One obviously can have metres per second per second, and that's useful and meaningful - but I'm not sure what use (or, even, what practical meaning) Watts per second would have.
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Solar panels and hot water
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I must have done.
As you say, currently of doubtful usefulness (and I don't see 'rate of change of the output of a battery charger' as being particularly useful
)
Rate of change of discharge current of a battery (I assume by measuring at regular intervals) is used in some battery capacity analysers as a means of calculatiing the AH capacity, apparently more efective than voltage alone.I must have done.
As you say, currently of doubtful usefulness (and I don't see 'rate of change of the output of a battery charger' as being particularly useful
Interesting - but ...
1... morqthana wrote of rate of change of charger output, not anything to do with a battery's discharge current
2... we were talking about rate of change of power (Watts/second), not of any current
3... both of those aside, I'm not sure that I really understand how rate change of discharge current of a battery can be an indicator of capacity. After all, changes in discharge current of, say 10 A in 1000 seconds and 1 A in 100 seconds are both rates of 0.01 A/sec, but I don't see why they should indicate the same capacity. Am I missing something?
I was struggling to come up with anything similar and that is the closest I came up with,
I don't think so, it was a long article explaining charging, discharging and analysing of different technology batteries. I'm sure it was correct but no I can't answer as I gave up with it.
Fair enough - and, as I've said, in turn I struggle to think of a practical usefulness of Watts per second (particularly if one thinks of it as "Joules per second per second") !
Discharge current multiplied by time (or integrated wrt time if not constant), over the full discharge cycle, is presumably essentially a measure of capacity - so it seems a bit odd that it should be suggested that discharge current divided by time can be used to estimate capacity
Clearly complicated stuff!
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Found pictures of hot water system. The pumps on the right are activated when the water is warmer than the tank, it was useless, I tried to fix it, I assumed it had worked, but the power to it was labelled immersion heater, and my father-in-law had turned it off, as he did not any longer have an immersion heater. So we assumed it had overheated as a result, so got the specialist in to recharge the system, and it still did not work.
To be frank, I look at my PV panels, which can produce 6 kW, and the panels on this system, and if area of roof covered is an indication then at best the panels were 500 watt. Likely a lot less, so producing even if working A1, not enough to maintain the DHW never mind heat it up, since to do it the immersion was removed, the only way to top up was to run the gas central heating, and that is what had been done until smart meter fitted, and the pilot flame went out.
It was only then we realised it was the gas central heating keeping the DHW hot, the solar panels were doing nothing. It never did work as far as I can make out, it was a con sold to an old age pensioner who did not realise what was going on. But it did raise the energy rating band, even when it did not work. Must admit it looks the part, pity it did not work, new owners ripped it out to gain more room in the house.
which is far bigger to start with, and with 14 panels (6 kW) it does make a real difference.
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It's a sound enough principle, provided that the water coming from the panels got hot enough for long enough to provide useful heating of the DHW. Hence, if it was 'useless' the,n either those conditions were not satisfied or else, as you suggest, the system was 'broken' in some way.
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To my mind, it is down to loses, with even a very small PV panel, any energy produced will heat the water, but with a direct water system one has to ensure the hot coil in the bottom of the cylinder is actually warming not cooling the water, so those two pumps must only be energised when there is heat to transfer.
Sure, and since 'heat rises', one obviously needs a pump. In addition, and for the same reason, unless the pump (when not energised) provides adequate 'isolation' (I doubt that it does) then there would also have to be be valves, to prevent 'heated water rising' from the cylinder to be 'cooled' in the panel (when cylinder temp was greater than panel temp)
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But the system I saw, (was in brothers-in-law old house) used immersion heaters and PV solar panels. The system worked very well, installed when the house was built, it allowed him to visit daughters in Germany, and on arriving back turn up heating with phone, and return to a cosy warm house. However, when he moved, he looked into installing the same system in the old farm house he had bought, and the work involved to reinforce the floor etc, meant it was not really an option for a retro-fit.
I do look at the sizes of some solar arrays, and some seem far too small to really do much, and others also seem far too big, to supply the house unless running an EV. And the cost of electric for EV home charging is so low, it is unlikely to pay to generate that much with solar, it is just a flag to wave outside one's house to say look how good I am at saving the planet, personally only interested in saving money, and do wonder how long it will last before the bubble bursts, there must be a point where the country can't use all the solar produced, and payment for export will be reduced to a point where they no longer pay for themselves.
I'm not so sure about that. When a hot water cylinder is 'up to temperature', the water at the bottom of it can be pretty hot, certainly hotter than the water in a solar panel on a cold day!
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My cylinder had a 9-inch immersion heater when we moved in. It did not heat very far down the tank, and has now been replaced with a 27-inch version, as the hot water was not lasting day to day. There is the Willis system which will heat the whole cylinder, but in the main stratification is reasonably well-defined, and heat does not go far below the immersion or hot coil.
Once my central heating starts to be used, it heats the DHW to a higher temperature as to the immersion heater, so solar water heating stops, but the immersion only kicks in after the export exceeds 200 watt, so it would be unlikely to be activated much in the winter anyway, so looking at only half the year anyway.
I have not had solar for 2 years yet, but I can see the production
and I am very pleased with the results. However, December one is not producing much solar, and the gains are mainly due to the battery, and using off-peak for a good proportion of the day. My software will only go back a couple of months to show use through the day, but I use around 12 kWh per day, so 19 hours (5 are at off-peak) and only 5.76 kWh of usable battery (10% reserved for power cuts) plus 3 kWh from solar average, so around 3 kWh short so paying peak rate for that. But the point is 6 kW solar panels are only producing 3 kWh average per day in December, so the output of direct water panels, is likely not going to exceed losses, so one is only going to get any useful output for 6 months at best.
Once my central heating starts to be used, it heats the DHW to a higher temperature as to the immersion heater, so solar water heating stops, but the immersion only kicks in after the export exceeds 200 watt, so it would be unlikely to be activated much in the winter anyway, so looking at only half the year anyway.
I have not had solar for 2 years yet, but I can see the production
and I am very pleased with the results. However, December one is not producing much solar, and the gains are mainly due to the battery, and using off-peak for a good proportion of the day. My software will only go back a couple of months to show use through the day, but I use around 12 kWh per day, so 19 hours (5 are at off-peak) and only 5.76 kWh of usable battery (10% reserved for power cuts) plus 3 kWh from solar average, so around 3 kWh short so paying peak rate for that. But the point is 6 kW solar panels are only producing 3 kWh average per day in December, so the output of direct water panels, is likely not going to exceed losses, so one is only going to get any useful output for 6 months at best.I think that people have a fair bit too much faith//belief in the temperature differences in a DHW cylinder. There is conduction, as well as convection, going on - and that (including conduction through the copper of the cylinder),unlike convention,goes 'down' about as easily as it goes 'up'.
I think that illustrates one of the things that confuses people. 'Hot water not lasting a day' does not necessarily mean that the water lower down in the cylinder was never hot. Even if (by whatever process) you started with the cylinder totally filled with 'up to temp' water, as soon as HW was used, cold would be drawn into the cylinder to replace it, and that would cool the water in the cylinder.
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