If you have excess generation during the day, why don't you cool your house to 72 in the late afternoon and then back to 78 when the sun starts setting? It would probably delay you batteries having to power your AC for about 4 hours.

This. Energy can take many forms. You don't have to store all in a battery.

Another idea: assuming you have an electric water heater, when your battery has been fully charged and you still have excess generation, use the excess to heat your water heater up to a very high temperature like 80 degrees C. You'll then be using very little hot water in the evening for showers and dishwashers, etc, and the water heater basically won't need to turn on at all.

> use the excess to heat your water heater up to a very high temperature like 80 degrees C

Wouldn't that be quite dangerous? That's basically instant scalding temperature if anyone accidentally turns on just the hot.

You can get a mixing valve that's installed at the heater. Very easy, then turn the heater up really high, they are only like $15-20 and will effectively double or triple your hot water capacity.

e.g. https://www.watts.com/resources/references-tools/thermostati...

Do not install these if you have hard water, they will clog up extremely fast - and the hotter your hot water is, the faster it will clog up.

Which is especially amusing considering this is PG&E territory. The bay area water was so hard you could make limestone castles by rinsing a glass.

Interesting, I didn't know those existed. Seems like it makes a lot of sense.

It also seems like if you simply leave it on a higher temperature 24/7 it will use more power due to thermal losses overall. This is a great hack for households with several people who like to take long showers (and thus run out of hot water), though, or if you can do some sort of variable temperature setpoint to store energy as described in the thread, though I think at least in the US electric tank-based hot water heaters are relatively uncommon.

There are new 120v heat pump hot water heaters that operate in this way:

https://cleantechnica.com/2021/11/29/120-volt-heat-pump-wate...

"120 volt heat pump water heaters come with a mixing valve integrated into the water heater itself. This mixing valve allows owners to keep their water at a higher temperature and as the water leaves the tank, the valve will mix “in the exact amount of cold water needed to ensure the water comes out of the water heater at the correct temperature.”

I've been thinking about this. Do you/anyone happen to know if it's a decently efficient use of the stored energy?

I love the idea of our hot-water boiler acting as battery (potentially along with another actual electric battery).

I have a handle on the hardware, but not on the efficiency of it.

Thanks,

Make sure you adjust your faucets so they won’t go full hot. Don’t want to scald someone.

Technology Connections does a similar thing, over-cooling his house at night as a thermal battery.

Video: https://www.youtube.com/watch?v=0f9GpMWdvWI

Reddit discussion: https://reddit.com/r/technologyconnections/comments/oo2b3i/b...

He estimates it at 16 KWh of storage. Same ballpark as a Powerwall, right?

And/or add more thermal mass to the house.

We do this here in Sonora, CA. Our PV array supplies more than our A/C uses. We turn the A/C on around 10am, cool to 70°, turn off at 3pm. House insulation has limited indoor temperature to 76° on recent 101° days.

If you live in one of the 26 states that have time-of-use rates (mine is 21¢ peak and 1¢ overnight), you can enroll in that, import your schedule in the powerwall app, and it will automatically deliver the bonus power to your house during the peak, allowing you to export even more solar to the grid during high demand.

Enphase batteries support this too. (I suspect all brands do.)

Do you have any documentation on that? I have a hard time finding the relevant details on this.

It looks like it’s cooler outside at night these days (below 70ºF between 9pm and 7am). I’d recommend that you air out your whole house with a big draft when that’s the case: fresh air, less CO2 indoors, but also a big saving on cooling. That’s what my grandmother did all summer in Provence, and she never needed AC. If you power-cool in the afternoon to use your house as a thermal battery, you might only need to do it in the morning, but it’s always very enjoyable.

People have mentioned roof insulation. It’s a good idea, although if you have solar panels, you might want to cool the outside of the roof under the panels to improve their efficiency. I’ve seen technology using water evaporation; maybe that one is less popular these days. There should be a way to do it by heating the water for your shower.

The most effective idea is a lot low-tech though: outside blinds. Covering your glass windows from the outside is what prevents most of the heat from getting in. Even better if you can have slated blinds that block the sun but let the air through. Anywhere traditionally warm in summer (i.e. built before AC), I’ve seen houses with wooden blinds that you can shut all day, while you keep the windows open.

If you consume that little electricity, the $2 they’d pay to pull from your power wall is probably 8-10x what you’d pay to refill it from the grid.

Nah the grid hook up fee is likely the bulk of the cost. Simply being connected is the most expensive cost

Where I live the connection fee is $20/mo and bi monthly bills are anywhere from $100 to $1900, we have electric heat in and older house

Electric baseboard heat with minimal insulation?

A heat pump is much more efficient than electric baseboard heat, you might as well run your computer to generate heat since it is equally as efficient as electric baseboard heat or space heaters.

Idea: sell space heaters that secretly are bitcoin mining rigs.

Funnily enough it's been done:

https://heatbit.com

https://bitcoinminingheater.com

If only we could have the heater PCs do something actually useful.

Imagine showing this real product to yourself 15 years ago.

And imagine actually using one of these. Space heaters are one of the leading causes of fires, these ones seem like they have much greater fire risk since the Bitcoin stuff adds complexity that regular space heaters dont have.

Lots of insulation but probably crappy tenants leaving windows open. Also it is -20 outside.

One thing to keep in mind, is that during periods of high demand they run the most inefficient, most polluting power sources, like diesel generators or natural gas peaker plants which are generally less efficient. So by dumping power on the grid when it's most needed you're reducing CO2 output more than if you just kept it for yourself. You then use it back when demand is low (early morning/late night) and efficient power sources are running.

This. There's an entire industry around getting companies to use their industrial generators at peak energy consumption times (and also do things like turn down their thermostats). The power bill for a huge electric user is absolutely massive if they're hitting hard at peak peak times. Like several percent of their annual energy cost can come from a few hours of use.

What does your attic insulation look like? Blown in cellulose to roughly R-60 made an instant difference and was the best ROI home improvement I've ever done.

This x1000.

Blow in, not spray on, insulation is the easiest, cheapest, bang for your buck home improvement I ever made. It took 3 hours and ~$1000 of insulation from Home Depot.

The house maintains its temperature so much better. Outside noise is reduced. My bills are smaller. And I can keep my AC at 72 now - or whatever temperature I feel like really.

Another one of the pitfalls of houses not being affordable.

I life in Maine. We get freezing winter every damn year. My apartment was built in like the 80s, there is no insulation (three of my walls are 3 inches of concrete and then the outside), windows and doors are the utter cheapest shit that doesn't even seal, heat is electric resistive hot water, electricity has always been expensive in Maine, but that's okay they make me pay my own.

Result, building owner got to cheap out in a hundred ways, pass the externalities on to me, I have no way to fix it, and my electric bill in the winter for one person in 600 sq ft kept to 70 degrees costs $250.

Where's Greta when you need her. I feel like I should have standing to sue the property owner on the planet's behalf.

Did you ask about the bill in winter before signing the lease? It’s a standard question before signing a lease in Chicago. Are you otherwise ‘getting a deal’ on rent and now you know why it was a deal?

No, I am not getting a deal, I am paying quite a bit. I had some warning, when I signed up with the power company they required a deposit "based on location usage" which they sized at $350, so I knew ahead of time that was going to suck.

We are in a similar situation!

To help with this, we had a second Tesla battery installed!

Although, sadly, in South Australia, Electricity is charge at a flat rate, day or night!

You get paid for the power your battery provides to the grid. Power is generally cheaper at night as there is less demand (at least the spot price is cheaper, not sure how your utility passes that savings on to you). It seems like it's totally possible that it's better for you economically to allow your battery to power the grid during the day. You'll have less charge in your battery for the night, but hopefully you can get power at a cheaper price.

I wonder if a whole house fan would help avoid using the AC through the night. Of course, the next obvious question about is it worth the installation cost...

We have a whole house window fan that was probably manufactured in the 50’s (“Homart Cooler”). It is excellent for upper Midwest summer nights. Our house is old enough to make ducted AC a nonstarter, so the ability to cool the interior of the house over night is very helpful.

Agree with ductless A/C, we are in a 100 year old house with radiator heating and the ductless A/C cools two floors admirably.

try high velocity ducted ac, via heat pump. the ducts are 1.5 inch diameter flexible insulated pipes. Alternatively, ductless AC (minisplit) via heat pump. That said, whole house fan is nice.

I have a whole house fan, and it's awesome. Cools the house down really quickly at night. I mostly did fine in the Pacific Northwest without any A/C until a couple years ago. A whole house fan is worse than useless, though, when you have wildfire smoke and it isn't getting below 75 outside at night. I finally had to cave and buy an air conditioner.

They also aren't that great in humid climates. They will cool the house, but the air is still damp, leading to mold and other damage.

Air King makes one (9166F) that can be put in a window and will cool the air pretty quickly. I've barely ran the AC this year since I've started pulling in cold air at night and closing the windows in the morning.

As another comment points out, with wildfires it's kind of useless when the air quality outside is bad.

They live in Fresno where it is quite hot even at night during this time of year. It isnt going to be below 80F for more than a couple hours during the night (early tomorrow morning).

The only thing that really concerns me about all of this is if I’m bearing the capital expense of the batteries and equipment that is being worn out by cooperative use. Can we socialize those costs?

But they are paying $2/kwhr aren’t they? They are socializing those costs.

Am I misunderstanding something?

No it’s probably me who is misunderstanding it. If that’s the case then yeah, problem solved!

$2/kwhr is also extremely generous—much more than normal

Not saying you should but can’t you stack the power walls to bring you to off grid?