Grid vs solar cost

mountainman
mountainman Registered Users Posts: 440 ✭✭
edited February 5 in General Solar Power Topics #1
I'd like to discuss a cost comparison between grid and off grid cost.
My power company charges 16 cents per kilowatt.
 For example a 100 watt light bulb left on constantly 24 hours a day cost roughly 38 cents.
What size system?
 (panel wattage and battery bank)
and how much would it cost for a off grid system to power a 100 watt bulb 24-7?.
My location is 34 degrees attitude.

2kw array 6 345 q cells  make sky blue 60 cc
 6 230ah GC @36 volts 
18 amp accusense charger. 3650 champion 
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  • JRHill
    JRHill Registered Users Posts: 379 ✭✭✭✭
    #2
    Since you have grid power I guess the biggest problem is a non-issue. But if that light bulb is as important as a water/well pump, a fridge and a freezer and you don't have an available grid connection or that connection would cost $250,000+ then all of a sudden things look a lot different.
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,655 admin
    #3
    That is a difficult question to answer...
    For me I'm California, that is $0.40 to $0.50 per Watt hour... Plus connection charges (today, it is a minimum monthly power charge, in the near future, hearing the charges may double).
    This is for Grid tied system... In about a year going from a roughly xx kwh overage to utility, I get xx kwh back for +free) (not really free, but close enough for this discussion).
    Some time in the next year lose grandfather plan and for every 8 kwh overage, get 1 kwh "free"...
    California does not want GT solar any more (as an engineer, I understand why).
    So now looks like the next most reasonable is (for example) Tesla power wall 3, new panels (mine old ones are failing now) and basically charge LiFePO4 bank during day, and discharge at night.
    For my 3.5 kw gt solar home. Looking at $6k for new panels. Or (roughly) $30k-10%=$20k for power wall+panels+permits+installation+etc. to go hybrid.
    For your question, I have used $1-2+ per kwh as a rough of grid cost.
    You can do math and
    10 years of kwh used
    $xxxx (5-10 year life depending on battery chosen) 
    $yyy solar panels (10-20 year life)
    $/kwh=total costs/total kwh used...
    If you go grid tied, it really depends on your utility and state and what they allow and their rate plans if gt solar makes sense now and 10-20 years in the future...
    I don't believe that solar will increase the value of the property and could scare off a future buyer.
    Adding batteries (lead acid or lithium ion) adds cost and complexity (and possibly extra maintenance).
    For me,I am really on the fence what to do next.
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Photowhit
    Photowhit Solar Expert Posts: 6,012 ✭✭✭✭✭
    #4
    Lots of things to discuss.

    What does your grid electric actually cost? Is there a per month fee? Are you a minimal user?
    I live where the per kWh cost is about 15 cents BUT!!! there is a monthly $44 fee to buy the electric!
    As a minimal user, say 100-200 kWhs a month 9 months out of the year That's pretty expensive electric. 200x.15=$30 + $44 = $74  /// $74/200=.37 cents a kWh!

    Next, we'd run calculations for a 100 watt load. Doubt you are actually running a 100 watt light. I guess there are 100-200 watt security lights, but you wouldn't run them 24 hours a day. A 100 watt equivalent LED bulb would use 13-15 watts.

    To calculate your system size we or you would need more location numbers than latitude. You can use the resource at PV watts to figure out how much available energy there is at your location. You would also want to let us know your maximum stress level. Some systems would be fine for storage for 4-5 days without sun (added energy), some would include a generator back up. Some would require you being there for snow removal if needed!

    My system shut down for the first real damaging time when we had 9 inches of snow followed by cold weather for over a week. I had hip replacement surgery and stayed with friends for 2 months. I had left a minimal light and radio running maybe 15 watts total, as well as my fridge (1-1.5 kWhs a day) and my base load of my smaller inverter 30watts. This was enough to run my battery bank down and shut down the system. Even with ice still in the freezer, most of the freezer food had thawed. Only thing I saved was 3 pounds of sealed cheese. 

    Nothing straight forward in calculating a system. My costs work out to be less than the grid now. When I started it was just close to being cost effective. Now with the added grid costs I'm cheaper than the grid;

    It's going to be close to cost effective! or Off grid at 26 cents a KWh! — northernarizona-windandsun
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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