Does a battery ever have a positive ROI with net metering

[mswlogo]

If I'm home, I would assume I could load shed and it would be useful for an extended outage (keep the fridge and freezer going). At least better than neighbors that had nothing.

But ultimately a generator with a local fuel source would clearly be the most reliable.

Problem is the GeoThermal is on 2 breakers. A 50A and a 60A. It has a backup straight electric heating element but the fan is on that circuit too. Plus hot water 30A. Plus well 20A. Plus Fridge 20A. That’s 160A + amps. They would design backup for peak load. So they would probably require 4 Powerwalls. Maybe 3. Normally Geothermal is pulling like 700 watts to maintain temp.

So with a Generator I back feed the whole panel and I manually “load shed”. Generator is small but it can handle “normal loads” with conservation. If it’s 50F below 0F when we lose power I might run into trouble. I’ll run Heat Only and disconnect the heating element, turn off well and hot water to keep house from freezing. Most Geo has ever pulled is 2000 watts but in theory could go much higher.

 

[cali8484]

Problem is the GeoThermal is on 2 breakers. A 50A and a 60A.

So, that's 26kW+ peak (21kW+ continuous @ 80% of peak) for heating? I don't know much about GeoThermal but I thought it's supposed to be efficient so the electricity requirement is surprising to me. Running batteries or generator even for 21kW of heating seems very inefficient. Have you considered hybrid heating systems that can take advantage of natural gas or propane at least during power outages?

 

[mikesm]

Grid is grid. Batteries are a very wise investment if your goal is energy reliability. ROI might not even make it onto the goal list for many people. It didn't appear on mine.

I disagree. If reliability is the number one goal, it's very hard to beat a quality diesel or natural gas/propane generator. They work when it's cold and overcast, and they work in the dead of winter when you have fewer hours of charging time available, and they work when you have a large house and a lot of energy demand (if sized properly), and if diesel they can even be refueled by you with a decent storage container.

Batteries depend on solar,, and even in CA where I live we had some pretty grey days with power outages this past winder. 3 days of power outage, and my diesel generator didn't even get to 60% of tank storage.

Now, I am not talking about some cheap home depot gas unit that needs oil or rebuilding after a couple days of runtime. You want a quality unit,. But if you have one, it's far better than depending on the sun always being there for your family.

 

[nwdiver]

I disagree. If reliability is the number one goal, it's very hard to beat a quality diesel or natural gas/propane generator.

 

[zƬesla]

The problem with backup is I use 50Kwh a day on average In winter. House is entirely electric. Geo thermal heat etc. spring / fall is 30kwh a day and summer ~40kwh a day.

Must be a well insulated house. We have mini-splits and can use ~80kWh in winter. On days the dryer gets run, it puts us over 100. Summer time we're around 30, and in between as low as ~15.

If TOU does come to Eversource NH then that could change numbers drastically.

There's the R-OTOD 2 rate: https://www.eversource.com/content/...riffs/nh-summary-rates.pdf?sfvrsn=eefadaef_24

I think 50kWh usage daily is a lot. We use like 15kWh or 20kWh daily if we aren't car charging. Of course, if it's not summer, we don't use much power/heat for anything.

You're in SoCal. We're in NH.

 

[TacoGuy]

But it can avoid putting gas in a car. I no longer do that, for example. Another factor to consider.... my own ROI calc for my entire system moved into "maybe I'll live to see it" territory when I threw in the cost of the Tesla car, the PWs, and the Solar Roof. Without the PWs, the date moves on out again. So, while batteries may not support a feasible ROI on their own, they can contribute to to an overall situation that reaches a feasible ROI when combined with other investments that enable the avoided cost part of the calc to get significantly larger. Especially if net metering isn't in the picture, or even if it is - but then disappears.
Every case is different though - my own did not involve a loan, and that always helps bring an ROI a little closer

I'd like to see how that works for your specific case. In my scenario there are pennies to be had daily, but no ROI on the Batteries in >10 years

 

[sunwarriors]

You're in SoCal. We're in NH.

Exactly. If the worst energy pricing in the USA (San Diego, $0.89/kWh I think peak summer at 130% baseline) requires no ROI calculations for a battery to consider whether it's worthwhile, I again thinks folks should not bother with ROI calcs and just weigh the other benefits is what I've been harping on since my own Solar/ESS install happened. I did do ROI math and we have bad ToU rates too where there is probably some timeframe, but legislation may change, warranty/issues/rates may drop (after massive monthly fees)/everything else.

 

[BGbreeder]

It’s a brand new Post and Beam with SIP panel roof and walls (solid foam). With GeoThermal it cost $150 to heat in January. The only fossil fuel I use is Propane for Generator and BBQ. It also has an ERV system because it’s so tight we’d poison our self’s without it.

You can see the SIP

This is the 15Kw Enphase Solar

So where would I put the added insulation again

Gorgeous!

Yes, I can see that if your geothermal needs back up resistance heat, that could be a significant issue.

If the geothermal runs 0.7kWh (16kWh/day) what creates the other 64kWh of load? I'm used to seeing heating dominate in NH in winter.

I would be tempted by a diesel generator, and use a branch of the geothermal to dump the generator heat, basically a heat pump boosted cogeneration system.

Again, even with 4 powerwalls, there really won't be a way to recharge them effectively in a winter storm under Tesla's current system.

All the best,

BG

 

[mswlogo]

So, that's 26kW+ peak (21kW+ continuous @ 80% of peak) for heating? I don't know much about GeoThermal but I thought it's supposed to be efficient so the electricity requirement is surprising to me. Running batteries or generator even for 21kW of heating seems very inefficient. Have you considered hybrid heating systems that can take advantage of natural gas or propane at least during power outages?

Geothermal is efficient. Peak load has nothing to do with average load. Like I said I’ve never seen it pull more than 2kw and typically it’s less than 1kw. But since it can pull those watts that’s what they would wire it up for.

Your Tesla can charge at 250kw. Does that make it inefficient?

 

[mswlogo]

I think it's just silly to assume having batteries alone will be enough/useful for anything other than ToU shaving, less peak grid use or outage usage. A week of no sun makes any battery setup dead in the water really (after 1 day). There could be storms, clouds, fires (in CA). Batteries alone will never be enough. You need another power source and the ole generator is still great for almost all those cases at a cheaper cost. Generators need maintenance though, are dirty, noisy, tells everyone you're running a generator, etc, but they do the job for longer term outages and it's the only solution currently I've seen here from following it here and everywhere else.

I've stated before and still suggest that folks think a battery will do ROI is wasting their time. Remove that from your equation and measure/value the other non-monetary ROI stuff. Simply, don't lie to yourself or convince the spouse that there is ROI. It makes the purchase so much easier/comfortable if you don't have it and decide after what to do.

I think 50kWh usage daily is a lot. We use like 15kWh or 20kWh daily if we aren't car charging. Of course, if it's not summer, we don't use much power/heat for anything.

That is with the car (but we don’t drive much) and I have zero fossil fuel heat sources and I live in the northeast. That is my total energy usage. I planned it that way so I could cover everything with solar. I might be a little shy. Partly why I was interested in a battery to squeak more out of the PV

 

[mswlogo]

Gorgeous!

Yes, I can see that if your geothermal needs back up resistance heat, that could be a significant issue.

If the geothermal runs 0.7kWh (16kWh/day) what creates the other 64kWh of load? I'm used to seeing heating dominate in NH in winter.

I would be tempted by a diesel generator, and use a branch of the geothermal to dump the generator heat, basically a heat pump boosted cogeneration system.

Again, even with 4 powerwalls, there really won't be a way to recharge them effectively in a winter storm under Tesla's current system.

All the best,

BG

Think of your Tesla wh/mile when doing 40mph. That’s what my geo is normally doing. Just maintaining. Now what is your Tesla wh/mi doing 0-60mph up hill -20F with heat towing 5k lbs.
That’s what geothermal can do if asked. It’s 4 ton water furnace.

 

[Transformer]

Must be a well insulated house. We have mini-splits and can use ~80kWh in winter. On days the dryer gets run, it puts us over 100. Summer time we're around 30, and in between as low as ~15.

We got an LG DLHC5502W heat pump dryer a couple weeks ago. It's energy report shows each cycle using only 0.24 - 1.7 kWh.

And since it's ventless, it doesn't pump indoor air to the outside. That saves heating/cooling replacement air.

 

[zƬesla]

We got an LG DLHC5502W heat pump dryer a couple weeks ago. It's energy report shows each cycle using only 0.24 - 1.7 kWh.

And since it's ventless, it doesn't pump indoor air to the outside. That saves heating/cooling replacement air.

heat pump dryer is on the buy list for when our current one bites the dust

 

[ItsNotAboutTheMoney]

We got an LG DLHC5502W heat pump dryer a couple weeks ago. It's energy report shows each cycle using only 0.24 - 1.7 kWh.

And since it's ventless, it doesn't pump indoor air to the outside. That saves heating/cooling replacement air.

Well, the heat still has to go somewhere, but you're using generating less of it. I have a regular electric dryer and it's vented. I've always thought that odd in a place that needs net heating when cooling is cheaper than heating.

 

[BGbreeder]

Well, the heat still has to go somewhere, but you're using generating less of it. I have a regular electric dryer and it's vented. I've always thought that odd in a place that needs net heating when cooling is cheaper than heating.

That's true, but the energy is used mainly to evaporate water from clothes (cooling the dryer air), and then the water is condensed and drained, and the refrigerant is compressed, and the warm refrigerant is used to warm the previously cooled dryer air. A little energy is lost due to friction in the movement of the clothes.

Net, the 1kWh or so of energy used by the dryer is transferred into the water, and down the drain. 1000W into a couple of pounds of water is the primary result; of course the dryer gets a little warmer in the process as well.

Why do you write that "cooling is cheaper than heating"? In what sense?

All the best,

BG

 

[ItsNotAboutTheMoney]

That's true, but the energy is used mainly to evaporate water from clothes (cooling the dryer air), and then the water is condensed and drained, and the refrigerant is compressed, and the warm refrigerant is used to warm the previously cooled dryer air. A little energy is lost due to friction in the movement of the clothes.

Net, the 1kWh or so of energy used by the dryer is transferred into the water, and down the drain. 1000W into a couple of pounds of water is the primary result; of course the dryer gets a little warmer in the process as well.

Why do you write that "cooling is cheaper than heating"? In what sense?

All the best,

BG

I meant that when _not_ using a heat pump, you use efficient heat exchange (air conditioning) for cooling, and combustion of fuel for heating.
So venting out the hot air just seems wasteful for those of us who live in cold climates.
I guess it's the humidity of the air that's the issue. Maybe it was more necessary to vent when drying laundry washed with low-efficiency washing machines that leave it more sodden.

(When people heat with wood here, they will sometimes _deliberately_ humidify because poor ventilation and the air pulled in by the wood stove lead to dry air.

 

[h2ofun]

I think it's just silly to assume having batteries alone will be enough/useful for anything other than ToU shaving, less peak grid use or outage usage. A week of no sun makes any battery setup dead in the water really (after 1 day). There could be storms, clouds, fires (in CA). Batteries alone will never be enough. You need another power source and the ole generator is still great for almost all those cases at a cheaper cost. Generators need maintenance though, are dirty, noisy, tells everyone you're running a generator, etc, but they do the job for longer term outages and it's the only solution currently I've seen here from following it here and everywhere else.

I've stated before and still suggest that folks think a battery will do ROI is wasting their time. Remove that from your equation and measure/value the other non-monetary ROI stuff. Simply, don't lie to yourself or convince the spouse that there is ROI. It makes the purchase so much easier/comfortable if you don't have it and decide after what to do.

I think 50kWh usage daily is a lot. We use like 15kWh or 20kWh daily if we aren't car charging. Of course, if it's not summer, we don't use much power/heat for anything.

In the winter with my heat pumps I probably use 60 to 100, especially now that I have an EV. My lowest solar production has been about 8kwh. So, NO WAY would batteries EVER make sense to say they could power my house.

 

[cali8484]

Geothermal is efficient. Peak load has nothing to do with average load. Like I said I’ve never seen it pull more than 2kw and typically it’s less than 1kw. But since it can pull those watts that’s what they would wire it up for.

Interesting. That's a lot higher running/peak ratio than regular HVAC. If your particular system only pulls 2kW max then it seems excessive to design backup for 10x that.

 

[offandonagain]

Interesting. That's a lot higher running/peak ratio than regular HVAC. If your particular system only pulls 2kW max then it seems excessive to design backup for 10x that.

The peak load is probably for backup heat / strip heat. That is a lot less efficient, but will only kick in if the geothermal system fails (or in case of air-source heat pumps, if the outdoor temperature is too low). You don't usually see backup heat installed in milder climates like CA.

 

[Unclepaul]

Overall, as Solar gets cheaper and electricity gets more expensive, the number of situations where Solar will make financial sense will grow.