Most people search “how to draw a solar system” because they want a clean diagram: solar panel, charge controller, battery, inverter. That drawing is wrong. Not because the arrows are wrong, but because it misses the pieces that keep the system safe. After nine years of building off-grid power for vans, trailers and cabins, I’d rather see a drawing with an ugly busbar and fuses than a pretty line from panel to inverter.
Here is the short version of what I draw for small 12V and 24V Victron Energy systems: the battery busbar comes first, the charge controller comes second, surge protection comes third, and the solar panel is almost last. I’ve spent about $6,300 learning why that order matters. This is the checklist I give new installers.
My credentials aren’t from a classroom. Since 2017 I’ve run a four-person shop that builds off-grid electrical systems. I’ve personally finished 140+ installs, and I keep a photo of every mistake. The photos are ugly, but they keep me honest.
Draw the Loads Before You Draw the Solar Panels
The right answer to “how to draw a solar system” starts with a load list. I don’t mean a rough guess of daily watt-hours. I mean the actual loads that can run at the same time. A fridge might average 60W, but when the compressor starts it can draw two or three times that. If the drawing misses that moment, the inverter will choose a bad afternoon to shut down.
EV charging is the cleanest example. A Level 2 charger is a continuous load, not an occasional load. An Ioniq’s Level 2 charger can sit at high current for hours. When I first drew a backup system for a customer who said “just an EV charger,” I didn’t put the charger on the load list. It was a 240V branch that pulled more current than every other load in the cabin combined. If the drawing doesn’t include that circuit, the wire sizes are fiction.
How to Draw a Solar System That Someone Can Build From
Once the loads are on paper, draw one line for positive and one line for negative. Label every fuse, every busbar, every wire gauge, and the expected current. Then go back and label every terminal torque if you want to keep maintenance calls low. The drawing doesn’t need to be artistic; it needs to be buildable.
For the physical side, I start at the battery. The Victron Energy Lynx Power In battery connector is where I land the battery in most small systems. It’s a compact busbar with a battery fuse position. The battery gets one main connection, and the loads and chargers land on the busbar instead of stacking four ring terminals on one battery bolt.
A drawing with no busbar means the battery terminal is the busbar. That was my first mistake. In 2022, I opened a customer’s battery box and found four ring terminals on one post. It worked, but the washer on the bolt was already heat-stained. That was the moment I added the Lynx battery connector to every drawing. Is the Lynx the only way to do it? No. But it’s the option that made my drawings clearer and my callbacks rarer.
The visual side matters more than I expected. Clients can’t see an MPPT algorithm, but they can see a clean battery end. A tidy Lynx busbar and labeled cables made clients treat the whole system as more credible. That perception is part of the work.
The Victron Energy MPPT 75/15 Is for Small DC Systems
The charge controller I reach for most on small builds is the Victron Energy MPPT 75/15. The “75” is the maximum PV open-circuit voltage, and the “15” is the maximum charge current. It is not a 75A controller. Victron’s datasheet, accessed January 2025, lists the practical array size at roughly 200W for a 12V battery and 400W for a 24V battery.
That makes it right for a campervan, a small trailer, or an off-grid monitoring station. It is wrong for a 48V house bank or a long series string of big panels. The limit isn’t only panel wattage. If the PV open-circuit voltage can get near 75V on a cold morning, choose a controller with more headroom. I’ve replaced enough controllers to know the smoke smell is the same regardless of the brand.
Buy the SmartSolar version if the budget allows. Bluetooth is not a luxury when a customer calls and says “sun is out but my battery is empty.” I can check PV voltage and charge history from my truck before I decide whether to drive over. That saves a ton of time.
Put a Surge Protector on the PV Input
A solar drawing also needs a surge protector. The array is outside, and a nearby lightning strike can push a spike down the PV wire even without a direct hit. That spike can destroy an MPPT input. The right place for the protector is between the solar array and the charge controller, not just on the AC panel.
Here’s the counterintuitive part: a surge protector with a long ground lead can work worse than no protector. The whole idea is to push spike current to ground quickly. A long ground wire adds impedance and slows the spike down. If your drawing shows a surge protector but not a short, direct ground path, you have drawn a decoration.
Use a real PV DC surge protector rated for the array’s open-circuit voltage. It isn’t a replacement for grounding. It is an extra layer that belongs in the drawing.
Where This Drawing Doesn’t Fit
A full Lynx busbar is overkill for a tiny 100W / 12V cooler setup. A properly fused battery connection is enough. The MPPT 75/15 is also the wrong tool for 48V systems or arrays above its 200W/400W envelope. And if the site is in an area with frequent direct lightning strikes, an SPD is not the whole answer; it needs a grounding design, not just a component.
If the building has an Ioniq Level 2 charger, start with the AC load, not with the solar panels. That boundary would have saved me one expensive drawing revision in 2024.
Before you call the drawing finished, trace the positive battery cable from the battery to every load. If it doesn’t hit a fuse or a busbar before it splits, the drawing isn’t ready. The sun will still be there tomorrow.