An odd battery sizing question

[notJEA]

I don't know how it is where you live but here in Florida is stays HOT even after the sun goes down so I still need to run my AC system when the sun don't shine..

You are correct you would have a hard time running any AC load directly from solar panels. You will need a battery buffer to maintain the voltage your loads need.

Oh discharging a battery more than 30% will shorten it's life and going more than 50% daily will certainly kill it so you will need a much bigger battery system along with about 5kW of solar panels.

The discharging % of a battery issue is really interesting.
You may recognize my posts from exploring grid tied options that work in an outtage.

The company i am working with has decided that a battery is the only way to go when working with utilities that do not offer net metering.
Mainly JEA offers 30 cents to the dollar (inspiration for my username).

To help with this sale we are aiming to send as little power back to the grid as possible.
I've been trying to find information on average KW usage by the hour to help me back into a minimum battery requirement and have been researching here as well.

If i used on average 8KW and installed a 10KW system.
What size battery would be necessary to achieve this?
A big part of this sale is the ability to use the system in the outtage as well. AC etc.

I'm thinking we want a 15KW battery??

Thanks so much

[SunEagle]

I already posted that I am well aware that this is uneconomic and will never come close to recouping my money, but to me that's not important. I am one of many electronics hobbyists who still build a circuit costing $10 from scratch when you can buy 10 of the same circuit ready built from China for $2. If you only do something because it makes economic sense then all invention and tinkering will stop.

I agree that tinkering can lead to inventing a new product.

I would just ask those members that want to tinker and build things, to mention in their First Post that the practice is usually not economical and should not be done if the reason to do so "is to save money".

Most people that come here are looking for solar technology to save them from paying high electric bills. When tinkerers come in they tend not to mention their actions tend to use up more money then it will save.

I just want the tinkerers to be clear when they make their posts so that others do not get the wrong idea.

[NeilTheCop]

Thus why a Swamp Cooler works so well. Keeps you nice and cool plus adds humidity. Using an air conditioner compounds the low humidity problem.

I did look at the solar powered swamp cooler once that cooled incoming air by evaporation then passed that air through a heat exchanger to cool the interior air. I would still have the problem with the high mineral content of our water but I'm sure that could be overcome. not sure what happened to that company.

[NeilTheCop]

More than likely the OP believes he can save money using solar panels to directly run his AC unit. The sad part is that there are a lot of people that have "drank the cool aide" and feel they do not need to spend very much to install a solar pv system which gives them "free" energy. It is a very misconceived belief.

I already posted that I am well aware that this is uneconomic and will never come close to recouping my money, but to me that's not important. I am one of many electronics hobbyists who still build a circuit costing $10 from scratch when you can buy 10 of the same circuit ready built from China for $2. If you only do something because it makes economic sense then all invention and tinkering will stop.

[Sunking]

To answer it drops to about 80 at night in mid summer but our humidity is around 10%. Here today it's 4% and you can feel the moisture being sucked from your skin.

Thus why a Swamp Cooler works so well. Keeps you nice and cool plus adds humidity. Using an air conditioner compounds the low humidity problem.

[NeilTheCop]

Neil you do not need AC where you live. Swamp Coolers work great.

True, but a couple of things put me off. Our water has so much mineral content you don't drink it, you chew it, so everything, including PEX pipe gets a calcium buildup. I had drip irrigation in my garden but after having the emitters clog up within days I gave up. The second and major problem is that we are surrounded by dairies with the associated 'waste' products, which when dry are carried by the ever present strong winds to our house, and no swamp cooler can remove that odor so we have to keep the house closed.

[NeilTheCop]

I don't know how it is where you live but here in Florida is stays HOT even after the sun goes down so I still need to run my AC system when the sun don't shine..

You are correct you would have a hard time running any AC load directly from solar panels. You will need a battery buffer to maintain the voltage your loads need.

Oh discharging a battery more than 30% will shorten it's life and going more than 50% daily will certainly kill it so you will need a much bigger battery system along with about 5kW of solar panels.

To answer it drops to about 80 at night in mid summer but our humidity is around 10%. Here today it's 4% and you can feel the moisture being sucked from your skin.

[Sunking]

I live in south east New Mexico where we have almost constant sunshine so A/C is essential.

Neil you do not need AC where you live. Swamp Coolers work great.

[Sunking]

Hi Mike,
Due to my utility company here forcing a different rate plan when you have grid-tied solar panels, my electricity bill would actually increase if I had grid-tied panels.

Solar users should pay more.

The point you are missing anything you take off grid is stil going to cost you 5 to 10 times more than buying power. You just set yourself up for a huge rate increase. Difference is you have to pay for it all up front in cash when you put the batteries in initially, and every few years with each battery replacement at even higher cost.

[bcroe]

I think you are correct. Someone needs to develop a cheap AC system that can work directly from a solar panel input similar to what a DC fan motor does. Although I still don't know how you can keep a compressor from having an issue if the sunlight doesn't stay constant while it is on.

That is a good point. These might have a couple operating modes, one with a PoCo connection and
explanation (and perhaps an indicator) that operation will revert to conventional power when good sun
isn't available. This would let owners run on solar without a net metering agreement.

The other mode would be off grid (not recommended with grid available) entirely, with shutdown
without good sun. This has the additional requirement that EVERYTHING (fan motors, logic)
be powered from the main rectified DC.

How is cheap defined? A unit requiring half the energy but costing twice as much will probably save
money most places. I don't have a handle on relative costs of central vs decentralized units. Mini
splits are almost unheard of in these parts, the local service people tend to look askance at anything
that high tech. Buying them near wholesale out of state and doing a DIY install doesn't seem so
much. Just a few holes in the wall, no duct work. Bruce Roe

[SunEagle]

I have seen ads for air conditioning equipment with solar panel input supplements, they looked like
the current (typ 14 SEER) stuff. Probably are the model using an internal inverter to drive a variable
speed compressor. In fact the variable is a bit more efficient, payoff may not be much different, but
reliability might be the bigger issue.

With the smaller mini splits, is available a doubling of SEER, am going that route now. Seems to me
its about time to work out the direct panel connection to this class of conditioner, commercially or at
least as a science project. Bruce Roe

I think you are correct. Someone needs to develop a cheap AC system that can work directly from a solar panel input similar to what a DC fan motor does. Although I still don't know how you can keep a compressor from having an issue if the sunlight doesn't stay constant while it is on.

[bcroe]

More than likely the OP believes he can save money using solar panels to directly run his AC unit. The sad part is that there are a lot of people that have "drank the cool aide" and feel they do not need to spend very much to install a solar pv system which gives them "free" energy. It is a very misconceived belief.

They really don't understand that to run air conditioning equipment directly from the DC output of solar panels requires the purchase of very specific equipment which probably costs much more than standard AC equipment and will take years to pay for itself when you figure in the total system cost.

I have seen ads for air conditioning equipment with solar panel input supplements, they looked like
the current (typ 14 SEER) stuff. Probably are the model using an internal inverter to drive a variable
speed compressor. In fact the variable is a bit more efficient, payoff may not be much different, but
reliability might be the bigger issue.

With the smaller mini splits, is available a doubling of SEER, am going that route now. Seems to me
its about time to work out the direct panel connection to this class of conditioner, commercially or at
least as a science project. Bruce Roe

[Sandman333]

Why not use simple Grid Tie and skip the batteries ?

Hi Mike,
Due to my utility company here forcing a different rate plan when you have grid-tied solar panels, my electricity bill would actually increase if I had grid-tied panels (and did not have a battery pack to carry my usage through the evenings and diminish load peaking). New solar installations have practically ceased here, but old ones are grandfathered into an older and more advantageous rate plan. I have considered going grid-tied with a zero-export system in place and not telling my electric company, but I would then be violating city code by installing such a system and not informing the electric company.

Just like Neil said about his project, this plan won't break even ever, but it is a fun project that is educational and doesn't cost much out of pocket.

[SunEagle]

Why not use simple Grid Tie and skip the batteries ?

More than likely the OP believes he can save money using solar panels to directly run his AC unit. The sad part is that there are a lot of people that have "drank the cool aide" and feel they do not need to spend very much to install a solar pv system which gives them "free" energy. It is a very misconceived belief.

They really don't understand that to run air conditioning equipment directly from the DC output of solar panels requires the purchase of very specific equipment which probably costs much more than standard AC equipment and will take years to pay for itself when you figure in the total system cost.

[Sunking]

Why not use simple Grid Tie and skip the batteries ?

I already pointed that out. Wants no part of that.