Okapi Solar Calculator App

The Okapi Solar Calculator app is a powerful tool that:
  • Uses the light meter on your phone or tablet to measure sunlight strength to estimate watts/m² or BTU/ft²
  • Track and share sun position reports (azimuth and elevation) anywhere in the world, on any date
  • Solar air heater calculator helps determine output in BTU or watts from a solar heater
  • Calculator can also be used to determine some HVAC calculations including equivalent diameter and how elevation affects watts or BTU output
  • Share data from the above functions to social media, email, Google cloud print etc.!

Additionally, if you own a wireless Okapi system, the app can be used to:
  • Connect Android phone or tablet to an Okapi system for real-time data viewing
  • Log data (thermal power output on an hourly basis)
  • Use the light meter on the phone/tablet to simultaneously estimate the sunlight strength and calculate efficiency ratings for your solar air heaters
  • Share all associated data, for reports, graphs and further analysis

Localized versions include: Nederlands, Français, Deutsch, Svenska, Español, Italiano, čeština
Enhanced sunlight strength estimation:  Additional controls implemented to both calibrate and fine tune the light meter readings.

Light filter set

Click or tap here to purchase low-cost Rosco Neutral Density filters for the light meter on your phone or tablet (set of three including ND.15, ND.3, ND.6).

Purchase Light Filter Set
Purchase Light Filter Set

How to setup your Android smartphone or tablet to measure solar irradiance

The following video shows the basic steps on how to perform this procedure

Please send feedback, questions or requests for new features or updates to info@greenhillenvirotechnologies.com.

Okapi Solar Calculator feature list:

Okapi real time data monitoring (Okapi system required)
Connects Android device via Bluetooth to Okapi Solar Air heater control systems
Displays output for each connected heater: Inlet and Outlet temperatures in °C or °F, Temperature rise between inlet and outlet, fan speeds and thermal power output (kWh or BTUh)
While connected to Okapi system, the app records all received data
You can share Okapi real time data to email or social media such as Facebook

Solar and HVAC calculator (Okapi system not required)
Enter measured temperatures from Inlet and Outlet (°F or °C)
Enter measured wind speed from the outlet (FPM or m/s)
Enter dimensions of the outlet (inches or cm), can be round or rectangular
Choose if equivalent diameter calculation (Huebscher) is required when a rectangular outlet is selected
Enter elevation or have the App calculate it automatically using GPS and an internet connection

App then automatically calculates:
  • Temperature rise between inlet and outlet
  • Output from the system in watts or BTUh
  • The area of the Outlet (or equivalent, if Huebscher is required)
  • The airflow (CFM or m³/min)
  • The F value (specific heat of airflow mass), which is based on the elevation
All unit conversions are also available, simply push a button to convert temperatures from °F to °C, another button to convert cm to inches (including squares and cubes where required), and another button to convert between watts and BTU.
This data can also be shared to social media, email etc.

Data logging (Okapi system required)
The app can be left running on an Android device connected to an Okapi system to log data over long periods
Features here include full SQL lite database that stores accurate hourly heating calculations
User ability to enter reports, including start and end date as well as identify which Okapi system (if data has been received from more than one Okapi system)
Ability to easily share reports from the app, for bragging rights, graphing or further analysis

Sun position activity (Okapi system not required)
  • Choose your location, or any location, either using GPS or by manually tapping the position on the built-in Google map (internet connection required)
  • Automatically determines the Timezone (internet connection required)
  • Or enter the timezone manually
  • Choose a date if you want a forecast or look at solar history
  • The app will tell you the sunrise time, solar noon time and sunset time
  • The app also displays the current azimuth and elevation of the sun
  • There's a slider so you can use a finger to slide all the way from sunrise to sunset and watch the solar azimuth and elevation change as you alter time
  • Calculates the equivalent Julian date
  • Has a built-in compass (requires specific sensors and works best outside)
  • Shows you the pitch of the Android device. Great for measuring sloping angles!
  • Also shows the bearing from GPS, if you have been moving and would like an estimate of the direction
All above output data can easily be shared via email, social media etc.
Sharing has two detail options. Basic is an hourly report that details sun position (azimuth and elevation) from sunrise to sunset. The "Detailed" option  reports the position of the sun for every five minutes between sunrise and sunset.
There's also a "Today" button to reset back to "now", once you're finished analysing other dates. You can also get the timezone offset manually (internet connection required).

Sun strength activity (Okapi system not required, however, if one is connected then efficiency data is available)
Uses light sensor on Android device to measure solar irradiance in watts per square meter or BTUh/ft² (and use this data to estimate insolation)
Some android devices have weak light sensors, therefore a clever system has been implemented to enable the weaker light meters to provide reasonable sun strength measurements
Functions are implemented to guide the user through the process of setting up the light meter for best measuring the sunlight strength
Toggle button to convert between watts/sq.m and BTUh/ft²
Share button available to send your data via email, social media, Bluetooth, Google cloud print, Android Beam, Google+, Hangouts, Facebook, etc

Settings (for entry of detailed data regarding connected Okapi systems)
  • Enter or automatically detect elevation at the location of the solar heaters (GPS and internet required)
  • Calculates the F value (heat capacity of airflow mass) based on elevation
  • Set whether share data should be in detailed or basic form
  • Privacy option:  Set whether or not you want to include your location (GPS coordinates) in share data
For each heater (up to two heaters attached to your Okapi system):
  • Enter a name
  • Set whether the outlet is round or rectangular
  • Enter the diameter, or width and height, of the outlet
  • Set whether equivalent diameter is required. It should be. (Equivalent diameter uses the Huebscher equation to determine the pressure losses in a rectangular duct and therefore give the equivalent diameter)
  • Enter the measured wind speed when the fan is running at 100% (FPM or m/s)
  • Enter the area of the collector's active surface area
Outlet area is then calculated for you, as is the Maximum airflow (in CFM or m³/min)
There's a button to toggle between metric and imperial units (all conversions are done for you) 
You can also disconnect the Okapi here, if you need to save battery power on the Android device

Connect and Disconnect Okapi systems is also available from the main menu, as is a link to the App's help section on our website

Sensors, hardware and features used by the Okapi Solar app:
GPS for location discovery
GPS + Internet for accurate Elevation detection
Bluetooth for connection to Okapi systems
Light Sensor used to evaluate the strength of sunlight
Ambient temperature sensor, used to display the temperature around the Android device
Magnetometer used for compass, heading and pitch detection
Accelerometer used for compass, heading and pitch detection
SQL Lite databases, used for storage and reporting of logged Okapi data
Preferences, all user settings are recorded on a per device basis, allowing easy use of multiple Okapi systems
Sun location activity uses GPS (and/or a built-in Google map) to set the location and is able to report on past, present and future sun positions during any day, anywhere in the world, with very reasonable accuracy

Help section

How to connect the app to a Wireless Okapi system