I’ve recently replaced the diverter which manages diversion of my surplus solar electricity to immersion heater for hot water and/or electric car charger. The new unit is a Myenergi Eddi. I also needed a Harvi to transmit the output of remote current sensors to the Eddi and an accessory digital input/output board to control my older car charger from the Eddi.
The panel below sits inside my airing cupboard for close proximity to the immersion heater in operation but lifts down as an assembly for maintenance.
From top to bottom:
Home Energy Management System (HEMS) – left
Junction box – right
Transmitter to activate my older car charge point
New Eddi
TalkTalk powerline internet device which connects HEMS and Eddi to the internet over the house wiring (more robust that WiFi). There’s a mains socket behind which includes a USB output to power the HEMS. The mains plug in front powers the transmitter (above) and the various relay-activated operations.
The Harvi is connected to two current clamps and transmits the signals from those clamps to the Eddi. Each Harvi can connect to three sensors but I only use two: (i) the import/export to/from the house and (ii) the output of the solar panels.
To the left on the Harvi is the isolator for the solar panels (which has a current sensor inside) and above is the generation meter for the solar panels.
The Eddi connects to the app via the internet connection described above. The app has a range of features but the screen illustrated shows (clockwise from 3 o’clock):
Power to/from the grid (measured via Harvi)
Power from solar panels (measured via Harvi)
Power diverted to immersion heater (measured via Eddi)
Power to home (inferred by calculation from the above).
Percentage of green energy (i.e. from panels rather than grid).
I’m pretty pleased with my purchase which I found intuitive to install and works well. The system also provides capability to add more sensors so I may well add to that including a sensor for my battery on the existing Harvi and possibly one in the garage for my older car charger.
A recent move to full fibre broadband prompted a reconfiguration of my home network as the incoming cable moved to the opposite side of the house from where the incoming telephone line had been. That’s not a normal situation but it turns out that my home had previously had two telephone lines in different places, but the cable that got upgraded to fibre was not the cable that had been in use in recent time. I’ve also had further additions which prompted the idea to create a diagram of how all the devices are connected.
I was somewhat surprised to count as many as nine protocols/networks in use between different devices.
Like many homes we have a WiFi router where the fibre or telephone line enters the home. However over time I’ve been moving some devices from WiFi to Powerline adapters which carry the internet over the house wiring. This helps reduce issues where devices on different WiFi networks can’t communicate with each other and provides more bandwidth so more data can be carried more quickly.
I have four Powerline adapters which communicate with each other over the house wiring and then have different internet-enabled devices plugged into them. One such Powerline adapter is in the lounge with the WiFi router plugged into it.
The second external connection to the home is to the smart meters. There are two networks associated with smart meters: the Wide Area Network (WAN) and the Home Area Network (HAN). The HAN (which uses a protocol called ZigBee) interconnects the meters (both electric and gas) and the in-home display IHD. The WAN communicates outside the home to send consumption data to one’s supplier via a national database called the DCC. The WAN can send data as frequently as half-hourly.
I also have an additional device known as a Consumer Access Device (CAD). The CAD connects the HAN side of the smart meter to an independent database. This offers me two two things: (i) a third party app to review my electricity and gas use and (ii) data on a minute-by-minute basis rather than at most half-hourly. The CAD acts as a bridge between the ZigBee and WiFi.
Much of my home automation, particularly home heating, uses Apple HomeKit. HomeKit runs on home hubs, rather than an external cloud server. The hubs commonly connect to the individual smart devices (such as radiators valves, smart plugs, door and window sensors etc) by Bluetooth Low Energy (BLE). The low power demand of BLE allows battery powered devices to operate for months between battery replacements. My original hub was an Apple TV.
Subsequently I’ve added an Apple smart speaker which can also act as a hub. HomeKit decides which of the available hubs to put in charge, but may relay signals to and from the devices via other hubs. The smart speaker also supports a protocol called thread which allows communications to and from smart devices like door sensors via other smart devices on their way to and from a hub. Thread thus helps to extend the area that can be covered by a hub by allowing signals to and from distant sensors and actuators to travel via nearer devices rather than directly to or from hubs.
Much of my energy smart equipment is divided between my study and the the airing cupboard. Each has a Powerline adaptor allowing wired internet communication. The Home Energy Management System (HEMS) in the airing cupboard gets electricity pricing and solar predictions from the cloud and then directs the Powervault battery and the ImmerSUN diverter (partially) via the cloud. The Powervault is connected to the internet via an internet switch in my study and thence via the Powerline adapter. The ImmerSUN in the airing cupboard connects to the internet via a proprietary protocol to a bridge in my study and then onwards via the same internet switch.
The nine forms of communication are:
Bluetooth – low power and low range device-to-hub communications for battery-powered smart home devices on Apple HomeKit.
Ethernet – wired mains-powered internet devices
Fibre broadband – high bandwidth connection from home to external internet
ImmerSUN proprietary – wireless communications between mains-powered ImmerSUN devices: power diverter, bridge to internet, and remote current sensors
Radio 868 MHz – radio signal to control car wallbox in garage from home
Powerline communications – carries the internet over mains house wiring using mains-powered adapters
Thread – an extension of Bluetooth allowing signals to travel from distant devices via nearer devices to a hub thus extending the area that a hub can cover
WAN – external connection to a smart meter
ZigBee HAN – internal connection between smart meters. ZigBee, like Bluetooth, is a low power low range protocol suitable for battery-powered devices (like a gas meter). It can be used for smart devices like Bluetooth, but in the form used in smart meters is secured and not accessible directly to consumers.
We will shortly have been in this house for six years. During that time I have created three smart control systems that improve my energy costs or efficiency:
heating controls to minimise gas purchase
self-consumption controls of the electricity generated by my solar panels to maximise value of self-consumption
smart tariff controls to buy grid electricity at the lowest price
Heating Controls
Most homes have a single heating zone with one timer and potentially one thermostat controlling the whole house with perhaps some thermostatic radiator valves (TRVs) capping the temperature in specific rooms.
By contrast we have seven heating zones created by electronic temperature control valves (eTRVs). Each zone has its own timer. There is no central timer or thermostat. Each eTRV can summon the boiler on when cold rather than simply cap the maximum temperature like a TRV.
Some rooms also have links to other smart devices such as disabling room heating when the window is open or turning off heating early when there’s no movement in the room.
The intent is to save energy by only heating rooms that are in use.
Smart controls – HEMS and immersun.
Hot water cylinder with immersion heater
Car charger
Powervault storage
Self-consumption Controls
These controls manage the diversion of any excess output from my solar panels rather than give that energy to the grid. The loads are prioritised as follows:
Powervault storage battery (fully proportional)
Car charger (stepped proportional driven by ImmerSUN relay output)
Hot water (driven by ImmerSUN fully proportional output)
Last year these controls helped me to use over 90% of the output of my solar panels avoiding buying £100s of electricity and gas. The priorities are set to maximise value – #1 avoid daytime electricity use at 16 p/kWh, #2 avoid car charging at 5-16 p/kWh, and #3 avoid gas consumption at 2.96 p/kWh.
Smart Tariff Controls
These controls manage my electric devices for lowest grid energy cost. The controlled devices are:
Battery storage (Powervault)
Dishwasher
Electric car charger
Hot water heating (ImmerSUN)
Washing machine
The hardware that has this control is known as a Home Energy Management System (HEMS). My HEMS is based on a simple computer known as a Raspberry Pi. The HEMS uses foreknowledge of the electricity price and predicted solar panel output to determine when best to run the above devices. It was designed around a tariff called Octopus Agile which has 48 half-hourly prices that change daily, but is currently working with a simpler two-rate smart tariff.
Hybridised Agile and Go
Raspberry Pi as HEMS
Bosch Washing Machine
Siemens Dishwasher
device
Central Heating
self-consumption
smart tariff
Battery Storage
#1
X
Central Heating Boiler
X
Dishwasher
X
Electric car charger
#2
X
Hot water heating
#3
X
Washing machine
X
Devices controlled by smart systems
Most of these solutions are made up of commercially-available items that I have perhaps combined in a way not anticipated by their manufacturers. In particular:
I created a relay module to enable the gas boiler to be turned on remotely and programmed a series of logical rules for the Apple TV’s that act as the controllers.
I identified a way to prioritise different self-consumption devices by configuring their current clamps.
I built my smart car charger integrating various items of hardware and writing the ladder logic program that runs it.
I built the HEMS from commercially-available parts and wrote the software that runs on it to control my devices.
It been over a year now since I last reviewed what return I was getting on my investment in energy smart technology – solar panels, battery storage etc – so I think an update is due. This time I’m going to take the input data from my immersun system – one year of data from start of June 2020 to end of May 2021.
ImmerSUN diverter
ImmerSUN monitoring – June 2020 to May 2021
Diverted – this is where the immersun sends any surplus solar electricity to my immersion heater to make hot water. In 2020/1 we diverted 1056.6 kWh to hot water saving gas at 2.82 p/kWh. However the gas boiler isn’t 100% efficient losing heat both via the flue to the outside world and also via the hot water pipes to the home rather than hot water. If we assume 80% efficiency at the tank then 2.82 p/kWh as gas at the boiler is 4 p/kWh as heat in the tank. 1056.6 kWh at 4 p/kWh saved £37.25.
Exported – this is where I’m unable to use the solar power that we generate and it overflows into the grid. I’m not paid for Export so this is worth nothing to me.
Generation – this is the energy that we generate in the solar panels. I’m on the UK’s legacy Feed-in Tariff (FiT) scheme which pays me to generate electricity. In 2020/1 I was paid 14.65 explicitly for every kWh that I generated. I also received deemed (rather than metered) Export which paid 5.5 p/kWh on 50% of the kWh that I generated (which is where the ‘deemed’ part comes from). 5.5 p/kWh on 50% is equivalent to 2.75 p/kWh on 100% of the Generation making my revenue 17.4 p/kWh per kWh generated or £693.51 on the 3985.7 kWh that I actually generated.
Imported and House – these are respectively the electricity that I buy from the grid and that which I used within the home including appliances and car charging, some of which will comes from my own solar panels. The difference between House and Imported is the electricity that I used from my solar panels which would otherwise have been bought from the grid. If I assume that each kWh that I use from my solar panels avoids buying a kWh of electricity from the grid at 16.36 p/kWh (current Energy Saving Trust value for the average UK electricity price) then I avoided buying £423.81 of electricity by using the output of my solar panels.
Diverted
1056.5 kWh
*
£0.04
=
£37.25
Exported
338.6 kWh
*
£0.00
=
£0.00
Generated
3985.6 kWh
*
£0.17
=
£693.51
Imported
4748.9 kWh
*
-£0.16
=
-£776.92
House
7339.4 kWh
*
£0.16
=
£1,200.73
Total
£1,154.56
Return on smart energy investment @ 16.36 p/kWh grid price
With an investment of £8,670, £1,154 represents 7.5 years to pay back the capital invested.
I’m actually on a smart tariff so my electricity cost in this period at 8.05 p/kWh was significantly less than the UK’s average 16.36 p/kWh. This lower price will arguably reduce the value of the energy generated by the solar panels for self-consumption, but equally the ability to maximize the value of a smart tariff is itself a saving.
Diverted
1056.5 kWh
*
£0.04
=
£37.25
Exported
338.6 kWh
*
£0.00
=
£0.00
Generated
3985.6 kWh
*
£0.17
=
£693.51
Imported
4748.9 kWh
*
-£0.08
=
-£382.29
House
7339.4 kWh
*
£0.08
=
£590.82
Total
£939.29
Return on smart energy investment @ 8.05 p/kWh grid price (excluding the tariff benefit itself)
Using my actual average energy price rather than the higher UK average grid price pushes down the return by over £200 (£929.29 versus £1,154.56). However the costs of buying the imported 4,748.9 kWh falls by £394.63 through the tariff benefit, increasing the annual return to £1,333.93, and reducing the payback period from 7.5 to 6.5 years.
Thus, had I invested in this technology at one time back five and a half years ago and shortly after we moved to this house, then we’d have been in sight of payback with 1 or 2 years left. In practice of course I’ve made the investments at different times (solar first five and half years ago, battery around a year later, smart tariff later still), so my payback will be achieved a little later.
A snapshot of the ImmerSUN diverting to hot water
Some other statistics:
Of solar panel output:
91.5% replaced bought energy (self-consumption)
65.0% replaced bought electricity
26.5% replaced bought gas for water heating
8.5% was exported to the grid
Of incoming electricity:
54.4% was from the grid
45.6% was from the solar panels (“green contribution” in ImmerSUN’s terminology)
As we look to install a second electric vehicle charger that becomes a challenge for the electrical supply to our home which is limited to 60 Amps. I recently saw a page online by which our DNO (District Network Operator) – UKPN – could be requested to install an uprated fuse.
60 Amp cutout and Economy 7 meter
100 Amp cutout and Smart Meter
A comparison of cutouts and meters
(Some readers may be curious regarding the irregular size of the hole around the cutout and meter. When we looked around the house I recall reflecting upon the fact that I didn’t know where the meters and consumer unit were. The mystery was explained when we moved in and these items were found to be behind a false wall in what is now my study having previously been concealed by pictures. We continued the practice by buying pictures to conceal three holes in the wall (now four) covering: electricity meter, gas meter and consumer unit (adding generation meter and isolator for solar panels).)
I’m delighted to report how smoothly the change went. I was advised that it might be the case that the work could not proceed on a first visit, and that it might be necessary for my electricity supplier to update meter and/or cables from meter to consumer unit; but the installation proceeded on the first visit with not only the cutout changed from 60 to 100 Amps but also the cables between the cutout and the meter renewed. All of this at a price of precisely nothing.
I had been reasonably confident in the meter as that had been renewed almost exactly two years ago when we moved from Economy 7 to a smart tariff, but I was less clear about the cables between the meter and the consumer unit. In the event all was fine.
The extra 40 Amps should now mean that I have no issues adding a 7.4 kW car charger which draws 32 Amps. I have previously posted about the new car charger. My task of writing the software for it is now considerably simplified as I shouldn’t need to worry about managing the after diversity maximum demand of the house to not exceed 60 Amps, and can concentrate on the other smart controls – tracking my solar surplus and responding to the smart tariff.
Regular readers will know that my Energy Smart home includes a storage battery. That battery is either charged from my solar panels (effectively free electricity), or low cost electricity bought from the grid, or some combination of the two depending on the solar forecast for the day ahead.
Powervault storage
Solar forecast
The logic of how much battery charging is required has until now been driven by a set value for the number of charging hours required. The number of hours of solar charging predicted is deducted from the the number of charging hours required to calculate the number of bought charging hours required outside the solar production window.
Bought charging hours required :=
Total hours required – Solar hours predicted
However with experience this appears to be a sub-optimal arrangement. At one extreme on a very sunny day the battery will fully charge and then be allowed to discharge continuously through all other hours, there is no middle ground in which the battery is not permitted to discharge through the night. However at the other extreme if the battery is replenished entirely from the grid then there will be hours when discharge is not permitted since, after accounting for cycle efficiency, the value of the electricity in the battery is higher than the cost of that from the grid and thus it’s better value to use grid electricity than stored electricity. As there are fewer discharging hours then fewer hours of charging will be required to refill. Thus the depth of discharge is greater when charged from solar than from the grid requiring more charging hours to refill. Leaving the longer charge time for a full charge in use then creates a risk of charging the battery when the grid price is higher than necessary leaving the battery possibly full by the time the lowest cost grid energy is available. Having a more accurate target for the charge time would enable the lowest cost charging periods to be selected more precisely.
Schedule with some solar
The new refinement is to automatically adjust the bought charging hours between two existing user-defined values: the existing target hours and the maximum charging hours currently used just to cap charging hours during plunge pricing events (i.e those with negative cost events). The new algorithm can adjust to any value between the two limits in half hour intervals. As currently configured that’s anything between five and seven hours. The new algorithm is:
Total hours required := minimum (Maximum hours from plunge, maximum (Target hours, Solar hours predicted + 1))
One of the challenges in the smart home world is to distinguish between a group of functions associated with remote control of devices in the home for aesthetic or convenience reasons versus automation associated with the management of electricity costs, carbon management, or smart grid integration. I thus choose to differentiate using the terms Smart Home and Energy Smart.
Space heating. In many homes space heating is controlled by a central thermostat and timer, possibly in combination with Thermostatic Radiator Valves (TRVs). In my home thermostats and timers are commonly pushed down to room level with individual rooms set points and schedules. General advice to reduce heating costs is to reduce heat loss through insulation and lower temperature set points, which I have but also add only heating rooms in which heat is required.
Window management. On occasions household members were known to go out leaving windows open. We now monitor the most commonly left open windows (plus the garage door) and use their status to illuminate and colour a smart bulb in the hall near the burglar alarm panel. The same window sensors can also be used to disable heating in rooms while the window is open.
Lighting control. We automate dusk-to-dawn external and internal lighting by the front door and in the downstairs hall. There’s overlap in bulbs between Window Management and Lighting Control.
Watchdog. To improve the robustness of all the rules operating the above functions, I have a smart plug that cycles on and off automatically at regular intervals and is used to trigger re-evaluation of the rules.
Battery Storage. Storing surplus output from my solar panels for later use, or buying energy from the grid when the price is low to avoid buying later when the price is higher.
Car charging. Managing my car charger to absorb surplus solar energy or buy energy from the grid when most cost-effective.
Water heating. Managing my immersion heater similarly. My immersun manages self-consumption of the surplus from my solar panels by diverting a proportional amount of power to the immersion heater, while the HEMS can boost the immersun at full power when the bought electricity price is suitably low.
Both Smart Home and Energy Smart
WIFIPLUG smart plug
Bosch Washing Machine
Wet goods. Controlling dishwasher and washing machine for lowest energy cost at the boundary of Smart Home and Energy Smart in both the Apple HomeKit ecosystem and with API integration for HEMS.
The Smart Home group of devices is managed via various user-friendly interfaces within apps like Apple’s Home or the Eve app where rules can be created of the form if {any trigger(s)} and {all conditions} then set {scene(s)}. These are processed by a hub which in my case is an Apple TV (or two).
On the other hand the Energy Smart devices are managed via the HEMS and are controlled by more fundamental programs (strictly in my case scripts) which are executed on my HEMS (which is based on a Raspberry Pi with HEMS-specific programming of my own creation.
Apple TV as Home hub
Raspberry Pi as HEMS
Contrasting Smart Home and Energy Smart controllers
In summary then, the Apple HomeKit ecosystem provides a smart home environment with a comparatively wide variety of supported devices managed from Apple’s own Home app or companion apps from the device manufacturers; while the Energy Smart side is in its relative infancy and (at least as far as my integration goes) quite a lot of bespoke software.
For me the need for much bespoke software is because I had the majority of the devices first with no thought when acquired of doing a HEMS-like project. They were originally bought or developed to maximise self-consumption of the output of my solar panels, so I had to develop the software to interface to what equipment I had. However for the Apple HomeKit, having settled on Apple HomeKit largely because we were iPad users, it becomes relatively easy to add additional devices that are sold as compatible with the HomeKit ecosystem.
Regular readers may recall that our hot water can be generated in 3 different ways: (i) conventional gas boiler, (ii) from grid electricity and (iii) from the surplus on my own solar panels. Attractions of these options are that gas is always available and stable in price, but my grid electricity is lower carbon and may at times be cheaper than gas, and my solar electricity is lowest in both carbon and cost but is subject to significant daily and seasonal variation.
Hot water cylinder with immersion heater
Smart controls – HEMS and immersun.
The logic to sort out which source to use is managed by my HEMS. Gas is the baseline and the gas boiler is set to heat water for an hour a day in the early evening to ensure that baths etc are possible. The heating is thermostatically controlled so it doesn’t heat if the water is already hot, and that thermostat is set slightly lower than the immersion thermostat too.
The ImmerSUN normally operates automatically to divert surplus solar electricity proportionately to the immersion heater after the needs of general house load, battery charging and car charging have been taken. However if the electricity price is negative (yes, really) then the HEMS may override the ImmerSUN so that water heating is not done by free solar but instead may be delayed to allow use of paid-to-use electricity.
The final part of this triumvirate is buying electricity from the grid to heat water. Here the price of bought electricity is compared either to the price of gas and a decision made to use electricity when it is cheaper (it’s always lower CO2), or compared to the price of surplus solar (effectively zero) to buy from the grid. Both of these are obviously comparisons with a price threshold but until now the choice of threshold has been made manually – typically against gas in winter when solar output is limited and against solar in summer when more readily available. However the reality of UK weather is that this is a compromise as it may be very sunny one day but very dull the next.
Solar forecasting
The new refinement therefore is to use the existing solar forecasting integration. Solar forecasting already informs HEMS decisions about when to charge the storage battery from the grid and when to operate the wet goods (dishwasher and washing machine). The latest change is that the solar forecasting is now also use to choose whether to base a decision to buy electricity for water heating against a threshold related to the gas price or against the price of surplus solar PV.
HEMS schedule for July 4th.
The above schedule shows that, as a result of no significant solar production anticipated on the 4th, the HEMS has compared electricity price to gas price and thus elected to buy electricity from the grid to make hot water overnight since at 1.7640 to 2.4675 p/kWh electricity is cheaper than gas.
It can’t be very often that an energy company blogs about its customers’ achievements. Last week it happened. Octopus Energy wrote a blog entitled “How to hack your home for cheaper, greener, energy with our open API” which featured the achievements of its customers, and Greening Me got two honourable mentions.
For those not familiar with geek-speak, API is Application Programming Interface which is a mechanism by which an app, webpage or computer program may give commands to, or receive data from, another program – often a web server. Such APIs are often closed (that is that they are only available for use by the creator’s own app or webpage etc), but in this case the Octopus APIs are open so that they can be used by others (including me) to create our own apps, webpages, or other integrations to get data from Octopus. That data may be future price information for a UK electricity region or the actual consumption from a specified electricity meter for example. Octopus document their APIs and encourage others to find innovative uses for them.
Other APIs that I use were either documented privately by the manufacturers of the equipment concerned, although the manufacturer has not put the API in the public domain, or were reverse-engineered by myself or others by looking at how the manufacturer used it or at the internet traffic that it generated and working out how we could use it ourselves for a slightly different purpose. Such purposes would include controlling equipment other than by the manufacturer’s own app, or collecting data into some non-supported form.
Diversity in third party solutions using the Octopus API.
Greening Me’s first mention in the blog came under the Smart Electric Vehicle (EV) Charging section where Octopus wrote..
One of our own smart energy pioneers, Greening Me, has used a Raspberry Pi and an add-on circuit board with our API to switch his electric car charger on/off and set the best time for his hot water immersion heater to run. He also has solar generation and so he can direct his solar power to either his smart car charger or hot water.
The first reference
Later in the “I’ll do it myself (tech level 🌶🌶🌶)” section after describing a group of “smart home pioneers” Octopus wrote..
Together with Western Power Distribution, Passiv Systems have also created something similar to Greening Me’s HEMS, which is currently being trialled and evaluated as another BEIS funded research project called MADE.
The second reference
So it’s official – I’m a “smart energy pioneer” and a “smart home pioneer”. I also quite like the idea of being a “home hacker” in the positive sense of someone who makes their own home conform to their wishes. If you’d like to read the full blog post from Octopus Energy then you can do so here https://octopus.energy/blog/agile-smart-home-diy/.
Most of us are used to a simple world of electricity where we pay for what we consume. For most folks like myself based in the UK that’s typically a fixed price per kWh/unit consumed regardless of time of day, even through dual-rate tariffs have been around for decades – the best known being “Economy 7” tariffs. However as the grid gets smarter then there are increasing opportunities to save on, or make money from, electricity.
Electricity opportunities for import / export and positive /negative cost.
Conventional – pay for power.
This is the area with which most of us are most familiar. We all get the idea of paying for the power we consume. Most UK households pay a fixed price per kWh/unit regardless of the time of day. We have a competitive electricity market, so there are the choice of 70 to 80 different providers who will make different offers regarding standing charge (sometimes marketed as a subscription) and unit cost.
There’s also the opportunity to choose between a flat rate tariff or Economy 7 even on conventional meters that provide a discounted night rate for 7 hours.. These typically provide a discounted night rate, but may charge a little more during the day. They used to advertise these as ‘less than half-price electricity’ but that’s often not the case now.
Stepping up in complexity (and opportunity) smart meters provide the opportunity for a more diverse range of tariffs including different cheap night time periods, more than two rates at different times of day (in extreme 48 half-hourly rates), and a free day at the weekend (i.e. a zero rate of a weekend day) etc.
Beyond that my own tariff (Octopus Agile) not only has up to 48 different half-hourly prices/day that change daily based on that day’s market prices. That might sounds a bit scary but it can yield very cheap electricity prices – 4.48 p/kWh for me in April/May 2020 (for example) which is a third of what most people pay.
My electricity costs April/May 2020
(The original version of this post wrongly had the table from my gas bill above and mistakenly claimed that I had paid “a quarter of what most people pay” rather than a third. Total consumption is untypically low at the present time due to limited miles driven.)
Agile – paid to consume
Top left on my initial diagram is Agile – paid to consume.
One of the features of the wholesale electricity market is that at times the market price for electricity goes negative. At such times the a significant excess of supply (typically because of high output from wind turbines) over demand (often but not always at night) yields a negative price so electricity companies looking to buy electricity are being paid to take it. Most electricity companies will continue to charge their customers the standard price in these circumstances but, with the octopus Agile tariff, the negative pricing is passed to the consumer so that you are paid to consume electricity. This is one of the reasons that my electricity costs are so low.
My electricity costs – Saturday 23rd May 2020
The above chart shows my electricity costs for Saturday 23rd May 2020. The blue line shows the half-hourly electricity price varying between minus 10 p/kWh and plus 15 p/kWh. The red bars show my electricity consumption in each half hour. You can see how consumption tends to be highest when the price is lowest leading to an average price paid of minus 6.22 p.kWh (i.e. they paid me to use electricity) – indeed they paid me 82.4 p to buy electricity that day.
Conventional export – paid to export
The next opportunity to make money from electricity is to sell it to the grid. Obviously that depends on having a source for the electricity typically a generating asset like solar panels or a wind turbine, possibly coupled with a storage device like a battery. It’s also possible with a battery alone, but I know no-one who does that as the economics are more challenging.
The UK currently has a scheme called Smart Export Guarantee (SEG) where you can sell your export to an electricity company. Prices vary enormously so it’s worth shopping around and not just assuming that your electricity company will give you a good offer.
SEG rates from the Solar Trade Association
There is also a smarter SEG option where Octopus offer a dynamic SEG based on market rates (Octopus Agile Export) which may at times offer a high rate, but also offers a lower rate at times, and is thus perhaps better suited to those with storage.
I myself am NOT on such a tariff as I’m on an older legacy Feed-in Tariff (FiT). Despite its name FiT is a generation incentive, not an export incentive. As a generation incentive FiT encourages self-consumption since each kWh that I consume myself does not reduce my income, whereas on SEG each kWh that I use myself (such as making hot water) would reduce export income. So, for example, if I use a kWh of electricity to make hot water that’s saved a kWh (or thereabouts) of gas at around 3 p/kWh, but if I was on SEG then I might have lost 5.5 p/kWh of export revenue to save 3 p/kWh on gas which is clearly an on-cost not a saving. There are other benefits of course because I’ve reduced my carbon footprint by using my own low CO2 electricity to replace a fossil fuel, but it’s not (in this case) improving my financial position.
A further area of research by others is V2X (V2H and V2G) – taking electricity stored in an electric vehicle and using that within the home (V2H) or exporting it to the grid (V2G).
Export penalty – penalised for export
A logical consequence of this smart grid that I’ve outlined is being penalised for export. If there are times when the market price for electricity is negative then if I were part of that market then I might expect to be penalised for export. This doesn’t actually exist in the UK, as the only model that links SEG payments to the market price, Octopus Agile Export, protects its customers from negative pricing.
Should consumers be exposed to this risk then a logical behaviours would be:
To manage self-consumption into the negative export periods, and potentially thus increase export in the positive export periods. For example disable diversion to an immersion heater or car when export price is positive, and then maximise self-consumption when the export price (and presumably the import price also) is negative.
To disable the generating asset to avoid the export penalty.
Conclusions
Some people like myself will find developments in the smart energy sector a fascinating and engaging topic with opportunities both the save money and engage in creating a cleaner and greener electricity system.
However given that many choose not to even participate in the competitive market for electricity supply created when the regional electricity companies were privatised in late 1990 (i.e. 30 years ago) then there will be a significant number who are not so motivated.
This then creates opportunity for a wider variety of smart offers. Some products, at the Agile Octopus end of the spectrum, giving the consumer the opportunity to benefit from their own decision making, while others look more like a traditional dumb tariff with a very simple price structure but potentially making the energy company a more active manager of the home appliances so that the consumer hopefully plays a lower unit rate while the energy company takes responsibility for managing the assets within the home.