"Half a million solar homes" - Sources and calculations

Please find an overview of sources and calculations as used in the infographic "Half a million solar homes" by CompareMySolar:

Graph 1: Half a million UK homes have solar 
Shows: Number of UK homes with solar panels by quarter from 2011-2013.
Source: Gov.uk - Weekly solar PV installation & capacity based on registration date
Calculations: Based on government installation numbers since 2011, which reached 500.000 end of 2013

Graph 2: And prices keep falling
Shows: Best price of 4kWp (16 panels) of solar PV including VAT by quarter from 2011-2013.
Source: CompareMySolar - Solar panel price index
Calculations: Based on CompareMySolar price index, of best 10 quote requests by month since 2011

Graph 3: So the state cut Feed-in Tariffs
Shows: Feed-in Tariff for solar PV up to 4kWp by quarter from 2011-2013.
Source: Ofgem - Feed-in Tariff tables
Calculations: In case the rate changed during the quarter the most prevalent (2 out of 3 months) tariff is shown.

Graph 4: While solar keeps a great return
Shows: Total year 1 return for solar PV up to 4kWp by quarter from 2011-2013.
Source: CompareMySolar - Solar panel year one return
Calculations: Combination of average price by quarter from CompareMySolar price index and total return in year one. Total return based on then valid Feed-in Tariff rate a south-facing roof in Bristol, generating 3.500 kWh per year, assuming 50% own use and 50% exported. Total return shown as percentage of ComparMySolar price index.

Picture 1: Two percent of UK households have solar
Shows: Percentage of UK households with solar panels by region, as of October 2013
Source: Gov.uk - Sub-regional Feed-in Tariffs statistics
Calculations: Percentage of households with solar panels by region visualised by suns. Unrounded numbers are: East Midlands 2.1%, East of England 1.8%, London 0.3%, North East 1.47%, North West 1.2%, South East 1.6%, South West 2.9%, West Midlands 1.3%, Yorkshire and The Humber 1.7%, Scotland 1.1%, Wales 2.2%

Picture 2: And create a lot of electricity
Shows: Half a million solar households generate 1.3 Billion kWh of electrcitiy per year, enough to charge 50 AA batteries for each household, every day!
Source: Gov.uk - Weekly solar PV installation & capacity based on registration date / All about batteries - energy tables
Calculations: Government installation data show that 1.5 Giga-Watt-peak of solar PV has been installed in domestic sector. Estimating the production using a south-facing roof in Bristol, generating 3.500 kWh per year for 4 kWp. Hence estimated generation per year is 1.5/8*7= 1.3 Giga-watt-hour, which equals 1.3 Billion kWh. One Alkaline Long-life battery can store about 2.6 Watt-hour, which is 0.0026 kWh. So 1.3 Billion kWh generated divided by 0.0026 kWh battery capacity divided by 26.3 million UK households divided by 365 days equals 52 AA batteries per household per day. A full year of electricity from half a million solar homes could:

Statement 1: Light 7 LED bulbs per household every evening
Source: CompareMySolar Calculations
Calculations: To light one 5-watt LED bulb for 4 hours per day requires 0.005*4*365 = 7.3 kWh per year. So 1.3 Billion kWh generated divided by 7.3 kWh for a lightbulb divided by 26.3 million UK households gives 6.85 LED lightbulbs per household.

Statement 2: Make 1,000 cups of tea per person in the UK
Source: Carbon Trust - Energy efficiency posters
Calculations: Making one cup of tea requires 0.02kWh. So 1.3 Billion kWh generated divided by 0.02 kWh for a cup of tea divided by 63.2 million UK population gives 1,038 cups of tea per person per year.

Statement 3: Drive 180,000 electric cars around the world
Source: Fuel Economy (USA) - Compare all electric vehicles side by side / Wikipedia - Earth circumference
Calculations: A mid-sized electric vehicle like Nissan Leaf uses 29 kWh per 100 miles. The earth circumference is 40,000 kilometers, about 25,000 miles, so it would take 250 times 29 equals 7,250 kWh to drive around the earth. So 1.3 Billion kWh generated divided by 7,250 kWh to drive around the earth equals 181,000 electric vehicles that can drive around the world.

Statement 4: Save enough coal to fill 5,000 London buses
Source: Wikipedia - Coal energy density and carbon impact / Ask.com - Density of coal / Ask.com - What size is a double decker bus?
Calculations: One kilogram of coal has an energy density of 6.7kWh. Assuming a coal power plant with a 40% efficiency, this results in 2.68 kWh of electricity. So 1.3 Billion kWh generated divided by 2.68 kWh saves 490 Million kilogram of coal from being burned in a coal power plant. A double decker bus measures 11.3 * 2.5 * 4.2 meters which equals 118 cubic meters. One cubic meter can contain 800 kilogram of coal. So 490 Million kilogram of coal divided by 800 kg per cubic meter divided by 118 cubic meters would fill 5,180 London double decker busses.

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