I've had panels since the winter, and now many days are providing lots of excess energy I'm using some of this to heat the water in the tank. This does work but I'm noticing that the amount of water heated seems far less than when gas is used, even if the immersion heater is switched to on all day. It's OK mostly, but very noticeable if a couple of people have showers.

 

I'm assuming that this is because the gas heating involves passing water through the boiler so you get water swirling around a bit, whereas the immersion heater just heats water at the top of the tank and not below the depth of the heating rod goes. 

 

My question is, is there anything anything I can do to heat more water in the day (when I'm passing loads back to the grid for nothing)? 

 

I can't think of any way to get the water swirling around, so that only leaves the length of the heating rod? I've got no idea how long my rod is (ahem) but I'm guessing that it's not super long.

My tank has two elements, one at the top and one at the bottom. My diverter is set to heat the top element first, then will heat the lower one when the top one is satisfied

6 minutes ago, elite said:

My tank has two elements, one at the top and one at the bottom. My diverter is set to heat the top element first, then will heat the lower one when the top one is satisfied

 

Ah nice. Was the tank always set up like this? My talk isn't that old but I can't imagine it's doing this given how little water is heated.

Have a look around the base of the cylinder and see if it has a boss blanked off.

You could try setting the thermostat to the maximum it will reliably go to i.e. 85°C.  Tat will at least allow more cold to be mixed with it at the tap.

You can also time your usage to allow a decent recharge time that coincided with PV production, i.e. use before 10AM, usage after 2PM.

Use less.

7 minutes ago, MrTWales said:

 

Ah nice. Was the tank always set up like this? My talk isn't that old but I can't imagine it's doing this given how little water is heated.

Tank was installed with two heaters, I believe this is quite common, the idea being that you don't have to heat the entire tank if you don't require the entire volume of water. Diverter was added later when solar PV was installed.

 

As @SteamyTea says worth checking to see if a second element can be easily added

5 minutes ago, SteamyTea said:

Have a look around the base of the cylinder and see if it has a boss blanked off.

You could try setting the thermostat to the maximum it will reliably go to i.e. 85°C.  Tat will at least allow more cold to be mixed with it at the tap.

You can also time your usage to allow a decent recharge time that coincided with PV production, i.e. use before 10AM, usage after 2PM.

Use less.

 

Many thanks - re the latter point, this makes sense but I can't control the kids always washing their hair at night etc. It just hacks me right off to give about 10Kwh to the grid in the day but then run out of water water at night!

 

I'll see if I can make sense of the cylinder. I'm still waiting for the diverter to be installed (I'm using the switch manually now) so it may be something I can discuss with the installer as an extra job, esp as immersion heating rods don't cost all that much. I'm generally keen to do what I can myself but this would be way beyond me.

2 minutes ago, MrTWales said:

I can't control the kids always washing their hair at night

 

1 hour ago, MrTWales said:

I'm assuming that this is because the gas heating involves passing water through the boiler so you get water swirling around a bit, whereas the immersion heater just heats water at the top of the tank and not below the depth of the heating rod goes. 

 

There's no active 'stirring' being done by the boiler, it's indirectly heating the water - just like the immersion rod. The big difference is your boiler is probably putting anything from 10kW to 20kW into the cylinder rather than the lowly 3kW of the immersion.

1 minute ago, Radian said:

The big difference is your boiler is probably putting anything from 10kW to 20kW into the cylinder rather than the lowly 3kW of the immersion

And from the base.

Use a solar diverter?

1 hour ago, MrTWales said:

 

Many thanks - re the latter point, this makes sense but I can't control the kids always washing their hair at night etc. It just hacks me right off to give about 10Kwh to the grid in the day but then run out of water water at night!

 

 

 

This might solve itself if you let it run its course. People are generally not keen on cold showers! 

 

 

Here is some time series data from my E7 heated cylinder.

 

1 hour ago, TonyT said:

Use a solar diverter?

I have one waiting to be fitted, but when I switch the immersion on by hand it draws the 3kw for about 60/90 mins but then flicks on and off very briefly for the rest of the day, but the quantity of water heated isn't as much as if gas is used no matter how long it's on for. I guess it just heats the top bit.

1 hour ago, Radian said:

There's no active 'stirring' being done by the boiler, it's indirectly heating the water - just like the immersion rod. The big difference is your boiler is probably putting anything from 10kW to 20kW into the cylinder rather than the lowly 3kW of the immersion.

I get there is no stirring as such, but doesn't the path the water takes with gas effectively cause some swirling? With the electric, it draws 3kw for a while then stops and flicks on only briefly for the day so I assume it's getting the top part to whatever temperature it's set for and then it stops. The gas heats more water in 30 mins (from cold) than the immersion heater does if it's on all day.

Just now, MrTWales said:

I get there is no stirring as such, but doesn't the path the water takes with gas effectively cause some swirling? With the electric, it draws 3kw for a while then stops and flicks on only briefly for the day so I assume it's getting the top part to whatever temperature it's set for and then it stops. The gas heats more water in 30 mins (from cold) than the immersion heater does if it's on all day.

Worth checking what temp the immersion is set to, could be this is set lower than the temp the boiler is heating to, therefore you will be using much more water from the UVC when heated by the immersion

4 minutes ago, elite said:

Worth checking what temp the immersion is set to, could be this is set lower than the temp the boiler is heating to, therefore you will be using much more water from the UVC when heated by the immersion

Yes this is a good point. I can't see this easily and assume I have to unscrew something, but I'll discuss this when the installers finally finish the damn job and fit the diverter. The water does get hot enough, but going from 55 degrees (say) to 60 would help make the hot water last longer.

If the immersion boss is in the top rather than side (more common in older tanks) you may be able to replace it with a longer one that heats the tank lower down.

 

Theoretically you can add a secondary circulation pump that agitates the water pushing it from the outlet back to the inlet connection (just be sure to have a non return valve), which you turn on after the tank reaches initial target temp. Maybe more hassle than a new tank tho.

 

My cylinder is called Megaflo cl210. Overall I've been very impressed with how it keeps water hot, but maybe I can improve this aspect somehow with a longer rod. Assuming I ever hear from the effing installers again I'll ask about this when the diverter is fitted.

element is near the bottom already is it not?

3 minutes ago, dpmiller said:

element is near the bottom already is it not?

 

I don't know! There are freaking all sorts of pipes sticking out and I have no idea how the damn thing works. It does seem odd if it's at the bottom though as it doesn't heat that much water, but maybe it is.

heat rises tho, so it;ll heat from the top down regardless.

 

Is there a square cover on the tank about a third of the way up? The heater is behind that.

A picture could help. 

Thanks, I get that but if it's heating from the bottom and cuts out at, say, 55 degrees then wouldn't it have to heat the whole lot before it stops?

I guess it's that little box thing near the middle? It seems fairly low! I'm even more confused than I was before now.

 

 

 

work out how many kWh you're putting in during your heating period vs how much it would take to heat the whole tank