Hot shower, cool planet

Why use gas or electricity to heat your water when the power of the sun will do it for free?

Faisal Ghani, a young Bangladeshi-Australian engineer, has invented a deceptively simple glass pyramid that takes cold water in at the bottom and supplies hot water from the top. He believes it can bring cheap, hot water to every home around the Equator.

In the first of a new series packed with carbon-busting ideas, Tom Heap visits Faisal at his Dundee production line to hear about his plans to bring hot showers to the world. Climate scientist Dr Tamsin Edwards helps Tom calculate just how much carbon hot water from the sun can save.

Listen now on BBC Radio 4

What our experts say

We asked Society Fellows Dr Nazmi Sellami from the Robert Gordon University, Professor Chris Sansom from Cranfield University, and Professor Henning Sirringhaus from the University of Cambridge to offer some observations on the potential of solar thermal collectors in reducing carbon emissions. Their points take some of the themes of the programme a step further.

Prof Chris Sansom

A large proportion of the energy we use in our homes is in the form of heat – heat to provide hot water and heat to keep our homes warm in winter. Whenever energy is converted from one form into another, for example from electrical energy into heat, some energy is lost. It makes sense therefore to provide domestic heat from the heat of the sun, wherever and whenever it is cost effective to do so. Solar thermal technologies do exactly that.

What are the limiting factors?

Dr Nazmi Sellami

• Solar thermal is not as effective in colder climates

• There are challenges of scaling up this technology and reaching remote areas

• This requires space for thermal storage (water tank)

• A backup heater or boiler would be necessary

Prof Henning Sirringhaus

• Insufficient roof space in high-rise buildings in cities

• There would be an up-front installation cost, particularly for retrofitted systems

What are the co-benefits?

Dr Nazmi Sellami

• Reduced deforestation as wood isn’t needed for fuel

• Reduces energy bills

• It is an established and simple technology, accessible worldwide

• It can be combined with any other source of thermal energy

• Large scale installations could be used to generate electricity in addition to thermal energy

• Uses environmentally friendly and recyclable material

• Cheap to run and maintain, especially thermosyphon systems

Prof Chris Sansom

• Reduces the demand for electricity

• It is about 10 times cheaper to store same amount of energy as heat, compared to storing electrical energy (batteries).

• Mirrors or lenses can be used to concentrate sunlight in cooler climates (more expensive, of course)

• Thermal storage can be used (to cover for cooler days)

• Seasonal heat storage could even be used (the research team at Cranfield University is working on a project looking into this) – it involves collecting solar heat in the summer and using it in the winter.

One drawback of most sources of renewable energy is their intermittency. Solar photovoltaic (PV) panels and solar thermal panels require sunlight, wind turbines require windy days, and wave energy needs waves on the sea. As a result, appropriate energy storage becomes a central issue to provide a stable grid, with supply matching any given demand. Solar thermal has an advantage here, because it is much easier and cheaper to store heat than it is to store electrical energy. Electrical energy storage requires batteries whereas all you need to store heat is an insulated tank and a storage medium. The simplest storage medium is water, but other materials offer greater advantages still. For example, phase change materials (PCM) will allow seasonal heat storage. Imagine that you can store the heat from your solar thermal panels in the summer and use it to heat your home in the winter. These materials already exist and are being trialled.

Currently, much heat is wasted, whether in the domestic or commercial setting. Recoup Energy Solutions is a UK company that manufactures a device to extract waste heat from your shower water.

Prof Henning Sirringhaus

• Health and hygiene benefits in developing countries as wood is replaced as fuel

Are there any potential negative impacts of this idea?

Dr Nazmi Sellami

• There is the potential of a negative visual impact

• A potential hazard: leaking of hot fluid

Prof Chris Sansom

• Solar thermal works much better in sunnier locations. However, it could work economically in central and southern UK.

• Prof Henning Sirringhaus

• There is potentially competition for roof space with PV, but solar hot water heating is probably the better choice

Further reading

• Duffle, J. and Beckman, W. (2013), Solar Engineering of Thermal Processes, 4th Edition, Wiley

• Hannah Ritchie and Max Roser (2020), CO₂ and Greenhouse Gas Emissions, OurWorldInData.org

• ICAX (2021), Carbon Emissions Calculator

• Kayser, M. (2011), Solar Sinter Project, Kayser Works

• MacKay, D. (2009), Sustainable Energy – Without the Hot Air, Green Books

• Seba, T. (2010), Solar Trillions, Tony Seba

• Terry, N. (2011), Energy and Carbon Emissions: the way we live today, UIT Cambridge

About the series

39 Ways to Save the Planet is a new radio series by BBC Radio 4 developed in partnership with the Society and broadcast in 2021. It showcases 39 ideas to relieve the stress that climate change is placing on the Earth. In each 15 minute episode Tom Heap and Dr Tamsin Edwards meet the people behind a fresh and fascinating idea to cut the carbon.

Programme website

Over the course of 2021, the Society will be producing events and digital content to accompany the series.