Hi All,

I've finally set up the website showing my attempt at automatically using the spare solar power to heat my hot water. The circuit is rough but it seems to work and will hopefully be improved. Its currently driving a 2kW heater and when the weather improves I switch the output to the immersion heater.

Cheers, Keith

www.talkingsolar.co.uk

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Some great ideas here.  I have a 3Kw system installed at a second house and it would be fab to utilise the power generated while the house is unoccupied.

As I have a laptop that continuously monitors the PV output and uploads it to the internet I was thinking of getting some software that would use a wireless X10 signal to switch on a socket (that could be either a heater or the hot water) when the PV output goes above 1Kw.

I'll be watching this with great interest.

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Well I'm now running with my final 'two stage' design... look at using heated towel rails in the bottom of the tank either via the 28mm fill or in my lucky case removal of the 15mm drain plug allowed me to put in a 600W electric towel rail heater element.    

As my invertor has a string of LEDs that light up based on power output and a light sensor opposite the 1KW LED fires up my site transformer immersion (720W), then should more sun come out at around 1.7KW another light sensor helps fire up the 600W heated towel rail.

On a super sunny day the immersion heater will trip at say 80 degrees but I'd keep running the towel rail as it'll never get super hot down there. 

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I've just ordered a couple of these devices David. Thanks for the 'heads up' on these. Commercial devices are usually more expensive. We will give them a test run on our rig to see if they are robust enough and will report back here.

Chris 

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I'm considering using Chrish Rudge's device to control of my immersion heater. Rather than using a builders step-down transformer has anyone tried using a voltage regulator -a 3.8kW unit is available on EBay see  http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=330708347873&fromMakeTrack=true&ssPageName=VIP:watchlink:top:en and if so, does it work ok, or do they quickly burn-out? Thanks David

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I've now put in my solution for now, couldn't find a wireless energy monitor....  however noticed my Invertor has 8 LEDS that go up in a bar depending on PV generation.  So I got of ebay a 12V solar light switch for @ £4.50 and blue taced it around the 1KW led and connected it to a 12V relay (usually closed) connected to the 240V of my 110V site transformer.  On a reasonably sunny day it heats water at top of tank from 60 degrees to 80 degrees.   My only mistake was the 3KW vairable dimmer switch I'd mentioned  it burnt out at a 3KW test, so sticking to meaty, builders site transformer unless anyone has a 5KW+ dimmer ?.

Chris - I would be interested in your latest design but what I really need  is two current sensors and a variable load output connected to 3KW immersion as such ANY PV surplus is pushed to hot water.

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 Re: Using an Energy Monitor as a switch source

I too thought this could be an easy way to switch my 1kW immersion but alas things are never that simple! I've seen two monitors with an alarm

1.The Efergy Elite

It emits a pulsed beep/flashing LEDs for 30 secs then goes to sleep for 5mins until it wakes up and if the power is still over the threshold it beeps and flashes again and then repeats every 5 mins. Also the alarm settings are in 1kW steps. So not terribly useful.

Some clever guys have attempted to hack it to access the serial data which I suppose is the more elegant way to do it.

http://jdesbonnet.blogspot.com/2010/09/smart-electricity-meter-based-on-efergy.htm

 2. The OWL CM160

Don't know anything about how the alarm functions on this and therefore would be grateful if anybody has any info rather than me shelling out for another surplus meter!

http://www.naturalcollection.com/download_docs/OWL+USBmanual.pdf

 Plus any other ideas on this gratefully received.

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Hi, i've just signed up to your site and have been looking to do this for some time, I have a 1.5kw solar install through a Fronius inverter. I really like the idea of using the transformer to drop the immersion value to approx 800watts. I see by you drawings that you are going through a set of normally open contacts in the current sensor for feeding the immersion contactor. I have been looking for a suitable contactor myself and would be interested to find out which type you use. I've been looking at a 20amp 2 pole contactor from good ole TLC but were not able to find a 10amp as you had suggested. I imagine this not to be a problem but would welcome your advice. Many thanks, Russ

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Please advise the total installed cost, including VAT if applicable, for your system.

Thanks

Fred

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James, they are consulting on raising the export rate. It may be worth encouraging as many people as possible to respond to the consultation on this issue.

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James@Joju

Could you please confirm the energy monitor you used was an http://www.efergy.eu/index.php/eu/products-1/electricity-monitors/elitev1-monitor-eu.html.   What I'd like to do is have a single transmitter sending to two receivers, one in airing cupboard set to 1KW alarm / relay out and one in house for my use.  I've played with two energy monitors so far and one beepd for 10 secs on over limit and then stopped, the other was continuous but and on/off beep so would need an extra circuit to trigger relay continuously.

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Rogercat,

that's exactly what I did, back in May last year. I used the Effergy unit, set to 1kW, but reduced it to 500W by putting the cable through the clamp twice. ( I had used a similar trick with the Current Cost clamp to roughly measure actual consumption - putting the clamp around both the incoming and inverter cables.)

Like others I was in two minds about green this was, and live in hope that we might get paid a proper rate for export (at least smart metering is coming sooner than you might think...) 

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Trick here might be mods to a £25 wireless energy monitor.... they support an alarm function usually preset at something like 7KW.    So reduce this alarm to say 1.3KW and then feed the alarm output from the buzzer into a relay connected to 1KW immersion.    

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Hi All,

 I had the British Gas rent-a-roof scheme installed in October.

Like many on here, I'm wanting to use the wasted power. In the summer to heat water and in the winter to run a heater (either convector, oil filled or storage)

I wanted to only use what was available and after many months I think I'm there.

 My children suggested that I patent the idea. I now discover that EMMA is beaten me to it, but at a huge cost.

 I'm planning to set up a web site showing the circuit, my design reasons and problems and suggest improvements. I'm not an electronic expert, but dabbled many years ago. Hopefully the circuit can be refined by visitors and be available to all.

Anyway, my circuit is a 3KW dimmer automatically controlled by the difference between the power being used and the power being generated.

I just need some sun for final testing before it goes in a box and it's fully live.

 The control circuit has been running 24/7 now for the last couple of months and is working very well. .

The 240V 3KW dimmer may need some more testing and tweaking.

Cheers, Keith

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Chris, Thank you for sharing your device on here. I am going to try it. I am quite fortunate as my two pv arrays feed in via a henley block which also feeds the main consumer unit. I am going to fit a mini consumer unit also connected by tails to the henley block to feed the immersion heater. I am therefore going to insert in series a second current sense unit (normally clossed) on the tails to the consummer unit. I willl set this to open at 500 watts. I will set the one on the tails from the PV arrays to close at 1000 watts. The output from the contactor will be fed through a variac transformer which I aleady have and will set this down to about 100 volts so that 500 watts is disippated in the immersion heater. Therefore if appliances like the kettle are switched on in the house the immersion heater will drop out of circuit. Also the first current sense unit which I ordered from Lamode were the fixed core type but I have sent these back as I thought the side adjusted pot was totally impractical to adjust and its proximity to the live terminal was crazy! I see the split core version has the pot top mounted and not so close to the terminals.

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Here's my cunning plan....  my Invertor has around 8 LEDS in a row that light up as the power level increases....  I intend to 'glue' a solar sensor connected to a relay over the diode that comes on at 1KW being generated.  Hence once 1KW being generated put on immersion - any tips with such a circuit maybe pop into Maplins.  

As for the site transformer I've seen these adjustable 3KW rated dimmer switches on ebay for @£8 and could mean upping the voltage output in peak summertime.  http://www.ebay.co.uk/itm/290612717016?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_4990wt_947

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thushar - I read on Chris's website that they only charge £50 for a 1kw immersion and that ebay item is £59 + £5 delivery

 CHRIS - was about to order this from you but just read there is a Mark2 version on the way that will take into account the actual AVAILABLE surplus PV. Any estimate as to how far off you are with the mark 2? I am keen to get something installed before the summer.

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Just found this 1 kW immersion heater on ebay - suitable for the circuit described here without a site transformer. Hope it will be useful to one who wants to implement this project - as 1 kW immersion is a rare item and really hard to find.

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190631227797&ssPageName=STRK:MESE:IT#ht_500wt_922

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pigasus

This ability is being worked on now, as will refine the existing deign without having to resort to a £1200 unit from elsewhere.  

This existing design we tried to keep very simple, thus cheap, but peoples demands are now increasing, so we are working on a mark2 version now. 

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Hi Gary K

We originally tried a light sensitive switch. Kits are available in places like Maplins. But the problem persisted that the switch sometimes fired up the relay when the inverter was not generating enough power, and vice versa.

The socket in the airing cupboard can be easily carried out using the existing design. Like your idea, another cable has to be run into the airing cupboard.

I tried to describe the circuit as a 'fits all' option. Everyones installation is different. Some people have the inverter in the loft, others in the garage, we have been to install this unit on installations where the PV inverter is in a completely separate building.

If the separate PV module is aligned exactly the same as the main array, this will probably work though if care is taken in correct positioning and switching design. 

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If you have to put a standard switched socket by the immersion, why not design a unit with a relay/contacter that is switched by the power from a small solar panel-say 20w that is mounted at the same orientation as the main PV system?

This could be placed between the switch and 3 pin plug like a rotary timer.

would this route not be simpler than changing MCB's and rerouting wiring?

Thoughts?

Gary

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Chris, will your Immersion Heater Relay only feed the hot water after all other demands for electricity are met?  Or is this ability still to come? Thanks.

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Nigeldodd you get that 3p per unit exported regardless of how much you actually use as there is no metering of exported power in most houses.  According to an EST report last year,  most households only use a quarter of their PV generated energy but you are deemed to have exported a half.  Using some of that energy to save on gas for water heating reduces your fuel bills and the resulting carbon emissions.

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The payment I get for an exported Kwh of energy is approx 3p.

This is about the same as it costs to heat by gas. So I do not benefit greatly by finessing my system to use solar pv electricity to heat domestic hot water. I might just as well export it and use gas to heat.

On the other hand,  to run my server and other electrical equipment that needs low entropy energy, I need electricity. 

It is less easy to use gas to run computers than to use electricity to heat water, but there is no economic advantage in the latter. 

So I shall use solar pv electricity to run my server but not heat my water.

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I like the simple idea of using a 115v site transformer.  I notice that specs for such transformers include duty cycles.  Can anyone tell me what those figures would mean in terms of feeding a 3kW immersion heater perhaps for some hours continuously?  Could a 3kVA site transformer feed simultaneously another immersion or other small wattage (eg 800W) heaters.

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Hi everyone who has been checking the response to this blog, we have now at last started production of the Immersion Heater Relay, which is available right now!

There has been almost a year, well, a Spring, Summer, Autumn and a bit of a Winter of testing on site, and we know that from late Spring to early Autumn, if your not excessive electricity users in the home, our unit will provide a daily supply of hot water.

As mentioned on this and other YouGen blogs, you will need at least a 3kWp PV system to regularly achieve this, but over 2.5kWp will give a benefit.

See the webpage on http://www.chrisrudge.co.uk/immersion.htm  for more info

Hope Christmas was a good one for you all :)

Chris Rudge 

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Thanks for your comments Chris, I agree with you entirely - my solution would be a hobbyist way of doing it and definitely not for everyone. I also agree that we would have to look at the other items that are on in the house. But we're getting good at that now!

Nick :-)

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I thought about the benefits of doing something like this myself, I even looked at whether batteries could be used to charge in the daylight and pump power back to the inverter overnight, and yes they are out there and available - but after thinking about it, I reached an entirely different conclusion.

If you are on the FIT scheme with 4Kw or less, I believe this is all fairly pointless, it will add complexity to your set up and cost you time and money, why do I think this? On FIT your payments are based on quarterly readings of your supply and export meters, so the net difference between these is your exported amount. This takes no account of day or night, or when you are a net generator or consumer on an hour by hour basis. Because of this, I came to the conclusion that the grid is already functioning as the equivalent of a giant battery for me, so my solution is that if I believe I am going to be a net generator over a particular quarter, all I need to do is leave my existing immersion switched on, and (as suggested) ensure the immersion thermostat is set to a slightly higher temperature than the cylinder thermostat for the gas heating.

So my next question was "how green is this?", at first I thought perhaps I am just being selfish and thinking of the money, but if you think about it, if thousands of us are pumping back into the grid in daylight hours, that will allow the generating companies to run less generation capacity and save carbon emissions in that way.

Perhaps there are still concerns, but my conclusion is that the most I think I would do is perhaps just fit a suitable timer switch to my existing electric immersion so it operates in daylight hours only automatically.

I'd welcome anyone else's comments on this, perhaps I have missed something here?

Simon

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Changed out immersion heater to  a 1 Kw.

Replaced contactor with solid state relay

set point on current sensor set at 1Kw plus any stand by use

Working brill

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Hi John

Your immersion heater will be powered by 230v AC mains, thus the modules will not be able to operate them at all on their own.

PV modules will need to be connected to a grid inverter, which is the device which turns the DC current from the modules into AC mains.

However, the 2 modules you have would hardly ever generate enough power to effectively operate an immersion heater, as this would ideally need a 2 KwP system or more (8 of your modules)

I would suggest the simplest method would be to connect one of our immersion heater relays to your existing PV system. It is connected in line adjacent to the fuse box, so will not interfere with the PV system and its warranty.

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Dear Chris,

Re-hot water via solar panels.

I have recently purchased a roof installation fitted profesionally and do not wish to tamper or modify this system!

However I have 2 additional panels.

Nominal Power 240w

Optimum Operating Current 30.2v    7.69A

Open circuit voltage 37.3v

Short circuit voltage 8.46A

Max system voltage 1000v

The rear of the house is facing East. My hot water tank is 36" by 18" with 27" by 3kw immersion heater thermostaticaly set to 60 degs coupled to a timer switch.

My question is: can the two panels be wired in to the existing terminals on the thermostat.

John

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If you what to use your excess electricity and save on your electric have a look at this site  about Intelligent Immersion.
http://www.electriciansforums.co.uk/central-heating-systems/23969-immersion-heater-pv-electricity-13.html
Re: Immersion Heater - PV electricity 

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Hi Westfielder

We also tried a Maplin light sensitive switch, and found with some tinkering it could be made to work. However, this is not something to simply easily set up in most situations and will remain the reserve of the experimental hobbyist.

In all the other points you have raised, the main item to pay attention is the fact that with this device, we assume no other big current consuming devices are being used in the house at the same time. Clearly, if the house is being used during the day with washing machines running, etc, the current sense threshold needs to be set at a higher point.

Chris 

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Thinking laterally...

1.If the immersion thermostat is higher than the gas, then if the immersion runs for an hour on a timer during the middle of the day free hot water abounds. Then the gas is set to heat at 5pm. If the immersion has been on then the gas won't kick in anyway because of the lower set thermostat. Money saved

2.If I can do this and only power the immersion when the sun is shining even better. A 2.7 kw heater doesn't need long to heat a tank. And once temp is reached, a well lagged tank won't use much energy if the immersion is left on.

3.So if I set the time switch to 2 hours and then switch when the sun is shining that should cover it. (and just avoid using m/w, w/m and dishwasher during those 2 hours) - No sun then gas is used as before.

A simpler/cheaper method to switch the immersion - many people (Maplin) sell light sensing kits for about £7 that are adjustable for the switching level of light and have a minimum time delay before each change of state. If one of these were stuck on the roof (or in direct light path), then a low voltage low current feed to a contacter to be installed inline with the timeswitch in the tank cupboard. (Not much work for a sparky because all the low votage/current stuff can be done by yourself.

Have I missed something obvious?

If not - I think I will go ahead and install such a system and update this blog

Nick

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Chris Rudge asked for suggested improvements to his admirable switching system. Here's a suggestion (by a non-electrician!).

I'm not sure of the advantage of knocking down the current using a 110v site transformer (£50 plus plugs and wiring) when for the same money you could buy (or have made) a lower wattage immersion heater, which would then use the existing (230-240v) wiring. There may be some point I'm missing here, but it seems to me that you'd have less clutter in the airing cupboard and a new immersion heater element. Those who want could still run the immersion heater overnight on economy 7 (you'd have to run it for longer, of course).

In these days of programmable timers, it's hard to see why the standard immersion heater has to be rated at 3kW anyway.

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I have a 3.8 kw solarpv sysyem in place; working well; I would like to use the daytime electricity to heat hot water; however, we have a condensing combi boiler, for hot water and ch, but no hot water tank.

There is space in the bathroom for a tank, but what would we need to do to get a supply of hot water to the shower/bath et.c?

I have read about the auto control, but am a bit concerned about the initial cost of installing a tank, and the neccessary wiring et.c.

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Hi all,

is it possible to set up a similar system for a wind turbine? I'm running an Eoltec Scirocco 6kW turbine off grid with a battery bank and Standby diesel generater. Is there a way that I can "dump" excess power into an immersion when my batteries reach float voltage? If so, how do I control the load to match generation?

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I am a little surprised that there is not a commercially available current sensor that is sensitive to direction of flow.  My meter (a current sensor) flashes rEd and switches on a bright red LED when we are exporting current.  Could not this technology be used as a sensor to drive an immersion heater switch relay? 

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This looks like a great idea.  Looking at the diagram, the sensor needs to go on the live coming from the inverter.  I have just had a system installed and there is only a single 2.5mm cable running from the inverter to the fuse box (I was surprised that it is such a small cable for a 4kW system).  The switch sensor looks like it needs to clip onto a relatively large cable to me.  Do you know if the system would work with the whole 2.5mm cable running through it or is there a way to work around this?  Thanks.

 John

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This is a great idea, but it means you need to be able to stop your existing boiler re-heating the hot water after early morning showers/baths. This in turn means you need to set your timer so that the hot water and central heating go off together (or get a new timer that splits them!).

One great solution it seems to me would be to somehow use the excess PV electricity to heat/warm the hot water in the central heating system. There seems to be real gap in the market or am I missing something?

I'm not looking to heat my house via PV, but have some background warmth during the day so the gas boiler has less to do when it comes on when everyone gets home from school / work. Air source heat pumps require a whole new system so are too expensive, don't work in older properties and also not renewable.

Ideas?

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I like your basic approach to the issue and feel it has real merit. I approached the problem from a different angle and analyse my export by pulse counting my A100C export meter. There are many ways of doing this. I went for an Arduino based reader but I have seen others based on Vellman kits used on other websites. Currently I control loads using X-10 but am considering starting again based on a Sunny Backup system M. The first question I need answering on that count is whether I'm going to have problems with it using my Fronius PV inverter instead of it's recommedation (of course) of an SMA one.

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If I've read this correctly, once this circuit has been installed the immersion can't be used on conventional mains? We already have SHW, so we'd need to turn this off during the summer, otherwise we'd boil the water! And 50C won't be adequate all the time, or attained during the winter. Or can we switch the immersion heater back to mains when necessary? As an aside, with 2 adults in the household, both at home all day (and no children) we're exporting about 60%.

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Hi Rob While I understand your concern, I don't think that it's likely to happen, as research the Energy Saving Trust is doing indicates that the average installation exports considerably more than the 50% deemed amount. I have a meter that records how much I export - and it's getting on for three quarters for a 2kW system. And I work from home, and actively try to use power hungry appliances when the sun's out. Also, given the old and decrepid nature of the grid, it makes much more sense for microgenerators to use as much of the energy they produce on site as they can - that's where it's most efficient.

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Even simpler, we had a timer switch fitted to our 2kw backup immersion heater, and set it for 90 mins in the middle of the day. It comes on come shine or rain. Tank is very well insulated. No gas for water heating needed and water is actually hotter than with the gas boiler. I monitor electricity and gas use weekly and we'll probably switch back to gas come winter.

No complications, no electrician needed, no implications for the FIT and I bet  80-90% of the electricity is free. 

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There is another side to this which I will air and hopefully avoid being seen as too judgemental! I think there is a need for caution with what's being proposed.

The unused energy from a typical grid-connected microgeneration system is exported to the grid. If you don't have an export meter, you are benefiting at the rate of 1.55p per generated unit - this year at least - on the basis that half your generation is deemed to be exported at a rate of 3.1p per unit.

If people build add-on control systems that detect when power is being exported or is above a certain level and make use of it locally, for example as above in a water heat store, this is distorting the basis of the Feed in Tariff.  If a lot of this goes on, the original estimates of how much would be exported from microgeneration schemes across the country will have to be re-assessed. DECC and The Treasury could quite reasonably take the view that the tariff structure needs to be reviewed and possibly adjusted. For example they might conclude that instead of 50% of generated energy being exported from solar PV, the actual figure is only, say 25%. Their response could then be to remove the deeming component for exported units and force everyone to get an export meter so DECC/OFGEM only pay for what is delivered.

If that happens, I will suffer, as will thousands of users who don't want to install an export meter or complex heating systems to absorb 'spare power'.

There is also a risk that this will generate a backlash from those who already believe the FiT is over-generous. And lead to DECC applying degression faster in later years than otherwise.

Or they might say 4kWp is rather a generous threshold for the first break point in the generation tariff and reduce it. Using the argument that generators at that size are milking the tariff by soaking up the excess generation that is being paid for at the highest rate.

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Yes Pigasus, it is possible to ask your tank maker to incorporate a 2 1/4 bps immersion heater fitting. Then rather than installing a 3kW immersion and a site transformer, simply install a 1kw immersion from the start.

For your proposed application it would be better to use the device to sense the exported power from the premises, than generated power from the inverter. We are working on this at the moment. The main problem to overcome is the current sense unit does not know which way the current is flowing, either into the house off the grid or from the PV to the grid is all the same to this little unit!

Watch this space.

Chris 

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I like the idea of diverting solar pv to heat domestic hot water, but I have a couple of questions.  I'm planning a new build with the heating and hot water to be provided by a wood pellat boiler.  Is there a way that I can make sure that the electricity provided by the solar pv is used first to provide electricity for other than hot water with only the excess being diverted to produce hot water?  I'm also planning to provide domestic hot water via a thermal store.  Is it possible to have an immersion heater in such a store?  Thanks.

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