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