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Posted by Eeyore on January 4, 2009, 2:50 am

dold@83.usenet.us.com wrote:

Might have hit the nail on the head there. What kind of payback period would
that give (including cost of finance) ?


Posted by dold on January 4, 2009, 7:59 am

PVWatts says London would see 5140 kWh per annum with 6500 Watts DC.
That would cut the value of PV to half the value of a Chico installation,
in terms of energy provided.  Energy rates, buyback arrangements with the
local grid supplier, and rebates and incentives would have a big impact as

Dropping the retail cost of $2,000 to $9,000 helps.  Producing twice as
much energy in Chico as London helps.  We don't know if $400 is the right
number for our OP, but if it is, the Kyocera calculator also shows charts
for a 25 year 8% loan with no down payment.

In year one, $0 loss per month.  $24 loan payment, $6 electric avoided,
$7 tax allowance on the loan, $-62 cash flow per month with PV.  At the
ten year point, it still shows a $-42 cash flow, but I don't think they are
correct in their analysis of the rate of the rise in electric rates in
PG&E territory, nor the impact of the tiered rate structure.

Some of that might because I just accepted all of the defaults.  I see that
the annual electric bill in the sample is $.  That's not good.  You can't
get credit, so you want to avoid going below zero.  My system was sized to
be an annual bill of about $00.  There are also some monthly minimums, so
a $00 annual bill is a good number.  

My three year old system is avoiding more PG&E costs than the monthly
payment on a 20 year loan, not counting the tax allowance on a home
loan in the US.  I have been remiss in tracking this years savings on my
web site, last updated right after last years annual settlement with PG&E.

For 2007, my system avoided $705 in PG&E charges, based on the total
energy I used, verses what I would have paid without PV at current rates.
Each month, I rate my "avoided costs", by taking my PG&E billing and
calculating the total energy at current "E1" tiered rates.  In the process
of doing that, I find what I call my "solar rate", which averaged $.234 in
2007, $.3146 in July.  My payback could be based on those values.

2007: $42 per month avoided PG&E costs.  
$0,000 @ 6.125 * 20yr fixed loan == 144.73/month
The interest is tax deductible.  

The Kyocera calculator has a default of 3% for the rise of utility rates.
http://spgsolar.com/residential/costs.html  has a graph of the tiered rates
in my area.  High energy users, like A/C, fall into higher rate categories
for usage over a baseline amount.  The low tiers have held steady since
2001, but the higher tiers have risen more than 3% per annum.

From Jan 08 to Oct 08, the increase was 0% for Tier 1 and 2, but 12%, 16%,
and 18% for the upper tiers.  The "average" rate supplied by PG&E was
$.17/kWh at the end of 2008, an increase of 6% from the start of the year.
If I put 6% annual increase into the Kyocera calculator, year 10 becomes
breakeven.  It isn't convenient to use this calculator to plot when the ROI
occurs, because it only shows one year at a time.

I have cobbled together analysis from my own observations, and web sites.
I was impressed with the thoroughness of the proposal prepared by my
installer.  His numbers seem to be holding true, and even a little

If you don't get an estimate from an installer that seems reasonable and
full, then you should find another installer.  If you find a reasonable
quote that is not financially attractive, that's unfortunate.

I recently received a one page proposal sheet from an installer for a solar
water heater and geothermal heat pump.  It was like a sales sheet for
building a fence.  No cost/benefit, no ROI, no projections, just cost, on
one line, with no workup of incentives or rebates.  And it was an entirely
different system than what we discussed, because he had gone to a seminar
and found the new perfect system.  I'm not interested in doing business
with him.

Clarence A Dold - Hidden Valley Lake, CA, USA  GPS: 38.8,-122.5

Posted by dold on January 12, 2009, 7:09 pm
 dold@83.usenet.us.com wrote:

I have updated my solar yield web page to include 2008.
$775 avoided in 2008, $47.88 per month.  
$1935.73 @ 6.125 * 20yr fixed load == 159.09/month

With the interest on the loan being deductible from income taxes, my solar
PV installation is cash flow positive.  

Clarence A Dold - Hidden Valley Lake, CA, USA  GPS: 38.8,-122.5

Posted by john on January 4, 2009, 5:07 pm
 There are some serious bugs in that calculator.  I have gotten different
power output from the same size PV array depending on annual electricity
budget, tax status, and/or income level (these affect payback, not power
output.  All other variables were constant.)  The bug also seems to vary
by zip code.


dold@83.usenet.us.com wrote:

Posted by dold on January 2, 2009, 2:10 am
 ashleyestep@msn.com wrote:

(Eeyore is in some foggy location and has nothing good to say about any PV
installation or installer.)

Do you mean Sun Power Geo?  That was my installer.

I see 97 installations with PG&E rebates in Chico.  7 of them use Sunpower
brand panels.  My installer, SPGsolar, did 16 of them.

9059 is probably the KW peak DC rating, not kwh, unless that's the estimate
of how many kWh you would produce in a year.  9059/2735 watts per panel.
9059kwh per year is about 1/3 more than my 4500    MaxWatts DC system, 3.783
CEC Rated KW AC system delivered in Northern California in 2007.

You would need to provide better transcription of the estimate to draw any
conclusions.  What is the CEC rating?  What was your electrical usage last
year?  You can download past bills from PGE.com to help build your
proposal.  The system should have been sized for 10 year ROI.

I have a several page booklet with charts and graphs of my previous PG&E
usage and projected solar benefit, in the SPGSolar proposal.

You casually mention "less rebates', but that can be 1/3 of the total.

Northern California, especially Chico, should be an excellent place to
install a PV system.  The rebates are good, the weather is good, you
probably have A/C on a PG&E tiered billing system, and 10 years might be a
conservative estimate of payback.  My system is cash flow positive by
comparison of PG&E costs avoided to a 20 year loan payment, so I think I am
ahead of the game almost from the start.


Account Activities
Completed Systems, 1998 to Present
This is an Excel sheet that you can sort by zip code or manufacturer, or

Clarence A Dold - Hidden Valley Lake, CA, USA  GPS: 38.8,-122.5

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