How much could we reduce our household CO2 emissions, exploiting the available technologies?

Let's consider different scenarios and analyse the energy consumption of some typical dwellings that we can find across Britain.

Energy consumption depends on many factors, such as the size, quality and age of the buildings, the insulation technologies adopted (if any), the energy efficiency of boilers, light bulbs, kitchen appliances and electronic gadgets, the outdoor climate, and, not insignificantly, the behaviour of the occupiers.

For these reasons, it is not easy to identify the typical average household in Britain, since its energy consumption is affected by many different factors.

What we can do is to take some possible examples and try to extrapolate an average British household consumption.

One of the worst scenarios in Britain is an old 100 m2 three-bedroom Victorian detached house, with no insulation, single glazed windows, a 10 year-old inefficient gas boiler, old kitchen appliances, incandescent light bulbs, and occupiers that don't use their thermostat and don't care at all about their energy consumption. A household like this can easily consume 30000 KWh/year just for the heating, as documented by David MacKay, professor at the University of Cambridge, in his book Sustainable Energy.

30000 KWh of burned gas energy corresponds to about 5507 KgC02/year, using the conversion factor proposed by the National Energy Foundation.

A more responsible household, still living in an old 100 m2 Victorian detached house, but maybe with double glazed windows and good use of their thermostat, could consume 20000 KWh/year for the heating, which is equivalent to 3672 KgC02/year.

An other example is a Victorian conversion. I currently live in a rented old two-bedroom 120 m2 flat, which is part of a big Victorian house with high ceilings, double glazed windows and an old gas boiler. I strictly control the use of the central heating by carefully using the thermostat and the whole family tries to use hot water responsibly. The total annual average gas consumption is about 25000 KWh, which is about 4590 KgCO2, which is roughly the weight of an African elephant!

Figure 1 - An African elephant, 4.5t

Sadly, these examples represent the majority of the residential buildings in Britain. As reported by the Passive House Institute, the British housing stock is probably the worse across Europe.

The typical British home has no insulation in the walls, very little in the roof, single-glazed windows, wind whistling through gaps in doors and windows and a redundant chimney sucking precious warm air into the sky. An inefficient boiler struggles to keep it warm by burning enormous quantities of fuel and spewing clouds of carbon dioxide.

The existing housing standard in Britain is hundreds of years old and needs to be replaced. There are millions of three-bedroom Victorian and Edwardian highly inefficient terraced houses across the UK. Additionally, there are millions of semis and detached homes built in the housing booms of the 1930s, 1950s and 1960s, and of course there are millions more built at other times, too. This legacy is responsible for 27% of the UK’s carbon emissions and, according to BRE, these homes will have to last an average of 1000 years before they are replaced because current rates of demolition are so low.

Possibly, this is the real problem. The best way to make an old British building energy efficient, is undoubtedly to tear it down and build a new one, but I'll came back to this point later on.

Let's have a look at what we can achieve just refurbishing and insulating an old Victorian or Edwardian house.

David MacKay carried out an experiment to evaluate the impact of different home improvements on the energy consumption of a typical semi-detached British house located in Cambridge over the period 2003-2008. Starting from an average annual gas consumption of 25000 KWh (4590 KgCO2), a number of improvements were made:

  • installation of a new energy efficient condensing boiler
  • insulation of external walls and roof
  • new double glazed windows
  • installation of an extra double-glazed front door
  • tight control over the thermostat settings
  • extremely responsible use of hot water and heating

These measures led to a reduction of the heating energy consumption from 25000 KWh to 5000 KWh per year, corresponding to just 918 KgCO2, with a net reduction of 3672 KgCO2 emissions.

This is a remarkable result, but, by MacKay's own admission, the result was to a large extent driven by the change in behaviour of the occupiers. In fact, although the total heating consumption reduction was a stunning 80%, the improvements in insulation reduced the leakiness (i.e. the loss of heat through the external "envelope" of the building, which is formed by walls, windows, doors, roof and floor slab) by just 25%, from 7.7 kWh/d/°C to 5.8 kWh/d/°C, which is still much leakier than any modern house.

Let's recap a bit. We started from the worst case of a typical British detached house, which can generate about 5500 KgCO2/year. A typical semi-detached three-bedroom house emits around 4600 KgCO2/year. Applying a big number of severe measures to improve the quality of the building and the behaviour of the occupiers, we can reduce the heating consumption emissions to about 920 KgCO2/year.

So far, we have considered just the heating consumption. What about the emissions due to electricity consumption? My current annual electricity household consumption is about 2600 KWh. I have all the typical kitchen appliances we can find in any kitchen, some are quite new and efficient, some others are not. I have energy saving light bulbs all over the flat and I keep under strict control any electricity use at any time. Therefore, although my electricity consumption is probably less than a typical British household electricity consumption, let's take it as the reference figure for the calculation. This annual electricity consumption corresponds to 1405 KgCO2 of carbon emission.

This is another important concept to explain. Let's consider the following equivalences:

1000 KWh of gas consumption = 184 KgCO2

1000 KWh of electricity consumption = 541 KgCO2

How can that happen? This happens because it is much more efficient to burn gas in a boiler on-site at home that burning fuel in a big centralized power station, convert the generated heat to electricity, transport this electricity to a substation near home, transform the electricity from high voltage to low voltage and finally give power to our kettles to make a tea. During this very long trip, we lose a lot of energy along the road. For this reason, to get the same amount of energy at home, we need to burn much more fuel at the power station, hence generate much more carbon dioxide.

The main concept here is that it is much better to generate electricity at home rather then in a centralized power plant very far away; and much better means much less CO2.

It's time to recap again. Considering the same electricity consumption for all types of households under analysis, we have the following scenarios:

  1. Very old and inefficient three-bedroom detached house: 5500 KgCO2 gas + 1400 KgCO2 electricity = 6900 KgCO2/year
  2. Old inefficient three-bedroom semi-detached house: 4600 KgCO2 gas + 1400 KgCO2 electricity = 6000 KgCO2/year
  3. Refurbished three-bedroom semi-detached house with tight thermostat settings and responsible occupiers: 920 KgCO2 gas + 1400 KgCO2 electricity = 2310 KgCO2/year, which is nearly the weight of a massive Range Rover.

Figure 2 - A Range Rover, 2.5t

Even though we have gone down a lot thanks to a number of drastic improvements, there are still 2.3 tCO2 spewed in the air. Can we get rid of them?

Of course a new building would be much better then that.

In December 2006, the government announced their ambition that all new housing should be built to zero-carbon standards from 2016; this means that the carbon emitted during a typical year should be balanced by renewable energy generation. Despite the UK being the first country in the world to adopt such a policy (from the worst to the best in Europe, at least on paper), the initiative was generally welcomed by the industry in principle, despite some subsequent concern over the practicalities.

The idea is to make a house independent from the electric grid and provide enough renewable energy generation facilities to cover in full the energy requirements of the building. The result would be as follows:

Zero Carbon Building: 0 KgCO2 gas + 0 KgCO2 electricity = 0 KgCO2/year.

This is actually possible: the trick is to reduce as much as possible the energy consumption of the building and at the same time generate on-site the small amount of energy required for the heating and other household needs.

1300 KWh/year is enough energy to heat and cool an average three-bedroom house designed and built according to the German PassivHaus standard, as described in details on The Passive House Institute web site. Adding other 2000 KWh for energy efficient appliances and gadgets we need to cover a total energy demand of 3300KWh/year. In London, this is possible by installing 18 Kyocera 210W PV solar panels occupying about 27 m2 on a South facing roof or by installing a small wind turbine.

We made it, we have managed to bring our carbon emissions to zero. However, this solution needs the construction of new houses, which is always welcomed, but not always possible. What about the millions of old energy leaking houses already existing across the UK?

The housing stock in the United Kingdom is amongst the least energy efficient in Europe. In 2004, housing (including space heating, hot water, lighting, cooking, and appliances) accounted for 30.23% of all energy use in the UK (up from 27.70% in 1990) as documented by the Department for Business, Innovation and Skills. The figure for London is higher at approximately 37%.

According to the Office of the Deputy Prime Minister, it's been forecast that the number of households in Britain by the end of 2011 will be 26.2 millions.

If each household generated 5000 KgCO2/year, this would add up to a stunning 131 millions of tCO2 per year. Just to give an idea of what this means, this weight is the same as 870 Emma Maersk cargo ships. Emma Maersk is the biggest and heaviest cargo ship in the world, it weighs 150,000t and is 400m long.

Figure 3 - The Danish Emma Maersk cargo ship, 150,000t

If we could line up 870 Emma Maersk cargo ships along the M1 motorway, we would go from London to York, which is about 216 miles or 348 Km; and this is just one year of emissions.

Figure 4 - London to York along the M1, 216 miles

The volume of one ton of CO2 is 556.2 m3, hence 131 millions tCO2 occupy 72862.2 millions of m3. How big is that? The Empire State Building, currently the tallest building in New York City, has a volume of about 1 million m3, which means that the annual total emission of CO2 of British households is equivalent in volume to 72862 Empire State Buildings, which would occupy one third of Greater London, packed one next to each other. This is pretty impressive.

Figure 5 - The Empire State Building in New York, 1 million m3

Conversely, if every house in the UK was a zero carbon PassiveHaus building, totally powered by renewables, the total emission would be 0 tCO2/year. It is shocking to realize that this would be possible in theory.

Of course, in practice this is "a little" less possible. But not completely impossible though.

I suggest we take just a little break before looking at a viable strategy to make that at least partially possible.

To wipe out 131 millions of tCO2 every year would be wonderful, wouldn't it?