We Tried the DIY Inverter Route Before Choosing Sunnova Solar Plus Storage — Here's What It Cost Us

Back in 2023, I was the guy who thought he could beat the system. Our shop was paying $1,100 a month in electricity. The solar quotes were coming in at $40,000–$60,000. So I did what any budget-conscious manager would do: I bought a TopBull 3000W power inverter, hooked it up to a bank of car batteries, and told my boss we'd have “free backup power” by the end of the month.

It didn't end well. Let me walk you through the comparison that finally made sense. It's not just about the price tag. It's about what the system does when you actually need it.

The Two Options We Compared

I'm a facilities manager, and I've been handling vendor orders for about 11 years now. In that time, I've made plenty of mistakes. The biggest one was thinking a backup power setup could be cobbled together from spare parts. Here's what we compared:

• Option A: Sunnova solar plus storage system (quoted through Trinity Solar)
• Option B: DIY emergency power station using a TopBull 3000W power inverter and car batteries

Both were meant to keep our office running during outages and cut peak demand. They are not in the same league. But at first glance, Option B looked a lot cheaper.

Dimension 1: Upfront Cost — The Trap

The TopBull 3000W power inverter was $289 on sale. Four “deep cycle” batteries from an auto parts store were $178 each. Add cables, fuses, and a plastic battery box, and I was all-in for about $1,100. Compared to the Sunnova lease quote, which required $0 down but a 25-year monthly payment, the DIY route seemed like a no-brainer.

But here's what I didn't calculate: the inverter's surge capacity. A 3000W inverter is rated for continuous power, but car batteries don't like to discharge below 50% without damage. I never understood the difference between a starter battery and a deep-cycle battery. Actually, even the “deep cycle” batteries I bought weren't true deep-cycle — they were marine dual-purpose. That distinction cost us.

Dimension 2: Reliability — Where the DIY Dream Died

For the first two weeks, the setup worked. We ran a few lights, a laptop charger, and a modem. Then we had a real outage. The inverter alarm started screaming when the battery voltage dropped under 11 volts — about 45 minutes in. We didn't have a proper low-voltage disconnect, so the batteries got drained hard. Two of them never recovered the same capacity.

I learned the hard way about how to connect a power inverter to a car battery. It's not just red clamp, black clamp. You need to think about wire gauge, length, terminal corrosion, and whether your battery can handle the ripple current from a modified sine wave inverter. I skipped all of that. The result: a blown fuse, a warm battery, and a five-hour outage where we sat in the dark anyway.

Meanwhile, the Sunnova solar plus storage system? I'll be honest — I didn't get to test it during this incident because we hadn't installed it yet. But we did check the equipment spec. The LFP battery (that's lithium iron phosphate) is designed for daily cycling. Car batteries are not. That's the core difference.

“A car battery can start an engine. It doesn't want to run your office for 12 hours.” — something I wish I'd read before my $1,100 experiment.

Dimension 3: Total Cost of Ownership and the NYSERDA Factor

Here's where the comparison gets interesting. The DIY setup cost $1,100 upfront. But after the first failure, I bought two more batteries ($356), a new charger ($140), and a bigger transfer switch ($90). I also spent hours on YouTube — that has a cost, even if you don't pay for it directly.

In 2024, we revisited the business case. I started reading NYSERDA energy storage news — the New York State Energy Research and Development Authority has been pushing storage adoption. There were incentives available for professionally installed systems, but not for DIY car-battery rigs. That alone changed the math. The Sunnova system qualified for the federal investment tax credit, and depending on your utility, there may be demand response programs that pay you for having your storage available.

We also got a Trinity Solar Sunnova quote. The equipment list was identical — same LFP battery, same panels, same inverter under the hood. It came in about $1,200 lower upfront than going direct with Sunnova. But the contract assumed we'd handle the permit paperwork, and service was split between two support lines. We ended up paying a little more for a single point of accountability. To me, that extra $1,200 bought a lot of peace of mind.

And the FTC has something to say about this too. The FTC Green Guides say environmental and cost-saving claims need to be substantiated. So when a vendor says “solar will cut your bills by 80%,” ask for the data. With the Sunnova lease, we didn't get a fake guarantee. We got a performance monitoring app, a production warranty, and a predictable monthly payment. That's more valuable than a vague promise.

By the time we factored in the labor, the second battery bank, and the two-day outage, the DIY route cost us closer to $6,000. The Sunnova route costs us a monthly payment that's roughly the same as our old coffee bill, but it includes service, software, and a battery that cycles safely.

The Unexpected Conclusion: The “Cheaper” Option Was Never Cheaper

I know this sounds obvious in hindsight. But I almost made the same mistake again when the TopBull 3000W power inverter caught my eye for this year's backup plan. I had to remind myself: an inverter is a component, not a system. A car battery is a starting device, not an energy asset.

We didn't have a formal procurement checklist back then. That's exactly why we ended up with marine batteries in an off-grid setup. After the third mistake, I finally created a one-page pre-purchase checklist for any major electrical equipment. It's saved us more than once already.

So here's my bottom line:

• If you need backup power for non-critical loads and understand battery limits, a small inverter setup can be okay for occasional use. But don't call it a business solution.
• If you want solar plus storage that actually reduces demand, and you can take advantage of NYSERDA-related incentives, a professionally serviced system like Sunnova solar plus storage is worth the monthly commitment.
• And if you're comparing quotes, get one from Trinity Solar and one from Sunnova direct. The equipment may be the same, but the contract terms are what you're really buying.

This was accurate as of Q1 2025. Solar incentives change fast, so verify current NYSERDA programs and your utility's interconnection rules before budgeting. I learned that the hard way too.