Immersion Heater - PV electricity

[old grouser]

Just found this 27" 2 1/4" BSP thread 1 kW immersion heater in ebay -
1 kw / 1000 W 27" Immersion Heater - Use Spare Solar Panels Power For Heating | eBay

Hope that will help

Similar available from Surejust | Manufacturing equipment for the marine industry for over 25 years -and at about the same price.

OG

 

[suntrap]

Similar available from Surejust | Manufacturing equipment for the marine industry for over 25 years -and at about the same price.

OG

Are they the same length though?

 

[Sparqui]

Plotty,
I have successfully created a remote monitor with a repeater in the kitchen which actually tracks my turning loads on/off and I have created logic to give a ramp up/down signal for a thyristor circuit. I had a false start when I bought a cheap 4 way 433MHz remote control and have since identified a more professional encoder/decoder transmitter system.
I have used the monitor mainly to confirm/justify putting tumble dryer etc on in the daytime while I've been at home. I created a hard wired link to a crude controller circuit with electric kettle (and light so as to see dimming effect) and proved to myself that the concept worked but needed some tweaking in the feedback loop, it was more on/off than dimming, but i know where to go to sort this now

My work has stalled as a result of re-entering the world of employment and lack of sunshine in theevenings to test it by.
I have a dilemma as whether to patent this, with searches costing ~£3k, find someone to develop this with me, or just publish and be damned so that the design is in the public domain.

Hi all,

Found this site via a PV thread: my eyes did glaze over as I waded thru all 44 pages.

I'm not an electrician or an engineer, nor am I interested in this field - I just want to use my free electricity to heat my hot water (apologies to those who think that's not green). However ...

it would seem to me that if a device monitored the pulse on the import meter so that it only switched on the immersion circuit when you're NOT importing, that would allow any excess PV electricity to be diverted to the immersion. (or is that too simple an idea?).

BTW, echase, claims for your system appear interesting, but there's too much secrecy to give me confidence - even your customers on this board are not willing to discuss something a simple as the price??

Would be good to hear about Sparqui's progress with that solution (post 338).

 

[Richchad]

Plotty,
I have successfully created a remote monitor with a repeater in the kitchen which actually tracks my turning loads on/off and I have created logic to give a ramp up/down signal for a thyristor circuit. I had a false start when I bought a cheap 4 way 433MHz remote control and have since identified a more professional encoder/decoder transmitter system.
I have used the monitor mainly to confirm/justify putting tumble dryer etc on in the daytime while I've been at home. I created a hard wired link to a crude controller circuit with electric kettle (and light so as to see dimming effect) and proved to myself that the concept worked but needed some tweaking in the feedback loop, it was more on/off than dimming, but i know where to go to sort this now

Isn't this a similar device that monitors the flashing generation meter light to help decide if to use spare electricity... or am I getting this completely wrong and there is more to it than just monitoring?

GEO SOLO PV Solar Energy Monitor

 

[Plotty]

Hi Sparqui,

Thanks for the update. Pleased that you're back earning. Now that we're moving towards longer days, I hope you can finish your testing. I'm in the market for one that I know works and won't burn my house down.


Richard

I too have a Solo PV but this just monitors the gen meter output. However, the same technology could monitor the import meter LED and only divert the excess PV leccy when you're not importing. I assume that in addition to monitoring your import meter, it'll also need to monitor your consumption to work out when you have excess. Or it could just monitor both import and export meters and do the maths. The only proven device I know that can do this is the EMMA, but it's not a feasible option for me at c£2K. Others on this board also appear to have solutions: echase - he had my hopes up but his reply speaks volumes; Paul; & inie meanie.

Me, I'm after a solution I can plug in straight from the box or get my electrician to fit.

 

[Richchad]

Thanks for the reply Plotty, I haven't got the Solo PV but was thinking of buying it to give a more visual display of generated electric, is it any good?

I have also looked at the EMMA and that is exactly what I want but not at their price... lol

With the PV growing market, although maybe slowed somewhat by reduction in FIT, there must be a market for what we are all looking for, a box to either fit or get someone to fit that does what the EMMA does at a much more competitive price, like less that £200..... :smiley2:

 

[Sparqui]

Richard et al.
Thanks for that, saved me a patent search I'm sure! I spent ages last year searching internet for EMMA alternatives and could find no other device. My device monitors the meter LED in the same way (but is hard wired back to repeater LED in kitchen). I have no need for digital display as my ultimate aim is still to use the flashing import or steady export state of the LED to control a 3kW dimmer so as to mop up any excess PV electricity by dumping it into the immersion heater - whether there is anyone at home or not. I estimate the component cost to make at home to be about £50 max, but I will not market it commercially because of the mains implications. However, the simple hard-wired LED repeater, using a spare USB PSU, one photo transistor, one transistor, one LED and about 3 resistors - only cost about £5. It is watching this that tells me if I can switch appliances on or off. It is fairly easy to judge what the consumption is since one flash represents 1Wh so one per second is 3600kW.

 

[echase]

Richard et al.
my ultimate aim is still to use the flashing import or steady export state of the LED to control a 3kW dimmer so as to mop up any excess PV electricity by dumping it into the immersion heater - whether there is anyone at home or not. I estimate the component cost to make at home to be about £50 max. It is fairly easy to judge what the consumption is since one flash represents 1Wh so one per second is 3600kW.

Think you will find it not so easy as you think. If you try to control down to say 100W accuracy the flash rate will then be only 1 per 36 secs. You need to let a few flashes go by so you are sure you are measuring it accurately. So you can't respond to small changes in power in less than a few minutes. Plus if the LED is not flashing for export how do you know it's exporting 1W or 4kW?

The SSR needed to do this may on its own be more than your £50.

 

[Sparqui]

Think you will find it not so easy as you think. If you try to control down to say 100W accuracy the flash rate will then be only 1 per 36 secs. You need to let a few flashes go by so you are sure you are measuring it accurately. So you can't respond to small changes in power in less than a few minutes. Plus if the LED is not flashing for export how do you know it's exporting 1W or 4kW?

The SSR needed to do this may on its own be more than your £50.

As soon as I see a flash, I ramp the power down, plus built in slow downward drift to cater for loss of communications. When seeing continuous LED, ramp up again, slowly, stopping when no LED. Ultra cautious, but for the money a marginal loss in maximum power usage. My £50 was for one-off component prices, building for myself. The trick is in getting the control loop gain and damping correct. My first attempt was too crude, resulting in a simple on/off cycle of about 10 seconds. I Know where I went wrong and is now a matter of breadboarding this - I could have done with another month's redundancy :icon9:!

 

[Fazzathebrave]

here is schematic for control loop. I haven't finalized the +- 15v supply components so haven't included them will post full schematic when finishedView attachment 8187

hi pmcalli. Many thanks for posting the circuit. I think it's a lovely simple solution to get the job (of not exporting) done. I wondered if you have updated the circuit diagram to show the +- 15 v supply and a parts list? I was hoping to go and buy the bits to build it.... panels being installed Tuesday! This whole thread has taken me back to the electronics degree I completed 22 years ago. No

Arduinos ​

then

 

[pmcalli]

hi pmcalli. Many thanks for posting the circuit. I think it's a lovely simple solution to get the job (of not exporting) done. I wondered if you have updated the circuit diagram to show the +- 15 v supply and a parts list? I was hoping to go and buy the bits to build it.... panels being installed Tuesday! This whole thread has taken me back to the electronics degree I completed 22 years ago. No

Arduinos ​

then

I have updated the circuit to use only one CT using sharpeners idea of a multiplier. Had a few expected problems with offset and gain errors from multiplier but these are overcome now. The results are very good with all but 30W diverted to immersion and no grid consumption. If you want the circuit and parts list send me a PM with your email address as posting an attachment on here is a pain

 

[TechyTim]

Hi all,
Just joined this thread as I am now manufacturing a PV controller to switch on the Immersion when the sun shines.
Very simple - it sits by the consumer unit and monitors the feed from the PV and when the PV output exceeds 1.5kW it switches a contactor and turns on the Immersion circuit. There is also a manual override plus some hysteresis to avoid chatter when the output is close to the switching point or a cloud passes over.
Yours for £205 plus VAT - much cheaper than EMMA and totally independent of the Inverter.

Tim Smith
SolarHeat Controls
01202 625070

 

[methley]

So does it monitor household consumption and only turn the immersion on when there is sufficient excess? If not, then there's a real danger of importing expensive electricity to heat your water...

 

[Fazzathebrave]

I'm sure it's great Tim but your system appears to miss the fact that the normal daytime load will affect how much "free" electricity is available. If there is a base load of 1Kw (more when you switch the kettle on) and a solar generation of 1.5kW then you will end up paying to heat the 3kW immersion at your normal tariff, ie 3kW immersion + 1 kW house load - 1,5kW solar = 2.5kW from the grid. It would work out cheaper to heat with gas would it not?
Forgive me if your system is actually clever and detects the existing load, solar generation and then controls the immersion heater on variable power in order to maximise benefit and minimise export. I think that's what we are striving for.

 

[Richchad]

much cheaper than EMMA

So, nothing like the EMMA unit then if it doesn't monitor house usage to detect "SPARE" electricity, or am I missing something.. :confused5:

 

[pauldreed]

....'Suitable for PV panels with an output in excess of 1.5 kW'
....'Suitable for Immersion Heaters up to 3kW'

So where does the additional 1.5kW come from?

Tim, you've either badly described your device in the post, or you've missed the point!

 

[inie meanie]

Hi Guys
As I have a standard large vented hot water tank, and the excess pv provides loads of heat but it is all at the top 1/3 of the tank, so as suggested to me on this forum by JohnBoyZ. I have fitted a small pump eBay - The UK's Online Marketplace it was very cheap. I used a eBay - The UK's Online Marketplace non return valve to stop cold water being drawn up from the base when water is drawn off. I teed into the output at the top of the tank and teed into the inlet at the base. I have just used a timer so that it turns the tank over for 15 minutes 4 times a day, but I will be using two very small thermostats to automate it ( on order ), so that when the top of the tank is 65 c and the bottom is below 60 c it will activate the pump. The pump is very small and very low power, and I have just used an old 12 vdc plug in power supply. So today I now have a tank full from top to bottom with 65 C . Very pleased :- ) If any body wants a pictures or more info email me.

 

[TechyTim]

First an apology - I didn't read the Rules when I registered (first time I have ever used a Forum) so should not have been so blatant in the advertising. There are now a number of these simple devices on the market but some are very basic.
Second - the SolarHeat device is designed to be as simple as poss (to keep cost down) so will provide power to immersion irrespective of base load. It has a switching capability of 3kW and the existing setpoint is 1.5kW (although I am working on an improvement to be able to select the setpoint on commisisioning) so could import 1.5kW if there was a mismatch between PV panel size and tank size. Majority of householders have a low base load during the day (but probably not most people using this forum) so small amount imported is not significant cost, e.g. 100 litre tank with 2.3kW heater and 2.9kW panel will get more than 2.0kW for 65% of time in summer so excess cost is less than £20. I am not aiming for the self sufficient household market or those (like most of the posts on the forum) who are avid DIY guys - it seems to have met a need with the PV installers. It does have an override to switch it off in the winter when the output is reduced and the boiler is providing heating and hot water at a reasonable efficiency.
The most significant issue is the combination of standard heating/HW controls and the immersion control - you need HW first thing in the day but then you have to suppress the boiler until the last minute to take advantage of any sun which is fine for people who are not in the house but not for people using HW during the day.

Thanks for the feedback - it helps to clarify the thought process.

 

[pauldreed]

First an apology - I didn't read the Rules when I registered (first time I have ever used a Forum) so should not have been so blatant in the advertising.

.......the rules have not stopped other posters from doing the same, so no worries!
I see your point and appreciate that for some readers this may be appealing as a no fuss solution, and probably better than nothing at all.
I have emails from people who dash upstairs every time the sun comes out and manually throw a switch, only to switch it off again a short while later when dark clouds appear! The exercise is probably good for them, but for me it's not a way to while away the days!!
But I think that most of us here are striving to develop a system(s) which use as much 'free unused' solar power as possible, and ensuring that we don't pay to supplement that solar power.
What are you using to measure the power, op amps or microprocessor?

 

[echase]

Tim please rename that from Fact Sheet to Myth Sheet as your £98 saving is in cloud cuckoo land. With the 10 panel system you quote the MCS approved annual generation is about 2000kWhr. If all that went into heating water you have displaced 2000kWhr of gas at about 4p per unit = £80. Due to the house load only about half is available to the immersion so it’s down to £40. Your unit does not accurately track the export and is turned off in winter so halve it again to £20. Then you are importing a lot of expensive electricity to make up the aforementioned 1.5kw. So the net benefit is negative. It’s probably negative even on a 20 panel system. Systems that do not accurately track the export are not worth any money at all.

 

[TechyTim]

Paul,
The controller uses a CT to sense the PV output to the consumer unit, then some clever electronics to inject the hysteresis so that there is a positive switching of the contactor. I don't understand that bit as I am not an electronics guy - a gasman by training.

 

[TechyTim]

With the 10 panel system you quote the MCS approved annual generation is about 2000kWhr. If all that went into heating water you have displaced 2000kWhr of gas at about 4p per unit = £80.

Your figures are incorrect for several reasons - The majority of use will be in the summer when the heating is not operating and the gas system efficiency when heating hot water only is usually around 60% (may be a bit higher with a modulating condensing boiler) due to the pipework losses, so the 4p/kWh is 6.7 p/kWh.
Heating 200 litres/day of hot water through 50 DegC uses 11kWh of gas or 74p, assuming the PV can do this for 150 days in a year, the saving is £110 - at 7kWh from the PV per day that is 1050 kWh or just over half the output from a 10 panel system or less for a system on the south coast which have much higher output figures than the MCS values based on the UK average,

Allowing for 10% amount of import - still a significant saving and less than 3 year payback.

 

[suntrap]

Possibly, if you use enormous amounts of hot water - 200 litres a day, and you're also being a bit generous suggesting as much as a 50C temperature rise, especially as you are claiming that most of the usage will be during the summer.

 

[echase]

so the 4p/kWh is 6.7 p/kWh.

for a system on the south coast which have much higher output figures than the MCS values based on the UK average,

QUOTE]

Let’s use your 6.7p then. With the 10 panel system you quote the MCS approved annual generation is about 2000kWhr. If all that went into heating water you have displaced 2000kWhr of gas at about 6.7p per unit = £134. Due to the house load only about half is available to the immersion so it’s down to £67. Your unit does not track the export and is turned off in winter so halve it again to £33, e.g. for significant periods of time the PV output will be above the house base load of a few hundred watts but below 1.5kW so that energy is exported.

So about 2000/2/2= 500kWhr has gone into the heater which has run for 500/1.5 hours = 333 hours at 1.5kW. Then you are importing electricity to make up the remaining 1.5kw. So every time you have the immersion on you are importing full price electricity up to 1.5kw at a value = 12pence, which would otherwise have been heated by gas at 6.7p. So it’s an extra charge of 333 x (12-6.7) x 1.5 = £26. So the net benefit is £33-£26=£7. That is a bit pessimistic as if the spare electricity is >>1.5Kw less is imported, but does a 10 panel system often exceeds 1.5kW by much?

I live near the south coast and my system does not exceed the MCS by a huge amount. Maybe 10-20%.

 

[pmcalli]

so the 4p/kWh is 6.7 p/kWh.

for a system on the south coast which have much higher output figures than the MCS values based on the UK average,

QUOTE]

Let’s use your 6.7p then. With the 10 panel system you quote the MCS approved annual generation is about 2000kWhr. If all that went into heating water you have displaced 2000kWhr of gas at about 6.7p per unit = £134. Due to the house load only about half is available to the immersion so it’s down to £67. Your unit does not track the export and is turned off in winter so halve it again to £33, e.g. for significant periods of time the PV output will be above the house base load of a few hundred watts but below 1.5kW so that energy is exported.

So about 2000/2/2= 500kWhr has gone into the heater which has run for 500/1.5 hours = 333 hours at 1.5kW. Then you are importing electricity to make up the remaining 1.5kw. So every time you have the immersion on you are importing full price electricity up to 1.5kw at a value = 12pence, which would otherwise have been heated by gas at 6.7p. So it’s an extra charge of 333 x (12-6.7) x 1.5 = £26. So the net benefit is £33-£26=£7. That is a bit pessimistic as if the spare electricity is >>1.5Kw less is imported, but does a 10 panel system often exceeds 1.5kW by much?

I live near the south coast and my system does not exceed the MCS by a huge amount. Maybe 10-20%.

In the summer you should really use the tier1 rates if you are able to turn the gas off completely. That said its still a rubbish return compared to a proper balanced system I am getting significant amounts of hot water on most days even in the winter and the system goes right down to 30W and no grid consumption.

 

[echase]

In the summer you should really use the tier1 rates if you are able to turn the gas off completely. That said its still a rubbish return compared to a proper balanced system I am getting significant amounts of hot water on most days even in the winter and the system goes right down to 30W and no grid consumption.

What is a Tier 1 rate?

In Feb I turned my gas off when going away for a w/e. Forgot to turn it on again when I got back on Sunday and the water kept hot till next Friday even in a relatively unsunny week.

 

[pmcalli]

What is a Tier 1 rate?

In Feb I turned my gas off when going away for a w/e. Forgot to turn it on again when I got back on Sunday and the water kept hot till next Friday even in a relatively unsunny week.

Tier 1 is first 220 kwhr per month if you pay monthly. This incorporates the old standing charge. If you can turn off gas all together then you are saving this higher tariff not the lower tier 2

 

[JohnBoyZ]

Hi Guys
As I have a standard large vented hot water tank, and the excess pv provides loads of heat but it is all at the top 1/3 of the tank, so as suggested to me on this forum by JohnBoyZ. I have fitted a small pump eBay - The UK's Online Marketplace it was very cheap. I used a eBay - The UK's Online Marketplace non return valve to stop cold water being drawn up from the base when water is drawn off. I teed into the output at the top of the tank and teed into the inlet at the base. I have just used a timer so that it turns the tank over for 15 minutes 4 times a day, but I will be using two very small thermostats to automate it ( on order ), so that when the top of the tank is 65 c and the bottom is below 60 c it will activate the pump. The pump is very small and very low power, and I have just used an old 12 vdc plug in power supply. So today I now have a tank full from top to bottom with 65 C . Very pleased :- ) If any body wants a pictures or more info email me.

Hi Inie,
Sounds like its working well and good work sourcing such value components. Once you have the thermostats in place it might be be nice to somehow only run the stats/pump when PV is generating.

 

[TechyTim]

Only potential drawback is that as you draw off a lot of hot water, e.g. for a couple of baths, all the tank will revert to a mixed temperature, which could be less than 40 C, until it has time to heat up again. I worked at a British Gas research station in the '70s and thinking at that time was that stratification was acceptable, as it avoided the need for a fast recovery, and tank cold feeds were designed not to mix with the existing hot content.

 

[pmcalli]

Only potential drawback is that as you draw off a lot of hot water, e.g. for a couple of baths, all the tank will revert to a mixed temperature, which could be less than 40 C, until it has time to heat up again. I worked at a British Gas research station in the '70s and thinking at that time was that stratification was acceptable, as it avoided the need for a fast recovery, and tank cold feeds were designed not to mix with the existing hot content.

I am running similar system with an old ch pump and what you say doesn't happen the pump stops as soon as hot water at top of tank temp falls slightly so hot water remains at top of tank as cold is added to bottom same as normal hot water is only added to the bottom when the top is hot enough a check valve prevents the cold being added to the top.

 

[inie meanie]

Only potential drawback is that as you draw off a lot of hot water, e.g. for a couple of baths, all the tank will revert to a mixed temperature, which could be less than 40 C, until it has time to heat up again. I worked at a British Gas research station in the '70s and thinking at that time was that stratification was acceptable, as it avoided the need for a fast recovery, and tank cold feeds were designed not to mix with the existing hot content.

Hi
No it's not a problem as the design is, Thermostat at top is normally open at 65 deg C and thermostat at base is normally closed at 60 C so If above 65 at top and below 60 at base pump will run. As soon as either top is below 65 or above 60 at base the pump is deactivated. I know you have to have a hysteresis on the stats but you get the idea. My tank is nearly 6 feet tall so this has been a God send as I used to only have the top quarter heated properly. Any way I run two tanks in series so I heat both of them and have 400 ltrs of hot water All heated by spare PV. I think I'll have two baths tonight!

 

[inie meanie]

Hi Inie,
Sounds like its working well and good work sourcing such value components. Once you have the thermostats in place it might be be nice to somehow only run the stats/pump when PV is generating.

Yes I was thinking that I might just leave the timer on. But It could be automated from my circuit, I'll have a think about it. Timer works really well and is so simple.

 

[pmcalli]

Yes I was thinking that I might just leave the timer on. But It could be automated from my circuit, I'll have a think about it. Timer works really well and is so simple.

If you are using a sma inverter they have multifunctional relay that you can set via sunny explorer to activate on error or at a particular power level.

 

[pauldreed]

The sun's power is starting to pick up now
Got almost 12.5kWh's of solar power today (about the same as yesterday), and 4.75kWh's of it was diverted to water heating (5.4kWh's yesterday).
The Gas boiler hasn't fired up for water heating since Sunday, not bad as we were home both days, and used the oven, washer, dishwasher, TV etc as well.

Paul

 

[pmcalli]

The sun's power is starting to pick up now
Got almost 12.5kWh's of solar power today (about the same as yesterday), and 4.75kWh's of it was diverted to water heating (5.4kWh's yesterday).
The Gas boiler hasn't fired up for water heating since Sunday, not bad as we were home both days, and used the oven, washer, dishwasher, TV etc as well.

Paul

Sounds a bit low I got 20.8 today 7kwhr went into the tank haven't perfected the pump controls yet and made the mistake of using the shower outlet instead of the top outlet.

 

[pauldreed]

Sounds a bit low I got 20.8 today 7kwhr went into the tank haven't perfected the pump controls yet and made the mistake of using the shower outlet instead of the top outlet.

I'm probably north of you (Yorkshire), but in any event I got a full tank of hot water and ran the usual household stuff from a 3.3kW system so I'm well happy with what I got!!
How are you monitoring your data?

 

[echase]

Tried to run a EMI test on my system this morning but was thwarted by the immersion already being up to temperature by 9am. I have a Solartwin solar thermal system too which, whilst not very effective in winter, does provide this pumped mixing system with its 5watt DC pump as a by product of it's method of operation, so almost whole 210litres is still >59C at midnight. I have 5 temperature sensors on the cylinder left over from developing a solar thermal controller.

Was trying to work out if the SSR phase control action, which pumps a lot of EMI down the mains cable below the EMC band, as EMC filters are not designed to take it out, is interfering with Ethernet over powerline adapters. These work in the aprox 100-150kHz band. Anyone had any problems with theirs? Never noticed any problems with mine but they are set up so that I would hardly notice a 5-15mnute break in transmission. Some baby monitors use this transmission method too.

 

[pmcalli]

I'm probably north of you (Yorkshire), but in any event I got a full tank of hot water and ran the usual household stuff from a 3.3kW system so I'm well happy with what I got!!
How are you monitoring your data?

Mine is 4kw so a bit bigger and in Hampshire quite high up 680 ft yesterday was perfect conditions sunny and cold wind the wind makes about 10% difference due to the cooling effect. I have split meter tails and have installed an extra meter on the house only tail. This means I can accurately measure house consumption and hence export without having to install an export meter which contractually I have to report to my fit supplier. I use a data logger on my immersion controller and a web cam on the supply meter to collect data.

 

[pmcalli]

Tried to run a EMI test on my system this morning but was thwarted by the immersion already being up to temperature by 9am. I have a Solartwin solar thermal system too which, whilst not very effective in winter, does provide this pumped mixing system with its 5watt DC pump as a by product of it's method of operation, so almost whole 210litres is still >59C at midnight. I have 5 temperature sensors on the cylinder left over from developing a solar thermal controller.

Was trying to work out if the SSR phase control action, which pumps a lot of EMI down the mains cable below the EMC band, as EMC filters are not designed to take it out, is interfering with Ethernet over powerline adapters. These work in the aprox 100-150kHz band. Anyone had any problems with theirs? Never noticed any problems with mine but they are set up so that I would hardly notice a 5-15mnute break in transmission. Some baby monitors use this transmission method too.

The emc filters are only designed for ce conformance so I would expect to have problems that said I have had no problems with a100mb one haven't tried such a low frequency one. Am about to embark on preliminary ce testing for my immersion controller so will post the results when I have them.

 

[echase]

Mine has passed CE. It's not straightforward.