power, maximizing the utilization of materials,
equitable work distribution throughout the year, andUsing a downdraft system on the burner, it has

the overall effectiveness of machines.

It issuccessfully produced a stable combustion effect.

necessary to set up and implement targets for each

The method’s effectiveness has been demonstrated inelement to reduce the overall cost.

an experiment conducted in a 6a experimentalgreenhouse.
4.3 Public involvement

MountainWood

To gain the public’s understanding, it is necessary toforest

storagestate that the project is designed to conserve the(1) timber

(3)

(4)

(5)

Ship

DryConvey(2) collectenvironment.
• Timbering within the growth range of mountain
forests is a resource cycle.
• Burning wood is carbon neutral.

Processing

Greenhouse• Planted artificial forests need to be thinned.

plantagriculture• High temperature combustion has no discharge

(8)

(9)

delivermanage(6) processof hazardous substances.
• Participation in CO2 emission trading.

(7) dry
It is important to inform people of these points in aFigure 4 Process breakdown
4.2 Development of a combustion appliance
In recent years, nationally supported projects

logical and an easy-to-understand way.

5. EXPERIMENTTO

VERIFYmoisture content fell off until around 25%.

EFFECTIVENESS
6. CONCLUSION
Generally, greenhouses are heated during the nightDuring the day, theWe consider greenhouse crops using fossil fuels totemperature in the greenhouses is higher than 20 ℃

be unnatural and unreasonable in terms of thedue to the solar energy. Required temperature may

environment, energy, and economy.

vary depending on the crops.

For example, anago, greenhouses were developed by combining theeggplant requires 12 to 16℃ and a green pepper

blessings of nature and a plastic sheet, which was an

requires 16 to18℃.

industrial product.

from November to March.

Half a century

We can imagine how surprised

and impressed people were when out of season
In our experiment using a 6a experimental

vegetables were grown in a plastic house and served

greenhouse, 16,000 Russell prairie gentian seedlingson the table.

were planted and grown. The temperature required

agriculture

to grow Russell prairie gentian should be higher thansatisfying many people’s wants.

15 ℃ and in the test, a burner using wood chips

various kinds of vegetables can be sold in thewith 60,000 kcal/h generating power (if the moisturemarkets regardless of the season.

content is within 10 %) was installed.

that this is not what truly society needs.

The minimum temperature in the greenhouse was set

However, this agriculture has been rooted in ourat 15 ℃ and by measuring the variation of thesociety as part of the giant social system as well as

outside temperature, inside temperature (temperature

created many layers of markets involving manysensors were installed in 6 points), and undergroundstakeholders.

temperature (temperature sensors were installed 10

system drastically. Actually, we have heard fromcm below the ground in 2 points), the relationshipfarmers that they are pressed to make their decision

between the amount of chips sent to the combustion

if they continue to run greenhouse farming due to theroom and the supply interval (g/min) was calculated

rise in the price of crude oil.

in order to develop an automatic chip supply

planted on mountains are left untouched, and if theyprogram.

are not taken care of them, devastation of the(In the experiment, the amount of wood

As time went by, heating greenhousebecamemoreandmore

popular,

As a result,

We are convinced

It is not realistic to change thisMoreover, trees

chips per time was 700g and the average moisturemountain forests will be the result.

In short,

content was 25%).

solving these problems has been a big motive for ourstudy.

Wood chips as fuel were processed from the woods
timbered in the scrub bush and artificial forests in

We found that the flow of timbering trees fromthe village, and waste wood discharged from amountains, gathering, and conveying to a plant, andsawmill, which was purchased and processed with aprocessing them in the plant is physically feasible

chipper.

according to our experiment.

Moreover, natural drying was performed

to dry the chips as much as possible.

We found out

However, anothertask, economical efficiency of the system has not yetthat if wood chips were dried in a greenhouse wherebeen validated at this point.

there was no cultivation after sun drying, theourcountry

hasa

Especially, because

complicatedgeographicalformation as well as steep mountain forests, it isexpected that the process of timbering, gathering,and conveying wood is going to be expensive.
There are two tasks specific to combustion in thisstudy.

The first task, development of a wood-chipburner is almost completed and we have the prospectof starting mass production. The other task, which is
to make drying wood chips more efficient andeconomical, is still left unsolved.
It is necessary for our society to demonstrate thatcirculation of the resources and energy helps
environmental

conservation,

toenvironmental

conservation

creates

prove

that

economical

benefits, and to establish the wood-based energy
supply system for heating greenhouse crops as acontribution to the sustainable development in a
local community. We believe that this is the first step
toward the innovation based on both environment
and economic points of view.

REFERENCES
2006. International Energy Outlook 2006, Energy
Information Administration, Japan, 32 p.
Forest biomass energy, National Forestry Extension
Association in Japan, 20011) 2006 Annual Report on Trends of Forest andForestry, Forest Agency, 2006
Biomass energy in forests, National Forestry
Extension Association in Japan