The Real Solar ROI: My Actual Numbers After 14 Months of Ownership
Fourteen months ago, I signed a contract for a solar system on my house in central Ohio. At the time, the sales deck showed me a glossy projection of savings and a payback period that made it look like an obvious no-brainer. I was skeptical enough — being an engineer helps — that I built my own spreadsheet before I signed anything. Now I have 14 months of real data. Let’s compare.
I’m going to give you actual numbers here. Not ranges, not “your results may vary” hedging. What I paid, what I was promised, and what actually happened. If you’re trying to make a real financial decision about solar, you deserve real data.
The System: What I Bought and What It Cost
I installed a 9.6 kW system — 24 panels at 400W each — on a southeast-facing roof in central Ohio. The system uses string inverter technology with individual panel optimizers, which I chose because of partial shading from a nearby tree.
- Gross system cost: $31,200
- Federal Investment Tax Credit (30%): -$9,360
- Net cost after federal credit: $21,840
- Ohio state incentives: None that applied to my situation (property tax exemption exists but didn’t affect my out-of-pocket)
- Financing: I paid cash. If you finance, the math changes significantly — loan interest is real money.
One important note on the federal tax credit: it’s a credit against taxes owed, not a refund. I had to have at least $9,360 in federal tax liability to use the full credit in year one. I did, barely. If your tax liability is lower, you can carry the credit forward, but that stretches your actual payback period.
What They Promised vs. What Happened
The sales estimate projected 11,400 kWh of annual production for my system. That’s the number they used in all their ROI calculations.
My actual 12-month production (I’m using the full first calendar year, not the partial install year): 10,210 kWh.
That’s an 11% shortfall from the sales projection. In a vacuum, that might sound small. But when you apply that gap to 25 years of savings projections, it’s meaningful.
Why the gap? A few factors:
- The sales estimate used slightly optimistic performance ratio assumptions (I discovered this when I finally got the simulation file — getting that file and knowing what to look for is central to my breakdown of what solar salespeople don’t tell you)
- Year one had an unusually cloudy spring in my area — below average solar irradiance for March and April
- Shading from the oak tree is slightly worse than the shading model predicted
Is 11% catastrophic? No. But it matters for payback calculations, and it illustrates why I say: always discount the sales estimate by at least 10% when doing your own math.
The Bill Savings: Also Not Quite What Was Promised
Pre-solar, I was averaging $187/month on electricity over the trailing 12 months. The sales deck projected I’d cut that to around $18/month — essentially just the grid connection fee.
My actual average monthly bill over the past 14 months: $34/month.
Better than I expected at that number? Honestly, yes — but I should explain. Ohio net metering credits accumulated over the summer offset winter months when I’m drawing more from the grid. The $34 average includes some months at $12 and some at $67 (January, February). On an annualized basis, I’m saving roughly $1,836/year compared to my pre-solar bills.
The sales deck projected savings of $2,100/year. Again, roughly a 12% miss — consistent with the production shortfall.
The Monitoring Setup That Makes This Possible
I want to be clear: I only know these numbers this precisely because I set up proper monitoring. My inverter has basic monitoring built in, but it only shows system-level production. To actually understand what I’m using vs. generating vs. importing/exporting, I installed an Emporia Vue 3 energy monitor on my main panel. It tracks consumption at the circuit level and integrates with my solar production data.
Without that level of monitoring, I’d be flying blind. I wouldn’t know that my old chest freezer in the garage is eating 900 kWh/year, or that my home office equipment runs at 180W whenever I’m working. That data has been just as valuable as the solar system itself. If you’re serious about understanding your home’s energy picture — solar or not — a whole-home energy monitor is one of the smartest $200 purchases you can make.
True Payback Period: My Calculation
Here’s where I part ways with the sales deck math significantly.
Sales deck projected payback: 8.2 years (based on $2,100/year savings on $21,840 net cost)
My actual projected payback: 11.4 years
The difference comes from:
- Using actual savings ($1,836/year) instead of projected savings ($2,100/year)
- Accounting for inverter replacement at approximately year 12–15 (estimated $1,200–1,800)
- Using a more conservative electricity price escalation rate (3% vs. the 4% they used)
- Not assuming any state rebates beyond the federal credit
Is 11.4 years still a reasonable investment? For a 25-year system, yes — and that number improves further if you combine solar with time-of-use electric rates, which make peak-hour generation worth significantly more. After payback, I’m generating roughly $1,800–2,200/year in savings assuming continued electricity price increases. Total net positive over 25 years on a cash-purchased system: somewhere between $18,000 and $28,000 in today’s dollars, depending on utility rate escalation.
That’s a real return. Not the fairy tale in the sales deck, but real. I used a financial planning book on energy investments to build the underlying framework for my spreadsheet — there are several good ones that cover home energy financial planning in a rigorous, non-salesy way. Worth the read before you sign anything.
What I’d Tell Myself Before Signing
A few things I wish I’d done differently — or done sooner:
- Discount all production estimates by 10%. Not because companies are lying, but because estimates are optimistic and the first year almost never hits projections.
- Model the tax credit carefully. If you can’t use the full credit in year one, your payback period gets longer. Know your tax liability before you count on that money.
- Account for inverter replacement. It’s not in the sales deck. It should be in your model.
- Finance carefully. A 25-year loan at 5–6% interest significantly changes the ROI math. I’ve seen people take out loans at terms that will cost them more in interest than they save in electricity. Do the math.
- Set up real monitoring from day one. The built-in inverter monitoring isn’t enough. Know what’s happening at the circuit level. I’ve covered what to actually watch in my guide to solar panel maintenance — it’s much less work than you’d expect.
The Bottom Line
I’m glad I went solar. The system works, the savings are real, and knowing that I generate most of my own electricity from a mechanical engineer’s “I built this” satisfaction standpoint is genuinely satisfying. But the sales pitch oversold it by about 10–12%, and the payback period is closer to 11 years than 8.
That’s still a good investment. It’s just an honest investment, not a magical one. Go in with realistic numbers and you’ll be happy. Go in with the sales deck projections and you’ll spend the first few years wondering why reality isn’t matching the promise.
If you want to build your own model before talking to a single salesperson, start with 12 months of actual electric bills, run your own usage audit, and get comfortable with the federal tax credit rules. Everything else is just inputs to a spreadsheet — and engineers love spreadsheets.