Immersion Heater - PV electricity

[echase]

My Aurora inverter has an RS485 interface whose protocol is actually known, and someone has written Linux software to interrogate it, to get instantaneous output figures .

Does not solve the need to measure consumed power too if controlling the immersion.

 

[suntrap]

Indeed not, but it provides one measurement.

 

[Mark Gee]

Re: Immersion Heater - PV electricity - MISSING THE POINT

What if "the sun don't shine?"

Surely a simple "solution" is to use a long 1kw element and a mechanical timer. With the timer set it to come on for 15 minutes every 'approproate' hour. This will trickle feed and topup the temperature whilst averaging out the time when the system is not generating anything.

Not perfect but a simple compromise. If the system generates more than 1kw then sure it is being 'wasted' but less so for people like me who work fom home a lot.

Total Cost : about £30? and two hours labour.

although not sure where you get a long 1kw element from

 

[suntrap]

I think you are misunderstanding how domestic PV installations work, which happened with some people at the beginning of this thread, before the situation was explained clearly to them.

To summarise, there is no such thing as "averaging out". Your meter does not go backwards when feeding power to the grid*; it only goes forwards when taking power from the grid. Therefore, if the immersion heater ever uses power from the grid, it will cost you and you won't get that cost back.

Hence, you need a system which ensures that the immersion heater is never fed more power than the surplus (generation minus consumption). The simplest way to do this is with a relay that switches it on and off (controlled by determining the surplus, not from a timer), but this is sub-optimal because you will never benefit until there is 1kW surplus. Better is proportional control, which will allow you to use whatever surplus is available, even if less than 1kW. Moreover, as you get to keep your current 3kW immersion heater, you can benefit from a surplus of more than 1kW, and you can use it as originally intended if your boiler fails.

By the way, long 1kW elements were also discussed earlier in this thread. They cost more like £80 than £30.


*in a few cases the meter does go backwards, but electricity companies seem to be becoming more aware of this, and when they know you have PV (which they will, because you have to tell them in order to get the FIT), they will replace your meter with one which doesn't.

 

[Mark Gee]

thank you. I do understand how it works. I appreciate that my idea will sometimes cost me as I import from the grid but sometimes, often, it won't.

Because this thread is so long it seems pretty obvious that there is no easy and cheap and legal technical solution.

My idea is very simple. Any savings of proposed techincal/battery solutions should be compared to such a simple idea to implement rather than the situation where most generated power is exported 'wastefully' to the grid.

If there are any simple/cheap ideas I would REALLY like to know as I am about to get a 4 kWp system and won't use all that I generate.

 

[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. :- )