Solar Panel immersion heater automatic switch.

[Earthstore]

I have often wondered why people will spend so much time and money trying to come up with a system to heat their domestic hot water.
Firstly, let's try and work out how much we actually use; Washing machine, cold fill, dishwasher, cold fill, so what else do we use it for? Baths/showers and hand washing, and that is it.
A modern hot water cylinder will hold it's temperature for around 24hrs, so minimal losses there.
So what is the true cost in £'s to heat the hot water from conventional methods? Well due to the amount we use it has to be very little.
What if you have no spare PV, how would you heat your water from cold? Most would just switch on the immersion heater to heat it up quickly, as the kids need a bath before bedtime.
If it were used as a way to add some free heat to a heatstore, then I feel it may be worth it.
Just my thoughts.

 

[Del Boy]

I think the benefits will probably be small... between £50 and £100 per year for gas, bit more for economy 7, probably double or triple for electric / oil / lpg. Once I figure it all out I'll post what I think and hopefully people can correct my inevitable mistakes.

I've got gas, so will get the least payback, and I want to make the payback within a few years, so alot better than Solar PV itself. If energy prices rise then you are protected even more. I'm thinking if it warms up the water during the day, the gas boiler won't be needed, so for at least 3 months of the year I won't need to pay to heat the boiler up for showers, baths, washing up etc.

If everyone just made one for themselves then yes it would be alot of effort for little benefit, but I'm quite interested in getting different ones working, so for me it's a bit of fun too. I've got a kit-car, I could've bought it cheaper already made... but where's the fun in that?

Appreciate your thoughts... constructive criticism will stop me spending way too long on this or making mistakes so please keep them coming!

Thanks

 

[Trader9]

Hi everyone

Seems this subject still has a long way to go.

I built my own automated Solar Dumper late last December 2011 using a 3.3kWA isolation transformer because I wanted to maximize the surplus solar from my new 3.76kWh PV system. I automatically switch between the 55 volt winding and the 110 volt winding to give 160W and 660W loads using a single 3kW immersion. However, because I also have a 3kW boost, I am able to switch through a combination of loads 160W, 320W, 660W, 820W and finally 1,320W all automatically using a £20.00 microprocessor called an Arduino andtwo Efergy current sensors and a hand full of relays.

Drawbacks of using a transformer are current inrush requiring a type C breaker and a thermistor with an additional relay. Also I have found if on all day it gets quite warm even with no load so I fitted a cooling fan too.

Total cost about £250.00 for all the electrics as I used quality components and £130.00 for the 3.3kVA transformer as I wanted a wall mounted version that had a continuous 1.65kVA rating. During the last four months of operation I have managed to dump 250kWh or 24% of all generation into the hot water tank that was surplus after house load. I expect about one MW hours each year to be diverted in this way.

I am currently working on a transformer-less version that still uses the Arduino for control, two efergy ct's, but instead of the transformer I will be using eight relays that act as a low volt – high volt interface to switch a resistance network that drives a 3,800W dimmer circuit to control the voltage in stages to the 3kW immersion.
I have a working prototype and I plan to switch the following loads as solar is available 100W, 200W,300W, 400W, 500W, 600W 750W 1,000W. From my experience it is better to use small loads, as even in winter up to 500W is readily available and heat transfer is better at lower wattages as you get less insulating bubbles forming around the heating element.

The beauty of this system is all the parts are readily available Arduino and sensors £40, eight relays onPCB for Arduino £10 (Hong Kong), 3,800W dimmer PCB £8 (UK or HongKong) the most expensive item is a 5V DIN rail power supply but you could use a cheaper 9V 1A mains adaptor if you wish. I mount all my components in a ABB 12 way consumer unit as it give me flexibility and looks professional. It also allows me to fit a DIN rail Wattmeter so I know exactly how many kWh I have diverted. Total cost around £100 excluding meter.

I also have a third system in the pipeline with no relays as the 3,800W dimmer can be driven directly by the Arduino. However, the Arduino is not able to monitor the current and trigger the triac at the same time, so I would have use two Arduino's. It also requires additional electronics for opto-isolation and zero cross sensing. All of the components parts I have working separately, but not sure I want to go down that route,as it seems overly complicated when I already have a working system and the eight relay system upgrade is so cheap and less complex.

All three systems use stepped loads to try and match the spare solar output a bit like digital sampling of an analog waveform used in the music industry.

My system is also compatible with off peak systems, as the Arduino can switch a change over relay as soon as spare power is available. The Arduino needs a interface to the current transformers so you will need soldering skills see linkhttp://openenergymonitor.org/emon/buildingblocks/ct-sensors-interface you will also need a lot of patience.

It took me two weeks of trying to write an Arduino sketch for current calculation and triac triggering only to conclude it can't be done with one Arduino.

Regards, trader9.

 

[garryp]

has anyone used this Solar PV switch for hot water. I can see lots of posts of people developping their own pro type but none actually saying whether they have used it. I know it does not compare to actual consumption, but if it does as it says will sweitch on 1kw heater when panels generate more than 1.5 KW.

Thanks

 

[Thomas101]

I think the benefits will probably be small... between £50 and £100 per year for gas, bit more for economy 7, probably double or triple for electric / oil / lpg. Once I figure it all out I'll post what I think and hopefully people can correct my inevitable mistakes.

I've got gas, so will get the least payback, and I want to make the payback within a few years, so alot better than Solar PV itself. If energy prices rise then you are protected even more. I'm thinking if it warms up the water during the day, the gas boiler won't be needed, so for at least 3 months of the year I won't need to pay to heat the boiler up for showers, baths, washing up etc.

If everyone just made one for themselves then yes it would be alot of effort for little benefit, but I'm quite interested in getting different ones working, so for me it's a bit of fun too. I've got a kit-car, I could've bought it cheaper already made... but where's the fun in that?

Appreciate your thoughts... constructive criticism will stop me spending way too long on this or making mistakes so please keep them coming!

Thanks

Just been looking at a website called solardivert and from them they say it is about £170 a year in savings. Although oil will be a lot more expensive. They also have a product that looks fairly good as it takes into account consumption of electricity in the house and not just the electric generated from the solar panels. Not sure how much it is but they say it's low cost.

Thanks

 

[ajn9000]

this is a link to the schematic of the current circuit

Detailed energy monitor system design | OpenEnergyMonitor
you make this circuit board and the take a cable from the pwm arduino pin to the 0-5v of the proportional controller.

Take a look at LEM current transducer eg hex 05-p/sp2

 

[ajn9000]

Take look at LEM ct eg HX 05-P/SP2

 

[Digon]

I would definitely recommend a fully proportional power diverter rather than a stepped type. I have built a Crydom based diverter based on a circuit supplied by a member of this forum.
If this last weeks production is anything to go by the proportional system will really come into it's own in the winter.For example this week my 4kW WSW system has only produced around 4 to 6 kWh per day but the diverter has sent 2.5 kWh of the 4 kWh and 4.6kWh of the 6kWh to the immersion. This is everything not being used for other things like base load, dishwasher, washing machine etc. and about 40- 60W export. On poor days like these the power going to the immersion from the proportional diverter can be as low as 10 or 20W and up to a maximum of say 300W yet the tank can still be up to a good temperature by tea time. A stepped system might not kick in until say 500 or 1000W and so would not provide any heat on days like these. On medium to good days my immersion thermostat will kick in by about 11am at this time of year but then that shouldn't be much different on a stepped system depending on the tank size etc.
The only drawback of a proportional system is the cost. The cost of parts to build mine was £170 but compared to a plumbed solar hot water system even the £300+ of a ready built proportional system seems cheap.

 

[Trader9]

I would definitely recommend a fully proportional power diverter rather than a stepped type. I have built a Crydom based diverter based on a circuit supplied by a member of this forum.
If this last weeks production is anything to go by the proportional system will really come into it's own in the winter.For example this week my 4kW WSW system has only produced around 4 to 6 kWh per day but the diverter has sent 2.5 kWh of the 4 kWh and 4.6kWh of the 6kWh to the immersion. This is everything not being used for other things like base load, dishwasher, washing machine etc. and about 40- 60W export. On poor days like these the power going to the immersion from the proportional diverter can be as low as 10 or 20W and up to a maximum of say 300W yet the tank can still be up to a good temperature by tea time. A stepped system might not kick in until say 500 or 1000W and so would not provide any heat on days like these. On medium to good days my immersion thermostat will kick in by about 11am at this time of year but then that shouldn't be much different on a stepped system depending on the tank size etc.
The only drawback of a proportional system is the cost. The cost of parts to build mine was £170 but compared to a plumbed solar hot water system even the £300+ of a ready built proportional system seems cheap.

Hi Digon

Thanks for your update, I am glad you have a good working system. I have been thinking of a fully proportional system but have only found a schematic without any other information on type of current transformers (CT's) set up etc.

Can you list all the parts you used please, so anyone else interested can also build one. And any useful information on the build process would be helpful

My problem is I can't get my head round the fully proportional concept. If you have two CT's measuring solar and house load, then as soon as you have more solar than house load you start to divert surplus to the immersion heater, but as soon as you do, the house load rises and you no longer have any surplus to detect. So how do you then maintain power to the immersion when both CT's are reading the same power levels?

My stepped system is easy, because as soon as there is 200W surplus I add a 160W load and then when this increases to 200W again I add an extra 160W load etc.

I currently have a microprocessor based five step system working using relays which cuts in at 160W then steps through 320W, 660W, 820W and finally 1320W.

My whole concept was to develop something cheap and simple for other people to copy. If I am successful my next system will require only basic components and should be well below £100.

Using a Arduino microprocessor interfaced via a opto-coupler to a 25A variable solid state relay SSRI could have as many steps as I want or if I understood the fully proportional concept I could maybe incorporate that instead.

The new system should be cheap, as the25A control SSR is only £8.52 mounted on a heatsink, Arduino £20,optocoupler less than £2, two efergy CT's with interface components £30, box and 9V mains adaptor £20. That's just £81 and the whole thing could more or less just be connected together with a screwdriver and no printed circuits to build.

Regards Trader9.

 

[solway-energy]

check out....solar24.... a good solution.

 

[Digon]

Hi Digon

Thanks for your update, I am glad you have a good working system. I have been thinking of a fully proportional system but have only found a schematic without any other information on type of current transformers (CT's) set up etc.

Can you list all the parts you used please, so anyone else interested can also build one. And any useful information on the build process would be helpful

My problem is I can't get my head round the fully proportional concept. If you have two CT's measuring solar and house load, then as soon as you have more solar than house load you start to divert surplus to the immersion heater, but as soon as you do, the house load rises and you no longer have any surplus to detect. So how do you then maintain power to the immersion when both CT's are reading the same power levels?

Regards Trader9.

I can't give specifics on the design because it's not my design. But there is another thread on here 40 odd pages long and a few guys on there have designed proportional systems. I pm'd one of the guys and he was extremely helpful getting this built and faultfinding. I know the designer is putting it through CE testing so I think he may be going to sell ready built diverters so won't want his circuit design made public however he may still share the design for personal use if you pm him.
It uses a single ct and can tell which way the current is flowing without having to cancel out the solar from the feed and sends a control signal to the crydom which does all the high voltage work.

 

[loskie]

we're planning to install a small area of Electric underfloor heating to a new bathroom. Will be about 4m2 so will need a consumption of 600w. As there are only us two in the household and we are out for a large prportion of the day I wonder if this type of switch would enable us to use surplus electricity from our 3.6kwp solar pv. I realise that the surplus is not ging to be there exactly when we need it and probably inadequate from Nov to mid March but feel this would be good for us. Also keep the bathroom heated and therefore drier.
Could a similar switch be used for UFH?

 

[MichaelB]

I found this which seems to do the job simply and cheaply www.mgb-stuff.org.uk/solar.htm without all the bells and whistles that EMA and Sunny Boy seem to think necessary.

 

[Scobo]

I found this which seems to do the job simply and cheaply www.mgb-stuff.org.uk/solar.htm without all the bells and whistles that EMA and Sunny Boy seem to think necessary.

Sounds interesting but couldn't see how much it costs. :confused5:

 

[Trader9]

Hi Digon
Thank you for your reply. I will go and read the 40 pages before I decide which way to go.

Regards Trader9

 

[st3ve]

...If this was sucessful I could quite easily change the plumbing to give the option of hot filling the washing machine to save a bit more.

FYI: Many have discussed this I believe, seems like a good idea, but the practicality is that the 'hot plumbed' washing machine / dishwasher will take in the mostly the cold standing water in the pipes leading from your heat store unless the pipes are very well lagged and 'washer is very close to the heatstore - probably unlikely.

Also, consider that for a dishwasher, the rinse cycle would be using hot water which may well bake on the chilli/egg/pasta etc!

 

[Digon]

Attached are a couple of graphs which give an example of how much variation in the amount of power my system was sending to the immersion at two different times of day on a mediocre day.

 

[steve Leese]

There is a very good product on the market called the solar iboost, its produced by Marlec engineering. it dumps your spare pv power to the emursion heater. i saw it at the ecobuild.

 

[madmurg]

There is an interesting thread at the
Solar Energy Management | OpenEnergyMonitor

http://openenergymonitor.org/emon/node/176?page=2
It looks like someone has built a fully controllable solar controller useing zero cross and burst firing. This removes the need to use expensive crydom or phase angle controllers, which cost £70 plus. So you should be able to build yourself a unit for under £50.

 

[solarcat]

There's a system called Greenologic which seems quite good to me, although I've had no luck getting any prices so far. Essentially it's a series of boxes, one reads the generation meter, an you can have one for your immersion water tank and one for each storage heater...when you start exporting the first box sends a wireless signal to the others and asks them to switch their storage devices on...

 

[RS-232]

There is an interesting thread at the
Solar Energy Management | OpenEnergyMonitor


The "OpenEnergyMonitor" thread is a bit too technical for me, with only a basic electrical knowledge, even though it might offer a solution to dumping excess solar power into an immersion heater.

I'd guess that for most of the time, there will not be enough power from say, a 4kW PV system to feed a 3kW immersion heater as well as all the other gadgets in the house, so some have suggested replacing a 3kW element with a 1kW element. The drawback with this is that it won't be much use if you need a supply of hot water quickly.

As a simple alternative, can anyone see a problem with using a dual-element immersion heater, with the 3kW elements operated individually for rapid heating and in series when powered by the PV system? If my maths is correct, this should give an effective load of 1.5kW, which is much more likely to fall within the PV system output.

I suppose the heater could be wired to some sort of relay, using a change over switch to select the mode of operation.

 

[Trader9]

Hi RS-232

I have two 3kW heaters in my tank so I use a 3.3kVA isolation transformer with the centre tap earth removed so I have use of 55V and 110V. I then use relays to switch between the two voltages to give me five different loads 160W, 320W 660W 820W and 1.320W. This works well and I have hot water by midday. I use a single Arduino to monitor the solar and house load and do the switching. Since January I have averaged 24% (272kWh) of all generation into hot water that would have gone back to the grid as surplus.

Regards, Trader9

 

[RS-232]

An interesting set-up Trader9, but controlling such a system electronically would be beyond my capabilities! When you say that you have two 3kW heaters, are they combined, as in a dual-element heater, or are they separate units? Also, suppose that you need to heat your water quickly - can you run one or the other heater from 240V (i.e. 3kW)?

 

[Trader9]

Hi RS-232

They are the normal 3kW immersion and the 3kW boost both wired separately. I could wire them in series but I normally rely on off peak heating overnight and then solar all day, so off peak is reduced. Also I don't suppose that 1.5kW will be available that often in the winter. I can always use the boost to heat water if needed.

Come the summer (if ever it stops raining) I hope to switch off the off-peak and run solar only. Did actually manage it for the last week of April when it was like summer. You do need a system that cuts in at a low wattage so you can use it in the winter.

The Arduino is only £22 and you would need two efergy sensors (CT's) four resistors and a capacitor for the sensor interface. I am working on a simpler version using the Arduino directly driving a solid state relay (SSR) and this could be a simple solution, but I am still waiting for the SSR from Hong Kong but all in would be a simple cheap solution if it works. About £70.00

Hell, if I am sixty-four years old and using microprocessors, SSR, Ct's and LED's then it can't be that difficult. I will keep you posted on how my new system progresses.

Regards, Trader9.

 

[madmurg]

There is an interesting thread at the
Solar Energy Management | OpenEnergyMonitor


The "OpenEnergyMonitor" thread is a bit too technical for me, with only a basic electrical knowledge, even though it might offer a solution to dumping excess solar power into an immersion heater.

I'd guess that for most of the time, there will not be enough power from say, a 4kW PV system to feed a 3kW immersion heater as well as all the other gadgets in the house, so some have suggested replacing a 3kW element with a 1kW element. The drawback with this is that it won't be much use if you need a supply of hot water quickly.

As a simple alternative, can anyone see a problem with using a dual-element immersion heater, with the 3kW elements operated individually for rapid heating and in series when powered by the PV system? If my maths is correct, this should give an effective load of 1.5kW, which is much more likely to fall within the PV system output.

I suppose the heater could be wired to some sort of relay, using a change over switch to select the mode of operation.

I too thought it would be difficult to achieve but after a week or 2 browsing the Internet forums I managed to build my own controller and it works great. It really is very easy.
you do not need high wattage from your solar panels as my system heats a full tank of water using just 400w of spare power, a 3kw element will work fine using low wattage. There is no need to change to a 1kw element.

 

[thushar]

There is an interesting thread at the
Solar Energy Management | OpenEnergyMonitor

Solar Energy Management | OpenEnergyMonitor
It looks like someone has built a fully controllable solar controller useing zero cross and burst firing. This removes the need to use expensive crydom or phase angle controllers, which cost £70 plus. So you should be able to build yourself a unit for under £50.

That sounds great.

Do you mean the power controller based solution from kemo electronic? I'm struggling to find the actual circuit or component relates to zero cross & burst firing.Could you please help with a schematic or part no or a link please ?

 

[mitul007]

hi guys you should try SOLAR24 from Engensa ltd. it works really well.

 

[madmurg]

hi guys you should try SOLAR24 from Engensa ltd. it works really well.

Not at £250

 

[echase]

Not at £250

People think they can make something similar for a lot less but the reality is often that after few false starts they have a box full of discarded or blown up parts that, together with the parts that do make their way into a working product, end up costing at least £250. So it is fun designing something yourself but often no cheaper.

Or you design something really simple and cheap that does not cost effectively heat much water.

 

[immerse]

What do you use in the way of an EMI filter? Outfits like EMMA, not to mention the DNOs, are very concerned about EMC, and I wouldn't want to ruin my computer!