Circular reasoning (Rolfe's solar energy system)

[Archev]

Yeah I started using a bread machine we inherited much more when we had the solar installed!

The electricity expense of it had been putting me compared to store-bought. Once I got on the givenergy App I realised it wasn't drawing as much as I feared anyway.

Yeah I’m buying all the weird and wonderful flours and seeds etc for my loaf production.

 

[Rolfe]

By all means keep the water in the cylinder very hot but have it at around 50 C at the kitchen and a max of 38 / 42 C at the taps on the wash hand basins and baths. Temperature blending valves can be fitted beneath / behind those taps to regulate the max temperatures at those taps. This leaves the storage cylinder at max temperature which makes the hot water “last“ longer and prevents bacteria build up.
I went to a tragic case of a wee laddie of three who had been scalded because the cylinder thermostat was set to max allowing nearly 80 C water to all taps in the house. That wee soul lost I think three fingers and suffered many skin grafts after trying to be helpful washing his own hands when everyone else was distracted.

I didn't know that was possible. I've had this issue for a long time and a previous plumber was unable to solve. In fact I settled on timing the water heating so that it wasn't scalding at the times I wanted to use it. I was just thinking today, back to scalding water here, what do I do now.

Many of the sinks and wash hand basins in the house have mixer taps, but a couple don't, and it's still an issue with mixer taps anyway. So thanks for that.

What a tragedy for the wee boy.

Yeah I started using a bread machine we inherited much more when we had the solar installed!

The electricity expense of it had been putting me compared to store-bought. Once I got on the givenergy App I realised it wasn't drawing as much as I feared anyway.

I cooked. I wanted to see what happened if I did my usual thing with the oven and the hob and the electric kettle.

The earlier green load spikes are the immersion heater, and happily it doesn't go on doing it after the solar has faded away. The wider one must be oven and hob, and I think the electric kettle went on once at the beginning to boil water for the potatoes and vegetables, and once at the end to make tea. It's all just one spike though, not that impressive.

That brought the battery down to about 93% and although it tried to recharge there was bugger-all sunshine to spare by that time. The rest of it is just the house base load continuing, fridge and freezer and things on standby (and the cat's wee electric blanket which can't be 40 watts, I never bother to switch it off, he likes his warm bed when he comes in from the hunt).

Then at nine I put some lights on - having swapped out 440 watts of incandescent bulbs for new low energy ones. My installer said, if you prefer incandescent bulbs in these wall lamps why not just do it, you'll have plenty in the battery in the evening. But I'm thinking it will be different in winter when the battery is being charged up overnight, then the lights go on a lot earlier in the evening. I'm a reformed character, start as I mean to go on. And I put on the TV for a zoom call that lasted about two and a half hours.

But look at all that sunshine! Hell of a display for Day One of the system. I've learned so much! I don't think it's going to be so sunny tomorrow so we'll see how that goes.

 

[Archev]

I didn't know that was possible. I've had this issue for a long time and a previous plumber was unable to solve. In fact I settled on timing the water heating so that it wasn't scalding at the times I wanted to use it. I was just thinking today, back to scalding water here, what do I do now.

Many of the sinks and wash hand basins in the house have mixer taps, but a couple don't, and it's still an issue with mixer taps anyway. So thanks for that.

What a tragedy for the wee boy.

View attachment 26647View attachment 26647

 

[Rolfe]

Thanks, good to know.

I remember about 15 years ago a politician who was in a bit of trouble for excessive expenses claims for his second home declared that he needed to get a new boiler because his hot water was too hot!

 

[Archev]

Thanks, good to know.

I remember about 15 years ago a politician who was in a bit of trouble for excessive expenses claims for his second home declared that he needed to get a new boiler because his hot water was too hot!

I’ve tried simple X’s to help with their hot air ?

 

[decrep]

To me that solar drop off doesn't look natural, especially as it coincides with 100% battery and you don't notice any change in the sky.
I'm fairly sure there's something going on in the inverter that is limiting solar.
But I have no knowledge of your English system, so I have no idea what.

 

[johnb80]

I didn't know that was possible. I've had this issue for a long time and a previous plumber was unable to solve. In fact I settled on timing the water heating so that it wasn't scalding at the times I wanted to use it. I was just thinking today, back to scalding water here, what do I do now.

Many of the sinks and wash hand basins in the house have mixer taps, but a couple don't, and it's still an issue with mixer taps anyway. So thanks for that.

What a tragedy for the wee boy.

My system I run the water at 80 degC plus but have a temperature blending valve on the outlet from cylinder to reduce it down to 45 deg C. The plumbing is dead simple with the two pipes needed being at the cylinder already it was literally a T piece, the mixing valve and a bit copper piping, from memory all from Screwfix and was less than £80. Running the tank at higher temperature increase effectively the hot water storage capacity.

 

[Archev]

My system I run the water at 80 degC plus but have a temperature blending valve on the outlet from cylinder to reduce it down to 45 deg C. The plumbing is dead simple with the two pipes needed being at the cylinder already it was literally a T piece, the mixing valve and a bit copper piping, from memory all from Screwfix and was less than £80. Running the tank at higher temperature increase effectively the hot water storage capacity.

That is a compromise solution. Bear in mind that 45°C is on the hot side. Hand wash basins in hospitals, hotels etc are usually required to be set and signed for between 38 and 42 after installation / servicing ( sometimes even lower ). With thermostatic showers again the air requirement was usually for the 38°C to be maximum / or where the override button was set depending on the type of shower valve installed.
I did encounter a number of valves installed at, or sometimes directly on the cylinders but found in practice they needed more frequent servicing and actually had to replace a good few where internal springs, diaphragms, “O” rings etc. just couldn’t cope.

 

[Coulomb]

Bear in mind that 45°C is on the hot side.

Really? Blood temperature is 37°C, so that won't feel warm at all. 45°C is only 8° above that.

 

[Rolfe]

To me that solar drop off doesn't look natural, especially as it coincides with 100% battery and you don't notice any change in the sky.
I'm fairly sure there's something going on in the inverter that is limiting solar.
But I have no knowledge of your English system, so I have no idea what.

Not English. Just saying.

Really? Blood temperature is 37°C, so that won't feel warm at all. 45°C is only 8° above that.

Seriously, you'd be surprised. 37°C does feel warm and it ramps up quite quickly above that. Try some experiments.

 

[johnb80]

That is a compromise solution. Bear in mind that 45°C is on the hot side. Hand wash basins in hospitals, hotels etc are usually required to be set and signed for between 38 and 42 after installation / servicing ( sometimes even lower ). With thermostatic showers again the air requirement was usually for the 38°C to be maximum / or where the override button was set depending on the type of shower valve installed.
I did encounter a number of valves installed at, or sometimes directly on the cylinders but found in practice they needed more frequent servicing and actually had to replace a good few where internal springs, diaphragms, “O” rings etc. just couldn’t cope.

Why is it a compromise, it works well for me.

45 deg C isnt too hot, IMHO, a recent holiday in Corfu witnessed temperatures over that in the shade.

 

[Archev]

Really? Blood temperature is 37°C, so that won't feel warm at all. 45°C is only 8° above that.

Really ?, I mean really really ?
One or two of that master race, the Ladies might shower nearer that level but, really ? Sorry I’m a mere mortal ?

Why is it a compromise, it works well for me.

45 deg C isnt too hot, IMHO, a recent holiday in Corfu witnessed temperatures over that in the shade.

I meant the compromise was between the figures I quoted. A bit too warm to have left a wash basin and not quite hot enough for the kitchens in hospitals etc.

Seriously, you'd be surprised. 37°C does feel warm and it ramps up quite quickly above that. Try some experiments.

Or - don’t please - if my signature is anywhere near the certification documentation.

Why is it a compromise, it works well for me.

45 deg C isnt too hot, IMHO, a recent holiday in Corfu witnessed temperatures over that in the shade.

After crossing the Mojave desert I burned my bum on a stainless steel toilet pan in a toilet behind a gas station at an air temperature of around 43C on the car’s dashboard. A truly crap experience I assure you ? ( for a fair skinned Scottish posterior ?)

 

[johnb80]

I meant the compromise was between the figures I quoted. A bit too warm to have left a wash basin and not quite hot enough for the kitchens in hospitals etc.

Ah OK, understood.

After crossing the Mojave desert I burned my bum on a stainless steel toilet pan in a toilet behind a gas station at an air temperature of around 43C on the car’s dashboard. A truly crap experience I assure you ? ( for a fair skinned Scottish posterior ?)

Conjures up an image

 

[Rolfe]

Why is it a compromise, it works well for me.

45 deg C isnt too hot, IMHO, a recent holiday in Corfu witnessed temperatures over that in the shade.

Air temperature and water temperature are two entirely different animals. Particularly as regards to how quickly and directly that temperature is transferred to the body.

 

[decrep]

Not English. Just saying.

Sorry, forgot that Scotland may be different to England

And our hot water is set to 50C I'd prefer it hotter for doing dishes.
You just get used to blending the cold in, before jumping into the shower.

 

[johnb80]

Air temperature and water temperature are two entirely different animals. Particularly as regards to how quickly and directly that temperature is transferred to the body.

I'm not where youre heading here but 45 deg C and washings hands compared to 50 degC in the shade completely surround my body, I know which I was more uncomfortable with, especially when I jumped in the unheated outdoor pool

I like having hot water in the taps, water that you cant bear your hands under BUT with grand children in mind we have dropped the temperature of our hot water supply to 45 degC which is hot enough I'm sure to give them a fright but not to do any serious damage. We always supervise them anyway at bath time etc.

To stay on subject, I've just done my figures for May so far and running 2 x Electric cars, air conditioning, immersion heater etc, our spend on electricity (taking export into account) is 10.23p per day. THAT makes it all worthwhile.

 

[Rolfe]

And our hot water is set to 50C I'd prefer it hotter for doing dishes.
You just get used to blending the cold in, before jumping into the shower.

It's something I need to look into.

I'm not where youre heading here but 45 deg C and washings hands compared to 50 degC in the shade completely surround my body, I know which I was more uncomfortable with, especially when I jumped in the unheated outdoor pool

I like having hot water in the taps, water that you cant bear your hands under BUT with grand children in mind we have dropped the temperature of our hot water supply to 45 degC which is hot enough I'm sure to give them a fright but not to do any serious damage. We always supervise them anyway at bath time etc.

To stay on subject, I've just done my figures for May so far and running 2 x Electric cars, air conditioning, immersion heater etc, our spend on electricity (taking export into account) is 10.23p per day. THAT makes it all worthwhile.

It's surprising how low a water temperature feels too hot to touch, that's all.

I'm still on the early stages of this learning curve. I don't quite know why the panels are clipping at 5.3 kW when the battery is full, and if this is something that will alter when (if?) this G99 comes through. I don't know how to manage the car charging right now, given that I don't have the overnight tariff yet. I don't know how to decide (in darker weather) whether the battery should fill up overnight from the grid at the cheap price, or whether to wait for morning in the hope or expectation that the sun will do the job.

I'll ge there though.

 

[johnb80]

It's surprising how low a water temperature feels too hot to touch, that's all.

Ah ok, understood.

I'm still on the early stages of this learning curve. I don't quite know why the panels are clipping at 5.3 kw when the battery is full, and if this is something that will alter when (if?) this G99 comes through.

What make and model of inverter did you get?

When the battery is full and the panels are producing the energy has to go somewhere or be lost i.e. not used. It sounds like you are exporting and that a limit of 5.3 kW has been set if that's what your graphs show.

What happens if you plug your car in when this clipping is occurring?

I don't know how to manage the car charging right now, given that I don't have the overnight tariff yet. I don't know how to decide (in darker weather) whether the battery should fill up overnight from the grid at the cheap price, or whether to wait for morning in the hope or expectation that the sun will do the job.

Once your tariff and G99 is sorted it's an easy decision with current prices. Everything generate, export. Any battery capacity you have left towards the end of the day export. All batteries, car, washing machine, tumble drier, run during off peak time. It may seem a little daunting at first but the reality is simple and straight forward.

I'll ge there though.

I have every confidence in you, you'll have it sorted in no time.

J

 

[Rolfe]

The battery and the inverter are GivEnergy. I think it's clipping because of the lack of a G99. Probably. Possibly.

... our spend on electricity (taking export into account) is 10.23p per day. THAT makes it all worthwhile.

Is that taking your standing charge into account?

I'm pretty sure that the solar would not clip if I plugged the car in. However, as the car is currently at 100% and has been since Friday, this experiment is not possible. I saw 5.76 kW this morning, momentarily, just as the sun broke through the complete cloud cover we had from daybreak to 11.15. (I saw similar yesterday, and on Friday there was a momentary peak at 7.37 kW during a blink of bright sunshine.) At that time the battery was still charging. But by the time the sun really got going, about 12.45 the battery was full and it was clipping again.

I see that the system started getting the hot water going as soon as the sun broke through, prioritising that over the battery charging. Then after that was done it was export all the way (boo, hiss). Not quite sure why there's that little battery blip after each water-heating boost, looks as if each time the immersion heater has used a little bit of the battery. It didn't do that yesterday. Maybe because the sunshine was a bit intermittent at the time?

But then, mid-afternoon, I had two thoughts. One was that I'd spilled something on the clean jeans I was wearing yesterday evening, that I wanted to travel in on Tuesday, and I wanted to wash them. So I chucked them and a few other items in the washing machine.

The other was vanity. Yesterday evening on a Zoom call I didn't like the colour of my hair. This afternoon I saw myself in the mirror and REALLY didn't like it. Again, I wanted it right for going away. So I decided to colour it, which involves having a shower. So after I'd started the washing machine I did that. I'm now dressed and decent again, but the washing machine hasn't quite finished. (Get on with it, I want these things on the line in the sun.) Oddly enough though, all that usage seems to have been mopped up and the system is back to exporting.

Hopefully I'll at least have the cheap night-time tariff by the time I get back from my trip to England. I don't know why they're being so obstructive about the G99. Still, I'm better off than before I had the system, at least if you don't count the cost of the system, which is where we came in.

 

[Bam Bam]

The battery and the inverter are GivEnergy. I think it's clipping because of the lack of a G99. Probably. Possibly.



Is that taking your standing charge into account?

I thought you got a 5kW inverter, though.

In which case 5kW (plus any change - sounds like you can get an extra 0.3) is all that it can output.

Good idea to test it out with the car but my guess would be that it can put the power in the battery because the battery is also DC. However, it cannot convert to AC more than 5kW.

This isn't an issue for us because we are East-West. The two are never in perfect sun at the same time.

5kW is plenty of output, but if my theory is right it sounds like you want to be filling your battery only/primarily during those peak hours when you get over 5kW from the panels.

So use as much as energy as possible during the morning when you are getting under 5kW (fill the car, hot water, export more during that time if possible). Then fill up the battery during the peak of the day.

You could play with it on a sunny day when you've got time to focus. Set to export a set amount (say, 2kW) in the morning, so that the battery doesn't get quite so full. Then see if you get higher solar generation for longer during the sunniest hours.