A sustainable catchup

Blog writing tends to fall behind as other aspects of life come to the fore so it has been a while since I wrote about the progress of my solar panels. Having just passed the eighth anniversary of their installation, this seems like a good point to revisit them and see whether they are living up to expectations, especially considering that the interest-free loan I received from the Scottish government has just been repaid.

As a reminder, the system is rated at 3.5kW-peak and cost me £14,300. That's about three times what a similar system would cost nowadays. However, in order to incentivise the take-up of domestic solar generation, the UK government set in place a system, known as the Feed-in Tariff (FiT), to allow people to sell their excess power to the grid at an attractive price. Early adopters, like me, got a very favourable rate that ought to make the panels a worthwhile investment. The deal paid 41.3 pence per kWh (plus an extra wee bit, the export tariff), guaranteed for 25 years with the rate rising with inflation.

At the end of the eighth year, the system had generated 19,689kWh and the income thus far has been £9,198. That's a £5,000 shortfall at this point. I had always had the expectation that the system would pay for itself within 10 years with the remaining term being pure profit and at first glance, with only two years remaining, it isn't going to make it. But part of my calculation is the value of the electricity that I did not have to buy.

It is only when the Sun is shining bright on the panels that they generate more than the house can use. Therefore, essentially all of the low level generation goes to the house. The amount of electricity I have to buy from the supplier is definitely lower and I think it is a fair estimate that I save £350 a year on electricity bills, rising over time as electricity becomes more expensive. If we conservatively say about £1,000 per three years then over 10 years, I should save over £3,000. Add that to the amount received so far, and that is £12,500 approximately. With about £2,500 likely to come in through FiT payments over the next two years, I'm more than likely to cover my initial costs. The next 15 years is profit and after 25 years, if the panels are working okay and although the FiT payments will stop, I'll still be getting free electricity.

Year by year power generation, showing how the most recent year has been the worst by far

Annual electricity generation has varied over the eight years with no obvious downward trend showing until now. The most recent year, 2017/18, was substantially down and it isn't at all clear whether it happened to be cloudier than usual or whether the panels are showing signs of ageing. I think that subsequent years will be required to give more insight. It is possible that the panels had accumulated a film of algae through two mild, snowless winters. There was plenty of snow this past winter and the hope is that the action of it sliding off the panels will have been sufficient to clean their surface.

This graph shows the daily generation throughout the eight years. Lines showing averaged values integrated over 30 days and one year are included to smooth out the inherent variability of the Scottish weather. The rise and fall of the seasons are clear. Small sections where the daily trace goes horizontal for a bit represent periods when I was away from home. The readings for those days are averaged out. A dip in the annual average over the most recent months is notable. Time will tell if this is a trend.

Electric car

One of the destinations for the spare electricity I have been generating is the Nissan Leaf I bought in 2015. If I see the Sun is out and there is a lot of spare power going to the grid, I'll head outside and divert it to recharge the car's traction battery. I've written before about the car and my thoughts on electric vehicle (EV) driving but an update is well in order.

The two years of my astonishingly good PCP deal finished in 2017. The balloon payment to keep the car was unattractive and would also have meant continuing to hire the battery at £80 per month. I elected to give the car back and walk away from the deal. Instead, I managed to source an almost identical Leaf for £2,000 less than my balloon payment would have been and without me having to hire a battery. This car's battery is fully owned. I am delighted with the purchase. The only problem that the car has is that the front brake discs are corroded and will need to be replaced very soon along with the front brake pads.

The previous Leaf had shown no problems with the health of its battery but I was keen to determine how the replacement car had fared over its previous life. The display that shows battery health still had the full 12 bars but this just meant it was above 92 per cent. Was it just above 92 and about to lose a bar, or was it better than that?

Most cars have an ODB2 port that comes to a connector to allow an engineer to plug the car to a computer and see what its electronics are saying. I bought an inexpensive dongle that could read this information and transmit it to a smartphone via Bluetooth. An app for the phone called LeafSpy then allows me to see the battery's true state of health.

A typical display from the LeafSpy app of the fully charged car. 

The LeafSpy display shows the voltage of each of the car's 96 cells. The large figure to right shows the spread of those voltages. only 13 millivolts means they all match each other very well. The red bars indicate that a shunt was used to equalise that cell's final charge. This balancing of the battery is something that the car does for a period of time once 100 per cent charge is reached. The state of charge (SOC) is indicated lower left. It shows that even when the car's dash display says 100 per cent, the internal system holds it back from a true 100 per cent.

For me, the most important figure is among the small writing at the top. This indicates the battery's true state of health (SOH). Very reassuringly, this is over 100 per cent! I've monitored the SOH figure and it hovers between just over 100 and 97 per cent. What makes it improve is a long drive on the motorway with a rapid or quick charge from a CHAdeMO point. These chargers push the power in at around 50kW, fifteen times faster than when I charge at home which the car's inbuilt electronics limits to 3.3kW.

The LeafSpy display also offers values for the battery's internal resistance (Hx), its voltage, the car's odometer and the total number of quick and slow charges it has had (77 and 829 in this example).

What? No Leaf?

Unfortunately, my professional circumstances meant that for a few months last autumn, I did not get to drive my replacement Leaf. I had a job on the Isle of Skye; 145 miles away by ferry and 192 by the Skye Bridge for when ferries are not available. While the ferries were on summer timetable, the Leaf was probably just about doable for returning home at the weekend. Indeed, I took it on a trip to my place of work on one occasion to give it a try.

However, with the sparse winter timetable and the cold weather hitting the car's range, travelling electric via the Skye Bridge did not seem wise, at least not using a 24kWh Leaf. I elected to swap cars with my son for a few months and he could not have been happier. He loves the car for its performance off the line and its tiny running costs. Meanwhile, I had to burn petrol which cost me a fortune compared to what I had been used to.

I am returning to Skye this autumn but for the first half of the job, I plan to use the Leaf and see how I get on. At some point, I'll attempt the long route via the Skye Bridge, as much because I want to try the section between chargers at Fort William and Sheil Bridge, a run of 58.2 miles. In the normal course of things, this should be a doddle in a 24kWh Leaf with a range of 80 to 100 miles in summer. However, when using the quick chargers, there is no point in trying to achieve a 100 per cent charge because the charging rate slows dramatically as the battery gets to around 90 per cent full. This means leaving Fort William with a less than complete charge.

Then to reach the halfway point requires a steep climb of over 1,000 feet from Loch Garry to a viewpoint. Hills are notoriously hard on EVs and I would like to get some experience of the road in conducive conditions to test the range. Coming downhill on the far side would allow a significant amount of power to be regenerated but if too much has been lost on the way up, the gains may not be enough to outweigh them. What would help is a quick charger at the Cluanie Inn which would knock 11 miles off the run from Fort William.

In the meantime, I still have a reservation for a Tesla Model 3. This exciting and very desirable car has been released in the US and for the most part, owners are very pleased with it. The cost of what is an entry-level luxury car is a bit of a stretch for me but I'm saving up for mid-2019 when Tesla say they will begin the production of the right-hand drive versions. I'm weighing up whether I would fork out the additional cash for the long-range version (310 miles versus 220 EPA range). If Tesla proves to be too much of a stretch, the long-range Leaf will be one of the increasing number of EV models available on the market at that time.

Range Rant

A point about electric car range and how it is understood. People make this big deal about the range of electric cars and figures are quoted as if they are the absolute truth. No. No. No. As electric cars become dominant, folk will have to come to terms with how incredibly variable the actual range of a car is, and here's why.

When you pump a certain amount of energy into your petrol or diesel tank, the distance you can travel depends on how much of that energy actually goes into moving you forward and keeping you going against friction and aerodynamic drag, and how much is lost as heat. It is an awful truth that in an internal combustion engine, about 70 per cent of the available energy is lost as heat, often more. So when there are variations in other possible losses, they are barely noticed.

If it becomes colder and the air is denser (and you want to keep warm), or it is wet and the water increases the stiction with the road, or if you find yourself driving into a gale, or the car is highly loaded, or there is a soft tyre, or you just want to go faster and hammer along the motorway at an illegal 80mph, or there is a 1,200-foot ascent to your destination - the effect of all these extra losses are so small compared to the massive loss through heat that only a particularly attentive driver will notice them.

But the efficiency of the electric drive train completely changes all this. With much less than 10 per cent of the energy in the battery being lost through unwanted heating, all these other variables suddenly become very noticeable and crucially important. The EPA range figure for my Leaf is 84 miles (a US standard rating). My experience has been that in summer, my 24kWh car is capable of over 100 miles on a full charge before coming to a halt. I would never let it get to that but I monitor its progress by watching the percentage drop as the miles go up.

In winter, when the variables stack up against the car, I've calculated ranges that go below 60 miles. The temperature had dropped to -5C, the traffic to work was stop/start (mostly stop) and I had the heating on. That's virtually a 2:1 ratio between seasons! Knowing that, it seems crazy to me that the industry fixates on quoting range figures. It misleads the public into thinking that they ought to get that kind of range month in, month out. They won't and they will sorely notice it when they get caught out on that bad day when all the variables stack up against them.

The situation will be improved as battery capacities go up, as they surely will, and the charging infrastructure improves. Again, Tesla leads the way. Their cars, though relatively expensive, always have decently large batteries and the company has been exemplary in its investment in charging infrastructure through the Supercharger network.

And my final rant for now. It is the height of corporate stupidity that not one of the other car manufacturers has taken Tesla up on its offer to share its superchargers. They are so far behind the curve, it beggars belief. The superchargers are sited to suit long distance travel. There are always plenty of stalls at each site. They are fast and easy to use and reliable. The rest of the charging infrastructure is pathetic in comparison - slow, isolated, unreliable, finicky to use requiring cards and apps. Yuk!

Moving on...

Heating solutions

Over a year ago, I wrote about my intention to upgrade our home's heating system with one that uses the principle of the heat pump. As with my solar installation, this would attract incentives which were meant to defray the high initial cost of the installation. The idea is like a refrigerator in reverse. Outside air is drawn across a heat exchanger where it is cooled. The heat that is given up to the exchanger is then taken into the house and concentrated to warm the radiators. No fossil fuel is burned except that which might have been used to generated the electricity that powers the system. As we are with Bulb who supply electricity from 100 per cent renewable sources, that wasn't an issue.

In the end, we elected not to go ahead with the work for various reasons. The main one was that the house would have undergone significant disruption as almost every one of our radiators would have had to be replaced. Also, because we were intending to get a hybrid system, one which would allow gas to contribute to the heat in the very coldest conditions and warm our hot water supply, the incentives were less than expected.

Instead, we did two things. First, we insulated the floor and roof space of my room at the back of the house. This made a huge difference to the comfort of that space. Second, we upgraded our boiler to a much more efficient condensing type. Not a perfect solution by any means but one that has made our home more comfortable while burning the same quantity of gas. As it happens, 10 per cent of the gas supplied by Bulb comes from renewable sources. Hopefully that ratio will increase.