Posted by Doug on March 13, 2008, 11:14 pm
Initially I planned to do the same thing, place panels on a patio cover. You
will need 80-90 sq. ft. per kW (my 6kW array covers almost 500 sq. ft., so
for a system sized for your load, you would need a very large patio cover).
I planned on the patio cover installation so that the panels would not be
visible, but mounting them horizontally generally will reduce their
efficiency compared to a south-facing roof mount (better solar angle).
Yes, I am running 3,000 gal/hr. koi pond pumps 24-7, an 11 amp 240AC pool
pump, pumped hot water recirculation throughout the house, sub-zero
applicances, etc., and I use less than 30kWh/day. Are you sure that you
don't have an extra zero on that number? Do you have electric water heater,
electric space heating, electrically heated spa, etc? I really don't know
how you could that much electricity without something like one of these
electrical heating sources malfunctioning
As you stated -- you surely do not need to run the pool pump 24-7, but since
you have a variable speed pump, that is not the culprit here, unless it is
running on full-speed constantly (control/configuration problem). On full
speed I am sure it uses closer to 1,200 watts (or more, mine uses 2,600 kW),
and that could add 28kWh/day plus to your bill.
If you don't mind me asking, what is the monthly bill (dollar amount)?
Could be, but they tend to run slower as they get older -- that is why the
utilities like to change them out.
Posted by old dirtbeard on March 13, 2008, 11:31 pm
I think I read this wrong last time -- are you saying the variable speed
pump will use between 150-3,200 watts? If it is stuck on high at 3,200 watts
for 24-7, that would account for about 77kWh/day., and now your numbers do
not sound so unreasonable. This might be the problem.
If it is, I think I might want to slap the pool guy on the side of the head
or make him pay my electric bill. Just this pump (77kWh/day) would be about
a $00 monthly bill here in LA on Edison rates.
Posted by sffogy on April 26, 2008, 6:36 pm
Hi Doug, I hope it's not too late to join this thread, I have a few
1. 9,559 kWh generated in one year with a 6 kW system, that's almost
1,600 kWh per year per kW system. That's good, almost too good. How,
exactly, did you measure the 9,559 kWh output? The picture of the
meter online says 99546 kWh, is that the meter you used to measure
2. Regarding paying itself back in seven years: if you pay 25 cents
a kilowatt hour, then you generated $00 of electricity per year per
kilowatt system. The system might cost $,000 per kilowatt. It
would take 15 years to generate $,000 of electricity. If you include
the fact that there is a cost to the upfront money, say an interest
rate of 4%, then it would take more than 20 years to pay back your
Posted by old dirtbeard on April 27, 2008, 7:57 pm
Yes, I am just going by the meter on the SMA 6000U inverter -- it now is
sitting at 11,077 kWh. It has apparent face validity when I compare it to
the Edison meter and my previous electrical consumption.
As far as it being too high, I suppose it could be wrong -- it showed that
we generated over 38kWh/day the last couple days. The highest daily output I
have seen was a little over 40 kWh/day. We are about 1,000 feet above sea
level on a hill near the ocean, so we get cool breezes which I suppose help
to keep the panel temperatures lower.
How much would you expect to generate from a 6kW system?
I think your estimates look very accurate, but due to incentives in effect
at the time I purchased it (almost a year before we installed it), it
dropped the upfront costs dramatically. California has since scaled-back
the incentive programs considerably.
I did not incorporate lost interest earnings on the cash outlay, but we were
paying $00-$50/mo. electric bills. Here in SoCal, Edison has tiered rates
starting at $.12/kWh for the first 10 kWh/day, and then dramatically jumps
them in tiers. With a swimming pool pump, koi pond pumps, and a 5 ton AC, we
would be in the 200% over baseline rates for much of the year where the
combined generation and delivery costs are around $.40 kWh.
So for me, with about a 40% upfront rebate, and additional tax deductions,
combined with the "privilege" of paying insane electrical rates, it will pay
for itself in seven years assuming no rate increases (rate increases already
have been announced).
If one did not receive significant installation rebates/incentives, and
could stay within the monthly baseline rates, I agree with you that it
probably would take closer to 20 years to break even.
Because of the tiered pricing here, for a quicker ROI, a "smart person" who
is in the top tier rates could just install enough PV capacity to replace
watts at the highest rate tiers and then gladly pay the $.12 kWh baseline
rate.Given the price of PV installation, it would be hard to cost justify if
one can operate at baseline usage levels.
Posted by Bob on April 28, 2008, 4:07 am
Actually, I asked if you were using the meter in the online picture
showing 99546 kWh -- that's the GE Itron I-210 meter
online says that the Itron I-210 meter can be used to measure energy
received, delivered, or net, but I'm not sure if the consumer can do
that or only the utility company. At the moment your picture was
taken, the meter shows an arrow in the "received" direction, but I'm
assuming that the number 99,456 kWh is net power delivered to you
since the meter was installed (ten years ago?). By Edison meter, you
mean the GE Itron meter, I assume.
But you say you are using the meter on the SMA 6000U inverter. I see
from the specs that it scrolls through 4 messages, with the 4th
message being accumulated yield in kWh and total operating hours.
I don't find any comment in the specs about accuracy of the kWh
reading, + or - 5% for example.
For insolation, I've been using the NREL NSRDB figures
because they match the average of the 11 SFPUC solar monitoring
stations in San Francisco, where I live. No stations for Palos Verdes
-- the closest station is Long Beach. If you click on Long Beach in
the link I just gave, there are links for the raw data, but it says
"No statistics files are available for this site." Very annoying,
they have removed the link sometime in the last few months and I don't
know why, I will get around to asking them. But the statistics file
_is_ still there
MO 13, AVGLO, Long Beach averages 4.90 kWh insolation per day per m2.
Your system is reported to get 9,559 kWh/yr = 1,593 kWh/yr per kW
system = 4.36 kWh/d per kW system. Performance ration = 4.36/4.90 =
89% That's amazing. I can show you systems that have a performance
ratio of less than 70%; 75-80% would be excellent. Maybe your
insolation in Palos Verdes is more than 4.90 kWh/d/m2. Or your output
reading is too high. The instantaneous reading in the picture of your
inverter, 5,207 Watts, is also high for a 6 kW system, it must have
been very sunny. Possibly the kW output figure could be checked, but
I'm not an electrician and I don't want to be responsible for burning
down your house, or even your garage :)
$.40 per kWh is your marginal rate, isn't it? Your overall rate per
kWh would be lower (maybe about $.25 per kWh?)