Central AC use at night in hot / humid climates

[Charlie Woods]

Were it financially feasible, it would be out there. It can be done, no doubt. But it’s not being done,

Exactly. The O.P. has not responded on this thread. I suspect he did some math and discovered how infeasible solar A/C is in Houston.

Like mesquito_creek said above...

So lets look at the OPs consumption " In July I pulled 1951kw in total (63kw a day)."

63000 watts in one day, divide that by 24 hours and on avg he uses 2625 watts an hour. You are only going to make good solar power for about 5-6 hours best case. Lets say from 10 am to 4 pm. That is being very generous. But lets focus on the time that you don't make solar, from 5 pm to 9 am, that is 16 hours.

16 hours at 2625 = 42000 watt hours of battery. So now during the 6 hours you make PV power you need to cover your load 15,750 + recharge 42000 watts or a total 57,750. Your array would need to make about 10000 watts an hour over that 6 hours. Probably need a 15K watt array to cover it. You gave yourself Zero room for error or other loads and you have designed it for 1 day with no reserve. You get anything less than your 6 full hour of PV and you are short.

1. Find the best electricity rate for zip code 77494 on http://powertochoose.org

2. Work up a dollar cost to install the solar system above.

3. See if the Return on Investment exceeds the expected service life of the system.

If it did, people would be doing it.

 

[Short_Shot]

I have a better idea for you...
Lower your ac load in the house to only need 3 tons of ac...
Seriously.
Describe the house.
Attic is a HUGE heat gain to the home, pull the roof off, and install insulation on the deck, set light color metal roofing on top, install full depth rockwool in the rafters, get the attic sealed, and bring it into the conditioned space environment.
Walls... 4" ? Pull the sheetrock, fir out the studs get 6" and vapor seal, then rockwool packed.
Crawlspace? Or basement? Get it air sealed.
All exhaust fans fed through an hrv... install dehumidification with ear exchange ventilation built in...
Then toss the 5 ton unit, install two units, one for the south side of the house one for the north.
Get 2 tons inverter driven unit on the south, 2 tons inverter driven north side... redundancy, and load balancing, and easy start loading.

Lol

I have a thousand square feet of house and I'd probably die before that ROI comes along, let alone 2600 square feet, vs just upsizing the solar and batteries.

Never mind the issues of powering 5 tons of ac in the first place. Or even 4.

 

[mesquito_creek]

Exactly. The O.P. has not responded on this thread. I suspect he did some math and discovered how infeasible solar A/C is in Houston.

Like mesquito_creek said above...


1. Find the best electricity rate for zip code 77494 on http://powertochoose.org

2. Work up a dollar cost to install the solar system above.

3. See if the Return on Investment exceeds the expected service life of the system.

If it did, people would be doing it.

The huge variable is does the utility connection exist and what would it cost to hook up to the grid and run a meter to your house. Most I see assume that the meter is installed and that cost was assigned to someone else. The ROI is fast when you are paying $20, $30K or more to get to have the privilege's of receiving a bill that contains all sorts of fees that have nothing to do with kwh!...

Additionally, some parts of the country you only have one monopoly power provider and no right to choose rates.

 

[Supervstech]

Lol

I have a thousand square feet of house and I'd probably die before that ROI comes along, let alone 2600 square feet, vs just upsizing the solar and batteries.

Never mind the issues of powering 5 tons of ac in the first place. Or even 4.

So many think this way, and it is silly.
Conservation lasts forever, nothing to wear out.
Ac equipment does.

 

[Sanwizard]

So many think this way, and it is silly.
Conservation lasts forever, nothing to wear out.
Ac equipment does.

And if you dont use a contract to grid tie, and just use the grid to supply complimentary power to your solar setup, you will pay less for energy use even with a very small solar install.

 

[Cheap 4-life]

Another Texan here, right off the Gulf Coast where humidity is omnipresent. I use solar for some smaller applications (running a fridge and an upright freezer) just to get some use out of my emergency solar setup built in 2020. I spent the last 3+ decades before a recent retirement in municipal government, in regular contact with contractors in my area. No one is running central AC units off non-grid-tie solar here.

Were it financially feasible, it would be out there. It can be done, no doubt. But it’s not being done, and there are some intelligent folks out there building homes, subdivisions, and commercials facilities. They have the money for up front costs, and the patience to recoup investment, yet… nothing. That tells me solar isn’t a fit for it yet, probably because having three or more days of autonomous power for a system that needs to run even when it rains for a week requires more PV and storage than is worth it. Most people don’t want a roof full of panels and a garage full of batteries just to avoid the AC part of their electric bill.

A room? Sure. A couple of rooms on mini-splits? Probably still squeezes into a cost vs return analysis on the positive side. Whole house requiring 5T and up? The mind says it can be done, the calculator and all the proof you can find on the ground says no. Or at least not yet.

Prove me wrong and you’ll be the next Elon Musk in Texas.

I agree. It’s very costly to cover all of a typical Americans homes loads. Usually they use way more power than they actually have to. Very few people fully power their central heat and air units completely offgrid. The amount of panels, batteries and inverters needed costs more than simply using grid power. If someone is completely offgrid the generally do not have central heat and air. They use smaller units or live in areas where heat or air conditioning isn’t needed.

 

[Cheap 4-life]

I had run across this video some time ago and this discussion made me think of it again. Yes, it will dehumidify the air, one would need to install a drain pan under the heat exchanger (radiator). As long as the ground temp is at that area around the 55F mark, this would actually work. Interesting idea.

A cheap system like this will work but not in really hot or cold climates. Unless your fine with it being a little warmer or cooler than most

 

[RickP]

Solar power is certainly viable. I don’t want to misrepresent that point. The smart money on solar is either using it to reduce grid-supplied power, or scaling use to accommodate the limited supply of a reasonably capable off-grid solar powered storage system.

It‘s a great option, and as storage costs come down it’ll get better. Reasonable uses, those which match loads to the supply characteristics, can see the best of what solar has to offer. Solar can become a real money pit if taken beyond that. Still, I’m a big fan of solar power, and very much enjoyed my experiences with it so far.

 

[Short_Shot]

So many think this way, and it is silly.
Conservation lasts forever, nothing to wear out.
Ac equipment does.

I don't last forever and probably won't live here that long though.

But you're right of course. It's just that's a huge investment which may not always be the answer.

 

[Sanwizard]

I don't last forever and probably won't live here that long though.

But you're right of course. It's just that's a huge investment which may not always be the answer.

So far I spent around $14K on solar. I will get 26% of that back. That paid for 50KW of lifepo4, 6KW of panels, and 13KW of inverter power. It also gave me about 2 years of college experience of solar and battery knowledge, along with linux and Python skills on Raspberry Pi.

My garage, workshop, and barn apartment with lights, fridge, and air conditioning are now all free.
If I lose power here, I am now good to go do the duration.
If the SHTF, no worries. Me and mine will have power and AC.
I now have a better idea of what works, and what does not. This forum has provided a huge amount of knowledge I never would have received if I never tried solar.
The cost? Around $10K net. The experience and peace of mind? Priceless.

 

[mesquito_creek]

I have had several hobbies that wasted a lot more money than solar! You don't have to always have ROI to do something interesting and provide some independence and personal satisfaction. I am not even trying to discourage the OP or the other guy from TX, I am trying to give you a chance at hitting the mark with a Big ol system. Make it easy to scale up, conserve and keep working on it, its very addicting...

 

[Partimewages]

I had run across this video some time ago and this discussion made me think of it again. Yes, it will dehumidify the air, one would need to install a drain pan under the heat exchanger (radiator). As long as the ground temp is at that area around the 55F mark, this would actually work. Interesting idea.

This doesn't work without a compressor based system. The ground temperature will not be 55 all year round. Colder in the winter and warmer in the summer. As you transfer heat from the house the ground will warm. If you live somewhere where the ground water is 55 or less you can pump water through a coil and cool. It take a 55 degree or less coil to dehumidify.

 

[Cheap 4-life]

This doesn't work without a compressor based system. The ground temperature will not be 55 all year round. Colder in the winter and warmer in the summer. As you transfer heat from the house the ground will warm. If you live somewhere where the ground water is 55 or less you can pump water through a coil and cool. It take a 55 degree or less coil to dehumidify.

It does work. But not when it’s really hot or really cold. Or in a really hot or cold climate. For people completely offgrid it’s better than nothing and doesn’t use hardly any power.

 

[Bluedog225]

From memory, our ground temp in central Texas is about 72F, about 200 feet down (chuckle).

 

[wattmatters]

In Australia we have both a lot of rooftop solar PV (nearly 1 in 4 homes has a solar PV system and the vast majority are grid tied) and lots of air conditioning due to our climate. Batteries are being installed but they are in less than 0.5% of homes, not so common.

Few set out or expect to have their solar PV to cover their whole demand. Elimination of grid imports is not the point of using solar PV here. Rather its primary purpose is to reduce utility bills. Fortunately the bill reduction here from solar PV is sufficient for most systems to have paid for themselves within 3 to 5 years.

Obviously it depends a lot on the cost in your area to install solar PV, and what tariff regimes apply. Our solar is relatively cheap to install ranging from US$0.50/W to $1.00/W for a professionally installed grid tied system with ~US$0.70/W being pretty typical.

Import tariffs vary a bit across the country but in the most populous areas they are ~US$0.15-0.20/kWh, while export tariffs are in the US$0.05-0.10/kWh range. We also have time of use (TOU) tariffs in some places so the tariff differential is wider under those. Where I am I can choose either TOU or a flat rate. It just happens TOU works out better for us, even though peak period is not when the solar PV is supplying energy.

Grid tied batteries however don't work financially here because they are just too expensive. Payback times are measured in decades and exceed their expected life. Solar PV does the heavy financial lifting when it comes to reducing bills and have a very good ROI.

We have both a central ducted air con plus other units. On a hot day our total consumption can go beyond 100kWh (worst day was 146kWh). On a day without need for aircon our daily usage is ~13-15kWh.

This shows our average daily electricity bills for the two years before and and since installation of our solar PV. No battery.

 

[Zwy]

This doesn't work without a compressor based system. The ground temperature will not be 55 all year round. Colder in the winter and warmer in the summer. As you transfer heat from the house the ground will warm. If you live somewhere where the ground water is 55 or less you can pump water through a coil and cool. It take a 55 degree or less coil to dehumidify.

Read the comments of the video, I finally did and there was one poster that had been using this for years.

I work in the HVAC field, I don't totally agree with your compressor based statement.

If the ground temp would warm as fast you seem to believe, then geothermal with a compressor based system would not work thru the season. All of this is based upon the length and depth of the lines.

This also could be used in conjunction with a compressor based geothermal system for load reduction. Considering that it cost him under $1,000, that's pretty good return on the cost.

 

[Zwy]

From memory, our ground temp in central Texas is about 72F, about 200 feet down (chuckle).

Then you shouldn't have been all freezing last winter when the power went out.

 

[Bluedog225]

Funny? Over 100 people died.

 

[Short_Shot]

Funny? Over 100 people died.

Not sure who you are replying to but...


And?

Heat waves, cold storms, and power outages can both kill the old and infirm. Combine any two? It's amazing its only that many.

We act all shocked and make in into such a huge tragedy and blame the government and utility companies when it occurs but keep in mind everything that IS done here to keep the effects so incredibly minimized.

It's a miracle it was only a hundred. In 2015 France, during a major heat wave, lost 7x that many people and their power didn't even go out.

While every individual life lost is a tragedy, the sum of the losses was remarkably low considering the situation.

Personally I applaud the community and anyone else responsible for responding and minimizing the losses so well.

And I'm happy to see people taking personal responsibility for their energy needs, even if it is reactionary in nature. I hope this leads to a big increase of solar use.
Even if they can make a minimal investment to keep a single room either hot or cold during an emergency it'll go a long way towards reducing the losses further.

Just one room staying warm (or cool) during a power outage cold save half a dozen elderly neighbors (barring covid stuff of course).

 

[A.Justice]

On a side note; I did some work for a guy who owns a commercial solar installer business. He has his entire 15k square foot house off the grid, HVAC included, and he keeps the house at 70° all summer in hot, humid, Virginia.

He had literally an entire wall of MASSIVE lead acid batteries in the basement
(apparently he's not hip to lithium yet), hundreds of cells, easily. The entire roof was covered in panels, and he has 2 ground mount arrays. I wasn't super into solar at the time so I didn't really know what I was looking at, but it was an incredible system.

He said that if he didn't own a business and do a lot of work himself, that the installation would cost more than $100k.

He actually gave me a few commercial panels to mess with when I finished my work, and started my solar adventures!