low-wattage immersion heaters

[Grenage]

I'm installing a 2kw solar array on my garage roof; I won't be getting FIT or have a battery, so I'm looking at making the most it.

I was planning on putting a diverter in place so that the immersion heater in our hot water tank kicks in when there is a suitable surplus. You can get 1kw immersion heaters for exactly this purpose, but I figure at 2kw max output and a passive house load of maybe 400w, that's not going to kick in enough to make it worthwhile.

If I could get a 500w (or 750w at a push), I think it would be ok. There doesn't seem to be any demand for this, at least I can't find anything sub 1kw. I wondered if anyone knew if they existed before I scrap the plan.

Cheers!

 

[ericmark]

When living in a caravan I got a 500 watt heating element for the under sink water heater. Look on boat and caravan websites.

 

[ebee]

if you get a twin heater cylinder and wire the heaters in series it gives you more play on the actual Kw values you can achieve . ohms law etc

 

[DetlefSchmitz]

As I understand it, products like Immersun divert just enough power to the immersion so as not to export. There are other products with a similar function. The cost, however, may well not justify the saving.

 

[Grenage]

Thanks guys,

I've seen a few small heaters that are either not large enough in thread size, or not long enough to be worth using (we have gas, so there's only one immersion and it's at the top).

I'll wait until it's up and running and I see how much excess I generate. Maybe it will be enough for a 1kw immersion, but probably not at a level that's worth it, as suggested.

 

[Jackrae]

You may well find that the available 1kW unit suits your system. Solar panel output droops as the load increases. For example connecting a 1kW load to a solar array producing 48 volts with no load may well cause enough voltage droop to reduce the effective load to much less than 1kW

 

[Why Not Indeed]

For a resistive load, if the diverter only allows 1kW into it, surely it doesn't matter if the element is 1, 2, 3 or 10kW?
Or resistive heating not "linear" like that, ie does only allowing 1kW into it actually someone result in <1kW of thermal output? Can't see it being that though.

 

[Grenage]

Ah you are so right. I assumed that the diverter would in reality just switch the heater on or off. Reading some more, I can see that (at least some) will go in line and feed the excess.

I won't even need to change the existing 3kw unit!

 

[SUNRAY]

6kw 3ph heater (3 x 2KW) will give the options of; 2000, 1000 or 666W when wired in series

 

[ebee]

6kw 3ph heater (3 x 2KW) will give the options of; 2000, 1000 or 666W when wired in series

or 1333W with two in parallel connected to one in series with them - certainly gives some scope
(providing they are all two terminal heaters so can be wired in series and not commoned for a N connection)

 

[SUNRAY]

or 1333W with two in parallel connected to one in series with them - certainly gives some scope
(providing they are all two terminal heaters so can be wired in series and not commoned for a N connection)

All the 2KW 3ph heaters I've encountered have been 6 terminal whereas the 9KW have all been star connected 4 terminal. I don't know if that is standard or just chance.

 

[SpecialK]

Will your inverter be grid connected? I use a mk2pvrouter to divert any export to my immersion as I don't get paid for export.

 

[Grenage]

No there won't be any FIT as it's a DIY install. The immersion seems like a sensible way to go.

I've redone my calcs and can get an extra three panels on there (but flat), which will increase the yield a bit.

 

[SpecialK]

No there won't be any FIT as it's a DIY install. The immersion seems like a sensible way to go.

I've redone my calcs and can get an extra three panels on there (but flat), which will increase the yield a bit.

You can still export with no FIT (now SEG). Just you wont get paid for it. Using a solar diverter is the easiest way to heat an immersion as it will use the export up. Once my hot water tank is up to temp I turn the export limit on the inverter down to 500W so it just trickles in to the grid.

 

[Grenage]

Thanks buddy, looks like the way forward!