Solar vs grid cost

Just as a cost comparison for off grid to power company rates. My poco rate is 12 cents per kilowatt. My ac ceiling fan runs 24/7 at 42 watts. ~1 kWh 12 cents a day. Or $3.60 a month. What size and price off grid system Would it take just to run my ceiling fan? For my location pv watts in Dec is the worst month 4.7 sun hours.
2kw array 6 345 q cells make sky blue 60 cc
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
Comments
Off grid you need, PV-charge controller-battery-inverter. Grid tie, PV-inverter. All that hardware adds costs and builds in loses.
tony
42w ÷ .85 (peak inverter efficiency) x 24hrs = ļ1.2kwh/day. 2 days no sun autonomy to 50% SOC is a ~4.8kwh bank. 2 strings of 6v (~450ah@12v = 5.4kwh) GC2, maybe $400-450?
You'd want about 600w panels to produce ~450w, and a 60a controller, maybe $750-1000, and another $150 or so for an inverter.
Call it maybe $1600 with wire, etc., plus racking.
Replace batteries every 4yrs, electronics 10yrs, panels at 20yrs; 400 x 5 +350 x 2 + 600 = ~$3300 ÷ 240mos= ~$14/mo, or about 4x grid.
You can play with assumptions, but likely won't beat $0.12/kwh in an off-grid system
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
42 Watts * 24 hours per day = 1,008 WH per day
1,008 WH per day * 1/0.85 inverter eff * 1/12 volt battery bank * 2 days storage * 1/0.50 max discharge = 395 AH @ 12 volt battery bank (2x 6 volt @ 200 AH * 2 parallel strings = 4x "golf cart" batteries = 12 volts @ 400 AH battery bank)
400 AH * 12 volt battery bank * 1/0.77 panel+controller eff * 0.10 rate of charge = 623 Watt solar array nominal for full time off grid
1,008 WH per day * 1/0.52 AC off grid system eff * 1/4.7 hours of sun Dec = 412 Watt array "break even December"
412 Watt array / 0.65 Base Load fudge factor (allow for bad weather ride through) = 633 Watt array for December Base loads
633 Watt array (based on load/sun) > 623 Watt array 10% rate of charge => 633 Watt array suggested minimum
Use a smaller AC inverter such as the MorningStar 300 Watt 12 volt AC inverter (only ~6 Watt inverter Tare losses).
Estimated costs (pure guess):
- 633 Watt array ~ $633 for panel(s) and shipping
- 300 Watt MorningStar inverter ~ $250 (including shipping/taxes)
- 4x golf cart batteries = $400
- Electrical + racking + misc = $200
- 633 Watt array * 0.77 panel+controller derate * 1/14.5 volts nominal charging = 34 Amp minimum MPPT controller
- 40 Amp or greater MPPT type controller, good quality, ~$484 nominal
- $1,483 + $484 = $1,967 initial system costs
- + 2x * $400 battery bank (assuming 3.3 year life for batteries--3 sets = 10 years life)
- Say 10 year system life
- 1,008 WH per day * 365 days * 10 years * 1/1,000 W per kWH = 3,679 kWH for 10 years
- $1,483 initial + $484 + $800 for 2 more sets of batteries = $2,767 10 year system cost
- $2,767 (10 year costs) / 3,679 kWH load per 10 years = $0.62 $0.75 per kWH off grid system price
No backup genset (for bad weather/system maintenance/failures). 3.3 year life for GT batteries is conservative. No distilled water pricing, no labor costs. Assuming no other major failures in 10 years (panels, AC inverter, etc.). Assume fan is shut down during bad weather > 2 days long.That is how I would estimate the overall cost of off grid power for your fan load. If this was a grid tied system, no battery costs, solar array would be almost 1/3rd the size... See what it would be:
- 1,008 WH per day * 1/0.77 GT system/panel derating eff * 1/5.5 hour of "average yearly sun for location) = 238 Watt array
- 238 Watt panel = $238 (including shipping)
- 238 Watt array * 0.77 panel+inverter derating = 183 Watt GT inverter
- $139 for Enphase micro inverter
- $100 for mounting + wiring + main panel breaker for solar
- $477 initial hardware costs + 0 maintenance
- $477 costs / 3,679 kWH per 10 years = $0.13 per kWH
- For 20 year life, assume 1 new inverter => ($477+$139) / (2x 3,679 kWH ten year) = $0.084 per kWH
Ratio of GT to OG system $/kWH using 10 year OG vs 20 year GT system costs- $0.084 per kWH / $0.75 per kWH = 0.112:1 for GT vs OG
- 1/0.112 = 8.93 x more expensive for Off Grid system vs GT
Anyway, quick stab at the design and estimated life costsThe above Off Grid system costs have been adjusted by adding the costs for an MPPT charge controller.
-Bill
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
-Bill
-Bill
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
Only thing "saving me" is that 3.5 kWatt GT system on my house (15 years ago), and being fairly conservation minded. So I pay around $10 per month connection fee/minimum power usage (used to be $5 a year or two ago).
Off grid solar is not to save money--It is to provide you power where the power lines do not run (and save on genset fuel/maintenance/noise/smoke).
-Bill
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
Then i added a 300 inverter for tv stereo and box fan etc. Thats when I realized how little power i had. Now that i have enough power to keep a ceiling fan going. 400 ahs and 780 watts for summer stays works much better for my useage.
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
-Bill
I have read for a near normal conservative life style. With an electric fridge and heat pump or possibly inverter window unit.
Microwave toaster. And well pump.
Lp heat stove dryer and hwh.
That it Would take a 3300 wh per day system.
Would this be better at 48 volts or 24?
I'm thinking 8 330 ah l16s. All in series for 48. A 60 amp cc. And 3200 watts of
72 cell panels. (Blacksburg Virginia)
Thought opinions? Cost? Edit on second thought with 12 60 cell panels 3 s 4 p
I could use a cheaper 150 volt controller.
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
"$100 for mounting + wiring + main panel breaker for solar" It might prove easier to spend $500 than $100.
My vote is easily for the 48 volt system.
Interesting to see the "peace of mind" mentioned about off grid power. I would say that depends on the reliability of your grid power vs off grid power. While there is satisfaction in creating your own power grid it may be more worrisome to have to fix issues yourself than simply call the utility company. That would likely depend on the make up of the individual.
I recently learned how easy it is to sabotage off grid power. After much consideration I realized that the only way that two of my panels could have lost their serial connection, going from ~80 volts to ~40 volts, is via intentional sabotage. That changed my charging voltage from ~80 volts to ~47.7 volts. Not to mention some inevitable battery damage from weeks of very low voltage. Few have to worry about sabotage, instead they may consider the possibility of theft.
Then we have labor costs. Most posters here can do their own systems but can the general population? I would guess 'no' unless they have a 'minimal' background in working with electricity. Yesterday I discovered an old 10" x 10" box of electrical connections with over two decade old writing on it. "Proving" that I have done more work than I easily recollected. Shoot, I used to advertise myself as a lighting specialist. My memory is slipping for sure. So are my abilities. Thinking that forced retirement may be more for the employer than the employee at times.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
lucky I found some free 8 volt cores. With used panels 4 190 for .30 cents a watt. a new cheap 40 epever cc. aims 300 pure sine. That's lasted 3 years so far. battery cables from junk cars and fuses to inverter and cc. 300 foot of 10 awg pv cable $75. I built my racking from treated wood and cement. So by cutting corners every way possible. For a 760 watt 416 ah system. Oh yea
Plus $140 for the Iota from naws
And $125 Craigslist briggs new generator.
Call it 1300 dollars. 1.70/watt.
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
I could write about how little my civil service father made vs how much responsibility he had. My brother does similar work and admits to being overpaid.
You wouldn't likely need building permits for a camper, but may for a permanent structure. If so, you may want to check with the AHJ on what your options are.
Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
I had planned to haul sewer from the future cabin on my 25 foot back hoe trailer in 4 275 gal totes. Nope not allowed to haul your sewer.
Unless it's in a camper. So I bought an aluminum frame junk camper to mount onto my trailer.
14 months ago I was quoted after buying a permit 12000. So i saved the money.
When I came back now the laws have changed its $35000
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
6 230ah GC @36 volts
18 amp accusense charger. 3650 champion
I use around 4 kWhs a day during the winter months and 12-15 during the summer running air conditioning along with the fridge and daily stuff.
In my situation, much of the energy used in the summer is directly off the array, our heat comes with sun. I have minimal storage, just a 16 kWh battery.
My system cost a bit less than $10K, and since I'm running the numbers raw here, I'll add in the $1K to install a wood stove, but not add in the yearly costs for that since it isn't off set by electric costs and would be viable heating method without solar.
So my cost is 11,000 for the solar electric system, replacement costs will be inverter and charge controllers every 10 years at $2500 (even though I have been using the same inverter for 15 years and the charge controllers seam to be doing well 8 years in), and replace the forklift battery every 12 years, (I had originally used 15, I think that is viable, but I want to use as realistic numbers as possible, mine is hanging in there even though it was poisoned early and it's 8 years old now.)
So with a 30 year life of the array(it will still be usable after than and have some residual value) the initial cost was 11K+$5kfor electronics 2X and $5K for replacement forklift battery 1.5X (though the original battery cost was $2250 delivered it is very close to the same today, it was sized for my cabin, and I will replace it with a 50% larger one), the cost over 30years will be around $21,000.
The current cost of grid electric to replace would be $39 x 12 = $468 + $172.80 (14.40x8months at 4kWhs a day) and $192($48x4months)=$832.80 per year x 30 years = $24,948.
I have mentioned the residual value of the array, but not included the $2K tax credit. There is some nominal cost of distilled water as well as lost interest. It does take some minimal amount of time, I spend perhaps as much as 2 hours a month on the system.
Several things collide to make this inexpensive. I don't need a lot of storage using much o the energy directly off the array. I have a very good energy use profile for solar. My local energy cost from the grid is quite high. I just did total numbers, but 120 kwhs a month for 8 months is 960 kWhs, add 1200 for the summer months, the total usage is around 2160 kWhs, and the total cost is $832.80, so $.385 a kWh. Using these slightly higher numbers than previously, my cost off grid is about $700 a year for 2160 kWhs or about $.325 a kWh. Originally I had figured about 26 cents a kWh and is likely not far off if the lower actual costs and the tax credit are included.
I have 'played' a bit. I bought the inverter I had spec'd to use this year, and it is installed but not more than trial run (I'm too lazy to build a 4/0 cable for it, mostly involves getting my bench vise installed again to use my hammer crimper) I've added none of the original extra panels yet, but have 1K of others ($250) on the frame and 4 of the others mounted but not wired. I still need to do a rerunning of the original numbers, but they will just be cheaper as I think I originally spec'd a new inverter, not a $600 used one (4000 watt magnum, was going to wait until the battery change over and switch to a 48 volt system)
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
And at this price, it's better than utility power in some places (like parts of Hawaii).
I am available for custom hardware/firmware development
Only had "professional solar" for 4.6 years now. Still learning. Being able to read the system voltage with a twist of the neck is one of the best possible moves there is. Spent about 5 years playing with make shift solar set ups - learned almost nothing it seems.