is my project economically viable ?

[RShackleford]

When the coop starts crediting peak-hour production at peak rate, things look a bit brighter. Since solar noon here is about 1:15pm in the summer, and peak hours are 1-6pm on weekdays, I'm gonna assume 36% of summer production is during peak (half of production for 5/7 of the days). In winter, solar noon is 12:15pm and peak hours are 6-10am, so I'll assume none of the production is at peak. If I additonally assume production is split evenly between summer and winter, that means 18% of production is peak (summer peak rate of 33 cents). So my average kwh is worth about 10 cents, or about $500/year, so back close to a 10 year payoff.

[RShackleford]

That sounds like it's borderline economically viable to me.
If it were much worse I'd probably not.

I made a math error (and edited OP); it's actually more like 14 years.

[foo1bar]

For a payoff slightly more than 10 years (ignoring the time value of money, and the increase in my house's value).

That sounds like it's borderline economically viable to me.
If it were much worse I'd probably not.
I'd probably want to have 1 source for the modules and inverter and such rather than 3.

[Mike90250]

Do you have the discipline to restrict your usage during TOU hours, to have effective credit ? Some TOU plans extend till 8 or 9 pm, well past dark.

What plans will you be offered when you change from "now" to Solar ?

Having heavy loads like dishwashing and laundry happen in the "off" hours will help your payback, but the same efforts will help with your plain billing.

Since there is the issue of shading, shade generally renders panels useless. if you expect ANY shade from 10am - 2pm standard time, you should rethink the site or remove the offending trees

[RShackleford]

I've started at least two other threads seeking information about equipment for my DIY project, and people keep warning me of the likelihood that my project is not economically viable. So I'm starting this thread to discuss that subject.

I plan to build a ground-mounted grid-tied system of approximately 5kw. I plan to do all the work myself. I've done quite a bit of carpentry and house wiring (and I am an electrical engineer); my county allows DIY, including electrical work, subject to inspection. I will build a simple wooden structure and use rails from someone like IronRidge for mounting (the structure will be used as semi-dry storage for trash cans, garden tools, etc).

Using PVWatts, with these assumptions: DC size 4.8kw, standard panels with open-rack mounting, all system losses default except shading is 30% (for total losses of 38%), tilt of 30 degrees and azimuth of 172 degrees (slightly sub-optimal, at a cost of about 1/3 of one percent of production), I get 5044 kwh per year. The biggest question mark in this analysis is the figure for shading loss; this is the figure derived by a big installer, who gave me a quote with a guaranteed output using that number); also, I have the ownership and the ability to cut down problem trees.

I'm estimating the cost as follows:
$3145 for 15 Canadian 320 watt panels from (delivered from A1 Solar Store)
$683 for 15 Tigo TS4-R-O optimizers(delivered from altestore)
$1186 for SMA inverter (delivered from Renvu)
$750 materials for structure
$750 mounting rails and hardware ($50 per panel)
$1000 miscellaneous supplies (mostly electrical)
$200 permits
$250 engineering seal for structure
... for a total of $7964, or about $5600 after the federal tax credit.

So the bottom line is $1.10 construction cost per annual kwh of generation.

I'm on a time-of-day rate, with net metering, paying about $0.30/kwh during peak (6-10am winter, 1-6pm summer) and about $0.05/kwh otherwise. In fact, my output will first be credited against my peak usage, and the remainder credited against my off-peak usage; all excess production will be credited at the off-peak rate. I calculate a return of about $368 per year. For a payoff slightly less than 14 years (ignoring the time value of money, and the increase in my house's value). Also, our rural coop will get improved metering equipment in "a few years", at which time excess production during peak hours will be credited at the peak rate.