Solar panel and water heating/towel rail

Other Devices & Integrations Power Management
1

Apologies if this has been covered before but I am wondering if my faithful Vera can mimic this interesting gadget http://www.immersun.co.uk/product/ which I was planing to install when we have PV panels installed next month. I figure it’s easy to measure power going back to grid but I need a way of controlling a resistive load of up to 3kw (I’ve am immersion heater element) - I need a UK compatible solution. I also would like anybody’s ideas on how to do the software aspect of the controller. I figure it is quite to straightforward in many ways ie periodically check power exported against and hot water tank temp (already do the latter as part of an array of Fibaro temp sensors) - if power is being exported and the tank is not up to temp then turn on or up the immersion heater controller in stages until just before you stop exporting.

It would be so cool as I could use the immersun budget ( at least ?300 ) to build an integrated, accessible and customisable solution (plan B is to use the same system to power a heated towel rail to solve the problem of drying towels in the summer when the central heating is off)

All ideas gratefully received.

2

First question will be:
How do you measure exported power as opposed to imported power. A current clamp will only measure current and not tell which direction the power flow is. You will either need a measurement which also uses voltage to tell direction for power flow or measure current from solar, current to house and current to grid and calculate whether power is in or out.

3

Hi - Yes I was thinking along the same lines - figured that actually you need only 2 sensors - logically the 2 that can only be >= 0 which are the Pv panel output and the total house consumption, the meter flow in/out can then be calculated.

So then I need a simple logic controller that checks whether power is available and decide what to do with it. So assuming I can control the heating elements in say 10 Watt increments for simplicity then

Power exported (Pexp) = Power Generated - Power consumed
IF hot water tank temp <= desired temp THEN tank power setting in Watts (Tp) = Tp + ROUNDDOWN (Pexp/10)

I’d need more code eg to skip this step if the tank was up to temp and the tanks power supply was set to off so I could potentially power something else

So the main project hurdle is how to control a resistive load of up to 3 KW.

The other question is how to write the code required - ie is if best done using some modules such as the PLEG or would I be better learning how to write code directly ( I wrote lots in the early 2000’s got the ADI Ocelot so I figure it can’t be that hard )

Thanks for the input so far.

4
  1. I had PV on a previous house and it was connected into the fuse box which made it difficult to measure house power consumption so you will have to ensure you can get just house consumption and then export is generation minus house use.
  2. I doubt there is a 3kW resistive load ‘dimmer’. You may need to consider [url=http://www.syxthsense.com/controllers/pr1-3/single-phase-thyristor-controller-(3kw)/]http://www.syxthsense.com/controllers/pr1-3/single-phase-thyristor-controller-(3kw)/[/url] and control that via z-wave somehow?
  3. I was in a similar position once before and i looked at getting a 1kW heater element instad of 3kW. I used fas heating for general heating but the 1kW did pre warming, was simple to use (on/off only) and left PV for other use too.

Hope this helps.