Mount Pinatubo and Solar Power Plants

Article

Reference

Mount Pinatubo and Solar Power Plants

MICHALSKY, Joseph J., et al.

Abstract

Researchers examine insolation data to determine the effect of the eruption of Mount Pinatubo on the performance of solar power plants.

MICHALSKY, Joseph J., et al . Mount Pinatubo and Solar Power Plants. Solar today , 1993, vol. 7, no. 4, p. 21-22

Available at:

http://archive-ouverte.unige.ch/unige:118711

Disclaimer: layout of this document may differ from the published version.

1 / 1

'',,;

':;:,

fv€ffiffiffig: ^iuër,ï* &s?

,".i dâ

.-' ;!

^Ë

'ii

^ffi

I _4**&

e!r*lr66qæ:i]:;:ri,.'

G

'ffi ff

^ajor volcanic eruptions oc-

f& .fæ ^{cur every few years, but} I K1ru ^most

^have

^{little effect}

^on

--L Y ."&. solar radiation or

climate.

In

the last ten years, however, two volca-

noes-El

Chichon in

Mexico

and

Mount Pinatubo in the Philippines-have

de- creased

solar radiation and influenced

weather at a level that

might

be expected at the frequency of about once a century.

During

the

winter

and spring of 1992,

Daggett læasing Corporation and

I(JC Operating Company, the operators of the Solar Electric Generating System (SEGS)

parabolic concentrator power plants in

southern California, noted that production was about 30 percent below normal.

This

drop was a result of a reduction

in direct

solar radiation and led to a significant

r+

duction in revenues. The operators'appeal to Sandia National

laboratoriesto further

quantily and, perùaps, predict

futule

inscr-

lation

levels related

to Mount

Pinatubo, led to this study and the results reported in this article.

Long-term Effects

Sulfur-containing volcanoes

with

suûE-

cient force

to

^penetrate

through the tro

posphere can have a long-term impact on direct solar radiation. Oftcn thc change is rrrinor

in

comparison to natural seasonal variations and goes largely unnoticed. The Mexican volcano El Chichon at 17.3 N lati-

tude

ancl

the Philippine

volcano

Mount

July/August

1993

As Mount Pinatubo erupted on June I 2, I 99 1 , clouds of ash and steam advanced 3.1-9.3 miles ^(5-15 km) down the

north, northwest

ançl

southwest flanks

of

the

volcano.

Pinatubo at

15.1 N

latitude are two dra- matic exceptions.

Satellite instruments show that El

Chichon ancl

Mount

Pinatubo deposited 6 and 20 million metric tons, respectively, of SO, in the stratosphere. Through a se- ries of chemical reactions, the SO, is con- vertecl to H,SO, ancl mixecl with water to proclucc'an aerosol that is approxinrately

75 percent HrSOn by weight. These

aero

sols are small and can elay suopended

for

years

until they

are removed

from

the stratosphere by natural atmospheric

pro

cesses. Once the aerosol reaches the

tre posphere, normal removal

processes

bring them to the

surfacÊ, €.g., as rain- drops, in a matter of days or weeks.

El

Chichon's effects were measurable at mid latitudes for at least three years af-

ter its

eruption.

The

peak monthly-aver- aged reduction in solar radiation was about 11 percent for visible wavelengths, occur-

ring in

the late

winter

of 1982, about ten months after the eruption. The following winter, after a summer minimum of 4 per- cent the drop in insolation peaked at about 6 percent, and

then

dropped

to

about 3

percent during the winter of 1985 follow- ing a summer minimum of 2 percent.

ln this

afticle, we study the effects of

Mounl Pinatubo at four

sltes: Geneva, Switzerland

(46 N);

^Boulder, Colorado

(a0 I9;

Kramer Junction, California ⁽³⁵

N);and las

Cruces,

NewMexico

(32

f0.

Wc uscd dircct normal irradiance data to examine the monthly-averaged effects

of reduced insolation

on

clear

days

by

aerosol

in the

stratosphere, and global

horizontal

irradiance clata

to

cletermine anomalous weather conditions. In the case ofBoulder, we used aerosol optical depth atvisible wavelengths to compare with tra- ditional solar irradiance data at the other

three

sites.

Only

data taken

within

two hours of solar noon were analyzed.

21

@ ^{R. PE,RE,Z, R. SEALS, P. INEICHEN}

\\

Sæâmf i 'u'-"ï,,''q,ri rt. $-}âmnâS

Researchers examine insolation data to deitermine the effect of the eruption of Mount Pinatubo on the

performance _{of solar} power plants.

oo

g

q f

:!!!FeFj"-,'t: : ,

oI o

(

q :)

Mount Pinaftrbo

Mount

Pinatubo

eruption

on

June

15, 1991

sent

ash 18.5-25 miles ^(3O-4O km) into the atmosphere.

Data Analysis

We wanted to separate the direct

Pinatubo effect, i.e.,

reduction of direct

normal insolation by aerosol, û orn the ef- fect of weather.

To

isolate direct effects, we used relatively clear days when direct irradiance exceeded a threshold value

of

190.2

or

126.8

Btus/fPlhr

⁽⁶⁰⁰

or

400 watts/meteC) for

las

Cruces and Geneva, respectively. \\re did not use the Kramer Junction direct data because

oflarge

data gaps. No threshold was used in compar- ing global irradiance data.

We determined what the background seasonal pattern was for direct irradiance

in I-as Cruces, New Mexico

based on

pre-emption

data

frorn January

^{1989 to} June 1991.

We found that the direct normal irradi- ance peaks in late winter and is aminimum in mid- surnrrer, parlially because the so- Iar distance is a maxitnum and aerosol lev- els

in

the surrurrer rnonths are higher. In the two and one-half years before the eruP tion, the depatlure

t

om backgt ound rarely exceeds 7.9

Btus/tr/hr

⁽²⁵ watts/meterr).

After the

eruption,

the

departure ex- ceeds this value by late

sulr)rler

1991, and reaches a rnaximum depletion in mid-win-

ter

1992

of

approxirnately 47.6

Btus/ff / hr ⁽¹⁵⁰ watts/neter2), staying low

throughout

thc

spring and then substan-

tially recovering by

summer.

This

47.6

Btts/

f(

/hr

⁽¹⁵⁰

watt/meterz)

minimurn corresponds to a 15 percent extinction

of the

317

Btus/ft2/hr

⁽¹⁰⁰⁰ watt/meter2) noon-time average

direct normal

irradi- ance in the winter tnonths.

To study weather effects, we examined all global horizontal inadiance data in a nor- malized, air mass-independent cleamess in- dex form. The cleamess peaks ⁱⁿ the spring and is at a minimum in the summer, but is rather conslant year round.

Tlre

background period

variallility

in

clearness

is

less

than

0.01, and

this

value

is not

exceeded

until

late fall 1991, reaching a minimum

in

the

winter

of about 0.045 and

recovering to

near background values during the summer ^{of 1992.}

The fractional change in clearness for this time of year implies a defi- cit of approximately 11.1 Btt:s/f(

/

hr

⁽³⁵

watts/meterr). Abouthalf of this

radiatiôn loss can be ac- counted

for by

reflection

in

the stratosphere. Therefore, we esti- mate

that

about 6.3

Btus/ff/hr

(20 watts/meter2) ^is lost because of unusu- ally bad weather during the middle of the 1992 winter season.

In

las

Cruces there were many totally clear

hours

of sunshine,

but in

Geneva,

Swiûerland's

case, the threshold chosen was 126.8 Btu

s/tr /hr

⁽⁴⁰⁰ watts/meter2), because totally clear hours are rare. The peak in background values occurs during the summer and is at a minimum during the winter, unlike the

las

Cruces pattern.

The

deviation

in

direct irradiance for the background period is twice ^as gleat as

las

Cruces', with sorne differences exceeding 15.9

Btvs/Îf /hr

⁽⁵⁰

watts/rnetef).

Nev- ertheless,

the

uragnitude of

the

drop

in

direct in adiance during the winter of 1992 is about the salre as in Las Cruces at 47.6

Btus/ff /hr

⁽¹⁵⁰

watts/rneter2). There

were no deviations greater than the back- ground deviations in cleamess databased on global hori zonatalin adiance, implying no decreases attributable to weather.

In the case ^of

Boulder,

Colorado, the data are

not

irradiance,

but

aerosol opti- cal depths. The data are acquired on clear days

with

no

cinus. The

analysis of this data showed a

foutteen

percent loss

in

beam radiation at 555 nm,

which

is con-

sistent with the

47.6

Btus/ftzlhr

⁽¹⁵⁰

watt/mete9

losses at the other two sites.

Since there is a longer data record fo'llow-

ing the eruption than at the other

two sites, we

confinned

^the expected extinc- tion increase in the winter of 1993, follow- ing the summer

minimum.

Since this fol- lows the El Chichon pattern quite well, we can anticipate

that

Pinatubo

will yield

a similar extinction pattern for the northern mid latitudes for the next two ^years

with roughly

a 50 percent

larger

magnitude than El Chichon exhibited.

Because

the extinction is similar

at sites between

the

latitudes

of.32

and 46 N, it is probable that this extinction in the

direct beam applies to

KramerJunction

and the SEGS plants ^as

well.

We have in- sufficient direct irradiance data ^at Kramer Junction ^to confirm this, however.

We do have

lGminute

^global horizon-

tal

in-adiance data

to

check

for

weather

anomalies.'lhe

clearness pattem, based on all data, indicate very clear weather at all times of the year. Unfortunately, data gaps create uncertainty

tliat is

nearly as large as the dip in clearness following the

eruption.

However, the dip is consistent with the loss in the direct beam, i.e., there does not appear to be additional loss due to a weather anomaly.

Gonclusions

Both direct irradiance (Geneva and Las Cruces) and direct illuminance (Boulder) measurements imply a peak extinction

in

the direct bearn radiation at mid latitudes during the winter of 1992 of

approimately

1F20 percent. The overall behavior ^of the time-dependent extinction is similar at all sites. We therefore believe that this direct solar beam extinction behavior applies to all sites between 32 and 46

N,

including the SEGS facilities in Southern California.

Assuming Pinatubo aerosol follows the same pattent as El Chichon aerosol, which

it

has to date, we can expect about 1G13 percent

extinction this winter

^(1993), 3 percent

this

summer (1993), and

t7

^per-

cent next

winter

^(1994).

The importance of

a long-term, con-

tinuous

and well-maintained data collec-

tion

system cannot be stressed enough.

The tas Cruces

data

set provided

the clearest signal of stratospheric aerosol and weather effects because of the complete- ness and

length

of

its

data record.

This

information is particular{y irnportant ^to the operators

of

solar

thermal

^{power plants} because these plants cannot produce en- ergy until a given direct inadiance thresh- old is reached. ^6â

JJ. Michalsky, R. ^Perez and R. Seals are Senior Research Associates

at

^the

^Atmo'

spheric Sciences Research Center, Uniaer'

sity at Albany, State Uniuersity of New York, 100 Fuller Road, Albany, New York 12205,

(518)

442-3808. P. Ineich.en is

an

Assis- tant Professor at the Uniuersite de ^Geneue, Groupe de Physique, Appliquee, Geneue 4 Ch-1211 Switzerland.

The authors thank Benoit Molineauxfor

first

^{noting the} descrepancies between mea-

sured and expected radiation leuels.

22

SOLAR TODAY