empire of the sun
Photo Credit:
Gilles Paire/shutterstock.com
you can Still
use solar power to heat your
greenhouse in the depths
of winter, even when the
snow is thick on the ground
outside, by using passive
solar power.”
76
Maximum Yield USA | January 2015
Solar power is the obvious solution to so many of our
gardening needs. You don’t need massive solar panels or
complicated installations to power something as small
and energy-efficient as a light, a garden fountain or a
water pump—panels for this sort of application can be
small enough to nail to a fence post. The smallest panels
are often incorporated into the fitting itself.
Sometimes it’s such a natural fit, it’s hard to see why we’d
do it any other way. For example, automatic irrigation kits
that only turn on when it’s hot and watering is required,
or fountains we only want to bubble on warm, sunny days
when we’re around to enjoy it. But solar power can boost
electricity supply when it’s cooler, too. That’s because
photovoltaic solar panels operate on light, not sunshine,
and light still reaches the ground even when it’s cloudy,
though usually at lower concentrations. That may cause
difficulties if you’re trying to power a house, but if all you
want to do is run a power drill, it’ll charge up a battery
well enough.
Photovoltaics are less efficient in winter, when light levels
can drop to a third of summer levels as days shorten and
the sun weakens, but you can still use solar power to heat
your greenhouse in the depths of winter, even when the
snow is thick on the ground outside, by using passive solar
power. Also known as solar thermal energy, this is the lowtech end of solar power generation and easy enough to set
up yourself without any special equipment required. The
idea is that you capture and i ntensify the heat from the
sun, a little like you do when using cloches, and direct it
into something dense that stores the heat and releases it
slowly—usually soil, water, bricks or concrete.
If you have a greenhouse, you already own a giant solar
panel. Just putting it up increases temperatures inside
about 3-5 degrees above ambient air temperature outside. If
it’s a lean-to, capitalizing on the heat-retaining capacity of a
house wall, it’ll hold onto that raised temperature for much
of the night, too.
You can boost this even more by installing the equivalent
of a solar-powered heater in your greenhouse. Paint a metal
radiator black, put it inside and hook it up to a circuit of
metal plumbing pipes running under a seedling bed. As the
winter sun heats the radiator, it warms the water inside. This
sends it around the circuit, delivering a steady warmth
to your young plants—your very own homemade,
solar-powered, heated propagator.
The same effect can be used to generate general heating,
too. Fill black-painted barrels with water and stand them in
the greenhouse. They’ll heat up rapidly in the most fleeting
of sunny spells and then slowly release the heat into the air,
keeping it frost-free even on the coldest days.