Solar Power for Air Condition System

[FionaZuppa]

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.

your owned batts certainly would help because then you dont need to give the excess back to util, that potential would be in my garage ready for use later. thus, if i oversized my kW in panels for daytime use, and i have batts, then the ROI becomes more favorable to me now that i can use my own generated energy at night. but the balance still holds, dont install a 20kW system if day use + nighttime use is only 12kW. max ROI is when generation(ability) = usage. granted, even a poor ROI has a return date, it just gets longer when there's that mismatch.

with the no-payback credit methods, the utils love it if you oversize and want grid tie.

 

[GoldDigger]

your owned batts certainly would help because then you dont need to give the excess back to util, that potential would be in my garage ready for use later. thus, if i oversized my kW in panels for daytime use, and i have batts, then the ROI becomes more favorable to me now that i can use my own generated energy at night. but the balance still holds, dont install a 20kW system if day use + nighttime use is only 12kW. max ROI is when generation(ability) = usage. granted, even a poor ROI has a return date, it just gets longer when there's that mismatch.

with the no-payback credit methods, the utils love it if you oversize and want grid tie.

You would be better off financially to simply throw away the excess power and buy an occasional difference back at POCO prices than to invest any money in battery storage.
FYI most of the country (with notable exceptions like Arizona and much of Texas) has statewide regulations requiring POCO to offer net metering (same price credit for excess as the retail price of power at the same time of day an usage tier.)

 

[jaggedben]

Currently you're not going to get payback on the batteries. You'll pay more for them than you'll save on utility costs. Give it a few years, maybe that will change. Right now, they are good as an expensive back-up power solution; the plus sides are they are clean, quiet, and not so subject to fuel availability if you have solar to recharge them. If that appeals to you, they might pay back a small percentage of their cost in utility savings.

 

[ggunn]

your owned batts certainly would help because then you dont need to give the excess back to util, that potential would be in my garage ready for use later. thus, if i oversized my kW in panels for daytime use, and i have batts, then the ROI becomes more favorable to me now that i can use my own generated energy at night.

That's what Tesla would have you believe, I guess, but it doesn't work that way in most jurisdictions without TOU tariffs. You know that I design PV systems full time, don't you?

 

[GoldDigger]

The one possible exception to the excessive cost of battery storage would be if you owned an electric vehicle with a generous battery warranty and cobbled together a way to extract power from the vehicle battery during non-solar hours. Just don't let the car manufacturer find out what you are doing.

It is also difficult for most people to arrange charging the car battery during peak solar hours.

 

[FionaZuppa]

Currently you're not going to get payback on the batteries. You'll pay more for them than you'll save on utility costs. Give it a few years, maybe that will change. Right now, they are good as an expensive back-up power solution; the plus sides are they are clean, quiet, and not so subject to fuel availability if you have solar to recharge them. If that appeals to you, they might pay back a small percentage of their cost in utility savings.

well, in my 10yr model i save ~$200 using batts vs buying the same power from poco.
if say i replace batts at yr 5, then i am break even with poco at 10yr mark <-- this model has no incentive to operate batt power, etc.


24v 100Ah AGM
the batts cost me $260 total
true sine inverter $150
-------------------------
210w for 8hrs daily
10yr batt life
10yr inverter life
$460/10yr
(assumed zero maintenance costs and zero degradation)
--------------------
poco is say 10c/kWh
210w for 8hrs daily
210w = 0.210kW
2.1c per hr
16.8c per day
0.168$/day
$613.20/10yr

 

[jaggedben]

That's not making much sense...

1) What are you charging the batteries from and what does that cost? You can't compare the cost of cycling energy through a battery to a flat cost of purchasing or producing the energy in the first place. The former is an add-on cost to the latter and to pay for itself the former has to somehow be charging with cheaper electricity than it is displacing when used. This can only be true if you're on a time-of-use rate schedule, or if the site does not yet have utility service and your including the cost of getting it.

2) You cannot power much of anything with a $150 inverter and such a thing is very unlikely to last ten years.

3) You cannot cycle AGM batteries to less than 40% SOC everyday and maintain their capacity for very long.

 

[GoldDigger]

That's not making much sense...
....

3) You cannot cycle AGM batteries to less than 40% SOC everyday and maintain their capacity for very long.

210 x 8 =1680 wH
24 x 100AH = 2400wH (actually more since the voltage will be above 24V much of the time?)

But that is going down to 30% SOC every day. That is significantly worse than 40%, and the lower you go the more each 10% costs in cycle life.
10 years at 365 days/year would be 3650 cycles. I say no way.
(Although I am sure you can find batteries that specify that kind of cycle life and offer you a 6 month warranty if you return them postage paid to China.)

 

[FionaZuppa]

That's not making much sense...

1) What are you charging the batteries from and what does that cost? You can't compare the cost of cycling energy through a battery to a flat cost of purchasing or producing the energy in the first place. The former is an add-on cost to the latter and to pay for itself the former has to somehow be charging with cheaper electricity than it is displacing when used. This can only be true if you're on a time-of-use rate schedule, or if the site does not yet have utility service and your including the cost of getting it.

2) You cannot power much of anything with a $150 inverter and such a thing is very unlikely to last ten years.

3) You cannot cycle AGM batteries to less than 40% SOC everyday and maintain their capacity for very long.

1) a site that has poco and then later installs solar. the poco delivery costs have been left out in my example, only the kWh cost is there. the power for the batts is coming from the oversized solar panel system, etc.
2) my inverter is a 300w continuous unit. the example given was just as-example, you can scale it accordingly.
3) from the data i have, decent quality deep cycle AGM can last 4-8yr, which can go 80% DOD, but do need to be properly charged.

 

[jaggedben]

1) a site that has poco and then later installs solar. the poco delivery costs have been left out in my example, only the kWh cost is there. the power for the batts is coming from the oversized solar panel system, etc.

Right. You are paying for the energy production somewhere, and then on top of that you are paying to store it. So yes, the full cost has been left out of your numbers.

2) my inverter is a 300w continuous unit. the example given was just as-example, you can scale it accordingly.

The problem is not just scale. It's the fact that you cannot really set up a multi-mode system for that cheap an inverter cost per watt. Not for systems that support AGM batteries, anyway.

 

[FionaZuppa]

Right. You are paying for the energy production somewhere, and then on top of that you are paying to store it. So yes, the full cost has been left out of your numbers.



The problem is not just scale. It's the fact that you cannot really set up a multi-mode system for that cheap an inverter cost per watt. Not for systems that support AGM batteries, anyway.

cheap of inverter? i honestly dont know the service life of all the makes/models.

but from what i can see, my 300W is 50c per watt, if i buy one 10x bigger (3kW) the cost is now 25c per watt, thats a 10x gain in output at 50% the per watt for hardware cost.

perhaps i am just not seeing how buying from poco at night is less $$ than storing that energy in batts from solar.

if batts are still more over 10yrs, then perhaps it is, but with modern day AGM's they are very close to util power. if i argue on the green side of things, if batts are the same $$ over 10yrs, then at that price you have saved emissions from the plants that make such power (obviously varies by locale, nuclear vs water/dam vs oil vs coal).

perhaps a 10yr ROI equation is too big of a period to look at? but 10yr is on par with many solar ROI graphs used by the folks selling it, many use a 25yr model.

when Tokamac comes online, solar/oil/gas/dam power production will be dead, which is quickly approaching.

 

[ggunn]

perhaps i am just not seeing how buying from poco at night is less $$ than storing that energy in batts from solar.

Gee, ya think?

...when Tokamac comes online, solar/oil/gas/dam power production will be dead, which is quickly approaching.

Tokamac (fusion generated electric power) has been "quickly approaching" for decades, and it doesn't look any closer to reality now than it did 30 years ago. I think that solar is safe from fusion for the time being.

 

[FionaZuppa]

Tokamac (fusion generated electric power) has been "quickly approaching" for decades, and it doesn't look any closer to reality now than it did 30 years ago. I think that solar is safe from fusion for the time being.

if it takes the next 200yrs to make Tokamac a live power generator, 200yrs in context is a very short period. however, seeing some of the hurdles already conquered, let's give them until ~2030 to see what the remaining challenges are.

Naysayers love to claim that nuclear fusion is always decades away -- and always will be -- but the reality is we've moved ever closer to the breakeven point and solved a large number of technical challenges over the past twenty years. Nuclear fusion, if we ever achieve it on a large scale, will usher in a new era for humanity: one where energy conservation is a thing of the past, as the fuel for our heart's desires will literally be without limits.

 

[jaggedben]

perhaps i am just not seeing how buying from poco at night is less $$ than storing that energy in batts from solar.
...

Let's take a best-case scenario (since your in AZ) levelized cost of residential solar energy production of about 7 cents/ kWh. Taking your very extremely optimistic numbers from post #10, it then costs you 7.5cents/kwh to save that energy for when the sun don't shine. There's some round trip efficiency loss, so best case your looking at a cost of about 15cents/kWh is the price the utility needs to beat. Doesn't make sense if they charge 10.

And that is extremely optimistic numbers for someone whose going to install it herself and not pay labor, I gather. I suppose you could save some on the solar, too, if you can DIY. Real world numbers for most ordinary people are probably more like 25-30 cents/kWh right now. Of course in Hawaii the utility can't beat that, so yes batteries already make sense there. Also for some time-of-use peak period rates in California. Not so much elsewhere yet. But give it some time.

 

[gadfly56]

Let's take a best-case scenario (since your in AZ) levelized cost of residential solar energy production of about 7 cents/ kWh. Taking your very extremely optimistic numbers from post #10, it then costs you 7.5cents/kwh to save that energy for when the sun don't shine. There's some round trip efficiency loss, so best case your looking at a cost of about 15cents/kWh is the price the utility needs to beat. Doesn't make sense if they charge 10.

And that is extremely optimistic numbers for someone whose going to install it herself and not pay labor, I gather. I suppose you could save some on the solar, too, if you can DIY. Real world numbers for most ordinary people are probably more like 25-30 cents/kWh right now. Of course in Hawaii the utility can't beat that, so yes batteries already make sense there. Also for some time-of-use peak period rates in California. Not so much elsewhere yet. But give it some time.

The fellow who runs "Watts Up With That" blog did a show-and-tell of his own install. His locale has peak pricing of ~$0.90/kW-hr, so his install made absolute economic sense. Here is his follow up with the numbers.

 

[jaggedben]

The fellow who runs "Watts Up With That" blog did a show-and-tell of his own install. His locale has peak pricing of ~$0.90/kW-hr, so his install made absolute economic sense. Here is his follow up with the numbers.

$0.90/kW-hr is astounding but I think there was something relatively unusual going on there. Also it's not clear if that's a peak rate (i.e. time-of-use) or if it's just high tier charges. If the latter, then it's of no relevance to our battery discussion.

BTW, he's either being disingenuous or misinformed when he says that $1200 came from PG&E and not the State of California. And a $7500 credit is not a 'small tax advantage.' :roll:

(Also... Grape Solar... Lol)

 

[FionaZuppa]

$0.90/kW-hr is astounding but I think there was something relatively unusual going on there. Also it's not clear if that's a peak rate (i.e. time-of-use) or if it's just high tier charges. If the latter, then it's of no relevance to our battery discussion.

BTW, he's either being disingenuous or misinformed when he says that $1200 came from PG&E and not the State of California. And a $7500 credit is not a 'small tax advantage.' :roll:

(Also... Grape Solar... Lol)

so get this, UniSource (which runs TEP and others) is now asking residential service folks to pick a billing plan (1 of 3). as jacked as it may be, the peak periods of the plans are in the sweet spot for running AC during the summer in AZ !!! which is the bulk of energy use when the temps are like they are this coming 7 days, 105-122F !

Let's take a best-case scenario (since your in AZ) levelized cost of residential solar energy production of about 7 cents/ kWh. Taking your very extremely optimistic numbers from post #10, it then costs you 7.5cents/kwh to save that energy for when the sun don't shine. There's some round trip efficiency loss, so best case your looking at a cost of about 15cents/kWh is the price the utility needs to beat. Doesn't make sense if they charge 10.

And that is extremely optimistic numbers for someone whose going to install it herself and not pay labor, I gather. I suppose you could save some on the solar, too, if you can DIY. Real world numbers for most ordinary people are probably more like 25-30 cents/kWh right now. Of course in Hawaii the utility can't beat that, so yes batteries already make sense there. Also for some time-of-use peak period rates in California. Not so much elsewhere yet. But give it some time.

i am not following you, why would i take util power and put that into batts. the batts get energy from the solar panels (free), etc.

and yes, it is in the realm of self install, or a friend helps, etc. i suspect though most would need a "batt guy" not unlike a pool service to come check on things once every 1-3mo.
batts also have with a safety hazard. pros and cons to everything.

 

[drcampbell]

... why would i take util power and put that into batts? ...

If there's a substantial-enough difference between the daytime & nighttime prices of electricity, it might be economical to buy cheap power at night, store it in batteries and consume it during the day. But if the daytime load is primarily air conditioning, thermal storage -- making chilled water or ice at night -- is probably more economical.

One example, not an endorsement:
http://www.calmac.com/large-energy-storage-project-university-of-arizona

 

[FionaZuppa]

If there's a substantial-enough difference between the daytime & nighttime prices of electricity, it might be economical to buy cheap power at night, store it in batteries and consume it during the day. But if the daytime load is primarily air conditioning, thermal storage -- making chilled water or ice at night -- is probably more economical.

One example, not an endorsement:
http://www.calmac.com/large-energy-storage-project-university-of-arizona

with the inverter losses in both directions, i dont see that as economical.

ice chillers only balance their usage, there's no free energy there. solar is "free" energy.

the solution (for now) to storing solar is salt water batts.

 

[K8MHZ]

the solution (for now) to storing solar is salt water batts.

Except for the fact they are not available.