TOU Calculations in Phoenix

[desertbeekeeper]

Would these panels be ok for roof mount?

 

[SignatureSolarJames]

Aptos is awesome! they perform well in high heat too.
about to carry them at Signature Solar

 

[phx]

I also live in Phoenix, and I'm also with SRP on the E27 TOU plan with "Net Metering." But the "Demand fee" is an ugly elephant in my electric bill making 70-100% of it.

Here are my experience and suggested solutions on how to mitigate it:

Mitigation of demand from utility with solar

Hi. I'm from Phoenix, AZ with 12.96kW grid-tied system up and running. It has 5 strings of panels and two SMA grid-tied inverters working in parallel. They are AC coupled before solar meter. It's a standard design recommended by SRP (utility company) published on their Web-site I'm on "Customer...

diysolarforum.com

These are my numbers from the beginning of 2023 and my bill for June:




My house is 2,000 sq. ft., and I have three EVs in my household charged 100% at home. So, the bill included the EVs energy consumption.

 

[desertbeekeeper]

I also live in Phoenix, and I'm also with SRP on the E27 TOU plan with "Net Metering." But the "Demand fee" is an ugly elephant in my electric bill making 70-100% of it.

Here are my experience and suggested solutions on how to mitigate it:

Mitigation of demand from utility with solar

Hi. I'm from Phoenix, AZ with 12.96kW grid-tied system up and running. It has 5 strings of panels and two SMA grid-tied inverters working in parallel. They are AC coupled before solar meter. It's a standard design recommended by SRP (utility company) published on their Web-site I'm on "Customer...

diysolarforum.com

These are my numbers from the beginning of 2023 and my bill for June:
View attachment 158128

View attachment 158130

My house is 2,000 sq. ft., and I have three EVs in my household charged 100% at home. So, the bill included the EVs energy consumption.

Just got through reading, that is a great idea with the AC, I am going to ask you a few more questions about that. So did you ever end up going with batteries or are you running 100% off solar and just adjusting usage?
Your on peak kW each month is very consistent, 5.3-5.8 Jan-June and you are only controlling the AC?

 

[phx]

I recently added 17 more solar panels, currently having 70 total. It was commissioned by SRP again just yesterday. So, I don't have enough statistics yet. The system is purely solar, with no batteries.

It produces much more energy than my annual consumption, covering all energy expenses, taxes, fees etc. EXCEPT of demand. However, with more panels, I'm coming closer to zero net payment.

Batteries are very expensive, and the problem is that they degrade in 5-8 years. So, they are not economically reasonable.

I'm waiting for the "EV to grid" technology to evolve and become more common. Using an EV as energy storage while you are not driving it might be the best solution to the "Demand problem."

 

[Shimmy]

Batteries are very expensive, and the problem is that they degrade in 5-8 years. So, they are not economically reasonable.

More like 10-15 years as a generalization. They are economically viable if the delta between daytime power and nighttime power is over $0.10/kWh, and the demand charges might make them an even better sell at a lower delta.

 

[Chris72]

I am going through the DIY process with SRP I am in it about 20k I am guessing I will be closer to 30k all said and done. That's 2 Sol-Ark 12k 30 Sunpower 360w and 9 REC 365 west. 10kw battery storage that's on the SRP approved list. Once I pass inspection I wii get 2 of the eg4 PowerPros 14.8kwh almost 30kwh for under 8k not SRP approved yet if ever.

 

[sunshine_eggo]

After learning of the customer generation plan and its net metering, I revisited GT solar for my primary residence on SRP.

FFS... it's worse than I remember.

Between the higher connection fee of $32 and the "demand fee" which is variable and can be very large. There is never a breakeven.

A 7kW system would meet 50% of my needs and reduce my bill by.... 15%. This is based on their solar calculator that looks at my actual usage, and we're already saving ~$500/year on the TOU hours plan by managing our consumption.

Given that the LION'S share of our consumption is the 5 ton A/C, I could save way more than that and have a very speedy payback period by getting the EG4 2 ton mini-split and mounting the panels I already have as a rear porch pergola.

I hate you SRP.

 

[Doggydogworld]

I hate you SRP.

It's not SRP. Everywhere with good sun faces the same issue. They can supply daylight loads with 2 cent solar. If they pay someone more, either in cash or net metering credits, they have to pass that cost on to other ratepayers. Their bit problem, and biggest cost, is servicing summer peak hours around sunset. Help solve their problem you deserve to be rewarded, make it worse and you should pay.

Given that the LION'S share of our consumption is the 5 ton A/C, I could save way more than that and have a very speedy payback period by getting the EG4 2 ton mini-split and mounting the panels I already have as a rear porch pergola.

I'm confused. How does adding a 2 ton unit save money?

 

[sunshine_eggo]

I'm confused. How does adding a 2 ton unit save money?

It runs directly from PV or AC. If I simply ran a 2 ton unit "free" from PV during solar hours, it would take a lot of the load off the 5 ton unit, especially during peak periods were power is 3X off-peak.

 

[Doggydogworld]

Ah, thanks. I was thinking about demand charges, but you're on TOU with no demand charges.

So basically buying the 2 ton instead of an inverter to feed the 5 ton. And avoiding inverter losses while you're at it. Interesting.

I used to turn my A/Cs off when ERCOT called for peak shaving from 3-7pm. The house would gain about 1 degree F per hour in full sun and 100 degrees. I never measured after sunset, but heat gain would be much less. I bet if I pre-cooled the house directly from solar then just shut the A/Cs off when the sun got low it'd be 3-4 hours after sunset before they needed to fire back up on grid power.

My house has a lot of thermal mass, though. I wonder what it'd take to build all new homes with enough thermal mass to avoid summer evening A/C? Or maybe even retrofit old ones. Thermal mass has other benefits, too, e.g. no climate control needed at all in spring and fall, especially with open windows at night. If I had passive solar I could probably avoid heat 90% of the winter, too.

 

[sunshine_eggo]

Ah, thanks. I was thinking about demand charges, but you're on TOU with no demand charges.

I didn't make it clear that the unit ran on PV.

So basically buying the 2 ton instead of an inverter to feed the 5 ton. And avoiding inverter losses while you're at it. Interesting.

Not so sophisticated, but basically the same. We have a great room (500 sq-ft) that's about 25% of the area of the house and > 25% of the volume due to the vaulted ceiling. Programmable thermostat forces the 5 ton to run from noon to 2:00 and then sets the main A/C 80°F until 8pm. The idea with the mini-split would be to:

1) provide an area comfortable even during on-peak times.
2) potentially feed cooler air into the intake of the 5 ton - the intake register is favorably located for this, i.e., the great room is adjacent the intake register - use the 5 ton's blower to distribute the cooler air through the house.

I used to turn my A/Cs off when ERCOT called for peak shaving from 3-7pm. The house would gain about 1 degree F per hour in full sun and 100 degrees. I never measured after sunset, but heat gain would be much less. I bet if I pre-cooled the house directly from solar then just shut the A/Cs off when the sun got low it'd be 3-4 hours after sunset before they needed to fire back up on grid power.

Dealing with months of 110+ with nights not dropping below 90 means, even having blown insubstantially more attic insulation during the remodel, we'll gain 2-3°/hr in the extreme temps.

My house has a lot of thermal mass, though. I wonder what it'd take to build all new homes with enough thermal mass to avoid summer evening A/C? Or maybe even retrofit old ones. Thermal mass has other benefits, too, e.g. no climate control needed at all in spring and fall, especially with open windows at night. If I had passive solar I could probably avoid heat 90% of the winter, too.

2x4 stick built with stucco. Not much thermal mass at all.

 

[Doggydogworld]

2) potentially feed cooler air into the intake of the 5 ton - the intake register is favorably located for this, i.e., the great room is adjacent the intake register - use the 5 ton's blower to distribute the cooler air through the house.

Series connected air conditioners

2x4 stick built with stucco. Not much thermal mass at all.

I had that in CA, but temps were never extreme so it was not an issue. Here in TX I have brick exterior, huge slab, radiant barrier in the roof, white "Polywood" shutters, etc. Plus it's a big, squarish two story so volume-to-surface area ratio is favorable.

IMHO our building codes focus too much on insulation and not enough on thermal mass. I sometimes wonder what could be done with water, or even phase change waxes if they were cheap enough.