Tuesday, 20 December 2016

Happy Solstice on December 21st: Designing with the Sun

Happy Solstice to everyone on December 21st. It will be the  midsummer solstice in the south and midwinter solstice in the north. What does this mean? Why is it important for good design of our eco-homes and food gardens?


Sunflowers track the sun. Our homes and gardens need be designed with work with nature too - to acknowledge the sun in different seasons. Image: Morag Gamble
For many cultures and people worldwide, the solstices have great significance. It's a time when celebrations and rituals of all kinds take place, and have done since ancient times. Throughout history too, people have built structures (from stone arrangements to temples to megalithic structures) to mark the solstices including Indigenous Australians, Druids, Egyptians, Mayans, Indians, Romans and so many others.

From a purely practical sense (as a permaculture design, gardener or owner-builder) knowing about how the sun moves throughout the year are central to good design, sustainable homes and productive gardens. You need to know when and where are the highest and lowest sun angles in order to place your elements in the best place. 


Where is the sun and where are the shadows cast in midsummer and midwinter at your place? Knowing this is crucial to the good design of your home and garden.

 What are the solstices and equinoxes?

Summer solstice (Southern Hemisphere: approx. Dec 21, Northern Hemisphere: approx. June 21)
  • midsummer
  • longest day and the shortest night 
  • when the sun is at its highest in the sky
  • when the pole closest to us is tilted toward the sun
The word solstice comes from an ancient Latin word  solstitium meaning sun-stopping which is derived from sol ‘sun’ + stit- ‘stopped, stationary’. This term was first used in the first centry BC, although tracking the movement of the sun is much more ancient.

Winter solstice (Southern Hemisphere: approx. June 21, Northern Hemisphere: approx. December 21)
  • midwinter
  • shortest day and longest night 
  • when it's lowest in the sky
  • when the pole closest to us is tilted away the sun.

The precise time and date can vary a couple of days from year to year becuase the path of the Earth around the Sun is an ellipse, not a circle, and because the Earth is off-centre on its axis . You can find out the precise time of the equinox and solstices on websites like time and date.  This year, where I live, the summer solstice is coming soon on December 21 at 8:44pm.

Sun path in southern hemisphere on midsummer and midwinter. (source)

Sun path in northern hemisphere on midsummer and midwinter. (source)


(NB: Equinox - 
The equinox is when there are equal hours of day and night. These happen around March 21 and September 21.  The word equinox comes from the Latin aequinoctium which is derived from from aequi- ‘equal’ + noxnoct- meaning ‘night'.)


Designing with the Sun - home design, energy design, garden design

Use the understanding of the sun path throughout the year to manage sun in your house and garden - to harness it's energy and to protect yourself from it's heat. Your Home: Australia's Guide to Sustainable Housing is a great resource for planning and design, and understanding how to work with local climate.

Sun Angles and Home Design

You could use computer modelling, but when we were designing our house, we checked our home orientation, eave design and window location by building a model and shining a lamp at the angle of the sun in different seasons. It worked perfectly. 

The sun shines through the windows in winter warming the thermal mass floor in the children's area which keeps the space lovely and warm into the night. Now in summer though, the floor is protected from the sun and it remains beautifully cool. On really hot days, that's where they are -  laid flat on the cool floor doing their schoolwork, reading or playing.

Thermal Mass: Source - Your Home (if you are in the northern hemisphere - change north to south)

Planning with the sun helps me to keep my house cool in summer and warm in winter mostly without heating and cooling. Only in the coolest month do we need to use our fireplace at night, and only midsummer (now) do we find ourselves using our ceiling fans. (And then to reduce our footprint - we grow our own firewood and produce solar power to power the fans.)

Considering the sun, the ideal orientation of a house is with the long side of the house running east-west. This reduces the heat absorbed on long summer days - particularly on western walls, and gives maximum surface for light and heat absorption on midwinter days when the sun is lower in the sky.


Home orientation: Source - Your Home (again, if you are in the northern hemisphere - change north to south)

Sun Angles and Solar Panels
We also need to understand the path of the sun so we can gather as much sun as possible on our solar panels and solar hot water systems. Solar panels placed at the ideal angle and orientation will provide maximum energy and heat production. 

Solar panels should face due north (south in the northern hemisphere), but the tilt angle varies depending on location and your main loads (eg: electric heating in winter, or refrigeration and cooling in summer). See the link below for more information on tilt:


As a rule of thumb, if the main loads are in winter months when solar availability is reduced, tilt angles should be more vertical (approximately equal to latitude plus 15┬║) to maximise exposure to the low winter sun. If major loads are cooling and refrigeration the tilt angle should be reduced (approximately latitude minus 10┬║) to maximise output during summer. For grid connect systems the summer optimum angle should be used to maximise annual output of the modules. Source: Your Home
Example of idea solar tilt from Sydney, latitude 34 degrees.  Source - Your Home

Vegetable Garden
In the garden too we need to plan with the sun of course. Food gardens will not produce unless they have enough light. We need to consider the shade of our home, our trees, and the homes and trees too of our neighbours too. I always look for a spot in the garden that has a minimum of 4-6 hours of sun a day.

It's important also to know how the sun angles and shadows in each season affect different areas of your garden. For example, there's a big section in my terrace garden that is shaded in winter by my neighbours big trees to the north. I have designed this area to have resilient shade tolerant perennial plants in that area, and in summer interplant with some fast growing annuals.

I also design the layers of the garden to ensure that sun can penetrate to the herbs and vegetables growing underneath the fruit trees.

In my garden, I use the slope to gain more solar access and build in more layers of food. Image: Morag Gamble

Worm Farms need shade
A good winter spot for a worm farm might be far too hot in summer. Make sure you work out a place that gives year round protection, or have a movable set up.

Chickens need a good balance of sun and shade
I designed my chicken pen to ensure they have protection from the strong summer sun and long hot afternoons. I have a a partial wall screening the sun and a deciduous mulberry on the west, and I allow pumpkin vines to clamber over in summer. By midwinter, the mulberries and pumpkins have gone so the sun can shine in for the girls, although here in the subtropics the winter sun can still be hot, so I've ensured some areas of year round protection.


Our chicken pen in midsummer (east elevation) - good chicken protection. The gap in the pumpkin vine allows morning sun to flood into the chicken pen, and the mulberries protect them in the afternoon. Photo: Morag Gamble

Observe and document the sun path where you live.
Do you know where your midwinter and midsummer sun rises and sets, and how it tracks over your house and garden in the middle of the day? Draw the sun path for your area...map these and understand the significance for design.  Do a mudmap of your site and note the solar qualities of each area.




2 comments:

  1. Over the years we've lived here in suburban Brisbane, I've become familiar with the path of the sun and its impacts, in terms of light/shade, heat etc. are felt here at our place. While some things about our home now can't be changed, built before I really knew much at all in the way of design and gardening, there is still much I do now to work with it. Out the front are predominately native plantings as this area faces South West and cops the scorching summer sun, my veggie areas are out the back which faces North/NE. Our block has areas of slope and so I've learnt to put in hardier plants at the top of those slopes. Solar panels are on our roof, positioned to get most out of the energy of the sun. I am still learning but have learn much through trial and error and observation. Meg:)

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  2. That is such good information, Morag. Thank you so much. I wish I had known that when I was younger.

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