I Walked Away From a Business With a 30% Annual Return
How a rooftop solar system turned into a business idea - and why I killed it after signing my first enterprise customer.
Friends in Koh Samui pay more than 8,000 baht (~$240) a month for electricity in a private villa, and still deal with frequent power outages.
We were paying around 4,000 baht in the villa we rented, and we never lost power.
There was a solar system on the roof that the owner had installed.
A friend told me you could get more out of it. By default, the battery keeps 50% of its charge in reserve in case the grid goes down. Lower the reserve to 30%, and you get more “free” electricity.
I went home and opened the electrical cabinet. Inside were a few sealed white boxes about a meter tall, plus a smaller box with a display. I took a picture and sent it to AI. It explained that they were batteries and an inverter.
The inverter had a QR code on it. I scanned it, which installed the app for managing the system. The app asked for a username and password, so I called the installer. His phone number was on another sticker inside the same cabinet.
He gave me access, and I started exploring.
I have no background in electrical engineering. At first I didn’t understand any of the numbers.
What is a kWh?
I learned that our system was rated at 5kW. Koh Samui gets about 4.5 effective sunlight hours per day, so the system produces roughly 22.5kWh daily. At about 5 baht per kWh, that’s almost 4,000 baht worth of electricity every month.
Our roof was turning sunlight into money.
I started reading about the industry and discovered that in the US and Europe, many customers don’t actually buy solar systems.
They lease them.
The model is called a Power Purchase Agreement (PPA). A company installs a solar system on the customer’s roof at its own expense, and the customer agrees to buy the electricity it generates for around 20 years, typically at about a 30% discount to the utility.
Solar panel prices have fallen roughly 90% over the last 15 years. Battery prices have dropped just as dramatically, largely thanks to the electric vehicle industry.
I started building a model.
Real estate investors in Koh Samui are happy with annual returns of around 10%.
I stress-tested the spreadsheet from every angle.
It came out at roughly 30% a year.
The investment paid for itself in about three and a half years. After that, almost everything was profit.
I even spent $12 on a Udemy course about building a solar business.
I never finished it.
I was too eager to move beyond theory.
I went back to our installer and told him I was bringing the PPA model to Koh Samui.
He said it was a stupid idea.
Nobody on Koh Samui finances solar over the long term. People pay cash and own the system outright. That’s how he’d been doing business for 15 years, and nothing else would work on the island.
I told him financing was my problem.
I just needed him as the technical arm. I would pay him upfront, and he would install the systems exactly as he always had.
I posted a message in a WhatsApp group for families living in Koh Samui:
“I’ll install a solar system on your roof at my expense, and we’ll split the savings.”
Within a few days, the installer and I were standing on the roof of our first potential customer - a family with two kids - taking measurements for a proposal.
At the same time, I hired a local lawyer to draft a PPA agreement for Thailand.
The clause I cared about most was enforcement.
Then we found out the family was planning to leave Thailand in about a year.
One year.
My investment took three and a half years to pay back.
The homeowner would still be contractually obligated, but a Thai court judgment isn’t worth much against someone living on another continent. Nobody starts international litigation over a 500,000-baht contract.
So I abandoned the residential market.
A business customer, by definition, should be more stable than a family spending a year or two on a tropical adventure.
I spoke with the owner of a successful restaurant I play padel with.
His roof turned out to be too old for solar panels.
I emailed my kids’ international school and scheduled a meeting with the principal.
Twenty minutes in, I realized he had no intention of evaluating the proposal.
He was simply curious how someone who sounded serious could be offering him something for free.
Then a real customer showed up.
Another international school had just expanded into new buildings and was consuming more electricity than the local grid could reliably supply. They were dealing with frequent outages.
The installer inspected the roof.
Perfect for solar.
I asked him for the engineering specifications of the mounting system and hired a structural engineer to verify that the roof could safely support it.
Between the engineer and the lawyer, I had already spent around 40,000 baht.
We signed the agreement.
They would get stable electricity with no outages at roughly 30% below utility prices.
I would get my first project.
Everything was ready.
We were waiting for one final document: formal approval to install a solar system on the school’s roof.
While we were waiting, the authorities carried out a surprise inspection.
It turned out the school was missing some of the licenses required to legally operate.
Even a school wasn’t guaranteed to still be around in three years.
I gave up on the solar leasing business and went back to building SaaS companies.
Using what I had learned, I installed a large solar system at our next house.
It now covers almost our entire electricity bill.
Not long ago we invited a bunch of friends over for Friday night dinner.
Halfway through the meal, the power went out.
It turned out I had forgotten to pay the electricity bill.
The utility had disconnected us two days earlier.
We’d been running on the batteries the whole time without noticing.