Grid vs solar cost

mountainman · 2025 02

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.

JRHill · 2025 02

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.

BB. · 2025 02

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

Photowhit · 2:02AM

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

mountainman · 12:02PM

mountainman · 12:36PM

Panels at 50° for better winter collection.
Friend of mine was talking about his
mid dec-january $280 light bill in nc.
1739 kwh usage $13 of which is night light.
$30 service connect fee.
He said that outrageous im going to off grid solar.
I replied probably gonna cost more for off grid with batteries, charge controller, panels, wiring
And inverters. Plus generator.
@Photowhit Snow is a non issue here.
2-3 inches every 5 years.
Just looking for a a approximate
Comparison.
100 watt bulb was just for an example.

With 4.22 December hrs and 1750 kwh usage
2.5 days anatomy with generator back up.
Ball park system price?
@bb offgrid battery system $1to$2 per kwh???

Dave Angelini · 4:33PM

As long as you keep the grid connection, do what you can afford.

You just do not want to lose the grid if the property has value to sell someday. Big Mistake if you do sell it or care about market value!

JRHill · 4:46PM

Dave Angelini said:

As long as you keep the grid connection, do what you can afford.

Bingo. If we had grid power available that would've been my power provider. I still would do solar because I love that kind of stuff. We live in the vicinity of the Dalles Dam and the electricity is at least as cheap as the OP so that makes solar a difficult proposition using strictly a return on investment basis.

BB. · 4:46PM

Granted, the $1+ per kWH was some math I did years ago with system based on Lead Acid batteries... Assumed that electronics lasted 10 years, solar panels 20 years (although, I have been averaging 10 years life on my solar panels), etc. costs, all against a 10 year system harvest life (again, the only thing that has over ten year life is probably the solar panels--But not always). That did not even include a genset (guess at least $1 per kWH based on just fuel costs).

The issue with Off Grid power is that the system needs to be pretty much 2x larger harvest design vs actual power usage to support those poor weather/poor sun days of winter...

The less power you use (say just a summer cabin), you have all the "lost harvest" of the rest of the year--Which also reduces actual power usage (kWH per year) vs the system potential. I.e., $/kWH used ... more $$$ for hardware, less kWH used -> gives higher $/kWH costs...

Over the years, we have had a few folks that have a well matched system "kWH potential" vs usage (use power when available, use less power when poor sun), get stuff on sale/used/etc. and could get down below $0.50 per kWH (was that Photowhit?)... Others that got used/failed fork lift batteries, and bypassed bad cells and built out a bank with the rest of the good cells connected.

But most of that has been discussed before our last 4 years of inflation, supply chain issues, China sourced hardware, COVID, and did not use Lithium Ion batteries in costing, etc...

And given the current "changes in the world", what will happen next?

In general, solar panel costs have crashed (at least for now). And battery/copper/hardware/labor costs have skyrocketed.

Electronics that have a 5 year support life from Mfg... And are basically unrepairable after 10+ years (no mfg support, parts no longer available, no "open source" schematics/parts lists, no software support...).

Could your panels last 25+ years, your industrial FLA batteries last 15+ years, etc... Yes. But the panels could last less than 10 years (mfg quality, destroyed by hail storm, high winds). Very iffy warranty support. having to run a genset for weeks while waiting for support/parts... Having to "chuck" the existing the present solar charger/inverter/etc. because the Mfg was sold/went out of business/old system not compatible with new system (repairs, upgrades).

Loss of insurance if system was not built to "code". Or if insurance company left your state because of lack of wilderness and water/infrastructure management, changes in utility/state PUC rules (see California fires, Grid Tied requirements changes, made either illegal for new connects or no longer economically viable)...

Add that Lithium Ion batteries are almost the ideal battery (very efficient, no maintenance, long cycle life, high energy density, etc.)--And the downsides of horrible failure modes... Fires and HF acid, heavy metals, etc.. Moss Landing (central California coast)... largest battery installation in the world(?), second or third "battery system fire" at the same site(?).

https://www.montereyherald.com/2025/01/27/moss-landing-fire-fallout-concentrations-of-heavy-metal-nanoparticles-found-nearby/

The results of these fires dropping all sorts of highly hazardous chemicals/materials on the local population and "Salad Bowel of the nation"...

I am at the point of looking at replacing solar array (would be 3rd set in 20 years) and changes in GT Rate Plan that make GT solar much less cost effective vs a new system (panels + Lithium Ion based PowerWall) replacement (adds off grid emergency power, and uses batteries to address changes in new rate plan--Store power locally instead of feeding back to grid for almost no return (8 kWH to grid, 1 kWH back from utility)... Worry about a Lithium fire creating a toxic waste site at my home vs crazy current (and proposed) electrically costs in California.

In the end, used a generator for a couple of days only once in the almost 70 Years I have lived here (60+ years ago, my parents could have used a Genset due to multi day outage from storm. A generator+some stored fuel seems to make more economic sense for backup power in my area (a few hours of outages every decade or so, mostly a car hitting a power pole or a wind storm taking down a power line--Is hybrid solar (GT/Offgrid) even make sense).

As Marc says, more questions than answers at this point.

-Bill

Grid vs solar cost

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