How To: Sustainable Energy

Creating a sustainable world is one of the greatest challenges of our time.

How do we work practically towards sustainable energy?

What are the tools and knowledge we need to make the right decisions that make sure our actions add up to the goal of sustainable energy?











Context: Sustainable Energy without the hot air

In his book Sustainable Energy without the hot air, David MacKay of Cambridge University highlights an approach using quite straight forward maths for quantifying our use of energy in full and then calculating how much renewables we would require to provide that energy. The book also explores clearly, the solutions that are available for better transport, smarter heating and efficient electricity use.

It is an open source, free to read online book on sustainable energy that lays the groundwork for much of this section. Read the book online here:

David MacKay makes use of energy stacks to illustrate how much renewable energy is required to meet our use of energy and the importance of creating energy plans that add up.

Climate change and sustainability is a global challenge, and the OpenEnergyMonitor community, and nature of open source web projects like this is global. The following is an example of the UK energy context, but many of the solutions are from, and applicable, in a much wider context. There will of course be differences dependent on context such as more air con vs heating in hotter countries. For a global context of CO2 emissions see this useful publication and graphic.

The UK Energy use context 2012

Figures based on uk energy statistics documents available here

1: Total energy use per person in Britain.

2: Energy use divided up into primary sectors plus losses.

3: Losses and transport reallocated to domestic, services and industry use.

4: Breakdown by end use type


Data sources:

Source code for stack graphic can be downloaded here: stack03.txt (rename file extension to .html)



Energy used for each sector broken down by type of use

Left: Energy used in the service sector

Center: Energy used in the industrial sector

Right: Energy used in the domestic sector


Data sources:

Source code for stack graphic can be downloaded here: stack04.txt (rename file extension to .html)



Space heating (end use) accounts for 19.5% of total primary energy, or 28.6% 
of end use energy.

Building services (space heating, water heating, lighting & appliances and cooking) 
make up 30% of total primary energy, or 44.1% of end use energy.

Transport (end use) accounts for 26.3% of total primary energy, or 38.5% of end use

The sources of non transport losses are: Losses in distribution: 5%, 
Used by energy industry: 23%, Thermal power station losses: 72%



The following highlights some of the main solutions that significantly increasing the efficiency of our energy use so that the remaining energy demand can be provided by sustainable energy sources. For a more thorough analysis see in depth calculators such as the DECC 2050 calculator and CAT's Zero Carbon Britain report.

Better building fabric and better heating

An average UK house now
Floor area: 85m2
Space heating demand: 12284 kWh/year
Space heating demand per m2: 145kWh/m2.year
Primary energy demand:
Primary energy demand per m2: 335 kWh/m2.year

Graphic from the CAT ZCB Report

The state of the art: passivehaus: 90% less energy
Space heating demand per m2: 15 kWh/m2.year                         90% reduction on 2012 average house
Space heating demand per m2 (retrofit): 25 kWh/m2.year           85% reduction on 2012 average house
Primary energy demand per m2: 120 kWh/m2.year                     64% reduction on 2012 average house

CAT's Zero Carbon Britain scenario applies an average space heating demand reduction of 50-60% taking into account the variation and complexity of the housing stock.

To calculate the energy savings potential of your own house you can use the SAP 2012 building energy model available here: (Navigate to Extras > OpenBEM)

Sustainable heating systems
There are two main types of sustainable heating systems: heatpumps powered by sustainable electricity and biomass from well managed forests. A well designed heatpump installation can deliver 3-4 units of heat output for every 1 unit of electrical input. A heatpump powered by renewables requires 66% (2/3rds) less primary energy than other heating systems.

A house that starts with a space heating demand of 40 kWh/d achieves a 70% reduction in space heating energy demand through better insulation and draught proofing, the new space heating demand is 12 kWh/d. This could then be supplied by a heatpump requiring just 4 kWh/d of primary energy demand from renewable sources. A total energy saving of 90%.

Better transport

Electric cars: 81% less energy
Amazing efficiency gains are also possible in transportation. A typical petrol car uses around 80 kWh to travel 100km [ref]. An electric car such as the tesla roadster uses only a fraction of this amount to travel the same distance around: 15 kWh per 100km [ref], which gives us a potential 81% reduction in energy demand potential for personal transportation.

Electric trains: 93% less energy
For longer distances, such as a trip climbing, or skiing, to the Alps, from the UK. A very normal looking electric train when full, consumes only 1.6 kWh per 100 passenger-km [ref], average rail transport may be closer to 6kWh per 100 passenger-km [ref]. At 6 kWh per 100 passenger-km, taking the train requires 93% less energy than the same journey by car with one occupant. Moreover, an electric train can be powered directly from renewable electricity as it's directly linked to the electric grid by the overhead wires.

An other important aspect of sustainable transport is reducing the need for transport in the first place or reducing the number of miles that we need to travel. The internet and associated web technologies makes it easier to work remotely reducing the need to commute as often. Linked in with our decisions on building design is building location and wider questions of planning. Things like the distance between housing, work and amenities and how walkable/bikeable the area is.

Incredible potential gains in efficiency

Almost 70% of the UK's end use energy requirements are for space heating and transport, and for these two large energy consumers there exists solutions that can achieve upwards of 80% energy use reduction with no reduction in comfort or transportation amount.

Better manufacturing

The energy required for manufacturing and the available solutions are perhaps more complex than those available to building energy demand and transport. One of the most popular books on improving manufacturing is the book Cradle to Cradle by Michael Braungart and William McDonough who argue for a fully cyclic material resource stream and give numerous real world examples of positive outcomes from cradle to cradle thinking applied.

Powering up with renewable energy

The remaining primary energy requirement after the large energy reductions from better building fabric, heating systems and transport are applied can then be provided by renewable energy. The Zero Carbon Britain report from the Center for Alternative Technology goes into depth on how this can be done and is well worth a read. The Zero Carbon Britain report also look in detail at the needs for energy storage and demand management at different timescales.

The energy stack on the right shows the resultant Zero Carbon Britain scenario compared with the 2012 national energy statistics stack divided by end use as above.

The efficiency improvements made possible by better buildings and transport are clear to see.







One of the clear things from the above energy analysis, is that we have a great amount of power over our energy future. If we all apply these solutions at home and in our workplaces with an eye to how it links to the big picture, then the sum of all our individual actions can achieve the transformation to our energy system that is needed.



A systematic approach to implementing the above solutions is to:

  1. Start with energy assessment of our buildings and transport use to understand where we are now.
  2. Second, to model the application of measures, and devise a mix of measures, that achieve the desired target.
  3. Third, the important part, to apply those measures.
  4. To check once those measures are applied, they perform as designed.

Much of the work that we have been doing so far focuses on creating tools that helps with step 1 and step 4. All of the tools are open source and available to anyone to use.

Create your own energy stack to compare with the national average, and the stacks for the average affluent person that David MacKay generates in his book
Login to and then navigate to Extras > Energy
For source code and development see

Electricity assessment and monitoring

The appliance list tool is a useful exercise for answering questions such as, how much electricity can be saved by using low energy lighting such as LED's? How much electricity is saved by turning off lighting when not in use?
Login to and then navigate to Extras > Report > Appliance list
The Electricity audit and savings case study provides more background on the appliance list exercise

Realtime monitoring: Build an electricity monitoring system that provides detail information on electricity consumption.

Whole house assessment including building fabric and heating

Carry out a full energy performance assessment of your house using OpenBEM and open source implementation of the UK's standard energy performance assessment procedure for domestic dwellings (SAP 2012). We have been working on this online SAP calculator in collaboration with carbon coop who will be using it as part of their retrofit assessment tool. Learn more about carbon coop here.
Login to and then navigate to Extras > OpenBEM
For source code and development see

Realtime monitoring: Use realtime temperature and heat input monitoring coupled with a dynamic building model to measure the heat loss rate of a building in order to cross check the theoretical figure derived in the OpenBEM SAP calculation. See: Building thermal performance monitoring and modelling

Performance monitoring of installed measures


Links of further interest

UK Energy use context (2008)


Amateur Earthling blog: Climate Change and the Insurance Industry climate science by climate scientists