Solar vs grid cost

mountainman

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.

icarus

Because of battery costs, conversion rates etc, “off grid” (battery based) systems are ALWAYS going to be more expensive.  In the old days, ( afew years ago) we used to say that battery based systems were twice the cost with half the performance. That probably has changed a little as PV has gotten cheaper, but batteries haven’t really.  

Off grid you need, PV-charge controller-battery-inverter.  Grid tie, PV-inverter. All that hardware adds costs and builds in loses.

tony

Estragon

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

BB.

Note, I had forgotten to add the cost of a nice quality MPPT charge controller (thank you Estragon) to the cost of an Off Grid power system--The updates are "Bolded". -BB

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 costs

The above Off Grid system costs have been adjusted by adding the costs for an MPPT charge controller.

-Bill

Estragon

I think Bill is missing a charge controller in OG numbers?

BB.

Woops... Your are correct Estragon... I will update.

-Bill

BB.

Updated.

-Bill

mountainman

So 40+ years just to break even on initial cost alone.

BB.

You do have to worry about inflation... In California my rates went from $0.10/$0.20 per kWH (off peak/peak) to $0.30/$47 summer TOU plan (higher tier 2 rates)... Or north of 2x in just a hand full of years.

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

MrM1

BB. said:

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

Agreed.  I can't tell you what a piece of mind it is the past 2 years to NEVER know when the grid goes down.  We usually learn about it either when one of our rural neighbors calls and asks "is yalls power out" to which we smugly reply, "No, Why?".  Or we look outside and see that the only street light is not burning down the way.  But being at least moderately self sustaining is very reassuring.  And while I have probably burned up my first set of batteries from over charging (out of fear of sulfation),  now that last summer forced me into a new LG inverter fridge that cut my daily Watt hours nearly in half,  I think I can actually do what I want to do with 4 golf cart 220 Ah batteries. 

But my cost per kWh including taxes and all fees here is just over .11 ... so no,  I'm not saving a thing in dollars,  but the peace of mind is priceless and generating your own power is very rewarding (to me).

mountainman

I disagree on off grid solar is just for places with out power lines. My 12 acres has power lines on the property right beside the highway. But they want 35000 dollars for sewer. Before I can connect.

mountainman

I started out with 400 watts and a 200 ah bank.  Was fine for the camper. Lp fridge Even ran a 10000 btu window unit and charged on extended raining days with a 1700 watt generator.
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.

BB.

Yep... Paper designs and spreadsheets of costs/harvest/etc. first. Once a person has worked out the details on cheap sheets of paper and on the computer, then you have a plan (off grid, genset, utility, etc.).

-Bill

mountainman

Sometime in the near future i plan on building a small cabin.
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.

softdown

Where is BB getting GC batteries for $100? We have to pay a $15 core charge here, with taxes the best price seems to be $113/battery. 

"$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. 

Estragon

mountainman said:

Sometime in the near future i plan on building a small cabin.
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?

Lots of choices and variables, but ball-park $10,000ish for that size system.  48v makes sense, if only because it wants 50% less charge controller than 24v.

mountainman

July 1 My 4 6 volt  208 Gc us battery where 97 tax included.  core was $20 each 
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.

mountainman

@Estragon much cheaper that a $35000 sewer system.

softdown

mountainman said:

@Estragon much cheaper that a $35000 sewer system.

The costs for "public works" is unbelievable. Until we consider how many government type employees reap six figure incomes along with some of the best benefits and retirement packages. It will eventually bite them in the ass. Unprecedented numbers are fleeing Illinois, New York, and plotting their California escape (an escape fueled almost entirely by bizarro politics). 

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. 

Estragon

mountainman said:

@Estragon much cheaper that a $35000 sewer system.

In some places (eg my city place) if utility water/sewer passes the property, hooking up isn't optional.  In some cases, existing structures can be grandfathered, but most new or refurbed structures require hook-up for permits. 

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.

mountainman

I already have checked. No permit required for rv. What gets old quick is I have to haul the camper 30 minutes away once a week to dump. You can build a 256 sq ft building no permit. You can only disturb 1000 sq ft of land before being permitted. And under 50 volts is allowed. 
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

bill von novak

mountainman said:

.
Would this be better at 48 volts or 24?

48V no question.  At SPI this year, there were exactly two kinds of residential battery systems - 48V and 400V.

softdown

I'd like to see a 120 volt system for several reasons. 

mountainman

I'm sure it would be more efficient. 120 dc to 120 or 240 ac. Would you use 60 2 volt batteries or 20 6 volt?

softdown

mountainman said:

I'm sure it would be more efficient. 120 dc to 120 or 240 ac. Would you use 60 2 volt batteries or 20 6 volt?

Sixty batteries seems a bit much. Ten twelve volt batteries sounds good to me. Perhaps also a 60 volt option for ten six volt batteries. But I don't think my wishes carry much weight in the solar world. Pretty sure of that actually. 

Photowhit

Well,  for  what it's worth, I'm  still happy to contend that my off grid system is now cheaper than the grid, in my location. I   do make some minimal sacrifices to make this happen. I don't use  a backup generator.  I  will reduce my  use about every  2-3 years usually in the  late fall when we have  an inordinately long cloudy period.  Grid  electric here is  very expensive for a minimal user.   It now costs $39 for the privilege of buying  electric  from the COOP.



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)

shawnj72

Wow... I guess my Motto is True " Anything worth doing is worth Over Doing." As these Are Real conservative examples. If You Looking to "Save Money" By Going Off Grid You probably wont. Even After 10 15 Years as You will Have to Upgrade Maintain components. Sometimes its Not About Saving On Utility but Having the Peace of Mind Being able to have Power when you Want it in case of Grid Failure for one reason or another. Sometimes it is the Battle with the Power company for Reason. Maybe a Little of Both. Having a bill Going From 325.00 A Month to 90.00 With just the first Array Up Is Satisfying Enough. Knowing that the Utility co Wants to Try To Lobby Congress for a Bill  That requires any solar Users a Utility Tax Just to have it.. Yes Our Local Utility co Wants Just that. so far it hasn't happened..They also Promised A town Near me Funds To help with a solar Farm and A Program to buy the Excess. After the The town purchased Everything And was near Completion they Reneged on the Deal Left them Hanging off the cliff..Big write up in many local newspapers and even national magazines..They are sour over the Whole solar Thing. As they offered Buyback for the first year now Brought that to a seizing Halt. If I had it to do over I would do it again.. Maybe start out smaller and work up to it.. As it is a lot of work that's for sure.. Consumes a lot of time but in the end well worth it in my opinion every cent. I have about 13,000 invested as I went big per say.. I have a 2000 SF House and 6 kids and a wife that are Power Hogs.. So I couldn't really go small.

Conext XW+ 6848

2x 60-150 MPPT

AGS

13KW GENSET

2X 4500W Array

804AH Forklift Battery Bank

Integrated with Home Automation Project.

It may or may not have a return on Resale value but it should if done correctly. While the Savings isn't really A Saving on utility. A peace of mind knowing you will have supplemental Power in case of emergency.. And Knowing you are not giving the Utility Every dollar a bit more Satisfying.. 

     

jonr

 > $.385 a kWh

And at this price, it's better than utility power in some places (like parts of Hawaii).

softdown

Photowhit said:

Well,  for  what it's worth, I'm  still happy to contend that my off grid system is now cheaper than the grid, in my location. I   do make some minimal sacrifices to make this happen. I don't use  a backup generator.  I  will reduce my  use about every  2-3 years usually in the  late fall when we have  an inordinately long cloudy period.  Grid  electric here is  very expensive for a minimal user.   It now costs $39 for the privilege of buying  electric  from the COOP.



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)

Congrats on "sticking it to the man". Your case is about as good as it gets for a pro solar argument. You got tremendous prices on most everything, your battery is very long lived, and you use the heck out of your panels when they are in peak summer time production. Using your noggin!

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. 

MrM1

mountainman said:

Sometime in the near future i plan on building a small cabin.
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.

I have $7k in my system of that size.  It lacks rapid shut down but otherwise would be very near code.  Probably my only code violation (except rapid shut down) was not using Metal Conduit / Raceway.  I used PVC for my DC runs out of ignorance.   My only regret was NOT using 48v.

Marc Kurth

Grid electric cost here is: $5.00 base charge, $0.057/kwh for energy, $0.039/kwh for delivery. Depending upon the value of your invested capital, it is difficult to build an economic reason for off grid solar when grid is readily available.

Most off grid systems that I get involved with, are emotionally justified, or solar is chosen because a $35K+ investment is required to have grid power brought to the property.