is my project economically viable ?

[RShackleford]

I decided to get more serious about figuring out my shading losses. One simplifying thing: I can model my shading as though my panels will sit at the bottom of a bowl with a very irregular lip, in other words, for any given azimuth the sun is blocked up to a certain elevation angle, and then it's clear above that. So I built this little gizmo (photo below) which I can aim in a certain direction, giving me an azimuth within a degree or so, and then aim the tube at the top of the treeline, giving me an elevation within a couple of degrees. I aimed it for every 10 degrees of azimuth from 120 to 240 (no chance I'm gonna get any yield from directions outside that range), and measured the elevation angle of the top of the treeline.

Then, in the pvwatts_hourly file that PVWatts generates (with shading loss set to zero), I added columns in which I compute the azimuth and elevation of the sun for every hour of every day. I put my measurements into a little lookup table. Indexing into that table for each sun azimuth position to grab the treeline elevation, I compared the sun's elevation to see if I'd be shaded. I also added a column for the degree of sun transmittance if the sun angle was below the trees; for now, I set that to 0 for all days except Dec 1 through March 15, for which I set it to 50% (optimistic perhaps). Finally, I computed a column for the overall percentage of transmittance (complement of shading) I'd see for each hour of each day: 1 if the sun's elevation is above the treeline, 0 if it's below the treeline for any days except Dec1-Mar15, and 0.5 if it's below the treeline and it's one of those winter days.

Finally I did a dot-product (Excel SUMPRODUCT function) of the "AC system output" column with this "percentage of transmittance" column, and came up with a kwh/year figure adjusted for my measured shading. Pretty grim result: just a little over 50% of the PVWatts number (which already has all the system losses except shading incorporated). Specifically, PVWatts gave 7315 kwh/yr with 0% shading (but all the other system losses). PVWattts gives 5107 kwh/yr with the 30% shading number the installer used for their guaranteed-production quote. And with my modeling of shade I get 3757 kwh/yr.


IMG_20191109_172619430.jpg

[RShackleford]

I ignored that [the effect of inflation]. And ignored the likely increases in cost of electricity from the POCO.
I figure those two will both be small percentages and in opposite directions so at least partially cancel each other out.

Good point. To the extent that electricity rates track with inflation, both can be ignored.

I think it also depends on how certain you are you'll keep the property for 7 (or 10 or whatever) years.

Pretty sure.

[RShackleford]

Anyhow, this is an important thing to consider, but ... does anyone have any answers/opinions for the questions asked in my OP here: https://www.solarpaneltalk.com/forum...for-diy-system ... from which thread this current thread got spun off ?

[foo1bar]

I suppose it depends on the time value of money, or inflation.

Somewhat.
I ignored that. And ignored the likely increases in cost of electricity from the POCO.
I figure those two will both be small percentages and in opposite directions so at least partially cancel each other out.

IMO 7-10 year is OK - probably worth doing. <7 year is definitely where I'd do it. >10 year I would be hesitant (but might still go for it after more analysis.)
I think it also depends on how certain you are you'll keep the property for 7 (or 10 or whatever) years.

[RShackleford]

No one should be using the possibility of increased home value in a ROI evaluation. If the ROI looks so bad that you have to start adding variables like "increased property value" to make it seem logical, you should not be going solar.

I'm not sure it looks that bad. I need to talk to the POCO coop again and make sure I understand the way the net metering works better - it really kinda sucks if I only get credit for as many peak-hour kwh's as what I used, and not for all I generate. Makes a big difference: PVWatts has me generating about 150 peak-kwhs per month for the 6 months of the "summer" rates, whereas I use about 50 in each such month.

Anyhow, what would you all say is the ratio of system cost to expected annual payback that makes sense ? Perhaps a range, between the number where it's definitely a good idea, and the number where it's definitely not. I suppose it depends on the time value of money, or inflation.

[azdave]

It's still a stretch to install a system where I'm depending on a likely increase in property value to make it economically viable.

No one should be using the possibility of increased home value in a ROI evaluation. If the ROI looks so bad that you have to start adding variables like "increased property value" to make it seem logical, you should not be going solar.

[ButchDeal]

Being able to identify a horse from a steer doesn't make one a good horse breeder or an equestrian.

well maybe a Stallion from a Gelding would help but horse from steer is equine to bovine simple.

[J.P.M.]

The area where I live is highly-educated. And there is a LOT of solar around, so people know what it is and are used to seeing it.

It's still a stretch to install a system where I'm depending on a likely increase in property value to make it economically viable. OTOH, since DIY I'll be paying about half of what the system would cost if installed by a company (what are people typically paying per watt for a ground-mount system in the 5kw range ?)

In what ways are they "highly educated" ? Being able to identify a horse from a steer doesn't make one a good horse breeder or an equestrian.

You want to play it safe on value added ? Assume a PV system will add nothing to a home's value and in so doing have a higher probability of being be pleasantly surprised when/if you sell.

Or, sort of like the B.S. of eggs are good/bad for you, don't start a chicken ranch in your back yard and assume the eggs you get will be in favor or that the exercise will add any value to your property if/when you sell it.

[RShackleford]

It only adds value if the Buyer is educated enough to understand it can benefit them.

The area where I live is highly-educated. And there is a LOT of solar around, so people know what it is and are used to seeing it.

It's still a stretch to install a system where I'm depending on a likely increase in property value to make it economically viable. OTOH, since DIY I'll be paying about half of what the system would cost if installed by a company (what are people typically paying per watt for a ground-mount system in the 5kw range ?)

[J.P.M.]

It only adds value if the Buyer is educated enough to understand it can benefit them. Who's going to educate the buyer ? I had to educate my sales agent, after he sold my house for MY asking, he put panels on his own house.
I had a well thought out GT system in Los Angeles, which nearly zeroed out my bill, and had copies of the bills before and after to prove it. $0 vs $150 (in 2003 dollars)

Or, as I've seen more often on a local level, and similar to a lot of the posters I see around here, residential PV may add perceived value if the buyer is uneducated enough to let others with skin in the game oversell the benefits and swallow the hype - a lot of it from friends and neighbors who are equally ignorant, and/or from sources such as the green wash media shills of the solar peddlers.

Reality is, folks see what they want to see, hear what they want to hear, and read what they want to read. Generally, what is portrayed as making life easier is easier to sell, objectively true or not.

Ignorance is the real enemy.

[Mike90250]

............ I think it boils down to the issue of whether or not the panels add value to the house. Lots of likely-biased articles (solar vendors etc) say they do.......

It only adds value if the Buyer is educated enough to understand it can benefit them. Who's going to educate the buyer ? I had to educate my sales agent, after he sold my house for MY asking, he put panels on his own house.
I had a well thought out GT system in Los Angeles, which nearly zeroed out my bill, and had copies of the bills before and after to prove it. $0 vs $150 (in 2003 dollars)

[foo1bar]

"I'd probably want to have 1 source for the modules and inverter and such rather than 3."

Why ?

"One throat to choke"

When/if there's a problem, it isn't "well my stuff is perfect, it must be what you bought from the other guy"

[RShackleford]

When the coop starts crediting peak-hour production at peak rate, things look a bit brighter ... so back close to a 10 year payoff.

So at some indeterminate time in the future, I may get to that 10 year payoff rate. Not so great.

So, I think it boils down to the issue of whether or not the panels add value to the house. Lots of likely-biased articles (solar vendors etc) say they do. This article seems even-handed though: http://money.com/money/5642057/home-value-solar-panels/ . And this gov't study actually includes my area, and suggests it'd add at least double the value of my estimated cost: https://emp.lbl.gov/sites/default/fi...nl-1002778.pdf

[RShackleford]

I'd probably want to have 1 source for the modules and inverter and such rather than 3.

Why ?

[RShackleford]

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 ?

Same plan as now, except for net metering. I've been living with the same peak plan for some years now and it works well. Very little activity 6-10am in summer. Like to sleep cold, so keep house chilling overnight, and it remains comfy during 1-6pm summer peak. Water heater is on a timer.