Calculators, Apps
& Measuring Tools

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Basic System Size-Up and Cost

PV Watts

Using the new Beta version of this app is sel-explanatory. Click the arrow on the right side of pages to progress through the steps. When plotting four points on the roof for your array, be sure to click each one in clockwise order.

Enter your zipcode, then you'll be asked to select your utility company from a list and input your average monthly electricity bill in dollars. (To get this amount, add the total you paid for electricity (not gas) on your last 12 utility bills, then divide by 12.) The calculator generates a report that includes average radiation for your city (e.g. 5.55 5.55 kWh/m^2 per day), and more importantly, the proposed size of a solar array (e.g. 3.2 k). Scroll down the page to fin info regarding the required roof area needed to install this array (e.g. 320 sq.ft.), estimated cost of the installation and the reimbursement you can expect from tax credits and rebates.

In My Backyard (IMBY)

NOTE: IMBY will be discontinued sometime in 2014.

First click on "Go". On the next screen, enter your address, which produces a Google Earth image of your house. You'll see an info box which explains the next step. Again, select "Go", then drag an array size icon onto your roof. (For residential solar, it should be the "4kw" icon.) Click on "Run" to generate a report.

Clean Power Estimator
California Solar Initiative

Site Assessment Form
Clean Power Finance

Solar Home Present Value Estimator

If you find all these calculators and reports unhelpful or hard to decipher, consider getting a home solar report from Click here for details.

Load Analysis and Sizing of System Components

Array Sizing, Load Analysis, and Module/Inverter Sizing

Solar Sizing - Excel Spreadsheet
When you click on it, the spreadsheet may download onto your desktop rather than appear onscreen.

Inverter/Array Sizing Tools and calculators
You'll find lots of links on this page for different products and manufacturers. Provided by Soligent.

Design Guide

Battery Bank Sizing

Battery Sizing Calculator

System Loads Worksheet
Battery Sizing Worksheet
Array Sizing Worksheet


The Navaile Electrical Calculator is a free mobile app (Android only for now) based on NEC 2008, 2011, and can identify the right utility company jurisdiction using your GPS coordinates. With it, you can calculate:

- Wire Size & Ampacity
- Grounding Tables
- Motor FLC Tables
- Voltage Drop
- Box Fill
- Ohm's/Ohms Law
- Conduit Fill

Wire Ampacity Chart and Temperature Correction Factors (NEC 2011)

Wire Size Calculator

DC Cable Sizing Calculator
Energy Development Cooperative

Wire Size/Amp Ratings Chart

Wire Parameter Calculator

Voltage Drop Calculator

Voltage Drop Calculator

Low/High Temperature Data for U.S. Cities

Wire / Conduit Chart
(scroll down)

Raceway/Conduit Fill Calculator

Electrician Calculator Pro
Low-cost mobile software app

Conduit Fill Calculator
SIMpull® Cable Pull Calculator

Electrician's and Power Calculators

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Send any feedback or suggestions to
info [at] thesolarplanner dot com.

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New at The City Edition:

Also be sure to checkout:

The Mega-Disaster Planner

Budget Guide to Europe (slide show)

Welders Universe


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Tax Credits & Incentives

Steps to
Going Solar

Guides & Videos


Tools & Apps


Site Map

The Unirac toolbelt app allows you to take solar measurements with your mobile phone. It includes a compass, clinometer (to measure slopes), and a theodolite (to measure altitude angles). Download it for free here.

Array Placement, Orientation , Peak Sun Hours, Wind Speed & Temperature Data

Roof Azimuth Tool

Allows you to find the compass orientation of a rooftop using satellite images. Requires free sign up. At Solmetric.Com.

Create a Sunpath Chart

Enter either your zip code or longitude and latitude. In Step 4, you can select "Crop azimuth axis to fit plotted data" and in Step 5 "Crop elevation axis to fit plotted data" to make the chart easier to read. All other default settings should be OK.

Magnetic Declination Calculator

Enter your zip code to compute the correct longitude and latitude for your area, then hit the Calculate button. The value is given in degrees, minutes and seconds (e.g. 12° 4' 10"), and either positive (East) or negative (West). Note: The negative symbol is used for western locations. The sample value shown above is thus a positive / eastern declination.

Solar Radiation/Insolation Data

Quick Average Insolation Lookup

Insolation Lookup Tool

Generate an Insolation Percentage per Array Orientation Diagram

Average Wind Speed
Western Regional Climate Center

Average Wind Speed
National Climatic Data Center

Low/High Temperature for U.S. Cities

Shading Analysis

Solar Pathfinder - The Solar Pathfinder estimates shade at a given site over the course of a year. It costs about $300, and an additional software program is available for simulation and modeling.

Solmetric SunEye - A compact electronic device with a built-in cameral that measures potential shading at a site. It costs $2,000 and includes simulation and modeling software. See also their free software downloads.

ScanTheSun - Android mobile app that calculates solar radiation and shading. Like the devices above, the app takes into account solar angles and geolocation data. Unlike those devices, the app is free.

Pilkington Sun Angle Calculator A much cheaper, less high-tech gadget than the two items mentioned above. It costs $25. (Note: For many tax credits and rebates, you may still need to submit a Pathfinder or SunEye report.)

Cost Estimator and Solar Contractor's Tools/Software

Clean Power Finance


Energy Periscope

Solar Nexus

Various PV software
Simulators, modeling and design calculators that you can purchase or download for free.

Energy Audits

Enter your zip code, then click the arrow next to Analyze Your Use.

Home Energy Saver

Enter your zip code, then click on Go. On the next page, select Detailed Input in the far left column, then Energy audit of actual house under "Purpose of this Assessment". Address info is optional. Then press either Calculate to get a report, or Next to add more details about your home. (This site offers a lot of report options, so you can try different combinations to see what works best.)

Home Energy Usage Calculators

Appliance, shower (water usage), lighting and other usage tools. From Sacramento Municipal Utility District (SMUD).

CFL Light Bulb Savings Calculator

Wattage Estimates for Most Appliances and Electronics

Incentive Calculators

California Solar Initiative

Return on Investment (ROI)

Inverter Sizing

PV Select

Fronius Configuration Tool

SMA Configuration Tool

Outback Power String Sizing

Solar Edge Site Designer

Solectra String Sizing Tool

Power-One Aurora Stringsizer™

Enphase Module Compatibility Calculator

Other Measurements

Metric Conversions
Temp, weight, length, etc.

Temperature Conversion

Compound Angle Tool

Online Scientific Calculator

Scientific Calculator

Scientific Calculator

Right Triangle Calculator

Enter either a side and an angle, or two sides, or two angles, to find a missing dimension. The tutorial section array placement discusses various roof and shade measurements that use the Pythagorean Theorem.