A friend was looking into solar with a Tesla wall (battery). I looked at 
her APS bill - it was $120/month. They were seriously considering 
spending $25K to cut down on the peak demand charge. The most they would 
save was $20/month. That's an ROI that would never be achieved.

I have solar. APS invited me to buy a battery and they would pay me 
$1250 if I let them manage it. The battery was quoted at $15K. Yeah, no. 
So let's say I use the battery to keep my 4pm-7pm APS draw minimized, 
what is my ROI? Looking at my past bills, my peak demand charge ranges 
from $5 to $121 per month. Let's average that out to $65/month. So $15K 
to save $65/month gives me an ROI of 230 months. It will be less due to 
APS price increases, but that's still 15-20 years out, and by then the 
battery would need to be replaced, nullifying any notion of an ROI.

Regards,

George Toft

On 11/26/2024 3:31 PM, Keith Smith via PLUG-discuss wrote:
> Hi,
>
> I have been curious about solar for sometime.
>
> I am looking at my electric bill and I use less than 600k watts a 
> month for 1/2 the year.
>
> My math does not seem to work out.
>
> 1) Convert 600000 watts at 120 volts * .1 = 60,000 watts at 12 volts.
> 2) 60,000 watts divided by 30 = 2000 watts at 12 volts per day.
> 3) If I can harvest solar for 4 hours a day that is 2000/4 = 500 watts 
> at 12 volts.
>
> That means I only need 500 watts of solar.  This does not take into 
> consideration loss of power in the system.
>
> If the system losses 30% then I need around 715 watts of solar panels 
> to meet my needs.
>
> I was expecting a lot more.
>
> Any help is much appreciated!!
>
> Keith
>
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