How the environmental footprint calculator works - please give input

I’m documenting below how the calculator works. Please give input on how you think it should be improved by replying to the relevant post.

Let’s make it better together!


What home do you live in?

Determines the kwhrs of heating energy used (sourced from energy saving trust):

  • Flat; 8500
  • Mid terrace; 12500
  • Semi detached; 15000
  • Detached house; 18000

How many bedrooms are in your house?

Gives a multiple to that energy usage (using some trial and error); 1 (0.75), 2 (1), 3 (1.1), 4 (1.25), 5 (1.5), 5+ (2)

What is your main source of heating?

Gives the carbon multiplier using this ical source of data, which includes kWh of heat delivered:

Gas: 0.215 kgCO2 per kwHr Oil: 0.320 kgCO2 per kwHr Electric: 0.361 kgCO2 per kwHr Wood: 0.155 kgCO2 per kwHr

What is your source of heating (for electric only selected)?

This is to account for those using heat pumps. With 3 times more heat energy produced per kwHr of input with an air source heat pump this provides a means to calculate that. The factors used are:

Air source: 0.313 Air to air: 0.313 Ground source: 0.249 Water source: 0.222

Are you on a renewable tariff

This is really either or; if on a renewable tariff no carbon emissions from electricity used - but I stand to be corrected on this!

What temperature do you usually have your house

There is a factor put in place here pulled off the energy saving trust which is a 24% saving or increase of heat energy used, from a baseline of 18-20 degrees.

Have you done any of the following to improve your energy usage

I’m not going into too much detail here but have used these factors pulled from the energy saving trust for these (below). For the solar I have used the a reduction in electricity consumption of 1/2 - which is fairly accurate methinks - but again am happy to recieve other input on this.

% energy saving
Solid Wall Insulation 14.27%
Cavity Wall Insulation 8.06%
Installing Loft Insulation (from none) 7.42%
Single to Double Glazing Windows 6.59%
Turning Down Heating by 2 degrees 5.79%
Installing Hot Water Pipe Insulation 4.03%
Solar Water Heating 3.59%
Installing Hot Water Tank Insulation 0.14%
Under Floor Insulation 2.26%
Double to Triple Glazing Windows 1.65%
Install Water Efficient Shower Head 1.19%
Turn off heating in unused rooms 0.79%
Improving Hot Water Tank Insulation 0.73%
Improving Loft Insultation 0.65%
Radiator Reflector Panels 0.02%
Draught Proofing Doors 0.01%

What savings will you pledge to make or have made as a result of interacting with Better Century?

Heating energy use can be determined by the calculations above. To calculate the electricity use I have multiplied the total heat energy by 0.4, which is a reasonable conversion factor.

The carbon footprint is determined by

(Total Heat Energy used (unexposed) - any heat energy savings) x ‘What is your main source of heating’ +

(Total Electricity Energy Used (unexposed) - electric usage savings) x (0.361 (electricity carbon emissions) x Are you on a renewable energy tariff (with a zero being used to eliminate emissions if you are))

The water footprint is determined by giving each person in the house a baseline of 50m3 of water footprint and then multiplying this by reductions of water use through reducing length of shows or number of baths or installed water efficient shower head.

The other reductions are determined by using similar assumptions as above


The underlying data to calculate food impact has come from Our World in Data Food Greenhouse Gas Emissions from the Supply Chain. This data has been downloaded and married against Uk Government Data Quantity of food and drink purchased for UK households (averages per person per week) data. This allows for us to determine the average spend against KG of Food, KG Carbon Emissions, Land Use and Water Use.

Where do you get most of your food from?

This is a question to help calculate food miles associated with getting food to an individual. We have calculated the food and packaging impacts associated from food from Our World in Data, and have extrapolated the following values to give multiples of 0.9 for Local Market and Veg Box Delivery and 1 for Supermarket, which is used to determine carbon emissions associated with these choices.

Do you do anything to avoid packaging on the food or drink you buy?

This is used to determine whether there are any reductions in packaging from food which is bought.

  • No packaging = 0
  • Avoid by buying non-packaged where I can = 0.8
  • Always get loose fruit and veg without packaging = 0.6
  • My food and drink very rarely has non paper or glass as packaging = 0.3
  • I do nothing to avoid packaging = 1

How much do you spend on food and drink per week? (for each person you shop for)

This gives a multiplier value against the 380KG of food bought each year (determined from average UK consumption data). The values simply reflect the spend up or down from £40-50.

How much food or drink do you buy out every week for yourself?

This gives an assumed value of 7.8kg of food bought per year for each value, which assumes that £5 gets you 150 grammes of food or drink.

What is your diet?

This a multiplier for land use, water use and carbon determined from Our World in Data and asserts that a reduction in certain foodstuffs results in the purchase of the equivalent weight of other foodstuffs which the individual will eat. The multiples are calculated against an average UK consumer:

  • Vegan: 0.43
  • Vegetarian: 0.81
  • Pescarian: 0.81
  • Flexitarian: 20%; 0.98, 40%; 0.94, 60%; 0.89, 80%; 0.85)
  • Meat eater: 1

How much food or drink do you throw away or waste when eating out?

This calculates the total weight of food determined from the above values multiplied by the percentage.

Annual impact from the food you eat

The KG of food that an individual eats is calculated by using a 380.4KG of food per year from the UK average consumption data multipled by values determined above. The calculus is:

  • Amount of Food eaten annually (KG) = (380.4 x How much do you spend on food and drink per week) + How much food or drink do you buy out per week

Food waste footprint

This uses the assumed value of 43KG of waste per person per year from food bought. This was derived from 61.4KGCO2e from packaging (World In Data against Average UK Food Consumed) divided by 1.4 (1kg plastic = 1.4 kgCO2e when burnt) to convert this into 43KG waste. The calculus was subsequently:

  • KG= 43*( How much do you spend… * Do you do anything to reduce avoid packaging… )

Food Carbon Footprint This uses a multiplier of 5.3KGCO2e per KG of food/drink as calculated from average consumption and global emissions data. The full calculus to get the value is

  • tCO2= = (Amount of Food eaten annually x 5.3 x (‘What is your diet’ x “Where do you get most of your food from”)/1000 + (Food waste footprint*1.4)/1000)

Food land use footprint

This uses a multiplier of 22.2m2 per KG of food/drink as calculated from average consumption and global emissions data (and there are 10,000 m2 in a hectare). The full calculus is:

  • hectares = (Amount of Food eaten annually x 22.2 x (‘What is your diet’)/10,000 =

Food water footprint

This uses a multiplier of 1208.5 ltrs of water per KG of food/drink as calculated from average consumption and global emissions data.

  • m3= ( Amount of food yo… 1208.5 ) x “What is your diet?” /1000

What savings will you pledge to make or have made as a result of interacting with Better Century?

Percentage of meat and diary taken out of my diet

The values of meat and diary taken out of your diet are a direct value multiplier (e.g. 5% = 5)

Growing my own food (indicate percentage)

Again a direct multiplier (e.g. 5% = 5)

Avoid packaging on the food or drink

This has some assumed multiplier values, which are reverse of the above to get savings:

  • Produce no waste from food or drink I buy = 1
  • Avoid by buying non-packaged when I can = 0.2
  • Always get loose fruit and veg without packaging = 0.4
  • My food and drink very rarely has non paper or glass as packaging = 0.7
  • Make no changes = 0

Annual Savings

Food carbon footprint reduction

The below calculation uses assumptions from above. The first part calculates a 2.89kgCO2e saving per KG of meat or diary which isn’t consumed (World in data derived multiple), with the second part calculating savings from transport and packaging from growing your own, using a 0.58 value (derived from world in data).

  • tCO2 = (( Percentage of meat you buy /100) x Amount of food you eat annually ) x2.89 /1000 + (( Growing my own food /100)* Amount of food you eat annually )*0.58/1000

Food land use footprint reduction

Food land use follows the same trend, but this time uses 14.9m3 per KG as the land use change for cutting out meat and diary and growing your food from home.

  • hectares = ((( Percentage of meat… /100) x Amount of food you buy… ) + ( Growing my own food… /100) x Amount of food you buy… ) x 14.9/10,000

Water use footprint reduction

Water use strangely uses exactly the same calculation as land use as the water saved is equivalent to land used.

Waste use footprint reduction

This waste footprint reduction uses the average 43KG of waste per person (explained above) to show savings in waste from avoided packaging and growing own food.

  • KG= 43 x Avoid packaging o… + (( Growing my own fo… /100) x 43)

Please do chip in your views below to the calculations used.


How many vehicles do you or your family own?

A direct value is used for this

What are these vehicles?

gCO2 per KM is used for each of these vehicles as determined by the values as prescribed in the answer (with conversion to miles) and the Low Carbon Vehicle report which details increases in carbon from manufacturing batteries for electric vehicles.

  • Electric two wheeler: 20 (LCV Report)
  • Car/van electric: 30 (LCV Report)
  • Motorbike: 96
  • Car/Van - Ultra efficient hybrid (<100gCO2/km): 144
  • Car/Van - Small (100 - 130gCO2/km): 177
  • Car/Van - Standard (130 - 150gCO2/km): 225
  • Car/Van - Large (150-200gCO2/km): 273
  • Car/Van - Pickup or Large SUV (>200gCO2/KM): 370

How far do you travel in these vehicles every year?

This is simply a value to multiply against the above values

Average occupancy

This is used to derive a personal carbon footprint from using the above vehicles. We haven’t quite factored these in as a fair division for personal carbon footprint though. The values are:

  • One: 1
  • Two: 0.7
  • Three: 0.5
  • Four: 0.4
  • Five: 0.3

Have you bought longer lasting tyres for your vehicles?

This is used to calculate savings in waste from tyres. It gives a multiplier for tyre waste per mile driven, which is derived from the average weight of a tyre multiplied by 4, with the assumption that tyres are replaced every 30,000 miles. This gives the following values:

  • No - just standard: 0.0005
  • Yes - 40,000 miles durability: 0.000375
  • Yes - 50,000 miles durability: 0.0003
  • Yes - 60,000 miles durability: 0.00025

In an average year how many hours do you spend flying?

In an average year how many hours do you spend on a train?

In an average week how many hours do you spend on the bus?

Domestic flight DEFRA conversion factors (advisory factors for businesses to calculate emissions) are used to create these values. Flights assume 500m/hrs, trains 52 miles per hour, and buses 20 miles per hour.

Annual impact from transport

Transport Carbon Footprint

To pull this together we also wanted to include embedded manufacturing costs from vehicles owned. The Lifecyle Analysis from Low Carbon Vehicles was very useful for constructing this value. It was determined that it was fair to assign a 0.6 tCO2e value for each vehicle owned on top of any other emissions value created. The calculus therefore was:

  • tCO2: (What are these vehicles? x How far do you travel… x What is the average occupancy…) /1000000 + (Number of vehicles x 0.6) + (Flights + Trains + Buses)/1000

Transport Waste Footprint

To pull together these values we extrapolated data from the Low Carbon Vehicle Lifecycle analysis for waste allowing us to identify that there is 151KG of plastic waste in a vehicle, giving a value of 12.6KG a year (giving a generous 12 year vehicle lifespan). We also used the tyre waste value, giving a calculus of:

  • KG: How many vehicles… *(151/12)+( How far do you tr… * Have you bought l… )

** Transport water footprint

The about of water used in constructing a vehicle is on average 150,000 litres. Per KG of plastic created you need 5,000 litres of water. Assuming a 12 year lifespan we therefore did the following calculation:

  • m3: How many vehicles… *(150/12)+( How far do you tr… * Have you bought l… *5 )

What savings will you pledge to make or have made as a result of interacting with Better Century?

This uses multiples as applied from above, and then uses the following calculations to established pledged savings:

Transport carbon footprint reductions

Got rid of one ca… *0.6 +( Move to an electr… *0.6)+( Given up flying o… 50.09) + ( Reduce car use by… * 0.2)+( Reduce car use by… *0.4) +( Reduce car use by… *0.6)+( Reduce car use by… * 0.8)

Transport waste footprint reductions

Got rid of one ca… *(12.6/9)+( Started using long-lasting tyres… * 10000 * 0.00025)

Transport water footprint reductions

Got rid of one car… *(12.5/9)

If you have any comments please share

Linking these two topics:

Calculating the impact from things you use

How many items of clothing do you buy new every year?

To determine the impact of clothing we looked to find a baseline of KG of clothes bought by each person each year. We used Statistica Data to establish that the average number of pieces of clothing were 33 pieces. We then found data on the average weight of clothing items from Parcl - averaged this data getting a value of 0.94KG per item of clothing. This was then used it as a multiple to establish the average weight of 31kg.

A value was then used to determine the weight of clothes for purchasing:

  • 0-10: 4.75
  • 10-20: 14.75
  • 20-30: 23.75
  • 30-40 (average): 33.25
  • 40-50: 42.75
  • 50-60: 52.5
  • 60+: 71.25

How many pairs of shoes do you buy new every year?

We could find much data on the average number of shoes bought so we used data in an article from Sun which identified in Britain we buy on average 3 pairs of shoes (welcome other suggestions :smile:).

To establish the weight of shoes (and for all other assumptions) about environmental impact we found this very useful life-cycle assessment that gave an average value of 1 KG per pair of shoes.

This meant that the number of shoes = the KG value.

On average every week how much do you spend on non food or drink household items? (including health and beauty products)

We needed to find a value of waste from these items, which was difficult to find. We therefore made some very broad assumptions. For each £5 there would be 0.1KG of waste - which assumed the average weight of a bottle is 20grammes and you would get 5 bottles (e.g. detergent/bleach) for your money. This meant each of the steps in value were given a multiple against 0.1.

On average every week much time do you spend out of the house using facilities for leisure activities?

This was used for carbon emissions. We assumed for each hour in a leisure facility you would use 2.73kWhrs per day (which is equivalent to being at home) and then used the assumption that 10 hours in a leisure facility equalled the energy use of a single day at home. We then multiplied this against the carbon emissions from using gas heating 0.316 (as used for homes). The calculation was:

(Number of hours x 52 (weeks))/10 x (0.316 x 2.73) = 8.971 kgCO2e (for two hours)

This then gave a kgCO2e per hour spent in a leisure facility:

  • 1-3 hrs: 9
  • 4-6 hrs: 22
  • 6-9 hrs: 31
  • 9-12 hrs: 50
  • 12-15 hrs: 60
  • 15@ hrs: 90

How many nights a year do you stay at a hotel or resort for leisure purposes?

We used this to also determine carbon emissions. The assumption was broad saying that for a night in a hotel you would use more than what you would use at home, we assumed a value of 3kWhrs to stay at a hotel @ 0.316KGCO2 per kWhrs (gas heating). The values there were:

  • 1-10: 4.74
  • 10-20: 14.22
  • 20-30: 23.7
  • 30-40: 33.18
  • 40-50: 42.66
  • 50+: 56.88

What of the following technological items do you have in your house?

These were difficult values to find but we did manage to truth the majority of them against lifecycle assessments. Each of these was given a value of 1 which we then multipled this against to get KG of waste and KG of CO2.

Manufacturing Annual Lifetime Total Carbon emissions KG Waste KG Waste Each Year
TV 300 52 8 89.5 7 0.875
Washing machine 240 10 24 77 7.7
Laptop 71 7 10.14285714 2.3 0.3285714286
Tablet 80 7 11.42857143 0.59 0.08428571429
Home desktop 7 15 7 1
Power tools 16.22 7 2.317142857 4 0.5714285714
Hair dryer 16.22 7 2.317142857 1 0.1428571429
Sound system 71 7 10.14285714 7 1
Home printer 2 18.3 3 1.5
Mobile phone 31 15.7 5 21.9 0.14 0.028

What best describes your attitude to technology?

This gave a multiple we’d use to establish KG of Waste and KGCO2 from each of the items a respondent gave to the above question. We gave the following values:

  • I use it until it dies: 1.3
  • Where possible I will get items fixed to extend their life: 1
  • I look for opportunities to upgrade devices before their lifetime is up: 1.6
  • I’m a techno junky - I love using and buying new stuff: 1.9

Do you do any of the following to reduce your impacts from things you buy?

Some broad values (some only proofed I’m afraid (links below)) were used to give a calculation as a reduction factor against the particular answer to an above question:

  • Buy clothes from ethical sources: 0.7 (multiplier)
  • Buy shoes from ethical sources: 0.7 (multiplier)
  • Use my clothes and shoes as long as poss then exchange: 1.5 (division factor)
  • I buy second hand clothes: 1.3 (division factor)
  • Use re-usable nappies for my children: 0.15 (as a multiplier to establish t of waste reduced (from life cycle assessment source))
  • Use refillable coffee cup: 0.07 (as a multiplier to establish t of waste reduced (from life cycle assessment source))
  • Avoid buying short lived disposable produce: 0.1 (as a multiplier)
  • Use refillable or non plastic packaged products: 0.1
  • Stay in eco friendly resorts and hotels: 0.5 (used for carbon reductions from staying at hotel)

Annual impact from things you use

To get any of the values above we established a ‘Things you buy weight’ and 'Things you buy carbon emissions), which is for all of the technological items. We used values from the table above to give a weight:

  • Things you buy weight (KG): ( TV - F521033 *0.875+ Dishwasher *7.7+ Washing machine *7.7+ Laptop - F521070 *0.32+ Tablet - F521072 *0.08+ Home desktop comp… *1+ Power tools *0.57+ Hair dryer *0.14+ Mobile phone *0.028+ Sound system 1 ) What best describ…

  • **Things you buy Carbon Emissions (tCO2): (( TV - F521033 *89.5+ Dishwasher *75 + Washing machine *100+ Laptop - F521070 *30+ Tablet - F521072 *36+ Home desktop comp… *45+ Power tools *5.9+ Hair dryer *5.9+ Mobile phone *66+ Sound system 30)/1000) What best describ…

Things waste footprint

The first of the calculation below established the waste from clothes, the second shoes, third takes off savings made using a multiplier of 10KG, and the forth includes technological items.

  • Things Waste Footprint (KG): How many items of clothing do you buy every year… /( Use my clothes and shoes as long… x I buy second hand… x Buy clothes from ethical sources ) + ( How many pairs of of shoes * Buy shoes from ethical… ) + 10 - (10*( Use re-usable nappies + Use refillable coffee… + Avoid buying short term… + Use refillable or non-package items… ))+ Things you buy weight

Things carbon footprint

The first part of the calculation looks at clothes, giving a multiple of 23.2KGCO2 per KG of clothes (taken from WRAP report). The second part looks at shoes and gives a multiple of 5.725KGCO2 per KG of shoes (averaged from shoes in this life-cycle assessment). We then include leisure facilities and hotels (which are already in values of kgCO2 and then converted into tonnes. We then use a value of 1.4 KGCO2e for each 1 KG of waste to include waste factor.

  • tCO2e: (( How many items of clothing… x Buy clothes from ethical sources x 23.2)/1000) +( How many pairs of shoes * Buy shoes from ethical sources x 5.725) /1000+((( On average every month … leisure facilities + How many nights at a hotel… ) x Stay in eco friendly… )/1000)+ Things you buy can buy carbon emissions… +( Things waste footprint *0.0014)

Things water footprint

We used data from the WRAP Report identify a Water use per KG of clothing, which was 7,060 litres for each KG of clothing. This then gave a fairly straightforward water calculation (which didn’t include Things you buy or shoes):

  • m3 water: ( How many items of clothing… * Buy clothes from ethical… *7060)/1000

Things land use footprint

Finding data for land use was really hard. What we did was establish a land use for each item of clothing. To do this we assumed cotton was predominantly used. A report was found identifying the KG per hectare of cotton production in China, to which we used an average finding that 1434KG are produced from 1 hectare. We found a report which gave a value of 8 onces of cotton were needed to produce one teeshirt. We then got a value of 0.158 m3 of land to produce 1 teeshirt. We also thought we’d do the same for a pair of jeans with this report giving a value of 0.68KG of cotton to produce a pair of jeans, giving a value of 0.42 hectares to produce a pair of jeans.

We thought it fair considering these calculations to give a value of 0.3 m3 for an average item of clothing, and used for the following calculus to give hectares of land used:

  • Hectares: ( How many items of clothing *0.3)/1000

We acknowledge that mineral extraction for things you use and shoes haven’t been included - we would love some data if anyone has any

What savings will you pledge to make or have made as a result of interacting with Better Century?

Similar calculation to above were used to identify the savings:

  • Carbon footprint reductions (tCO2e): (( How many items of… *( *Buy less clothes… + *Buy clothes and … ) *23.2)/1000) +(( How many pairs of… *( *Buy less clothes… + *Buy clothes and … ) *5.725) /1000)+(( How many nights a… * *Stay in eco frie… ) /1000)+(( Things waste foot… *1.4)/1000)

  • Things waste footprint reductions (KG): ( How many items of… + How many pairs of… )*( *Exchange and buy… + Buy clothes and … )+(10( *Use re-usable na… + Use refillable co… + *Avoid buying sho… + *Use refillable o… ))+( Things you buy we… * *Use the technolo… )

  • Things water footprint reductions (m3): ( How many items of… 7060)( *Buy clothes and … + *Buy less clothes… + *Exchange and buy… )/1000

  • Things land use footprint reductions (hectares): (( How many items of… 0.3)/1000)( *Buy less clothes… + *Buy clothes and … + *Exchange and buy… )

Please provide comment on the above by hitting reply to this post - we want to improve the calculator!

I realised there was a flaw in the calculus around the hectares of land used to grow food. I was stunned when mine came up at 9 hectares. I realised there has been a flaw in the calculations which has just been fixed - there are 10,000 m2 in a hectare, not 1,000 m2 in a hectare. Important as now the food I eat results in me using 0.9 hectares of land!

Sorry if this confused others as well!

HEATING options too limited. We have radiators attached to our wood burning stove which we use in winter evenings, and at other times we use immersion heater topping up heat from solar thermal panel. We have 12 solar panels helping reduce electricity demand. We use a gas fire to warm the living room.

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Food waste. No mention of composting. We compost everything we can but put in industrial compost collection anything organic that would attract rats.


No healthy food options at local markets.

No mention of growing own food except in list of improvements.

We use local organic shops and Suma with our wholefood cooperative group, but some basic things from supermarkets.

Typo 'Meat and Diary" heading.

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No mention of bicycles. Surely that’s one of the biggest changes going on.

Hi Tom,

This is a very comprehenisve piece of work and I applaud the attempt. I will work my way through the methodology and post my suggestions as I go. I am a private individual with no specific axe to grind, but working in my local community to support our vision (Stroud District) to be carbon neutral by 2030. One thing I have spent the last few months researching is carbon footprints and I too have been developing a personal tool using publicly available data and references.

My first comment is why guess/try to calculate what people use for heating? We all know accurately - from kWh on the gas bill (a requirement by law to have the annual amounts stated), from litres of oil delivered, from sacks of coal delivered or from amount of logs or woodchip burned in a year.

I am in a dedached house and use only 6,500 kWh of heating gas. Using the EST figures is highly misleading.

Same goes for electricity, the annual amount will be on your bill.

Saves guessing and saves having to regularly update the guess (as it does change as the nation changes habits).

The figures you are using for energy intensity of fuels are well out of date. .gov publish figures several times a year for company reporting of carbon footprint, so this gives the latest (delayed by 6 months) view of carbon intensity of fuels.

Electricity is currently 0.2556kgCO2e/kWh Gas is: 0.1838kgCO2e/kWh Heating Oil: 2.5404kgCO2e/litre Coal: 2.744kgCO2e/kg Wood logs: 0.063kgCO2e/kg

I agree that in the normal state of things that ~50% of solar generation is directly used in the home. Again, you can know exactly how much is generated from the quarterly FIT statements. If you use the actual kWh from electricity bills in the first place, this will have already accounted for the solar generation by reducing your bills. If you don’t have PV then a fair assumption is that 50% is used (I monitored my energy use and can confirm this). However, some people like me now have battery storage. This results in ~95% of the solar energy staying on the property. So this needs to be included as an option, as more and more domestic battery systems are being installed.

With solar generation, however, you need to account for 100% of the energy as a reduction in your footprint, whether or not you consume it. Reason being is that it IS 100% renewable energy and when you export it onto the local grid, you reduce the carbon intensity of the local grid (i.e. the neighbour uses what you don’t).

The same cannot be said for having a 100% renewable tariff. This is a hot potato at the moment, because of the way that Ofgem account for renewable energy from suppliers. There are two markets, one for the renewable energy generated by wind/solar/biomass etc. and one for the REGO (renewable energy guarantee of origin) certificate. These certificates are often not sold with the energy, so many so-called green energy tariffs back up the electricity supplied by REGOs bought on the REGO market, but the energy is just the same brown energy from the grid as the rest of us. To truly make a difference with your energy supply you need to buy from someone who 1) builds their own new generation or 2) only buys the power WITH the REGO from generators.

Both Which? and EST have looked into this recently (links to follow) and conclude that there are only a handful of suppliers who fall into this category: Good Energy, Ecotricity, Octopus Energy and Green Energy.

The truth is that it is government action that is greening the grid. Even these 4 suppliers don’t build assets for 100% of their energy needs - they buy green energy + REGO from the market. It is the likes of Scottish Power Renewables, Dong Energy, SSE Renewables, Fred Olsen etc. who have the size, and resources, to borrow the £billions needed to build offshore wind farms, 100MW solar parks etc. The smaller companies cannot do this. The goverment sets the direction for the grid, gets new generation through the annual auctions for the CfD (contract for difference, their mechanism to encourage new large-scale generation to be built) and ultimately that is what makes the grid greener. People buying energy from green tariffs account for a very small proportion of the energy that an offshore wind farm produces - they simply sell to the grid in the normal way (+ sell the REGOs so there are a lot of REGOs at very low prices available for the so-called green tariffs to buy. The REGO price bears no relation to the energy price).

In fact the reduction in the carbon footprint of the UK in recent years has largely been one of a reducing grid carbon intensity (closing coal power stations and building renewables and dash to gas) - this has done the “heavy lifting” for the UK. See the CCC report Table 3.1 with progress on KPIs

There is perhaps another route to have truly 100% renewables (and therefore zero carbon footprint for electricity) which is to be part of an energy club - a group of people who club together to buy energy direct from a local generator connected to the same sub-station as they are. Using smart meters and the fact that this is at the local, distribution, level means that you are truly getting electrons from that green generator. There are already examples of this happening now e.g. Energy Local offers a scheme in co-operation with Octopus Energy (who are pioneering many smart-meter based systems).

So to conclude this bit, a 100% renewable tariff may not be renewable and probably won’t cause new renewable generation to be built. We all get the same electricity down the wires at whatever the current carbon intensity happens to be (currently 0.2556kgCO2e/kWh), driven by government policy and targets to achieve net zero. So a renewable tariff is not the same as having zero carbon footprint for your electricity - it is more of a signal to the market that you want the grid to be greener. The grid is only as green as it is on average, unless you 1) self-generate (eg solar PV or mini-hydro) or 2) be part of a pooled buying scheme to get energy from a local generator at your sub-station level.

Hope this helps! More anon… Alex

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Which? link on renewable energy tariffs:

EST Link on renewable energy tariffs:

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Link to Energy Local, buying energy direct from a local generator on the same sub-station as you:

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Thanks Alex. These are great additions. The factors used for heating should be changed, but will bring the footprint down - I liked the factors used as they were for actual heat delivered - not wholly accurate and easy to change.

I think we should include an option for people to enter in their data - will look at the technical feasibility of this.

On renewables tariffs it’s quite tricky - surely those on renewables tariffs should feel some sense of reward for making this decision?

Thank you for your input!

Hi Tom, the icax data is for the CURRENT (i.e. today) carbon intensity, so will go up and down on a daily basis (or 1/2 hour basis) according to what is happening on the grid. So these change every 1/2 hour. The .gov figures will be 12 month average. So of course will need to be updated each time the .gov issues an update, but much less than every half hour! Unless you intend to link to the carbon intensity API and pull in live data?!

As I said, renewable tariffs are a thorny issue because of the REGO situation. So, whilst you may want to feel good about chosing a “green” tariff, not many are really green - as I have indicated. Of the companies I named, only one (Green Energy) generates 100% of customer needs from its own generation. Ecotricity generates about 15% of their needs, Good Energy a little more (this data may be found on their websites) - the rest is bought on the open market (from renewable generators with the RGEO attached).

So maybe if you select these companies you can feel a lot better - at least they are building some new generation, but it is only in the MW scale not GW. That is the sense of reward. Also many of the green tariffs come out cheaper than buying energy from the standard tariffs, so there is another reward. Octopus Tracker, for instance, is the cheapest in the market and they buy 100% of their customer requirements from green generators along with the REGOs.

I think the whole REGO market needs reform becasue companies can claim a green tariff without buying any energy from a green generator!

As I said the volume of energy bought by retail renewable tariffs is a tiny proportion of the total ~20GW of wind and solar, 1.3GW of hydro and 7.5GW of bio energy capacity. Government policy drives the rise in renewables, not retail choices. And this impacts the grid energy mix for everyone.

It is tough to explain that chosing a “green tariff” does not lower personal carbon footprint. The rise of smart meters and smart tariffs (like Octopus Energy are doing) may give a real opportunity to buy “direct” from the generator (they can match your consumption against the generation of the wind turbine or solar PV at the time of consumption) - then that can be claimed as a carbon reduction.

Also, as I said, your own Solar PV is a direct reduction in your footprint and there you get 100% of the generation credited to your carbon reduction.

Of course energy companies are selling green tariffs as a positive choice, some promising to build new generation. But a green tariff does not lead to your carbon footprint reducing. It does send a clear message that more renewable generation is demanded by the consumer. And eventually we all benefit from the reduced carbon intensity of the grid.

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If you have a heat pump - yes it has the “multiplier” in that you get 4kWh of heat for 1kWh of electrical input - but the point is this will all be covered by your electicity bill kWh, there is no need to calculate a new factor. icax want to show how they stack up against using gas, I appreciate.

If you want to model switching from gas heating to a heat pump, then sure you need the multiplier for the heat pump and the carbon intensity of gas and electricity, as per the .gov figures.

To reach our net zero ambitions we will need 20m houses converted to heat pumps, currently install around 22,000 a year (see the same CCC report same table 3.1), so there is a mountain to climb!

I do recommend reading the CCC progress report already shared and their report on achieving net zero

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Factors to improve energy efficiency/reduce energy use.

This is another tough nut. The EST % figures I believe represent a blended average view of an average house. The average EPC for houses in England is now 63 (D but borderline C), meaning that a great deal of energy efficiency measures have already been implemented (ref: 2018-19 English Housing Survey Headline Report, ONS). However, there remain a large number of houses (pre-1970) that have not been treated and have correspondingly lower EPC for whom the efficiency gains will be very much larger than the figures EST present. (Ref: UK Housing Fact File 2013, ONS)

So for instance a house needed solid wall insulation will get a much greater than 14% reduction in energy use - the EST in fact estimates that they will save (on average) 6,700 kWh (solid wall external cladding) - which is likely to be more like 30-50% of the heating energy for the house. I recommend reading this EST report which puts it in context (2013 figures, but the facts remain the same for kWh saving): (Ref: 2013/12/Review-of-potential-for-carbon-savings-from-residential-energy-efficiency-Final-report-A) link below.

There is a tool that EST developed for calculating the heat load needed for a house (intended for boiler installers, but easy to use) In this you can set the size of house and the type of fabric - becasue to get a true picture of the heat loss you need to model the U-value (the thermal resistance) of the fabric of the house (EPCs use the same calculation - called SAP Standard Assessment Procedure). (Ref: CE-54 domestic-gas_calculator from EST) link below.

I have done a model for my house and played around with changing the fabric settings. When I do this, for instance, for loft insulation I can save 37% of the heat energy in going from an uninsulated loft to 250mm of insulation. However, this is not what I have (I have a year 2000 built house): to go from 100mm to 250mm results only in a 3% saving (law of dininishing returns). Both these numbers are a lot higher than the table you have used. EST tends to state savings in terms of £/year saving rather than kWh, so will be dependent on the £/kWh spend assumption. I will email this spreadsheet to you.

Turning the thermostat down by 1 degree has a larger impact than stated. For instance in the case of my house model, the total energy demand is 248W/K (248 W of energy required for every 1 degree Kelvin (C) that I want to maintain the house above outside temperature). So to turn the thermostat down by 1 deg C saves 248W. If I heat for 13 hours a day and 180 days a year this equates to 581kWh, 12% of the total. Hence turning the stat down by 1 degree saves 12% of the energy.

Draughts are a bigger issue, again probably for the harder to treat, older houses. EST state that “Draught-proofing around windows and doors could save you around £20 per year* . If you have an open chimney, draught-proofing your chimney when you’re not using it could save around £15 per year.*” (link below) As ever they have stated this in money terms. But if you take the average gas price £45 per year = x.kWh * 0.044 (avg. gas price) therefore 1,022 kWh, so a saving of 8.5% (based on 12,000kWh average gas use). However, 20% of average gas use is for water heating so the saving is 10.6% on space heating. A hard to treat house, however, will have a higher starting point for space heating (another reason to ask for kWh originally for home energy rather than taking an estimate), then draughts represents potentially 10-20% of the heat loss. A very much larger number than in the table.

If solar water heating gives you 100% of your hot water demand, then the saving will be ~20% of your total gas energy (ref: English Housing Survey for proportion). Probably not the case in the UK, but even 50% will give a 10% saving on gas.

I think the problem with the EST figures is that they are not clear how they have been calculated and are based on “averages” - someone with a well insulated, modern house, won’t need cavity insulation or loft insulation, so these numbers don’t really work for them.

The challenge is how to convert all this into something meaningful, based on the type of house that you have. The EST report I have shared and the spreadsheet I will email may help steer this discussion.

Enough for today. Alex


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Thanks for the pointers on the conversion factors. I’m going to rebuild the calculator in a new program so these will be very helpful during that rebuild.

In terms of REGO certificates. The big issue I have is that whoever you have a green tariff with, essentially the energy you are using has been produced (somewhere) from renewable sources - this is the purpose of REGO certificates.

One argument is that the purchase of REGO certificates simply influences the market to produce more renewable energy, therefore affects the average CO2, and everyone benefits. This takes away any incentive for people to switch to renewable energy apart from the altruistic element.

The other argument is that everyone purchases from a supplier who sources their energy in different ways, and you are a customer and therefore benefit from suppliers sources of energy purchase. This support the non altruistic, I want my energy to be zero carbon incentive.

What I think we need to find is a happy medium in the calculator. You don’t get zero carbon energy in any case anyway - therefore we need a figure that works, and if possible not to take one of the extremes.

Thanks for this Alex - especially the report. What I’ve done for the Heat Pump multiplier is use it as a means to add this to the total household electricity use (as you suggest). So it’s the total energy required to heat the house x the multiplier gives the kWhrs of additional electricity required.

I’m not modelling the conversion from gas heating to electric - I want to get all electric energy together and then multiply this against our conversion factor for electricity.

This is so thorough and educational, I exclaimed a few times WOW!

Your depth of information here is great but I’m going to need to ponder how to use it effectively in a calculator. I accept that average savings completely depend on the type of house people live in but how do we get people to tell the calculator (with ease) in what condition their house is?

I think the challenge is converting really technical thinking into practical quick returns for the average carbon foot printer.

On rebuild I’ll have a think but if you have any suggestions of questions we could use to better qualify the leakiness of the house those would be much appreciated!

With thanks,