Sizing a System

[PerfectReign]

I live in Southern California. I'm comparing bids from a few different sources. I've given up on the lease idea. (You can see my other thread.)

The next question is size.

Two of the quotes I have are for 3 Kw systems. (I believe both use CEC-AC as the reference.)

MrSolar at least mentioned I should get a 6Kw system. I don't know the cost from these suppliers as yet. (I did get a cost from mrsolar.com for $24,000 plus hardware plus installation for a 6.5 Kw system.)

I noticed that sungevity did put an estimate of the array on my SE-facing roof.




Now, with that being a 3.5 Kw system, would I have room for a 6 Kw system?

Also, I looked at my August electric bill. I get a baseline usage of 403 kWh for the month. From there, I pay at various tiered rates. Tier IV is at $0.18/kWh. I spent 323 kWh at that rate in August. (My total for August was 1,129 kWh.)

Would I then want at least a 400 Kw system to get rid of that tier IV? Not sure how they compare...

[PerfectReign]

Answering at least part of my own question...

I had also contacted Cooler Planet. They have a generic calculator here: http://solar.coolerplanet.com/Articl...alculator.aspx (It is on a wintendo server but will work in Firefox.)

I did a quick sizing and was told that - to remove 50% of my utility bill - I'd need a 3.8 kW system taking up 380 sq ft.

I'll keep looking...

[russ]

I suggest you try PV Watts2 at www.pvwatts.org

I don't have your zip code so didn't run your situation. Google earth is misbehaving for me so I have no idea where Diamond Bar, CA is.

PV Watts is from NREL - a bit more complex than the cooler planet one though that calculator is also from NREL and PV Watts - cooler planet linked their site to the calculator. They should have mentioned that point.

The figure cooler planet provides for solar radiance is meaningless as that amount is available for a few minutes per day.

For a 4.0 kW system, PV Watts1 gives 5800 Kwh annually for Bakersfield and 6800 for Dagget - while 6600 would be 50% of your bill. PV Watts1 only allows whole numbers - no decimals it seems

[Mike90250]

From the photo, it looks like they allowed enough space around the stuff on the roof that can cast shadows.
No South or SW areas ? Bummer. SE won't help the hot afternoon offsets as much.

[PerfectReign]

Thank you all. I kad looked at pvwatts for the different power ratings an immolation.


I wasn't sure how to use it for physical size of any system.

The house is SE facing. I have a small area on the garage that is SW facing, but not sure what can go there.

[Mike90250]

Now, with that being a 3.5 Kw system, would I have room for a 6 Kw system?

See if you can fill your SW garage roof with PV. use 2 inverters, one for each direction. Also, run the numbers for both SW and SE. I have a N/S ridgeline, and had a choice, east faceing, or west. West worked out better for me, avoids the morning marine layer.
In Florida, East is better, because it avoids afternoon storm clouds and power sag from heat.

[russ]

Most (if not all) of the simple estimators make a very rough calculation assuming some arbitrary inclination and orientation based on a generic setting for your approximate location. May or may not have much to do with reality - could be either high or low.

Like Mike pointed out, your garage roof might support enough panels to capture a good bit of the afternoon sun. From the photo (it appears it was taken in the morning) your garage roof may well be a good location for as many panels as there are room for.

Directly facing the sun is best as in a tracker unit but not by all that much. Units facing east or west produce well also - a couple of more panels and all is equal or close to it.

Questions:
1) What is your zip code? Maybe I can chase this a bit more
2) Do you have net metering
3) What is your peak electric rate?

Russ

[PerfectReign]

Again, thanks all.

I have several bids going now. I'm reviewing them all.

Who knows, maybe I'll have a main inverter installed by a contractor and then see about a DIY for a second unit on the garage. (Just thinking out loud...)

In any case, I'm at 91765. That's about 30 miles east of Los Angeles and 15 miles north of Disneyland.

PVWatts gave me this rating for a 4.2 watt system and they gave me this estimate for a 6.0 watt system.

I have tiered pricing. I get a base amount of 403 kWh. I then pay tiers up from there. Tier 4 is at $0.18 per kWh and that's what I'd love to get rid of. I'd love to get out of tier 3 ($0.15/kWh) as well.

Here's the detail of my September bill, in case anyone is interested.

[russ]

Here is a comparison of different orientations E, SE, S, SW, W and potential kW production.

http://www.readysolar.com/uploads/So...s-june2010.pdf

[Mike90250]

Beware. When you change over, your billing plan may change to a time of day, and tiers.
AFAIK, the new ToD plan, extends peak hour to 9pm, well past sunset, and your SE panels may not shave anything off that portion. 2pm-9pm SCE added this late hour to screw PV adopters.

[russ]

The output from PV Watts 2 - This assumes south facing optimum orientation. For your SE and possibly partially SW orientations there would be a small penalty as suggested in the last post I made.

"PVWATTS v.2: AC Energy and Cost Savings"

"Station Identification"
"Cell ID:","0175361"
"State:","California"
"Lat (deg N):", 33.93
"Long (deg W):", -118.40
"PV System Specifications"
"DC Rating:"," 6.0 kW"
"DC to AC Derate Factor:"," 0.770"
"AC Rating:"," 4.6 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 34.1"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","20.0 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.59, 620, 124.00
2, 5.11, 624, 124.80
3, 5.70, 765, 153.00
4, 6.11, 779, 155.80
5, 6.38, 836, 167.20
6, 6.77, 840, 168.00
7, 6.78, 856, 171.20
8, 6.90, 870, 174.00
9, 6.31, 773, 154.60
10, 5.56, 722, 144.40
11, 5.07, 654, 130.80
12, 4.37, 587, 117.40
"Year", 5.81, 8926, 1785.20

So a 6 kW DC fixed array would give you from 587 to 856 kWh/month - an annual total of 8926 kWh or monthly average of 744 kWh.

Possibly you have 10% less due to the 'off south' orientation.

As Mike suggested, it would be good to try to learn the billing method you will have to live with. May not change anything but it is nice to know rather than be surprised.

[PerfectReign]

Yuck! Time of Day AND tiers??

Okay, thank you both.

I'm going to do some calling.

[PerfectReign]

Actually, time of use doesn't sound that bad.


I just got a quote last night for a 6.5 kW system with Kyocera units from One Block Off Grid.

I now have three quotes. I missed an appointment for one so am waiting on that to come in.

With HELOC rates really low right now (I have about $300,000 in equity in my house.) I can see easily paying for a bigger system and still having way lower overall costs.

I just looked into NG-powered fuel cells. That doesn't seem to be a viable option for me, as I have an electricity bill of less than $500/month.

Onward!

[russ]

Here is a URL for a calculator Sharp USA provides. You enter your zip code, electric bill amount and click go. It allows you to adjust direction, tilt, costs and other factors. It automatically enters rebates/incentives and adjusts the system cost. It allows you to enter the type of rate you have.

http://sharpusa.cleanpowerestimator.com/sharpusa.htm

With a 6.5 kW system at 7 USD/watt it gives a 11 year payback
With a 10 kW system at 7 USD/watt it gives a 12 year payback

All in all a good calculator and a good deal for you it seems.

[PerfectReign]

Nice calculator.

I punched in some numbers - 6.5kW and the rates. (I'm looking at a net system cost after taxes of $22,000 right now.)

It gives me a 10 year payback.

Hmmm.....