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