### A back of the envelope calculation for the amount of energy used by one of our Microworld exhibitions.

We wanted to calculate how much energy was used by our recent Microworld exhibition in Wolverhampton. We thought of it in these terms – where could you drive to (return trip) in an electric car from Margate (our home town) if you used the same amount of energy as the exhibition? The exhibition was on daily for 6 weeks, 9am to 4pm and used 9 projectors, 13 computers, 4 webcams, 5 Kinect sensors and 4 monitors. Have a guess at the distance.

We’ll show you how we estimated the power usage and tell you how far the car could have travelled. We’ll then calculate the same thing in a different way using information in the book How Bad Are Bananas? The Carbon Footprint of Everything by Mike Berners-Lee. Hopefully the figures approximately match. We’ll then shrink the numbers down for a typical 4 screen Microworld running for 1 month to get a unit of Microworld Power usage and give some other comparators to this Carbon Footprint.

The only thing we are calculating is the electrical power used to run the equipment in the exhibitions. We are digital artists and we use a lot of electrical devices. Each one has its own power usage which can be found by looking up the machine’s power consumption, both when running and on standby. We are not counting the energy required to get the equipment to and from the gallery, because we mainly carry this ourselves and travel by train when we install the shows. We would have to travel anyway, whatever type of artists we were. We are not counting the energy spent in making the works – some of which have evolved over years. We would be using this energy to do something else with or without the exhibition. So to reiterate – we are only interested in the electrical running costs of the exhibition. Whenever we go on about how our project encourages people to be interested in, and by extension be good to, the planet’s natural ecosystems – we sometimes get the riposte ‘but you are using so much technology’. By the way, that’s another thing we are not counting – the huge hidden costs of manufacturing the technology in the first place. Just the electricity usage. OK. Let’s begin.

In our shows, the biggest and brightest users of electricity are the projectors.

In Wolverhampton we used Benq projectors (2200 Lumen) which use approx 350W of power and 0.5W when on standby.

W stands for Watt and is the standard unit of Power. When a 100W bulb is on for 2 hours it uses 100 * 2 = 200 Watt Hours (Wh). So we can calculate the daily usage like this.

**Projectors**

Each projector is on from 9am-4pm = 8 hours and then on standby for 16 hours.

350W * 8h + 0.5W * 16h = 2808 Wh

*9 projectors = 25,272 Wh = 25.272 kWh

We can do the same for all the other equipment. Computers and monitors use about a third as much power as projectors, and webcams and Kinects use a much smaller amount and a negligible amount when on standby.

**Computers**

85W (11W standby)

85W * 8h + 11W * 16h = 856 Wh

*13 computers = 11,128 Wh = 11.128 kWh

**Monitors**

100W * 8h + 10W * 16h = 960Wh

*5 monitors = 4800Wh = 4.8 kWh

**Webcams**

2.5W * 8h = 20 Wh

*4 webcams = 80 Wh = 0.08 kWh

**Kinects**

13W * 8h = 104W

*5 Kinects = 520 Wh = 0.52 kWh

So we can add all these up to give the total per day Watt Hour power usage for the Wolverhampton show = 41.8 kWh

Now we can round this down, because if our show was not on there would still be another show and the lights in the gallery would be on. In our show the lights are off – we like things dark, so we save a bit there.

**Microworld Wolves (13 pieces) : Power usage = 40 kWh / day**

Now the calculation can speed up a bit, because it turns out that the total battery capacity of an electric car is also measured in kilowatt-hours. An average electric car consumes 0.346kWh to travel 1 mile. So as we have 40kWh we can do 40 / 0.346 = 115 miles per day. The show was on for 6 weeks = 42 days, so we could travel 115 * 42 = 4830 miles. This is a long way – approximately the distance to Moscow and back.

So If you guessed Moscow , well done. Tim’s original guess was Edinburgh and Nicola didn’t think we’d get to London, which shows how unintuitive it is to estimate these things. This seems a depressingly large power usage but lets try and get a better handle on how much energy this is by looking at other consumptions. First lets shrink Microworld down and create a typical power usage across 1 month.

A typical piece in a Microworld uses one projector, one computer, and one webcam. Using the figures above we can estimate the Power usage to be 2808 + 856 + 20 Wh = 3684Wh per day = 110 KWh per month. A small Microworld might have 4 pieces so rounding up this would be 450 kWh and this would get you to Edinburgh and back with some to spare.

**Mini Microworld (4 pieces for one month) Power Usage (MMPU) = 450 kWh**

What else could you get for this amount of energy spent?

In How Bad are Bananas, Mike Berners-Lee has calculated the Carbon Footprint of everything. The trouble is that he is using the measure of CO2e (Carbon Dioxide Equivalent) ie. the amount of CO2 (or related) gases and this amount is in grams, kilograms, and tonnes. This gas is emitted whenever we burn fossil fuels in homes, vehicles, factories or power stations. And burning it in the power stations is what provides us with the electricity we need to light up our digital art. So we need to convert between his CO2e measurement and our Mini Microworld Power Usage (MMPU). Handily Mike gives what we need to convert on page 51 – The Carbon Footprint of a unit of electricity. He puts using one unit of electricity = 340g of C02e. Handily one unit of electricity is equivalent to one Kilowatt Hour. So because our MMPU uses 450 units our Carbon Footprint for a Mini Microworld = 450 * 340g = 153,000g = 153 kg.

Going through the chapters of the book we can find equivalents for this amount of CO2e.

One Mini-Microworld =

173kg = One 50-Litre tank of petrol

145kg = A new thick wool carpet (2m*4m)

155kg = An average sized pet cat for 6 months

184kg = One months food shopping (vegetarian)

148kg = small electric car journey to Glasgow and back (so our calculations roughly match)

130kg = 100 bottles of French Wine

150kg = 1300 bananas

150kg = 15,000 emails (100 times as many as it took to organise the show)

150kg = A return flight to Paris

According to British Gas and Ofgem, the average British household has 2.4 people living in it and uses 2,700 kWh of electricity and 11,500 kWh of gas. This works out at 242 kWh of electricity and 1,000 kWh of gas per month.

By this measure things are looking more in proportion. A Mini Microworld lasting one month uses less electricity than an average household and absolutely no gas at all.