As you will know, at room temperature, materials that are electrical conductors, have electrons which are free from their atoms, buzzing around at random like bees… and all it takes is a push from a battery for those electrons to flow as an electric current.
Attach a battery to an insulator and nothing happens. In an insulator, the electrons are held tightly to their atoms…no buzzing bees ready to be pushed in one direction… and no current flows.
But semiconductors are in between these two extremes. Normally they are like insulators but supply a bit of energy and the electrons are freed and a current can flow. Depending on the material, different amounts of energy will get things going so, for example, an infra red detector, which is used in a heat seeking camera, will respond to body heat.
Some time ago, when I was at university, we learnt how to make a solar cell – the type that you have in your calculator. A really thin layer of the semiconductor silicon is formed, like the cheese in a sandwich, between one positive and one negative material. Sunlight provides just enough energy to free the electrons in the silicon and because, as we know, electrons are negative, they are repelled by the negative layer and attracted towards the positive….and so, like magic, sunlight has made a current flow through the circuit.
Physics is amazing I hear you say… and it is. Without any fossil fuels being burnt, not even the whirl of a wind turbine, the energy form that the modern world needs so much, electricity, has been made from a beam of sunlight.
Of course there are downsides. Especially in this country, the sun doesn’t shine all the time and, furthermore, the period of the year in which it shines least, on cold grey winter days, is exactly when we are likely to want electrical energy most. Added to that, solar cells are inefficient. I remember being told, all those years ago, that to provide sufficient electrical energy for the UK would require an area the size of Wales to be covered with solar cells - which would raise the odd Welsh eyebrow.
Since then, solar cells have improved but back then, the motivation was the knowledge that fossil fuels were running out. Today that is still true, but a far bigger worry is the impact that the burning of fossil fuels is having on our climate, and indeed our planet, now.
Thursday 22nd April 2021 is Earth Day and, across the world, events linked to Earth Day start today. Over the past half century, the Earth Day movement has sought to educate and encourage improvements in the way we look after our planet, particularly with regard to education, pollution, the climate, communities and conservation. It is thought that over a billion people across the world will engage with the activities this year. On Thursday, President Biden’s global climate summit will take place and it will be interesting to see how the new US administration will behave in relation to these issues.
The Earth Day theme for 2021 is Restore Our Earth, which focuses not only on the need to reduce our impact on the planet as we recover from the effects of Covid-19, but also on how we can play a role in repairing the damage that has been done in the past. Writing recently, the President of the movement says that we must look at natural processes, green technologies, and innovative thinking that can make a lasting and transformative impact to restore our Earth. Using and improving photovoltaic cells, (solar cells), is just one possibility.
As you may have read, as countries around the world went into the first lockdown, global CO2 levels dropped and there was talk of nature having the chance to heal itself. But, already, they have increased again and are apparently higher than they were before. That would suggest that they will rise still further when the pandemic restrictions are reduced further… and what that means is that the challenge of keeping global warming to 1.5 °C above the pre-industrial levels (which was the target agreed in 2015) is very significant. If the average temperature rise of the Earth does rise by more than 1.5 °C , it is predicted that there will be very significant impacts on health, livelihoods, food, water supply, and economic growth.
I am very conscious that when I give these assemblies there will some who think….what’s he going on about now…why is this relevant to me? But this really is relevant to us, all of us, now and in the immediate future. Unless the world’s population does think carefully about how we use and care for the planet, our planet, there will be serious consequences for all of us. There is, indeed, a need for innovative thinking and science and people working together to make things better… so that we reduce pollution, global warming and damage to the natural environment.
It is nearly a generation ago that students like me learnt about solar cells in a university lab and that was very really interesting… interesting enough to be talking about it two or three decades later. The need to develop and use technologies like that really effectively has grown significantly over that time. It is not just an academic exercise. There will be a demand for scientists and engineers to be innovative simply so that we can live our lives in a way that doesn’t harm the Earth and so that future generations continue to enjoy all that we have now. But also, there will be a need for all of us to live in different ways; to think about the journeys we make, the energy we use, the food we eat and where it comes from, and the homes we live in, so that separately and together we all make things better and particularly stem the rise in global warming.
I would encourage you to follow the events of Earth Day, the science, the predictions of what could happen and what we need to change. All of us can, and need, to play a part in that, and perhaps a positive of the Covid-19 pandemic is that it has made us all realise how delicate life on Earth is and that we all need to work together to preserve it.
Read more about our activities for Earth Day 2021 across the school.