Number of PGE panels, do they approve? Make you remove some?

[charlesj]

PG&E gas tier 2 (anything over 0.49 therms/day) was $1.90021 in June. Off-peak net generation benefit for me is only $0.06934 so using your x25 would be $1.7345. My understanding is that the electric hybrids are more effective than gas, so I think your x25 is pessimistic.

Yes, if the water heater doesn't gobble up your over generation for the year. If it does, you would be paying the rates in effect when you used the electricity for the hybrid, no?
That x25 refers to energy conversion from a therm of gas, 100,000 BTU, to an equal quantity of electrical energy in BTU calculation so you can compare. The real number is x29.3, this is fixed for comparing equivalent energy not subject to pessimism. You need X BTU to heat water regardless the source, gas or electricity. The meters read usage.

 

[charlesj]

I think that analysis leaves out the COP of a heat pump. For heating a house, a good modern heat pump uses about 1/4th of the electrical energy that resistance heating would do. For a water heater, especially a hybrid, I gather that the COP is poorer, but still better than 2. so instead of multiplying by 25, maybe multiply by 10 or 15.

I think there is a misunderstanding about what I posted. What I posted is for energy equivalence, a fixed quantity of gas energy, a unit of therms on your gas bill, 100,000BTU and how much electric kWh you need to use for 100,000 BTU of electric energy. 1 kWh is 3412.14 BTU. 29.3 kWh equals 1 therm of gas usage, 100,000 BTU. So, to heat the water, you need X amount of BTU to get up to the temperature you want. BTU is energy equivalence and to get 100,000BTU from electricity, you need 29.3 kWh of usage. How much does that cost vs 1 therm of actual gas usage. Usage what shows up on the bill.

So, if you know how many kWh your heat pump uses in a given time period, say a year and how many therms your heater replaced would have , then you can calculate which costs less. Usage will already include any COP of either heater as it is an usage measurement.

 

[dareed1]

I think there is a misunderstanding about what I posted. What I posted is for energy equivalence, a fixed quantity of gas energy, a unit of therms on your gas bill, 100,000BTU and how much electric kWh you need to use for 100,000 BTU of electric energy. 1 kWh is 3412.14 BTU. 29.3 kWh equals 1 therm of gas usage, 100,000 BTU. So, to heat the water, you need X amount of BTU to get up to the temperature you want. BTU is energy equivalence and to get 100,000BTU from electricity, you need 29.3 kWh of usage. How much does that cost vs 1 therm of actual gas usage. Usage what shows up on the bill.

So, if you know how many kWh your heat pump uses in a given time period, say a year and how many therms your heater replaced would have , then you can calculate which costs less. Usage will already include any COP of either heater as it is an usage measurement.

I've bolded an assertion which is flatly wrong. To get 100,000BTU from electricity, one needs about 6 or 7kWh of electricity, using a modern heat pump or AC unit. One would need 29.3kWh only if using a resistance type heater.

 

[charlesj]

I've bolded an assertion which is flatly wrong. To get 100,000BTU from electricity, one needs about 6 or 7kWh of electricity, using a modern heat pump or AC unit. One would need 29.3kWh only if using a resistance type heater.

My bad, sorry guys. So then the cost comparison of gas and electricity for a hybrid is cost per therm over 6x or 7x cost per kWh.
So then, at tier 2 gas of $1.90/therm electricity cost needs to be less that about $0.22/kWh to break even just for the energy costs of a hybrid.
If ones solar generation is not enough to cover the heater's needs for a year, one might be paying more.

 

[Redhill_qik]

Yes, if the water heater doesn't gobble up your over generation for the year. If it does, you would be paying the rates in effect when you used the electricity for the hybrid, no?
That x25 refers to energy conversion from a therm of gas, 100,000 BTU, to an equal quantity of electrical energy in BTU calculation so you can compare. The real number is x29.3, this is fixed for comparing equivalent energy not subject to pessimism. You need X BTU to heat water regardless the source, gas or electricity. The meters read usage.

Pulling data for 3 different real world water heater types:

Type	Uniform Energy Factor	Energy Guide Usage (annual)	kWh/Therm
Standard Electric	0.93	5334 kWh	27.5
Electric Hybrid	3.70	1240 kWh	6.4
Gas	0.87	194 Therms	1

With PG&E gas cost of $1.90/therm at Tier 2 (anything over 0.49 therm/day which I am well into with just my gas cooktop and the water heater) would be the equivalent of $0.2969/kWh for an electric hybrid. I expect my net generation to be around 4,000 kWh, so I would still be a net generator with around another 1,240 kWh consumed.

My best case net generation credit at Peak is $0.12225/kWh, but the actually consumption would likely be during Off-Peak (mornings after showers, plus advanced controls that understand peak/off-peak) at around $0.060/kWH, so this is better financially plus the benefit of a lower carbon footprint.

 

[BGbreeder]

FWIW: NREL released a report in 2016 studying heat pump water heaters in the Northeast. Observed COPs in actual use were 1.5-2.6, in unconditioned basements. Supposedly the efficiency has improved towards 4. in the last five or six years.

https://www.nrel.gov/docs/fy16osti/64904.pdf

All of the units used auxiliary electrical heat.

 

[charlesj]

Pulling data for 3 different real world water heater types:

Type	Uniform Energy Factor	Energy Guide Usage (annual)	kWh/Therm
Standard Electric	0.93	5334 kWh	27.5
Electric Hybrid	3.70	1240 kWh	6.4
Gas	0.87	194 Therms	1

With PG&E gas cost of $1.90/therm at Tier 2 (anything over 0.49 therm/day which I am well into with just my gas cooktop and the water heater) would be the equivalent of $0.2969/kWh for an electric hybrid. I expect my net generation to be around 4,000 kWh, so I would still be a net generator with around another 1,240 kWh consumed.

My best case net generation credit at Peak is $0.12225/kWh, but the actually consumption would likely be during Off-Peak (mornings after showers, plus advanced controls that understand peak/off-peak) at around $0.060/kWH, so this is better financially plus the benefit of a lower carbon footprint.

Interesting, thanks.
We have a 40 gal gas tank with 2 adults now. We use about 18 therms a month for water heating, gas dryer, and cooktop. Oven is electric. So, that table may assume a different size and usage but not bad.

I am really surprised you have that much over generation. How did you get it approved by PG&E?

 

[Redhill_qik]

Interesting, thanks.
We have a 40 gal gas tank with 2 adults now. We use about 18 therms a month for water heating, gas dryer, and cooktop. Oven is electric. So, that table may assume a different size and usage but not bad.

I am really surprised you have that much over generation. How did you get it approved by PG&E?

I currently have a 75 gallon water heater and those numbers were for 80 gallon models. We have a gas cooktop and a gas dryer, consuming 30-32 therms/month with two adults.

The PTO used the allowed highest annual amount for the last 3 years which was before I switched out every incandescent with LEDs and then a blanket statement that expected usage would increase that resulted in positive 150 kWh IIRC. Which I'll now be doing and eventually I'll add an EV.

I don't think that PG&E has any grounds to challenge that assertion. Unless you're @holeydonut in which case they will question everything, want it in triplicate and written in blood.

 

[holeydonut]

I currently have a 75 gallon water heater and those numbers were for 80 gallon models. We have a gas cooktop and a gas dryer, consuming 30-32 therms/month with two adults.

The PTO used the allowed highest annual amount for the last 3 years which was before I switched out every incandescent with LEDs and then a blanket statement that expected usage would increase that resulted in positive 150 kWh IIRC. Which I'll now be doing and eventually I'll add an EV.

I don't think that PG&E has any grounds to challenge that assertion. Unless you're @holeydonut in which case they will question everything, want it in triplicate and written in blood.

I wonder if the 120 percent rule calculation changes if you do it in blood instead of in ink.

 

[charlesj]

I currently have a 75 gallon water heater and those numbers were for 80 gallon models. We have a gas cooktop and a gas dryer, consuming 30-32 therms/month with two adults.

...

Not including house heating? That is a lot. Hard to imagine the 75gal tank takes that much more but certainly more than a 40 gal. We had 3 adults and 2 kids on that 40 gal tank before house thinned outa good 10 years ago but I'd have to look at old bills to see what summer gas costs were without a need for radian floors to be used.

 

[charlesj]

I wonder if the 120 percent rule calculation changes if you do it in blood instead of in ink.

I have not tried that but it must be so. I got 110% but doing about 125% now.

 

[Redhill_qik]

Not including house heating? That is a lot. Hard to imagine the 75gal tank takes that much more but certainly more than a 40 gal. We had 3 adults and 2 kids on that 40 gal tank before house thinned outa good 10 years ago but I'd have to look at old bills to see what summer gas costs were without a need for radian floors to be used.

It's on summer, so no house heating. The cooktop is used at least twice a day, but I'm sure that the main usage is the water heater.

 

[h2ofun]

I currently have a 75 gallon water heater and those numbers were for 80 gallon models. We have a gas cooktop and a gas dryer, consuming 30-32 therms/month with two adults.

The PTO used the allowed highest annual amount for the last 3 years which was before I switched out every incandescent with LEDs and then a blanket statement that expected usage would increase that resulted in positive 150 kWh IIRC. Which I'll now be doing and eventually I'll add an EV.

I don't think that PG&E has any grounds to challenge that assertion. Unless you're @holeydonut in which case they will question everything, want it in triplicate and written in blood.

Do you have this information somewhere in writing I can find

The PTO used the allowed highest annual amount for the last 3 years

If this is the case, I will have no issue getting my 30kw of panels approved, since I use 40,000KWh a year ago.

 

[Redhill_qik]

Do you have this information somewhere in writing I can find

The PTO used the allowed highest annual amount for the last 3 years

If this is the case, I will have no issue getting my 30kw of panels approved, since I use 40,000KWh a year ago.

Hmm, no I can't. I thought that was allowed in 2020, but the looking at my interconnect document it does say the previous 12 months. The number that is there however could have only come from a previous year. If I was a new homeowner without the 12 months of history then using the building size * 3.32 (2020) option my system would be undersized, however with the new (2021) 3.00 multiplier it would go back to oversized, but closer. My historical usage has been less than 10,000 kWh per year and I installed an 8.16 kW PV array with 2 PWs. PG&E likely didn't scrutinize the interconnect document as much as as they would for much larger systems like you are contemplating.

The wording in the interconnect document does say "NEM2 systems should be sized" and not "NEM2 systems must be sized" and I am planning on increasing my electric usage my switching natural gas appliances to electric and gas powered vehicles to EVs, so I sleep easy at night.

I can understand real grid related concerns if everyone in a local grid was to oversize to 150-300% as during peak solar generation times there may be a real possibility that exported energy from all households would exceed transformer ratings coming into the local grid. Keeping it close to 100% would eliminate the need for detailed analysis that might prevent your neighbors from adding solar because the grid can't handle it without a costly upgrade.

There needs to be some real discussion and planning with the CPUC and IOUs on how to handle the transition towards much higher electric demand that includes residential solar as a vital contributing source and not seen as a blood sucking leech.

 

[Zabe]

Do you have this information somewhere in writing I can find

The PTO used the allowed highest annual amount for the last 3 years

If this is the case, I will have no issue getting my 30kw of panels approved, since I use 40,000KWh a year ago.

40,000 kwh. Do you have multiple EV's? Are you heating/cooling uninsulated spaces? That is a massive amount of power for a home. If I were you I would get a real energy audit. You need to figure out what is wasting a crap ton of energy.

 

[h2ofun]

40,000 kwh. Do you have multiple EV's? Are you heating/cooling uninsulated spaces? That is a massive amount of power for a home. If I were you I would get a real energy audit. You need to figure out what is wasting a crap ton of energy.

Yep, it was nuts. over 2000 per month electrical bills. This is when my heating and air was removed. I had to heat the house with 10 plug in heaters. And boy did I learn these suck the power!!!!!!!

 

[charlesj]

40,000 kwh. Do you have multiple EV's? Are you heating/cooling uninsulated spaces? That is a massive amount of power for a home. If I were you I would get a real energy audit. You need to figure out what is wasting a crap ton of energy.

He may have forgotten to mention that he has a smelter on his property.

Yep, seems a huge amount.

 

[h2ofun]

He may forgotten to mention that he has a smelter on his property.

Yep, seems a huge amount.

Take 10 1500 watt heaters, turn them all on full blast to 80 degrees, and see what you meter does. 240kwh per day

 

[Zabe]

Take 10 1500 watt heaters, turn them all on full blast to 80 degrees, and see what you meter does. 240kwh per day

Why are you running 10 space heaters, I thought you had heat pumps? Do you have 10 heat pumps? I mean its your energy bill so you can do whatever you want. Maybe you are working on a warp drive...

 

[h2ofun]

Why are you running 10 space heaters, I thought you had heat pumps? Do you have 10 heat pumps? I mean its your energy bill so you can do whatever you want. Maybe you are working on a warp drive...

For 3 years, while my house was being fixed from my gravel truck hitting and and dumping 150 gallons of fuel in the ground, I have not heating and air, so had to use portable stuff. I only got my heat pumps put back in a year ago.