Day storage heaters. for PV.

[Marvin]

Having analysed the historical data output form the PHOTOVOLTAIC GEOGRAPHICAL INFORMATION SYSTEM for my PV setup in the winter of 2019-2020 the results show me that even in January I would fail to use about 75kWh of PV, even after taking into account all mernipulations

[Marvin]

Try again....

 

 

Having analysed the historical data output form the PHOTOVOLTAIC GEOGRAPHICAL INFORMATION SYSTEM for my PV setup in the winter of 2019-2020 the results show me that even in January 2020 we would fail to use about 75kWh produced by the PV, even after taking into account all manipulations we could possibly do (except wasting power) like only washing, heavy cooking, washing, tumble drying, and topping up every rechargeable battery we have (about 12kWh) on sunny days.

 

Doing all this we still expect to buy in about 200kWh in January.

 

In order to keep our bills down we are installing night storage heater and converting the energy supply to come from excess PV during the day producing "Day Storage Heaters".  Looking at the raw data (the PGIS broken down into hourly records over a year and weather broken down to half hour records) its easy to conclude that the days in winter when sunny with a clear sky give rise to high PV generation and cold nights.

 

We are low tech here and will be using CT clamps and relays to engineer the charging control. I am testing out a different way, but won't comment until tested. Just to say the storage heaters will only be using a resistive and not an inductive load. There are multiple issues regarding output control which will be addressed at the time. 

[JohnMo]

Could you not use an immersion diverter, after all, a storage heater is just a series of immersion elements in stone/metal/concrete blocks 

[Marvin]

3 minutes ago, JohnMo said:

Could you not use an immersion diverter, after all, a storage heater is just a series of immersion elements in stone/metal/concrete blocks 

I didn't want to mention until tested. 

[SteamyTea]

A few years back I did a small experiment with my storage heaters.

Rather than limit the temperature, I limited the power they could draw, by removing one, and then two, elements (4 in total).

I then compared the house temperatures to letting it run unhindered. Cost less, but house was cooler.

Then I put on extra timers to limit the E7 charging window to just 4 hours, and the last 4 hours of the E7 period. That was cheaper and hit my target temperature better.

Have now limited it to 3 hours, so around 9 kWh a day maximum storage, rather than 21 kWh. Temperature variation is a bit greater, but I can live with that.

If I had 'excess' power, I would definitely look at topping up the night stores more, and enjoy the extra warmth. I grew up in the tropics and don't take my jumper off till it is over 80°F.

I am still wondering about the best way to control output from old storage heaters, box them in and control airflow from the base seems to be the obvious way to me.

 

Keep us informed about how it goes, it is an interesting subject.

[Marvin]

1 hour ago, SteamyTea said:

A few years back I did a small experiment with my storage heaters.

Rather than limit the temperature, I limited the power they could draw, by removing one, and then two, elements (4 in total).

I then compared the house temperatures to letting it run unhindered. Cost less, but house was cooler.

Then I put on extra timers to limit the E7 charging window to just 4 hours, and the last 4 hours of the E7 period. That was cheaper and hit my target temperature better.

Have now limited it to 3 hours, so around 9 kWh a day maximum storage, rather than 21 kWh. Temperature variation is a bit greater, but I can live with that.

If I had 'excess' power, I would definitely look at topping up the night stores more, and enjoy the extra warmth. I grew up in the tropics and don't take my jumper off till it is over 80°F.

I am still wondering about the best way to control output from old storage heaters, box them in and control airflow from the base seems to be the obvious way to me.

 

Keep us informed about how it goes, it is an interesting subject.

Thanks for all the info. Yes were really looking at background warmth and SWMBO has already commented about controls which we will be experimenting with. (as SWMBO says I cant help myself!) 

 

Edited August 28, 2022 by Marvin

[TonyT]

1 hour ago, SteamyTea said:

A few years back I did a small experiment with my storage heaters.

Rather than limit the temperature, I limited the power they could draw, by removing one, and then two, elements (4 in total).

I then compared the house temperatures to letting it run unhindered. Cost less, but house was cooler.

Then I put on extra timers to limit the E7 charging window to just 4 hours, and the last 4 hours of the E7 period. That was cheaper and hit my target temperature better.

Have now limited it to 3 hours, so around 9 kWh a day maximum storage, rather than 21 kWh. Temperature variation is a bit greater, but I can live with that.

If I had 'excess' power, I would definitely look at topping up the night stores more, and enjoy the extra warmth. I grew up in the tropics and don't take my jumper off till it is over 80°F.

I am still wondering about the best way to control output from old storage heaters, box them in and control airflow from the base seems to be the obvious way to me.

 

Keep us informed about how it goes, it is an interesting subject.

use smaller storage heaters under 13 amp and use smart plugs to turn in and off or use a smart plug to control a 20 amp contactor

[SteamyTea]

16 minutes ago, Marvin said:

background warmth

Rather a misleading term.

I prefer a binary view in heating. It is either warm enough, or not.

It is the 'not' that costs the money.

Probably the cheapest method is to directly wire in a kW_p of PV and have no control, except an isolator.

Then just use the built in flap control to limit the output.

When it is not warm enough, accept that external input is needed, or a jacket.

 

[Temp]

3 hours ago, JohnMo said:

Could you not use an immersion diverter, after all, a storage heater is just a series of immersion elements in stone/metal/concrete blocks 

 

And water has the best specific heat capacity so most likely easier to insulate as the temperature woukd be lower.

 

Only thing better might be some exotic wax filled store that uses the latent heat as well as the specific heat.

[SteamyTea]

2 hours ago, Temp said:

 

And water has the best specific heat capacity so most likely easier to insulate as the temperature woukd be lower.

 

Only thing better might be some exotic wax filled store that uses the latent heat as well as the specific heat.

Think it really comes down to volumetric capacity. Smaller volume and you can add more insulation.

[Marvin]

Having spoken to the manufacturers of the Solic 200 (the immersion heater diverter I have) about diverting power to day storage heaters I have been advised of the following:

 

You cannot have two of these type of diverters connected to your system even if you put the CT clamps at a distance from each other as they will "fight each other" for the excess power. Having said that I think some other companies make bigger ones but I think you would need a potential output of over 7kW of power to make this practical.

 

The way to go is a relay switch.

 

On 28/08/2022 at 14:02, SteamyTea said:

Rather a misleading term.

I prefer a binary view in heating. It is either warm enough, or not.

Yes your right. However the aim is to take any unused power from the PV and use it to store heat overnight when the home has the potential of getting cold. The aim is to use less purchased power in the night when PV is not producing. So the result could be some heat from the day storage heaters, and some heat from another source, which would make the warmth required less costly to maintain.

 

The diverter would first heat the hot water tank to temperature with otherwise unused PV power, and then a day storage heater and then another day storage heater. These two heaters are positioned in the coldest parts of our home. The system used must not include any inductive load being supplied via the diverter. 

 

The way we are proposing to achieve this is through the following set-up:

Diverter (in our case the Solic) supplies power into a 2 way relay

The separate digital temperature controller supplies power to close the relay causing any excess PV power to go to the immersion when the hot water tank has a lower temperature.

When the hot water tank is hot enough the relay is opened causing any excess PV power  to go to a second relay and on to one of the day storage heaters. When the first storage heater is full a CT clamp relay will switch heaters.

 

[Radian]

2 minutes ago, Marvin said:

You cannot have two of these type of diverters connected to your system even if you put the CT clamps at a distance from each other as they will "fight each other" for the excess power.

Oh that's very interesting. It implies a degree of 'dead reckoning' where a decision is made to energise the load for a certain amount of time based on previous measurements. Of course the loads in a house are dynamic so something else may energise and soak up the apparent excess. By then it may be too late to 'call off the dogs'.

 

My diverter measures the power for every cycle and 'sees' the dump load along with everything else (including any other diverters) and reponds accordingly. If this isn't done then the dump load may be burning unnecessary power.

[SteamyTea]

12 minutes ago, Radian said:

If this isn't done then the dump load may be burning unnecessary power.

Comes down to the dump load being a 'thing' that is useful, usually later in the day.  So hot water is useful, as is a charged battery.

Extra lighting and a freezer at a degree cooler is probably not useful.

[Marvin]

1 hour ago, SteamyTea said:

Comes down to the dump load being a 'thing' that is useful, usually later in the day.  So hot water is useful, as is a charged battery.

Extra lighting and a freezer at a degree cooler is probably not useful.

A diverter will only divert the excess power and, as far as I understand, can only supply equipment which uses all Resistive load, no Inductive load. As I understand it, a battery charger uses an inductive load so cannot be used with an immersion only (well, a resistive load) type of diverter.

[Marvin]

1 hour ago, Radian said:

Oh that's very interesting. It implies a degree of 'dead reckoning' where a decision is made to energise the load for a certain amount of time based on previous measurements. Of course the loads in a house are dynamic so something else may energise and soak up the apparent excess. By then it may be too late to 'call off the dogs'.

 

My diverter measures the power for every cycle and 'sees' the dump load along with everything else (including any other diverters) and reponds accordingly. If this isn't done then the dump load may be burning unnecessary power.

What brand/brands of diverters are you using?

Edited September 7, 2022 by Marvin
clarification

[Radian]

1 hour ago, Marvin said:

What brand/brands of diverters are you using?

The best, home brewed 

[Wil]

I use the Solic 200 (or did until I got the power walls). I just put a couple of Shelly 1 Relays on the various immersions and just switch them in or out depending on which part of the tank/ tanks needed heating. You’d need a dedicated circuit to feed your storage heaters, then you could choose to fill them all one at a time or all together (the dumb resistance heaters just share the supply from the Solic). Means you only need the one Solic and it throttles it’s supply to 3.6kW max apparently. 

 

Now it’s simpler to bypass the Solic and just do 1 hour hits on the Immersion using a Shelly 1PM to act as remote switch. If the solar isn’t quite enough the batteries make up the shortfall and the solar can take it’s time to fill the batts instead.

 

When I get some more solar I might swap the Solic and immersions onto another phase but at the moment it just steals from the batteries.

[Marvin]

So, due to day storage heaters using only excess PV power we still have not turned on the ASHP yet.

 

Works well through diverter. Set to hot water until temp met, then on to day storage heaters.

[SteamyTea]

1 hour ago, Marvin said:

Works well through diverter. Set to hot water until temp met, then on to day storage heaters.

Have you got a meter on the storage heaters?

Be interesting to know how much goes into them.

 

Not got my storage heaters on yet, house it is 19.9°C and it is 13°C outside, and raining.

Edited October 12, 2022 by SteamyTea

[Radian]

1 hour ago, Marvin said:

Works well through diverter. Set to hot water until temp met, then on to day storage heaters.

Is that an automatic cascade function provided by the diverter?

[Marvin]

1 hour ago, SteamyTea said:

Have you got a meter on the storage heaters?

Be interesting to know how much goes into them.

 

Not got my storage heaters on yet, house it is 19.9°C and it is 13°C outside, and raining.

Hi @SteamyTea

No meter on them but I will bung one on. Tomorrow a dull day so expect little....

[Marvin]

1 hour ago, Radian said:

Is that an automatic cascade function provided by the diverter?

No. Er, excess power gets sent to day storage heaters unless the water temp is below set level when digital thermometer powers the relay switch to the immersion.

[Radian]

At the weekend I did a little experiment to see how well I could heat our garden room using excess PV generation alone. I say alone which isn't quite accurate as this side has 9m² of patio doors pointing S.E. so we also harvested about 2.5kWh of solar gain on this occasion. It had gotten up to 24^oC by 11:30AM and everyone was sweating buckets:

 

 

The import power total (magenta plot) flatlines between 9AM to 1:30PM as the excess PV is diverted to the 2kW convector (except for the kettle going on for elevenses) I haven't started logging the PV output to the database yet but we generated 8.6kWh on this day in the second half of November - which is frankly better than I anticipated.

 

 

At least the robot cat (mouser) was enjoying the heat.