Winter Solstice 2021 in the Northern Hemisphere was today at 15:58 GMT Tuesday, 21 December.
Winter Solstice is the day with the least hours of sunlight. Shetland with just five hours and 49 minutes being the most extreme example. Winter Solstice occurs when the North Pole has its maximum tilt away from the Sun and usually heralds a spell of cold weather. Indeed this year it is predicted that parts of Scotland and northern Europe will have a ‘White’ Christmas. The forecast comes after the UK’s coldest night of the winter for the third night in a row, with temperatures recorded at -9.3C in Braemar.
The days have been getting shorter and the nights longer for the past six months. The good news is that from today on, the days will gradually grow longer and we can begin to look forward to lighter and brighter days.
The summer solstice has always been associated with Stonehenge, but the winter solstice is also highly significant here as the stones were carefully aligned to frame the sunset on the shortest day of the year.
The winter solstice is also a celebration event at Portobello in Scotland, with revellers gathering for a community swim at sunrise, on the Beach.
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.
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.