Student open space day tackles barriers to Zero Carbon Britain

Students from the Centre for Alternative Technology’s (CAT’s) Graduate School of the Environment held an interactive Open Space day to discuss barriers to bringing about a rapid transition to a low carbon economy. The outcomes of the day are being fed into the Zero Carbon Britain – Making it Happen research currently being undertaken by CAT.


The open space style of the event meant the day started with 40 people but no agenda. The participants came up with and held 16 smaller group discussions on a diverse range of topics during the day. This 2-minute film gives a flavour of the day.

The 16 discussions covered a broad range of topics, but the structure of the day allowed each session to be focused, and useful for developing the research. Topics covered included:

  • Reaching a wider audience, including reaching out within workplaces
  • Using the resources of new build property developers and retrofitting existing buildings
  • Community energy, and how you create strong community groups
  • Political action, both local and wider
  • Creating an inclusive movement, that is founded on equality and diversity
  • Looking at a more individual level, at setting personal goals, behaviour change, valuing resources and handling both ‘eco-guilt’ and bad news on climate change
  • Values and learning from nature
  • Having a hopeful vision that inspires us

If you are interested about finding out more about CAT’s next research project, you can read about Zero Carbon Britain: Making it Happen initial findings online, or come along to our short course on the 28-29th April, which is just before the Machynlleth Comedy Festival, meaning you can combine the two for a stimulating long weekend in Machynlleth.

The top 5 renewable energy questions from the National Homebuilding and Renovating Show

If you went to the National Homebuilding and Renovating Show a week ago, you might have been inspired by the live demonstrations of thatching, or felt the sudden urge to redecorate when you passed the stall full of sheepskin rugs. Or perhaps you realised you really did need a 2-metre 3D TV in your lounge, or maybe you simply wanted to browse whilst enjoying an ice cream from the Yorkshire Dales food cart (it’s a permanent installation).

Nestled between two full-size timber frame houses, one of which was the Eco Home Theatre, the CAT stall was a small hub of renewable energy debate in this varied crowd. Enthused by Tobi’s daily talks, a stream of visitors made their way to us to ask often highly specific or technical questions. Some of the same concerns kept coming up, so we’ve collated a list of the five most common questions and Tobi’s answers.

Lots of people also asked us questions about architecture and design, but we’re going to save those for a later feature. Stay tuned!

  1. What’s PVT, and is it a good idea?
  2. Is there a case for thermodynamic systems?
  3. Are heat pumps right for me?
  4. Micro hydro: yes or no?
  5. Should I heat my house with biomass?


1. What’s PVT, and is it a good idea?

PVT is the combination of solar photovoltaic systems (the “PV”), which produce electricity, and solar thermal systems (the “T”, also known as solar water heating, SWH), which produce hot water.

In principle, you can see the potential for synergy between these technologies. PV modules convert only 10%-20% of the solar energy that falls onto them into electricity, and a good proportion of the remaining solar energy is converted into heat – solar PV get hot in the sun. So why not use this heat to heat water for showers? This is what PVT modules do – basically, they are solar PV modules put onto a solar thermal absorber. In principle, this is a brilliant idea. In practice, it’s not so easy.

Solar PV modules actually operate more efficiently when they are colder (because their electric resistance is lower) whereas for your showers you want your water to be hot. Under some conditions that works out perfectly – as long as your hot water cylinder is cold, the solar thermal part will actually cool your solar PV module down. But on a sunny summer’s day you ultimately want your solar thermal system to produce very hot water, and in fact UK legislation actually requires water to be heated to temperatures of 60-70C to kill dangerous Legionella bacteria. Ideally you’d want your solar panel to be colder than that.

You can get around this by using a heat pump to produce very hot shower water while pumping lower temperature water through your solar PVT panels. But that of course means additional expense – and much higher electricity consumption than the circulation pump of a normal solar thermal system. Also, it is worth pointing out that most PVT systems on the market today actually cost more than the combined cost of a conventional PV system and some solar thermal panels.

The Upshot: If you have enough roof space you’re probably better off installing separate solar PV and solar thermal systems.

2. Is there a case for thermodynamic systems? So-called “thermodynamic” systems (a fancy term that doesn’t really mean much) are essentially simple (unglazed) solar thermal panels connected to a heat pump. They haven’t been on the market for long enough for us to have good data, but there’s reason to be very sceptical. In the UK there simply isn’t much solar energy available in winter because days are short and the sun is low down and very often hidden behind clouds altogether.

Under those conditions, a “thermodynamic” system is essentially an air-source heat pump (ASHP) that relies on heat transfer from the ambient air to the solar panel. Manufacturers claim that the system will provide hot water at every time of the year – and that is probably true, but during dark winter days this energy is not solar energy but rather energy produced by a heat pump, which consumes a lot of electricity.

Furthermore, because the “thermodynamic” panels usually use a type of solar panel that’s less efficient than a normal (glazed) solar thermal panel, they’re probably also not a good choice during the sunnier parts of the year when a normal solar thermal system can produce hot water at a much lower electricity cost.

The Upshot: A large dose of scepticism is currently warranted when it comes to these systems. This is also reflected by the fact that their accreditation under the Microgeneration Certification Scheme (MCS) has been suspended, which means you won’t get Renewable Heat Incentive (RHI) income.

3. Are heat pumps right for me? The answer is “it depends”. Heat pumps use electricity to extract ambient heat (heat in the air or ground) and supply that heat into your house. Today most electricity is produced very inefficiently – for instance, our coal and gas power stations consume two or three units of fossil fuel heat energy for every unit of electricity they produce. If electricity from these inefficient power stations is used to run heat pumps, then these heat pumps need to be very efficient. Basically, your heat pump would need to supply three units of heat for every unit of electricity it consumed, otherwise you might be better off heating directly with oil or gas!

To work efficiently, heat pumps need to run at a relatively constant rate supplying heat at low temperatures. This is a realistic option for a (usually new-built) house that is well insulated and has underfloor heating with densely spaced pipes. In this case even when it is very cold outside the water in the heating system need only be lukewarm (maybe 30-35C). On the other hand, if the heat pump needs to supply much hotter water, for a badly insulated building or a building heated by radiators, then the efficiency of the heat pump will likely be too low to make it a good choice.

4. Micro hydro: yes or no? Hydropower is great, and if it benefits a whole community rather than one individual then all the better! Unfortunately, only a minority of communities in the UK have the kind of site that’s suitable for hydropower: A stream with a large flow rate of water and a good height drop. If you have a site of this type then it’s definitely worth exploring the option of installing a micro-hydro scheme.

5. Should I heat my house with biomass? Biomass can be a good choice, especially where wood can be sourced locally and/or for buildings where heat pumps would not work at high efficiency. But it’s important to stress that wood fuel is a limited resource and that there are potentially negative side effects to burning it (e.g. local air pollution from smoke, time lag between when CO2 is emitted and when a new growing tree absorbs it again). This doesn’t mean we shouldn’t burn wood, but it means we should try to use it as efficiently as possible. This means always reducing a building’s energy consumption first, and using the most efficient appliances available for burning wood. For example, modern log batch boilers (wood gasification boilers) get more heat out of the same amount of wood, and emit less smoke, than traditional wood stoves (or, even worse, open fires!).

Have a question about renewables and your home that we didn’t answer here? Check out our Home Energy Handbook, or give our Free Information Service a call!


New book from CAT provides a manifesto for the community energy revolution


On June 7th the Centre for Alternative Technology publishes what Transition movement founder Rob Hopkins has described as a ‘manifesto’ for a revolution in home and community energy. The Home Energy Handbook will increase community participation in energy projects, deepen social resilience and help to re-direct the profits of energy production back to the households and communities that generate, save and use it.

Based on progressive social values and tried-and-tested environmentally responsible technologies The Home Energy Handbook is the first practical book to cover all the key areas of home and community energy in one volume; from mapping out the great energy challenges of the 21st Century, through calculating and cutting your carbon emissions, to implementing practical energy projects in your home and community.

Rob Hopkins has described The Home Energy Handbook as “a hugely valuable resource for individuals, households, communities and local and national decision makers”.

“No other book offers such a complete and dedicated guide to all the major energy saving and renewable energy generation technologies, whilst showing how these technologies can be used to create social change,” says Allan Shepherd, co-author and publisher. “It is a powerful tool for anyone who wants to regain control of their energy future.

The Home Energy Handbook features ten inspiring case studies that show how community focused energy projects enhance living standards, cut carbon emissions and create community cohesion and resilience. Some also show how money earned from electricity generation can be used to support community services, cut fuel poverty and create employment opportunities.

Case studies include a self-build housing scheme in Bristol, a renewable energy scheme in the Scottish islands and a community woodland project in rural Lincolnshire. Technologies covered include: solar PV and thermal, insulation, energy efficiency, biomass wood fuel, heat pumps, ventilation, passive solar, combined heat and power, wind- and hydro power.

Please contact for review copies, pdfs, interviews, extracts or any media enquiries related to the book. 01654 705980
Contact for general media enquiries about CAT. 01654 705 952

Editor’s Notes

The Home Energy Handbook: A guide to saving and generating energy in your home and community

Allan Shepherd, Paul Allen, Peter Harper, Nicky Ison, Jarra Hicks

ISBN 9781902175713, 224pp, 189×246 mm, full colour, fully illustrated, £19.95

• The Authors: Allan Shepherd has written over 15 books, including The Organic Garden (a Daily Telegraph ‘Book of the year’) and 52 Weeks to Change Your World. Peter Harper is Head of CAT’s Research and Innovation department and co-author of Zero Carbon Britain 2030. Paul Allen is Director of CAT’s Zero Carbon Britain project and sits on the Science Advisory Council for Wales. Nicky Ison and Jarra Hicks are community renewable energy specialists.

• Endorsement: “The Home Energy Handbook helps communities and householders take control of their energy destiny with its fresh attitude, positive outlook and creative mix of practical information and inspiring case studies. Innovative and life-changing.” – Caroline Lucas, Green MP for Brighton Pavilion.

• Endorsement: “The Home Energy Handbook is a hugely valuable resource for individuals, households, communities and local and national decision makers. There is a revolution afoot in terms of how we imagine energy generation. This is its manifesto.” – Rob Hopkins, founder of the Transition movement.

• The Home Energy Handbook has been published with the support of the Carnegie Foundation and printed with support from Good Energy. For information about Good Energy contact

• The Centre for Alternative Technology is a leading environmental education centre based in mid-Wales striving to reach a realistic, achievable sustainable future through the dissemination of knowledge and skills for sustainability across all levels and disciplines. CAT is home to the Graduate School for the Environment, the Zero Carbon Britain project and the Wales Institute for Sustainable Education. Contact for general media enquiries about CAT.

CAT Publications publishes a range of renewable energy, environmental building and ecological books.