Wall of 10 Tesla Powerwall 2 units

[Patrick66]

I'm not familiar with it. Since most heat is lost through the ceiling, as heat rises, that is where we started. I'm skeptical about retrofitting foundations as being effective for much of anything. If you technical information about it, I'd be interested in seeing it. Thank you.

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I had a white paper somewhere that I will try to find, but here is a quick link: Frost-Protected Shallow Foundations - Fine Homebuilding While convection heat losses are significant, conductive losses through the slab can be quite substantial once your roof is properly insulated and your walls are tight.

If your home started as a barn and the slab is not insulated then it can make a big difference. Beyond the absolute heat loss, the perception of cold reduces significatly if you have any tile or concrete floors in the home. If you have an non-contact IR thermometer, see what your floor temperature is relative to the space temperature— that should give you an idea if it is worthwhile. More than about 5 degrees below your indoor temperature and you should see some improvements.

If you have already put a floating floor above the slab on grade with insulation then the benefits would be minor.

 

[Jason Bloomberg]

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I had a white paper somewhere that I will try to find, but here is a quick link: Frost-Protected Shallow Foundations - Fine Homebuilding While convection heat losses are significant, conductive losses through the slab can be quite substantial once your roof is properly insulated and your walls are tight.

If your home started as a barn and the slab is not insulated then it can make a big difference. Beyond the absolute heat loss, the perception of cold reduces significantly if you have any tile or concrete floors in the home. If you have an non-contact IR thermometer, see what your floor temperature is relative to the space temperature— that should give you an idea if it is worthwhile. More than about 5 degrees below your indoor temperature and you should see some improvements.

If you have already put a floating floor above the slab on grade with insulation then the benefits would be minor.

If we lived where there was colder ground temperatures, such as in the arctic that might be true, but not so much in our climate. New construction uses that, but no one around attempts such a retrofit. It simply is cost prohibitive. Doing our insulation project of removing the old R38 blown insulation, sealing the airgaps, and blowing in to R-90 was a week long job costing about $12,000. The benefit is already evident with the Waterfurance (ground source heat pump) using about half the electricity as last year this month. I put a blue dot on the AFI Map from the article at your link so you can see where we live and why it would not make much yield for us as a retrofit. Thanks for the information. It may be more useful for someone else, so I'm glad to have it in the thread. While we don't have a "floating floor" the house is carpeted throughout with a thick padding which also gives us some separation from the slab.

 

[Ed Hart]

You just needed to provide them with an updated green button file. My first pass they reject my five and said I only justified 2. My second pass they approved 5 when I had justified 7

Well....I probably won't get another shot at it.
Good going!!

 

[h2ofun]

Well....I probably won't get another shot at it.
Good going!!

Yep, PGE money gone

 

[mswlogo]

why do you need that much? I don't think I could use more than 100kwh in a day even with a 5T ac running in the hot summer.

That’s what I was thinking. What is the ROI, a 100 years? When the equipment might last 20 years?

 

[Big Earl]

why do you need that much? I don't think I could use more than 100kwh in a day even with a 5T ac running in the hot summer.

Here’s an example from my own 1954 house. 1,200 square feet, three adults with three EVs and a plug-in hybrid. Gas heat, hot water and cooking. 2 ton 10 SEER A/C.

Summer:

Winter:

 

[Jason Bloomberg]

why do you need that much? I don't think I could use more than 100kwh in a day even with a 5T ac running in the hot summer.

Our home is all electric in a cold climate. The ground source heat pump is a 5 ton system. While cooling in summer isn't a big load here compared to sun/wind power generation, in winter, here in Cheyenne, Wyoming heating the house is. We easily can use 20 - 30 kWh per vehicle and 30 - 70 kWh for home heating. On low or no gain days (little to no wind or usable sunshine [overcast or snow/ice covered PV]) we can use the full 135 kWh of reserve in little more than 24 hours. The Powerwall 2 system we have has reduced the amount we net metering with the grid, but is too small for us to transition to becoming an off grid system. Here's some screenshots from January. Since then Tesla has made some adjustments from afar and the system has improved because of those changes. It will be interesting to see how it in February and March.

Part of how we sized our system was based on electricity usage by the ground source heat pump last year.

 

[Jason Bloomberg]

Here's a link to a short video about our system. Enjoy.

 

[Jason Bloomberg]

Here is a link.to another video about our system.
Not narrated. Returning home after an overnight shift in the hospital. Here is what I see when I drive upto our home and plug in our electric car, powered by wind and sun harvested on our property. "We drive by perpendicular magnetic fields fueled from wind and sun."

 

[Puma2020]

Wow.
Great information. Thanks.

 

[StealthP3D]

This is crazy. Either it is some community of 20 or so residences, or the Tzar's winter pallace. My 2000 sf house never uses more than 25 kWh a day either with peak winter heating or peak summer cooling with a Heat Pump AND Tesla charging.

Spending just a little on insulation and passive heating might be 10 times as cost-effective.

I agree. The first step towards sustainability should always be reduction in what you need to live a productive and fulfilling life. Many people greatly overestimate what that is.

When talking about manufacturing, Elon Musk said, "The best part is no part." I'm pretty sure he would also say, "The best energy is that which is not needed."

 

[Jason Bloomberg]

I agree. The first step towards sustainability should always be reduction in what you need to live a productive and fulfilling life. Many people greatly overestimate what that is.

When talking about manufacturing, Elon Musk said, "The best part is no part." I'm pretty sure he would also say, "The best energy is that which is not needed."

 

[Jason Bloomberg]

This is crazy. Either it is some community of 20 or so residences, or the Tzar's winter pallace. My 2000 sf house never uses more than 25 kWh a day either with peak winter heating or peak summer cooling with a Heat Pump AND Tesla charging.

Spending just a little on insulation and passive heating might be 10 times as cost-effective.

We actually upgraded our attic insulation from R-36 to R-90 after having the ceilings air sealed in the attic. We also replaced all of our windows and replaced our propane furnace with a ground source heat pump, and have added direct solar PV water heating. There are significant differences in home energy usages between Flagstaff, AZ where you live and Cheyenne, WY where we live.


On an annual basis we produce more electricity than we consume. One of the technical challenges for us is to balance generation and usage in order to minimize utilizing the grid. This is where the batteries fit into our system beyond being a backup source of electricity during grid outages.


Our home is all electric. We monitor our electricity use using SENSE (R) which helps us understand which which devices are using electric at any given moment as well as daily, weekly, monthly

, and annual consumption. It also gives a comparison of our electricity usage with other homes equipped with SENSE (R) in Wyoming and the United States. While our electric vehicles account for ~30 kWh/day, our overall daily use of electricity in February 2021 was ~102 kWh/day, which is the average in Wyoming for typical homes which also have fossil fuel heating. Nationally in the United States the average electricity use for the same period was 69 kWh/day.


There are 100,000 BTUs per therm of natural gas. There are 91,740 Btus per gallon of propane. There are 3413 BTUs per kilowatt hour of electricity.


Comparing electric home heating to combustion is not intuitive because it takes a large quantity of electricity to creating the same amount of heat as combustion, but because electricity can be made by renewable sources, when it is sourced that way it remains the environmentally better wat to do it. That does not make it cheaper in the short term. When people talk about monetary costs, rarely do they include the environmental costs of man made climate change or the health impacts of air pollution. From my perspective, fossil fuel use can be seemingly cheaper for the end user, but that is due to cost shifting the real expenses of environmental and health impacts on to others.


Here is a link to information about SENSE (R): Sense: Track energy use in real time to make your home more energy efficient.


It's a device / system we use. Others may use other similar equipment. I'm posting the link so you can understand what I referred to, not trying to promote it.

 

[Jason Bloomberg]

I agree. The first step towards sustainability should always be reduction in what you need to live a productive and fulfilling life. Many people greatly overestimate what that is.

When talking about manufacturing, Elon Musk said, "The best part is no part." I'm pretty sure he would also say, "The best energy is that which is not needed."

See my reply to Zeronet for some details, but we already have done the appropriate mitigation of use. It is much more challenging to retrofit an existing home to make it more energy efficient.

Our home stated out as a pole barn and was finished out as a house in the 1980's by its original owners. We have been upgrading it since we purchased it in 2001. We looked at tearing it down and rebuilding it, but that did not make sense environmentally, and was outside of our financial reach at that time, so we have made substantial, but incremental improvements while living in it.

 

[Dave EV]

We actually upgraded our attic insulation from R-36 to R-90 after having the ceilings air sealed in the attic. We also replaced all of our windows and replaced our propane furnace with a ground source heat pump, and have added direct solar PV water heating.

Nice, sounds like you have done a lot to minimize your energy use, which isn't easy in an all-electric house in the winter in Wyoming.

On the topic of efficiency upgrades, have you considered or have you had blower door test to look for air leaks in your house? My research in the area has shown that leaks are the biggest source of heat leakage in a home and things like insulating beyond R30 or so quickly reaches the point of diminishing returns unless you have sealed your home well.