### Smaller system

Light Energy Systems' worksheet suggested you could get a 1.8 kW system for about \$16,000.  Here is how the numbers work out for that one.
```             SOLAR PV SYSTEM WORKSHEET
(SoCalEdision variant)

You must input the following:
your summer and winter baseline quantities
your summer and winter usage
your summer and winter `peak sun hours' (insolation)

The baseline quantities can be found on your bills, and go by
`territory' and whether you have electric heat.  Summer is defined
as June through September, give or take a bit.  The baseline is
given in kWh/day.  For instance baseline for SCE region 17 is
13.1/10.5 (summer/winter) or 16.9/24.1 (all-electric).  By contrast,
region 10 is 9.1/9.2 (summer/winter) or 10.0/16.2 (all-electric).
(Interestingly, this means `summer' is 122 days and `winter' is
243.25 days.)

Peak sun hours depend on location and local weather conditions.  I
do not have much data on these but have sample cities.  Unfortunately
the average listed in this data is not the computed average,
which may throw some of these calculations off.

city             summer winter   average   average
(table)(table)   (table)   (s+w)/2
Davis              6.09   3.31      5.10      4.70
Fresno             6.19   3.42      5.38      4.80
Inyokern           8.70   6.97      7.66      7.83
La Jolla           5.24   4.29      4.77      4.77
Los Angeles        6.14   5.03      5.62      5.58
Riverside          6.35   5.35      5.87      5.85

You will also need a target system size (in watts or kW).  This is
determined by the number of solar PV modules and their rated (peak)
output.  Your inverter will have to be hefty enough for this as
well.  The system size will affect the price, which you must also
enter.  Finally you have to enter a system efficiency factor, to
account for losses in the modules and inverter.  Efficiencies of
82, 71, and 75 percent are typical for batteryless or battery-
backed-up systems.  The 75% efficient battery systems are slightly
more expensive.

Finally, you need to enter your utility's rates and tiers, any
local city taxes you pay on electricity, and -- for financial
comparison purposes -- the rate you would expect to pay on a 30
year mortgage, and your marginal tax rate for tax deductability.

CONSTANTS

30.50 summer days/mo           4 smmr mos
30.41 winter days/mo           8 wntr mos

UTILITY RATES

tier        rate  limit  smmr kWh  wntr kWh
I        \$.1301   100%    399.55    319.27
II       \$.1516   130%    119.87     95.78
III      \$.2300   200%    279.68    223.49
IV       \$.2800   300%    399.55    319.27
V        \$.4000   none      rest      rest

INPUTS

baseline       13.10< summer (kWh/day)
(region 17)       10.50< winter (kWh/day)

usage       33.00< summer (kWh/day)
26.00< winter (kWh/day)

insolation        6.35< summer (PSH/day)
(sun hours)        5.35< winter (PSH/day)

system size        1.80< kW
system cost  \$16,000.00<
efficiency         82%<

city tax        5.0%<

mtge rate       6.75%<           36.0%< your tax bracket
term          30< years

RESULTS - SUMMARY

w/o PV     \$202.18/smmrmo   \$172.41 avg.
\$157.53/wntrmo

w/PV     \$122.26/smmrmo   \$101.79 avg.
\$91.56/wntrmo

saves      \$79.92/smmrmo    \$70.62 avg.
\$65.97/wntrmo

mortgage     \$103.78/mo        \$66.42 (after tax equivalent)
net savings       \$4.20

RESULTS - DETAIL

without PV system
summer     1006.50 kWh:
I        399.55 kWh       \$51.98
II       119.87 kWh       \$18.17
III      279.68 kWh       \$64.33
IV       207.40 kWh       \$58.07
V          0.00 kWh        \$0.00
--------
subtot:   \$192.55
tax:     \$9.63
--------
\$202.18

winter      790.56 kWh
I        319.27 kWh       \$41.54
II        95.78 kWh       \$14.52
III      223.49 kWh       \$51.40
IV       152.03 kWh       \$42.57
V          0.00 kWh        \$0.00
--------
subtot:   \$150.03
tax:     \$7.50
--------
\$157.53

with PV system
summer gen      285.86 kWh/mo
winter gen      240.11 kWh/mo             3064.31 kWh/yr

summer      720.64 kWh:
I        399.55 kWh       \$51.98
II       119.87 kWh       \$18.17
III      201.22 kWh       \$46.28
IV         0.00 kWh        \$0.00
V          0.00 kWh        \$0.00
--------
subtot:   \$116.43
tax:     \$5.82
--------
\$122.26

winter      550.46 kWh
I        319.27 kWh       \$41.54
II        95.78 kWh       \$14.52
III      135.41 kWh       \$31.14
IV         0.00 kWh        \$0.00
V          0.00 kWh        \$0.00
--------
subtot:    \$87.20
tax:     \$4.36
--------
\$91.56
```