Winter Solstice 2019

John Williams

20 Dec 2019

The 2019 Winter Solstice is at 04:19 GMT on Sunday 22 December in the Northern Hemisphere. This is the day with the least hours of sunlight. It occurs when the North Pole has its maximum tilt away from the Sun. Read more from the Royal Museums Greenwich about this annual astronomical event.

Celebrations and festivals

Across the world, mid-winter is celebrated in various spiritual and religious traditions. Atheists and agnostics can still rejoice! After the Winter Solstice, the nights are shorter and the days are longer.

Famous ancient monuments, such as Maeshowe in Orkney, Newgrange in Ireland and Stonehenge in England, were built to be carefully aligned with the Winter Solstice. It’s a special experience to stand inside the inner circle at Stonehenge joining many others who make a pilgrimage to this unique place on the Winter Solstice.

In Brighton, England, people gather together during the Winter Solstice to take part in Burning the Clocks. They craft lanterns made of paper and willow which they then carry through the streets until they reach the beach. The lanterns are then burned to commemorate the end of the year.

Solar PV still works in winter!

The days are shorter and the temperature is lower so it is reasonable to expect that solar PV will not be as productive as in the summer. However, solar PV panels need light, not heat. They can actually perform better when kept cool. Read some of the science from UC Santa Barbera.

Snow can also reflect light and help improve PV performance. This is known as the albedo effect. However, if the panels are covered with snow there is a modest reduction in performance rather than a blackout. See this study from the Northern Alberta Institute of Technology for more information.

Burning wood: not so cool

There are upsides of course, but wood is a relatively inefficient fuel and can create air quality issues. There is also great debate about the carbon footprint.

Science writer Fred Pearce reported in Yale Environment 360 that using wood pellets in electricity generation is a “loophole”. He worries that this could cause an unseen surge in carbon emissions and fatally undermine the Paris Climate Agreement.

Burning wood may be close to carbon neutral if cut trees are replaced sustainably. However, burning wood immediately releases carbon and it can take up to a century for a replacement tree to absorb the same amount of carbon whilst the original carbon emission continues to drive climate change.

“Unless forests are guaranteed to regrow to carbon parity, production of wood pellets for fuel is likely to result in more CO2 in the atmosphere and fewer species than today.” William Schlesinger (the eminent biogeochemist).

Schlesinger points out that timber plantations do not store as much carbon as natural forests and that it could take 40 to 100 years for a managed forest to capture the same amount of carbon as a natural forest. Unfortunately, most plantation forests are harvested at 20-year intervals and never make it to the carbon-neutral point.

In conclusion, to be sustainable biomass requires a long-term approach and proper management of the replanted forests.