Emergency Off-Grid Solar System Checklist: SRNE Charge Controllers, Inverters, EV Loads and Costs

Look, I get it. You have a client who needs an off-grid system spec by Friday, or a project that lost three weeks to permitting and now has a hard delivery date. In my role coordinating solar equipment for commercial installers, I've handled 200+ rush orders in the last six years. This is the checklist I use when speed matters but wasting money is not an option. It has seven steps, and it won't give you a beautiful theoretical design. It'll give you a buildable one.

Step 1: Name the loads that actually matter

Do not spec a system for every outlet in the building. You'll end up with a 12 kW inverter, a 30 kWh battery bank, and a quote that kills the project. Separate loads into three lists:

• Must-run: lights, router, water pump, refrigeration, basic tools
• Maybe-run: workshop equipment, coffee maker, space heater
• Never at the same time: welder, large motor, EV charger

Here is an example of solar system sizing for a small rural workshop:

• 15 LED lights: 150 W
• 0.5 hp water pump: 375 W running, 1,100 W surge
• Laptop and router: 150 W
• 7 cu ft refrigerator: 500 W running, 1,500 W surge

Total steady load: about 1,175 W. That number is what drives battery size. Surge drives inverter size. Do not mix those calculations.

Step 2: Pick the voltage before you pick the battery

For anything above 1.5 kW of continuous load, 12 V is a bad idea. Current at 12 V is four times current at 48 V for the same power, so cables get hot, losses add up, and component costs go sideways. A 48 V bank keeps wire sizes manageable and is the right call for most off-grid systems over 2 kW.

This matters for the SRNE solar charge controller and the SRNE off grid inverter too. Both have input ranges that depend on the system voltage. If you choose 12 V first and later need 48 V, you're buying the whole electrical board again. Choose voltage first.

Step 3: Size the battery bank for overnight, not sunny afternoon

The battery bank should cover the energy use between sunset and sunrise, plus a safety margin. For the workshop example above, assume 1,175 W runs for an average of 8 hours overnight. That's roughly 9.4 kWh delivered. With a LiFePO4 battery at 48 V, that means about 200 Ah of usable capacity, and since you don't want to cycle to 100%, add another 20%: 240 Ah nominal.

Here's where total cost thinking enters. A cheap lead-acid battery might save $1,500 today, but if it needs replacement every 3 years, the cost per kWh over 10 years is higher than a LiFePO4 bank. Honestly, I'm not sure why some installers still choose lead-acid for critical systems. My best guess is upfront price bias. But I've seen the replacement invoices, and the math doesn't lie.

Step 4: Size the SRNE solar charge controller for cold weather and wire losses

The SRNE solar charge controller is the piece people underbuy. MPPT controllers are better than PWM for off-grid because they convert higher array voltage into usable charging current. A 60 A MPPT controller at 48 V can handle around 2,880 W of PV. That's fine for the workshop example, but only if the PV array voltage is within the controller's max input range.

Check three numbers on the spec sheet: max PV voltage, max PV current, and rated battery current. In cold temperatures, solar panel voltage rises. If the manual says max PV voltage is 150 V, design the string so it stays under 150 V on a cold morning, not just on paper at 25°C. I don't have hard data on how many failures are caused by cold-weather overvoltage, but based on our service records, I'd guess it's a lot more than most people think.

Also, use an MPPT controller with enough current for future expansion. Buying a 40 A controller now because it's $60 cheaper than a 60 A unit is exactly the kind of savings that costs extra later when the client adds two more panels.

Step 5: Choose an SRNE off grid inverter by surge, not continuous watts

An SRNE off grid inverter rated 5 kW continuous may handle 10 kW surge for a few seconds. That surge is what starts motors. A refrigerator, water pump, and compressor can all start close together in a small system. If the inverter cannot supply the combined surge, the lights flicker, the alarm goes off, and the client calls you angry.

For the workshop example, a 5 kW continuous inverter with 10 kW surge is comfortable. If you add an induction motor or a larger pump, go to 8 kW. Also, if the system will ever connect to a generator or utility backup, choose a hybrid SRNE inverter with a transfer switch. In North America, make sure it's UL 1741 listed if there is any chance of grid connection. The question is not 'What size inverter is cheaper?' It's 'What happens when all three loads start at once?'

Step 6: Add future loads. Yes, I mean EV chargers.

The step I see skipped most often in rush orders is this one. Every solar system I've quoted for a B2B customer has eventually faced an EV question. If you look at ChargePoint Level 2 charger specs, the headline numbers are 240 V, 16–50 A, and up to 12 kW maximum output. That is more power than the entire workshop load in our example.

If the client says 'we might add an EV charger later,' you have two options:

• Design for it now: larger PV array, much larger battery bank, larger inverter, and a transfer switch to avoid backfeeding problems.
• Design a charger circuit now but size the solar system for everything except the EV charger, then make the EV charger grid-only or generator-only.

The second option is more realistic for off-grid. But don't pretend the question doesn't exist. The worst thing you can do is install a 5 kW system and let the client plug in a 12 kW EV charger. The inverter will shut down, and you'll get the midnight call.

Step 7: Know what the alternatives actually cost

Every third client asks the same thing: 'What is the price of a wind turbine?' The honest answer for a small rural system is roughly $3,000 to $8,000 per installed kilowatt, based on U.S. DOE and NREL public cost data. A 5 kW wind turbine can easily land at $20,000 to $40,000 installed, before batteries. It only makes sense if the site has a genuinely good wind resource, no nearby turbulence, and enough room for a tall tower.

Compare that with a 5 kW solar array. You can build the entire solar side, excluding batteries, for a fraction of that wind turbine price in most locations. And solar is easier to forecast, easier to maintain, and easier to expand. Wind can be a useful secondary source, but as a primary 'add a turbine' decision, it usually fails the TCO test.

This is total cost thinking: not what something costs today, but what it costs over 10 years including replacements, fuel in a generator's case, maintenance, and the cost of downtime. A $30,000 wind turbine that saves $100/month in generator fuel is not a good deal. A $15,000 solar system that runs a remote workshop for 15 years is.

Before you place the order: three warnings

First, do not assume every battery works with every inverter. The SRNE manual has a battery type table. Check it. In March 2024, I was rushing a replacement charge controller to a client who had a 48 V battery bank. The supplier had the same model listed at a good price, and I almost clicked buy. At the last second, I noticed the product page said '12V only.' That would have been a wasted $320 plus $85 in rush freight. Dodged a bullet.

Second, don't skip the disconnects and overcurrent protection. In the US, NEC 690 requires disconnects and overcurrent protection on both DC and AC sides. In a rush, it's tempting to strip the BOM down to the charge controller, inverter, and battery. But a missing DC breaker can void the UL listing, fail inspection, and turn a 48-hour delivery into a three-week repair. Put it on the order the first time.

Third, get every spec in writing. Surface prices on a charge controller can look great, but if the unit doesn't match the manual's PV input limit, you'll pay for return shipping and a second rush order. When I'm triaging a rush order, I ask the supplier to send a screenshot of the model number spec. It takes two minutes and prevents a lot of pain.

That's the checklist. Seven decisions, done in order, with the total cost in mind. If you do that, your off-grid system will be right even when the timeline is tight. The clients who call back in a panic are the ones who skipped the voltage step or bought a 12 V controller for a 48 V system. You won't be one of them.