I have earlier looked at Norway with it's very challenging topography and found that DAB is 20 times greener than FM. The mountains and valleys do however help digital coverage as the signals can bounce back and forth, making them stronger. The opposite is the case for analogue signals that are weakened or even killed in the case of reflections from mountains. There are few mountains in the UK.
I do not have inside knowledge about the transmitters in Britain, but the BBC is open about such matters and have made the info on transmitters publicly available on their website. Based on this, I have looked at all their FM and DAB transmitters listed there. The figures listed are however in ERP (effective radiated power), whereas the actual power usage is typically 2.5-10 times lower. Here are the figures (based on my own count, estimates and calculations):
FM, 99.8% coverage
Number of sites (towers/antennas): 395
Number of transmitters: 1,194
Wattage: 2,349kW
Average wattage per transmitter (not ERP): 1.97 kW
Increase in power needed due to amplifiers: 140%
Electricity used per year: 28,829,694 kWh
DAB, 86% coverage
Number of sites (towers/antennas): 231
Number of transmitters: 231
Wattage: 107 kW
Average wattage per transmitter (not ERP): 461W
Increase in power needed due to amplifiers: 400%
Electricity used per year: 3,736,836 kWh
The 1-6 radio stations transmitted via FM (based on coverage areas) does in other words use 7.7 times more electricity than the 11 radio stations transmitted via DAB. But the coverage of some of the FM channels are better than for DAB in certain areas, so we have to take that into account.
The current coverage of DAB is 86%, with 231 transmitters. It is always more costly to cover the last few percentages than the first, so let us assume that the BBC needs twice as many DAB receivers as today to cover 99.8% of the UK. That means 462 transmitters and sites. I'll even round that up to 500.
Based on the average wattage of the existing transmitters, we'll then get the following scenario:
DAB, 99.8% coverage (estimate)
Number of sites (towers/antennas): 500
Number of transmitters: 500
Wattage: 230 kW
Average wattage per transmitter (not ERP): 461W
Increase in power needed due to amplifiers: 400%
Electricity used per year: 8,088,390 kWh
With this estimate FM still consumes 3.6 times more electricity than DAB. Electricity prices in the UK are typically between 6.5 and 12 pence per kWh. Let us say that the BBC has managed to bargain on the price as they use a fair amount of juice. I have calculated electricity costs based on three different scenarios.
1) Great bargaining skills, paying an average throughout every day of the year of 5p per kWh.
2) OK bargaining skills, paying an average throughout every day of the year of 7.5 pence per kWh.
3) Poor bargaining skills, paying an average throughout every day of the year of 10p per kWh.
That gives us the following costs, in electricity alone, per year.
Scenario 1, 5p per kwH, 99.8% coverage
FM: 1,441,485 GBP a year
DAB: 404,420 GBP a year
Savings: 1 million GBP per year.
Scenario 2, 7.5p per kwH, 99.8% coverage
FM: 2,162,227 GBP a year
DAB: 606,629 GBP a year
Savings: 1.6 million GBP per year.
Scenario 3, 10p per kwH, 99.8% coverage
FM: 2,882,969 GBP a year
DAB: 808,839 GBP a year
Savings: 2 million GBP per year.
What's the damage?
BBC can in other words save approximately 1.6 million British pounds or 2.5 million USD a year, based on electricity costs alone in the least extreme scenario, if shutting off FM and transmitting only digitally. That is 74% less that what it costs for FM, in electricity that is.
Note that the numbers of transmitters are lower for DAB, whereas the number of sites are actually higher. This is the opposite of what is the case in Norway. Why is this? Topography plays a role, as mentioned above. But if you look at the transmitters you can also see a major power difference. Some of the FM transmitters are very powerful, the most powerful ones outputting 250 kW. The most powerful DAB transmitter does in comparison only output 10 kW.
FM can be shut off in 2015 if 50% of the listening in Britain happens digitally by 2013 (two years notice is required). You can in other words contribute to the BBC saving money (paid by you through the licence fee) on radio distribution and leave more money to quality programmes by listening to DAB instead of listening to FM. You will also help the environment and get a better selection of radio stations as a bonus.
Go green and help the BBC save your* money.
* Only applicable if you live in Britain and do pay the licence fee.
Also relevant:
DAB 20 Times Greener Than FM.
