Getting Energy out of Hot Air

Australia looks set to be the first country in the world to build a

full sized “Solar Tower” power station, capable of meeting the

electrical demands of a regional city of 200,000 inhabitants with

no Greenhouse gas emissions. The power station project (the

first of five planned) is to be constructed about 600km west of

Sydney under licence from Energen Global Inc. Bifk Par-I,d;r”,

Refocus reports.

The 200MW project being developed by of a large greenhouse driving large turbines

EnviroMission Ltd is a scale-up of a 50kW to produce electricity was viable. Moreover,

project which was a joint venture between the Manzanares project addressed the clues-

the then West German Government, the tion of round the clock supply usually

local electricity utility and Schlaich raised by critics of solar energy plants.

Bergermann and Partner. It was built to the EnviroMission Ltd is a stock exchange

south of Madrid, Spain at Manzanares in listed company with a significant sharehold-

1982. The Manzanares “solar chimney”, ing held by Global Energen Inc of

(perhaps chimney is an unfortunate term California, who in turn owns the Solar

for a zero emission electricity generation Tower licenses for several other countries,

technology) demonstrated that the concept including the USA. SBP is known for its

lightweight construction of towers, roofs,

bridges and suspended buildings, including

the Munich Olympic Stadia and the Ting

Kau Bridge in Hong Kong, and Prof Jorg

Schlaich is well known for his work in tower

construction.

Why Australia? The modelling groundwork commenced

over eight years ago, and several potential

sites around Australia were identified using

data derived from the Manzanares plant.

Grid access, favourable market, economic,

climatic and weather conditions prevail in

southeastern Australia, and hence the

choice of site for the first plant. The plant

will be situated about 25km from the near-

est access point to the grid, (north of the

Murray River on the New South Wales

Victorian border) on land that has margin-

al value for farming.

So although the first site is not in

Australia’s region of highest solar radiation

which are remote areas with little or no

inhabitants, it should be noted that the

modelling process is based on more than the

sole parameter of solar radiation. The size of

the proposed plant is thus based on many

years of modelling, and 200MW is the min-

imum viable size and in a location that will

work economically according to

EnviroMission and SBP

Impressive structure The dimensions of the proposed plant are

impressive. The tower itself will be about

IOOOm high, substantially taller than the

world’s current tallest engineered structures.

This tower is a 130m diameter hollow

structure constructed in re-inforced con-

crete situated at the centre of a 7km diame-

ter flat greenhouse. The tower walls will be

Im thick at the base, tapering to 25 cm at

44 November/December 2002 RE , www.re-focus.net

r,t FEATURE WORLD’S FIRST DOWN UNDER

the top. The greenhouse base will be suffi-

ciently far off the ground for maintenance

vehicles to gain access. The tower is

strengthened and ovalization minimized by

placing a series of six steel horizontal sup-

ports (like bicycle wheel spokes) at intervals

inside the tower.

The key to the technology lies in creating

a temperature differential between the

inside and the outside of a greenhouse. Air

inside the large circular glass greenhouse

moves inwards and upwards to the sloping

ceiling at the centre, creating a near con-

stant wind. Thirty-two shrouded turbines

situated at the base of the tower produce

electricity without any interruption to out-

put. The constancy of flow gives the plant

operators an advantage over wind farms.

The plant design and operating parameters

are flexible and thermal storage for example

could reduce the peak capacity from 200

MW to a constant 80 MW, although the

intention is to operate as a peaking station.

Annual production from the proposed

power plant is expected to be just over 700

GWh with zero emissions apart from dur-

ing the construction phase. The predicted

capacity factor is 38%. The project has

benefits beyond electricity production.

Apart from the creation of jobs and employ-

ment, the tourism industry will also benefit.

The need for moisture control to ensure

maximum energy extraction from the air-

flow and to protect the concrete structure

could also have spin offs in such areas as

crop drying and even salt production.

There are also telecommunication and

defence opportunities.

Some critics have voiced the opinion that

the scale up from the pilot is too great.

However, the proponents are certain of

their engineering, as are the external engi-

neering consultants. Others have suggested

that the size of the greenhouse could be a

problem with the phenomenon known as

“albedo”. By trapping heat, the greenhouse

base could reduce the Earth’s ability to

reflect light back into space. Thus, by trans-

forming solar radiation into heat, a solar

tower and its greenhouse might actually

contribute to warming the earth’s atmos-

phere - even while reducing emissions of

greenhouse gases. ‘l‘his has been refuted by

EnviroMission who say that the contribu-

tion of fiarmland and rocky desert to the

total value of earth albedo is relatively low

(approximately 5 %). Secondly, a solar air

collector is characterised by reflection losses

of approximately 22 to 26% percent com-

pared to 20% to 24% for fidrmland and

rocky desert respectively, and depending on

the location, could increase albedo.

Finances The present proposal, being the first full-

scale plant, has been costed at between

A$600 - $700 million with costs of the

tower and the greenhouse being about equal.

Work is still to be done to optimise COP

struction materials to minimize capital costs.

The project has been given two significant

boosts by governments. The Federal gov-

ernment has conferred Major Project

Facilitation status and the New South Wales

government has given the project a State

Development Significance declaration. This

recognition gives EnviroMission benefits

associated with tax and other funding that

will assist the development phase.

RE certificate opportunities? The solar tower project will play a very sig-

nificant part in Australia’s Renewable

EnerW Certificates market. RECs are pro-

duced as part of Australia’s Mandatory

Renewable Energy Target (MRET). The

project qualifies under the legislation and is

expected to meet 7.5% of the national tar-

get in its own right. EnviroMission will

thus compete directly with other renewable

energy projects in the RECs market.

However, unless things are changed, the

MRET may be too limited. At the outset,

the renewable energy target was to be 2% of

all generation, as announced just prior to

Kyoto. L.ater, when the legislation was

introduced, a fixed ceiling was set at

95OOGWh. Recent analysis done by the

Australian Eco-Generation Association sug-

gests that a substantial share of that

3500GWh target can be met by “old”

hydro, without any need for new invcst-

mcnt, thus limiting the need for new pro-

jects to meet the 95OOGWh demand by

2010. Effectively, the market for RECS

may have less scope for new major projects.

The Federal government will review the tar-

get next year and it has been suggested that

20,OOOGWh will be the new ceiling.

Boosting Australia’s green credentials Because of the Federal government’s unwill-

ingness to sign the Kyoto Protocol, there may

be unwanted implications for renewable

energy projects in Australia. EnviroMission

say that any exclusion from international car-

bon trading will not affect its position, but if

Australia did sign LLP, the company would see

that as a bonus. Right now, Australia needs a

boost for its failing environmental rcputa-

tion. The construction of the world’s first

solar tower power station by EnviroMission

could be just that and Prof. Jlirg Schlaich’s

long held vision of solar power plant5 that

run around the clock will be realised.

November/Dccembrr 2002 RE www.re-focmnet 45