I'm the office administrator who handles purchasing for a company with three locations. Every year I process roughly 200 purchase orders and manage about $150,000 across vendors. In early 2025, leadership approved a combined project for our facilities: EV chargers for the company fleet, rooftop solar, and battery backup units. I had to evaluate vendor proposals without being an engineer. This checklist is the result of that review. If you're a buyer walking into a similar upgrade, it'll save you the headaches I hit.

1. Define the Business Problem Before You Look at Specs

Vendors love to lead with battery capacity and panel efficiency. I made myself stop looking at that and wrote down the actual business problem. For us, it was: "Our delivery vans sit in traffic all day, and we keep paying for diesel. Also, our office loses internet during 2-hour power cuts, and staff can't work." Those two sentences did more for our purchasing decision than any data sheet.

Don't cheap out on the work output here. If the system fails during a client visit or a staff training day, people notice. I've seen that dynamic play out with bad office equipment; the same goes for energy infrastructure. The quality of what you install becomes the quality of what people think of your company.

2. Check the Real Battery Capacity, Not the Brochure

The BYD Sealion 7 was one of the vans we considered. If you search for BYD Sealion 7 battery capacity, you get multiple answers, which is confusing at first. The reason is that the same model can come with different battery configurations, depending on the trim level and market. When I asked the vendor, the usable capacity ranged from roughly 72 kWh to just over 80 kWh depending on the version. That range changes your charging time and range planning.

So my advice: ask for the specific trim you plan to buy, then ask for three numbers—total battery capacity, usable capacity, and maximum DC fast-charge rate. If the salesperson can't give you usable capacity, that's a red flag.

3. Verify Warranty Terms—and Define Everything

Battery warranties sound great until you read the fine print. A good example is the BYD 250000 km battery warranty that gets quoted for some models. That's a strong number on paper. But what does "battery warranty" actually cover?

Most EV battery warranties only replace the battery if capacity drops below a certain threshold—often 70% of the original. So a battery that's lost 25% of its capacity may still be considered "healthy." Ask the vendor to define a defect in writing. Ask whether the battery casing, cooling system, and internal wiring are included. I also ask whether the warranty is transferrable if we replace the vehicle before the battery dies.

I still kick myself for a supplier deal years ago where I accepted a verbal promise of "we handle it"—it cost our department $2,400 in rejected expenses. Now I get every warranty condition in writing before signing. If a vendor won't put warranty definitions in the contract, I move on.

4. Simulate Your Longest Power Outage

When someone pitches a battery backup, they usually describe the best case: the battery charges automatically, and you're covered for eight hours. But what if an ice storm takes down the grid for 40 hours, or longer?

That's when I started researching whether you can charge Tesla Powerwall with generator power. The answer, in most installations, is yes—but only if your installer configures the system for generator input. It isn't always automatic. Some inverters need a specific generator input setup, and if the wrong generator is used, it can overload the system or fail to charge the battery. If you need generator backup, put it in the work order. Don't assume a battery alone will handle a multi-day outage.

5. Ask What the Solar Panel Is Made Of, Not Just How Many Watts

I asked our solar vendor a weird question during the review: how much silver is in a solar panel? The answer is that a typical silicon panel contains roughly 11 to 20 grams of silver, mostly in the conductive paste on the front and back. I'm not a materials scientist, but I asked this for a reason. Silver matters for recycling, supply chain cost, and long-term repairability. A vendor who could answer that question without guessing showed me they understood the product beyond the marketing datasheet.

I don't think you need to quiz every supplier on chemistry. But the willingness to explain material quality—panel frame quality, junction box build, connector brand—tells you whether you're buying a premium product or a discounted one. The output quality affects your brand perception.

6. Verify the Paperwork and Invoicing Before Installation

This sounds boring, but it's where buyers get burned. I once accepted a low price from a vendor who couldn't provide a proper invoice. The hand-written receipt didn't match our accounting requirements, finance rejected the expense, and I ate the cost from my department budget. Never again.

For an energy project, ask these questions before the crew arrives:

  • Who provides the certificate of warranty registration?
  • Who files the permit paperwork with the local authority?
  • What insurance certificates does the installer provide?
  • Are as-built drawings included in the final package?
  • What documentation does your finance team need from them?

7. Calculate Total Cost of Ownership Over 60 Months

The lowest quote isn't the cheapest project. The real cost of an energy system includes installation labor, electrical panel upgrades, permits, maintenance, monitoring subscriptions, repair downtime, and the cost of money.

One vendor in our bidding process skipped the main electrical panel upgrade in their quote. Another included it, plus a slightly higher equipment price. The first quote looked cheaper, but the second one was the actual total. Ask every bidder to break down line items. Then calculate the cost per year over five years, and compare that number—not the first-page total.

A Few Final Checks I Wish I'd Made Earlier

After the project, a few items stood out that weren't in any of the sales brochures:

  • Expansion capacity. Can the inverter handle more panels later? Can the battery cabinet be expanded?
  • Monitoring access. Who logs into the monitoring dashboard? Does the facilities team get alerts?
  • Weather assumptions. Cold climates change battery charging speed and solar output. Check the local temperature data.
  • Physical quality on day one. Look at the cable routing and panel mounting. A neat installation says more than a slick proposal.

One last thing. In school, I remember a science chart that showed eight planets, and anywhere else didn't matter. Today we know there are more than 5,000 confirmed planets not in our solar system. Hidden variables are everywhere. The same rule applies to energy procurement: if you only review what's in front of you, you'll miss what's orbiting around it. My advice is to treat the vendor's proposal like a starting point, not the whole universe.