Solar Position, Sun Charts, Solar Climatic, Collector Orientation...

Tools that give sun position, climatic data for solar design, and radiation on a solar collector.


Tools to design window overhangs.


Directory of page:

New -- SketchUp for sun modeling...

Solar Site Survey

Solar Site Survey...


If you are going to do a solar project, you need to do a Solar Site Survey to make sure that your site gets enough sun during the right times of year to make the project work.
This free and simple survey only takes an hour and is fun and educational.

Its a must do for any type of solar project!
Skyview app to do solar shading surveys skyview solar surveyThe free Skyview app is normally used to allow iPhones etc. to find stars in the night sky, but it can also be used to do a first cut solar survey to find obstacles that shade your solar collectors.

To use it, you make sure it is set to your location, then set the date and time of interest, then select the sun object.  Standing at your your proposed collector location, pan across the horizon -- the path of the sun will be projected on the screen so you can see when it is lower in the sky than nearby trees, buildings etc.    The logical first date to start with would be Dec 21 (the winter Solstice) when the sun is lowest.

I tried this on my iPad, and it worked pretty well, but I would still do the site survey listed just above rather than relying fully on Skyview -- it can be a real disaster to get the shading wrong.

Thanks to David for finding this and sending it in.
Solar Shading and Other Solar Tools for Android Phones... solar shading calculatorThis is reported to be a good set of tools to analyze your solar shading situation for PV or solar thermal installations.
Cost is $16.
Comments from Lawrence...

They also offer several other PV and electrical oriented tools for Android.
Sun Tracker -- an iPhone application


This is a nice application from Andrew for the iPhone that allows you to do a solar site survey using the iPhone's built in sensors for measuring elevations and azimuth angles for the survey of the horizon.
While I've not had a chance to actually try it, it looks to me as though it would do a good job.

Price is now up to $40 at the Apple App Store.
Solar Pathfinder


The Solar Pathfinder has been around for many years, and is used by many solar professionals to do solar site surveys.  Basically its a glass dome, and the reflection of the objects on the horizon is used to assess the effect of objects on the horizon that would block the sun.  Now offered with software assistant.
Probably a bit of overkill for the DIYer building one or two projects.

Bright Harvest Solar Survey

Bright Harvest solar surveyBright Harvest offers a new kind of solar survey.  Based on aerial photos, they make a digital model of your house and surrounding obstacles, and then try various arrangements of collectors and estimate the shading for each.

They did a report for my house, and here are my thoughts on it... 
In a nutshell, the service is not inexpensive, but the report is impressive.

Effect of Collector Orientation On Performance
Effects of Tilt and Azimuth On Annual Incident Solar Radiation For the United States Locations
Craig Christensen and Greg Barker

The full paper... (pdf)
This very good paper provides a very simple set of contour plots that show optimum collector orientation, and the performance effect for deviations from optimal.
Covers only the US, but the general relationships would be useful elsewhere. 
Some limitations -- read the cautions in the paper.


The very useful PVWatts tool can be used to work out the best orientation for solar PV or thermal collectors at your location. 
Simply try different tilt and azimuth angles until you maximize solar irradiance on your panels over the desired time frame.
Solar Position,  Solar Radiation, Solar Design Climatic Data
Sun Charts

A Sun Chart for your area is a must have tool to determine how much of the time sun will shine on your collectors.  See site survey for how it works.


This site gives sunset/sunrise times, as well as solar insolation, temperatures, precip, ...

(thanks to WYWhiteWolf for suggesting this)

Climate Consultant,
UCLA Energy Design Tools



Climate Consultant is one of the UCLA Energy Design Tools.
It provides a variety of ways to visualize weather for a specific location.  Weather data files are available for hundreds of locations.  This is a brand new version, and is very easy to use. 
"It graphically displays climate data in either metric or imperial units in dozens of ways useful to architects including monthly bar charts, timetable charts, and psychrometric charts, sun shading charts, and sun dial charts."
One of the most interesting charts is the Psychrometric chart with overlays that show the design strategies (e.g. passive solar, evaporative cooling, ..) will work for the location in question.


This new site gives very nice summaries of weather for more than 4000 locations.

The graphical presentation is very well done, and conveys a lot of information in a very readable format.

Weather Underground
weather historyThe Weather Underground under the Local Weather -> History tab provides very nice weather summaries for the time period you can enter.
Psychrometric Charts

US units psychrometric chart...

SI units psychro chart...

Tutorial on using psychrometric chart...

Psychrometric Charts are very useful for working human comfort problems and air conditioning schemes, and working out condensation problems.

Climate Consultant (just above) provides temperature/humidity data overlaid on a Psychrometric Chart for many locations.

Thermal Comfort Tool...

Hoyt Tyler, Schiavon Stefano, Moon Dustin, and Steinfeld Kyle, 
2012, CBE Thermal Comfort Tool for ASHRAE-55. 
Center for the Built Environment, 
University of California Berkeley 
comfort calculatorThis is a web based comfort calculator.  It allows you to change air temperature, humidity, air speed, ... and then shows where this condition falls on the comfort chart. 

(Thanks to Nick for finding this)
NOAA Solar Calculator
noaa solar calculatorThis very handy calculator allows you to zero in on your house using satelite images.  You can then see how your house lines up with south, find solar noon, sunrise and sunset times for any date.
Solar Time to Local Time -- Solar Noon,



A helpful calculator that gives sunrise, solar noon, and sunset in local time for any location and any date.
Helpful in many situations, including finding true south at your location.


Sun CalcA very simple and easy to use calculator to show sunrise, sunset, solar noon, ... at your location.
Print Your Solar Noon Calendar


Very handy tool that prints out solar noon for every day of the year for your exact location.


(thanks very much to Bill for suggesting this)

Surface meteorology and Solar Energy



Solar radiation and solar geometry data from derived from satellite observations.  Provides data for anywhere in the world. 

Provides solar parameters for solar thermal, PV, solar cooking, etc. based on 10 year history for your exact location. 

Solar Radiation Tables... The tables provide solar radiation on a south facing collector at various tilt angles and for a range of latitudes.
NOAA - Climate Data Online

NOAA - Climate Data Online
This free online service allows you to search a huge collection of climate data for the US and the world, and then to download the data you select.
More Solar Radiation and Weather Data Sources


NOAA CLIM20 Weather Summaries by City

NOAA year to date degree days

NREL (and other) Solar Radiation and Climatic Data


Total and diffuse radiation or building surfaces:
Solar Radiation Data Manual for Buildings


Typical Meteorological Year weather files

NOAA provides a variety of weather related products and data.

The CLIM20 product provides pretty detailed historical weather summaries for many US towns.  It includes temperatures, precip, and heating and cooling degree days.  Lots of good data.

NOAA year to date degree days provides deg day totals for the current year.  Updated each week.

NREL Redbook: Average weather conditions and solar radiation of collectors at various orientations for many US cities.  Based on 30 year weather records.  Try downloading the pdf version for your state.  Can be used to roughly calculate gain for collectors.

NREL Bluebook: The Solar Radiation Manual for Buildings gives total and diffuse radiation on S, N, E, W and horizontal surfaces.
This can be used as base data for many passive gain calculations.

TMY weather files give provide typical hour by hour weather files to provide weather input for simulations.

Climate Data



Climate dataOne of the Sustainable By Design tools that provides a variety of climate data -- things like sunny days, heating degree days, precipatation, ...
Solar Electricity Handbook -- Irradiance Calculator

Note that PVWatts, which is a PV oriented calculator by NREL also provides solar irradiance on the surface you specify, and this can be used as input for solar thermal calculations in the same way.
solar radiation calculatorThis is a very easy to use calculator that gives solar radiation levels for many locations worldwide by month.  It provides radiation levels for equator facing surfaces, and allows you to pick from several tilt angles.

Output is in KWH/sqmeter -- 1 KWH/sqmeter = 317 BTU/sqft

Thanks to Andre for suggesting this
Clear Sky Charts


This is really a tool for astronomers, but if you are a solar energy nut and you are always obsessing over whether the next 48 hours are going to have any good sun, this tool can be handy.
It gives a cloud cover forecast by hour for about 48 hours for thousands of locations.
The Solar Spectrum... Shows the distribution of solar radiation energy by wavelength.
Borst Engineering and Construction Calculators

Many Calculators...
Borst Engineering has a whole raft of calculators -- HVAC, solar position, shading, and incident heat, water wheels, pipe sizing, ...
Heating and Cooling Degree Days
Energy CAP Free Degree-Day Weather Tools


A nice set of free web tools that give heating and cooling degree day information for 1200 locations.
Provides historic, current, and even near term degree day forecasts.
Very easy to use.
Note that a default balance point temperature is 55F is used -- you can change it to the more usual 65F if you wish.
Year to Year Degree Day Comparisons
(see: FREE Degree Day Report)


An example of how to make apples to apples comparisons of fuel use in for two years ...

This report provides month by month comparison of heating and cooling degree days between two years you select.

This allows you to make apples to apples comparison of fuel use for two years, and  to see the actual effect of changes you made to reduce energy use.

An example of how to make apples to apples comparisons of fuel use in for two years ...
Degree -- Worldwide Degree-Day Tool



Nice tool for heating or cooling degree-day summaries for locations around the world.

The data comes from Weather Underground stations, so it may be easier to find a location near you.
NCDC Degree-Day Maps

Heating and Cooling Degree Day Maps
Heating Degree Day Map of US (130K)
Cooling Degree Day Map of US (100K)

National Climatic Data Center

Heating and cooling degree-day maps for the US.
Window Shading and Overhangs
Designing Shading Overhangs with Google SketchUp



Example -- Using SketchUP to model sun and shadows on a home...

SketchUp is a free 3D drawing tool from Google.  In addition to being easy to use as a general purpose drawing tool, it offers a built in sun. 
You can easily draw a wall with a window and overhang (or a whole home), and play the sun over it for various times of day and times of year. 
Shading structures of all types can be modeled, including trees, solar sails, shade walls, window fins, ...
Sun patterns inside the home are also shown. 
It would be good for modeling sunspaces and greenhouses as well.

An example showing how to set it up for home ...

Sustainable By Design Solar Tools

Several other useful tools listed on the same page.
Some very well done (and free) tools for designing overhangs, determining sun position, ...

The overhang design tool is very good, and is the best way to get a quick feel for how overhangs work.

Got Wind? -- How to use  the Wind Resource Atlas of the United States



The Wind Resource Atlas of the United States will give you a rough idea if you are in a locations with wind potential -- here is how to use it.
PVWatts  -- A Performance Calculator for Grid-Connected PV Systems

This is a really useful tool.

An easy calculator you can use to find out how much power you will get from a PV installation in your area.

It calculates PV system performance based on hour by hour records for sun in your area.

Version 1 is very easy to use, and works worldwide.
Version 2 allows more detailed inputs, but seems rather complex and puzzling at times to me.