EPA/AA/CTAB/89-07
                        Technical Report


      An Overview of Photovoltaic and Battery Applications
                               by
                          J.  D.  Murrell
                         Karl H. Hellman
                          October 1989
                             NOTICE

     Technical Reports  do  not  necessarily  represent final  EPA
decisions or positions.   They are intended  to  present technical
analysis of issues using data which are  currently available.  The
purpose  in  the  release of  such  reports  is  to  facilitate  the
exchange of  technical information  and to inform the public  of
technical developments which may  form the basis  for  a final  EPA
decision, position or regulatory action.
              U. S. Environmental Protection Agency
                   Office of Air and Radiation
                    Office of Mobile Sources
              Emission Control Technology Division
           Control Technology and Applications Branch
                       2565 Plymouth Road
                   Ann Arbor, Michigan  48105

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                        Table of Contents


                                                            Page
                                                           Number

I.    Introduction  	   1

II.   Energy Uses and Fuel Sources	   1

III.  Solar Electric Power  	   3

IV.   Energy Storage for Solar Photovoltaic Systems ....   8

V.    Batteries for Electric Cars	   9

VI.   Other Vehicle Applications	11

VII.  Conclusions	12

VIII.  Bibliography	13

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I.    Introduction

     Solar  energy  is  pollution-free,   and  politically  and
economically stable.  Its  source does not,  on  whim, change its
availability  or  its  price.    Its  reserves  are  essentially
inexhaustible and its users can collect it  at no direct  cost. Its
disadvantages  are  its diffuse  nature and  the  fact  that  it  is
sometimes unavailable in two ways:  a predictable one (at  night)
and an unpredictable one (due to cloud cover).

     For these reasons,  solar  energy  is  attractive as an  energy
source, and especially so  from an environmental standpoint as a
potential replacement for the consumption of coal and petroleum.
Coal and petroleum generate significant quantities  of particulate
and S02 emissions  when burned  in stationary uses, and petroleum
used in  transportation  vehicles generates  large  amounts  of VOC
and CO emissions,  even at  today's levels of automotive emission
control.
II.   Energy Uses and Fuel Sources

     Two-thirds of all energy consumed  in  the  U.S.  goes to heat—
for  stationary uses,  or propulsion—  for  transportation;  the
remaining  third  is consumed by power utilities to  generate
electricity.    The distribution of  this energy  use  among major
user  sectors  is  shown  in  Table  1, with liberal  rounding  for
clarity.
                             Table  1

       Distribution of  U.S.  Fuel  Energy by  User  (percent)


                     Consumed by      Consumed by Utilities to
   User              User As Fuel    Generate User Electricity

   Industrial            25                      10

   Residential           10                      15

   Commercial             5                      10

   Transportation        25


   TOTAL                 65                      35

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     Accounting for the fuel mix  consumed  directly by the users,
and  the  mix  of fuels  used for  utility  power generation,  and
apportioning  that  among the using  sectors,  the distribution  of
energy fuels is as shown in Table 2, again with liberal rounding.
                             Table 2

               Distribution of Source Fuel Energy
                  Among Using Sectors (percent)
     User          "     Coal     Oil     Gas

     Industrial          10       11      11        4
     Residential          7374
     Commercial           6253
     Transportation               27

     TOTAL               24       42      23       11
     The intersection of Tables 1 and 2 for coal and oil is given
in Table 3.   It shows that a  new  energy technology such as solar
would have the most  impact  on coal use if  applied to electrical
power generation,  and on oil use if applied to transportation.
                             Table 3

                      Coal and Oil Use, by
                   Purpose and User (percent)
                           Percent of        Percent of
                            Coal Use          Oil Use
     Electricity:

     Industrial                30               low
     Residential               30               low
     Commercial                25               low

     Fuel:

     Industrial                15                25
     Residential              low                 5
     Commercial               low                 5
     Transportation           low                65

     TOTAL                     100               100
                             - 2 -

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     Although the industrial use of coal and  oil  as  fuels  is  not
insignificant, most of it is for process heat, only half of which
is amenable  to solar heating.   The other  half of  process  heat
energy needs could use solar thermal energy:   about  half  of  that
involves low  temperature processes which  could use  simple  flat
panel solar  collectors;  the balance  goes  into high temperature
processes  which would  require solar  concentrators.   Thus  the
industrial sector's  fuel use  is not  really  very  fertile  ground
for simple (non-concentrating)  solar thermal technology.

     The use of oil for residential and commercial heating is not
very significant  at  the national  level (10  percent of all  oil
use).  Energy for heating is significant to  individual  homes  and
businesses, however,  with  space heating accounting  for some  40
percent  of  their total  energy consumption.   Home  and business
space heating  energy comes nearly  half from  natural gas,  about
one-third from  oil,  and  most  of the remainder from  electricity.
Hence  solar  thermal space   heating  could  provide  consumer
benefits, but  not much  environmental  benefit.  It  would  reduce
the consumption of natural  gas,  making more  of it  available  for
other purposes.


Ill.  Solar Electric Power

     Table 4 illustrates that large-scale electrical energy needs
could be met using modest fractions of land area,  if solar energy
could be collected and  converted  to  electricity  at an  overall
efficiency of 10 percent.
                            Table 4

               Solar Power Area Requirements vs.
             Electricity Needs. Large-Scale Areas
U.S.

Texas

California

Michigan

Rhode Island
Total Annual
Solar Energy,
Gigawatt-hrs*

   15 billion

  1.2 billion

  790 million

  170 million

  3.7 million
Annual Elec-
 trical Use,
Gigawatt-hrs

 2.5 million

   215,700

   190,300

    79,300

     5,900
                                              Solar Array Area:
                                              % of
Total

0.17%

0.17%

0.24%

0.47%

1.58%
   Acres

3.8 million

  280,000

  240,000

  170,000

   11,000
* horizontal flat plate

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Things Smaller Than Rhode  Island

     For  smaller  areas,   electrical  energy  use  is   more
concentrated,  of  course.    Table  5 is  a worksheet  which  shows
typical annual energy requirements per unit  floor space for five
types of buildings;  note  that  the electrical energy consumption
density at this scale is in the 5 to 25 kwh/sq ft range.

     Photovoltaic  arrays  sized   to   meet  these  buildings'
electricity needs  would  have areas  of the same order of magnitude
as the floor space.  Solar thermal collector areas sized  to meet
heating needs  are  smaller.

     In sunnier  areas  at  lower  latitudes, air conditioning
requirements  will  increase electrical demands,  but  energy
available  from photovoltaic  arrays will   increase also;  the
reverse is  true  for less-sunny  locales at higher latitudes.


                             Table  5

     Annual Energy Required Per Sq  Ft Floor  Space:  Buildings


Type of Building        Electricity. kWh/ft2    Heat. Btu/ft2

    Residence                      6.3                80,000
    Warehouse                      6.1                50,000
    School                      12.2               100,000
    Wholesale/Retail            21.7               150,000
    Hospital                    23.9               200,000


Photovoltaic array size* needed to  furnish electricity needs
(assuming  10 percent overall conversion and  power conditioning
efficiency):

    Residence                 42% as  large as  floor space
    Warehouse                 41% as  large as  floor space
    School                   81% as  large as  floor space
    Wholesale/Retail        145% as  large as  floor space
    Hospital                159% as  large as  floor space


Solar thermal  collector  array size*  needed to furnish heat needs
(assuming  80 percent collection/distribution  efficiency):

    Residence                 20% as  large as  floor space
    Warehouse                 12% as  large as  floor space
    School                   24% as  large as  floor space
    Wholesale/Retail         37% as  large as  floor space
    Hospital                 49% as  large as  floor space
                                                       2
* Based on a nominal  U.S.  solar insolation of 150 kWh/ft ,  or
  512,000 Btu/ft2,  on a  horizontal flat surface.
                            - 4 -

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   ,. Table  6  illustrates this  kind of  regional variance  for a
more or less typical residential photovoltaic system (one without
energy storage);  it  also illustrates how the  purchase of night-
time energy from the power grid can be offset by energy generated
in excess of the  house's daytime  needs.   It is worth noting that
a PV-powered  house or business  thus has a double benefit:   it
does not contribute to daytime peak load demands on the grid, and
in fact, can furnish power into the grid at that time.


                             Table 6

          Solar PV Residential Energy Balance, kWh/Year
         (same Solar Array all sites, approx. 700 sq ft)


                            Fresno CA   Madison WI   Washington DC

Electricity requirements:     8,500        9,420        8,140

Electricity generated        12,710        9,420        9,440
Consumed by house             4,590        3,600        3,520
Sold to Utility, day          8,120        5,820        5,920
Bought from Utility,  nite     3,910        5,820        4,620
Net bought/sold               4,210 sold    even        1,300 sold
Things Smaller Than a House

     Photovoltaic powering  of  a realistic  car extends  into  the
range wherein power demand  is too  concentrated for the area that
can be used  for  solar panels,  as  shown  in Table  7.   Even using
solar power just for vehicle air conditioning is not practical.


                             Table 7

           Vehicle Energy Requirements vs.  Photovoltaic
           Panel Capacity. Small Sedan (watt-hours/mile)
         Electrical energy required for
         vehicle propulsion:                           300
         Electrical energy required for
         air conditioning— full capacity:
                         — slimmer- avrr-
                              65
— summer avg:                30
         Electrical energy available* from
         photovoltaic panel on roof:
* 100 watts/sq ft solar insolation,  10 percent conversion
  efficiency,  20 sq ft available on  roof.
                             - 5 -

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     Although running cars solely by means of  solar  cells  on  the
cars shows no  early potential  for practicality,  solar power  for
cars can  be quite  feasible,  by  using  battery-powered cars  and
recharging  them from  stationary  solar arrays  at  the  home  or
workplace.  Table  8 shows  that a solar array  of  reasonable  size
can handle the energy requirements of a reasonable car operating
at  a  reasonable usage  intensity.   Note  that the  photovoltaic
array to run the car is about  half the  size  of the one (Table 6)
to run the house.

     Another  way  to power  vehicles  from  a photovoltaic  base
station would  be to use the electric  power to generate  hydrogen
via the  electrolysis of water,  and  use the  hydrogen  as  a  clean
fuel for combustion engines or fuel cells in the  vehicles.
                             Table 8

             Battery Electric Car and Solar Recharger


  Vehicle Energy Requirement:    0.300 kWh/mile from battery;
                                 0.460 kWh/mile into charger

                                 5,040 kWh/year at 30 miles/day

  Solar Array:                   at 150 kWh/ft2 insolation,
                                 10 percent efficiency,

                                 340 sq ft
Utility Compatibility and Cost

     It would appear that  the best niche for  solar  photovoltaic
power generation  is  electric utility  use,  and the  best  utility
niche is  peaking  power generation  rather  than base  load  power.
Peak  power  demand  for utilities  occurs in  the  summer  in  the
afternoon, just at the  same  time that the solar  insolation,  and
therefore solar array output,  is also at a maximum.    Some  parts
of the  country  receive nearly 60%  of  their annual  solar  energy
during the five peak power demand months.   Such  an  application,
without  the cost burden  of night-time energy  storage,  is  a
natural match between solar photovoltaic power and utility  power
needs.

     Table 9 summarizes the  magnitude  of  installed   capacity  of
U.S.  utilities.    The typical  capacity of peaking  power units  is
that of new plants fueled  with natural gas or petroleum; all  of
the new gas- or oil-fired plants  in 1987 were  combustion  turbine
or internal combustion  units.
                             - 6 -

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                             Table 9

  U.S. Electric Utility Plant Capacity.  Summer megawatts.  1987
           Total Capacity;
        Avg.  Plant Capacity:
Fuel
Coal
Gas
Nuclear
Hydro
Oil
Other
All
Plants
292,600
118,200
93,600
89,700
76,100
4,000
New
Plants
2,100
200
8,300
270
50
--
All
Plants
230
59
875
26
23
35
New
Plants
354
43
1,034
15
2
--
Capacity Range
New Plants
1.0 to 800
2.4 to 65
833 to 1,259
0.3 to 207
0.1 to 7
--
     In  order  to  compare  the  costs  of  a  potential  solar
photovoltaic  powerplant  to  those  of  current  powerplants,   the
typical  capital  costs and  operating costs  for current peaking
power units were  determined;  these are given  in table 10,  with
costs for base load plants  also shown.
                            Table 10

                    Utility Powerplant  Costs
    Fuel

    Size


    Capital cost

    Operating and
    Maintenance cost

    Fuel

    Total Operating
Peaking

Natural gas

50 mW
(gas turbine)

$300-$340/kW


1.355 $/kWh

2.52  $/kWh

3.88  $/kWh
Baseload

Coal

1000 mW
(two 500 mW boilers)

$1100-$1360/kW


 0.429 $/kWh

 1.52  $/kWh
 1.95  $/kWh
                             -  7  -

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     These   are  nominal   values.    Electricity  costs   vary
significantly  across  utilities.    Some  operating costs  run  much
higher,  such as  27-53  


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the battery charger from that system.  The cost of  such  a  system
would then depend on the cost of the charger, the batteries, and
the power conditioning needed to make the battery  output  usable.

     Any  excess  power  that  couldn't  be  utilized  by  the  then
current load  or  the  battery could be  sold back  to the  utility,
used for hot water heating,  or other uses.

     Using data from the EPRI Journal  article and  assuming  that
the system needed to power an air  conditioner overnight  requires
about 30 kWh, then a storage  system cost of  roughly $3,000 would
be projected.


V.   Batteries for Electric  Cars

     Two  parameters  of critical  interest   for  batteries  for
electric cars are:   specific power and  specific energy.   Specific
power (watts/lb)  can  be related to the  acceleration  capability of
the electric  car,  and  the  range of an electric  car is  a  strong
function of a battery's specific energy (watt-hours/lb).

     One way to look  at the  capabilities  of batteries  is  to use a
Ragone plot in which specific power is plotted against  specific
energy.   Figure 1 is based on the  one  in the  JPL  report  entitled
"Should We Have A  New  Engine?",  but we have  modified it to  show
where the gasoline-fueled conventional  engine would  be.

     On the plot, higher and farther to the right is better. The
figure  shows that there is  a  substantial  difference  between
batteries of different  types and that none  of the  batteries shown
match  the  energy density   of  the  conventional  engine  using
gasoline as  the  fuel.  The  log-log nature  of the plot  tends to
visually  reduce  the differences.  For example,  gasoline is
hundreds of times better than the lead-acid battery  shown.  It is
no wonder  that  battery cars  accelerate  slowly  and  have limited
range capability.

     The batteries for electric cars can represent  a substantial
portion of the car's  cost, between  25 and 50  percent depending on
the  battery  type,  according  to  Hamilton's  report   and  the
Claremont report.   A  summary of  some characteristics of batteries
considered potentially applicable  is shown in Table 11.  Most of
these values were excerpted  from the Claremont report.

     Batteries that are  substantially  better in  one  or  more of
the  performance   indices   in  Table  11 would   be  considered
attractive candidates for electric car use.   It  should be noted
that some  of the  best current  battery technologies,  from  the
standpoint of high watt-hour/lb  capability, can release hazardous
and/or toxic  materials  into the environment.   We  are  not  sure
these problems  are receiving  sufficient attention  by  electric
vehicle designers  and proponents.
                             -  9  -

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                        Figure 1
 Ragone Plot:  Battery Power Density vs.  Energy Density
(Triangle  Indicates Today's Gasoline-fueled Auto Engine)
     1000
  J3
  I
  i
      100-
      10
                                     i-Clj
                  Ni-Cd
Pb-ACID
                    10            100
                   ENERGY DENSITY, W-hr/lb
                                 1000
      Source:  JPL, "Should We Have a New Engine?
                          - 10 -

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                            Table 11

                     Battery Characteristics
Battery Type

Na-S
Li-Metal Sulfide
Ni-Metal Hydride
Zn-Cl
Zn-Br
Ni-Fe
Pb-Acid
Ni-Cd
Specific
 Energy
fw-hr/lb^

  41-75
  36-64
   33
  27-32
  25-30
  20-25
  20-23
  11-26
Specific
 Power
 fw/lbl

 45-80
 45-64
  84

 36-41
 36-50
 27-47
 36-91
kW-hr per
 cu ft

3.1-9.9
  3.1

  2.1
2.4-2.8
  2.4
2.5-3.0
120-130
 90-130
  60
  95
 75-80
125-400
 70-95
300 plus
Safety/
Toxicity
Concern?

   Yes
   Yes
    No
    No
    NO
    NO
   Yes
   Yes
VI.  Other Vehicle Applications

Solar Photovoltaics

     Given  that photovoltaic  power tends  to  be  low  in watts
generated per  square  foot  it is of  interest  to investigate how
photovoltaic power could be used for mobile  applications.

     One attractive application is  for  ventilation.   When a car
is parked  in the  sun on a  hot day,  interior  temperatures can
exceed ambient temperatures by a substantial amount.   On a 100°F
day,  interior  temperatures  can reach  120 °F or more.   such hot
interior  air   sets   the  maximum   design  capacity  point  for
automotive  air  conditioning systems,  since performance targets
are usually based  on "pulldown,"  i.e., reducing  the  vehicle
interior temperature to a comfortable level  in a short period of
time.    If  a way could be  found  to  reduce interior heatup while
parked, then the air conditioner could potentially be downsized,
yielding cost and/or weight and/or fuel  consumption benefits.

     Solar photovoltaic ventilation  units  that can be retrofitted
to cars are available for sale  today at  a  retail price of $30-35.
If they were to be integrated into the  design of the  air-handling
system of  the car and produced  in car-type production volumes the
cost  would probably fall to somewhere in the $10 to $15 range.

     Another possible application is for powering the vehicle air
conditioner itself.   As shown earlier,  solar photovoltaics cannot
provide enough  power  for  current  technology  automotive  air
conditioners;   however,  current   belt-driven  compressor  air
conditioners were not designed  to utilize  solar photovoltaics, and
some air  conditioner R&D could possibly  yield  more promising
results.  The match  between the problem (hot cars caused  by sun
loading) and  the possible  solution  (solar  photovoltaics working
best  under the same conditions)  is too  close a match to ignore.
                             -  11  -

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     It  is  likely  that  solar photovoltaics  could  be  used  to
assist in battery charging.  This could reduce the charging power
from the engine substantially, but not much  has  been reported in
that area.
Advanced Batteries

     Advanced batteries  have  applicabilities in addition  to  the
obvious potential for electric car or  hybrid car propulsion.   An
advanced  battery with greater  power  density could  replace  the
current  starting,  lighting,  and  ignition (SLI)  battery  and
achieve a weight  savings.   To the extent that  the  package could
be smaller, that would also be an advantage.   Alternatively,  the
same weight or  volume could be  used to provide more electrical
power or  energy,  and given the  trends in  increasing electrical
power demand for  cars, this  is  the. route that  we expect  will be
taken.
VII.   Conclusions

1.  As concerns increase over greenhouse gas emissions due to the
consumption of fossil fuels to generate electricity, solar photo-
voltaic power will become more and more attractive.

2.  Solar photovoltaic  power has a natural match with  peak  load
electrical power demands caused by air conditioning usage.

3.  The environmental benefits of solar photovoltaic power should
be assessed  by comparing its  negligible  emissions to  the  emis-
sions of particulate, SOx, NOx, VOC, CO,  and  toxics from utility
peak load power plants,  not base load plants.

4.  Why  aren't solar peaking power units in  widespread  use  now?
Because no one has invested  in  high  volume  solar  cell panel  pro-
duction  capacity  to  make  economy-of-scale  reductions   in  panel
costs needed for cost-competitiveness.

5.  When considering advanced technology batteries for  power  or
transportation needs, the safety and environmental impact aspects
of the  battery materials and designs may  need closer  scrutiny
than it appears is being given.
                             - 12 -

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VIII. Bibliography

The Claremont Graduate School (Hempel et al), "Curbing Air Pollu-
tion in Southern California- The Role of Electric Vehicles," Apr.
1989.

Electric Power Research  Institute,  "Technical Assessment Guide,"
Vol. 1, Dec. 1986.

Electric Power Research Institute Journal, "How Advanced Technol-
ogies Stack Up," July/Aug. 1987.

Electric Power  Research Institute Journal,  "Emerging Strategies
for Energy Storage," July/Aug. 1989.

Energy  Information Administration,  DOE,  "Cost  and Quality  of
Fuels for Electric Utility Plants, 1987.

Energy  Information  Administration,  DOE,  "Electric  Power Annual,
1987.

Energy  Information  Administration,  DOE,  "Monthly Energy Review,
1988 Annual Summary, Dec. 1988.

Intersociety Energy Conversion  Engineering Conference,  "Advanced
Energy Systems, Their Role in Our Future," Aug. 1984.

Hamilton, "Electric and Hybrid Vehicles, Technical Background Re-
port for the DOE Flexible and Alternative Fuels Study," draft re-
port, May 1988.

Hoff, "The  Value  of Photovoltaics:  A Utility Perspective," IEEE
Photovoltaic Specialists Conference, May 1987.

Jet Propulsion Laboratory, "Should We Have a New Engine? - An Au-
tomobile Power Systems Evaluation,"  Aug. 1975.

Mazria, "The Passive Solar Energy Book," 1979.

Personal Communication,  Energy  Conversion Devices,  Inc.,  Troy,
Michigan.

Photovoltaic Energy Technology Division, DOE, "Five Year Research
Plan: 1987-1991," DOE/CH110093-7, May 1987.

Photovoltaic Energy Technology Division,  DOE,  "Investing in Suc-
cess," Nov.  1988.

Society of Automotive Engineers, "Recent Advances in Electric Ve-
hicle Technology," SP-793, Aug.  1989.

Solar Energy Research Institute, "Toward a New Prosperity," 1984.
                             - 13 -

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