getting Solar evaluated...need some guidance

[slopoke]

ok, I'm going to call a couple other places tomorrow and get some more info. I have a feeling I'm going to get some seriously different numbers. I really have to thank all you guys for your help with this. This is NOT easy to navigate. You've all been a huge help!!

I got all of the info on this forum to get an idea on what is an acceptable price for me to pay here in California. It's a great resource. This forum has a lot of California residents and the benefit we have is that we have access to thousands of California solar systems installed in Ca. Not only can we see the size of the system but we can also see the installer, size, price paid, what panels and inverters, plus a whole lot of other info in Excel format. Big tool when it comes to negotiating prices. Go to the link below and download the "raw data set" and you'll get an idea of prices. Good luck.

http://www.californiasolarstatistics.ca.gov/current_data_files/

[jlatenight]

ok, I'm going to call a couple other places tomorrow and get some more info. I have a feeling I'm going to get some seriously different numbers. I really have to thank all you guys for your help with this. This is NOT easy to navigate. You've all been a huge help!!

[slopoke]

Uh oh...is it possible there's inherently that big a difference in the price of a system between CA and MA?

I don't think so, materials costs are the same and depending on where you live, the labor costs might be lower, I doubt higher. I live in the San Francisco Bay Area and our labor costs are not low.

[slopoke]

I might not have calculated it right. My last bill was $123.29, so I divided by 704kwh, the total I used. For the first $600 I pay .035 and .042 above that which was only $4.37, so I didn't think the difference was worth calculating.

Your numbers don't add up. You say you pay ".035 for the first 600 kW hours, then .042 above that. 600 x .035 = 21 and 104 x .042 = 4.37 for a total of $25.37.

[jlatenight]

Holy poop!! You need to run away from this person. He's selling you a system for $7.05 a watt. Totally unacceptable. I paid $3.85 per watt BEFORE incentives and I'm about 30 to 40 cents higher than others with similar equipment. But I live in N. CA and we typically have been paying more than the folks in S.CA.

Uh oh...is it possible there's inherently that big a difference in the price of a system between CA and MA?

[jlatenight]

So in your previous post you stated you pay ".18 cents per kW hour". Is that the average of the tiers you go into or is .18 cents tier one only. Makes a big difference on the money numbers side.

I might not have calculated it right. My last bill was $123.29, so I divided by 704kwh, the total I used. For the first $600 I pay .035 and .042 above that which was only $4.37, so I didn't think the difference was worth calculating.

[slopoke]

He didn't say I'd be going positive on production, he said I'd still get an electric bill but it would be much less. Here's the actual worksheet he gave me. See if makes any sense to you.

Holy poop!! You need to run away from this person. He's selling you a system for $7.05 a watt. Totally unacceptable. I paid $3.85 per watt BEFORE incentives and I'm about 30 to 40 cents higher than others with similar equipment. But I live in N. CA and we typically have been paying more than the folks in S.CA.

[jlatenight]

I would be very weary of the installer if he said you would be going positive when you will not. Big RED FLAG in my book.

He didn't say I'd be going positive on production, he said I'd still get an electric bill but it would be much less. Here's the actual worksheet he gave me. See if makes any sense to you.

[slopoke]

YEs, I saw your post, thanks! yes I'm aware that I'll still be pulling from the grid, but obviously much less. Plus MA has tiered pricing certain amount for up to 600kwh and then higher after which I always exceed.

So in your previous post you stated you pay ".18 cents per kW hour". Is that the average of the tiers you go into or is .18 cents tier one only. Makes a big difference on the money numbers side.

[jlatenight]

If you did not read my post on the previous page, even if you get the numbers he quoted you for production, you will still be paying for electricity, because your usage exceeds the production.

YEs, I saw your post, thanks! yes I'm aware that I'll still be pulling from the grid, but obviously much less. Plus MA has tiered pricing certain amount for up to 600kwh and then higher after which I always exceed.

[jlatenight]

I'm told the guy that came to do the assessment (not the same guy that presented the findings this afternoon) used some expensive piece of equipment (he said the name but I forget) that has historical weather data for 100 yrs or something and he put it in the four corners of the roof and took readings. They showed me pictures that it took showing where the sun would shine from each spot. Seems very legit, but who the hell knows?? Now you guys have me thoroughly spooked, which I'm very thankful for. I'm tempted to just post all the info he gave me for you guys to assess.

[slopoke]

Yeah I used .77. I reran it again w/ .83 and got 6447...better but still 673 less than he said. Should I be concerned or is that just the margin of error?

If you did not read my post on the previous page, even if you get the numbers he quoted you for production, you will still be paying for electricity, because your usage exceeds the production.

[pleppik]

Yeah I used .77. I reran it again w/ .83 and got 6447...better but still 673 less than he said. Should I be concerned or is that just the margin of error?

In my case, I managed to get within 1% or so. My installer gave me all the parameters he used, and stepped me through the whole thing and explained why he used the values he did.

The thing is, there are a ton of different ways your actual production is likely to be below the optimum. PVWatts generally defaults to a nearly optimal configuration, so if your installer is telling you to expect 10% more power than PVWatts, there's some assumption your installer is using which is significantly higher than the PVWatts assumption. Until you get a good explanation for this, it's safer to assume that PVWatts is closer to the truth.

Your installer is (or should be) using base data for available solar resource which is nearly identical to the base data in PVWatts, so there's no room for differences in the basic amount of sun available.

Any differences between the two have to be attributable to:

• Orientation of the array (I sure hope you got the right azimuth and elevation from the installer!)
• Shading (lots of room for differences here)
• Efficiency of the electronics, wiring, etc.

So assuming that you are using the same numbers for the orientation, a 10% difference between your estimates can only be explained by either (a) not using a realistic shading factor, or (b) assuming a lot more efficient wiring and electronics.

You should ask for these numbers. Specifically, ask what he used for a shading factor, and what the assumptions for the system efficiency are. And tell us what he tells you. People here can tell you if those numbers make sense.

[Ian S]

Yeah I used .77. I reran it again w/ .83 and got 6447...better but still 673 less than he said. Should I be concerned or is that just the margin of error?

My PV Watts calculation seems to work better with 0.85 derate but YMMV. Since you have no cost upfront, this must be a lease right? If so, then they usually guarantee some level of production. Is that the production number he quoted?

[jlatenight]

What was the derate factor that you used?
Default will always come in very low
Average derate is about .83 Default is .77

Yeah I used .77. I reran it again w/ .83 and got 6447...better but still 673 less than he said. Should I be concerned or is that just the margin of error?