Size the system. Then price it.
Start from the customer's annual kWh, the site's peak sun hours and your loss assumption. The calculator sizes the array, rounds up to whole panels, and prices it at your installed $/W. Every input is yours, so the number matches how your shop actually bids.
- kWh → kW DC
- Whole panels
- Installed $/W
- Simple payback
Energy use
Site & system
Pricing
Save your results
Copy these results, then add your approved sample files in the trial brief.
Planning estimate only. Model production for the address with NREL PVWatts, and confirm incentives, interconnection and structural requirements before quoting.
The four numbers behind a solar quote.
Annual kWh
From 12 months of utility bills. Use the monthly average if that is all you have.
Peak sun hours
Daily average for the site. NREL's PVWatts tool models it from the address, tilt and azimuth.
System losses
Wiring, inverter, soiling, shading, mismatch. PVWatts uses 14% as its default.
Installed $/W
Your all-in installed cost per DC watt, from your own past jobs.
What the quick number leaves out.
Use it to qualify the lead. The proposal needs the details.
Roof layout
Setbacks, obstructions and orientation decide how many modules really fit.
Electrical service
Main panel capacity and interconnection rules can add a service upgrade.
Structure
Older roofs may need an engineering review for added dead load.
Incentives
Programs change. Confirm eligibility and amounts at the time of the proposal.
Calculators check one number. Bids need every quantity.
For commercial electrical bids, RenderDraw proposes fixture, device and panel quantities from the drawings with the source sheet on each row, and your estimator approves them before pricing.
- Source on every row. Each proposed quantity keeps the sheet and location it came from.
- Estimator approval before pricing. Your estimator accepts, corrects or rejects proposals; nothing is priced until it is approved.
- Addenda through the same review. Changed sheets go back through takeoff and estimator review.
- Your assemblies, your rates. Approved rows hand off to your assemblies, labor units and pricing inputs.
Solar estimate calculator, answered.
How do I estimate the size of a solar system?
Divide the annual kWh you want to offset by (peak sun hours × 365 × (1 − system losses)). For 10,800 kWh a year at 4.5 sun hours and 14% losses, that is about 7.6 kW DC.
How many solar panels do I need?
Divide the system size in watts by the module rating and round up. A 7.6 kW system with 400 W modules needs 20 panels.
What system loss should I use?
NREL's PVWatts calculator uses 14% as its default total system loss. Adjust it for known shading, soiling or long wire runs.
Where do I get peak sun hours?
Run the address through NREL PVWatts. It models solar resource from location, tilt and azimuth, which is more reliable than a regional average.
How do I estimate solar installation cost?
Multiply the system size in watts by your installed cost per watt, then subtract incentives the customer qualifies for. Use your own recent jobs for $/W. The default here is only an example.
Send one plan set. Judge the result yourself.
A focused, no-obligation evaluation on your own drawings. Your sample files remain private while we assess the request.
- Upload one representative plan set (a legible PDF set is the most reliable starting point), plus an addendum if you have one.
- RenderDraw reviews the set and the scope you want tested.
- We follow up with what was extracted, what was flagged for review, and the most useful next step.