Install in San Diego questions

[bmms8]

I think it's safe to say we should stick to a bigger unit?

i won't change my usage in fact it'll go up. Paying $15 or $30 per month won't bother me. Bottom line I'll be recovering within 5 years which I'm fine with

[J.P.M.]

I also wanted to note that most installers quoted me for a 5.7 kw system but one major player offered a 4.4 kw system.

My average is about 734 kw per month and they quoted after solar install:

594 kWh per Month
81% Electrical usage offset
105% Electric Bill offset

Does this seem correct? Thanks

Correct may be too strong a word. Possible ? Yes. Likely ? perhaps not, at least in the 105 % bill offset part.

Not considering whether or not future needs from things like expanded family size or an EV may be in the picture for a minute or two:

734 kWh/month X 12 months/yr. = 8,808 kWh/yr., but a download from SDG & E on actual per month, or better yet, 15 min. increment use would be more representative and useful.
- It's likely that a decently oriented, unshaded system in most of San Diego co. will yield ~ 1,700 kWh/yr. per installed STC kW. That vendor claims ~ (.81) X (8,808 kWh/yr.) /4.4 STC kW) ~ = 1620 kWh/yr./STC kW.
- So, a 100 % offset of 8,808 kWh/yr. = 8,808 kWh/yr./(1,700 kWh/yr./STC kW) ~ 5.2 STC kW.
4.4/5.2 = ~ .85 or so, making the 81% load offset seem reasonable +/- a bit. I think the vendor's a bit light on the estimate in the same fashion I mentioned in a prior post. Run PVWatts, get your own estimates and don't let some vendors take you to the cleaners due to self inflicted ignorance.

As to whether or not a 105% offset of the electric bill is possible takes a bit of understanding about how SDG & E will bill you on a T.O.U. tariff, which sounds like what that vendor is using. How those things work vs. a tiered tariff, and when/how such things interact with daily and hourly use patterns is part of your necessary education.

If on a T.O.U. tariff, it can be helpful to think of a PV system as a revenue generator whose income can be used to offset an electric bill. Getting that estimate is a bit involved, but once done on a spreadsheet, rates and details need only be updated when rates change. Doing it this way, the system revenue can be separated from the bill caused by not only use, but also by use pattern.

For my location (92026) using Miramar MCAS TMY3 data, and using my est. of 1,700 kWh/yr per STC kW, and using current T.O.U. tariff, every STC kW of my system will, under current T.O.U. tariff (DR-SES) produce the equivelant of (or offset) $465 of T.O.U. billed electricity by virtue of when that power is produced (and BTW, not completely NEM due to less than 100 % rate buyback). If your system is oriented similar to mine and close to inland north county, a 4.4 kW system will produce something like (4.4 STC kW) X ($465/yr.* STC kW) ~ $2,046 income/yr., based on (4.4 STC kW) X (1,700 kWh/yr.*STC kW) ~ 7,480 kWh/yr. system output, or 7480/8808 ~ = 85 % use offset.

Now, that $2,046/yr. system revenue can, for all intents and purposes, only be used to offset your electric bill, which under T.O.U. tariff, will vary not only as you use more or less electricity, but also the times of that use. An (unrealistic) example: If you manage to use 8,808 kWh/yr. and all of that is used at off peak rates/times, your approx. average per kWh charge would be ~ $0.22446/kWh and your resulting annual bill would be something like ($0.22446) X (8,808) ~ = $1,977/yr. Or, if you used the same 8,808 kWh/yr. all at peak time (equally distributed over summer peak and winter semi peak, there being no winter peak time), your average annual per kWh rate would be something like ~ $0.37124/kWh. Thus, in the case of all use being at the times of highest rates, an annual bill might look something like: ($0.37124/kWh) X (8,808 kWh/yr.) ~ = $3,270/yr.

The reality is most likely somewhere between those two numbers, depending on your actual use, and actual use patterns.

So, If a vendor is saying a 4.4 STC kW system will off set 105 % of an 8,808 kWh yr. bill on T.O.U. billing tariff, that means, in effect, they are saying (and using my production numbers) ~ $2,046 of revenue will be 105 % of a bill, or the annual bill will be ~ $2,046/1.05 ~ = $1,949/yr.

That means they are also saying that your use pattern (on usage of 8,808 kWh/yr.) is such that it creates an average per kWh billing rate of ($1,949/yr.)/(8,808 kWh/yr.) ~ = $0.22128/kWh.

Based on the above back of the envelope analysis, that per kWh rate of $0.22128 seems a bit low, specially since SDG & E's lowest per kWh rates for the DR-SES (T.O.U) tariff is $0.22171/kWh for winter off peak with the summer off peak being $0.22721/kWh.

So, bottom line: T.O.U tariff can reduce the required (or desired) size of a residential PV system, but only within the context of how much the per kWh rate can be influenced by current or changed use patterns by the user, with that per kWh rate being dependent (to some extent) on when electricity is used.

FWIW, an 80-85 % offset, as counterintuitive as it may seem, may well be a more long term cost effective option than a 100 % offset. That, of course, is an individual decision and based on choice, future plans (EV ?, bigger family ?, pool addition ?, etc.).

One last thing: Excess generation is not cost effective, anything overgenerated in excess of annual use is reimbursed at ~ $0.03/kWh or so. Don't waste tor money.

Unfortunately or not, and absolutely NOMB or actual concern, but my experience is that most folks are both unrealistic about future plans and also, for the most part, completely and willfully ignorant about learning things that help make cost effective choices.

[bmms8]

J.P.M. thank you for the informative post!!

One installer said the say they install is "the bracket comes with a 0 air patented flashing. Then we install a layer of commercial grade henry over the bottom flashing. Then use 3 layers of reinforced fabric and second layor of henry for the bottom flashing. Once it's dried. We will install the second flashing which replaces the entire tile. It is more than 2 flashing. It is the best way of doing this."

Can anyone comment on this method? Is this what Baker or Sullivan would use? Thanks in advance!

[J.P.M.]

J.P.M. thank you for the informative post!!

One installer said the say they install is "the bracket comes with a 0 air patented flashing. Then we install a layer of commercial grade henry over the bottom flashing. Then use 3 layers of reinforced fabric and second layor of henry for the bottom flashing. Once it's dried. We will install the second flashing which replaces the entire tile. It is more than 2 flashing. It is the best way of doing this."

Can anyone comment on this method? Is this what Baker or Sullivan would use? Thanks in advance!

I'm ignorant of what " 0 air patented flashing" is. Without more info, sounds like hype/B.S. to me. I'd get some pictures or literature.

These days Baker seems to be using "Quick mount PV", "Q Base", or tile hooks, or simple post/double flashing around my neighborhood, but everything here is tile - composition roofing is not allowed by the CC & R's. Sullivan seems to be doing about the same, although they haven't put a system in around here in about a year or so.

I'd call and ask both those vendors what they use after I brushed up on what roof flashing is, why it's needed, how it works and what's available. There's lots of open literature around. Part of the education process. While I'm partial to tried/true post and double flash methods that have worked to keep roof penetrations of all types leak tight and secure since long before solar, I'm sure there are other systems that are fit for purpose. The overall goal is to keep moisture away from roof penetrations for a long, long, LONG time. Getting the roof penetration system right is about the most important and least addressed parts of a solar roof installation. They will be out of sight and mostly inaccessible. A failure /leak can be very costly and there are a lot of failure points. It's the last place to cheap out.

Add: It's always a good idea to get your roof inspected and serviced if necessary before a solar install. A PV system will last a long time. Give the roof under it the bst chance of lasting as long. Cheap insurance you will not regret, especially if your roof is getting a bit long in the tooth.

[sensij]

J.P.M. thank you for the informative post!!

One installer said the say they install is "the bracket comes with a 0 air patented flashing. Then we install a layer of commercial grade henry over the bottom flashing. Then use 3 layers of reinforced fabric and second layor of henry for the bottom flashing. Once it's dried. We will install the second flashing which replaces the entire tile. It is more than 2 flashing. It is the best way of doing this."

Can anyone comment on this method? Is this what Baker or Sullivan would use? Thanks in advance!

You are describing a compression seal (zero air) protected by standard three course flashing (sealant/mesh/sealant). Probably Quickmount PV, especially with the tile replacement flashing on top. You can find pictures and video on their website showing this in more detail. Same as what Baker would do, I think.

[bmms8]

J.P.M. sensij

Thanks guys! I will confirm that they are using the same method as Baker and if there is a difference what it might be.

Are any of you guys familiar with G C Electric? That is the installer who gave me this info. Ty

[J.P.M.]

J.P.M. sensij

Thanks guys! I will confirm that they are using the same method as Baker and if there is a difference what it might be.

Are any of you guys familiar with G C Electric? That is the installer who gave me this info. Ty

I haven't, but that means precisely squat. A couple of the pictures on their website look like quick mount or post/flashing.