﻿100 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  194 
  3 
  

  

  calories 
  may 
  be 
  assumed 
  as 
  the 
  average 
  for 
  the 
  day 
  of 
  solar 
  energy 
  

   on 
  a 
  surface 
  normal 
  to 
  the 
  beam, 
  except 
  while 
  clouds 
  obscure 
  the 
  sun. 
  

   This 
  corresponds 
  in 
  ordinary 
  power 
  units 
  to 
  1.15 
  horsepower 
  per 
  

   square 
  yard. 
  

  

  Whether 
  or 
  not 
  it 
  is 
  worth 
  while 
  to 
  employ 
  the 
  solar 
  energy 
  for 
  

   power 
  depends 
  on 
  the 
  efficiency 
  which 
  can 
  be 
  achieved 
  in 
  converting 
  

   solar 
  radiation 
  into 
  mechanical 
  energy. 
  On 
  that 
  factor 
  depend 
  the 
  

   size 
  and 
  cost 
  of 
  the 
  equipment. 
  An 
  efficiency 
  of 
  only 
  1 
  to 
  5 
  percent 
  

   would 
  be 
  apt 
  to 
  involve 
  prohibitively 
  cumbersome 
  and 
  costly 
  equip- 
  

   ment. 
  But 
  a 
  solar 
  engine 
  with 
  an 
  efficiency 
  of 
  10 
  to 
  15 
  percent 
  might 
  

   be 
  commercially 
  competitive 
  with 
  other 
  sources 
  of 
  power, 
  even 
  at 
  

   present. 
  As 
  times 
  goes 
  on, 
  it 
  is 
  to 
  be 
  supposed 
  that 
  the 
  cost 
  of 
  the 
  

   major 
  power 
  sources, 
  coal 
  and 
  oil, 
  will 
  rise, 
  though 
  the 
  limited 
  supply 
  

   of 
  water 
  power 
  may 
  remain 
  relatively 
  unchanged 
  in 
  cost. 
  Hence, 
  

   in 
  the 
  future, 
  unless 
  some 
  as 
  yet 
  unused 
  source 
  of 
  power 
  becomes 
  

   important, 
  it 
  is 
  probable 
  that 
  solar 
  power 
  will 
  be 
  extensively 
  employed. 
  

  

  If 
  such 
  a 
  change 
  in 
  the 
  major 
  sources 
  of 
  power 
  should 
  occur, 
  it 
  would 
  

   tend 
  to 
  alter 
  very 
  much 
  the 
  distribution 
  of 
  population. 
  Such 
  a 
  State 
  

   as 
  New 
  Mexico 
  would 
  become 
  a 
  great 
  manufacturing 
  center. 
  With 
  

   machines 
  of 
  the 
  type 
  already 
  devised, 
  that 
  State 
  could 
  furnish 
  from 
  

   solar 
  radiation 
  more 
  power 
  than 
  is 
  now 
  used 
  for 
  heat, 
  light, 
  trans- 
  

   portation, 
  and 
  manufacturing 
  in 
  the 
  United 
  States, 
  and 
  at 
  a 
  cost 
  not 
  

   perhaps 
  exceeding 
  the 
  present 
  cost 
  of 
  power 
  from 
  coal. 
  

  

  There 
  are 
  two 
  major 
  difficulties 
  in 
  the 
  way 
  of 
  utilizing 
  solar 
  radia- 
  

   tion. 
  First, 
  except 
  on 
  overcast 
  days, 
  the 
  sun's 
  rays 
  come 
  from 
  a 
  moon- 
  

   sized 
  spot, 
  which 
  moves 
  daily 
  through 
  the 
  sky 
  from 
  the 
  eastern 
  to 
  the 
  

   western 
  horizon, 
  and 
  yearly 
  from 
  23° 
  north 
  to 
  23° 
  south 
  of 
  the 
  celes- 
  

   tial 
  equator. 
  Second, 
  from 
  sunset 
  to 
  sunrise 
  the 
  sun's 
  rays 
  are 
  wholly 
  

   cut 
  off. 
  

  

  EARLY 
  EXPERIMENTS 
  

  

  In 
  one 
  interesting 
  series 
  of 
  experiments, 
  reported 
  by 
  Willsie 
  and 
  

   Boyle 
  in 
  Engineering 
  News, 
  May 
  13, 
  1909, 
  the 
  first 
  difficulty 
  was 
  

   avoided 
  by 
  employing 
  a 
  stationary 
  horizontal 
  receiver. 
  This, 
  how- 
  

   ever, 
  is 
  at 
  great 
  cost 
  in 
  thermodynamic 
  efficiency, 
  owing 
  to 
  the 
  low 
  

   temperatures 
  of 
  operation, 
  and 
  to 
  losses 
  of 
  radiation 
  by 
  reflection, 
  due 
  

   to 
  the 
  very 
  oblique 
  incidence 
  of 
  the 
  rays 
  during 
  many 
  hours 
  of 
  the 
  

   day 
  and 
  year. 
  It 
  would 
  seem 
  fatal 
  to 
  sacrifice 
  so 
  much 
  efficiency. 
  

  

  The 
  work 
  of 
  Shuman 
  at 
  Tacony, 
  Philadelphia, 
  also 
  reported 
  in 
  that 
  

   same 
  issue 
  of 
  Engineering 
  News, 
  led 
  on 
  at 
  length 
  to 
  the 
  very 
  different 
  

   experiments 
  of 
  Eastern 
  Sun 
  Power, 
  Ltd., 
  described 
  by 
  Ackermann 
  in 
  

   the 
  Smithsonian 
  Report 
  for 
  1915. 
  These 
  experiments 
  came 
  nearer 
  

   being 
  a 
  commercial 
  success, 
  I 
  believe, 
  than 
  any 
  others 
  on 
  solar 
  power 
  

   up 
  to 
  that 
  time. 
  A 
  large 
  plant 
  was 
  erected 
  near 
  Cairo, 
  Egypt, 
  and 
  

   used 
  for 
  a 
  time 
  for 
  irrigation 
  from 
  the 
  Nile. 
  It 
  appears 
  to 
  have 
  been 
  

  

  