After a series of quite detailed posts, I think that the time has come for an updated high level overview of what we have.
We moved to our early 1970s house almost 4 years ago bringing with us our electric vehicle. The house had already been refurbished with new double-glazed windows, had cavity insulation (although that wasn’t recorded on EPC so must have predated the prior owners), and a token level of loft insulation. The existing gas boiler was arthritic, couldn’t heat the whole house, but was quite good at heating the header tanks in the loft! We had gravity-fed gas hot water (i.e. no thermostat or pump on the cylinder) which was completely obsolete, the cylinder dated back to the building of the house and had no immersion heater (although we had the wiring for one). So what did we do?
We substantially increased the loft insulation to reduce heat loss.
We had a modern condensing gas boiler installed to improve efficiency.
We updated to smart controls using eTRVs to set both temperature set points and schedules at room level. I built a smart interface to the boiler so that heating can be enabled remotely. I programmed a series of rules into Apple Home allowing the smart thermostats to enable the boiler when any thermostat wants heat and disable it when no thermostat wants heat. Some rooms also have additional rules linking heating to open windows or movement sensors. All of this reduces heat losses by only heating rooms that are (or will be shortly be) in use.
We installed our own solar panels given 4 kWp generation. (I also own a small share of a solar farm although there’s no contract that I’m aware of between that farm and my home energy supplier)
I invested in an immerSUN to maximise self-use of our own solar by enabling loads when surplus solar is available.
We switched to a green electricity supplier so when we need to buy electricity it comes from renewable sources.
We bought a small storage battery 4 kWh to store some of our solar production for use later in the day. Subsequently I can also use it in winter to buy when the electricity price is relatively low to avoid buying when the price is relatively high.
We chose a dynamic smart tariff to buy electricity at the lowest price based on market prices established the day before. The prices change each half hour and are established in the late afternoon on the day before.
We replaced the old hot water cylinder with a modern insulated one (to reduce heat loss) with a low immersion heater (to allow more of the water volume to be heated).
Our principal water heating is now by diverting surplus solar electricity proportionately to the immersion heater, that’s backed up by the gas boiler which is enabled briefly in the evening for water heating in case the water isn’t yet up to temperature, and when the electricity price falls below the gas price I can enable the immersion heater on full power.
All accessible hot water pipes are insulated.
Electric car charger:
I built my own electric car charger that takes an external radio signal to switch between four settings 0, 6, 10 and 16 Amps to help me adjust consumption to match to availability of output from my solar panels. (Subsequently such products were developed commercially with continuously variable current limits, but the limitations of my immersun and on/off radio signal don’t allow me to go quite that far. Having said that my car only does 0, 6, 10 and 14 Amps so I would gain no benefit from a continuously-variable charger paired with a 4-level car).
Smart electricity controls:
We have two systems for smart control of electricity:
The immersun to maximise self-use of our solar electricity by proportional control of loads.
A HEMS to manage the purchase of electricity (when necessary) at the lowest price by maximising consumption when the price is lowest.
When both systems want to enable loads (because the bought price is low and we have a surplus from our own panels) then cost is prioritised, so we’ll buy from the grid any demand not being met from our own panels.
Both systems are linked to 3 devices:
Battery storage. The immersun is configured to work alongside the battery storage with the battery storage as the top priority to receive surplus solar PV. The HEMS can switch the status of the battery as required to charge from the grid when the price is lowest, or to discharge when the price is highest, or indeed to revert to default behaviour.
Car charger. Second priority for the immersun after battery storage.
Immersion heater. Third priority for the immersun after car charging.
I have no firm plans for the future. I’m toying with adding to the HEMS various features including:
Making the display switch between GMS and BST as appropriate (it’s all UTC at the moment).
Edit configuration via the web interface rather than a virtual terminal.
Control a domestic appliance. Our washing machine was replaced relatively recently, but the dishwasher is playing up a little and may be a candiadte for HEMS integration where the optimum start time is selected to deliver lowest energy price.
The above images show four different perspectives on the same day of data (April 24th) from different sources within the home.
Firstly, the Smart Meter HAN image shows bought electricity to the home. Each smart meter sits on a Home Area Network (HAN) which is how the In-home display provided with the meter gets its data. The in-home display is an example of a Consumer Access Device (CAD). In my case I also have a Hildebrand Glow Stick as a CAD. The Glow Stick, which looks something like an oversized USB stick, also connects as a CAD to the smart meter allowing the meter to be read. An associated app, Hildebrand’s Bright, allows the Glow Stick to be read via the cloud. In principle the Bright app can display either energy in kWh or cost, but in my case can only display energy in kWh as Octopus don’t push the price data into the smart meter so energy cost always reports as zero. The data is presented by the minute.
Secondly, the Smart Meter WAN image shows the same data but from the perspective of the Wide Area Network (WAN) whch connects the smart meter to the energy retailer (Octopus for me). This half-hourly data is reported via the Octo Watchdog app. The data reported is cost per kWh (the blue line) and energy consumer / kWh (the red columns). The energy data in the red columns follows that of the red line in the prior illustration but in lower resolution (half-hourly versus minute-by-minute). You can clearly see most energy being bought when the price is lowest.
Thirdly, the Powervault image shows grid in/out and battery in/out. The green grid-in line mimics the red data from the above images. The battery in/out data is solely visible in this image. The resolution is good enough to see shorter events like kettle boil cycles.
The final image, from the Immerun, is probably the most useful although it lacks energy price and hides battery in/out within the House data (hence ‘House’ being zero at times). The immersun alone reports output data from the solar panels and diversion to the immersion heater. It also lumps the car charger energy within ‘House’, indeed none of these views can directly report the car charger behaviour although its the dominant energy consumer here.
I’m planning to construct my own view showing all the different prices of data together in one place. I already have access to:
The Immersun data via the same API called by their app. I came across a blog post that described how to do this.
The Powervault data API (I only have a control API at the moment) which should give me battery in/out (at least I’m on a promise of the API at the moment).
The Hilbebrand data which duplicates the Powervault Import/Export at the moment, but has the potential to provide independent monitoring of my car charger.
In principle then that would leave me able to report 3 x energy sources (grid, panels and battery; of which grid and battery would be bi-directional) and report 3 x energy consumers (car, water heating and home).
A recent discussion centred on whether, as someone in receipt of UK feed-in tariff (FiT) and having a smart meter, I should be on metered export or deemed export. I had previously been advised that my smart meter did not have an export register, but playing with the buttons revealed an active export register.
There could be an opportunity to use the export meter as part of an export tariff instead of the FiT export component, which wouldn’t have a restriction on buying and exporting grid power, but my high levels of self-use make this unattractive compared to deemed export at 50% of generation.
Earlier in the week I received notification from my electricity and gas supplier that my 12 month contract was coming to an end. I did my usual search for the best value Economy 7 tariff but drew a blank – everything including renewal with my existing supplier was rather more expensive than I’m paying now – so I decided to be rather more adventurous.
My decision was a significant change – not just a move from Economy 7 to a smart meter, but also the addition of a smart tariff (one that changes rate multiple times per day), and indeed my chosen tariff is dynamic so it potentially changes every half hour and day-to-day. As I don’t yet have a smart meter then I’ll continue on Economy 7 until the meter is replaced, but then adopt the dynamic tariff. With flexible loads like electric car charging and my storage battery then I should be well equipped to make the most of such a tariff.
On the dynamic tariff rates are published each day at 4:00 PM for the next day. Some times (not very often!) prices even go negative so one is being paid to consume. At other times electricity is relatively expensive (early evening’s principally) but the battery should help me minimise purchases during such times.
I’ve already checked the battery storage and it has the ability to be programmed very flexibly around different electricity prices at different times of day so that it doesn’t just absorb surplus solar but charges at lower cost times to discharge at higher cost times.
I also want to explore opportunities to automate the response to tariff changes – potentially linking storage battery, car charging, and water heating to tariff as well as self-consumption.
In the last few days I’ve reported our status on electricity generation from our solar panels and our gas consumption, so here comes some thoughts on electricity purchase from the grid.
Starting in late 2015 after the meter was changed to Economy 7, there’s a general downward trend from November 2015 to March 2016, before my car charger project kicks in maximising use of my own solar electricity to charge my car (when available) which causes a significant drop in purchased electricity between march and April 2016. That seasonal saving gradually drops through the autumn, although it’s interesting that by November 2016 we’re back on what seems to be a continuation of a downward trend from January to March 2016. Electricity purchased is also significantly lower than 2015 as we enter the second year.
The second significant change is the addition of the storage battery in December 2016. However from January to August 2017 (yellow) electricity purchased is significantly below the prior year (magenta) – potentially showing the benefit of the battery in saving electricity generated during the day to reduce consumption later in the day. This benefit largely disappears from September to December 2017, presumably because my increased vehicle mileage after my daughter started school is offsetting the prior savings.
2018 (orange) generally falls somewhere between 2016 and 2017 as it combines both the storage battery and the higher vehicle mileage throughout the year to date.
Summer is definitely upon us now as we enjoy the glorious summer weather. Disappointing weather earlier in 2018 has given way to two record months in May and June which yielded the highest monthly outputs for their respective months since the system was installed back in 2015. Some days we buy no measurable electricity or gas (given that the electricity meter has a resolution of 1 kWh) depending on what the need to charge the car. If the car is at home then I can fully charge it from the solar panels, whereas if the car is at away from home during the day then I may need to give it some charge overnight. When charging overnight I have been tending to charge for the minimum number of hours up to 7:30 AM when I typically leave home on a weekday – that pattern provides for mostly Economy 7 Energy from the grid less whatever comes off the solar panels from the rising sun less whatever might be left in the PowerVault from the previous day as illustrated below:
The green ‘hill’ from around 3:30 to 7:30 AM is created by car charging. Normally this would be seen as a rectangular block as the car charger effectively runs at a constant 10 Amps (2.3 kW) through the operating period. However in the illustration the charging event (at least in terms of power drawn from the grid) seems rounded at both the beginning and the end. At the beginning of the car charging period the mustard ‘Device Power Out’ curve shows the last remaining stored energy from yesterday being drawn from the PowerVault, while at the end of the charging period the ramp down is a result of increasing output from the solar panels reducing the need for power from the grid. Hence at the moment the car charging ends there’s a sudden switch to charging the PowerVault at full power (the blue line) and some surplus power not used by the PowerVault (the purple line) – suggesting that something around 1 kW is suddenly available. Although the purple line is described as ‘Grid Power Out’ that’s not strictly true here as much of that surplus is being diverted to make hot water (although this is invisible to the PowerVault).
After that digression, my actual purpose in making this post was to reflect upon relative energy costs and the best use of my solar power to reduce energy cost.
n/a - no economic case to charge battery from grid during day
Optional - need to consider value of saved energy versus cost of 1 cycle of battery cycle-life
Self-use Priority #1 via PowerVault (daytime electricity -> solar)
Manual 3rd backup (typically only used for long journeys when charging en-route becomes impractical)
Manual 2nd back-up
Automated 1st backup
Self-use Priority #2 via ImmerSUN (nighttime electricity -> solar)
Manual 3rd backup (never used in 3 years)
Manual 2nd backup (never used in 3 years)
Automated 1st backup for dull days
Self-use Priority #3 via ImmerSUN (gas to solar)
n/a - a summer solar surplus is a poor match to winter heating demand but could be Priority #4
The table above shows columns of energy sources ordered by reverse energy cost versus the major energy consumers in the house: battery storage, car charging, space heating and water heating. Energy consumers are ranked according to the value of displacing the the alternative energy course if not solar:
Battery storage – I currently only charge the battery storage from solar, although there would be a seasonal economic argument to charge from cheap rate electricity if the differential between day and night rates was higher.
Car charging – I generally charge on cheap night-rate electricity when I don’t have enough solar. In summer I program my car charger via the ImmerSUN’s 7-day timer to deliver sufficient charge for the day ahead, but sufficient headroom to make use of any available solar.
Water heating – water heating is my 3rd priority for solar self-use and is automatically based up by the gas boiler which runs for an hour making hot water in the early evening if the tank isn’t already hot from diverted solar power during the day. The gas thermostat is also set slightly colder than the immersion heater – still very usable for a bath or shower from gas but giving some ability to delay water heating from a dull day to a following sunny day.
Space heating – my space heating is generally gas. It would be possible to run a heater (or heaters) such as storage radiators via the ImmerSUN’s third output, but I consider that the cost of the heater(s) and installation is unlikely to be recouped given the major mismatch between surplus solar generally being in summer and heat demand being in winter.
Today my energy supplier Tonik wrote to me inviting me to consider solar panels, a car charger, or a storage battery – all of which I already have. However on their website I found a wider vision of the future home which they thought could halve energy consumption. I thought it would be interesting to compare their vision with my status.
As you can see from the table below the content is quite similar, although I have more ambitious use of solar and more sophisticated smart heating management.
My Q3 2017 status
My Q3 2019 status
Switch to Tonik for lowest cost renewable electricity.
Now that we’re half way through 2017 it seemed appropriate to have a look at energy usage from the solar panels – especially as those six months reflect the first six months with the battery storage system.
The graph is taken from my ImmerSUN smart controller which automatically diverts surplus solar electricity to the car charger or immersion heater. The battery storage system has independent controls but its benefits can be seen via the ImmerSUN.
The purple line shows the consumption of electricity (excluding the immersion heater) and is relatively stable month by month. Consumption is relatively large due to my electric car and cooking with electricity.
The green line shows the generation of electricity from my solar panels. Not surprisingly output is lower in the winter, but from April we generate more electricity than we use despite our relatively high consumption. In principle we could be electricity independent during those months but for the time of consumption not matching the time of generation.
The red line complements the green line as it shows the import or purchase of electricity from the grid, and thus reduces as the generation rises.
The blue line shows the diversion of electricity to heat water via the immersion heater when neither the battery storage system nor the car charger can absorb the available electricity.
Finally on the graph the turquoise line shows export of electricity to the grid when all smart capability within the house to use electricity is exhausted i.e. battery storage system at maximum power or full, electric car battery full or absent, and water in cylinder is hot.
Among the numbers:
‘Savings” at £80 refer only to the value of the water heating achieved from solar electricity versus buying electricity (although our backup is mains gas).
“Self consumption” at 86% refers to the proportion of solar panel output used i.e. not exported to the grid.
“Green contribution” at 59% refers to the proportion of total electricity consumption (excluding water heating) derived from the panels rather than from the grid.
Yesterday I produced a graph of the number of units of electricity that I’d bought or imported each month since we changed to Economy 7 metering back in October 2015 – a change that I made to reduce the costs of charging my electric car. I rather surprised myself.
Key features that caught my attention were:
If I ignore the months of significant solar generation where significant electricity is available that isn’t bought, then from November 2015 to March 2016 and November 2016 to December 2016 there are 6 months of consecutive month-on-month reduction in bought electricity.
Comparing November and December between 2015 and 2016 (the only 2 months available for direct comparison) there’s a reduction of a round a third in bought electricity.
Comparing December 2016 with January 2016, bought electricity is down by a quarter.
That seems to be a compelling case for a significant reduction in import having taken place. Such a reduction could be combination of 2 sorts of things, firstly fundamental reductions in electricity use such as through having a more energy-efficient appliance, or secondly shifting use from paid-for electricity to free solar electricity (albeit that the months in question are winter months where less solar is available).
Potential contributors to this effect are as follows:
November 2015 to March 2016 – Increasing availability of the garage for car charging. In November 2015 I demolished an internal partition within the garage that had rendered the remaining space too small for a car. That created an open double garage which allowed a car in for the first time since the partition was created in the 1980s. In March a suspect garage door was replaced making routine access much easier since the old door was badly corroded, required considerable effort to lift, and had an odd locking arrangement. Thus during this period garage use went from 0 to 100% utilisation for car parking/charging. This might seem an odd item to include but my rationale is that if the electric car is in the garage then it will be warmer than if outdoors and charging will be more efficient as there will be less heating and more charging. Charging also has potential to be at higher current in the garage due to the availability of a Mode 3 charger which I think is also more efficient.
December 2015 – gas boiler replacement. Again perhaps not obvious at first sight, but if the new boiler gets the water hotter then less work needs to be done pumping water round radiators to take place to deliver a certain heat output at the radiators.
January 2016 – fridge freezer replacement. In January we replaced the former separate fridge and freezer with a single combined fridge-freezer. Although considerably larger in combined volume, the new fridge freezer replaced a freezer that I’d had for over 25 years so I anticipate an energy saving there. The new fridge-freezer is rated A+ at 496 kWh/annum.
April 2016 to September 2016 – charger control project. Development of the charger control project shifts some electric car charging from overnight bought electricity to daytime free electricity even in winter. Previously even on a sunny winter’s day I probably wouldn’t have charged in the daytime due to a risk of import ruining the economics, but now I just leave the car plugged in virtually all the time and let the charger run automatically if and when sufficient free power is available.
July 2016 – double oven replacement. In July the failure of the fan on the oven prompted a oven replacement as the old fan was inaccessible for replacement due to corrosion of the surrounding bolts. I’m not sure how old the prior oven was (although I have evidence of the kitchen being remodelled in 2005) , but anticipate an efficiency gain due to replacement. The new double oven is rated A/B – i.e. the smaller oven is efficiency A and the larger one efficiency B.
December 2016 – storage battery. Installed too late in December to have much of an influence here, the ability of the battery to capture electricity that would have been exported as surplus to requirements for later use should reduce bought electricity. The secondary ability of the battery to storage cheap night time electricity for later day-time use is likely to be of interest only in the winter months, and then won’t reduce demand (indeed it will increase demand slightly due to its round-trip efficiency) but it will reduce costs.
It will be interesting to see how this develops through 2017.
The immerSUN provides a useful app showing electricity use which includes an annual option. The graph below shows the 2016 annual data:
Although some of the data was only collected from mid-March 2016, the graph still shows useful information. I think that the graph overstates bought / imported electricity in January to March but understates generated electricity proportionately in the same period.
The purple line shows monthly electricity consumption and is broadly consistent month-to-month.
The green line shows the generated electricity from the solar PV system. Its seasonality is clearly visible. Solar generation exceeds electricity use in four summer months, and is very close in a fifth.
The red line shows bought electricity. It’s generally a mirror image of the green line reflecting more purchased electricity in winter and less in summer, but is not zero even in months where generated electricity exceeds used electricity due to time of day issues – cooking and car charging often occur at times when solar output is low such as cooking in the evening and charging at night.
The blue line shows surplus day-time electricity being used to heat water, and thus saving gas.
The turquoise line shows surplus day-time electricity being exported once the water has reached its set point.
It will be interesting to see how this changes in 2017 as a result of a full year of solar car charging in its current mature condition and with the new battery storage that should help get more of the generated electricity used by saving it for evening use.