Off the grid
HARNESSING SOLAR ENERGY OPENS UP A FIELD OF CHALLENGING POSSIBILITIES
How to heat your home using solar rays and warmed air
Igrew up a petrolhead, in a petrolheaded world. As a teenager, I could discuss Nuvolari’s 1935 German Grand Prix win, Jim Clark’s jaw-dropping arrival at the Brickyard, Henry’s iconic 1912 twin-cam Peugeot, Ettore Bugatti, George Eyston, two-stage superchargers on the Merlin … Then I read the 1976 McGraw-Hill Encyclopedia of Energy, which still graces my bookshelf. And came across the writings of M King Hubbert, sometime petroleum geologist, sometime professor. And realized that not only do we use fossil fuels incredibly wastefully but that — very soon in human history terms — they would be moving away from us.
The chase begins
That spurred a lifetime of studying, and chasing, energy efficiencies. It can be a whole lot of fun and a satisfying mental challenge. Take the development of our downhill-racing trolleys as an example. It started with our six-year-old on a conventional grandad-built four-wheel rig, rolling on solid rubber.
The ensuing years saw rubber being removed in the lathe, wheels drilled for lightness, diesel being used as a bearing lubricant. Then we dropped to three wheels to reduce inertia and friction. Then we lengthened the wheel base to eliminate steerage energy waste, which sped us into aerodynamic-drag territory. This induced first a prone (head-first) rider position, and finally, a full fairing over a full roll cage.
Retaining solar energy
Tracing all energy back to solar and realizing the enormity of the challenge facing society, I read everything that I could on ‘passive solar’ housing, the object of which is to gain, then retain, solar energy. Passive solar has been around forever, but since 1944 (when Frank Lloyd Wright designed the Jacob house) we’ve had no excuse for not applying it to modern housing. The concepts are easily understood: maximize your north-facing glass, minimize your south. Deflect your prevailing wind (because it’s a chill factor). Have some sunlit, energy-retaining thermal mass (concrete, stone, contained water). Insulate to the max. Simple.
When we bought an old bach (called a ‘crib’ down thisaways) as a first house, it was inevitable that we’d add to it in this manner. Being on a north-facing hill, we built above and behind it, open plan to allow the sun all the way into the ‘behind’ part. We were brave enough to use cool-store panel (steel/styrene/ steel) as the super-insulative roof, but not the walls.
Lessons learned
In the spirit of those trolley improvements, we learned a lot of lessons from that build and were keen to put them to work when building our second house from scratch. The aim was to maximize the passive use of solar energy before adding active inputs (like photovoltaic [PV] panels). This time we’d use cool-store panel for the whole external envelope to minimize the loss of any energy that we’d captured. This time the mezzanine would be down-sun, casting less shadow. The solar gain from the all-glass north wall would shorten the period when lights would be required — lessening the need for battery capacity. The wood stove would be downstairs and dead centre, as far from the outside world as possible. It would wet-backheat the water, effectively importing solar energy from outside the house.
We all know that wet-backing takes advantage of the fact that hot water rises from the firebox, enters the top of the cylinder, descends coolingly through it, returning at its coldest from the bottom of the cylinder to the firebox. It’s called ‘thermo-syphoning’, and we figured that if we applied it to the air in the house we’d be tapping into free circulation. It was a simple thing to provide opening vents high in our northfacing conservatory to allow hot air into the house where it cools, sinks, and returns via the open conservatory doors.
What about the morning sun?
I was lying in bed one night, smugly contemplating how well that conservatory circulation worked and regretting that we couldn’t build a conservatory on the east side of the house to grab that morning sun (there’s stairs in the way and the solid wall is a bracing component). Then I thought, hang on, who says a person needs to be there? How thick does a
It’s called ‘thermo-syphoning’, and we figured that if we applied it to the air in the house we’d be tapping into free circulation
conservatory have to be, solar-capturewise? You need the glass, then you need a back wall — they only need to be far enough apart to let the air move! I used old ranch sliders, 50mm offset from the wall, over a black sheet-steel backing. There’s a kilowatt per square metre available (in theory) from square-on sun. I reckon we’re getting about 1.5kW, allowing for losses through the glass. It blows in the top vents, of a morning, like a fan heater — for free!
Automatic vent control is next
After midday, of course, it reverts to being a back syphon, increasingly chilling the air in the column (and therefore the house) as night comes on. Currently we close the vents manually, but I’m working on an energy-free automatic control (an air piston driven by a sun-drenched bladder is one idea, a bimetallic strip being a maybe more practical other).
Given that society will be chasing energy efficiency in the years ahead, with most of the existing housing stock still in existence, someone should type/ approve a proprietary version and sell/ install it. There have to be so many old weather-board walls deflecting so much sunlight that, after double glazing and insulation, it might be the next best housing move we can all make.
There is a physical limit to energy efficiencies, of course, and a law of diminishing returns applies. That said, we’ve hardly scraped the surface of what’s possible. As we have done with double glazing, we will groan about — then accept — efficiency-improving regulations, but efficiencies deliver permanent returns.
It’s hard to beat that.