Longer immersion

In theory the US mains is actually 120V but I don't know if the transformers you purchase are truly 110V or 120V. Obviously there is load regulation on top.

To get 2kW from a 3kW inverter you need sqrt(2/3) x 230V which is 0.82 x

I would use say a 230V to 48V transformer, to drop to 182V

Some might think a variac might be idea, but the issue with those is the limited current capability they generally have, and so you would need to specify a 3kVA variac.

So 500Ah at 12V or 125Ah at 48V ? That sounds an expensive battery.

There are pieces of kit that are specifically designed for the purpose of sending excess power from a PV array to an immersion heater. However most are expected to be hardwired to mains rather than a Lithium bank. I would strongly suggest you research these, but only if your batteries are regularly at 100%.

Hmm, well mine is not that long but it still heats water for a bath as the water changes itself around inside, you can hear it sometimes. The not enough for a bath syndrome unusually comes because the hot water comes out of the top and the cold goes into the bottom so the longer it takes to fill a bath, the longer there is to cool the hot water by the cold coming in. Brian

When there is power on the bottom element the water won't stratify because of the convection.

but both elements are on so any water rising from the bottom element will be heated again by the top one so a hotter top lay stays at the top

Ok but at least transformers are efficient, finding one may be the problem.

Yes but they cost about £300 plus fitting and just as easy for me to decide IF battery 75% charged AND earlier than 13:00 THEN run immersion one hour

Wrong. Water will ascend from the bottom element and therefore have to descend from the top region. It's called a convection *current* for a reason.

three 2.4 kWh or two 3.5 kWh packs works out about £2k either way

Top element is a heat source so its hot water has the lowest density

Only next to the element. The water next to the bottom of the bottom element will also be much hotter than the surrounding. Where do you think that goes, and how does it get replaced?

If this is a standard, vented system, how about adding another immersion heater boss (you can get retrofit ones) lower down?

Two standard 3kW heaters connected in series would give you double the resistance and half the power, giving 1.5kW.

It's not something I am sure of but from what I understand of thermal stratification the water that warms from the element rises and cooler water from above falls to replace it. Water is a poor conductor so cold water below the element does not get involved or get hotter.

If both elements are on together in series, the hot water rises to the top and cooler water drops to the lower element zone but the top element zone is still being heated by the top element as well as that part of the lower element in the top zone so that hottest water will never fall to the lower element zone or trigger the lower element thermostat, that will only be satisfied when the lower element heats up the whole of the lower zone. In the meanwhile the top will be above the desired temperature.

A bit beyond my capabilities and I think it needs to be 2kW to be optimal.

This is my first look:

There might be cheaper frame style transformers.

That would be 10% of your current installation costs, and would provide a full 3kW if there was no other power draw.

???? Its only rated to 0.5kW

Quite. 10A @ 48V is 500VA

Transformers are generally specified with a VA rating rather than power. Though in this case, given the resistive load they would be equivalent.

Forgot about invertor, wouldn't use a C dropper on one with such a large load. If the invertor will give 110v that'll provide about 1/4 rated power.

If it's a 12v source, easier, cheaper & more efficient to wrap resistance wire round the tank on glassfibre tape.

that's normally enough. Only if you more than drain all the hot in one run would you need more.

very heavy & unnecessarily expensive

An smpsu is yet another option.

the transformer's only supplying 48v, giving the element 192v.