Solar Design Calculators

Solar Design Calculators

Accurate solar design starts with accurate math. SurgePV’s solar design calculators give installers, engineers, and sales teams free access to 13 specialized tools — string sizing, wire sizing, voltage drop, inverter loading, battery sizing, and more. Every calculator runs in the browser, requires no signup, and returns code-aware results you can use in quotes, permit packages, and engineering reviews.

These are the same calculation engines that power SurgePV’s full design platform. Use them free here, then graduate to the integrated workflow when you are ready to go from a single number to a complete 3D design and proposal.

Electrical Calculators

Electrical calculators handle the NEC-driven side of a design — conductor sizing, voltage drop, string voltage windows, and load calculations. Run these before you submit a permit package or finalize a bill of materials.

Calculator	What it computes	Best for
String Sizing Calculator	Max and min modules per string based on Voc, Vmp, and temperature extremes	Matching module strings to inverter MPPT windows
Wire Size Calculator	Conductor gauge from current, run length, and ampacity rules	Selecting DC and AC conductors that pass inspection
Voltage Drop Calculator	Percent voltage drop over a circuit run	Keeping DC and AC runs under the 2% rule of thumb
Inverter Load Calculator	Inverter capacity from connected loads	Sizing inverters for backup and off-grid systems
Busbar Size Calculator	Busbar ampacity and the 120% rule check	Verifying panel interconnection compliance

Sizing Calculators

Sizing calculators answer the question every customer asks first: how big should the system be? These tools convert loads, bills, and site data into concrete system, inverter, and battery capacities.

Calculator	What it computes	Best for
System Size Calculator	Array kW from annual kWh usage and local sun hours	First-pass residential and commercial sizing
Battery Size Calculator	Battery kWh from critical loads and backup duration	Storage add-ons and backup system quotes
Inverter Load Calculator	Continuous and surge inverter capacity	Hybrid and off-grid inverter selection
AC Size Calculator	Cooling load in tons and BTU for a space	Estimating HVAC loads that drive system size
UPS Calculator	UPS capacity and runtime from connected equipment	Critical-load backup planning

Production and Financial Calculators

Production and financial calculators turn a design into a business case. Use them to estimate generation, dollar savings, and equipment wattage before you build a full proposal.

Calculator	What it computes	Best for
Solar Power Calculator	Expected kWh production from system size and location	Verifying production estimates for proposals
Solar Savings Calculator	Bill savings and payback from production and utility rates	Early-stage customer conversations
Wattage Calculator	Total wattage of appliances and devices	Building the load list behind any sizing decision

System Design Calculators

System design calculators cover the geometry and site physics of a project — sun position, shading inputs, and the angles that determine real production.

Calculator	What it computes	Best for
Sun Angle Calculator	Solar elevation and azimuth by date, time, and location	Tilt, row spacing, and shading analysis
String Sizing Calculator	Temperature-corrected string lengths	Final electrical layout before stamping

For full shading, layout, and 3D modeling beyond these quick calculations, use SurgePV’s shading analysis tool and panel layout estimator.

How to Use These Calculators in Your Workflow

The calculators work in sequence, mirroring a real design process. Follow this order on your next project and each tool’s output feeds the next step.

1. Start with the load. Use the wattage calculator to total the customer’s appliances, then the electricity bill data or system size calculator to set a target kW. For storage projects, run the battery size calculator on the critical-load list.
2. Size the equipment. Run the string sizing calculator to match modules to the inverter MPPT window. Use the inverter load calculator to confirm capacity for hybrid or backup systems.
3. Check the wiring. Enter each conductor run in the voltage drop calculator, then verify gauge and ampacity in the wire size calculator. Check panel interconnections with the busbar size calculator.
4. Validate the site. Use the sun angle calculator to confirm tilt and row spacing assumptions before you commit a layout.
5. Build the business case. Run the solar power calculator for production and the solar savings calculator for payback. Both outputs feed directly into your proposal numbers.

Free calculators are ideal for quick checks and early-stage quotes. When a project moves to contract, manual math becomes the bottleneck — SurgePV carries every one of these calculations through 3D design, shading simulation, and proposal generation automatically, so a number you compute once stays consistent from first quote to final permit set.

Frequently Asked Questions

Are these solar design calculators really free? Yes. All 13 calculators on this page are free, run in the browser, and require no signup or account. SurgePV offers 36 free tools in total across design, electrical, and financial categories.

Which calculator should I start with for a new project? Start with the system size calculator to set a target array size from the customer’s usage. Then run string sizing and voltage drop to validate the electrical design, and finish with the solar savings calculator for the financial case.

Do these calculators follow NEC requirements? The electrical tools apply NEC-driven rules, including conductor ampacity, voltage drop guidance, and the 120% busbar rule. They support design decisions, but a licensed engineer should verify final stamped drawings.

How accurate are the production estimates? The solar power calculator uses location-based sun hour data to estimate production. For bank-grade accuracy with shading, soiling, and system losses, use SurgePV’s full simulation engine, which models 3D shading scene by scene.

Can I use these calculators for commercial projects? Yes. String sizing, voltage drop, wire sizing, and busbar checks apply at commercial scale the same way they do residentially. Large projects benefit from the integrated platform, where calculations stay consistent across hundreds of strings.

What is the difference between the battery size calculator and the inverter load calculator? The battery size calculator determines storage capacity in kWh from your critical loads and desired backup hours. The inverter load calculator determines the power capacity in kW needed to run those loads at once, including surge.

Do the calculators save my results? No. Free tools compute results in the browser without storing data. For saved projects, version history, and shareable reports, run the same calculations inside a SurgePV account.