Immersion Heater - PV electricity

[thushar]

Message for EChase - yes me too - I have a customer who is particularly interested in a system to supplement a PV system we fitted recently. Could you send me some details

Have you tried the automatic immersion heater switch and immersion heater power reducer ( reduces a 3 kW immersion to 1.5 kW) from http://solarimmersionheaterswitch.co.uk ? Looks like one of the best system available for less that £150 .

 

[echase]

Have you tried the automatic immersion heater switch and immersion heater power reducer ( reduces a 3 kW immersion to 1.5 kW) from http://solarimmersionheaterswitch.co.uk ? Looks like one of the best system available for less that £150 .

As well discussed here a couple of months ago these and some others like them are pretty useless. They do not track your export so are significantly under or over using your generation. If not well set you could be spending more money than you are today and have paid £150 for the privilege or probably more as you have to buy a new £50 element and maybe pay a plumber to fit it.

A proportionally controlled unit may be twice the price but will give much more than twice the benefit and needs no new element. Even with the atrocious Jubilee holiday weather over last few days I have managed to generate enough hot water from the odd bright periods to avoid needing any gas top up, indeed not used gas for weeks. A switched unit would never have done this.

 

[Whip1971]

I agree with echase! A Proportional controler is the way forward. I also have also turned my gas boiler off. And still manage to get a tank of hot water off of my surplus pv energy, love it!!! Thanks to pmcalli...

 

[suntrap]

Hi Suntrap

Open Ebay and search using SSR-25VA Resistance Type Adjustable SSR Solid State Relay 25A w Heat Sink

The cheapest in the list was £8.39. Bigger heat sinks are also available for about £4.00.

I'm becoming less and less convinced about these: everything points to them being just glorified light dimmers. Have you managed to control one with anything other than a potentiomenter? Judging by the high resistance values required (akin to light dimmers), I think there will be a high AC voltage across them, not isolated from the mains. Does a multimeter (on diode setting) register anything other than infinite resistance between input and output pins? If infinite, it might be safe to connect an earthed oscilloscope across the input pins to see what's going on.

The most comprehensive data I can find is here. The block diagram shows no isolation (unlike the data sheet for the switched version). Note that there is a different family for control by external voltage - called 'L' rather than 'V'. I can't find any of those for sale.

 

[Trader9]

Hi All

Don't knock these SSR's I have managed to interface the SSR input with a LDR driven by a LED from the PWM output of an Arduino monitoring the solar and house load using the OpenEnergyMonitor sketch. So you have a microprocessor controlled, fully proportional system for about £50.00. Using a LDR and LED heat shrunk together in this way makes a very safe opto isolator interface.

Regards, Trader9.

 

[suntrap]

Ah - mystery solved - thanks!

 

[stevegs]

You'd be better of with a solar thermal system! True, you'd need a dual coil tank and a thermal type collector, but these are about 3 times as efficient in converting sunlight (to heat) as PV (45% vs. about 16%). My thermal system was installed 11 years ago, so it's an older type with thick (4") tubes. Fortunately, I put it on the flat roof at the back, so I was able this year to cram 6 PV panels on the pitched roof early this year. An added advantage of thermal - it's simple plumbing and no G85 regulations to worry about - the only electrical connection required is for the controller and pump. Installation of the former is similar to a central heating control unit, and the latter is a bog standard CH pump - so only a 3A switched fused spur is required.

 

[Trader9]

Hi Stevegs

I think you have missed the point here. Most of my daily electrical usage is offset by the solar PV and the electricity used for heating the water is FREE. Efficient or not, I was paid 45p a kW to generate and I get to use the surplus to heat the water for nothing. Better still I can deliver 1MW a year into my hot water tank offsetting any importing that I may have done.
You can't use a solar thermal system to watch your TV, make a cup of tea or run your fridge, but you can use your solar PV to heat your water. Electricity is much more versatile.
Best get rid of your old solar thermal system and add an extra 10 PV panels I reckon.

Regards, Trader9

 

[stevegs]

You can't use a solar thermal system to watch your TV, make a cup of tea or run your fridge, but you can use your solar PV to heat your water. Electricity is much more versatile.

Can't argue with that, but my 1.4kWp system on a cloudy day produces little more than the fridge and freezer require if they're both on at the same time, so these run for free. I can only export on bright (not necessarily sunny) days - so if I time it right, I can mow the lawn for free. The kettle is only on for minutes, so the amount of energy it uses overall is minimal. I haven't got time for a TV, but even if I did, I probably wouldn't watch it during daylight!

Best get rid of your old solar thermal system and add an extra 10 PV panels I reckon.

I take it you've got the maximum (4kWp) system you can have on a single phase supply. My problem here is a tiny roof on a tiny house so no room for 10 more panels even if I got rid of the thermal. The thermal occupies most of my flat roof - PV would need a mounting frame to angle it to face south - dodgy owing to risk of wind damage. Don't forget - if you add to a PV system you only get the FiT rate prevailing at the time the addition was made (21p/kWh now, dropping to 16p/kWh from 1st August 2012 - delayed one month - see here). Also, 4kWp is just that - peak - it averages at 30% of that. On a really hot day the PV efficiency goes down so (surprisingly) you get more out of it on a cold and not particularly bright day. That explains why most systems did so well last March, despite the days being shorter. The thermal chugs along producing what it can, which is sufficient, even on a really dull day, to wash a few dishes etc. I only need a top-up if I want a shower or bath and the weather has been lousy - apart from that, the thermal produces all I need for 7 months of the year and takes the chill off for the remainder, leaving the CH boiler to make up the deficit. I have an immersion heater backup, but I can't remember when I last used it! My only regret with the thermal is it's too old to benefit from the RHI.

 

[jbella]

Hi all,

I believe this might be a home energy controller (solar version) the most of us have been looking and waiting for:

Home - solarpowercontrol.net (please be aware that this address might be just temporary for the time being)

This unit has got two current monitoring clamps with wireless transmitters (one way) for home electricity consumption and generation, smart energy controller unit and three (up to twelve) remotely controlled (two way) wireless power sockets. Unit controls up to three items wirelessly and switches them according to excess solar being generated. The unit measures the power consumption of each plug and only switches the plug on if there is enough excess power.

Good news is that this unit is reasonably priced too:

Solarcontrol | eBay ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649#ht_500wt_1156

You can find more reading about it here:
Home Energy Monitoring and Control System Solar Version with automatic operation function

Although I do not have yet my immersion heater I've just bought this controller and I can report on it in couple of weeks.

Juraj

 

[Whip1971]

Hi juraj,
The controler you've found sounds cool. However you state it can control up to to 12 outlets but the controler only can operate 3. ?? Also what's a 2 way socket outlet? I've heard of a 2way light switch..??
it doesn't sound like a propational controler. If I plug a wireless outlet into my immersion circuit 3kW I doubt if it would ever turn on, as I only have a 3kW system. It might be ok if you only want to plug 40w lamps into your outlets. Maybe I'm missing something ? Pmcalli's system diverts any spare pv energy, proportionately to my immersion. It works flawlessly..
Regards

Oh sorry I misunderstood the 2way outlet, this reports back to the controler how much power is being consumed??

 

[pm.hughes]

Trader9 . I am new to this forum and trying to follow your idea of using a ssr 25va with a relay board, have you managed to sort out the problems of harmonics? or have you a better idea?

 

[suntrap]

Look at the OpenEnergyMonitor forums - it seems at least for some meters you can use burst firing of complete cycles as they average over a whole watt-hour so will not charge you provided you take less than one watt-hour out of the mains before putting it back. No need to worry about filtering.

 

[sedgy34]

Can't argue with that, but my 1.4kWp system on a cloudy day produces little more than the fridge and freezer require if they're both on at the same time, so these run for free. I can only export on bright (not necessarily sunny) days - so if I time it right, I can mow the lawn for free. The kettle is only on for minutes, so the amount of energy it uses overall is minimal. I haven't got time for a TV, but even if I did, I probably wouldn't watch it during daylight! I take it you've got the maximum (4kWp) system you can have on a single phase supply. My problem here is a tiny roof on a tiny house so no room for 10 more panels even if I got rid of the thermal. The thermal occupies most of my flat roof - PV would need a mounting frame to angle it to face south - dodgy owing to risk of wind damage. Don't forget - if you add to a PV system you only get the FiT rate prevailing at the time the addition was made (21p/kWh now, dropping to 16p/kWh from 1st August 2012 - delayed one month - see here). Also, 4kWp is just that - peak - it averages at 30% of that. On a really hot day the PV efficiency goes down so (surprisingly) you get more out of it on a cold and not particularly bright day. That explains why most systems did so well last March, despite the days being shorter. The thermal chugs along producing what it can, which is sufficient, even on a really dull day, to wash a few dishes etc. I only need a top-up if I want a shower or bath and the weather has been lousy - apart from that, the thermal produces all I need for 7 months of the year and takes the chill off for the remainder, leaving the CH boiler to make up the deficit. I have an immersion heater backup, but I can't remember when I last used it! My only regret with the thermal is it's too old to benefit from the RHI.

Solar Pv isn't just for roof spaces if you have some garden for it you can frame mount it happy days, don't forget the tarif is dropping and so will the cost of install but same return for your money

 

[jbella]

Hi Whip1971,

It is really not a proportional controller but it is a smart unit. Outlets indeed report back to the controller how much power is being used so you can change the load on that socket and controller will readjust the settings and switch that socket ON only if there is enough excess of pv power.
Unit can remotely control up to 12 sockets but only first three are controlled automatically by unit.
I've just installed it yesterday and played a bit today and to be honest so far impressed by its performance.

Juraj