I'm back ... where is roof mount pricing nowadays in San Diego area

Here is a recap I did a short while ago about sizing a basic roof top config

Finding the power of the solar array you need to cover your desired electricity production:

• Deciding how much electricity you want to produce per year:
  • Get your last year total kWh consumption from your provider (if they give you access) or sort through your last 12 monthly electricity bills.

• Decide if you want to cover all of it with your panels, or more or less.

• Finding your roof orientation and pitch:
  • Go on Google maps where your house is
  • Switch to satellite view so you can clearly see the picture of your roof, and see what roof sides face south or are the closest to south.
  • Estimate the approximate orientation angle of the most south facing roof side(s). A south facing roof is oriented 180 deg from north. If you don't have a pure south side but have both a south east and a south west, estimate angle for both.
  • Estimate the pitch of your roof which is the angle between horizontal and your roof slope (between 0 /horizontal and 90degre/vertical). An average low pitch is 20 degrees.
• Figuring the production capacity of your roof:
  • Go to the PVwatts site: https://pvwatts.nrel.gov/
  • Enter your complete address and hit GO
  • Once location found, click "Go to System info" on the Top right
  • In DC system size, put 5 (kW)
  • Module type: Premium
  • In Tilt deg: enter your estimated roof pitch estimated above
  • In Azimuth deg: Enter the estimated orientation of your roof side that is the closest to south facing (180 deg) use the side closest to south
  • Click Go to PVWatts results at the top right
  • Check the Annual Energy for the AC Energy (kWh) Column
  • Compare that to what you wanted to cover (ie 9000 kWh)
  • If it is too low or too high, click "Go to System" Info at the top left to go back to the previous page, and change the DC system size to try and get closer to the proper production.
  • Do the back and forth until you get the annual kWh production you want. Or do the math. ie: if 5kW array produces 8000kWh per year and you need 9000kWh, the array you need is 5 x (9000/8000) = 5.625 kW
  • Now you know the Power of the solar Array your need which is the DC system size, Like for example 5.625 kW

Finding approximately how many Panels you will need

• Use the Array DC power calculated above like 5.625 kW or 5625W and divide by an individual solar panel power. Panels exist in many different power like roughly between 280W to 350W. The more power per panel (high efficiency panel), usually the more expensive per watt.
• If you have a lot of unobstructed roof surface, you can choose lower power panels as they are cheaper per watt
• If you don't have a lot of unobstructed roof surface, you may need to use higher power panel, so you need less panels to match your required array power.
• For example, reaching 5625W would require 20 x 280W panels, or 19 x 300W panels, or 16 x 350W panels.
• If you cannot reach your needed array power with one roof side, you may need to consider several arrays on different roof sides. You can use PVwatts site to figure out the production capacity of each roof orientation. Ultimately, drawing the exact size of each roof area and checking how many panels they can hold will be required. A complicating factor is that the fire code in your area may require a certain space to be left free for firemen in case of a fire.

Full posts below
https://www.solarpaneltalk.com/forum...530#post393530

There are many other things, some that apply here.

Ground or roof mount?
Any snow considerations?
Any seasonal tilt changes?
Is it sized for something different than past consumption?

Bruce Roe

No snow, roof mount.

I will probably size new house the same, roughly 8kW DC. It looks like any size is a guess as new house consumption is unknown.

I'm still left wondering what pricing I should be expecting here in 2019. Perhaps JPM will chime in -- we will be less than five miles apart as the crow flies.

Charlie: Welcome back. i was wondering how things were going.

On Pricing: If anything, my sense is pricing has dropped a bit since 2017, but maybe not much, or not as much as the cost effectiveness of PV has dropped as nongrandfathered NEM 2.0 T.O.U. rates have dented PV cost effectiveness (~ 20-25 %). Also, Seems to me the differential between S.P and other quality stuff may have decreased a bit, meaning the S.P. premium might be down to 10-20% with some sharp negotiating instead of the 20+% it was. FWIW, and IMO only, and not an endorsement, around here, Baker, Sullivan and Milholland are still the best chance for a quality job. Seems to me Sullivan's the highest in price of the 3, Milholland's the lowest. Milholland's the most amenable to negotiation, especially if you know what size you want. Baker and Sullivan less so on negotiating. If you call them, or any vendor, don't use my name. All the vendors will add a whore's finder fee of ~ $500 thinking I'll come snooping around their door (I don't and won't) and that'll wind up in your price in ways you'll never see or find.

On an estimate for electrical usage: You will, or ought to have/get an estimate of hourly building heat loss/gain with the Title 24 requirements form the builder. That's pretty useful for estimating HVAC loads. If you're heating with propane or nat. gas, I expect you're concerned more about how your A/C and other electrical loads will be different than the old home than you are about heating loads ?

I'd suggest that overall, your non HVAC electrical loads will be similar to what they are now, maybe a bit less, provided you're heating water the same way as the old house.

The title 24 requirements will lower the HVAC load a noticeable amount from what they are for the old house, maybe by a third or more if the dwellings are similar in size, and more if the HVAC in the old house is as old as you say, and /or if the new house is significantly smaller than the old house, and/or if the new house has any passive solar features.

I'm pretty sure I can see where you are building from my kitchen , unless you're on a north facing slope or in a bunch of trees. I can easily and clearly see the Blackinton airport as I'm just about directly south of it ~ 2 1/2 miles from the south end of the runway.

Anyway, if you have the hourly building heat gain/loss for the new dwelling from the Title 24 calcs, or can do a heat loss/gain on your own, I've got daily history of a lot of temp. and weather variables and a boatload of other stuff for every day since 10/10/2007. I bet your local climate isn't and won't be much different than mine. Probably the easiest to understand and perhaps the most useful for what you may have use of it for, is the daily high/low/ 24 hr. average. I've got other stuff, including all the rest of the weather variables in 1 minute increments, but that gets a bit cumbersome to handle. All of it's on spreadsheets.

If you get the heat loss calcs, the daily temp. records, using those with what I can provide in the way of daily temp. records can give you something maybe a bit better than a dart through for an A/C sensible load by subtracting the outside ave. daily temp. from the ave. indoor temp. you want to maintain and multiplying that diff. by (24*hourly building heat loss per deg.) Add 20-25 % to that sensible load for an est. of the latent (condensing) load and you'll have a guesstimate of the A/C load for the new house for that day. Add all such results for days with a cooling load and you'll have an estimate of the annual A/C load. Then size the A/C equipment according to standard residential HVAC practice. (Note - and a bit off topic: Do not oversize A/C equipment. That's a fool's errand and the wrong way to do it. Bigger is worse for A/C as it can make a dwelling clammy and uncomfortable from short cycling times that don't get rid of the moisture as efficiently.) From all that, and the electrical draw of the equipment, you'll get the annual kWh load of the A/C.

Bottom line: I've got daily temp. data that's probably representative of your site. Yours for the asking. I drive on Old Castle rd., regularly. Holler back with a way to get together if you want a disk.

Regards,

J.P.M.

Add: Thinking about this overnight while roaming the halls, FWIW, I didn't get my weather station until 10/2013. Since my station is on the roof about 4 ft. north of my array C.L., and at an elevation ~ 7" above the north edge of the array, the temps. it reports are not representative of what the house sees or what's needed for HVAC work. So, all the weather data I use for HVAC work/calcs re dwelling HVAC loads since 10/10/2007 is based on data from the Weatheunderground station in Hidden Meadows. To keep consistency, I've kept using that data as a reference point. Therefore, you can easily ref. the same raw data that I can provide for historical weather. There is also a weatherunderground station a bit west of your new home site, although it looks like their pyranometer data has a problem.

Charlie: See my latest epistle. Hope it doesn't make you gun shy about what you ask for

BTW, if you want to, give me your array orientation and I'll give you a pretty close estimate (+/- the faguaries of residential PV modeling and using PVWatts) of how much revenue it will produce per installed STC kW that can be used to offset an electric bill based on latest SDG & E rates for DR-SES schedule under NEM 2.0 for either grandfathered or nongrandfathered rates.

Tesla's price is $2.8 a watt. Just go on their website and they now have a fixed price for their installations.

That from someone who calls moderators liars, can't or at least declines to backup opinions with details or reasons for those opinions, and appears to be a fanboy for Tesla/SolarCity.

Just google "Tesla and solar panels" and you will get a quote from Tesla. There a number of news articles of Tesla/Solarcity offering fixed prices. Charlie is here to get information of solar panel pricing, just trying to help.

I think Charlie's been here and around the block enough to be able to make his own judgements about Musk and his ponzi scheme, house of cards games.

Thanks for all the replies.

Given that at my new house I have zero shading, I'm likely going to go with string inverter technology. I've got a quote from a quality installer for Anitec AXIblackpremium 300 watt modules (15 year manufacture's warranty, 0-5 watt positive power tolerance, 15 year 90% manufacture performance guarantee, 85% @ 25 years), Fronius Primo 8.2-1 inverter, installed using Everest Solar rack system.

$2.59 a watt vs the $3.65 SunPower / SolarEdge system. But I'll give the other installer an opportunity to see where he can come in for a string inverter based system.

Given my roof area supports either 5 rows of 6 columns landscape or 4 rows of 7 columns portrait, for $2.59 a watt I'd likely go 28 panels @ 4 x 7 portrait for 8.4 Kw DC.

Given the less favorable peak TOD structure I'd be subject to, at the $2.59 pre-tax credit, I'll opt in for a larger system.

JPM, you probably can see my house. I'm about 1/2 mile due west of the runway (maybe 2/3 towards the northern end), west facing.

As to downsizing, epic failure. Large house, larger garage, new workshop.

Title 24 didn't really help tell me what my cooling load will be, It definitely dictates tightness, insulation, window solar gain, etc. I only committed to a 3 kW DC system, as this got me to the "green build" threshold that netted priority going through the permit process and about a whole $500 building permit fee reduction. And it isn't the building fees that are the worst, it's all the impact fees.

But, it's going to be a great house and is worth some pain of building.

Thank you. Understood. I'd call getting what I want a success, but not my call. If you got what you want, it probably ain't a failure.

As for heat gain per hour per degree of delta T, for sensible heat gain, it's a somewhat simple matter to calc. transmission losses off the drawings and insulation data. For infiltration gain, I've found using about 1/2 air change/hr. for new and decently detailed envelope sealing seems a reasonably close approx. of reality. For latent (condensing) loads, for this area, I add about 20 % to the calc'd sensible heat gain. Then I add 10 % to the total for the hourly heat gain. Again, don't oversize the A/C. It'll already be oversized using std. sizing methods, depending on how high you set your thermostat. The higher the setting, the more often you'll have excess system capacity. Variable capacity systems help a lot by making lower hourly system cooling capacities possible. That will help with interior humidity control.

House is west facing. How about the array orientation, az. & tilt ? I can at least get you a decent SWAG for the offset revenue the array will produce if using PVWatts data.

An example: Since we're almost neighbors, as long as the array is not oversized in terms of annual output vs. annual use, at 270 az. and 20 deg. tilt, the array will produce ~ $440/yr per installed STC kW using PVWatts modeled hourly output and latest SDG & E DR- SES schedule rates. The array will produce something like 1,544 kWh/yr. per installed STC kW (~ 12,970 for an 8.4 kw array) per the PVWatts model at that orientation, at an average rate of $0.286/kWh generated.

You then get to spend that revenue on an electric bill.

For the example above: Spend it all at off peak pricing hours and the revenue will offset ~~ ($440 kWh/yr.)*(8.4kW)/($0.279/kWh)= 13,247 kWh/yr. (and as you will remember from prior stuff you, I and Sensij hashed out a couple of years ago, more than your system will generate using the PVWatts model), but as you also know, NBC will affect all of that power that's imported and the $120/yr. min. will always apply.

If, at the other extreme, all your usage is at peak pricing hours, and the same usage each day of a 365 day year, your average/blended cost/kWh at peak pricing times over a year would be ~ $0.3788/kWh and your generation revenue would offset ~~ ($440 kWh/yr.)*(8.4 kW)/($0.3788/kWh) = 9,778 kWh/yr. with NBC and min. annual charges still applying, and you'll be billed for (whatever your annual usage is - 9778 kWh) * $0.3788 +/- some for NBC and min. billing adjustments & taxes, etc.

Obviously, your use patterns will be different than the two extremes of all off peak or all on peak, and the actual use will be different. This is no more than a way to see how usage patterns under T.O.U. can give the user some control over the size of their electric bills.

If your usage is less than you generate in any year, the system generation kWh will be the same (at least as far as the PVWatts model is used), but the system "revenue" will drop because all the "revenue" is assumed to have the same value as SDG & E's per kWh NEM pricing value only when it is used against usage. Excess system generation will then have a value only of the excess generation compensation paid by SDG & E of ~ $0.045 at this time. When that $0.045/kWh is rolled into the average "value" of system revenue that value will be lowered just like putting cold water into a bathtub full of warmer water will lower the temp. of all the water. The comparatively small excess generation reimbursement rate will chew into and lower all the per kWh bill offset rates.

That's another way to look at the effect system oversizing has on residential PV cost effectiveness.

As for the $440/yr./STC kW *8.4 kW = $3,696 annual revenue, to the degree it's a reasonably accurate number, it can be compared to your system cost of (8,400 STC W)*($2.59/STC W)*(0.7) = $15,229 for some feel for system cost effectiveness. An ~ 4.1 yr. payback, even with the non grandfathered NEM 2.0 DR-SES rates and times as exampled above is probably low enough to maybe start thinking about not worrying as much about the time value of money when analyzing the cost effectiveness of a residential PV system.

Take what you may want of the above. Scrap the rest.

The detached garage roof solar is on faces southwest, more or less about 235 az. Roof is 4 in 12, so unless tilt will be 18.43 degrees.

Had a longer response but got destroyed by degree symbol. I'll post again later.

Redoing my example #'s for 235 deg. az. and 18 deg. tilt., the offset revenue per STC kW at that orientation goes to ~ $470/yr. per STC kW, up from the $440/yr. per STC kW revenue offset for the 270 deg. az., 20 deg. tilt.

Add:
Annual generation from the PVWatts model goes to ~ 1,673 kWh/yr., up from 1,544 kWh/yr. per STC kW.
Ave.offset revenue/kWh goes to ~ $0.2819/kWh, down a bit from $0.286/kWh. That's the red herring POCOs try to pull off and some folks don't see through. The product of the (annual generation)* (ave. value per kWh generated) = what counts.