Spreadsheet to overlay pvwatts gen vs. act usage?

[cebury]

I've developed and downloaded various spreadsheets to use my GreenButton pge downloaded usage data to "bin" it into correct peaks and tiers and then calculate expected bills based on rate structures.

However, I'm at the last step now needing to overlay pvwatts hourly generation data on top to net-out the usage data to estimate potential bills after solar.

Anyone have a sheet to do this before I spend x number of hours doing this myself?

Another question: Based on your experience in e6 or EVA, if i estimate a system will annually leave x number kWh remaining (net consumed) what rate is this usually billed at, assuming a typical homeowners usage patterns? If I know it'll all be in tier 1, is it usually winter off-peak rates that are left at true-up since summer peak dollars offset all summer usage and winter partpeak?

I know mathematically how true up works in pge territory, just wondering if an equivalent generalization can be made for typical customers.

[sensij]

I have a sheet I started to build before I saw how complicated tiering is on E-6, and lost motivation to finish it. However, the basic structure for overlaying model data from PVWatts is sound, and works well in my functional spreadsheet for SCE and SDG&E.

https://www.dropbox.com/s/8o4z5j4hjgqj94l/PGE%20TOU.xlsx?dl=0

Some things to keep in mind:

1) PVWatts does not consider daylight savings time, and assumes -8 UTC offset throughout the year. During DST, you'll need to shift the PVWatts data by an hour forward (data showing up at 9 am, for example, should be accounted for in the 10 am bin for TOU), since clock time will be -7 UTC offset, but solar time is still -8. In my sheet, you can see I did this by determining the hour of the year for each point being evaluated, and offsetting the rows by 1 during DST when calculating the modeled net once generation is included.

2) Consider building in a scaling parameter. With it, you can just download hourly data from PVWatts for a standard size array (say, 1 kW), and then scale it to see the sensitivity to actual array size. Without it, you'll need to download new hourly results for each array size you want to test.

3) You might notice some logic in my sheet about ignoring negative values when scaling. PVwatts does not output negative values, but NREL's Systam Advisor Model (SAM) does. The negative values are to capture the idle energy consumption of the inverter overnight. It won't amount to a significant number, but I didn't want to scale it the same way that the true generation numbers get scaled when testing different array sizes.


I'm not sure what answer to give for default cost of consumed energy, it will depend very much on the consumption patterns. True-up credits on a monthly $ basis (see page 4 here), not kWh, so whatever the residual kWh cost at the time the energy was consumed is what it will be. Some people are heavy summer consumers (A/C, kids home). Others are heavy winter consumers (electric space or water heaters, christmas lights?). For a properly sized array, it should all be tier 1, but for very uneven usage patterns, or with limited roof space, higher tiers might still be hit.

[cebury]

Thanks for the reply.

1) PVWatts ... assumes -8 UTC offset throughout the year.

How can I confirm this is still true? They even have the GMT offset by using the location data, but then to export it back to hardcoded -7 UTC offset is really hack. Shifting that 1 hour later made an annual $120 difference (from $110 net annual to -$10).

My Final Results (boy are my fingers tired):
====================================
I ran scenarios using 2016 rates for E1/E6 1) without PV, 2) 5.46 DC KW @ 74% kwh usage, 6.76 DC @90.4% usage.
It was as I suspected, our usage is a bit different because someone is here 24x7 and lots of A/C in summer. Changing E1 to E6 (with 90.4% PV) resulted in only $50/year benefit for E6.

@90.4% coverage yields $-80/yr withOUT meter charges, with minimum bill (7 mo. @net consumption >68 kwh).
@74% coverage is $335/yr withOUT meter, with min. bill.

$1700 more for the 90.4% system.

Future Factors:
===========
* Removed gas oven to electric (gas ovens >24" wide are much too expensive for us).
* Replacing old 1960's metal single pane windows with lowE3 vinyl. <-- hoping for bigger reduction.
* Adding more insulation from R19 to R38.
* 1-2 more people in house next year.
* We had an EV from Mar-Dec this year, so full year would probably eat up that -80. Usage is fairly low that the EV-A rates were $300/yr more than E6 for our profile.

I have no idea how to plan for those Future Factors at this point.

Assuming cash is available for purchase, what would you do?

[solar_newbie]

I would vote for 90% or 100% reduction as you will use more once you get Solar ...

[sensij]

Thanks for the reply.

How can I confirm this is still true? They even have the GMT offset by using the location data, but then to export it back to hardcoded -7 UTC offset is really hack. Shifting that 1 hour later made an annual $120 difference (from $110 net annual to -$10).

You can confirm it is true by looking at the hourly output data. If there was accounting for savings time, the modeled output on the day before the time change and the day after the time change would be similar, but shifted by one hour. You won't see that shift in the data.

It is unusual that the savings time correction is hurting your difference. Usually, shifting solar production later in the day will help, since "Peak" tou periods tend to be in the afternoon and peak generation occurs earlier than that. Think about it... under standard time, your solar peak might be 12:00 pm. Under savings time, it will be 1:00 pm.

My Final Results (boy are my fingers tired):
====================================
I ran scenarios using 2016 rates for E1/E6 1) without PV, 2) 5.46 DC KW @ 74% kwh usage, 6.76 DC @90.4% usage.
It was as I suspected, our usage is a bit different because someone is here 24x7 and lots of A/C in summer. Changing E1 to E6 (with 90.4% PV) resulted in only $50/year benefit for E6.

@90.4% coverage yields $-80/yr withOUT meter charges, with minimum bill (7 mo. @net consumption >68 kwh).
@74% coverage is $335/yr withOUT meter, with min. bill.

$1700 more for the 90.4% system.

Future Factors:
===========
* Removed gas oven to electric (gas ovens >24" wide are much too expensive for us).
* Replacing old 1960's metal single pane windows with lowE3 vinyl. <-- hoping for bigger reduction.
* Adding more insulation from R19 to R38.
* 1-2 more people in house next year.
* We had an EV from Mar-Dec this year, so full year would probably eat up that -80. Usage is fairly low that the EV-A rates were $300/yr more than E6 for our profile.

I have no idea how to plan for those Future Factors at this point.

Assuming cash is available for purchase, what would you do?

I don't understand the -$80 a year if you are including some kind of minimum bill. The minimum bill, by definition, will need to be paid, and represents the floor of what your bill would be. It can only go up from there, unless you shift to overproducing and are counting on the excess generation credit at wholesale prices to chip in.

Based on what you've written, I would probably leans towards the ~90% system. The electric oven can be a meaningful load if you use it regularly, and the windows aren't likely to help that much.

[solardreamer]

Thanks for the reply.



How can I confirm this is still true? They even have the GMT offset by using the location data, but then to export it back to hardcoded -7 UTC offset is really hack. Shifting that 1 hour later made an annual $120 difference (from $110 net annual to -$10).

My Final Results (boy are my fingers tired):
====================================
I ran scenarios using 2016 rates for E1/E6 1) without PV, 2) 5.46 DC KW @ 74% kwh usage, 6.76 DC @90.4% usage.
It was as I suspected, our usage is a bit different because someone is here 24x7 and lots of A/C in summer. Changing E1 to E6 (with 90.4% PV) resulted in only $50/year benefit for E6.

@90.4% coverage yields $-80/yr withOUT meter charges, with minimum bill (7 mo. @net consumption >68 kwh).
@74% coverage is $335/yr withOUT meter, with min. bill.

$1700 more for the 90.4% system.

Future Factors:
===========
* Removed gas oven to electric (gas ovens >24" wide are much too expensive for us).
* Replacing old 1960's metal single pane windows with lowE3 vinyl. <-- hoping for bigger reduction.
* Adding more insulation from R19 to R38.
* 1-2 more people in house next year.
* We had an EV from Mar-Dec this year, so full year would probably eat up that -80. Usage is fairly low that the EV-A rates were $300/yr more than E6 for our profile.

I have no idea how to plan for those Future Factors at this point.

Assuming cash is available for purchase, what would you do?

Given that someone is always home and lots of AC usage in the summer, your probably should go with the larger system. I have done quite a bit of simulation with EV-A and one key conclusion for me is that it's often misleading to focus on total annual usage. Instead, one should maximize NEM credit during summer peak hours to minimize your overall annual usage cost. You can do so by reducing/shifting usage from summer peak hours and/or maximize solar generation during summer peak hours. However, given you are in central CA it's probably not practical to reduce AC usage much during summer peak hours. So, I would suggest you focus on your summer peak hours usage as a key factor to determine your solar system size to maximize generation during summer peak hours.

[cebury]

I misunderstood the UTC disclaimer in pvwatts, so I backed out all adjustments.

Below reflects 2016 rates, from prelim E6 proposal, based on usage not changing (already increased as Nov/Dec bills reflect 2014). The larger tier1 is medbaseline (assuming that doesn't change).

PGEUsage_NoPV.jpg <-- 99.99% sure these are accurate.

Here is same usage data with pvwatts adjustments made (12% loss, 97.5% inverter):
* 90.4% kwh coverage: 6.76 PV @ <$3.00/w DC string (CS6p-260/SB7k) + elec.panel,
* no adjustment for DST in pvwatts,
* no adjustment for holidays in E6,
* no minimum billing amounts (or meter charge, if not gone).

PGEUsage_6.76_NoAdj.jpg <-- same numbers, just pasted in pvwatts hourly data along with pge download. XLS calc'd them both.

Yields $109 max on E-6 plan (if PV performs exactly per pvwatts each yr). So, 5 months the minimum wasn't achieved, add another $50?

If no PV route, using PG&E's proposed increase thru 2020, in ~6.0 years I'd pay the same $14k (after tax) to PG&E. Hopefully home value would increase by at least few thousand from the PV.

Opinions? Corrections?

Credit: Used PG&E_Electric_Rate_Calculator_v1.7a spreadsheet developed from miimura on Tesla Motors Club forum.

[cebury]

After reading the minimum calculation posts on other thread, if my annual TrueUp was really $109 there would not be an additional $50 charge (5 x #mo's below minimum) but rather ~ $11 charge to be sure you pay at least $120/yr at True Up. The only things allowing anyone's TrueUp under $120 is the renewable credit, or as a net kwh producer credit, or some other kind of over payment credit or adjustment. Right?

[sensij]

After reading the minimum calculation posts on other thread, if my annual TrueUp was really $109 there would not be an additional $50 charge (5 x #mo's below minimum) but rather ~ $11 charge to be sure you pay at least $120/yr at True Up. The only things allowing anyone's TrueUp under $120 is the renewable credit, or as a net kwh producer credit, or some other kind of over payment credit or adjustment. Right?

Yes, that is correct now. It is all subject to change as NEM 2.0 gets developed. The pocos would like to move away from annual billing, and if they can find a way to do that which doesn't violate the legislated NEM 1.0 guidelines, you can be sure they will.

[wwu123]

Thanks for the reply.




Future Factors:
===========
* Removed gas oven to electric (gas ovens >24" wide are much too expensive for us).
* Replacing old 1960's metal single pane windows with lowE3 vinyl. <-- hoping for bigger reduction.
* Adding more insulation from R19 to R38.
* 1-2 more people in house next year.
* We had an EV from Mar-Dec this year, so full year would probably eat up that -80. Usage is fairly low that the EV-A rates were $300/yr more than E6 for our profile.

I think these two home improvements will probably have a huge effect on the seasonal portion of your electric bill, both the hump that peaks in summer for A/C but also the smaller hump from the typically 500-watt PSC motor on your likely older gas furnace not having to run as long cycles. When we did those improvements as part of a whole house remodel in the Bay area, which has less seasonal extremes as Central CA, the impact on heating/cooling was very noticeable. Part of the impact is due to better insulation, part is due to less air leakage and a tighter building envelope that often comes with better sealing when installing the new materials.

[J.P.M.]

I think these two home improvements will probably have a huge effect on the seasonal portion of your electric bill, both the hump that peaks in summer for A/C but also the smaller hump from the typically 500-watt PSC motor on your likely older gas furnace not having to run as long cycles. When we did those improvements as part of a whole house remodel in the Bay area, which has less seasonal extremes as Central CA, the impact on heating/cooling was very noticeable. Part of the impact is due to better insulation, part is due to less air leakage and a tighter building envelope that often comes with better sealing when installing the new materials.

Use reduction through life style adjustments and then conservation measures are always more cost effective first measures than PV.

[cebury]

Use reduction through life style adjustments and then conservation measures are always more cost effective first measures than PV.

I'll be honest, we won't be doing further lifestyle adjustments past our current changes. We've either done most of them, they don't apply, or DW won't have any further unless we really need it during financial stress.

It's a 1967 home. We've replaced our 30 yr old HVAC with 16.5 SEER, existing ductwork insulated and sealed @10% leak rate, there is foil back insulation in all the walls, weather stripping done, cfl or led bulbs, ceiling fans, etc. Our usage would be much higher without those in place. We've had two EE audits already.

The last EE contractor left our home last weekend disappointed, hoping to sell us on various improvements, but said once the windows & insulation are completed there isn't anything left near cost-effective.

Roof Replacements Needed?
We are teetering on replacing the south facing roof with cool roof shingles, if we have to replace the roof anyway under the solar. We collected wildly differing opinions if replacement is needed or not. All visiting installers commented along the "you have a new roof" when they walked up, but if you look closely on south side you can see the wear I'm talking about. The most technical installer said "not needed, roof won't age under the panels". But one roofer estimated 1 year left (most expensive quote), another other 5 years. Both said it was a quality 40yr roof when installed (no idea when).

Here is why it's difficult: The portion where the panels would go looks the best, the worst near the HVAC. There is some visible granule loss and asphalt fraying at the very tips (fiberglass is visible) on only ~ 1 out of 20 shingle "leafs" . It is only on the lowest ones, low=closest to sheathing, I assume due to rain pathways but we get <10" year here. The higher leafs of every shingle barely look worn at all.

Once PV installed near roof peak, there should be relatively little heat, no sun and next to no rain (if it ever does here) under the panel. <<--- please correct me here if I'm wrong.

Wife wants to take the risk of added 2k later to remove panels if replacement needed after 10 years. Seems kind of silly to pay/plan for repairs some 10-20 years from now. This isn't our retirement home.

[J.P.M.]

I'll be honest, we won't be doing further lifestyle adjustments past our current changes. We've either done most of them, they don't apply, or DW won't have any further unless we really need it during financial stress.

It's a 1967 home. We've replaced our 30 yr old HVAC with 16.5 SEER, existing ductwork insulated and sealed @10% leak rate, there is foil back insulation in all the walls, weather stripping done, cfl or led bulbs, ceiling fans, etc. Our usage would be much higher without those in place. We've had two EE audits already.

The last EE contractor left our home last weekend disappointed, hoping to sell us on various improvements, but said once the windows & insulation are completed there isn't anything left near cost-effective.

Roof Replacements Needed?
We are teetering on replacing the south facing roof with cool roof shingles, if we have to replace the roof anyway under the solar. We collected wildly differing opinions if replacement is needed or not. All visiting installers commented along the "you have a new roof" when they walked up, but if you look closely on south side you can see the wear I'm talking about. The most technical installer said "not needed, roof won't age under the panels". But one roofer estimated 1 year left (most expensive quote), another other 5 years. Both said it was a quality 40yr roof when installed (no idea when).

Here is why it's difficult: The portion where the panels would go looks the best, the worst near the HVAC. There is some visible granule loss and asphalt fraying at the very tips (fiberglass is visible) on only ~ 1 out of 20 shingle "leafs" . It is only on the lowest ones, low=closest to sheathing, I assume due to rain pathways but we get <10" year here. The higher leafs of every shingle barely look worn at all.

Once PV installed near roof peak, there should be relatively little heat, no sun and next to no rain (if it ever does here) under the panel. <<--- please correct me here if I'm wrong.

Wife wants to take the risk of added 2k later to remove panels if replacement needed after 10 years. Seems kind of silly to pay/plan for repairs some 10-20 years from now. This isn't our retirement home.

Tough call. Some things to perhaps think about:

In all likelihood, the array will have a life about as long as a new roof and, depending on how long the existing roof has been there, longer than that one.

One, practical and realistic consideration, but not very pretty: What's the probability you'll be there when the existing roof needs work ?

One other thing: with solar, there will be a lot of penetrations in your roof that weren't there before the array(s) went up. With a relatively new roof - one that does not need work/replacement - there may well be a higher probability of problems from the new penetrations than from leaving the existing roof in place (or from a new roof for that matter). I had new paper put under my array, and contracted and arranged w/ the roofer and solar vendor to have the roofer place (affix) the supports and double flashing on the roof while I watched (out of the way) each one being placed and attached, and inspected each one at day's end before tile replacement the next. The solar vendor supplied the standoffs and verified locations and dimensions. I also made sure they hit the rafters.

I'm of the opinion that new paper /shingles under an array is cheap insurance, but less so if there is insufficient attention to the penetration details.

On the distance from the top of panel to roof peak: Unless you get a variance, you'll probably have something like 3' distance from top of panel to peak. You'll get less H2O on the roof under the array, but still some as there is some small separation between the panels, from a some fraction of an inch to an inch or so. Some water will get under the array How much ???

One thing I've noticed: roofing material at the bottom of an array, and at the bottom of rows of arrays to a somewhat lesser extent, tends to get a "waterfall" effect - that is rainfall that would normally be distributed more or less uniformly over a roof tends to fall down a panel surface and cascade onto the roof surface below, with the velocity and volume of impact probably not accounted for when planning/designing the integrity of the original roofing system. I've placed metal sheathing painted the roof color on the roof below the array to act as sort of a strike plate. I did that as a result of something I learned when servicing an existing solar water heater. The roof below the 2, 4' X 8" collectors was intact, looked OK and seemed to have not been serviced/repaired. However, I reoriented the collectors and upon removing the tile to set new supports, discovered that what I believe to be the waterfall effect I spoke of had done some fair amount of water damage and rot.

Finally, while having less solar radiation under the array will tend to keep the roof cooler, the possible downside to that is water that does get under the array will not evap. as quickly, with the possible consequence of greater probability for mold growth or other problems in a relatively large area you probably can't see or get to. A more recent roof may improve the chances of handling such unforeseen and/or unknown problems better.

Just sayin'.

[solar_newbie]

I'll be honest, we won't be doing further lifestyle adjustments past our current changes. We've either done most of them, they don't apply, or DW won't have any further unless we really need it during financial stress.

It's a 1967 home. We've replaced our 30 yr old HVAC with 16.5 SEER, existing ductwork insulated and sealed @10% leak rate, there is foil back insulation in all the walls, weather stripping done, cfl or led bulbs, ceiling fans, etc. Our usage would be much higher without those in place. We've had two EE audits already.

The last EE contractor left our home last weekend disappointed, hoping to sell us on various improvements, but said once the windows & insulation are completed there isn't anything left near cost-effective.

Roof Replacements Needed?
We are teetering on replacing the south facing roof with cool roof shingles, if we have to replace the roof anyway under the solar. We collected wildly differing opinions if replacement is needed or not. All visiting installers commented along the "you have a new roof" when they walked up, but if you look closely on south side you can see the wear I'm talking about. The most technical installer said "not needed, roof won't age under the panels". But one roofer estimated 1 year left (most expensive quote), another other 5 years. Both said it was a quality 40yr roof when installed (no idea when).

Here is why it's difficult: The portion where the panels would go looks the best, the worst near the HVAC. There is some visible granule loss and asphalt fraying at the very tips (fiberglass is visible) on only ~ 1 out of 20 shingle "leafs" . It is only on the lowest ones, low=closest to sheathing, I assume due to rain pathways but we get <10" year here. The higher leafs of every shingle barely look worn at all.

Once PV installed near roof peak, there should be relatively little heat, no sun and next to no rain (if it ever does here) under the panel. <<--- please correct me here if I'm wrong.

Wife wants to take the risk of added 2k later to remove panels if replacement needed after 10 years. Seems kind of silly to pay/plan for repairs some 10-20 years from now. This isn't our retirement home.

I have couple colleagues spend 50-60 a month on electric and gas. Just remove furnace and AC from you life.

[solar_newbie]

If you want a new roof, go for it but do the whole house.

If you want economic way, do the following
- cost of install new roof -- 10k-20k
- cost of bring array down and put back --2k

Roof life time - 40 years

If the roof can last 10 years, your cost of install now is 2.5-5k vs later. Economic is shown already.

Next is array life time. Is it less than 40 years? Some can say longer ... Some say it is.

If you replace roof now, you might consider another things in the future to keep or not keep array. But it is long time later.

If you plan to stay in the house for 10 years . It is more effective to sale a house with new roof vs old roof.