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I bet solar w/ battery is about to get wildly popular in Texas. Minimum system size?

Maast

Maast

Compulsive Tinkerer
Joined
Oct 31, 2019
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773
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Washington State
What do you think the minimum sized system would be to keep the lights on, refrigerator running, and the furnace going while doing extreme conservation in the average Texan house? I did a quick set of calculations and assuming a gas furnace it came out surprisingly small inverter at only 3000W but with a large-ish 24kwh battery for 3 days of autonomy.

When I used a reversible 3 ton heat pump (as Texas is AC country vs furnace country) it jumped to 8000w (for startup surge) and a huge 70kwh battery bank.

Those numbers all just dont seem right though.
 
5kwh keeps my refrigerator, computer and network stuff going for about 24 hours. During testing, a 1500 watt room heater ran about an hour.
 
If you can't get natural gas for your furnace, it doesn't matter.

3 ton 14 SEER will have a run of about 2500W, and it would likely run nearly continuously even just maintaining 60°F in that weather, so 60kWh.

Dolly the fridge out to the garage, and it will barely use any power at all.
 
My cheap Reliable 48V 2500W inverter easily runs my fridge and furnace. The golf cart has an older FLA battery set so I cannot estimate the KWH capacity remaining. With the furnace constantly cycling the batteries lasted 6 hours, and only running the furnace a couple of times easily lasted the 10-12 hours before the rolling power came back on and fully recharged with the wall charger. Did not run the fridge as I moved all perishables into the cold garage.
 
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I’ve used a https://emporiaenergy.com/ “Vue” to monitor each of the circuits in our summer home for over a year. It is on the coast of New England ( we have winter - regularly). During the winter when the house is in “survival mode” - heat at 50F ( oil furnace), refrigerator running and all house automation running, the house uses about 5 kWh / day, with a peak 1 sec load of 3000 watts. You can keep the pipes from freezing and the food cold with 3kw.
 
Trying to plan for a rare nature event is going to be tough. A normal house isn't optimized for off-grid operation. Further, given the latest situation, the design would have to account for at least three days of backup operation. A couple friends of mine that live down there were without power for four days. A reliable backup solution is going to cost a significant amount of money. $30,000+ is my guess.

I haven't heard that natural gas wasn't available.

I lived in Houston in the 80's and 90's. I can sympathize with the folks down there. I think I would rather deal with extreme cold than a category 5 hurricane.
 
HRTKD said:
I haven't heard that natural gas wasn't available.
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Me neither, ours was available the whole time.

HRTKD said:
I think I would rather deal with extreme cold than a category 5 hurricane.
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I heard this from someone, and heard the opposite from someone else :)

I've also been looking into how to power our furnaces during grid outage, but it seems like too much. Is there anything less energy demanding than a space heater that could keep 1 room warmish?
 
snoobler said:
Dolly the fridge out to the garage, and it will barely use any power at all.
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This is something I've thought about and posted on another forum.... why don't home fridges have a vent/port to the outside with automatic closable flappers? When it's cold outside, the flapper opens and uses outside cold air to cool. Can't do much about the summer months, but the saving for 3-5 months would be significant.
 
dmholmes said:
Is there anything less energy demanding than a space heater that could keep 1 room warmish?
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Yup. I use a vented kero heater in the garage, draws air from the outside and vents to the outside. 300 watts to start it up, 80 watts for continuous operations, 40,000BTUs.

I also use a pellet stove in the house, not as energy friendly, but way less than a furnace.

Either one can heat most of the house.
 
Rider said:
Yup. I use a vented kero heater in the garage, draws air from the outside and vents to the outside. 300 watts to start it up, 80 watts for continuous operations, 40,000BTUs.

I also use a pellet stove in the house, not as energy friendly, but way less than a furnace.

Either one can heat most of the house.
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I was just looking at propane and natural gas heaters. How do those compare to kerosine?
 
HRTKD said:
I haven't heard that natural gas wasn't available.
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Natural gas when it comes from the ground has water in it (as well as other contaminants, including CO2) and has to be dried. Last week gas was not available to some gas power plants due to freezing of the lines and domestic use (think home heating) has priority. There are solutions for all that, but solutions not already implemented are usually because they cost money.

And in general I agree, rooftop solar, with battery is rapidly becoming a cost effective solution. We can make that more reliable if we in turn connected the homes to a micro-grid, which is then connected to ever larger grids again. It would satisfy the people who like to be independent, as connection to the micro-grid would be optional and like minded communities can vote on connections upstream.
 
dmholmes said:
I was just looking at propane and natural gas heaters. How do those compare to kerosine?
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I looked at propane when researching, but this is going back a number of years. Both my kero and pellet stoves are at least 20 years old. At the time, kero was much cheaper. I use a 55 gallon drum. Once filled, it would heat a very drafty greenhouse for weeks in the winter.

These days I only use the kero heater when I'm working in the garage.
 
Fossil fuel (something with good shelf life) for heating and generating electricity is the way to go, and quite affordable.
Coupled with PV, inverter and batteries even better although a bigger investment.
Battery could be as little as 24 hours worth or just one night. Then in the daytime if not enough sun you run the generator periodically.

Ordinarily I would say turn off everything at night, stay warm with sleeping bags.
But pipes freeze? Possibly can shut off water and drain, but without knowing exactly how pipes are routed, can't rely on that.
I also saw a picture of a toilet with a crystal water tank. That is, the porcelain tank broke and fell off, leaving just an ice "tank" with fill valve.
Times like these and I see the value of keeping the fires burning all night.

"Natural gas pipes freezing" - I doubted that at first, consider what it takes to liquefy.
So I looked that up, and apparently just where the gas expands it causes localized cooling, so the water it carries can freeze and restrict flow even at higher ambient temperatures.


1613950571619.png
 
HRTKD said:
I lived in Houston in the 80's and 90's. I can sympathize with the folks down there. I think I would rather deal with extreme cold than a category 5 hurricane.
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Nope. I grew up in Wisconsin and had enough of extreme cold. Granted I am in Conroe away from the coast, and not affected by flooding, so am protected from a Cat5 direct hit. During hurricane Ike was out of power for ten days. I will take 100F over 8F any day.
 
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Rider said:
why don't home fridges have a vent/port to the outside with automatic closable flappers?
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To build energy efficient structures, we try to make the house airtight. To bring in fresh air in those houses, we use a heat recovery unit to reduce losses. To maintain that seal, you will need to enclose the fridge area and vent outside, either with a van or by convection. It is possible, but not an easy task and it would be better if the fridge came with an optional kit. If you don't use air conditioning your idea could well work.

I had a condenser dryer when I lived in Europe, it reduced the power use by half. Hard to find them here in Canada. I did see some at the time, but at a ridiculous price. In the end we decided dry the clothes outside or in the garage, which uses even less power.
 
Hedges said:
Fossil fuel (something with good shelf life) for heating and generating electricity is the way to go, and quite affordable.
Coupled with PV, inverter and batteries even better although a bigger investment.
Battery could be as little as 24 hours worth or just one night. Then in the daytime if not enough sun you run the generator periodically.

Ordinarily I would say turn off everything at night, stay warm with sleeping bags.
But pipes freeze? Possibly can shut off water and drain, but without knowing exactly how pipes are routed, can't rely on that.
I also saw a picture of a toilet with a crystal water tank. That is, the porcelain tank broke and fell off, leaving just an ice "tank" with fill valve.
Times like these and I see the value of keeping the fires burning all night.

"Natural gas pipes freezing" - I doubted that at first, consider what it takes to liquefy.
So I looked that up, and apparently just where the gas expands it causes localized cooling, so the water it carries can freeze and restrict flow even at higher ambient temperatures.


View attachment 38043
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That looks like my fish tank did in 95 when Charlotte was hit with an ice storm and power was out for a week...
those poor goldfish... RIP...
I don’t remember the toilets freezing though... it is possible we drained them down when the power went out. We did not have any pipes burst... grandpa probably knew better and prepped the house for the cold.
 
Johnson said:
I had a condenser dryer when I lived in Europe, it reduced the power use by half. Hard to find them here in Canada. I did see some at the time, but at a ridiculous price. In the end we decided dry the clothes outside or in the garage, which uses even less power.
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Here in Europe, condenser dryers are the standard. Those with heat pumps are better.
In winter, the inside air is too dry anyway. Drying the clothes naturally inside helps both to save energy and to improve your air quality. Beside that, they smell well.
I "finish" them in the dryer 15 minutes cold, to get a fluffy fabric
 
I never lost power or natural gas, so I was never in any danger, but All of my solar stuff wouldn't have done me any good. It was cloudy every.day. and the panels were covered with snow. Also, it was too cold for me to want to run those expensive Lithium batteries batteries for risk of damaging them.
I lucked out this time, but I think I'l get a generator, convert it to run on propane/natural gas, and get a giant tank to store gas in. It's folly to think it's a good idea to try to heat a house with solar.
 
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