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Letters to the editor: volume 16, issue 10

Image credit: Patrick Tomasso/Unsplash

In the November 2021 issue of E&T, readers discuss the problem of switching battery packs between power tools, the mathematics of heat-pump performance, and experiences of electric car ownership.

Who benefits from incompatible batteries?

Following a recent house move, I purchased a number of cordless tools, most of which use 18V battery packs. These are functionally identical, of similar capacity, shape and size, and use very similar cells inside, yet are totally incompatible between manufacturers. As not every manufacturer makes every type of tool, this means I have five different batteries and chargers for five tools, which is not only inconvenient and expensive, but hardly environmentally friendly.

I am unlikely to use a drill, a lawnmower and a vacuum cleaner at the same time, so the ability to share batteries between tools would be extremely useful; three batteries and a single multi-charger would be plenty for my needs, saving money and the environment while leaving me with more spare batteries for each tool than I have now.

Why on earth can’t we have a standard 18V battery pack that fits everything? The double-A battery and its cousins solved this problem for most gadgets years ago, yet with the modern trend for proprietary or (worse) built-in batteries we seem to have gone backwards. A handful of cross-brand 18V batteries exist, but are not widely supported.

I can’t see any valid reason for manufacturers to insist on their own proprietary batteries and chargers, except that it’s a nice little earner. A universal 18V rechargeable battery could power almost any 18V tool, reducing emissions during battery manufacture and at end of life, preventing old tools from becoming landfill due to unobtainable batteries, and the standard could be easily extended for more demanding applications. Manufacturers could still differentiate their batteries by offering USB charging or Bluetooth, and adaptors could even be made to upgrade existing tools to the new standard. Win-win for consumers and the environment.

Andrew Howlett CEng MIET

By email

Power cut dilemma

Last year I explored the installation of solar panels and batteries for my home but rejected the offer. Payback exceeded my life expectancy, an export tariff can only be obtained via a smart meter, which my electricity company said they couldn’t fit, and in the event of a mains failure the solar panel/battery combination would also be switched off.

This year I can swallow the first of these to polish my green credentials; and my supplier has installed a smart meter. However, the third objection remains problematic. Power disconnects are not uncommon in the rural area where I live, and with the looming hiatus in energy supplies generally I expect they will become more frequent and prolonged. It seems daft that I could generate my own electricity but be unable to use it in the one circumstance where it would really be needed.

I understand that the system controller supplies the house from solar when available, reverting to mains automatically when it isn’t. I was told that the way the system works means that if the mains supply failed I would end up trying to power the whole of Suffolk from my batteries, which is why they are disconnected. I should have thought a simple mains-energised contactor could sort that. I guess the other problem may be that the solar inverter needs a mains feed to synchronise its output with the incoming supply so if the latter fails the inverter loses the will to live.  

Not being a power engineer, I wonder if readers could shed any light on this issue and maybe propose a solution?

Peter Finch CEng FIET

Bury St Edmunds

Volume 16 Issue 10 letters section cartoon

Image credit: E&T

Tackling EV inaccuracies

I’ve noticed a common theme in letters in E&T raising concerns about the move to electric vehicles, and often find myself irritated by significant inaccuracies that are cited to make the point. I would be called an early adopter, as I bought a Vauxhall Ampera EV in 2013. At that time options were essentially a Nissan Leaf with real-world range of about 70 miles, or the Ampera with its range-extending petrol generator. This vehicle is now over eight years old and has covered 85,000 miles.

The common observation that batteries have only an eight-year useful life is not true. Our vehicle new has a ‘battery-only’ range of 50 miles. This was a deliberate choice by the development engineers whose research confirmed that it covers the vast majority of people’s daily use – very rarely does our vehicle need to move into range-extended mode and actually run the petrol generator, often going months and months without starting it.

Virtually all manufacturers have active battery management that ensures longevity greater than that of the rest of the vehicle. The Nissan Leaf is admittedly one exception where there is no active thermal management and it does suffer battery degradation, but newer models have corrected this.

Do electric cars take hours to recharge? Again, no. We might know of the Tesla super chargers’ rapid pace, but they are high-end vehicles. At the other end of the spectrum, the humble Vauxhall Corsa-e can be bought new for £23,000-25,000. It has a range of more than 200 miles and can charge at a pace that means it can go from 10 per cent charge to 80 per cent in 30 minutes. In other words, even the humblest of electric vehicles won’t need to be parked at the motorway service station any longer than its ICE sibling. It’s not refuelling the vehicle that sets the down time, it’s refuelling the driver.

Steve Price CEng MIET

Maidstone

EV ‘pure enjoyment’

I was surprised to read about the dissatisfaction felt by Andy Leslie (Letters, August 2021) with his Kia e-Niro. I have avidly followed the progress made by the manufacturers of electric cars over the last 22 years since the Toyota Prius was launched, with a view to one day making my own electric car purchasing decision when the price, range and battery warranty all ticked the right boxes. That moment arrived a few weeks ago, with the purchase of a Kia e-Soul.

Having spent a period of my working life testing batteries, I have always had reservations about the reliability aspects of these very expensive parts of electric cars. However, I have been pleasantly surprised by the apparent excellent reliability achieved by the manufacturers of these items. There will nevertheless always be the odd failure and Mr Leslie unfortunately got one of them.

As an electrical engineer, I felt bound to take a close personal and professional interest in the installation of my home 7kW charger, and experienced no problems. I have to say that my experience to date with my Kia e-Soul has been nothing but pure enjoyment – I exhort Andy Leslie to hang in there!

John Adams MIET

Knebworth

The case for heat pumps

I believe JR Ball’s figures about heat pump performance (Letters, August 2021) are unduly pessimistic. For a typical heat pump to operate at a COP of 1.8, its delta T (the difference between output and source) would have to be in excess of 60°C. In a well-designed system with a flow temperature of 40°C this would only occur when the outside temperature is below -20°C – not impossible but very unusual in most of the UK. Or it could occur in a system with an excessively high flow temperature and outside temperatures of around 0°C. A more typical seasonal average COP for a reasonably well-designed system would be approaching 3 if air source or 4 if ground source.

The only current gas-turbine-powered generators with efficiencies of 35 per cent are open-cycle. These are rarely used and peaks in demand are normally met by combined-cycle units with an efficiency approaching 65 per cent, plus pumped storage.

When I recently looked at manufacturers’ data for condensing boilers, many were quoting efficiencies of about 90 per cent, so 95 per cent is perhaps restricted to a small number? However, a study by the Energy Saving Trust a few years ago found that, in practice, most condensing boilers don’t achieve these figures as they are set too hot to operate properly in condensing mode. The average was between 82 per cent and 85 per cent, with combis returning 73 per cent in hot water mode. These figures don’t include electricity usage, which varied from 100kWh to over 750kWh per year.

Looking at these figures, a heat pump operating at an easily achievable COP in excess of 2 will result in lower emissions than a gas condensing boiler. And let’s not forget that the grid is getting cleaner all the time, so the case for heat pumps will get even stronger.

Rob Cannell MIET

Stafford

JR Ball presents an interesting calculation about the relative carbon dioxide emissions of heat pumps and conventional gas heating for homes. I am no expert in this field, but from my limited personal experience staying in a house where the rooms and water are heated by a ground-source heat pump I suspect one of the assumptions may be incorrect. In the house where I stay, the heat pump runs continuously, the radiators are just slightly warm at all times and the room temperature remains pleasant all year round.

By my understanding, the electricity demand of the heat pump is more or less continuous. However I would agree that the annual electricity consumed by the heat pump costs around half the annual cost of gas heating. As the demand is continuous, the electricity for the heat pump should be supplied from renewable sources, including, no doubt, a contribution from solar panels on the property itself, as is the case with the house I stay in.

It is the ‘peaky’ demand of fast space heating in the morning and evening that would have to come from gas turbines. This is why few homes rely on electric fires or radiators to heat them when required, but use either electric storage heaters, or gas/oil burnt locally.

The use of heat pumps instead of gas/oil heating, and the use of electric car charging points instead of petrol stations, will inevitably require a considerable increase in electricity generation and distribution capacity in the future. I hope the necessary investment is being made.

Bob Barnard CEng FIET

By email

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