Upgrading our present solar system.

[K-fab]

We presently have a pair of Fronius Plus inverters with 70 250W (total of 17.5kW) panels powering our house.
Located in North Scottsdale, AZ. The sun abounds.
We feed back into the grid from approximately 10:30 to about 5, at least during the summer months.

June, July and August (peak usage months) our APS bill shows that the daily power consumption for the house is about 95kWh. (just under 4kW per hour average). This is what I based my numbers off of. Worst case scenario.
The peak usage is when the solar starts dropping down and the AC systems (three units, each programmed to be as efficiently used as possible) have to work to cool off the day's heat saturation. We also have an Audi etron that we try to charge during peak hours (30 amp input). We try to use things that load the system during peak production times.

I'm wanting to add battery storage ability. The Fronius does not have this (it's 10 years old now).
Have been watching a lot of Will's videos and have come to the conclusion that this system will probably suffice but I'm not quite sure of the math to prove it:

Here's what I'm thinking, please correct/guide me.

EG4 18kPV inverter ($4,900). - https://www.currentconnected.com/product/eg4-18kpv-hybrid-inverter/
EG4 Wall Mount indoor battery 48V, 280Ah, 14.3kWh ($3,300) - https://signaturesolar.com/eg4-wall...0-year-warranty-pre-order/?ref=cPwLcVc0SW-BjN
I'll pull about half the old solar panels and replace them with Aptos 370W bifacial panels. A pallet (31 units at a cost of $3,300) has a total of 11.47Kw - https://signaturesolar.com/11-47kw-...a-120-bf26-370w-full-pallet-31-11-47kw-total/

Is this overkill?
Should I consider using one of the EG4 12kPV inverters ($3,500) instead of the 18kPV? - https://www.currentconnected.com/product/eg4-12kpv-48v-hybrid-all-in-one-inverter/

Do I keep the present solar panel array and just upgrade the inverter and add battery storage?

I'm not concerned with going fully off grid but I'd like to be able to offset the power used at night and the closer to off grid the better.
Right now with the above listed items I'm at about $11,500 investment so my payoff would be roughly 2.75 years. My last 12 months worth of APS bills total about $4,000.

If I just went with the battery and the 12kPV the cost of the system would be about $6,800. (shipping not included in any of my pricing).

So let's hear everyone's thoughts. I'm fully open to suggestions and comments as I'm just now starting to really get serious about upgrading.

Corrected my panel wattage. Climbed up and took a look. They're 250W so I have a total of 17.5kW of PV. That's more than enough.

 

[Hedges]

If those are really 100W, they are 20+ years old and were 13% efficient (130W/m^2)
New panels are 20% to 22% efficient, 200W/m^2, so you get 50% more in same area.

(Of course design Voc, Ioc, Vmp, Imp of array appropriately.)


In Arizona do you get to keep your net-metering plan, or is that being changed to something much less favorable like in California? If you do have net metering, then batteries only save you money if there is a price spread between buy/sell or TOU pricing, demand charges, etc. The added cost of battery may eat up a significant fraction of the spread. For instance, my present plan in California has a $0.20 spread. When I get bumped to NEM 3.0, then the spread may be $0.30 to $0.60 and return from battery is much greater.

You've mentioned payoff (ROI) but not the details of your tariff.


Fronius 10 years old? Was that replaced, or is entire system 10 years old?

Fronius is Tier-1. EG4 is not. So adjust your expectations accordingly.

Look at Midnight. They have a new AIO and are bringing out a battery any day now. Highly respected company.

 

[K-fab]

Half of this is Greek to me. As stated, I'm a newbie here.

Whole system is 10 years old. Was installed when we built the house. I really need to get up on the roof and get the specs of the panels - but the 110+ temps are a bit of a deterrent. I can't find them/the specs in my house's build logs.

Net metering plan - This is the plan we're on here: RATE SCHEDULE LEGACY E-12

https://www.aps.com/-/media/APS/APSCOM-PDFs/Utility/Regulatory-and-Legal/Regulatory-Plan-Details-Tariffs/Residential/Frozen%20Plans%20and%20Riders/e12_StandardGrandfathered

Details on Tarif? Not following that at all.

Gawd I hope we don't end up with Cali plans. Don't California my Arizona. (no offense, it's not you, it's the CA government)

Tier-1 versus "not". I'm guessing this is the level of equipment? Fronius is top shelf and EG4 is WallyWorld sort of statement? The house was built with upper end equipment.

I will look into the mentioned equipment.

Thanks for the response.

 

[Hedges]

Total peak wattage divided by number of panels should give actual power production per panel. It's STC rating may be 15% +/- higher.

Yes, Fronius (and SMA) are top-shelf products, mostly made in Germany. SMA now makes some in US and Canada. Expect 20 year lifespan. I calculated 34 year MTBF for 5 SMA 2500SWR inverters I operated, with a couple failures, over 17 years.

EG4 is selling a massive quantity. Chinese product with distributor over here. We hear from squeaky wheels on the forum, and some happy customers. Actual success/failure ratio data eludes us.

Tariffs, utility plans, etc.
What price(s) do you pay per kWh? What do you get credited for backfeed? Are credits rolled over for one year, then erased annually? Or paid in cash?

For some plans, batteries smoothing out consumption will save money, others it won't. Batteries cost money. It can all be reduced to dollars, although only assuming we know what the future holds. In California, we can guess (there was an attempt at a "photon tax", dropped for now. But another state has one.)


OK, your plan costs $0.12 to $0.22/kWh in the summer, $0.12 in the winter.
I haven't figured out what credit you get for backfeed. Is is same as retail?

"daily power consumption for the house is about 95kWh" x 30 days = 3000 kWh/month (is that net after your PV, or total including what you produce?)

So power costs you $0.20/kWh

If you paid for turnkey GT PV today, expect $3/W of equipment and $0.10/kWh amortized over 20 years.

Batteries cost about $0.05/kWh amortized over over 6000 cycle life and 16 years.

At $0.10 + $0.05 = $0.15, and that's amortized not considering time value of money, not a great investment to avoid paying $0.20
I'd say better to look for other investments that pay a return in cash.
But DIY so investing labor could change that somewhat. Hardware for GT PV is 1/4 the turnkey installed cost. However, DIY outside your normal expertise is slow, so again not a great return.

In California we have rates more like $0.45 to $0.65. The spread between off-peak and peak is hardly enough to justify battery, but the price itself justifies PV. For new systems, credit for backfeed around $0.02 means batteries are necessary.

I haven't spotted how battery helps you at all. Unless, system expansion knocks you off your net metering plan to something worse, and an off-grid or zero export addition is a way around that. We have similar issue in California.

 

[K-fab]

Fantastic info! Thank you very much.

 

[K-fab]

I climbed up on the roof (not fun in 115F!) and took a look at the solar panels (made comment in my first post about the edit).
I have 70 250W panels for a total of 17.5kW. I would imagine that it's degraded to somewhere around 15kW over the 10 years they've been in the desert sun.