Panels
Your napkin math from Know Your Numbers gave you a wattage target. Now let’s turn that into actual panels — and start thinking about how they’ll interact with your inverter.
One thing upfront: panels and inverters are linked. You can’t fully spec one without the other. We’ll cover that loop at the end of this page. The iteration is normal, and it costs nothing.
Wattage Options
The residential panel market has settled around 400 watts as the sweet spot. You’ll find panels ranging from 300W to 550W+, but 400W hits the right balance of output, physical size, price, and availability. Most DIY builds use them, and most inverters are designed to work with them.
Lower wattage panels (100-200W) mean more of everything — more mounting hardware, more connections, more wiring, more potential failure points. Fine for portable setups and testing, not great for a permanent installation.
Higher wattage panels (500W+) are physically larger and heavier. Carrying a 500W panel up a ladder with two people is doable but awkward. With one person, it’s a real workout.
Physical Size and Fit
A 400W panel is roughly 6.8’ x 3.4’ — about 22 square feet. They weigh 45-55 lbs each. Two people can carry one up a ladder; one person will manage but will feel it.
Before you commit to a panel count, sketch out your mounting surface with real measurements. Account for:
- Gaps between panels for mounting hardware (typically 1-2 inches)
- Clearance from roof edges — no overhanging
- Airflow underneath — panels run hot, and heat reduces output; a few inches of clearance helps
- Obstructions: vents, chimneys, plumbing stacks, skylights
A sketch with actual tape-measure numbers beats any online calculator. Don’t assume — measure.
How Many Is Enough?
From Know Your Numbers, the formula is:
Daily kWh ÷ PSH ÷ 0.70 ÷ panel watts = panel count
That’s your minimum. Buy more if you have the space and budget. Panels are the cheapest part of the system per watt of capacity. Extra panels mean faster battery charging, more cushion on cloudy days, and headroom if you add batteries later.
Shipping panels is expensive. Adding two extra to your initial order costs a fraction of what you’d pay to order two panels separately later.
Mounting
Three main approaches, and the right one depends on your property.
Roof mount is the most common. Panels attach to rails, which attach to your roof through mounting brackets. The brackets anchor into the rafters and penetrate the roofing material. Done right — with proper flashing kits and sealant — they don’t leak. If the idea of putting holes in your roof makes you nervous, that’s a completely reasonable reaction. Take your time, watch several installation videos, and use quality flashing hardware. Most roof leaks from solar installs come from skipped steps, not from the approach itself.
Ground mount uses a rack at ground level or slightly elevated. Easier to install, easier to access for maintenance, easier to adjust the angle. Trade-off: longer wire runs from the panels to your equipment, and it uses yard space.
Shed or pergola mount is a solid middle ground. You’re not cutting into your house roof, the structure is lower and more accessible, and it can serve double duty as a covered area.
Tilt Angle
Optimal tilt for most of the continental U.S. is roughly 30-45 degrees from horizontal. Steeper angles favor winter production (sun is lower in the sky). Shallower angles favor summer. Most residential roofs already fall somewhere in this range.
Shade
Shade is the biggest hidden performance killer in a solar system.
On a string of panels wired in series — which is how most systems work — the weakest panel limits the whole string. One panel at half output doesn’t just underperform on its own; it drags down every panel in that string. The whole chain is only as strong as its weakest link.
A tree branch that shades one panel for two hours in the afternoon can meaningfully reduce your entire string’s daily output. A chimney shadow that crosses your array in winter can nearly eliminate production during those hours.
Your options:
- Avoid it. Place panels where they get clean sun for the longest part of the day.
- Separate MPPT strings. If you have shade you can’t avoid, put those panels on a separate MPPT input. A shaded string won’t drag down an unshaded one.
- Remove the source. Trimming a branch is cheaper than buying extra panels to compensate.
- Oversize. If you know you’ll lose 20% to shade, build in 20% extra panel capacity.
See String Design for how to configure separate MPPT strings.
The Panel-Inverter Dance
You can’t fully spec your panels without knowing your inverter — and you can’t fully spec your inverter without knowing your panels. This sounds circular, but it’s just how the process works.
Two main paths:
Consumer path (Bluetti, Anker, EcoFlow and similar): All-in-one units designed to be approachable. Lower voltage MPPT windows — typically 12-150VDC — with matched battery ecosystems and good apps. Trade-offs: lower input capacity limits your array size, and shorter MPPT windows mean fewer panels per string.
Prosumer path (SRNE-platform and similar): Higher input capacity, wider MPPT voltage windows (120-500VDC), more configuration options, steeper learning curve. Better headroom for larger systems.
Neither is automatically better. It depends on your goals, budget, and how much system you want to manage.
The iterative loop:
- Estimate your panel capacity from your available space
- Find inverters that can handle that input
- Check whether your string voltage works within the inverter’s MPPT window
- Adjust panel count, string configuration, or inverter — and repeat
Go through this on paper before you buy anything. Inverters covers the specs. String Design covers the voltage math. The 200W starter build shows a complete worked example on the consumer path.
DATA SOURCED FROM: Panel dimensions and weight from manufacturer datasheets (standard 400W mono PERC). Production derating factor (0.70) based on NREL PVWatts system losses methodology. Consumer/prosumer inverter voltage ranges based on published product specifications.