Fuel efficiency calculations

Some maths to try and understand the comparative fuel efficiency of vehicles using petrol, diesel and electricity as their fuel. For example, is a 3 mile per kWh electric car more or less fuel efficient than a 80 mile per gallon diesel car? (Spoiler: more)

First we need to understand the energy content of the fuels in question. According to the UK Government there is 9.6kWh of energy in a litre of petrol and 10.9kWh in a litre of diesel. We can then work out the miles per kWh by dividing the miles per gallon figure by 43.5 for petrol cars, and by 49.5 for diesel cars.

So a 50 mpg diesel car is doing roughly 1 mile per kWh. And a 22 mpg petrol car is achieving 0.5 miles per kWh. Almost all electric cars can manage at least 2.5 miles per kWh, so a diesel car would have to do 123.75 mpg to be using its fuel as efficiently as that, and for a petrol car it would be 108.75 mpg. Electric motorbikes can usually achieve twice the fuel efficiency of an electric car, so those figures would be double.

Why is this? Optimistically only about 35% of the actual energy in diesel and petrol is converted into motion, the rest is mainly wasted as heat from combustion of the fuel. Meanwhile electric motors generally turn over 90% of their fuel into motion, with the batteries wasting energy as heat at the extremes of their performance envelope.

Raw fuel efficiency is one aspect, but fuel cost is equally important, i.e. £ per mile. Right now in our part of the UK the cost of petrol is about £1.20 per litre, and diesel about £1.24 per litre. Electricity can cost up to £0.30 per kWh from a commercial fast charger, or as little as £0.045 per kWh on an EV-friendly domestic energy tariff.

To work out the £ per mile we simply divide £5.45 by the fuel efficiency of a petrol car, or divide £5.63 by the fuel efficiency of a diesel car. So our 50 mpg diesel car costs £0.113 per mile, and the 22 mpg petrol car costs £0.248. The electric car calculation is the same, divide the cost of a kWh, say £0.30, by the fuel efficiency, say 2.5 miles per kWh, and in this case get £0.12 per mile.

Purely on fuel costs, a 50 mpg car filled with £1.24 per litre diesel is cheaper to run than a 2.5 mile per kWh electric car charged with £0.30 electricity.

However, charge the electric car overnight at home at £0.045 per kWh and the £ per mile drops to 1.8 pence per mile. Almost a tenth of the £ per mile of the diesel car. And the electric motorbike mentioned above is going to easily cost less than a penny per mile to run.

Finally, if the electricity you charge your car or motorbike with has come from the solar PV panels on your rooftop, then the pure fuel cost is zero...

Agile energy

It has been an ambition to both reduce our energy usage, and clean it up. Our (very) local power station was converted from coal to biomass in 2012, after over 40 years of burning through 1.2m tonnes of coal each year, and then turned off altogether in 2015. Friends of the Earth had claimed that Ironbridge B was the second worst polluting power station in the UK, so I'm not sorry to see it, its dirty electricity and its pink cooling towers go from the landscape.

The key to our twin ambitions is smart meters. Not because they are smart, as they're not, but because the increased frequency of metering enables energy suppliers to offer a much wider range of pricing options. Energy suppliers can offer varying pricing levels during the day, as a mechanism to shift energy usage to times of the day when the electricity on the grid is predominantly coming from clean sources. Something not possible with monthly readings.

Last year our energy provider had contacted us about upgrading our electricity and gas meters to new SMETS2 meters, so we took them up on the offer. Now we have a Landis & Gyr E470 electricity meter and Toshiba SKU1 cellular modem in the outside cabinet. Once or twice a day this automatically sends half-hourly meter readings back to the Data Communications Company (DCC), whom then send our readings onto our energy supplier. Unfortunately our gas meter couldn't be upgraded, so we still have to manually take readings and send these off ourselves. The electricity meter also came with an In Home Display (IHD), which is connected to the meter via ZigBee, so that we can see near real-time usage on a screen in  the kitchen.

IHD, with red LED to indicate excessive power usage

Our energy supplier only offered a fixed rate tariff, so we looked for alternatives and found Octopus Energy. As well as dual rate tariffs, like an Economy 7 tariff, that are aimed at charging electric vehicles overnight, Octopus offer a time-of-use tariff called Agile, where the price of electricity changes every half an hour. And every day.

Agile Octopus tariff for a 24 hour period

If you can change your electricity usage so that you avoid the 4pm to 7pm period, then the cost comes down from the 20p/kWh flat rate we were paying our old energy supplier, to around 7p/kWh. Or less if we're paying attention.

Usage over a 24 hour period

The graph above shows a car charging over night, then being topped up again in the middle of the day after a short trip. During the rest of the day there's about 600W of power being used constantly. Having visibility of this information is the first step to identifying where we can reduce our usage.

A side benefit of chasing the cheap periods in the day is that they correlate well with the times when the electricity on the grid is also the cleanest. Power from wind and solar are the cheapest being fed into the grid, with gas and nuclear being the most expensive. So if the power on the grid is cheap, it is likely to be predominantly from wind and solar.

Honeywell Evohome - Off, but on

In May we had a (brief) period where the weather was fantastic, and I decided to turn the central heating off using the Quick Action on the Evohome controller. It was then a bit of a surprise to feel that a couple of radiators were still being turned on, confirmed by the green light on the BDR91 wireless relay in the airing cupboard.

After a bit of internet searching I came across this Knowledge Article from 2018 on the Honeywell Support website:

https://ensupport.getconnected.honeywellhome.com/s/article/The-evohome-controller-and-radiators-are-in-off-setting-but-the-boiler-continues-to-fire?language=en_US

It appears the two main reasons in the list that applied to us were a) weak batteries and b) loose adaptors. A couple of the HR92 TRVs had been knocked, and so weren't tight to their valve adaptors, which meant that they couldn't completely shut the valve. And my experiment using rechargeable batteries in the HR92s was causing me more work in comms faults and recharging them than it was saving me in money.

So I've gone around and changed all of the HR92 batteries back to non-rechargeable alkaline batteries, as well as the two AA batteries in the CS92 storage cylinder water temperature sensor. I bought a pack of 50 Duracell Industrial AA batteries from Amazon, working out at less than 32p per battery. There's no mAh capacity rating on the batteries or packaging, so we'll have to see how long they last.

Digital car radio

Our 12 year old Ford has a factory fit FM/AM/CD audio system made by Sony. So in an effort to bring it up to date, I was contemplating changing the head unit to one that supported DAB/DAB+. However I was filled with trepidation around changing the roof-mounted aerial for one that had a dedicated DAB cable, in addition to the FM/AM cable. This would mean removing the headlining inside the car, the A-pillar surrounds, and probably lots of poking around behind the dashboard to run a couple of new aerial cables.

Instead I decided to try a different approach, and bought a Kinetic DAA-­7001 splitter. This takes in the feed from the existing roof-mounted aerial, amplifies the signal, and splits out the FM/AM component into a male DIN connector, and the DAB component into a female SMB connector. The splitter is powered from the vehicle's switched power feed (red cable into the back of the ISO 10487 connector at the back of the head unit).

The roof-mounted aerial needs a wide frequency response, as it is trying to pick up both long wave (0.15MHz to 0.28MHz) and medium wave (0.52MHz to 1.6MHz) AM signals, FM signals (88MHz to 108MHz), and DAB signals (174MHz to 237MHz). Before fitting the splitter the two concerns I had were that the aerial wouldn't have a wide enough frequency response to pick up DAB signals, and that the splitter would be amplifying the signal at the end of the cable run, rather than at the aerial. Between these two concerns I wasn't expecting to get great reception, but the potential savings of not having to fit a DAB aerial made the £20 cost of the splitter a worthwhile experiment.

However despite my concerns, the splitter was an easy fit and after giving the head unit a minute to autotune into the available ensembles the car now has a working DAB radio. Admittedly this is only based on the car sat in the driveway, so we'll see how it fares out and about on journeys in the near future.

UK HGV platooning trial

A very long time ago (October 2017) I wrote that the UK government had given the go-ahead for trials of vehicle platooning on UK roads. I wrote that these were "expected to happen later in 2018". Ah, I was younger and naïve then.

In reality the consortium led by TRL that won a £8.1m UK government contract to run the trial spent 2018 in the planning phase of the project. The second phase of the project is scheduled to begin in the spring of 2019 and last for four months. This will shake down the vehicles and technology, before the third phase of the project involving DHL drivers and DAF trucks, and lasting eight months. 280 journeys of around 100 miles each will be data logged, half of which will be HGVs in normal operation, and the other half will be three HGVs platooning. The final phase of the project, presumably running into 2020, will be the analysis and reporting to make an economic case for HGV platooning.

Surprisingly neither the UK government, via Highways England which is overseeing the project, nor TRL list the project on their websites. The report from the 2014 case study, also led by TRL, is available here. But to get an update on the HGV platooning trial you have to delve into the commercial haulage press to read about TRL's chief executive, Rob Wallis, delivering a project status update to a Transport Conference back in May 2018. The bits that I'm interested in, such as which V2V technologies they'll be using, are still a mystery. As a publicly funded project, I'd like to think it would be a bit more transparent than this.

What is available is the 2018 report on the public dialogue carried out by Kantar on behalf of the Department for Transport, which included the public's reaction to HGV platooning (on pages 35 and 36). Bizarrely there are statements in this report that imply that only the lead HGV in the platoon would have a driver in the cab. This is reinforced by the report's feedback on business reaction (on pages 66 and 67) where there is talk of "platoon hubs" at motorway junctions where drivers wait to take vehicles out of the platoon and onto local roads. If this is how platooning was portrayed, then no wonder the reaction was predominantly negative.

Yodel lies and incompetence

I recently bought some PC components from Ebuyer and they were shipped to me by Yodel. Not recently, but I've used Ebuyer numerous times in the past and had good service from them. I've never used Yodel before, and now when I shop online I'm minded to ask if they're going to be involved. Yodel go beyond poor service, and into the realm of deceit. I can handle poor service, but I can't handle companies that actively lie and mislead you.

Here's one of my parcels' journey with Yodel:

For reference I placed an order with Ebuyer on the 3rd, a Monday, without expedited shipping, and expected to receive it the following Monday, the 10th.

According to Yodel the parcel arrived with them on Sunday the 9th, and went out for delivery on the 10th. I had a SMS from Ebuyer on the morning of the 10th confirming the delivery slot between 3pm and 5pm. Around the middle of the afternoon I used Yodel's website to track the parcel, and saw that the vehicle had 65 deliveries to make, but was in the Telford area and my delivery was the 55th of the day. So far so good. But not for long.

A couple of minutes before 5pm I checked the Yodel website again, and saw that the vehicle was in Broseley and had 2 more deliveries before mine. At this point I'm still hopeful of receiving the parcel on the 10th. But when I checked again just after 5pm the website informed me that the driver had called at the house, I hadn't been in to provide a signature, and a card had been left to inform me. All 3 of those are lies.

I was furious as I had taken time out of my day to wait for the delivery man, and this was the 2nd of 5 Yodel deliveries in a week which had not arrived. Additionally I was going to away from the next day until the end of the week. So I went back online around 5.30pm and re-arranged the delivery for the 17th, the following Monday.

You can see from the image above that despite re-arranging the delivery date Yodel loaded the parcel onto a vehicle the next morning, Tuesday the 11th. Then at 9.21am the delivery date re-arrangement must have been processed by a human, and I received email confirmation that the parcel was going to be delivered on the 17th. Despite this later that day, the 11th, there's a note that the delivery slot has been changed to between 5.32pm and 7.32pm! Why this couldn't have been done the day before?

The following day, the Wednesday, and also on the Friday, there's a note to arrange to collect my parcel from the Yodel depot. I believe my nearest depot is in Willenhall, a mere 55 mile and 90 minute round trip from Ironbridge. Again, this is despite having had confirmation that my delivery has been re-arranged for the next Monday.

Finally on the 17th Yodel found me, and my parcel arrived!


I mentioned above that this was the 2nd Yodel delivery they had messed up. The other parcel has disappeared into Yodel, never to be seen again.

I'm still trying to get a replacement order out of Ebuyer, although when I checked Yodel's website again they're now claiming that they returned the parcel to Ebuyer before Ebuyer informed me that they'd lost it. Given my recent experience with Yodel, I'll take that with a pinch of salt.

It appears I'm not the only person having this experience with Yodel:

https://uk.trustpilot.com/review/yodel.com

Key fob battery change

Recently the car started to complain that the battery in the keyfob was "low", so it was time to find out how the car and keyfob work together.

Our 2015 Outlander has "keyless" operation, meaning you don't have to insert the key into a lock to operate the car. However if the battery in the keyfob does go completely flat then the car can still be used, via the physical key stored in the keyfob.

Flip the keyfob over onto the side with the Mitsubishi logo.

Slide the releasing mechanism, just above the logo, and slide the key out of the keyfob.

You can use the physical key to unlock the driver's door, then put the key back into the keyfob, and place the keyfob into the slot in the central console, just to the right of the cigarette lighter socket. You can then operate the car as per normal. I'm going to infer that the slot has an RFID reader built into it, and the keyfob has a passive RFID tag, with the code required for the car's immobiliser to allow the car to be used.

Keyless operation is far more convenient, and changing the battery in the keyfob is very quick. At the end of the keyfob where the physical key is located there is a notch in the plastic. Using a screwdriver you can pop the two halves of the keyfob case apart.

The top case of the keyfob, with the buttons, has a CR2032 "coin cell" battery in a holder. The C of CR2032 indicates that the battery is 3V lithium, the R indicates that it is round, 20 is the diameter in millimetres, and 32 indicates a thickness of 3.2mm.

If you can't get hold of a CR2032 you can substitute a BR2032 battery instead. BR2032 are also 3V lithium batteries, but use a different material for the positive electrode. CR2032 are better at delivering the short bursts of current needed for keyfob operation than the BR2032, whereas BR2032 batteries are better for supplying a constant current, as you might find in the real-time clock of a computer. However in a pinch a BR2032 will work in a keyfob.

The old battery can be lifted out.

And a new battery fitted with the positive side,  indicated by a "+", upwards. Try to not touch both the positive and negative sides of the new battery while you're fitting it, as you'll discharge the new battery if you do.

Simply snap the two halves of the case back together, slide the key back into the keyfob, and you're good to go for another few years.