Have 48 panels, want to install (flat roof, SFH, SF CA)

[chuckledog]

One last chart then I'll shut up. I took the historical power consumption (SUM of kWh use chart above) and divided each cell by the number of days that month. The result shows the total kWh used during that hour, on average over that month. I color coded this to match the Emporia color scheme.
Screenshot 2024-03-12 at 11.43.54 PM.png
It matches really nicely with our net consumption / generation graph from the Emporia. During March of last year we saw a net generation of around 4.1 kWh each day around noon. This year we're a bit higher (probably because the wacky heat pump water heater isn't chewing up alot of juice anymore).

[chuckledog]

So what if we were to switch to the new E-ELEC 2024 rate plan? That rate plan is shown below:
Screenshot 2024-03-12 at 11.35.52 PM.png

Well, the matrix multiplication comes out like this:

Screenshot 2024-03-12 at 11.37.19 PM.png

According to this, we'd see a net bill of $362 if we switch rate plans -- a $200 savings.

We'll hold off on any changes for now, but it's nice to finally have a good way to visualize the net metering rates. Hope it helps inspire some good ideas.

[chuckledog]

So all that detail helped us to isolate what was our big power consumer last winter. It was our heat pump water heater (Rheem 80 gal) which we had on a recirculating pump. It was not plumbed properly and was wasting alot of energy for 2 months. Once we resolved that we were ok on consumption... the whole-house heat pump radiant uses a surprisingly low amount of energy.

Ok so for the second cool thing. So I downloaded our usage from PG&E into a spreadsheet and it looks like this.
Screenshot 2024-03-12 at 11.18.07 PM.png

I used a Pivot Table to summarize that data in a really useful way. I aggregate by month on the Y-axis, and by hour on the X-axis. So each cell in the grid represents the total power production / consumption for a specific one-hour of every day in that month. 0=midnight, 12=noon to 12:59pm, etc. On the far right I total up the net power consumption for that month. (Compare the PG&E measured peak of 1205.91 kWh generated last July, with the Emporia Vue measured amount of 1210 kWh shown above, it's within 1%).

Screenshot 2024-03-12 at 11.20.36 PM.png

Ok now for the interesting part. I captured PG&E's (astronomical) rate plan in a similar tab. Their posted rates vary by hour and by month. This grid shows the rate nicely:

Screenshot 2024-03-12 at 11.26.12 PM.png
It's $0.62 per kWh during the peak hours 4pm-9pm of the peak summer months June through September. (Yes that's 10 times as high as some other places in the country! Welcome to California!)

That's painful but when you multiply those two matrices together, you get some cool stuff. Basically you can see in green where we have net gain in terms of money. The peak moolah rolls in during the 2pm-3pm window in July (deepest green). That hour alone earns us $129 over the course of the month. Of course that gets canceled out by the other hours. Still overall we earned $668 in July. But that got chewed up by the $823 per month we spent in January. The Grand Total is an annual bill of $585 due at true-up (lower rightmost number).

Screenshot 2024-03-12 at 11.29.38 PM.png

[chuckledog]

It's been about a year, maybe overdue for an update here. Mainly wanted to share two cool things with the community.

One, I bought, one of these suckers https://www.amazon.com/Emporia-Monit...dp/B08CJGPHL9/

We have somewhere around 30 circuit breakers (!), I only am monitoring the 16 biggest consumers, which works out ok to track some of the major appliances e.g. heat pump vs. electric dryer vs. refrigerator. The app provides really nice graphs!

Here is our solar production right now (10pm, clear night, not much moonlight). I guess we're generating 5.97 watts. It's interesting (briefly) to watch the second-by-second power output e.g. when clouds come over our house on a sunny day. The second-by-second is really useful for seeing power spikes from e.g. random stuff plugged into the wall outlet.
IMG_8384.png

Hour by hour, you can see our solar production. Hour-by-hour (left), looks like today 3/12 was a little less sunny than yesterday 3/11.
Day by day (middle) you can see we're generating between 3kWh and 32kWh per day, in March, from that leg of panels (we have 2 such legs).
Month by month (right) you can see we haven't generated alot in March yet, but are on track to hit about 650 kWh total this month, compared to 1010 kWh we generated during July 2023.

IMG_8385.pngIMG_8386.pngIMG_8387.png



The Emporia Vue also shows /net/ power generation. Net generation shows up in green (as above) while net consumption shows up in blue.

Month by month (left) you can see we have about equal amounts green and blue, meaning we're kinda sorta "net zero". We generated 1210 kWh net during July 2023 (double the 1010 kWh solar above, minus whatever we consumed). That 1210 kWh net gets credited to us to cover the net-loss months e.g. Nov 2023 - Mar 2024.

Day by day (middle) you can see that in March we have some net-generator days (green) and some net-consumer days (blue).

Hour by hour (right) you can see we were a net generator today from about 10am to about 5pm.
IMG_8388.pngIMG_8389.pngIMG_8390.png

[chuckledog]

Nice, thanks for that update and ray of hope!
We only charge 1 EV to your 2, and we don't have a battery.
I'm still running the numbers on why the Jan-Mar bills were so high. One factor was that we had our heat-pump water heater in electric-resistance mode for some of that time. (since its compressor is kindof loud, and at the time we were sleeping right near it). We also had some trouble with our recirculating hot water plumbing. Those apparently conspired to triple our HPWH energy usage. It's now under control with proper plumbing, no more "electric resistance" in the schedule, and more conservative recirculation settings.

[Ampster]

It's been a year since I updated this thread --..... Would we get hit with a huge electricity bill in September?

......

Thanks for the update. I had a similar winter and can offer some hope based on my experience last year.
I installed solar on this home in September 2021 and my true up in 2022 showed a Net consumption of one mega Watt hours of consumption but I had a small dollar credit. Those items washed so in addition to the 11 mWhs my 8 kW system produced that first year I also got another one mWh of import for just the minimum charges which amounted to about $150. I had also abandoned my 60 year old Forced Air Unit and installed a three zone heat pump A/C. My energy consumption is higher in winter and by February of 2022 I had a Net consumption of 2.2 mWhs but reduced that and generated a dollar credit by True Up in September. This year my Net consumption peak was 2.7 mWhs in March but I am on track to reduce that and again have a small dollar credit at True Up this September. I should add that I charge two EVs and have a battery system which reduces my peak TOU usage and allows me to earn some credits at peak rates.

[chuckledog]

It's been a year since I updated this thread -- it's time for an update! We've finished our remodel and made it through a cold wet "winter" (lots of rain, if not feet of snow). We've been comfortable and hardly needed to use the backup gas heat -- our two heat pumps (one for the whole house radiant heat, the other for the water heater) sufficed and were quite efficient. It seemed like we would be net generators and perhaps over provisioned for solar.

Things were almost getting boring! Then when the rains let up I looked back at our January + Feb + March energy bills. They were very high. Would we get hit with a huge electricity bill in September?

Screenshot 2023-06-18 at 8.41.20 AM.png

I've installed an energy monitoring system in my circuit panels so I can see per-second graphs of solar generation vs. whole-house-heat-pump vs. hot-water-heat-pump vs. electric-car-recharging. I captured our PG&E bills in detail and learned how CleanPowerSF energy credits work *in practice*. We will be a net consumer this year, unless the summer is REALLY hot and sunny. We'll dip into our stored energy credits from last year (shown in light green above) to pay for this. That should be interesting to capture.

I'm posting here to see if anyone has questions about our install. The fact that we've run into high bills might make it an interesting discussion!

So much has changed in the residential solar landscape. "Net zero" homes like ours barely raise an eyebrow anymore. Tax incentives exist to ease the pain of some of the up-front costs. Still, there's generally a lack of expertise and experience around installing this stuff. Our install is 5 years old, and I've got a handle on many of the issues that are likely to arise with an all-electric home.

So -- ask me anything! I'd be happy to share advice. Note, I won't recommend going all-electric at this time, even in San Francisco... keeping backup gas makes sense, based on the way I see things shaping up...

[Ampster]

Since this thread started I have moved to different home that had an old forced air unit. It was forty years old, inefficient and was either full on or full off. Fortunately the home is well insulated. After installing solar panels the next project was to start a plan to install a minisplit. I got that done in December and I was amazed at how little energy it took to heat the two rooms that we spend most of our in during the winter. I agree with your analysis about electric heat versus gas, and that is why a lot of new homes are going in that direction. It does not hurt that the Net Zero calculations, which are required for new construction, skews things in that direction as well.

[chuckledog]

bcroe this approach makes alot of sense. I would not say that's excessive at all. I'm assuming these are air to air heat pumps. Those have matured really nicely over the past few years. The decentralized approach is key.
I DIY installed an 18kBTU MrCool unit in a cold climate residence and it works very well, quieter than our 40kBTU Chiltrix.

One huge advantage of electric heat over gas heat is the cost of the in-home infrastructure. I'll try to capture it in a table:

	Gas Furnace	Air-to-air heat pump	Air-to-water heat pump
Supply lines cost	gas line: $500	220V line: $200	220V line: $200
Heater unit cost	furnace: $3000	Mini-split: $1000	A2W pump: $4000
Heat distribution cost	bulky ducts: $3000	~requires decentralized / ductless approach	warm water lines: $5000+
Typ. BTU capacity	200000 BTU	20000 BTU	40000 BTU
Cost for 80000 BTU house load	$6500 (1 heater)	$4800 (4 heaters)	$13200 (2 heaters)
Cubic feet of in-home soffits required for home	200	25	10

Basically if you can hide your mini-splits in soffits, you don't need any soffits for the central furnace ductwork, and you come out ahead on all counts.

All the numbers above are ballpark for a 2000 sq ft home in a moderate climate, and there's huge variance. But the mini split approach makes sense for an increasing number of homes. I think I mentioned earlier in this thread -- our high-end energy consulting company said they're spec-cing mini splits in most of their custom high-end home designs. They tuck the units into inconspicuous spaces e.g. above a fridge, above a closet, etc. totaling e.g. 25 cubic feet per home. They then don't need e.g. 200 cu ft of ugly soffits running under the basement joists.

Apologies if your system /isn't/ based on mini-splits

[bcroe]

bcroe that's great! What are you using for a heat pump now? Ours is a Chiltrix CX34, it's working really well but a bit noisy. 2 month delay getting it even shipped here of course...

Our recirculating hot water has surprisingly been easy. It works and doesn't break the bank on kWh. It's misinstalled though so the plumber will fix that; we'll see how it holds up.

My Heat Pumps are all the variable speed type, chosen first for below
0 F capability, and second for high efficiency. SEER up to 36. They
are all extremely quiet. Since they come pre charged, a DIY install
can save more than half the cost.

I have 6 in place around 2 buildings. Some would say excessive, but
I have my requirements.
1. By having a lot of capacity, spread around, I am unlikely to ever need
to use another backup heat source. Time and frustration saved.
2. I wanted to de centralize, so no single failure would be an emergency.

3 are Mitsubishi, 2 are Fujitsu, and a Senville.
Bruce Roe

[chuckledog]

bcroe that's great! What are you using for a heat pump now? Ours is a Chiltrix CX34, it's working really well but a bit noisy. 2 month delay getting it even shipped here of course...

Our recirculating hot water has surprisingly been easy. It works and doesn't break the bank on kWh. It's misinstalled though so the plumber will fix that; we'll see how it holds up.

[bcroe]

THANKS for the continued updates. The thing about hot water
circulators and software may become a problem here later. The
last energy holdout here, hot water is still a far from elegant setup.
I suspect dual arrangements for summer and winter would be good.

Here in IL we cannot PV pay down our electric bill until True Up.
Starting with zero in April, using more than generated means paying
cash for it at the end of the month. April was tough this year, but we
did sneak by with a 500KWH surplus.

The more you can run heat pumps instead of resistance heaters,
the better. There are still a few big resistance heaters in place
here, but they have been shut down since enough low temp
capability heat pumps went on line. Bruce Roe

[Ampster]

Thanks for the update. I can't believe it has been three years since you initially posted about this project. There was some scepticism but you worked through it.

[chuckledog]

So far so good with the heat pump water heater and house heating. We've had negative electric usage just about every day for over a month now.

It's a bit crazy to be using ZERO gas or gasoline.

This graph shows the net metering thing pretty nicely:
- We racked up a $300 bill in December when it was cold and we were still using space heaters to stay warm.
- In March the heat pumps finally got connected and now we're paying down our bill.
- We'll see if we actually can pay it down to zero by September (5 sunny months from now). If so then we're likely well under our energy budget.

solar_summary.png


(Yes it is a little sus that February is missing)

[chuckledog]

Update --

We're in the thick of the remodel, picking out tiles, countertops, etc. However the drywall is up, and *most* of the HVAC has been running now for 2-3 weeks.

The big news is, after a couple of scary days with high electric bills, we're back in the "green" producing more electricity than we use. This is in late March / early April, where we have good amounts of sun, and relatively moderate temperatures. Our gas is (temporarily) completely shut off, and we're heating the entire home with a combination of radiant and electric space heaters.

Energy supply:
- 48 solar panels, 12.7 kW peak panel wattage, clipped by our 10kW inverter. 3 years of history show that this rooftop system generates 19MWh per year
- PG&E service with "E-TOU-C" rate and net metering, without this there's no way we could keep up with the winter heating load

Energy consumption:
- Space heating:
- Chiltrix CX-34 air-to-water heat pump, heating PEX tubing (radiant slab + staple-up under-floor), 40000BTU modeled load
- 1 750W electric space heater, heating
- Domestic hot water heating:
- 80 gal Rheem heat pump water heater
- Recirculating hot water pump (mainly to conserve H2O)
- Automobile:
- low-end electric car, 200 miles / week, mainly charged at home
- Appliances:
- Electric dryer, non heat-pump
- not many other appliances hooked up. Just a microwave, toaster oven, induction hot plate, washing machine, fridge

Note the purple line shows the ambient temperature, the blue lines show energy consumption in excess of production, and the green columns show production exceeding consumption. Green = good. The green kWh get "banked" for us for use in the colder months of winter.

Energy Usage early April 2022.png
The big blue spike was a single 80kWh day. This was pretty terrifying, but likely corresponded to the system warming up our 1600 sq ft concrete slab from 52F to 63F. If the system had continued using this much money per day, we'd have to shut it off! but it didn't -- we went into the green.

Granted the temperatures have been higher. So it's still up in the air whether this system will break even. I wanted to share the early positive indications and will update with more data in a few months.

Solar Production.png