Solar + Battery Procurement: The 9-Step Checklist I Run Before I Sign a PO

I'm the office administrator for a 55-person company. I handle basically all of the facilities and service ordering — roughly $380,000 a year across 11 vendors — and I report to both operations and finance. Somewhere back in 2023, "get quotes for solar on the roof" landed on my desk because it was a capital expense with a utility bill attached, which apparently made it mine.

I'm not an electrician. What I am is the person who has to explain to finance why the cheapest quote wasn't the one we signed. That's the whole angle here.

Below is the checklist I actually run. Nine steps, in order, and I'll tell you up front which one people skip. I built it for a small commercial building, but it works the same if you're speccing a solar panel for your house — the numbers shrink, the traps don't.

The Nine-Step Checklist

Step 1: Pull 12 months of interval data before anyone quotes you

When I took over purchasing in 2020, I used to forward the utility bill to vendors and let them size things. I did that twice before I learned better. A monthly bill tells you almost nothing about whether storage makes sense, because storage is priced against demand charges and time-of-use windows, not against total kWh.

Ask your utility for interval data — hourly or 15-minute usage, plus the demand register. Then look at three things: your peak demand in kW, when that peak happens, and whether your rate has a meaningful difference between on-peak and off-peak. If the spread is small, a battery is a lot harder to justify and you should say so in the business case.

Checkpoint: you can state your annual kWh, your peak kW, and the time of day that peak occurs. If you can't, don't take a quote yet.

Step 2: Decide whether you actually need backup, before you pick a brand

This is a scope decision, not a product decision, and getting it wrong is expensive either way. A straight grid-tied string inverter is cheaper per kW and simpler to permit. A hybrid inverter adds battery-ready terminals and a backup output, and it costs more for the same nameplate rating.

Most of what Deye sells sits on the hybrid side — inverter, battery input, and backup output in one box. That's genuinely convenient, but it's not free, so be honest about whether you need it. Our building has a small server closet and a card-access system. Those stay on. The HVAC doesn't. That list took twenty minutes to write and it determined the entire battery size.

Checkpoint: a written list of what must run during an outage, in watts, with run-time in hours.

Step 3: Size the array to the roof, not to the sales sheet

Every proposal I've received has opened with a system size in kW. What I want to know first is azimuth, tilt, shade at 9am and 3pm, roof age, and structural capacity. If the roof needs replacing in six years, you're paying for the removal and reinstall of the array in year six, and that number belongs in the comparison now, not later.

Sanity-check the production estimate yourself. A reasonable installer will show you kWh per kW per year for your region and it should land in a defensible band — not the optimistic end of it.

Checkpoint: a production estimate you can trace to a shading study, plus a roof condition note.

Step 4: Confirm the battery is on the inverter's approved pairing list

This is the step people skip. It took me about 18 months and three projects to understand that the battery is the component most likely to quietly not talk to everything else on the wall.

The deye rw-f16 battery is the one that came up when we scoped a larger cabinet build. It's a rack-style unit, which means it lives in a cabinet with a breaker and a bus, and it depends on a closed-loop communications handshake with the inverter for state-of-charge and charge/discharge limits. If that handshake isn't proven for your specific inverter model and firmware version, you get a system that runs in open-loop mode — or doesn't run.

Ask for four things in writing: the exact battery model number, the inverter model number, the firmware versions on both, and the comms protocol. Then ask the distributor — not the installer — to confirm the pairing. If the answer is "yeah, it works," that's not an answer.

Checkpoint: written compatibility confirmation from the manufacturer or an authorized distributor.

Step 5: Price the balance of system line by line, including the solar panel box

The solar panel box — the DC enclosure where your strings land — is where I've seen the most padding and, on two quotes, the most cutting. Inside it you've got the combiner, fuses or breakers, a DC disconnect, surge protection, and often the rapid-shutdown electronics. Outside it you've got racking, conduit, conductors, AC breakers, and the monitoring gateway.

Ask for part numbers on all of it. "Balance of system — $6,400" is not a line item, it's a shrug. When I asked one integrator to itemize, the number went down by $900 because he'd bundled a gateway we already owned.

Checkpoint: every BOS component listed with a manufacturer and part number.

Step 6: Compare the all-in number, not the sticker

Here's what deye battery price comparisons actually look like in practice. Three quotes for the same inverter model and the same RW-F16 battery units came back at roughly $2,180, $2,390, and $2,540 per battery, ex-works. That spread was on identical hardware — $360 a unit, which on a six-unit cabinet is over $2,000 before anyone touches a conduit bender.

I'm not 100% sure those figures hold today; freight and tariffs moved a lot through 2024 and I'd re-quote before budgeting. Treat my numbers as a shape, not a price.

And the sticker is only half of it. The line items that changed our comparison most were the ones that weren't on the first page: inbound freight (which varied by $400 between quotes), commissioning (excluded by one vendor, then billed as an $1,800 change order), engineering and stamped drawings, permit fees, monitoring subscription, extended warranty, and labor coverage on the warranty.

That last one matters more than people think. A 10-year parts warranty with no labor coverage means you pay a crew to come out in year seven and you're still paying it in year ten.

Checkpoint: an apples-to-apples sheet with freight, commissioning, permits, monitoring, and labor warranty as separate rows.

Step 7: Answer the EV charging question before operations asks you

Someone will ask whether you can charge an electric car off the system. It's fair — if you're buying 30 kWh of storage, charging a car is the obvious next thought.

So: can a solar generator charge an electric car? Technically yes. Practically, a portable "solar generator" power station is the wrong tool. An EV uses somewhere around 0.25 to 0.35 kWh per mile at the wall, so 40 miles of range is 10 to 14 kWh. A 2 kWh portable unit gives you a handful of miles after conversion losses, and most of them cap the 120V output low enough that you'd be charging overnight for a commute you could have walked. Fine for an emergency top-up. Not a charging strategy.

The realistic version is a hybrid inverter, a 15 to 20 kWh battery bank, and a 7 to 11 kW level-2 charger, sized against your service capacity. If you're already buying Deye inverters and batteries, their EV chargers can sit on the same monitoring platform, which sounds minor until you're the person juggling three apps and two logins for one building.

Checkpoint: kW math on paper — charger size, battery usable kWh, and panel capacity.

Step 8: Nail permits, interconnection, and grounding before you sign

Grounding is where I got surprised, and I've since learned it's where a lot of small commercial projects get surprised. The relevant references for the US are NEC Article 690 for PV systems, Article 705 for interconnection, and Article 250 for grounding and bonding — specifically the table that sizes the grounding electrode conductor against your service conductors. Inverters need to be listed to UL 1741 SB, storage systems to UL 9540, and grid support functions follow IEEE 1547. Verify the current edition your AHJ enforces rather than assuming.

On our second project, the installer proposed a 6 AWG grounding electrode conductor. The AHJ wanted 4 AWG based on our service size. That's a few hundred dollars at install and a much worse number after the inspection fails and the crew comes back.

Checkpoint: the installer shows you the grounding electrode conductor calculation, and you confirm the model-specific listing with the AHJ rather than accepting a brand-level claim.

Step 9: Lock down commissioning, monitoring, and the paper trail

This is the step that separates a system you can maintain from a system you inherit. Before final payment, get: as-built drawings, a commissioning report, string-level IV curve traces, a torque log for the DC terminations, warranty registration in your company's name, and the monitoring account created under your credentials.

That last one is not a detail. If the installer owns the monitoring account, you lose the historical data the day they lose interest in you — and you'll find out during a warranty claim, which is the worst possible time.

Checkpoint: you can log into the monitoring portal yourself and export a month of data.

What I'd Watch Out For

A few things that have bitten me or come close:

• "Battery included" with no model number. That phrase in a proposal is worth nothing. Make them name the model, the quantity, and the usable kWh.
• Letting the vendor own the permit. It feels efficient. Then the permit sits for six weeks and nobody tells you. Ask for the permit number and the portal login.
• Comparing dollars per watt on DC nameplate. Two systems with the same nameplate can differ by 20% in annual production. Compare on estimated kWh and on what's backed up during an outage.
• Not budgeting the replacement cycle. A battery bank is a 10-to-15-year asset and the replacement cost belongs in the TCO from day one, not in year eleven.
• Signing under a deadline. I did that once — had 48 hours before a quoted price expired. Normally I'd get a fourth quote, but there was no time, so I went with the incumbent. In hindsight I should have let the price expire. It didn't expire. It came back $300 higher, and I'd already committed to a scope I hadn't fully reviewed.

Even after we signed the third project I kept second-guessing the battery sizing — what if 20 kWh wasn't enough for the server closet plus the access system through a long outage? I didn't relax until we ran an actual outage test four months later and it held with margin.

If you take one thing out of nine steps: the battery price on the quote is the least interesting number in the document. The interesting numbers are the ones on the second page, and the ones nobody wrote down at all.

Pricing references above come from our own 2024–2025 quotes and public distributor listings. They're for general reference only — actual prices vary by vendor, specification, and time of order, so verify current rates. Regulatory references are for general guidance; confirm current requirements with your local authority having jurisdiction.