The electrical hookup isn't that big of a deal. You might have issues with local codes though. I can't see getting enough wattage easily, unless you use a lot of batteries. How many years of marginal utility rate savings will it take to offset the cost of the battery/inverter system? Batteries never seem to work as well in real life compared to on paper.

If this is a serious plan, I wonder if it would be a better idea to rewire the AC blower and compressor fans and compressor to DC? Not sure what voltage the sweet spot would be, if anything. Convert line AC to DC for the AC. Maybe use the heat from that to heat your water? Might help with the solar system.

 

Out of curiosity why are you doing this?

 

it's not practical at all to run such a large load off a battery. your 4 ton a/c if it's 13 seer will be burning up 4kwh/hr of run time or even more if it's less, so you're looking at displacing maybe 3 hours of run time?

and if the battery is totally discharged every hot day it won't last.

not sure if tesla power wall even puts out 240v, if not you're looking at a very expensive inverter.

it's a waste of money.

if you want to do solar, charging a battery, only relying on the grid for backup you have to get your electrical use down to 5kwh per day or less, otherwise the cost of prohibitive. central air is out of the question.

off the gridders use hardly any electricity; most don't have a/c, a wood or propane or gas stove does the heating and gas is used for hot water and cooking as well.

off the grid houses are fossil fuel dependent for 90%+ of their energy, it's a myth that you can have the north american life-style without fossil fuels. (unless you live on a wood lot and harvest wood for heating, cooking, hot water yourself without any gasoline)

A much more practical approach now is to pre-cool when the rate is low and allowing it to warm up a bit during the day. you can run the fan during the day to keep the air circulating. A decent programming t-stat with programmable fan is all you need.

If you want you can add solar and do net metering, so the power produced by the panels when it's sunny offsets the a/c use. You would need 4 to 5kw of panels, at a very high cost.



solar is stupid when you have the electricity grid, unless it's for emergency backup power to run some leds and small appliances. there's a reason it's not widely used.

 

how much can you really save though? What is the payback time on this?

 

Here in Texas you can contract to track the wholesale price of power, which can run from 2¢/kwh at night to as high as the PUC price cap of $9.00/kwh on a hot July afternoon. To make some serious money back you just need to be able to get off the grid for a few hours a day, not all the way. Basically you can get maybe 75% of the savings with only 25% of the investment.

I think the 100+ kwh batteries that come in an electric car will be able to fill the same or better role in a few years, so I'd like to get an early start on that concept while you can still get a 30%(?) tax credit for a 2017 setup.

Finally, I think solar and net metering and maybe a grid crisis will be in my future. This is a way of getting a favorable start on those things.

I hope that answers everyone's questions. Now, about mine....

 

your area may have some program with integrated thermostat where they automatically raise the temperature when the rate is high.

do some research and see what's available in your area.

if you're worried about the grid going down, get a generator first, then a battery backup system and wire it to only run essentials.

 

someday the cost of solar panels will drop. Then, the only issue will be inventing better batteries

 

they already have dropped. they've been working on batteries forever.

the trick is getting the energy use down to next to nothing, then solar becomes very viable. but the masses are never going to be running electric central heat or air off self contained systems.

 

Why is it when someone wants to drop an extra 50 grand on a BMW or wants to move into a 4,000 foot house people say "go for it, it's your money," but when someone wants to shell out five grand on a solar or other green deal people post that he's stupid, just pissing his money away?

Okay, any thoughts on the electrical hook up?

 

but when someone wants to shell out five grand on a solar or other green deal people post that he's stupid[.quote]

Because a lot of these things are bad investments. if it's for the novelty or fun, like a crap mcmansion or gas guzzling car, or vacation yah go for it. I actually think those things are a colossal waste of money myself.

If you're trying to save natural resources or money, go with what gives the best return on investment.

LEDs have a fantastic return on investment and should be used.

If you're heating water with electricity, solar thermal is a good option to look at, would provide much more renewable energy at a lower cost than pv. (or just get a bigger electric tank and shift the use to off-peak with a timer)


pv is very expensive and the money is better spent on other conservation/renewable energy projects.

If you could shift your a/c use off the peak periods with a $100 thermostat and pre-cool before hand, why spend thousands of dollars?
(and get further savings doing low tech things like adding exterior window shading?)

Use the right equipment for the right application. PV is really good if it saves you from spending $10000+ to get electricity to your property in a rural application.

It's also good if you want a backup power system to run refrigeration and lighting, but not a central a/c. You only need like 5kwh per day or less to run the basics.

PV is not necessarily better for the environment or saves resources because of the toxic materials in the panels and batteries, but has it's place. The power output is so low that the real environmental savings only come from being forced to dramatically cut your energy use in the first place.

 

Here in Texas you can contract to track the wholesale price of power, which can run from 2¢/kwh at night to as high as the PUC price cap of $9.00/kwh on a hot July afternoon.

Those are spot prices, not long term contract prices.

The wholesale cost of power on the spot market is not directly connected to what you pay, even when on a time of use rate structure.

POCOs can pay big $$ to buy the last few mWh to meet peak demand. Averaged out over total generation and other purchases, it only has a slight impact on their average cost of power.The purchases are made to avoid brown outs, blackouts, and/or other power curtailments.

If you are basing your savings calcs on 2¢-$9 you are using the wrong numbers.

 

The wholesale cost of power on the spot market is not directly connected to what you pay, even when on a time of use rate structure.

Maybe not in California. Texas is deregulated. My retailer sells me power at wholesale spot + 1.7¢/kwh + about 4¢ for the local distribution company. Spot prices are recalculated every 15 minutes by the Independent System Operator.

My bill this winter has run 8.0¢ - 8.5¢ I expect it to be higher this summer and much, much higher in the afternoons. Like I said, one kw could get as high as $9.00/hr. That's what I'm trying to save with this plan.

Most people here though do go for long term contracts, which run around 12¢ or more, day or night, all year long. Probably more like in California. Buying power at night and storing for day use doesn't work for them.

 

My bill this winter has run 8.0¢ - 8.5¢ I expect it to be higher this summer and much, much higher in the afternoons. Like I said, one kw could get as high as $9.00/hr. That's what I'm trying to save with this plan.

program your t-stat so that it doesn't run in the afternoon.

pre-cool when the rate is lower so it doesn't get too hot.

low tech solutions are best.

 

I've been toying with going solar for a while and the idea of running central A/C on solar is something I looked at myself, when you need it most, there just happens to be lot of sun out. There's various options such as only putting some stuff on solar, or whole house etc. They all have their pros and cons from complexity (splitting up circuits etc) to cost. For motor loads such as AC or even washing machine you need a very powerful inverter that can handle the startup load, and that will get very expensive. I'm sure it's doable though.

Something like this could probably work:

http://outbackpower.com/outback-pro...power/radian-series-inverter-chargers/item/radian-series-gs8048?category_id=529

One MIGHT be enough but I'd probably put at least 2 in parallel.

The inverter is probably going to be your biggest cost, you can choose batteries based on how long you want to be able to go for. Start with cheap Canadian Tire or equivalent batteries, and later on get better ones. Of course TOO big of a battery bank and your solar panels may not be able to charge it fully fast enough within the day. So need to size appropriately. Oversizing is never a bad thing if you can avoid discharging it fully though. Ex: if you only use 10% each day and it fully charges then those batteries are going to last very long.

If your solar array can actually provide enough power to run the A/C + some left over power then you can probably get away with a smaller battery bank, as you can run off solar during the day when it's hottest and sun will be at it's peak. Then run a bit longer off the batteries then by then it will be "off peak" and you can switch back to commercial hydro. Could possibly automate that.

 

any of this is doable. It boils down how much do you want to spend and what is his ROI.

But i would submit, that *we* on the forum do not have the expertise to give sound financial advice on this matter.

I will stick with my first assessment, Even living in sunny Texas, this would be cost prohibitive. His solar array would have to be fairly large and his Battery bank would therefore be fairly expensive.

I would also strongly suggest he call these guys

https://www.wholesalesolar.com/

They can give you an accurate quote on the cost involved

p.s.: I have no affiliation with these guys and only suggest calling experts in this field

 

Conceptually speaking. If you consider the Powerwall as a generator, use a transfer switch to change power sources. You need to isolate the battery from the grid to prevent backfeeding if there was a grid outage.

 

Conceptually speaking. If you consider the Powerwall as a generator, use a transfer switch to change power sources. You need to isolate the battery from the grid to prevent backfeeding if there was a grid outage.

thats is what a Power wall is (or battery bank), This "generator" has to be big enough to run whatever appliances you want without help from the grid.

The issue is replenishing the batteries.

In the Northeast you need enough battery to last 3 days without recharging. Or you need to be tied to the grid or you need a (fossil fuel) generator to charge the batteries if you don't have any sun for three days or more. Which up here is quite common.

you have other considerations too. Your Inverter to the house must be "pure sine wave" type. Because almost everything nowadays has a computer. Computer do not like 'dirty electricity' they also don't like spikes. Pure Sine Wave Inverters are NOT cheap.

In Texas, it's probably not that big a deal as they get WAY more sun that we do in the Northeast.

If I lived in Texas, I would go completely off grid with a Wind/Solar Hybrid system. Generally speaking, if you don't have sun, you DO have wind.....generally speaking.:vs_cool:

Now some people maybe able to get away with a Forktruck battery. But their are issues. The first and most obvious, weight! These things weigh a ton ( or more)

second, they are expensive but they have a ton capacity

Third, you're going to need a LOT of solar panels to charge the battery over the course of a day.

The OP ( original poster) should call a solar professional, tell them what he wants to do and they can put a package together for him

The rest of us are just guessing

 

I think there is a device that has not been invented yet. Something that produces more energy than the energy needed to power that device. An electronic version of a gear system. A small gear that uses little power but attached to a larger gear that is doing more work than the smaller gear.

 

Solar fill would be down the road. Here is a typical price curve to Houston, On that day in the hour of 4-5 PM I'd make $.70 x about 5 kwh. Then refill at night for $.02.
Of course sometimes the high prices last longer and get up into the dollars range. If it hit $9.00 for two hours I'd make $90. More, if I could sell some extra back into the grid. Making a quick profit is not my primary goal, though. This is the Green Forum, after all, right?

It'd be nice if my transfer switch could get real-time informed about prices!

 

Im a little confused? what do you mean by "refill at night"

 

Refill the batteries from the grid for $.02.

 

Do you know how your utility's policy for net metering? I have grid-tie system and all that matters is the meter reading at the end of the month. If it's less than the start, they credit my account in dollars. If it's more I pay/deduct the credit. My rates are fixed regardless of time of day. Depending upon your utility's policy, you could use the grid as your battery.

 

In Texas everyone is required to use time-of-use "smart meters." These send your power use in 15-minute intervals to the power company's server, where it can be accessed by you or your retail electric company.

My company charges TOU. So if you use less when the wholesale rate is $0.70/kwh, you save the full $0.70/kwh, which could seriously lower your system payback. Most people don't use that TOU feature, they just pay at one fixed rate for their total monthly use, like you do. They can turn the A/C on full blast at 4PM and it only costs them ten cents, why not?

 

The credit you get would be like 10¢/kwh, the average price for the month. I want the credit to be at the peak pricing, which is when I delivered the kw.

 

Deep thoughts - How many stages of cooling do you have? If by chance it's two stage, you could lock out the second stage for the price of a timer and some wiring. It would reduce your peak use and still provide some cooling.

 

so after doing a bunch of looking around, I found THIS from wholesale solar:

https://www.wholesalesolar.com/1440...ative=176443232371&adposition=none&product_id=&gclid=CP_tjLOI6tICFdmKswodmm8HHg

AND it puts out 240v......there ya go, Good luck :vs_cool:

 

From that web page:

Not appropriate for: Air-conditioning, heating or agricultural irrigation pumps.

 

I'm not sure a 7KW peak draw is enough to start the A/C condenser on a hot day.

Condenser would need a hard start kit to get the compressor up to speed as quick as possible to get the KW draw down fast.

Does your A/C have a TXV or piston metering device. Easier to start against a piston than a TXV.

 

Thanks, Been, good info. I have a Lennox XC16 model 048 two stage scroll compressor that uses a TXV and the manual says a hard start kit is required where voltage is less than 230V. With all the neat stuff I read about those kits it seems like I should put one in there anyway to save compressor life. Might cut down on startup racket, too, the unit is just outside the bedroom window.

 

It won't hurt it to have one.