device to use unused soler pv export power to run heater or hot water

zeupater

John_Pierpoint wrote: »

Hi Graham (and all the other engineers & scientists reading this),

It is over 50 years since I did "O level" physics, but isn't the power of five relationship referring to sources in a vacuum radiating heat (best known example: that round golden thing in the sky we don't see much of these days).

The hot water tank is losing most of its heat by convection and conduction (especially if the copper expansion pipe coming out of the top goes straight up) and for practical purposes the heat loss is proportional to the excess temperature?

eg Normal temperature of the "airing cupboard" 15 Celsius, Tank set at a warm enough for washing, 65.
Now boost the excess temperature by 5 and get 100 / 50 * 55 = 110.
That 10% is much the same as your 8% but a lot more easily understood and acted upon by the average UK citizen, who still has problems doing percentages "I was never any good at maths at school; can you pass me the homoeopathic remedy your highness"

Time to turn down the setting on the thermostat for my immersion I think [Question, will she notice and run off all the hot water in the hope that it will get really hot? ].

Hi

I'd agree with the above approach based on relative differentials & simply calculate .... ((65+5-15)/(65-15))-1 = +10%

HTH
Z

dougieuk

Hello, I'm all new to this solar PV lark, having a 3.7kw system tomorrow
could you send me a copy of your switch circuit etc.
Cheers

solarpvman

ooooh me too please

solarpvman

Dave_Fowler wrote: »

There's no great problem in achieving this using a combination of analogue and digital circuits. I'm working on a very simple design at the moment, but family commitments mean I won't be able to put much time in before mid April. A simple pulse-rate detector with variable threshold can be made with off-the-shelf components for very little cost.

However using the wonderfully simple circuit suggested by ESE I can't quite work out what will happen under the following circumstance:-

I've chosen to turn a 2.5kW heater on when the panels are generating 3kW. (This allows a base-load of 500W). Let's say a 1kW toaster is now turned on. The import meter LED starts to flash so the logic device turns off the 2.5kW heater. Import LED stops flashing (only 1.5kW in use, 3kW generated) - therefore 2.5kW load turns on again. Import LED starts to flash again, heater load turns off .....

What is needed is a method of varying the 2.5kW load to match the surplus energy. The use of a phase-angle controlled triac - as used in some variable electric heating systems - can cause a great deal of electrical interference if the design is not closely controlled and screened and possibly would not appear as a reduced load to a modern meter because of the 50Hz pulsed load. (Can anyone help with this knowledge?)

A phase-angle controlled system would probably cost around £50 if you built it yourself, but you'd have to be quite adept at electronics building and also understand the dangers of 240V circuitry.

Dave F

could some form of delay be introduced eg a couple of seconds to REDUCE continually turning on and off.

Dave_Fowler

solarpvman wrote: »

could some form of delay be introduced eg a couple of seconds to REDUCE continually turning on and off.

The design by moneysavingexp did have a delay built into the detector on the import meter so that it did not immediately allow the immersion heater to turn on again when the import meter stopped flashing. (I've sent you a PM of the original design). The solid state relay would not mind being turned on and off as there are no moving parts so it could cycle through on and off without any damage.

The main disadvantage of the circuit was that you had to be generating the full amount of power spare. The phase-angle system as used by products similar to the Immersun sends whatever spare power there is to the immersion. This can range from a few Watts up to the full power required by the immersion.

Dave F

legoman62

I've been using MSE's idea for well over a year now with no problems;)

All I did was fit a 1kW immersion in my cylnder. I made provision for another 2 immersions but, in our 2 people household we have enough hot water in the summer months, and some of the winter ones too.:D

welshlady33

Hi there -please can you pm me with the plan for this and yr water saving idea

Many thanks

Skip.C

Hi Could I have the details please
Thanks

countryman_2

Please would you send me a copy of the plans/schematic for this device. I've recently had a 4kw PV system installed and am looking to make good use of the generation.

Thanks

CrazyCol

Hi
Please can you send me the info on this idea too, getting a system installed & want to make full use of it.
Thanks in advance