Please can you supply me with a complete list of all previous electricity price cap figures?

I have searched your website and can only find the current price-cap.

Specifically, I would like to know the per kWh price cap for electricity in the London region from its introduction until today.

If these are on your website, please point me in the right direction. If not, a CSV of the data would be appreciated.”

A month later, and without any fuss, they emailed me a comprehensive spreadsheet. In Excel format, but let's not quibble!

There are a few formatting oddities - not least that the caps are expressed with 13 decimal places of precision. Was the daily cap really 60.9345205479452p?

Similarly, the dates are expressed as 1 April 2022 to 30 September 2022 rather than programmatic date ranges. It's also inconsistent, with some saying 1 July to 30 September 2025.

Averages are hard-coded not calculated.

I've requested that they add these data to their website but, until they do, here's the original file they sent me.

I've used a bit of R to tidy them up, giving proper start date and end date columns, rounding to 2 decimal places, and saving as CSV. You can download the tidied version.

Copyright and Copyleft

As per their copyright page these data are © Ofgem, 2026 and are licensed under the Open Government Licence 3.0. This is compatible with CC BY and ODC-By.

Please treat my update as Creative Commons Attribution.

By design, the smart-meter is limited in how much data it can send back. You can choose to have readings sent monthly, weekly, daily, or half-hourly. There's no option for minute-by-minute precision. That's useful from a privacy perspective - and no doubt makes the network engineering simpler - but slightly annoying from a home-monitoring perspective.

The smart-meter has the ability to send real-time information to a local device using the ZigBee network. If you have an in-home display (IHD) then you'll have seen just how accurate it is.

As I've discovered, you can't just pair any-old ZigBee device to your meter. Luckily, Octopus have sent me the "Mini". A little device which connects to the smart-meter and your home WiFi, then reports usage every 10 seconds. Let's put it through its paces.

Size

Mini by name, mini by nature!

It's rare to find a device smaller than its plug. I half-wonder if they could have integrated it and just made it into a smartplug.

Annoyingly, it is micro USB. I am a USB-C maximalist. There's no reason this device shouldn't use the same cable as everything else I own.

Installation

Plug the Mini in - ideally within 5m of your smartmeter - and wait for the blinkenlight. Follow the in-app instructions. Because, like every modern device, it needs an app. You need to install the standard Octopus Android app, and can then add the Mini to your account and to your WiFi.

Like all cheap IoT devices, it will only work on 2.4㎓, so you may need to adjust which network your phone is on.

And then…

That's it. Every 10 seconds it sends an update to Octopus. You can use the app or the website to view your current consumption or to see your last 5 minutes or last 30 minutes usage.

If you're a dab-hand with the API, you can poll that. Or you can connect it to HomeAssistant.

Downside

In theory this is nifty, but there are a few things I'm not keen on.

• Export readings simply don't work for some brands of smart meter. That's an annoyance - my meter can send half-hourly readings for export, but the Mini just shows that I'm using zero Watts.
• No local connection. It sends the data to Octopus, so I have to use their API to get the data. I'd like the ability to stream it directly from the Mini.
• USB-micro. We live in the future. USB-C or GTFO!

Honestly, a bit disappointing. If you don't have solar panels - or your meter works correctly - this could be very useful. Even so, the lack of an local API is a bit of a buzzkill. Sadly, for my purposes, it isn't very useful.

Nukes are clean! They are cheap! They are safe and healthy! They are brilliant! Nuclear power will save us all!

Look, I 100% agree that nuclear power is theoretically better than every renewable power source. Nuclear totally clean⁰! Fewer people die of nuclear radiation poisoning than fall from roofs installing solar. Governments never need to cover-up the true cost of nuclear fall-out and decontamination¹. Why can't people get it through their thick skulls that nuclear power is just so fricking cool?!

I agree! Harnessing the power of spicy rocks is a pretty nifty way of making electrons flow.

But here's my real test for nuclear power. Why can't I have a mini-nuke at home?

I'm quite serious.

On my roof I have 5kWp of solar panels which provide 100% of my electrical needs throughout the year. I also have 4.8kWh of battery storage. This technology exists. It works.

If I wanted, I could install a wind turbine. I don't think I need planning permission for that. It might not be cost effective - but plenty of people will sell me one. Again, totally feasible.

I have an incoming gas supply which I use for heat. I suppose I could buy a mini turbine to turn that into electricity. Or I could use a thermoelectric device to turn gas heat into electricity. Bit of a faff, but doable.

Similarly, I can burn wood (or coal) at home and use that for energy. I can go into the woods right now and pick up some sticks which will turn into lovely heat.

I could even buy a petrol / diesel generator and - although the fumes would be disgusting - I could make electricity that way.

Finally, if there were a river running through my property, I could install a hydroelectric generator. There isn't, so I can't. And I don't think my domestic water pressure could do more than power a few LEDs.

So where's my home-nuke kit?

Every other form of electricity generation has a version which can be reasonably installed in the home. Some of them have to be installed by a competent and qualified person. Some of them need yearly check ups. Some of them require planning permission or emissions controls. But they all provably work.

Except nuclear.

Is it because it isn't cheap enough at a smaller scale?

Would the risk of a small nuclear explosion be that much worse than the occasional gas explosions we have?

If my solar panels fell from the roof, they're fairly light but would still give you a nasty bump on the head. A fly-away wind turbine could probably kill someone nearby.

Burning wood, coal, oil, and other combustibles can create some pretty noxious pollution. Would a micro-nuclear reactor be better?

Perhaps there's an alternate future where Chernobyl and Windscale and Three-Mile Island never happened and we're all driving around with Mr Fusion reactors on our cars².

I would be perfectly comfortable living next door to a large, well-managed nuclear power station. But would you sleep soundly knowing your neighbour had a small Generation IV reactor in their basement?

In 1954, the first grid-tied nuclear power station went online. It's 70 years later and nuclear power is no closer to a domestic version. Perhaps the pro-nuclear dudes have an answer for that?

It starts off reasonably enough by describing the evolution of our legal system:

1. Law 1.0 says "Thou shalt not kill".
2. Law 2.0 says "Thou shalt not pollute. But, rather than specific legislation, we'll spin up a body to do the tedious work of enacting our policy".
3. Law 3.0 says "Thou shalt not drive over the speed limit. And we'll fit all cars with a chip that prevents them doing so".

I think that's fair enough assessment. Is "Law 3.0" a good thing or a bad thing? Perhaps we can have a discussion about the limits of technology and political philosophy? No, we just get this "argument":

The tyrannical implications of such a mode of governance are so obvious that it really ought to go without saying.

Ummm.... no? Perhaps we could discuss these supposed tyrannical implications?

The author is terrified that the Government is going to stop him running his dishwasher. You see, the Energy Bill says that technical experts can send a signal to smart appliances asking them to reduce their electricity use at certain times.

That's it. That's the horror he is railing against.

Pollution a bit high? Send a signal to ask your freezer to reduce its cooling temperature. Electricity prices going to spike in an hour? Tell people's cars to start charging now, but to throttle back later. That sort of thing. You know, save you a bit of money, reduce pollution, stabilise the energy supply. Terrifying...

Now, there might be a dystopian use of this. Perhaps the state could command all TVs to turn off when the opposition's political adverts are on. Perhaps they could turn off the car chargers of known protestors - thus preventing them from attending a demonstration. Maybe they'd turn off everyone's freezers in order to boost Tesco's profits?

This leads to some interesting questions. What sort of safeguards should we have? What level of control do people want? Who chooses the experts? Who secures the system? What similar problems have happened before? What are the positive ways this could be used?

But, nope, the post doesn't discuss that. It just continually reiterates a pathological fear of "technical experts" telling people how to behave. He wraps it up in a vague coat of morality - saying that we should be allowed to choose to break laws and face the consequences.

But, what are we actually talking about here?

A Thought Experiment

Let's say a power station fails unexpectedly in the middle of winter. There are several options available to us.

1. Wait until Parliament can reconvene to debate and pass a law which limits people to x kWh of electricity per day with a maximum of y kW at any moment.
2. Let people suffer rolling blackouts / brownouts as the energy supply struggles to keep up with demand.
3. Have a team of technical experts send signals to people's washing machines asking them to only switch on when there's surplus power.

Quite obviously (1) is impractical. The lack of speed and expertise is one of the (many) reasons Law 1.0 doesn't work in large complex systems which require a swift reaction.

And (2) is the sort of self-sufficient Libertarian nonsense which imagines a hellscape for everyone except themselves. Great! You can choose not to follow the law and let everyone else suffer the consequences.

And (3) is... boringly pragmatic. I guess with the slight risk that it might be abused to... what? Deny people their constitutional right to run a high power vacuum cleaner whenever they want?

Morality

The article makes this moral argument:

The speed limit does not compel us: we can choose to abide by it, or not. And this, most crucially of all, means that we have moral agency. We can choose to do right or wrong.

[...]

in its way, [Law 3.0] is the worst affront to the dignity of man out of them all, because it destroys the very conditions of moral agency. I reiterate: if one does not have the freedom to choose, because one is compelled to act morally, then one’s moral conduct is not really moral at all.

I don't really get that. We ban guns so that people can't choose to wave them about recklessly - because impinging on your freedom is better than clearing up corpses.

Rather more prosaically, we ban the sale of inefficient domestic appliances. Yes, the experts are being mean by forcing you not to make a moral decision about whether to waste electricity. Boo-fucking-hoo.

But, if this moral agency is so important, why isn't it available to "the experts"? Why shouldn't they be allowed to choose to take a bribe from a washing line manufacturer to switch off the nation's tumble-dryers? They can suffer the consequences of being caught, tried, and punished.

Law 1.0 - which the author is so fond of - would do that.

Or, we could use Law 3.0 to implement a technical measure which says such a signal can never be sent unless 4 our of 5 experts agree to it.

Civic Hygiene

A decade ago, I wrote up my thoughts on Civic Hygiene.

Civic hygiene isn't about saying we distrust our current government - it's about not trusting the next government.

I still stand by that. We should make it hard or impossible for a corrupt entity to abuse the power it is entrusted with. But that doesn't mean giving them no power.

In a democratic society we accept that we sometimes have to do things aren't in our direct personal interests in order to keep society functioning. Sometimes we can choose whether or not to obey (e.g. by breaking the speed limit) other times the state restricts us (by banning the sale of poisons).

If we don't make the transition to smarter and more responsive energy consumption, then we risk grid stability, more pollution, and higher energy costs. That damages all of us.

We should embrace new ways of organising ourselves. And we should embrace technological limitations which protect the majority. And those limitations must be safeguarded.

I don't know whether this law is well written, or whether there are adequate safeguards, or whether abusers of its powers can be punished. But I do know that this moral pontificating doesn't even begin to address the practical issues.

We installed 5kW of solar panels on our roof in 2020. Half are East-facing, half West-facing.

Over a full year, they've generated 4,165kWh.

By comparison, the average UK household uses about 3,800kWh of electricity per year.

But working out exactly how much we've used is slightly trickier. We have a smart meter which reads our import and export. And a generation meter which shows how much we've generated.

MATHS!

Our Import - that's the electricity we buy from the grid - was recorded on our smart meter:

Meter Reading on 2020-03-21 was 1,904kWh
Meter Reading on 2021-03-21 was 4,665kWh
Total Import = 2,761kWh

Our export - when we sell electricity back to the grid - was also recorded on the smart meter: 2,768kWh.

We exported exactly the same amount as we imported! We are net energy neutral!

How much did we use directly from our panels?

Generated: 4,165 kWh
Exported:  2,768 kWh

Generated - Exported = Domestic Solar Use

4,165 - 2,768 = 1,397

1.4MWh went directly from our panels into our gadgets. That's about a third of what we generate.

So, our total consumption is:

Import + Domestic = Total consumption.
2,761+1,397=4,158

Roughly, our annual electricity use is 4.1MWh. That's the same as we've generated from our roof.

Offsetting Usage

We got a 2kWh battery a few months ago. It has enough storage to charge up during a summer's day and discharge over night. Ideally, we'd have a couple of MegaWatt hours of storage to charge in summer and discharge all the way through winter. But that tech is a long way off.

We try to run things like the tumble-dryer and dishwasher during the day to make use of the green energy. The big electricity cost is our oven - it's hard to run that during the day if we want a hot meal in the evening.

Our overnight use is a fairly constant 100W - a bunch of smarthome devices and fridge/freezers doesn't take too much. Not many efficiencies to be found there. Some things just need to run continually.

Having spent a year working from home (thanks COVID!!!!) our domestic usage is significantly higher than previous years. WFH means that our computers consume lots of electricity in the day, and our TV & games consoles are powered all through the evening.

Money

In an ideal world, we'd sell electricity for the same price that we pay to import it. Sadly, that's not the case. See "Some thoughts on selling electricity back to the grid" for the details. Basically, we pay 15p/kWh to buy electricity, and we sell it back for 5.5p/kWh. When we sell electricity, the money is taken off our monthly bill.

Over the full year, we've saved about £365. Basically a quid a day. Or, to look at it another way, we've reduced our electricity bills by 60%.

It isn't the most profitable investment - but it makes me extraordinarily happy. And, if energy prices rise, we'll save even more.

What's Next?

We're currently with Octopus Energy (get £50 if you join using that link). They offer a time-of-day tariff. Prices fluctuate based on electricity demand. If we can hook our batteries up to their API, we can discharge the battery when prices are high - and potentially sell back to the grid at a more profitable time.

I blog about our solar panels a lot. But they are pretty boring. They just sit there working. The cost of installation varies depending on where you are in the world and how complicated your roof is. But our small roof generates all the electricity that we use in a year.

This isn't the future - it is now.

I've switched to energy provider Bulb (£50 off if you join using that link). They offer a "peak time" electricity charge which looks like this:

• 23:00 to 07:00 = £0.0815/kWh
• 07:00 to 16:00 = £0.1235/kWh
• 16:00 to 19:00 = £0.3263/kWh
• 19:00 to 23:00 = £0.1235/kWh

By contrast, the standard tariff is £0.1359 per kWh. That means my electricity is 2.4x more expensive for 4 hours per day, during peak time. But cheaper the rest of the time.

Let's look at a typical(ish) day's usage. This is what our home monitoring says we consumed on February 28th. If we ignore the solar power and battery storage, this is the result:

• Normal tariff = £0.95/day
• Smart tariff = £1.06/day

Ooof! Considerably more expensive. We come home in the evening and start cooking and watching TV right on the peak schedule.

Solar

We have solar panels. When the sun is shining, it reduces consumption from the grid. If the amount of power generated by the panels is greater than or equal to our home's energy usage, the meter stands still and we don't get charged.

This is what happens when we sum in the solar power:

• Normal tariff = £0.68/day
• Smart tariff = £0.91/day

Yikes! Dramatically more! During the daytime, we import virtually no electricity. Even when I'm working from home, the sun provides most of our needs - so we wouldn't benefit from the cheaper day rate.

Batteries

We also have a 2kWh solar battery. When the solar panels generate more power than the house can use, the battery is charged. When we're importing electricity, the battery slowly discharges. Let's sum in that as well.

• Normal tariff = £0.60/day
• Smart tariff = £0.76/day

Quite an impressive drop. The battery tends to discharge in the early evening, after the sun has set. So usually peak time for the Bulb tariff. With a bigger battery, we'd save even more in the evening.

Based on this average(ish) day in February, you might think that the smart tariff isn't right for our set up. But that's not the whole story. Let's take a look at a few more interesting days.

Car Charging

We have an electric car. I'm using a regular 13 amp charger (3kW) - rather than the fast (7kW) charger. Here you see the car being charged to full over the weekend - right at peak time:

Solar power was also pretty pathetic those two days, and there wasn't much in the home battery.

• Normal tariff = £3.15 for two days
• Smart tariff = £2.97 for two days

Aha! Even without shifting my car charging time to be after 19:00, the smart tariff could save us money.

Very roughly, if we'd deliberately not plugged the car in until after 19:00, the cost for two days would have been £2.26!

A whopping saving of 45p per day compared to the regular tariff.

Changing behaviours

And that's kind of the point, isn't it? If we shift our energy usage a bit, we get a significant saving. Can our lifestyle cope with waiting until 19:00 to start cooking? That sounds doable.

Can we set our battery to prioritise those peak times? Moixa - the manufacturer - have said they can set the battery to be aware of tariff rates.

Do we need the car to be fully charged? Nope - telling it only to charge in the cheap hours works for us.

If we're willing to change, our power bills drop.

Big Exhaustive Data Crunching

Over 2017-2018 I recorded all of our energy usage. I used it for graphs like this:

@Edent's Home

@edent_home

pic.x.com/FLPfIpv5g0

---

Here's what happens if we compare the Bulb standard tariff with a year of data.

There are a couple of caveats. Previously we charged our car with a 7kW charger. We've purchased new electronics and appliances which are more efficient. We also have a part-time lodger. So the energy profile isn't identical - but hopefully illustrative.

• Normal tariff = £386.93
• Smart tariff = £321.83

Assuming my calculations are correct - and I've got my daylight savings time the right way round - we could save a fairly hefty sixty quid per year!

With some lifestyle tweaks the savings could be even greater.

If you'd like to take advantage of this smart tariff, switch to Bulb (we each get £50 if you join using that link).

In the UK we have a competitive electricity market. Only one set of wires comes to your house, but you can buy your electricity from a number of providers. Some only offer organic, corn-fed, Wind Farm power - others promise price stability - another gives you a discount at their electric car chargers - one gives you loyalty points at a supermarket.

We increasingly have smart meters. Second-by-second they measure our energy consumption and report it back to our power suppliers.

Domestic appliances are increasingly coming with Internet connectivity. We may laugh at the "Internet of Shit" - but soon every device we own will come with an app. We will control them from our phones, and they will report back their usage to their manufacturer.

Let's mash these ideas up.

According to the Energy Savings Trusts' report "Powering The Nation" a typical fridge/freezer uses 427kWh per year.

At an average price of 15p/kWh that's an annual running cost of £64.

Suppose your fridge manufacturer buys electricity in bulk at wholesale prices. The current wholesale price per MWh is £40. That's 4p/kWh. Or about £20 to run a fridge for a year.

Would you buy a fridge which costs £100 more but comes with 5 years worth of free energy?

You register your fridge online. It *wavy hand technobabble* talks to your smart meter and tells it how much electricity it has used that day, the sum is deducted from your bill.

Perhaps it does clever things like works out when the spot price for electricity is low and then cools down. Or it keeps your food a little bit warmer when energy prices are high.

Or perhaps it could *mumble mumble* blockchain *something something* cloud computing?

Is this the future? I think so.

I've been reviewing WiFi connected plug sockets which measure how much power an appliance consumes. They cost about $10 per unit at retail pricing. Soon it will be normal to receive an electricity bill which shows you just how much your Playstation 5 costs to run.

Your typical bill will tell you how much energy each of your appliances use. At which point it will become obvious that replacing your old TV with something newer will save you money in the long run.

Tesla gives customers £50 worth of "free" electricity with their cars - but that's only at their branded charging stations.

In the future, a new electric car will come with 10,000 miles worth of "free" electricity when you charge at home. You won't notice an extra £300 on the price of a new vehicle, and the manufacturer can securitise their wholesale energy purchases.

Your appliance talks to your smart meter which talks to your energy provider. With a little bit of thought, this could change how we buy energy consuming products.

Energy efficiency is the next battleground for electronics. As the price of electricity soars, people will become less and less enamoured with charging their devices every single day. Even if cold-fusion brings us unlimited free energy - plugging your gadgets into a wall just seems so primitive!

That's where BlueTooth Low Energy (BLE) comes in. It's an ultra low powered transmitter which can be found in FitBits, iBeacons, pacemakers, and all sorts of other devices.

The key, as per its name, is that it uses very little energy. A simple watch battery should be enough to power an iBeacon for a year.

When Life Gives You Lemons…

Today was one of The Lab's regular hackdays. We challenge ourselves to spend a day playing with new technology, trying to get it to do something interesting.

I'm sure you remember from school building a simple power source using a lemon or potato. Zinc plated nails, copper wiring, an acid source, and - hey presto - a lightbulb comes on.

So, can we harness the awesome power of fruit to bring life to a little iBeacon?

Terence Eden is on Mastodon

@edent

A vital part of today's hackday in @thelab_uk.... :-) #blemon (@ Sainsbury's) 4sq.com/1iCOUKo pic.x.com/ejidwromyx

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We used RedBear Lab's BLE Mini board. It can be powered via USB (boring!) or via a direct electrical contact on the back.

Better BlueTooth Through Chemistry

It's been ages since any of us in The Lab did basic physics and chemistry at school, so we turned to the Mighty Internet for help.

With three lemons wired in parallel, we got approximately 0.5 Volts and 120μAmps.

According to Red Bear's support forum, we'd need about 3 volts and 340μAmps.

With 6 lemons, we were at ~200μAmps, closing in on the figure we needed.

It occurred to us that we may need to construct some kind of super-fruit mega battery in order to get the voltage up as well. I really wish I'd paid more attention in GCSE physics. Sorry Mrs Perkins…

10 is the Magic Number

With 10 C. limon in parallel, we hit 369μAmps! Perfect!

That still wasn't enough to get the BLE Mini board to power up - we needed to raise the voltage. But how?

Errr…. with difficulty…! Turns out it's really frickin' hard to get enough power out of a bunch of lemons to power modest hardware.

So we did what any enterprising startup does - pivot!

Power Extreme!

Ok, so can our juicers deliver sufficient juice to act as an emergency battery for your smartphone?

We found the lowest powered phone we could - the GeeksPhone Keon - running FireFox OS.

In keeping with our fruit theme, we butchered an old BlackBerry charger - and got to work…

Wires stripped, plugged into our lemon battery… What was the result?

Errr… The square root of nowt! Nothing happened. The power wasn't high enough for the phone's charging circuitry to register anything.

We grabbed a Nexus 5, installed a power monitor widget, and tried again.

Ooooooh!

This is the very definition of trickle charging. The amount of energy from 10 lemons, zinc plated nails, and copper wire is just enough to give you a few more minutes of talk time - nothing more. In a MacGyver situation, you're probably better off squeezing the lemons into your enemies' eyes.

Lessons Learned

Hackdays are a great way of playing about with technology and having a bit of experimental fun.

It's temping to think BLE is so efficient that it can be powered from harvested kinetic energy and stray WiFi beams - that's not the case. Modern battery technology is pretty complex - and that's why tiny button cells can power modern electronics and a whole bunch of lemons doesn't even get close.

One of the reasons The Lab exists in O2 is to develop a culture of "Fast Failure". We didn't spend millions of Euros and half-a-dozen months in planning meetings, requesting proposals from suppliers, and updating PowerPoint decks to do this - instead, two of us spend half a day actually trying to build something and finding out pretty quickly that it wasn't going to work.

For those of you wondering just how much of your monthly bill we spent on this? The cost was a couple of quid for the nails and wire, and we had the multimeter already. The lemons cost £3.00 for 10. I wonder if I should have splashed out on organic ones…. ;-)

What's Next

It's possible to power Xmas tree lights from hundreds of Brussels Sprouts. Would it be possible to set up a "Charge your Apple with apples" stand at one of O2's larger stores? Sure! It could make a great marketing stunt - and teach people a little basic science - but, for now, I'll stick to my wall socket.

Toodle pip!

So, when they announced their new app, I was expecting something a little bit special. And that's exactly what I've got.

An automatic torch to help you when you're rooting around in dark cupboards trying to read your meter. Brilliant.

So, not only does the app fulfil its main purpose (submit gas & electricity meter readings, see my bill, etc), someone has obviously taken the time to see how the app works in the real world. Sure, there are plenty of standalone torch apps in the world - but this is the first time I've seen one so thoughtfully integrated into an app.

Ultimately, this app is probably going to be used once per month. It needs to be simple enough to use that the customer doesn't have to relearn how to operate it every time. More than that - it needs to be delightful to use.

As much as we would all love our users to open our app several times a day, the reality is that they won't. That's why we need to concentrate not on beauty, not on overall UX, but on tiny moments of joy which reminds people why they should keep our app on their phone and keep coming back to it.

We based our estimations on the Europa Solar Calculator which estimated that they would generate around 2,700 kWh per year.

Annoyingly, we haven't been able to hook the panels up to the Internet, so I can't get daily readings. So, every three months we have to manually look at the meter. Last month, after a year of operation, it stood at...

03172.42 kWh

That totally busted through our estimations!

The last three months saw them generate a whopping 489 kWh.

Now, I'm not sure if the weather this year has been particularly favourable, and I've no idea if next year will be as sunny, nor do I know whether the panels effectiveness will degrade over time.

But, still, that's pretty damn impressive!

Money Money Money

The current Feed-In-Tariff set by the Government (and guaranteed for 25 year to rise with inflation) is around £0.454 per kWh generated, plus £0.03 per kWh exported to the grid. It's assumed that 50% of what you generate is exported.

That means, over a year, our solar panels have earned us, roughly £1,500! (The price has recently gone up, so it's not a straight calculation.)

That's comfortably ahead of our expectations of £1,200 per year. It also doesn't take into account energy savings - we don't live there - so with the recent energy price rises, that's a decent saving for the tenants.

I'm really looking forward to seeing how they perform over the next twelve months.

If you'd like solar panels installed, I can highly recommend Sunny Future Solar.

The good news is that Sam from Humm is actively working on making the Adobe Air upload application work under Linux. So, how does the process of uploading your data to the service work?

All in one

The Application is a real "one click" experience. It autodetects your SD card, sees which files are there, and sends them straight to the server after you click the button.

Here we go...

So, after waiting a few hours for the data to process - what do the graphs look like.

Monthly Electricity Usage (click for bigger)

Well, they're a little underwhelming and a bit of a mess. Now, in fairness, I've only uploaded a few weeks' of data - no doubt the graphs will be richer when I've uploaded more data. This is a beta service and it's clear that there are a lot of improvements being made.

Weekly Comparison (Click for bigger)

Annoyingly, you can't compare two different Plug Bugs - so I've no way of knowing if my computer is more energy efficient than my laptop.

There doesn't seem to be a way to go into historic data

There's no graph to show my gas usage. I've questioned the wisdom of a gas monitor - it only looks at hot water so doesn't measure cooking or hot air systems.

Overall, this is a pretty good start. I can see my hourly, weekly and monthly usage and compare how I'm doing.  It could do with some spit and polish to make the graphs more intuitive and useful.  I wonder if there's any way to get the data into Pachube or something similar.

In order to visualise the data, I have to manually upload the files to the Green Energy Options MyEnergy site.  Rather than a simple web based uploader - GEO have decided to go with Adobe Air as their platform for uploading and viewing the data.

Here are the steps I had to take to get the service working - as you will see, it wasn't easy and ultimately failed.

The site asks me to install some software in order to upload the files.  My Operating System is Ubuntu Linux - I was afraid this software would be Microsoft Windows only and I'd have to use WINE.

Let's go!

Then the site tells me I'll need to install Adobe Air.  Luckily, this can be done through the browser.

Nice and Easy?

The installation through the browser was fairly swift and painless.

Installation of Air

The installer popped up some fairly scary warning messages.  If you're going to be asking people to install your software, you need to make it as easy as possible to get.  Signing and certifying your software will reduce "error" messages like this and increase confidence in your product.  Without it, I've no way of knowing that your site isn't compromised.

DANGER, WILL ROBINSON

True to the installer's word, I ended up with an icon on my desktop.

Desktop Icon

So, I double click...

This looks hopefull...

The software has a think before popping up this helpful error message.

...DENIED!

I know what you're thinking.  "The silly sod has forgotten to plug the SD card in."  Ummm.... nope!

SD card inserted

The SD card is inserted - using the supplied reader - and my system has identified and mounted it correctly.

At this point, I'm stuck.  So I give up.

What's so frustrating is that it doesn't have to be this way.  I've no idea what the benefits are of Adobe Air - but asking your users to install something new is always problematic.  Plain old Flash - which has its fair share of problems under Linux - allows you to upload multiple files - take a look at the standard WordPress image uploader.

WordPress Multiple Select

As with everything - Keep It Simple and Stupid.  Do your users really want to install extra software for your product? Do they really need to? Is there another, simpler way which gets the same results?

I'm sure - uber-hacker that I am - that I'll figure out a way to make it work. But the point is, I shouldn't have to.

The left half of the Duet is concerned with electricity. I want to focus on the "Speed Dial" on the top and the "Daily Counter" in the middle. The units can be £, kWh or Kg of CO2 - a click on the fascia buttons switches between the three modes.

Cold Hard Cash

As you will see in the first picture, the speed dial shows how "fast" you are using electricity. The more you are using, the more the dial lights up. A perfect metaphor for usage. There's an indicator in the middle of the dial which gives you a numeric representation of your speed

In the middle of the unit is a daily counter.  This shows how much you have used since midnight.  The above image shows monetary usage, this next image shows kWh usage - the actual amount of electricity.

kWh Used

Immediately two things are obvious - kWh are more precise and simultaneously harder to understand.

Perhaps the least useful of the three modes shows Kg of CO2 released due to energy usage.

Kg of Carbon Dioxide

Given that the duet doesn't know whether my electricity is being generated by coal burning or wind turbines, it's a slightly spurious figure.

As Joe Baguley points out in his article about the Humm Trio, understanding the read-out makes it easier to understand what's going on.

I now know my dishwasher costs 16p/cycle, compared to my washing machine at 7p, and that running it on the thermonuclear remove the spot-welded lasagne from the dish mode only takes it to 17p.

Money is highly conceptual.  You can't hold a kWh in your hand and most of us have never seen a Kg of CO2 - but we can all visualise the pennies trickling from our wallets.

The problem is that the monetary graph doesn't have enough precision in it; pennies are counted - not tenths of pennies.  Switching your oven on may generate a leap from 8p an hour to 50p an hour - but switching off your lights may only drop you from 8.8p to 8.1p - a change that you won't see on the dial.

I would make the following suggestions

• Where possible include as much prescision as possible.  There's space on the readout for fractions of pennies - make use of it.
• Allow the different readings to be displayed in separate units.  For example, the Speed Dial could be in kWh while the daily total could be in £.
• The Duet allows you to set your unit cost of electricity - perhaps it should allow you to set how green your tariff is to ensure the Kg CO2 count is correct?
• It's fascinating to watch the speedo jump when the oven switches on, or drop when the TV goes off - perhaps large events should be recorded on the SD card.  Currently it only has 30 minute precision.  Given a whole day of 30 minute readings takes ~50KB of a 2GB card - I wouldn't think it unreasonable to record either twich the amount of data or only where there have been significant changes in usage.

Overall, the speedo idea is neat - you don't need to understand everything that goes on to get a quick visualisation of how much energy you are using.

As I mentioned in the unboxing - there's an integrated 2GB SD card for the Duet to record the energy usage.  As the trial progresses, I should be able to upload the data to the website for them to analyse.  They faithfully promise to send me a spreadsheet of the data if I want it.

Well, what kind of geek would I be if I didn't have a tinker with it my self :-)

I was expecting the files for each day to be rather large - they're only about 50KiB per day. So a 2GB card is good for about 40,000 days - or a little over a century. Guess I won't have to worry about making room on the card.

Each file is named with a datestamp, so my first was GEO90914.DAT.

I was sort of expecting it to be compressed, encrypted, munged and otherwise impenetrable.

It was CSV.

14/Sep/2009 20:00,GMU1   ,00000.000,1,09.68
14/Sep/2009 20:00,GMU2   ,00000.000,1,09.68
14/Sep/2009 20:00,GMU3   ,00000.000,1,09.68
14/Sep/2009 20:00,BSU    ,00000000,00000000,00000000,00000000,00000000,0
14/Sep/2009 20:00,SAU1   ,00000.000,0,09.68
14/Sep/2009 20:00,SAU2   ,00000.000,0,09.68
14/Sep/2009 20:00,SAU3   ,00000.000,0,09.68
14/Sep/2009 20:00,SAU4   ,00000.000,0,09.68
14/Sep/2009 20:00,SAU5   ,00000.000,0,09.68
14/Sep/2009 20:00,SAU6   ,00000.000,0,09.68
14/Sep/2009 20:30,GMU1   ,00000.000,1,09.68
14/Sep/2009 20:30,GMU2   ,00000.000,1,09.68
14/Sep/2009 20:30,GMU3   ,00000.000,1,09.68
14/Sep/2009 20:30,BSU    ,00000000,00000000,00000000,00000000,00000000,0
14/Sep/2009 20:30,SAU1   ,00000.000,2,09.68
...

Oh happy day! I'm guessing that GMU1,2,3 refer to the "plug bugs" - the electricity sensors - not sure yet what the others are, but I'm sure I'll figure it out soon.

Having all the data in CSV makes it really easy to whack into a spreadsheet or on to a webserver to do some nice data visualisations. Good job, Humm!

However, it's a bit of a pain walking from one room to another with an SD card. It also means that my visualisations will be out of date until I manually update them. If only there were a way to automate the process...

So, I'm now looking at something like Eye-Fi. The Eye-Fi is an SD card with built in WiFi. It's supposed to be used for instantly uploading pictures from a digital camera - but I see no reason why it shouldn't be made to upload the .DAT files the duet creates.

We'll have to see...

Pairing the device was easy and the manual was very clear as to which pipes need to be monitored. A velcro strap makes it really easy to attach the wires to the pipes.

Once it's all plugged in, this is what it looks like

Clips and Cupboards

The monitor now shows whether your hot water and radiators are on.  It will show whether the water is cool, heating up or hot.  It can optionally show how long the hot water has been heating.  All very swish.

Cookin' on Gas, Baby!

There's only one slight problem with the set up - and it's our flat.  Rather than conventional hot water radiators, we have hot air.  The same boiler that heats are water has a fan which pipes hot air around out house.  We also use a gas hob to cook.

The Duet only monitors gas usage by hot water.  So I'm not sure how much use it will be for monitoring our gas usage.  In the last year, we used around 15,000kWh of gas.  Here's how our energy company recorded our usage.

Yearly Gas Usage

To really monitor gas usage, I think we'll have to go with Alistair MacDonald's ersatz suggestion - stick a webcam by the meter, upload images every hour and use OCR to figure out what the reading is.

That won't tell you what appliance is using the gas, but it will give a more accurate reading of how much gas you use per hour.

I'm already becoming quite a pain - running around turning lights off. Might need to get our boiler thoroughly serviced and our pipes and hot water tank properly insulated to make sure it's as efficient as possible.

This is a great looking unit. It has a fool proof instruction manual - however they didn't count on someone as foolish as me!

As you can see from the unboxing - this device is pretty svelte. Once on its stand and plugged in, it will nestle unobtrusively on a bookshelf.

Smaller than a paperback book

Set up is fairly straightforward.  Plug in, set the date and time, set your tariff costs, pair the device with the sensor.  That's where I came unstuck.  I was left facing the "WAITING" screen for ages.

Pairing

I tried everything. I even went to the back of the manual to find out how to reset the damn thing. I know a true geek never reads the manual but it was late and I was desperate... Then, inspiration stuck.

Take a look at the back of the unit.  There are two small black buttons.

Left button. Right Button

One of the buttons is for pairing the electricity sensor, the other is for pairing the gas sensor.  Like a fool, I'd been trying to pair the electricity sensor with the gas unit.

As anyone interested in usability knows, such things are never the fault of the user... ahem...

I was being daft, but a small label next to each button wouldn't go amiss on the next version of this device!

Once paired, I clipped the sensor around the live wire coming in to my meter. Then I plugged the sensor into the transmitter.

Near the meter

The transmitter is fairly small, so it's easy to rest it somewhere in your utility cupboard.  The sensor wire is quite long, should you not have a shelf near.  The transmitter has a range of about 30 metres according to the manual.

Both the gas and electricity sensors have multiple inputs - should you have a complicated setup such as three-phase electricity or an unusual boiler.  The Duet comes with one set of sensors for each - you can buy more if you need.

Lots of sockets

The majority of the size of the units is taken up by battery housing.  The batteries should last a year - there's a display on the Duet to tell you when they're getting low.  You can buy AC adaptors for the units if you have power sockets nearby.

Pairing the individual plug-bugs was simplicity itself.  So I've ended up with this rather fine little display.

Success!

Having done the electricity, I left the gas sensor for another day.

It's already an addictive little display.  Switching on the halogen lights in the kitchen doubles the number of kW of electricity the house uses.  Something as switching off a TV from standby is enough to make a noticeable drop.

The Duet is smarter than most other monitors I've seen.  Rather than just showing you how many kWh you've used or how much your electricity is costing, you can set a "limit" for the day.  It suggests about 10kWh per day for a small family - the speed dial then tells you whether you're over or under your daily "allowance".

Our current energy supplier allows me to crudely track my usage based on my meter readings - here it is.

Electricty Usage

I don't know whether 12kWh a day is particularly excessive.  I mean, all I've got running are a fridge/freezer, a FreeView box, a TiVo, my home server, my security camera, my DAB alarm clock, my ADSL, my WiFi router, my cordless DECT phone, my phone chargers, my...

I'm going to unplug stuff now. I may be some time...