We’re going to use ENF matching to answer the question “here’s a recording, when was it was (probably) taken?” I say “probably” because all that ENF matching can give us is a
statistical best guess, not a guarantee. Mains hum isn’t always present on recordings, and even when it is, our target recording’s ENF can still match with the wrong section of the
reference database by statistical misfortune.
Still, even though all ENF matching gives us is a guess, it’s usually a good one. The longer the recording, the more reliable the estimate; in the academic papers that I’ve read 10
minutes is typically given as a lower bound for getting a decent match.
To make our guess, we’ll need to:
Extract the target recording’s ENF values over time
Find a database of reference ENF values, taken directly from the electrical grid serving the area where the recording was made
Find the section of the reference ENF series that best matches the target. This section is our best guess for when the target recording was taken
We’ll start at the top.
About a year after Tom Scott did a video summarising how deviation over time (and location!) of the background electrical “hum”
produced by AC power can act as a forensic marker on audio recordings, Robert Heaton’s produced an excellent deep-dive into how you
can play with it for yourself, including some pretty neat code.
I remember first learning about this technique a few years ago during my masters in digital forensics, and my first thought was about
how it might be effectively faked. Faking the time of recording of some audio after the fact (as well as removing the markers) is challenging, mostly because you’ve got to ensure you
pick up on the harmonics of the frequencies, but it seems to me that faking it at time-of-recording ought to be reasonably easy: at least, so long as you’re already equipped with a
mechanism to protect against recording legitimate electrical hum (isolated quiet-room, etc.):
Taking a known historical hum-pattern, it ought to be reasonably easy to produce a DC-to-AC converter (obviously you want to be running off a DC circuit to begin with, e.g. from batteries, so you
don’t pick up legitimate hum) that regulates the hum frequency in a way that matches the historical pattern. Sure, you could simply produce the correct “noise”, but doing it this way
helps ensure that the noise behaves appropriately under the widest range of conditions. I almost want to build such a device, perhaps out of an existing portable transformer (they come
in big battery packs nowadays, providing a two-for-one!) but of course: who has the time? Plus, if you’d ever seen my soldering skills you’d know why I shouldn’t be allowed to work on
anything like this.
I’m increasingly convinced that Friedemann Friese‘s 2009 board game Power Grid: Factory Manager (BoardGameGeek) presents gamers with a highly-digestible model of the energy economy in a capitalist society.
In Factory Manager, players aim to financially-optimise a factory over time, growing production and delivery capacity through upgrades in workflow, space, energy, and staff
efficiency. An essential driving factor in the game is that energy costs will rise sharply throughout. Although it’s not always clear in advance when or by how much, this increase in
the cost of energy is always at the forefront of the savvy player’s mind as it’s one of the biggest factors that will ultimately impact their profit.
Given that players aim to optimise for turnover towards the end of the game (and as a secondary goal, for the tie-breaker: at a specific point five rounds after the game begins) and not
for business sustainability, the game perhaps-accidentally reasonably-well represents the idea of “flipping” a business for a profit. Like many business-themed games, it favours
capitalism… which makes sense – money is an obvious and quantifiable way to keep score in a board game! – but it still bears repeating.
There’s one further mechanic in Factory Manager that needs to be understood: a player’s ability to control the order in which they take their turn and their capacity to
participate in the equipment auctions that take place at the start of each round is determined by their manpower-efficiency in the previous round. That is: a player who
operates a highly-automated factory running on a skeleton staff benefits from being in the strongest position for determining turn order and auctions in their next turn.
The combination of these rules leads to an interesting twist: in the final turn – when energy costs are at their highest and there’s no benefit to holding-back staff to
monopolise the auction phase in the nonexistent subsequent turn – it often makes most sense strategically to play what I call the “sweatshop strategy”. The player switches off
the automated production lines to save on the electricity bill, drags in all the seasonal workers they can muster, dusts off the old manpower-inefficient machines mouldering in the
basement, and gets their army of workers cranking out widgets!
With indefinitely-increasing energy prices and functionally-flat staff costs, the rules of the game would always eventually reach the point at which it is most cost-effective
to switch to slave cheap labour rather than robots. but Factory Manager‘s fixed-duration means that this point often comes for all players in many games at the same
predictable point: a tipping point at which the free market backslides from automation to human labour to keep itself alive.
The demise of the automated car wash may seem trivial next to these former triumphs of homo technologicus but it sits on the same continuum. It is just one of a gathering
list of technologies that we used to be able to use, but can no longer express (through market or state spending) a purpose for. More worrying, however, is the direction in which we
are willingly going in our collective decision to move from complexity to simplicity. The demise of the automated car wash has not followed a return to the practice of people
washing their own cars (or paying the neighbours’ kid to do it). Instead we have more or less happily accepted serfdom (the use of debt and blackmail to force people to work) and
slavery (the use of physical harm) as a reasonable means of keeping the cost of cleaning cars to a minimum (similar practices are also keeping the cost of food down in the UK).
This, too, is precisely what is expected when the surplus energy available to us declines.
I love Factory Manager, but after reading Watkins’ article, it’ll probably feel a little different to play it, now. It’s like that moment when, while reading the rules, I first
poured out the pieces of Puerto Rico. Looking through them, I thought for a moment about what the “colonist”
pieces – little brown wooden circles brought to players’ plantations on ships in a volume commensurate with the commercial demand for manpower – represented. And that realisation adds
an extra message to the game.
Beneath its (fabulous) gameplay, Factory Manager carries a deeper meaning encouraging the possibility of a discussion about capitalism, environmentalism, energy, and
sustainability. And as our society falters in its ability to fulfil the techno-utopian dream, that’s perhaps a discussion we need to be having.
But for now, go watch Sorry to Bother You, where you’ll find further parallels… and at least you’ll get to laugh as you do
Thanks to the modern electric grid, you have access to electricity whenever you want. But the grid only works when electricity is generated in the same amounts as it is consumed. That
said, it’s impossible to get the balance right all the time. So operators make grids more flexible by adding ways to store excess electricity for when production drops or consumption
About 96% of the world’s energy-storage capacity comes in the form of one technology: pumped hydro. Whenever generation exceeds demand, the excess electricity is used to pump water up
a dam. When demand exceeds generation, that water is allowed to fall—thanks to gravity—and the potential energy turns turbines to produce electricity.
But pumped-hydro storage requires particular geographies, with access to water and to reservoirs at different altitudes. It’s the reason that about three-quarters of all pumped hydro
storage has been built in only 10 countries. The trouble is the world needs to add a
lot more energy storage, if we are to continue to add the intermittent solar and wind power necessary to cut our dependence on fossil fuels.
A startup called Energy Vault thinks it has a viable alternative to pumped-hydro: Instead of using water and dams, the startup uses concrete blocks and cranes. It has been operating
in stealth mode until today (Aug. 18), when its existence will be announced at Kent Presents, an ideas festival in Connecticut.
As Tesla expands its Supercharger network, the automaker intends to up its game, building higher-end, retail-rich locations that CEO Elon Musk has called “Mega Superchargers” but that we’ll call just
CEO Elon Musk has speculatively described them as “like really big supercharging locations with a bunch of amenities,” complete with “great restrooms, great food, amenities” and an
awesome place to “hang out for half an hour and then be on your way.”
The move makes sense. Superchargers are currently
located through the US and other countries, providing the fastest rate of recharging available to Tesla owners. The station can have varying numbers of charging stalls, however,
and they aren’t always located in the best areas for passing the time while a Tesla inhales new electrons, although Tesla typically tries to construct them near retail and dining
Because I’m a data nerd, I decided to monitor our energy usage, production, and total cost in order to fully understand the economic impact of our tiny power station. I appreciate that
many of you might not be able to appreciate how cool this kind of data is, but that’s because you don’t have as good an appreciation of how fun statistics can be… it is cool,
If you look at the chart above, for example (click for a bigger version), you’ll notice a few things:
We use a lot more KWh of gas than electricity (note that’s not units of gas: our gas meter measures in cubic feet, which means we have to multiply by around… 31.5936106… to
get the KWh… yes, really – more information here), but electricity is correspondingly 3.2 times more expensive per KWh – I have a separate chart to measure our daily energy costs, and it is if
anything even more exciting (can you imagine!) than this one.
Our gas usage grows dramatically in the winter – that’s what the big pink “lump” is. That’s sort-of what you’d expect on account of our gas central heating.
Our electricity usage has trended downwards since the beginning of the year, when the solar panels were installed. It’s hard to see with the gas scale throwing it off (but again,
the “cost per day” chart makes it very clear). There’s also a bit near the end where the electricity usage seems to fall of the bottom of the chart… more on that in a moment.
What got me sold on the idea of installing solar panels, though, was their long-term investment potential. I had the money sitting around anyway, and by my calculations we’ll get a
significantly better return-on-investment out of our little roof-mounted power station than I would out of a high-interest savings account or bond. And that’s because of the
oft-forgotten “third way” in which solar panelling pays for itself. Allow me to explain:
Powering appliances: the first and most-obvious way in which solar power makes economic sense is that it powers your appliances. Right now, we generate
almost as much electricity as we use (although because we use significantly more power in the evenings, only about a third of what which we generate goes directly into making our
plethora of computers hum away).
Selling back to the grid (export tariff): as you’re probably aware, it’s possible for a household solar array to feed power back into the National Grid: so
the daylight that we’re collecting at times when we don’t need the electricity is being sold back to our energy company (who in turn is selling it,
most-likely, to our neighbours). Because they’re of an inclination to make a profit, though (and more-importantly, because we can’t commit to making electricity for them when they
need it: only during the day, and dependent upon sunlight), they only buy units from us at about a third of the rate that they sell them to consumers. As a result, it’s worth our
while trying to use the power we generate (e.g. to charge batteries and to run things that can be run “at any point” during the day like the dishwasher, etc.)
rather than to sell it only to have to buy it back.
From a government subsidy (feed-in tariff): here’s the pleasant surprise – as part of government efforts to increase the proportion of the country’s energy that
is produced from renewable sources, they subsidise renewable microgeneration. So if you install a wind turbine in your garden or a solar array on your roof, you’ll get a kickback for
each unit of electricity that you generate. And that’s true whether you use it to power appliances or sell it back to the grid – in the latter case, you’re basically
being paid twice for it! The rate that you get paid as a subsidy gets locked-in for ~20 years after you build your array, but it’s gradually decreasing. We’re getting paid a little
over 14.5p per unit of electricity generated, per day.
As the seasons have changed from Winter through Spring we’ve steadily seen our generation levels climbing. On a typical day, we now make more electricity than we use. We’re still having
to buy power from the grid, of course, because we use more electricity in the evening than we’re able to generate when the sun is low in the sky: however, if (one day) technology like
Tesla’s PowerWall becomes widely-available at reasonable prices, there’s no reason that a house like ours couldn’t be totally
independent of the grid for 6-8 months of the year.
So: what are we saving/making? Well, looking at the last week of April and the first week of May, and comparing them to the same period last year:
Powering appliances: we’re saving about 60p per day on electricity costs (down to about £1.30 per day).
Selling back to the grid: we’re earning about 50p per day in exports.
From a government subsidy: we’re earning about £2.37 per day in subsidies.
As I’m sure you can see: this isn’t peanuts. When you include the subsidy then it’s possible to consider our energy as being functionally “free”, even after you compensate for the
shorter days of the winter. Of course, there’s a significant up-front cost in installing solar panels! It’s hard to say exactly when, at this point, I expect them to have paid for
themselves (from which point I’ll be able to use the expected life of the equipment to more-accurately predict the total return-on-investment): I’m planning to monitor the situation for
at least a year, to cover the variance of the seasons, but I will of course report back when I have more data.
I mentioned that the first graph wasn’t accurate? Yeah: so it turns out that our house’s original electricity meter was of an older design that would run backwards when
electricity was being exported to the grid. Which was great to see, but not something that our electricity company approved of, on account of the fact that they were then paying us for
the electricity we sold back to the grid, twice: for a couple of days of April sunshine, our electricity meter consistently ran backwards throughout the day. So they sent a couple of
engineers out to replace it with a more-modern one, pictured above (which has a different problem: its “fraud light” comes on whenever we’re sending power back to the grid, but
apparently that’s “to be expected”).
In any case, this quirk of our old meter has made some of my numbers from earlier this year more-optimistic than they might otherwise be, and while I’ve tried to compensate
for this it’s hard to be certain that my estimates prior to its replacement are accurate. So it’s probably going to take me a little longer than I’d planned to have an accurate
baseline of exactly how much money solar is making for us.
One of the great joys of owning a house is that you can do pretty much
whatever you please with it. I celebrated Ruth, JTA
and I’s purchase of Greendale last year by wall-mounting not one but
two televisions and putting shelves up everywhere. But honestly, a little bit of DIY isn’t that unusual nor special. We’ve got plans for a few other changes to the
house, but right now we’re pushing our eco-credentials: we had cavity wall insulation added to the older parts of the building the other week and an electric car charging port added not
long before that. And then… came this week’s big change.
Solar photovoltaics! They’re cool, they’re (becoming) economical, and we’ve got this big roof that faces almost due-South that would otherwise be just sitting there catching rain. Why
not show off our green credentials and save ourselves some money by covering it with solar cells, we thought.
Because it’s me, I ended up speaking to five different companies and, after removing one from the running for employing a snake for a salesman, collecting seven quotes from the
remaining four, I began to do my own research. The sheer variety of panels, inverters, layouts and configurations (all of which are described in their technical sheets using terms that
in turn required a little research into electrical efficiency and dusting off formulas I’d barely used since my physics GCSE exam) are mind-boggling. Monolithic, string, or
micro-inverters? 250w or 327w panels? Where to run the cables that connect the inverter (in the attic) to the generation meter and fusebox (in the ground floor toilet)? Needless to say,
every company had a different idea about the “best way” to do it – sometimes subtly different, sometimes dramatically – and had a clear agenda to push. So – as somebody not suckered in
to a quick deal – I went and did the background reading first.
In case you’re not yet aware, let me tell you the three reasons that solar panels are a great idea, economically-speaking. Firstly, of course, they make electricity out of sunlight
which you can then use: that’s pretty cool. With good discipline and a monitoring tool either in hardware or software, you can discover the times that you’re making more power than
you’re using, and use that moment to run the dishwasher or washing machine or car charger or whatever. Or the tumble drier, I suppose, although if you’re using the tumble drier
because it’s sunny then you lose a couple of your ‘green points’ right there. So yeah: free energy is a nice selling point.
The second point is that the grid will buy the energy you make but don’t use. That’s pretty cool, too – if it’s a sunny day but there’s nobody in the house, then our
electricity meter will run backwards: we’re selling power back to the grid for consumption by our neighbours. Your energy provider pays you for that, although they only pay you
about a third of what you pay them to get the energy back again if you need it later, so it’s always more-efficient to use the power (if you’ve genuinely got something to use
it for, like ad-hoc bitcoin mining or something) than to sell it. That said, it’s still “free money”, so you needn’t complain too much.
The third way that solar panels make economic sense is still one of the most-exciting, though. In order to enhance uptake of solar power and thus improve the chance that we hit the
carbon emission reduction targets that Britain committed to at the Kyoto
Protocol (and thus avoid a multi-billion-pound fine), the government subsidises renewable microgeneration plants. If you install solar panels on your house before the end of this
year (when the subsidy is set to decrease) the government will pay you 14.38p per unit of electricity you produce… whether you use it or whether you sell it. That rate is
retail price index linked and guaranteed for 20 years, and as a result residential solar installations invariably “pay for themselves” within that period, making them a logical
investment for anybody who’s got a suitable roof and who otherwise has the money just sitting around. (If you don’t have the cash to hand, it might be worth taking out a loan
to pay for solar panels, but then the maths gets a lot more complicated.)
The scaffolding went up on the afternoon of day one, and I took the opportunity to climb up myself and give the gutters a good cleaning-out, because it’s a lot easier to do that from a
fixed platform than it is from our wobbly “community ladder”. On day two, a team of electricians and a solar expert appeared at breakfast time and by 3pm they were gone, leaving behind
a fully-functional solar array. On day three, we were promised that the scaffolding company would reappear and remove the climbing frame from our garden, but it’s now dark and they’ve
not been seen yet, which isn’t ideal but isn’t the end of the world either: not least because Ruth’s been unwell and thus hasn’t had the chance to get up and see the view from the top
of it, yet.
We made about 4 units of electricity on our first day, which didn’t seem bad for an overcast afternoon about a fortnight away from the shortest day of the year. That’s about enough to
power every light bulb in the house for the duration that the sun was in the sky, plus a little extra (we didn’t opt to commemorate the occasion by leaving the fridge door open in order
to ensure that we used every scrap of the power we generated).
Because I’m a bit of a data nerd these years, I’ve been monitoring our energy usage lately anyway and as a result I’ve got an interesting baseline against which to compare the
effectiveness of this new addition. And because there’s no point in being a data nerd if you don’t get to share the data love, I will of course be telling you all about it as soon as I