Solar Power for Air Condition System

[K8MHZ]

'Tis true; Michigan's not the optimum climate for solar electricity, either meteorologically or politically. But the original question was about Georgia.

I was actually surprised about the amount of insolation we have where I am on the west side. It was way more than I thought, but we do have lots of sun during the summer and fall. Almost drought like at times. We are at 5.0 - 5.5, northern GA is 5.5-6.0 kWh per meter squared per day.

 

[ActionDave]

Well, Renewable Energy World says that the average cost of PV in the US in 2017 is about $3/Watt. A 10kW system will cost you about $30k, but the ITC will pay for 30% of that, so if there are no other incentives available your out of pocket would be $21k. In my area, PVWatts calculates the production to be about 15,100kW/year from a well placed 10kW PV system. Over the 20 year expected life of a system that's 302,000kWh. Electricity is cheap around here at about $0.11 per kWh, but even at that rate, that's $33,200, or over $12,000 to the good, and that's assuming that the price of electricity won't go up during that time.

And there are places where electrical power is much more expensive than it is here.

So for the OP, if his electric bill goes from seventy five dollars a month to one hundred and fifty dollars a month for June, July, August, and September and all he has to do to make up that three hundred dollars is spend a thousand dollars a year for the next twenty years, up front if he has the cash or plus interest if he finances it, and as a bonus at the end of that twenty years he has an aged out system that needs replaced.

I'm not an anti solar guy I'm just a realist.

 

[growler]

Well, Renewable Energy World says that the average cost of PV in the US in 2017 is about $3/Watt. A 10kW system will cost you about $30k, but the ITC will pay for 30% of that, so if there are no other incentives available your out of pocket would be $21k. In my area, PVWatts calculates the production to be about 15,100kW/year from a well placed 10kW PV system. Over the 20 year expected life of a system that's 302,000kWh. Electricity is cheap around here at about $0.11 per kWh, but even at that rate, that's $33,200, or over $12,000 to the good, and that's assuming that the price of electricity won't go up during that time.

And there are places where electrical power is much more expensive than it is here.

I have never had to deal with solar power but I have read the customer rewiews from some of the biggest and best of the solar companies. There are many people that seem well satisfied after 6 month or 2-3 years.

There are a number of problems I noticed by reading the reviews. Not all people live in the same house for 20 years. When they sell the house they have trouble getting another person to take over leased equipment. If they need a new roof after installation that's an added cost they didn't count on. The critter guard for squirrels is an added cost they didn't count on. If they do have problem then customer service from most of these companies didn't sound very good.

You calculate how much power he can produce but why not first calculate power saveing from other sources such as new AC equipment and see what that cost is. Over a 20 year period it could be considerable. And if he needs to sell the house a new AC system or water heater can be a bonus.

 

[ggunn]

So for the OP, if his electric bill goes from seventy five dollars a month to one hundred and fifty dollars a month for June, July, August, and September and all he has to do to make up that three hundred dollars is spend a thousand dollars a year for the next twenty years, up front if he has the cash or plus interest if he finances it, and as a bonus at the end of that twenty years he has an aged out system that needs replaced.

I'm not an anti solar guy I'm just a realist.

Solar makes sense for a lot of people. I am a design engineer at one of the largest solar companies in Texas; there are three of us designing full time and we can barely keep up with the demand.

 

[jaggedben]

So for the OP, if his electric bill goes from seventy five dollars a month to one hundred and fifty dollars a month for June, July, August, and September and all he has to do to make up that three hundred dollars is spend a thousand dollars a year for the next twenty years, up front if he has the cash or plus interest if he finances it, and as a bonus at the end of that twenty years he has an aged out system that needs replaced.

I'm not an anti solar guy I'm just a realist.

Your numbers are off man. :happyno::slaphead:

The 10k system ggunn gave numbers for is not what everyone needs, and it's certainly more than one needs to cover $300/year in electric bills.

At 11cents/kWh that $300 would be 2727kWh, requiring approximately 1800 watts nameplate solar power. At $3/watt that's $5400, which is the total cost for over twenty+ years. The system pays for itself in about 12.5 years with the tax credit. And at the end of twenty-five years he will probably have a system that needs to be refurbished, not replaced, at something like half the cost to get another twenty years out of it.

11cents/kWh is towards the cheap end of things. At the electrical rates typical in California, a cash purchased system typically pays for itself in 5-7 years.

Also, the guy is an electrician: if he can do it himself the actual equipment and material cost is ~$1.5/watt and thus would pay for itself in 6-7 years.

The caveat in this case is that I don't think Georgia's regulatory system is set up to give the kind of credits needed to save the full billing cost. In other states the economics would be great.

 

[ggunn]

Your numbers are off man. :happyno::slaphead:

The 10k system ggunn gave numbers for is not what everyone needs, and it's certainly more than one needs to cover $300/year in electric bills.

At 11cents/kWh that $300 would be 2727kWh, requiring approximately 1800 watts nameplate solar power. At $3/watt that's $5400, which is the total cost for over twenty+ years. The system pays for itself in about 12.5 years with the tax credit. And at the end of twenty-five years he will probably have a system that needs to be refurbished, not replaced, at something like half the cost to get another twenty years out of it.

11cents/kWh is towards the cheap end of things. At the electrical rates typical in California, a cash purchased system typically pays for itself in 5-7 years.

Also, the guy is an electrician: if he can do it himself the actual equipment and material cost is ~$1.5/watt and thus would pay for itself in 6-7 years.

The caveat in this case is that I don't think Georgia's regulatory system is set up to give the kind of credits needed to save the full billing cost. In other states the economics would be great.

I just picked 10kW to make the math quick; it's certainly more than the OP needs. Sorry about that.

OTOH, the 400W system the OP mentioned is way too small to do him any good. It's probably from one of those fly-by-night guys that try to sell you something that plugs into an outlet. They are junk at best, illegal and dangerous at worst.

 

[macmikeman]

This isn't for every situation, but in some select cases, when you owe a whole bunch of money for taxes and that year you decide a photovoltaic roof mount system is in order, you might possibly make that tax bill pretty much go away for that year. Don't ask me how I know this, but anyway my power bill from the local utility HECO is seventeen dollars a month now instead of $300 and I have seven mini split system ac's going on the hot days..

Hot being defined as above 84 degrees....... sometimes it happens..... last year we got all the way to 88 once or twice.

 

[ggunn]

This isn't for every situation, but in some select cases, when you owe a whole bunch of money for taxes and that year you decide a photovoltaic roof mount system is in order, you might possibly make that tax bill pretty much go away for that year. Don't ask me how I know this...

The 30% income tax credit for renewable energy projects isn't a secret.

 

[FionaZuppa]

if you want to build solar for an existing AC system, then amp clamp the components to get the watts needed to run that system. then depending on %avg sunlight degradation due to clouds you can upsize the solar accordingly.

using batt banks also changes things some.

near me, you can buy 40 panels for a ~9kW system (installed) and have ROI in about 3-5yrs. unfortunately, AZ corp commission is allowing utils to play games with any extra power the resi solar creates, you can no longer get paid for extra power, you only get something in form of a credit, thus if your resi solar system is too big, then the best you can do is buy/manage batts to hold that potential energy, or, if you dont have batts then you impact the ROI break-even point. ROI usually does not account for maintenance of the system.

so as mentioned many times, solar varies across the US, and varies in many ways.

a real example near me, one resi went with solar city, 20yr lease (youch), and it saves the homeowner about 40%. solar city usually does all the homework to properly size the system, so all that homework it only saves homeowner 40%. these solar city city systems do not have batts.

 

[GoldDigger]

If you have to add batteries you generally are not just delaying the time period until break even, you are changing it to a system with a negative ROI instead.

 

[ggunn]

...your resi solar system is too big, then the best you can do is buy/manage batts to hold that potential energy...

If your PV system is overproducing, batteries will do nothing to change that. Batteries are good for storing energy to use later in a time of use tariff system, or for backup when the grid goes down, but they do not affect the net production from a PV system other than a bit of loss in the charge/discharge cycle. In a non-TOU utility that has good reliability (the grid has been down at my house for a total of a couple of hours over the last ten years), buying batteries is generally a waste of money.

 

[zbang]

Going back to the original premise-

I've been thinking about putting the AC system on solar power. What information do I need to get about my AC system in order to purchase the correct solar power setup.

You could also consider using hot-water panels and an absorption cooling system although they may be too big, there are AC units with direct PV panel connections, and there are some interesting geothermal heat-pumps that can be used for cooling.

As already mentioned, even a new system will be much more efficient than an older one and you really need to look at all the cost figures.

 

[FionaZuppa]

If your PV system is overproducing, batteries will do nothing to change that. Batteries are good for storing energy to use later in a time of use tariff system, or for backup when the grid goes down, but they do not affect the net production from a PV system other than a bit of loss in the charge/discharge cycle. In a non-TOU utility that has good reliability (the grid has been down at my house for a total of a couple of hours over the last ten years), buying batteries is generally a waste of money.

whaaaa? maybe i wasnt clear in what i said earlier, so i try again.

if daylight can give me 80kW and my home uses only 40kW for that period, the system is oversized by 100%. when it goes dark the system gives zero and has zero potential. thus i paid too much $$ for that PV system, its too big.

if i have lots of Ah in batts i can then store that extra 40kW for use when its dark, and if i use the 40kW from batts at night, then the PV system is sized just right.

 

[GoldDigger]

And maybe I was not clear that if you have access to grid power and pay less than $.50 per kWh you are better off just paying for power than storing "free" energy in a battery.
With current battery technology when you include battery replacement costs your stored energy will end up costing you from $.50 to $1.50 per kWh.
If you have access to free batteries the reckoning will be different.

Sent from my XT1585 using Tapatalk

 

[ActionDave]

Well there you go. Why do we even need power plants? Some solar panels and the right amount of tax credits and everything is good.

 

[jaggedben]

...

if daylight can give me 80kW and my home uses only 40kW for that period, the system is oversized by 100%. when it goes dark the system gives zero and has zero potential. thus i paid too much $$ for that PV system, its too big.

if i have lots of Ah in batts i can then store that extra 40kW for use when its dark, and if i use the 40kW from batts at night, then the PV system is sized just right.

If your state has a decent net-metering regime, you size the system for annual kilowatt-hours. (Also nobody's home uses 40kW.)

Batteries are getting to the place of paying for themselves in Hawaii, to my understanding. It will probably take a few years for California's TOU rates to get there, but I'm not holding my breath. Battery prices have to drop, too.

 

[drcampbell]

... hot-water panels and absorption cooling ...

The eternal dream: Direct, non-electric air conditioning.

Unfortunately, it's almost impossible to achieve the high temperatures an absorption machine requires without using concentrating solar collectors, and the concentrating (focusing) optics are only effective on direct solar radiation. Diffuse solar radiation -- which is a significant fraction of the total solar insolation anywhere that's not a desert -- doesn't focus. Thus the paradox: In hazy/humid places, it's almost impossible to make solar-absorption air conditioning work, and in clear/dry places you can usually substitute evaporative cooling for refrigeration-based cooling.

 

[ggunn]

whaaaa? maybe i wasnt clear in what i said earlier, so i try again.

if daylight can give me 80kW and my home uses only 40kW for that period, the system is oversized by 100%. when it goes dark the system gives zero and has zero potential. thus i paid too much $$ for that PV system, its too big.

if i have lots of Ah in batts i can then store that extra 40kW for use when its dark, and if i use the 40kW from batts at night, then the PV system is sized just right.

But if your system is grid tied, then the excess goes into the grid during the day and you draw it back out at night. The result is the same and you haven't paid for batteries.

 

[FionaZuppa]

But if your system is grid tied, then the excess goes into the grid during the day and you draw it back out at night. The result is the same and you haven't paid for batteries.

whaaa? likely not. the excess is already used elsewhere and sold by utility at retail price, and in my area you only get back a credit at the much lower wholesale cost that the util can get from their large solar farms or bought from a large solar farm.

the util doesnt "store" your excess for you to use later. the util gives you a small credit so they can lighten up their generation load.

i have to verify, but i believe AZ corp commission is allowing utils to cap the credits, so the util is happy to take your power, but not willing to pay for all of it, etc.

its part of the reason Solar City only wants to install what you need, no more than that. they really dont like new customers because there is no good history on power use. however, they can estimate based on a few items (calendar temps, avg AC use for home size, age of home, gas or electric appliances, etc etc).

 

[ggunn]

whaaa? likely not. the excess is already used elsewhere and sold by utility at retail price, and in my area you only get back a credit at the much lower wholesale cost that the util can get from their large solar farms or bought from a large solar farm.

Most places that's trued up over a billing cycle or even over a year, not instantaneously; you wouldn't want to build a system that produces more in a true-up cycle than you use if you get little or no credit for your excess, but batteries wouldn't help with that.