A bit of a diversion

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.

Eddi installed in airing cupboard

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.

Harvi transmitter
The Myenergi app

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.

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Powervault battery control states

One of the roles of my Home Energy Management System (HEMS) is to switch the control state of my Powervault storage system. Many users would probably leave the system in Normal where it always either charges or discharges proportionally to solar surplus or deficit respectively. Other users on time of use tariffs might also program charging on cheap night time electricity in a fixed time window. However my HEMS integration allows for automatically charging in varying cheap windows only when solar production won’t be enough to fully charge the battery.

Powervault G200 storage system

The Powervault has six Control States covering different combinations of charging and discharging behaviour. Only three of these are used in my implementation. The other states could be more relevant if I was paid to export to the grid, and the value of that export started to exceed bought electricity costs; but in my case I’m not paid for export and thus any export is an error state.

Control stateChargeDischargeWhen used
Force dischargeNoFull powerunused
Only dischargeNoProportionateunused
NormalProportionateProportionateHigh electricity cost
Only chargeProportionateNoMedium electricity cost
Force chargeFull powerNoLow electricity cost
Powervault Control States

While I could use the HEMS to load a full daily schedule into the Powervault, instead I store all my schedules in the HEMS itself and switch the state of the Powervault (and indeed my other devices) every half hour as dictated by the schedule. This approach also gives me some flexibility to nuance Control State as a function of state of charge which isn’t available via the Powervault’s own scheduler.

The HEMS thus has three roles:

  1. Creating the daily schedule from future electricity prices and the solar forecast.
  2. Switching the states of the devices every 30 minutes following the schedule.
  3. Real time data display and data upload to Solcast the solar forecasting service.
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Home networks

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.

Home networks

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.

Smart metering and external networks to home

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.

Apple HomeKit smart devices

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:

  1. Bluetooth – low power and low range device-to-hub communications for battery-powered smart home devices on Apple HomeKit.
  2. Ethernet – wired mains-powered internet devices
  3. Fibre broadband – high bandwidth connection from home to external internet
  4. ImmerSUN proprietary – wireless communications between mains-powered ImmerSUN devices: power diverter, bridge to internet, and remote current sensors
  5. Radio 868 MHz – radio signal to control car wallbox in garage from home
  6. Powerline communications – carries the internet over mains house wiring using mains-powered adapters
  7. 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
  8. WAN – external connection to a smart meter
  9. 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.
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Reviving the battery II

Last December I wrote of reviving my Powervault home storage battery with new internal batteries. However subsequently I decided that my old batteries were worth more to me for their remaining storage capacity than they were to me as scrap, and instead I would try to use both my old and new batteries.

I knew that there wasn’t space inside the case for two sets of batteries so I planned to add the additional batteries in a separate rack outside the standard case.

Powervault G200 storage
Electronics side of G200

I decided to explore the right hand side of the Powervault where the controls reside. The picture shows a large blue box which is the inverter/charger and handles the conversion of AC to DC to charge the battery, and DC to AC to discharge the battery. The open green circuit board to the right controls the inverter/charger and connects it to the internet for monitoring and control. Down the middle is an umbilical that connects the batteries (on the reverse side of the panel) to the inverter/charger. Each pair of batteries on a shelf is connected separately to the inverter/charger.

I fairly rapidly determined that there wasn’t space to add additional battery cables to the inverter/charger so instead I added two terminal blocks (see right) in the free space to the right, moved the existing battery cables from the inverter/charger to the blocks, and then added new cables from the blocks to the inverter. At this point the system was checked to ensure that all was working correctly.

Terminal block with applications
DC fuse

I then added two DC cables from the blocks, through a suitable fuse, and through new cable glands to the external batteries.

All the additional parts including batteries, blocks, cables, fuse and glands are intended for similar battery storage applications in boats or caravans.

The results of this are that the battery continues to function correctly supporting the needs of the house. The above graphs, from Powervault and smart meter respectively, show:

  • 00:00 to 00:30 – home still running on stored energy from yesterday having already run through yesterday evening on stored energy.
  • 00:30 to 01:00 – battery charges for half an hour on cheap rate power (7.5 p/kWh) as HEMS predicts that today may not be sunny enough to fully charge the battery.
  • 01:00 to 04:30 – battery idle while other household loads charge from cheap power.
  • 04:30 to 07:00 – house runs from stored energy until sun comes up.
  • 07:00 to 18:00 – house running from solar with battery charging, car charging and water heating at times from solar. Some export from 15:00 as all storage devices (battery, car and water cylinder are fully charged).
  • 18:00 to 00:00 – home runs from battery.

Through the day the battery supported the house to the tune of 5.18 kWh and then the next day for 30 minutes until the cheap rate started. The Powervault had notionally 4 kWh usable capacity as supplied, although theoretical capacity was higher (3 x 120 Ah x 24 Volts = 8.64 kWh). Theoretical capacity is higher now, but I suspect that the control board continues to limit the usable capacity. A low ratio of usable capacity to theoretical capacity should be good for battery longevity as depth of discharge is limited. The older batteries have now been in use for over six years, although they have only been supported by the newer batteries for a couple of months.

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Transportation update

It’s approaching sixteen years since I bought my first electric vehicle.

Things have moved on enormously from my first electric vehicle – a REVA G-Wiz. The G-Wiz is a small vehicle similar in size to a Smart car, but strictly was not even a car at all but rather a quadricycle. As a quadricycle it is limited by law in both weight and power resulting in a tiny underpowered vehicle compared to even a small car, however that was all that was available at the time. It was good for 30 to 40 miles according to time of year and speed and maxed out at around 50 miles per hour although 30-40 miles per hour was more achievable.

2007 REVA G-Wiz
2014 Vauxhall Ampera

In the summer of 2014 I bought a new Vauxhall Ampera. I’d initially seen the Ampera at a motor show and dismissed it as neither a full electric vehicle or a plug-in hybrid. However a few years later and now married with a young child I was looking for something bigger. Now I saw it as being more capable than the G-Wiz in size, range, and safety with the bonus of having an engine for the occasional longer trip. I’ve now owned it for over eight years.

The latest addition to the household is a 2020 Ford Kuga PHEV. This is similar to the Ampera in many respects with some variations.

2020 Ford Kuga PHEV
AttRiutereva g-wizVAUXHALL Ampera Ford kuga PHEV
Usable battery size10 kWh10 kWh10 kWh
Range30-40 miles30-40 miles30-40 miles
Seats2+2 seats4 seats5 seats
ConnectedNoNo (at least in Europe)Yes
Electrical capabilityLow (heavily compro-mised versus ICE)High (Same as ICE)Medium (Poorer than ICE but keeps up with traffic)
Electrical inlet connector3-pin caravan5-pin BS EN 62196 Type 1 / J1772 7-pin BS EN 62196 Type 2
ICE capabilityn/a (BEV)Conventional 1.4L Atkinson 2.5L (for economy)
Transmission Simple reduction between electric motor and wheels. No ICE or variable transmission ratio.Similar to Kuga but has additional clutches and brakes allowing transmission to either work as powersplit or separate into a series hybrid with a generator set connected only electrically to the motor and wheels.Powersplit – combines two electrical machines with torque trans-mission from ICE to wheels via both electrical and mechanical means. Lacks the ability to split the transmission into a separate generator and motor set.
Comparing my plug-in vehicles
Powersplit transmission

Both Ampera and Kuga use epicyclic or planetary transmissions to create a variable ratio between engine and wheels. Both gear together three shafts such that the speed and torque on any two shafts determines the speed and torque on the third shaft. Both have the wheels connected to one shaft, the engine to the second, and an electrical machine to the third. However Ampera and Kuga differ in that Kuga places the second electrical machine on the same shaft as the wheels, while the Ampera places the second electrical machine on the same shaft as the engine (which helps when splitting the transmission to create a series hybrid).

I’d differentiate the Ampera from the Kuga as describing the Ampera as a short range electric vehicle with an ICE for occasional longer trips, while the Kuga is more of an enhanced hybrid optimised more for those longer trips with a higher efficiency Atkinson engine. The Ampera on the other hand has greater electrical capability (uncompromised performance electric versus ICE) with greater transmission sophistication having the ability to switch between being a series hybrid or a powersplit.

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Battery Economics

Having recently spend around £600 replacing the internal batteries in my Powervault G200, I thought I’d look at the economics of that decision.

Powervault G200 storage

Originally I bought the Powervault to store the surplus electricity from my solar panels and then use that electricity later instead of buying electricity. I don’t receive any revenue for exporting electricity so to fill my battery from my solar surplus costs me nothing. I currently pay 35 p/kWh for daytime electricity. So, if I fill my battery from my solar surplus then I save 4 kWh (the capacity of the battery) x 35 p/kWh = £1.40 per day.

More recently I also charge the battery on cheap overnight electricity when there won’t be enough solar to charge the system fully.

I only get four hours of cheap power which isn’t enough to fully charge the battery. The battery charges at 0.8 kW so in four hours would use 4 hours x 0.8 kW = 3.2 kWh which at 7.5 p/kWh costs 24 pence. The system has a cycle efficiency of 80% so 3.2 kWh in gives 3.2 kWh x 0.8 = 2.56 kWh out. 2.56 kWh energy out is worth 2.56 kWh x 35 p/kWh = 89.6 pence. Having spend 24 pence to save 89.6 pence then I’ve made net savings of 65.6 pence per day.

G200 User Portal

A day like that shown in the portal with 4.75 kWh in savings is a bonus in terms of annual savings although it may accelerate the deterioration of the battery as it’s been double-dipped during the day with both overnight and solar charging.

If I assume that half the time the system is filled by solar and half from the grid then my annual savings are 0.5 x (£1.40 + £0.656) x 365 = £375.22. Having spent £600 on the new batteries then my payback time is £600 / £375.22/year = 1.6 years. The previous batteries lasted for 6 years although the new batteries were relatively cheap and might not be expected to last for so long. However even if the new batteries only have half the life of the prior ones then that still seems like an attractive investment.

My total investment in the battery storage is now £2600 – £2000 to buy it six years ago plus the £600 just spent on new batteries. That’s a payback of about seven years with expectation that the new batteries will extend the life of the system to nine years.

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Reviving the battery

Powervault G200

My Powervault battery is now six years old. Initially I used it only to store surplus electricity from my solar panels but more recently have also managed it from my HEMS to reduce my energy costs by charging it when electricity is cheapest to offset consumption when electricity is most expensive. However it’s become clear in recent weeks that the working capacity of the battery had significantly declined.

Powervault portal for G200 before battery replacement

My Powervault is designed to have a reasonable life – its 7.92 kWh internal batteries (6 batteries x 12 Volts x 110 Ah) are limited to 4 kWh to maximise the number of charging cycles. However after 6 years working capacity had dropped to less than half of that and I decided that the time had come for replacement. Declining battery capacity is illustrated above with the blue line showing battery charging between 00:30 and 04:30. If the battery had continued at constant power (about 750 Watts) then it would have charged 3 kWh (4 hours x 750 Watts / 1000 Watts/kW). However here the battery has ceased to draw 750 Watts from around 02:00 and thereafter power consumption has significantly declined – this may be about 1.75 kWh rather than 3 kWh.

These figures (1.75 and 3 kWh) are also energy into the battery – but you don’t get out everything that you put in. With a quoted round trip efficiency of 80% then 1.75 and 3 kWh in would deliver 1.4 and 2.4 kWh output versus the original capacity of 4 kWh.

I reached out to both my installer and Powervault themselves but neither got back to me with any proposal to investigate or replace the batteries so I resolved to do it myself.

Powervault G200 internals

Initially I did a little investigation by removing the top and side panel of the Powervault (after turning off the power). Inside I found six twelve Volt one hundred and ten Amp hour batteries arranged over three shelves on plug and socket connections – so fairly straightforward to replace. A search of eBay for deep cycle batteries of similar capacity indicated prices range from around one hundred to around three hundred pounds per battery (six required). I eventually decided to go for the cheapest as I wasn’t entirely sure of success and I don’t know for how long my six year old system will be supported even if battery replacement was successful.

6 x Numax CXV31MF Batteries 105Ah

The Numax batteries are sold as deep cycle batteries ideally suited for solar installations.

Powervault G200 installation.

The process for installation of new batteries consists of unplugging and removing all the batteries from top to bottom, and then installing new batteries from bottom to top – two on each of the three shelves. I found it necessary to undo the fixing screws on the back of one of the shelves in order to flex it upwards to create enough clearance to get the batteries on the level below out.

Powervault portal for G200 after battery replacement

It’s only been just over a week now, and it’s fairly dull weather at the moment, but it does seem that the replacement has been successful. The dashboard above for example shows both that the system has charged at full power for 4 hours overnight (3 kWh in) and also that 4.75 kWh has been saved (versus 4 kWh working capacity) as to a degree there’s some double-dipping going on with the two partial charges of more than half capacity (one overnight on cheap mains power and one during the day on surplus solar power).

Time will tell what the longevity of these cheap batteries is.

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Connecting to Home Connect

For some time now, I’ve been automating my wet goods (dishwasher and washing machine) using smart plugs to enable them to be started (or perhaps more accurately restarted) by the HEMS at the best times. However declining performance of the dishwasher prompted its replacement which now allows for improved capability.

The new dishwasher is actually quite similar to the the old one as I suspect Bosch and Siemens brands are different sides to the same coin but has a few differences:

  1. It has a cutlery drawer rather than a removable canteen for cutlery which I quite like but does mean less height in the now middle drawer. That means in turn that taller glasses now need to be washed in the bottom drawer previously the preserve of larger plates and pans.
  2. It is more energy-efficient using water-activated zeolite technology for drying.
  3. It’s a connected device using Home Connect. Home Connect provides an app to configure and receive notifications from devices, but also an API. Over the next few weeks I plan to use this API to my HEMS.

It should be relatively straightforward to replace the existing script file for the smart plug with one to activate the dishwasher directly via Home Connect.

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AA Breakdown Cover Discount

I’ve had AA breakdown cover for many years. The AA provide the reassurance of fixing and/or collecting my car if it breaks down. The AA are currently providing a discount to those who sign up via this link.

AA provides 24/7 roadside assistance and will try and fix your car on the spot. You can even track the mechanic right to your side. Just tap our free app and help’s on the way. 

  • Call AA out as many times as you need to, as long as it’s not a recurring problem with your vehicle
  • AA covers vehicles of any age including cars, electric vehicles, vans, motorcycles, campervans and caravans
  • Get up to 25% off at over 1,300 restaurants, pubs and service stations with the app
  • If you have an accident, AA can support you with its Accident Assist service


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Electricity rates

It’s now 3 years since I became an Octopus Energy customer. Each month I’ve been noting the average unit rate from my electricity bill. These average rates vary month-by-month as I’ve always been on a smart tariff where the price is different at different times of day, and thus my average rate varies depending on how my consumption is divided between different times of day

MonthYear 2018/19Year 2019/20Year 2020/1Year 2021/2Year 2022/3
November14.27 p/kWh8.96 p/kWh6.69 p/kWh7.37 p/kWh12.75 p/kWh
December10.17 p/kWh6.51 p/kWh9.61 p/kWh7.66 p/kWh14.26 p/kWh
January6.86 p/kWh9.74 p/kWh8.32 p/kWh15.36 p/kWh
February5.59 p/kWh11.18 p/kWh6.93 p/kWh11.36 p/kWh
March5.02 p/kWh8.85 p/kWh6.88 p/kWh10.14 p/kWh
April8.35 p/kWh8.74 p/kWh7.36 p/kWh9.33 p/kWh
May4.48 p/kWh11.50 p/kWh6.36 p/kWh8.59 p/kWh
June7.03 p/kWh3.49 p/kWh12.52 p/kWh9.48 p/kWh (part old Go at 7.5 p/kWh)
11.28 p/kWh (part new Go at 9.5 p/kWh)
July8.20 p/kWh4.40 p/kWh15.60 p/kWh (part)
End Agile / Start Go
5.92 p/kWh (part)
10.09 p/kWh (new Go with 7.5 p/kWh overnight)10.62 p/kWh (to 30/6)
10.39 p/kWh (from 01/07)
August6.29 p/kWh (part)
5.99 p/kWh (balance)
6.15 p/kWh6.19 p/kWh 11.82 p/kWh11.63 p/kWh
September5.63 p/kWh7.62 p/kWh6.30 p/kWh11.07 p/kWh13.41 p/kWh (to 15/09)
12.66 p/kWh (from 16/06)
October6.86 p/kWh6.97 p/kWh6.83 p/kWh13.76 p/kWh13.66 p/kWh

For most of this time I was on a very complex tariff called Octopus Agile which is directly linked to wholesale prices and, while historically that has been very good value, rising wholesale prices recently have caused that tariff to get increasingly expensive and so I’ve switched to Octopus Go which provides a 5 p/kWh inc-VAT night time rate for 4 hours. This is ideal for charging our electric cars and also the home battery if the next day’s solar production looks as if it will be limited.

Both of these tariffs are so-called smart tariffs enabled by smart meters. Some people can be very negative towards smart meters and indeed smart tariffs, but based on my experience it seems to me that if you have some flexibility to move electricity consumption to off-peak periods these can be excellent value for money.

I currently use the FiT revenue from my solar panels (about £700 annually) to offset my energy bills and am left paying £20/month towards household energy. I also earn a little income from referrals.

If you fancy an energy company that can provide excellent value for money, has good customer service, and that’s been recommended by Which? magazine for years why not switch with this link and earn an additional £50 credit? share.octopus.energy/ochre-beach-637

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