I must say my experience of 3k for an m a professional was enlightening.. even if traumatic 

@majordennisbloodnok Oh sorry, I didn’t see that preference previously, sorry @paultheheating ! I didn’t mean to impose my prejudices (plural?!) on your preferences. Toodles.

Posted by: @toodles

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@majordennisbloodnok Oh sorry, I didn’t see that preference previously, sorry @paultheheating ! I didn’t mean to impose my prejudices (plural?!) on your preferences. Toodles.

Not a problem, @toodles; introducing another option backed up by a cogent argument will do nothing but add to @paultheheating's available information on which to base a decision.

I wouldn’t try a direct linked system of DC at all since you have too little control and you surely want the excess to go to the house? and I suspect few electricians would consider it.
So assuming an AC system I would think it appropriate if south facing and unshaded. In winter you get the low angle of light capture and although in summer the angle isn’t as efficient there’s a lot more sun. You will need immersion back up for very wet grey days though.
I asked our current PV installer about panels on the house wall, since we have lots of south facing wall but it’s outside his MCS registration scope. A friend has some and it’s very good for low level winter sun BUT the pigeons started nesting behind them, sitting on top and dirtying them thoroughly. So many baffles and spikes (by a different installer) later they are OK.

Practical issues dominate!

Thanks for all your suggestions, am thinking that a few 4-6 pv panels would drive a DC immersion in the CH system just enough to raise water temp up a few degrees and thus reduce the gas boiler usage. should save me some money and help the evironment. thinking of dc immersion as trying to minimise installation and kit cost.

surely there must be plently of other people using vertical pv panel to heat water, and not wishing to be a pioneer , happy to copy someone else.

Spending on 6 panels to save a bit of gas does not sound very efficient..

With that budget, I think panels, micro inverter and plugging onto the consumer unit may allow you to warm the tank and use leftover electricity.. 

Posted by: @paultheheating

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Thanks for all your suggestions, am thinking that a few 4-6 pv panels would drive a DC immersion in the CH system just enough to raise water temp up a few degrees and thus reduce the gas boiler usage. should save me some money and help the evironment. thinking of dc immersion as trying to minimise installation and kit cost.

surely there must be plently of other people using vertical pv panel to heat water, and not wishing to be a pioneer , happy to copy someone else.

Just to avoid any chance of crossed wires, @paultheheating, I'm certain there are plenty of installations of vertical PV panels, so I don't see you'd be a pioneer there. The only question mark being raised is how the power those panels create is then used. In my home, our DHW tank consumes about 2-3 kWh of the heat pump's energy which, given a ratio of about 2.5 (DHW temperatures never play that well with heat pumps) means about 5-7.5 kWh of delivered energy. Even with 4-6 panels, I don't think it would take all that long in the summer before you were exceeding that amount and, with a DC connection to the tank, there's nowhere else for any surplus energy to go, giving rise to two points:

1. Would you really want to waste perfectly useable generated power once your water's hot?
2. How would you envisage a cutoff to ensure the water didn't heat above a certain point and turn your water tank into a pressure cooker?

I think the fundamental problem is that you're assuming the panels will just supplement the boiler whereas I suspect (at least in the summer), that's a significant underestimate of the output the panels will provide. 

Posted by: @batpred

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Quick googling shows there are DC water elements..

Yes, I have one in my Thermal Store.

In the days before my wind turbine caught fire(!) the DC Immersion was the 1st level of Dump Load.

I went through two DC immersion heaters, which blew open-circuit...
before coming across TP Fay, who make them in UK.

Running the output of PV panels directly into a standard 'mains' immersion heater is a no-no.

The panel requires an electronics device with an MPPT algorithm in order for it to deliver any usable power.
Without Maximum Power Point Tracking, the voltage will simply fall to the minimum level to match the 'near short-circuit' presented by the load.

The algorithm continually scans the input, and adjusts the current being drawn to keep the voltage at the 'knee' of the curve.

I have a single solar panel fixed to the south wall, because I ran out of room on the roof.
The output is acceptable, despite being in series with two other rooftop panels at a different angle.

There's also no problem with having PV panels completely vertical.
That orientation has been part of experiments to work out the optimal positioning for bi-facial panels.

You will see that I also have a vacuum-tube-based solar-thermal array on my lower roof.

If it's just heat you want, then they are greatly more efficient.

PV panels can operate at around 19% - 20% efficiency in full sun.
Whereas solar-thermal will be at 80% and above.

Posted by: @batpred

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Posted by: @batpred

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Quick googling shows there are DC water elements..

Yes, I have one in my Thermal Store.

I thought you would! 

Posted by: @batpred

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If it's just heat you want, then they are greatly more efficient.

PV panels can operate at around 19% - 20% efficiency in full sun.
Whereas solar-thermal will be at 80% and above.

When I talked about spending efficiency, I was talking about the efficiency of using @paultheheating 's capital, which may well not be the most efficient in terms of using wall space! 

In terms of: spending on parts, installation/certification costs and then operation/maintenance costs. 

The point you make about heating systems blowing up would suggest non-obvious operating costs of using immersion DC heaters. 

A simple solar inverter or a microinverter may be: 

- cheaper to install

- be more easily maintained as it is a common technology  

Of course @paultheheating may be looking to complete your circuit with an MPPT controller and have a custom solution..  

As for spending more on bi-facial panels, a vertical wall location would not make much use of the back face.     

Posted by: @batpred

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As for spending more on bi-facial panels, a vertical wall location would not make much use of the back face.

The original strategy behind the production of bi-facial panels is that they would pick up the reflected light bouncing off the adjacent roof area, particularly when positioned on 'flat' roofs.
There are several designs of brackets and frames which allow PV panels to be held away from the mounting surface, as my own wall unit is.

Each manufacturer has their own idea of how much additional generation can be obtained by using the reverse surface.
It's a matter of going through the (online) literature and checking the specs.

Since a bi-facial panel costs little more than a standard panel, the extra couple of percent efficiency isn't to be so easily overlooked.
Midsummer Wholesale have several bi-facial panels available, including some 440W units from Jinko for £67 +VAT.

It's not necessary to buy a full-blown solar inverter in order to have an MPPT input, and then deliver 240v AC for an immersion heater.

There are also devices called MPPT Charge Controllers which are intended to allow solar charging of 12v to 48v mobile-home batteries.
Thus they output DC at whatever voltage is needed by your choice of battery.

It is, however, worthwhile checking that the unit really does operate a proper MPPT algorithm.

Some Far East manufacturers use the 'MPPT' term too loosely, simply to indicate that a solar panel can be connected.

Posted by: @transparent

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Posted by: @batpred

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As for spending more on bi-facial panels, a vertical wall location would not make much use of the back face.

The original strategy behind the production of bi-facial panels is that they would pick up the reflected light bouncing off the adjacent roof area, particularly when positioned on 'flat' roofs

Mine is grey but perhaps with a few cans of white paint.. 🙂

Posted by: @transparent

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Midsummer Wholesale have several bi-facial panels available, including some 440W units from Jinko for £67 +VAT.

Amazing how the prices came down! 440W has to be mono crystalline .. 

And the flat mounting frames are now more expensive than the panels..

Thank ou all for comments, just to refocus I am not looking to install anything complicated that needs certification, maintenance, am not fixed to 4-6 panels could  put in one or two panels if that is enough to bring cold water up to 20-30.C In reflection I should have said 

does anyone have a dc immersion running off vertical panels to reduce gas consumption, is there a switch that can turn off panels if they produce too much heat energy.