I would like to add an extra string of solar panels to the east side of the house, but I need to keep the cost right down to be able to afford it. Because of that I was thinking about over sizing and not upgrading the inverter. Because the roof is east/west both strings should peak at different times, which should help reduce the max current. I think my inverter can pass through any excess current to fill the battery too. If I also added an extra Fox ESS EP6 5.76 kWh battery that would mean I could take 11.5 kWh of clipped solar power to use when the peak is done. I would also like to have more capacity during the non peak months of the year.

Does anyone know how much extra capacity would be reasonable to add? Since the panels are east/west they will not be able to reach their peak of 3.6 kW, so there should be some extra play there as well as with the battery.

So far all the old radiators are out and about half of the news ones have been fitted to the wall (but not yet plumbed in)

New small consumer unit added in the plant room and power cable from the main consumer unit in the garage has been fed to it. There's a fuse for the immersion in the new Grant 250L DHW cylinder (yet to be plumbed in) and a second for the Grant R290 9kW, also yet to be plumbed in

Trunking has been laid out and a small bit of path around my house has been dug up (pipes needed to go overhead or under an outdoor step, I opted for going under). It's a short run to begin with and I didn't see the harm in going under a single concrete flagstone if it's insulated. Big name installers wanted to do a deep trench but also said they can't do a trench for such a small distance.

The heat pump itself has plenty of room around it whilst also being shielded from wind from all angles, and should also benefit from solar gains as it is in a south facing garden

Is there any checklist I can follow to ensure everything has been done properly? I don't want to bother the guys doing the work too much. I'm meaning to ask if they flushed or will be flushing the system (I kept a few old radiators and the existing pipework)

Bought for project that is not going ahead.

I know, low loss headers (LLHs) aren’t necessarily ‘low loss’ but, if set up carefully, those losses may be minimised.

Our own installation ‘features’ an LLH, I didn’t know that they intended to fit one until I saw the pipework and had to enquire what the device was. Once I knew what had been fitted, I was determined that it should be adjusted via the secondary pump to run as efficiently as possible.

The secondary pump (Wilo Pico) has a number of settings including a variable range – and this is the means to run the LLH with as close a balance for the flow as possible. I am using the term low loss header in this article but the same procedure could be used for a 4-port buffer tank as the working principle is the same.

I should say now that the primary pump in our Daikin heat pump seems to run at three different flow rates but the majority of the time, it settles down to the lowest flow rate of ~7 litres per minute; I decided to optimise the secondary flow to match this.

Four temperature probes were attached to flow and return ports (these were purchased from a well known South American river company fairly cheaply as a pack of four and, as such are not calibrated and thus ‘vary’ from each other). It is wise to compare the readings from the four probes and make a note of the differences; please see note at the end of the article about calibration.  

The probes are attached tightly to the four ports on the LLH and then covered with several layers of  insulating reflective foil ‘wrap’ to give the probes the best chance of sensing the pipe temperatures fairly accurately. I arranged my four sensor displays to mimic the position of the four ports; thus the top left senses flow to LLH, top right senses flow from LLH, lower right senses return from heating to LLH and lower left senses return from LLH to heat pump. The secondary pump (Wilo Pico) is connected to the flow out from the LLH to feed the heating circuit.

With the heating system running and settled down, note the various readings from the four probes – the aim is to minimise any differences between the flow in to the LLH and the flow out from the LLH to the heating circuit. It is also desirable to minimise the differences between the return into the LLH and the flow out that returns the water to the heat pump. There should be a difference in temperature between these two pairs of ports as the return circuit has dissipated heat in the emitters.

The aim is to reduce the ‘distortion’ to the minimum; should the secondary pump be running too fast, this will cause excessive mixing of the return with the flow from the heat pump. It may be a delicate balance to match flow from the heat pump, but if running too slow, less heat will be drawn into the secondary pump from the LLH.  This 'balance' requires patience and small increments of change in secondary pump speed and then waiting to see the difference such an adjustment has made. After a few iterations, it will become apparent what effect any change is making.

My own setup shows a difference of ~0.1- 0.2C (after applying the correction factor) between in and out port pairs on a good day and when the primary flow is ~7 lpm., this is the best I have managed to achieve. This suggests that I have an efficiency loss of ~0.1-0.5% but I am leaving things at this as removing the LLH and re-plumbing the system is a relatively large step to make in our airing cupboard; the expression ‘leave well alone’ comes to mind!

Calibration of Temperature Probes.

These ‘cheap’ probes are not calibrated and to be at all meaningful, it is advisable to carry out a basic check to discover the difference between the probes before use. Tying all four probes into a bunch and close together, they should be observed over a number of hours and any differences between them noted.

I didn’t place mine in water (though this might improve the reading accuracy) as I was not sure if the probes and leads are sealed and thus water proofed. I did place a Govee device on either side of the bunched probes as a sanity check though. I found that two probes were within 0.2 degrees of each other and the same as the Govee readings, the other two were also within 0.2 degrees of each other but the ‘pairs’ were a full degree apart.

When setting up my displays, I arranged them so I knew that the left hand displays were showing ~1 degree higher than the ones on the right and made the necessary allowance (correction factor) in reading the values. Without spending considerably more for accuracy, I felt this was perhaps an acceptable compromise. Rather than trying to measure an absolute value, this method which shows a comparison, should suffice for the purpose.

I've had my system for well over a year now and I'm very happy. The Samsung ASHP plus 5.2kW solar & the Powerwall 3 are all doing very well.

I've been reviewing my water law settings & would appreciate any comments.

The dhw temp is now 46°

Quiet mode is on 2400-0730, although I can't find any info on what this actually does. I know - makes it quieter! It's next to our bedroom and is pretty quiet anyway.

201   15° & -2°

202  31° & 44°

I still use my Hive thermostat, mainly to monitor the house temperature & graphs.

I have it set to 19° daytime & 18° overnight.

I know I should scrap or at least raise the thermostat up high. What values would then be needed in the water law...

Cheers 

Steve

The final piece in our fossil fuel puzzle is sorted today. We finally got an induction hob installed and the gas is ready to be disconnected. We still have a gas fireplace in the open plan kitchen living area, but doesn't get used other than on Christmas day. So happy to switch off gas supply permanently!

When I spoke to Octopus, they mentioned that they have forwarded the request to their engineering team and once they give the sign off they would schedule a visit to cap the supply. Is this just a stock response, or are there things they have to check before they give the approval. This is a freehold property and we are the homeowners, so hopefully they don't require any paperwork from the district council or anyone else. Has anyone here turned off their gas connection? I'd love to hear about your experience.

Occasionally, during a Set Back period the compressor either randomly comes on or cycles very rapidly (see graph). I’ve tried adjusting the ‘Set Back’ and ‘Decreasing Fixed Water Temp’ to stop the compressor activating in relation to flow temperature.

Here is one example: During a night last summer, the outside, inside, and flow temperature were all between 20 & 24 degrees. The Set Back was at 5 degrees and Decreasing Fixed Water Temp set to 15 Degrees, yet the compressor came on and heated the rads up. The following night I changed the Set Back to 18 degrees, and the Decreasing Fixed Water Temp back to 4 degrees. Again, the compressor came on during various times in the night.

If you look at the two graphs, one shows normal operation during ‘Set Back’ where the compressor remains off. The second graph shows the compressor coming on randomly. The internal and flow temp was around 22 degrees, and the outside temp is between 5 and 7 degrees, so the compressor should not have come on.

Conversations with Grant, and reading the manual confirm with pump blockade off, the compressor is controlled by the flow temp and not the room temp. Yet despite the flow, inside, and outside temperatures being the same during different Set Back periods, the compressor remains off on some nights and randomly switches on during others.

No one I've spoke with to date can offer any suggestion to what is going on.

In the archives of forgotten patents and yellowing trade journals from the Edwardian era, one sometimes encounters a name that reframes everything one thought one knew about the slow, grinding ascent of clean energy.

For me, that name was George Cove, a Canadian inventor whose work on solar electricity surfaced quite by chance while I was tracing the prehistory of technologies that now heat our homes. What struck me was not merely the technical ingenuity on display more than a century ago, but the counterfactual it poses: how profoundly different the thermal (and indeed the entire energy) landscape of the developed world might look today had his vision been allowed to take root rather than being violently uprooted.

Cove’s device, first demonstrated around 1905 and refined in workshops in Halifax and later New York, was no laboratory curiosity. It was a practical solar generator designed for ordinary rooftops, converting sunlight directly into usable current and storing the excess in batteries for use after dusk.

Contemporary descriptions suggest arrays that would not look out of place on a modern semi-detached house: flat, modular panels capable of powering lights, small motors and (crucially) electric heating elements. In an age when most households still relied on coal scuttles or wood stoves for warmth, the promise was revolutionary.

Electricity generated on-site could have displaced the smoky, labour-intensive business of hauling fuel indoors, offering a cleaner, more convenient source of domestic heat at a time when winter fuel bills were a genuine source of hardship. Investors evidently saw the potential. By 1909 his Sun Electric Generator Corporation had attracted significant capital and periodicals spoke of a coming era in which sunlight itself would keep families warm and illuminated without recourse to distant mines or central stations.

The broader energy context of the period makes the invention’s timing all the more poignant. The early 20th century was a moment of genuine flux in how societies met their power needs. Oil was beginning its ascendancy, coal still dominated industry and electricity grids were in their infancy.

What is remarkable is that even then, at the very dawn of the modern energy age, the fossil fuel industry (together with the nascent electric utilities that depended upon it) already displayed a willingness to suppress promising alternatives that threatened its emerging dominance.

Cove’s system offered a decentralised alternative that bypassed the emerging logic of large-scale combustion and long-distance transmission. It was, in essence, an early sketch of the very model now championed by advocates of renewable heating: generate power where you use it, minimise losses and pair it with efficient end-use technologies.

Here the story acquires an even sharper intellectual edge when one recalls that, half a century earlier, Lord Kelvin (then William Thomson) had already laid the theoretical foundation for the heat pump.

In 1852 Kelvin described the thermodynamic principle by which a modest input of mechanical work could extract heat from a colder reservoir (the air, the ground, a body of water) and deliver it at a higher, usable temperature indoors. The efficiency of such a system, he noted, could far exceed that of direct combustion or resistive heating.

Yet the idea remained largely dormant, awaiting affordable and reliable electricity to drive its compressors. Had Cove’s solar arrays achieved even modest commercial success in the 1910s and 1920s, the two innovations might have converged at precisely the right historical moment. Cheap, on-site solar electricity could have provided the power to run early heat pumps, multiplying every kilowatt-hour generated on the roof into three or four units of useful heat.

The learning-by-doing that drives down costs might have begun in earnest decades before the silicon breakthroughs of the 1950s, and the architecture of warmth could have evolved around distributed generation and high-coefficient-of-performance heat transfer rather than remaining tethered to fossil combustion.

Instead, the opportunity was lost. In October 1909 Cove was seized in Manhattan, reportedly told that continued promotion of his patents would cost him his life, and released only after refusing to surrender his intellectual property.

The episode has never been fully explained. Some contemporaries dismissed it as a hoax orchestrated for publicity, while others pointed to the obvious suspects... entrenched interests in oil, coal and the nascent electric utilities who had every reason to fear a competitor that required neither fuel contracts nor centralised infrastructure. Whatever the truth, the effect was decisive. The company faltered, production ceased and Cove himself faded from public view.

To dwell on this episode is to confront the truth that progress in energy is rarely a pure contest of ideas and efficiency. Economic historians have long studied how incumbent technologies can lock in advantages through network effects, complementary infrastructure and political influence.

Cove’s story adds a darker chapter: the possibility that outright intimidation can accelerate that lock-in. By the time solar re-emerged in a serious commercial form, the world had already committed trillions to pipelines, refineries, boilers and the cultural expectation that warmth arrives via flame or resistive wire. The result was a heating sector that, until recently, lagged far behind electricity generation in its decarbonisation efforts.

Consider the quantitative shadow this casts. Models of technological learning curves suggest that solar’s price trajectory could have been markedly steeper had deployment begun in earnest before the First World War. A modest but sustained rollout in the 1910s and 1920s might have brought photovoltaic costs into competitive territory by the late 20th century, rather than the 2010s.

For renewable heating, the knock-on effects would have been profound. Cheaper electricity would have made resistive heating more palatable earlier, buying time for the development of heat pumps whose efficiency multiplies the value of every kilowatt-hour generated on the roof. An earlier solar surge could have shortened the painful decades when electric heat was dismissed as prohibitively expensive.

Buildings themselves might have evolved differently – better insulated from the outset, designed around distributed generation rather than central boilers and equipped with thermal storage that complements intermittent solar supply. The synergy between Cove’s panels and Kelvin’s principle could, in short, have altered the trajectory of both heating and electricity itself.

One can only speculate how different the world could have been if renewables had been embraced as the natural path forward in the days of George Cove. An earlier convergence of decentralised solar power and heat-pump technology might have spared us a century of escalating fossil dependence, with its attendant geopolitical tensions, urban smog and mounting carbon emissions. The entire infrastructure of 20th-century energy (from vast extraction networks to centralised grids and combustion appliances) might have taken a gentler, more distributed form. Instead, the suppression of that early promise helped lock in habits of thought that still shape our energy choices today.

There is a deeper intellectual resonance here, one that transcends any single inventor. Energy transitions are not merely technical substitutions; they are social and institutional rearrangements. The 20th century’s reliance on fossil fuels entrenched not only physical infrastructure but assumptions that energy must be dense, extractive and centrally controlled.

Cove’s panels, paired with the heat pump’s elegant thermodynamics, challenged that assumption at its root, offering abundance that was diffuse yet democratic and efficient. Their marginalisation helped ensure that heating (the largest single end-use of energy in many temperate climates) remained the province of combustion engineers rather than systems thinkers. Only now, with the return of solar at scale and the maturation of heat-pump technology, are we rediscovering the possibility of warmth without extraction. The irony is that the solutions feel novel when they are, in many respects, the delayed realisation of an early 20th-century dream.

Yet this history need not breed fatalism. If anything, it sharpens the case for vigilance in the present. Today’s renewable heating sector faces subtler forms of resistance: regulatory inertia that privileges gas connections, supply-chain bottlenecks in heat-pump manufacturing and the lingering political weight of incumbents who benefit from the status quo.

The lesson of Cove (and of the unrealised meeting between his solar generators and Kelvin’s heat pump) is that such barriers are not inevitable; they are the product of choices, some of them deliberate. Policymakers and practitioners alike would do well to recall that innovation’s greatest enemy is rarely physics. It is more often the failure (or refusal) to imagine alternatives once a dominant system has taken hold. By accelerating deployment of solar-coupled heat pumps, hybrid thermal stores and smart district networks, we are not inventing the future from scratch. We are resuming a trajectory that was interrupted more than a century ago.

In the end, stumbling across George Cove’s story leaves one with a sense of tempered possibility. The world he glimpsed (a place where rooftops quietly convert sunlight into the steady warmth of daily life, amplified by the thermodynamic elegance of the heat pump) was not technologically fanciful. It was politically inconvenient. That inconvenience cost us decades of unnecessary emissions, higher energy costs for households and a slower reckoning with the limits of fossil dependence.

But the same contingency that allowed one era’s promise to be derailed also suggests that today’s momentum is not guaranteed. It must be defended, nurtured and accelerated. The renewable heating technologies now entering our homes and communities represent more than engineering progress; they are the vindication of a vision once nearly extinguished. If we recognise that earlier detour for what it was (an avoidable fork in the road) we may yet ensure that the path ahead leads, at last, to warmth that is both sustainable and sovereign. The sun, after all, has been waiting. It is time we fully honoured the appointment.