Powerwall - Numbers don't add up (for me at least)

[dckiwi]

Doesn't even matter it is still apples/oranges. CO has no humidity, nightime temps drop quickly reducing radiant energy trapped in the building structure, etc. The actual cooling degrees is just a fraction (about 1/3 give or take quite a bit depending upon where in CO) of what you see in the DC area. Then you factor humidity.

Good point. Regardless, I'm blown away that a ~4,000 square foot house only uses 150 kWh of electricity a month. The average refrigerator uses 29 kWh.

I guess maybe he doesn't have a forced air system of any kind? (presumably the air handler consumes a lot of power, regardless of whether the AC unit is running). Really need more details.

Anyway, this thread has been an eye opener for me. I'll never get to 150 kWh /month but I'm sure we can do a lot better.

 

[SageBrush]

Doesn't even matter it is still apples/oranges. CO has no humidity, nightime temps drop quickly reducing radiant energy trapped in the building structure, etc. The actual cooling degrees is just a fraction (about 1/3 give or take quite a bit depending upon where in CO) of what you see in the DC area. Then you factor humidity.

EDIT: Although do you need to run AC in the summer where you live in Colorado? If not, kind of apples to oranges comparison.

You are confusing 'want' and 'need.'

Most of the homes in my locale use AC in the summer, although it is certainly true that the annual cooling load is less than VA or DC. Perhaps you two should be asking yourselves if your home consumption drops to 150 kWh a month in the months off summer peak ?

 

[SageBrush]

The average refrigerator uses 29 kWh.

Actually, at least 2x, if not 3x if you include appliances over 10 years old.

This graph shows evolving standards:



A one kWh per day fridge (plus freezer) is an unusual beast. I had to look long and hard for a 400 kWh per year appliance for my Albuquerque home when I bought a replacement a few years ago. Our rental home appliance is ~ 700 kWh a year.

 

[SageBrush]

but I'm sure we can do a lot better.

That was exactly my starting point about a decade ago when I decided to cut my home's pollution contribution. IIRC I was averaging close to 1000 kWh a month back then.

I started by inventorying all our uses. Then working from the largest to the smallest I cut out waste, changed behaviors, and learned to buy stuff with efficiency a top priority. I spent years at it (mostly waiting for stuff to age) but no rocket science was required.

 

[dckiwi]

Perhaps you two should be asking yourselves if your home consumption drops to 150 kWh a month in the months off summer peak ?

It definitely does not - it drops to about 1k kWh in the winter. Of course, we are still using the air handler in our HVAC system (gas heat). I'm still curious - do you actually have a central forced air system in your house or not?

 

[SageBrush]

It definitely does not - it drops to about 1k kWh in the winter. Of course, we are still using the air handler in our HVAC system (gas heat). I'm still curious - do you actually have a central forced air system in your house or not?

Our home in Abq does; I'm not sure about the Colorado home because it has an attic I have yet to crawl into. At least two vents blow AC into the home from their so if it is "central," it is probably a short run. Heating is from sub-floor radiant that uses a wall of pumps to circulate the heated water.

You absolutely right that central air is an energy hog. I do my best to minimize it's use by using fans, windows, and ventilation instead.

 

[dckiwi]

Our home in Abq does; I'm not sure about the Colorado home because it has an attic I have yet to crawl into.

Wait so you don't live full-time in the Colorado home? That would help explain the low power usage as well. I only have one house

 

[bak_phy]

Really?

Btw, why is the residential electricity consumption so high in the US?

My annual electricity consumption is 3800 kWh, my 4-person house is about 300 m^2 (but not using electricity for heating nor for transportation).

It's mostly due to AC. Each Degree Celsius costs me 200Kwh a month in the summer. Since Munich is about 6 degrees C cooler than NJ where I live that's 1200KWh right there. And NJ isn't even very warm by US standards. Many places you not only have much higher summer temps you also have to run the AC for 8 months.
The fridges also tend to be quite a bit bigger but I don't know how much that adds up to.
I have an old 600m2 house and in the winter I use about 750kwh per month of which 300kwh or so is for charging the car.

 

[AB4EJ]

Good point. Regardless, I'm blown away that a ~4,000 square foot house only uses 150 kWh of electricity a month. The average refrigerator uses 29 kWh.

I guess maybe he doesn't have a forced air system of any kind? (presumably the air handler consumes a lot of power, regardless of whether the AC unit is running). Really need more details.

Anyway, this thread has been an eye opener for me. I'll never get to 150 kWh /month but I'm sure we can do a lot better.

I'd like more details on the 150 kwh/mo house. Maybe the climate is favorable; maybe there are very few items in the house that use electricity. Here in the southeast US, with punishing heat in summer and still cold winters, I would be very excited if I could get my average usage down to 1,500 kwh/mo.

I know how this can be done, at least in the vicinity of Mobile, AL, because a friend of mine did it... but he was starting from scratch (nothing but a vacant lot there to begin with). The house has foot-thick walls with urethane foam inside, same for the attic (something like R-30 insulation); geothermal is used for cooling (i.e., no compressor); due to location, heating is almost never required. Windows are triple-glazed. All lights are controlled to go off automatically when nobody is in the room. The family rations its use of TV and other appliances. Computers are laptops that turn off automatically after 2 minutes of non-use. Everyone in the family is trained and committed. That wouldn't work at my house, my wife doesn't realize that any appliance or light has an off switch. And believes that one shouldn't have to worry about this.

So, to make at least some impact, I put in a 10 kw solar system (grid tied), and at least I can do laundry or charge the Tesla between noon and 3 pm during peak solar production. Between the low payment rate for excess generation (3.5 cents/kwh) and the steep monthly fee for the interconnect ($50/mo), it will never pay for itself (due to shading from trees during the morning, solar production doesn't start in earnest until around noon, which also limits my total production); but at least I'm trying.

One thing I need to do is (as mentioned earlier in this thread) is a complete energy audit. I'm sure I have air leakage and insulation problems that could be remediated... still, 150 kwh/mo would not cover the energy needs even of a single bathroom in the typical American house...

 

[bak_phy]

As a side not 150kWh a month is just running 2 100W bulbs 24/7.

 

[dckiwi]

As a side not 150kWh a month is just running 2 100W bulbs 24/7.

Maybe his house only has one 100w bulb?

 

[bak_phy]

US total electricity usage peaked in the middle of 2008 after increasing pretty consistently each year for more than 100 years! It's been pretty steady since then but we are about 15% below trend.

 

[SageBrush]

Wait so you don't live full-time in the Colorado home? That would help explain the low power usage as well. I only have one house

We live full-time in Colorado -- for the past two years. I mention the Abq home for comparison and more data for you. It is not sold yet so I still call it mine. And the inefficiencies present in my rental home annoy me ;-)

There is no hidden trick to my consumption data, and I do follow it close enough to report pretty accurately.

 

[electracity]

 

[SageBrush]

As a side not 150kWh a month is just running 2 100W bulbs 24/7.

We run a lot less lighting than that:

• About six night lights at 0.5 watt each run every night
• All bulbs used more than a few minutes a day are either LCD or LED that range from 70-90 lumens/watt.
• The kitchen has 5*10 watt, the work-room 3*12 watt
• The remainder of the house has single, ~ 5 - 10 watt bulbs (somewhere in the range of "60 - 90 watt incandescent" equivalent

Lights are off unless they are being used. In the summer, lighting use is perhaps an hour a day. In the winter more like 3-4 hours.

 

[SageBrush]

still, 150 kwh/mo would not cover the energy needs even of a single bathroom in the typical American house...

... at my house, my wife doesn't realize that any appliance or light has an off switch. And believes that one shouldn't have to worry about this.

That pretty much sums things up.

Conservation requires an effort.

 

[electracity]

With LEDS I started automatically turning on lights again. I don't think that nagging about lights is worth the 50 cents a month it may save.

 

[aesculus]

That wouldn't work at my house, my wife doesn't realize that any appliance or light has an off switch. And believes that one shouldn't have to worry about this.

Well to be honest she and everyone else are a bi-product of the electric utility and appliance industries touting you 'can have it your way' for the last 75 years until just recently. So it's to be expected.

 

[nativewolf]

We run a lot less lighting than that:

• About six night lights at 0.5 watt each run every night
• All bulbs used more than a few minutes a day are either LCD or LED that range from 70-90 lumens/watt.
• The kitchen has 5*10 watt, the work-room 3*12 watt
• The remainder of the house has single, ~ 5 - 10 watt bulbs (somewhere in the range of "60 - 90 watt incandescent" equivalent

Lights are off unless they are being used. In the summer, lighting use is perhaps an hour a day. In the winter more like 3-4 hours.

Do you cook? Is the water heater, oven, and heating all gas? I mean if you are a family person and cook an hour a day on a decent stove/oven you are going to use 90 per month alone. That's without really doing a lot of fancy cooking. Do you have kids? Just curious. I think with just basic appliances/cooking I'd blow 150/month without blinking. Curious

 

[winfield100]

context please