Immersion Heater - PV electricity

[suntrap]

Sorry, but I don't understand how putting your heater on for a quarter of an hour every hour is any better than just leaving it on all the time during daylight hours, unless you arrange to switch off your other loads during that time. That's why I assumed you didn't know how it works. I agree that fitting a 1kW heater is less likely to have you drawing from the grid than the standard 3kW one, but having a timer switch it on and off at regular intervals doesn't help, because there is no "averaging" when it comes to how you are charged for your electricity.

No one has mentioned batteries by the way, as far as I remember - the whole point is to use water to store the energy.

 

[Richchad]

Would the SMA Sunny Home Manager, due out end of 2011, give the right output when spare power available to run immersion heater etc?

SUNNY HOME MANAGER. SMA Solar Technology AG

Or have I read the little information on it wrongly?

 

[suntrap]

Yes, it looks like it will, but I bet it is far from cheap!

 

[Richchad]

Yes, it looks like it will, but I bet it is far from cheap!

Well it may be cheap compared to Coolpowers EMMA unit at £1500 that I was considering at one point............. or maybe not?

 

[inie meanie]

Hmm I think it must wait until full power level is available for each item before then switching it on, so still very wasteful compared to my comparison circuit. But could have it's uses. But as Suntrap says. I bet it will be a pretty penny or two. :- )

 

[echase]

The unit I am selling is not that expensive and was not that difficult to design. But it did take 100s of hours to perfect the software.

 

[Mark Gee]

Sorry, but I don't understand how putting your heater on for a quarter of an hour every hour is any better than just leaving it on all the time during daylight hours, unless you arrange to switch off your other loads during that time. That's why I assumed you didn't know how it works. I agree that fitting a 1kW heater is less likely to have you drawing from the grid than the standard 3kW one, but having a timer switch it on and off at regular intervals doesn't help, because there is no "averaging" when it comes to how you are charged for your electricity.

No one has mentioned batteries by the way, as far as I remember - the whole point is to use water to store the energy.

Because weather is irregular and changes.As I said originally "what if the sun don't shine?" By simply spreading the "immersion-on-periods" throughout the day you are more likely to coincide with the sun being 'on' eg my strategy would work better than yours on a day when it is cloudy in the morning and sunny in the afternoon. I would also of course refine it to leave periods of no immersion for planning to consume elec for meals/drink/dishwasher/etc

Although your second point is quite correct the thread is about immersion heaters not batteries (or elec car batteries for that matter)

 

[Mark Gee]

Yes, hysterisis has been a problem, and I had to modify my circuit after a few weeks as the relay couldn't cope with the rapid switching.
I have never used, or know anything about micro-controllers, so I can't comment on your suggestion, but good luck.

so get it to turn on the immersion for 5 minutes or 15 minutes! if the sun is shining now you could reasonably expect it to shine for another 5-15 minutes...although obviously it might not. But it probably would.

 

[suntrap]

Because weather is irregular and changes.As I said originally "what if the sun don't shine?" By simply spreading the "immersion-on-periods" throughout the day you are more likely to coincide with the sun being 'on'

No you aren't. If the weather is truly random, and I think we both agree that it is, then pick any time during the day and you will have exactly the same chance of the sun being out.

eg my strategy would work better than yours on a day when it is cloudy in the morning and sunny in the afternoon.

And my "strategy"* would work better than yours on a day when it is sunny in the morning and cloudy in the afternoon. They cancel out. You cannot make any predictions about a random value based on when you sample it.

*I'm inferring that you mean I'm suggesting putting the heater on for one long period in the morning.

I would also of course refine it to leave periods of no immersion for planning to consume elec for meals/drink/dishwasher/etc

That is indeed a sensible use of a timer.

 

[inie meanie]

Because weather is irregular and changes.As I said originally "what if the sun don't shine?" By simply spreading the "immersion-on-periods" throughout the day you are more likely to coincide with the sun being 'on' eg my strategy would work better than yours on a day when it is cloudy in the morning and sunny in the afternoon. I would also of course refine it to leave periods of no immersion for planning to consume elec for meals/drink/dishwasher/etc

Although your second point is quite correct the thread is about immersion heaters not batteries (or elec car batteries for that matter)

Err I think that you TOTALLY missed the point of this blog. It was set up to discuss a way of automatically measuring and controlling the spare power so that it can be used to heat your water for free. Setting a switch for random periods during the day is not controlling anything. It may be cheap to setup but will quickly cost you more than the systems setup by members here.

 

[bradburts]

Hi,
I am about to have a PV system installed. I did not understand the need for the system to be patched in in a particular way so as to make easy measurements etc. Please explain (in simple language!).
I presently have an OWL energy monitor in the external meter cupboard and would expect to attach another current sensor somewhere after the invertor in the loft so don't understand the need for a seperate panel.
Looking back at earlier suggestions; a light dimmer board was thought to be a simple solution, having all needed interference protection etc, but was rejected through having a potentionmeter control.
It may help to note that you could use digipots, digitally controlled potentiometers, to replace the light dimmer potentiometer. You would have to use a microcontroller to control the digipot of course but to my way of thinking the microcontroller circuit has got to be the best way forward with its meter, display and perhaps wireless control capabilities.
I will research and post suitable devices and provide programming examples if converting a light dimmers make electrical sense!
PS
Think the SUNNY Home Manager is Euro 1,300, which is a lot. A small linux wireless microcontroller would cost around £30, software would be technically straight forward but take the usual 'while' to write code for & test.

 

[suntrap]

Hi bradburts - more ideas flowing in! I too have an OWL, given to me as a present. This sort of energy monitor is compromised in that it can't determine power factor, but this shouldn't be a big problem with solar inverters as they have power factor correction. The other annoying thing about it is that the resolution is not great - the reading goes up and down in fairly large steps.

I think that the issue of making easy measurements is that you need a single-core cable (such as a meter tail) to clamp the current transformer round; if it's twin core the opposing currents will cancel and you will get no reading. If your installer uses a separate "garage unit" (small consumer unit) just for your PV installation, there will be meter tails from this which you can use to measure your PV current. My installer put an RCBO in the existing consumer unit (it's split load and there was a spare way on the unprotected side). Although this means there are no meter tails, he pointed out that there is space in the consumer unit to clamp the current transformer around one of the twin and earth cores where the outer insulation is removed, and that's what I have done. The OWL's reading is a bit erratic but it still gives a good indication, which tallies broadly with what the inverter is telling me.

I too am interested in getting an extra current transformer for my OWL, as I noticed the transmitter has three sockets on it (unless that's just for three phase supplies?). I haven't investigated it further yet, though.

 

[Graeme Harrold]

Simples use SMA Inverters. My immersion kicks in when the inverter is at 1.8Kw using the built in multifunction relay. FREE to use, and the additional kit cost about £50

 

[suntrap]

Not so simples - that neither provides proportional control, nor does it take any account of other loads in the house, nor does it allow you to use your existing immersion heater (so if you need to heat your water with 3kW in an emergency, you can't).

I think we need a FAQ for this thread!

 

[Graeme Harrold]

Actually with very little on in the house during the day, its not a problem. Also have the immersion switched between 1.5 and 3kW, so no need to change that either all with an 89p diode.