Am I thinking this through correctly?

rootusrootus

Solar Enthusiast
Joined
Jan 17, 2021
Messages
54
Just got a quote for a professional install of ~13kW of panels for ~19K after rebates. Sounds great, and I am tempted. But when I work the numbers, I come up very short. If I drop 19K on PV right now, I could cut my bill from $200 to probably $50 (still have some basic grid fees and such, plus I don't think 13K would quite meet 100% of our needs). So let's say I net $1800/year in savings. Sounds good, break even in just over 10 years. But probably around 15 years from now I'll need a new roof, and the panels will be old, the labor to remove/reinstall is a big part of the cost, etc. So the effective lifespan of the array would be 15 years, right? So for my 19K investment I have 27K and the panels themselves have very little remaining value. If I can average more than about 3% in any other investment vehicle over the same timeframe, I'd be ahead.

I seem to be talking myself out of this. I thought that with $1.5/W installed cost it would be a slam dunk. I think the problem is the roof lifespan. I'm not replacing a 9 year old roof so I can get 25 years instead of 15 from the panels.

Am I wrong?
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,434
You're right.

What are your utility rates? Maybe too low to make PV very attractive.
How much is your consumption? Maybe PV system is oversized for optimum return on investment.

Some of us told ourselves we did PV to save money, but somewhere along the line it became just like owning a boat. A hole we keep throwing money in because we're hooked.

Maybe you would like a nice patio roof?
The structure built to hold it up should count toward tax rebates ...
 

rootusrootus

Solar Enthusiast
Joined
Jan 17, 2021
Messages
54
You're right.

What are your utility rates? Maybe too low to make PV very attractive.
How much is your consumption? Maybe PV system is oversized for optimum return on investment.

Some of us told ourselves we did PV to save money, but somewhere along the line it became just like owning a boat. A hole we keep throwing money in because we're hooked.

Maybe you would like a nice patio roof?
The structure built to hold it up should count toward tax rebates ...

I'm on time-of-use, so it's somewhat variable, but overall I'm usually right around $0.115/kWh before taxes & such. Consumption is higher in the summer, but overall average about 1500kW/month. I'm in Oregon, so the amount of sun we get isn't ideal.

They did quote me an even larger system than I requested information on -- they claim it's for maximum ROI, it should be targeting 100% replacement. OTOH, the plan they gave me would put almost half the panels on a west-facing roof, which lowers their yield around 25% if my research is correct.

I'm a little hooked ever since I did the small solar setup on my RV, and that is definitely a factor that is making me want to try it on the house itself. It helps that it's summer so I'm just seeing how great it works with the sun so high in the sky and clouds a rare occurence :). But 20 grand is a decent chunk of change for a toy project. Maybe I could scratch the itch with a smaller ground-mount system where I could DIY a good chunk of the manual labor.
 

Hedges

I See Electromagnetic Fields!
Joined
Mar 28, 2020
Messages
8,434
DIY all the way.

Check out SanTan Solar for used and overstock PV panels.

PV panels + GT inverter can cost about $0.50/W. With rack mounts and electrical stuff maybe $1.00/W. Labor of love. Over 10 years, amortized cost $0.05/kWh. If an inverter dies and gets replaced, over 20 years amortized cost $0.03/kWh.

Add-on battery inverter or use hybrid inverter, possibly batteries optional, and the price gets higher but you can size it for minimal battery and keep it reasonable.

1500 kWh/month / 30 days = 50 kWh/day. 5 hours effective sun, 10 kW PV system.
That can be 10 kW PV inverter with 12 kW (STC) of panels all one orientation. A bit big for the allowed extra backfeed current in a breaker panel.
Could be 7.7 kW PV inverter with the panels in two arrays, 6 kW 10:00 AM sun and 6 kW 4:00 PM sun. Or a bit more panel to make up for some inefficiencies of this arrangement, so try to fit 15 kW of panels within space, and inverter voltage/current limits.
 
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