Will an immersion heater still warm up with a restricted current?

Kernel_Sanders

I'm having solar panels fitted, which will be producing nearly 4 Kw in the summer. Even this isn't enough to fully power an immersion heater, so what I want do is to temporarily cut the incoming supply from the mains so I'm not using expensive daytime power. Am I right in thinking the element will still warm up, but not as much? I realise that all other household appliances will be starved of power during this period.

HappyMJ

If your system can provide off grid power but can't provide the current requested then it won't supply any at all so the answer is no.

partan

HappyMJ wrote: »

If your system can provide off grid power but can't provide the current requested then it won't supply any at all so the answer is no.

do they shut off if the voltage dips below a certain point?

am just bein a nosy buggger like :cool:

HappyMJ

partan wrote: »

do they shut off if the voltage dips below a certain point?

am just bein a nosy buggger like :cool:

Depends on how they are designed. It should cut off the power supply if the current drawn increases to a point where the voltage drops below a certain level. A fuel driven generator would increase it's generating capacity by powering the engine more to maintain the voltage however a solar system can't do that so it should cut off supply.

DVardysShadow

The question is a bit unanswerable from here. Photovoltaics produce DC at a voltage all of their own. They could feasibly feed a DC immersion heater of the right voltage [which will not be commercially available] and the heat output would vary according to the degree of illumination. But photovoltaic cells are connected to your mains via an inverter which provides 230V 50Hz AC. Doing what you want all depends upon the capabilities of the inverter. I dare say that the inverter may even refuse to work if there is no incoming supply voltage to set the AC waveform required.

ormus

only the biggest elements need 4.5kw, most will require just 3kw.
at 240v.
can your system deliver that?

TimBuckTeeth

As mentioned above the inverter will shut down if input voltage drops too low. You wouldn't want a varying output voltage, although it would be fine for the immersion heater it could play havoc with other appliances connected to the mains.

If the sun is not bright enough to allow the panel to operate at near full capacity there will no output at all from the system if the (3kW) immersion heater is switched on, or it will never work if the load is over the 4kW maximum output.

Heating water with power from photovoltaic solar panels is very inefficient, a direct water heating vacuum-tube solar panel would be a much better solution. I'm not sure on the figures but the vacuum-tube panels are about double the efficiency of the photovoltaic panels then there is not the loss with the inverter. Some heat would be provided on overcast days compared with none at all with a photovoltaic panel (unless it is hugely oversized, ie. several times bigger than the roof).

TimBuckTeeth

Deleted - duplicate post

Kernel_Sanders

TimBuckTeeth wrote: »

the vacuum-tube panels are about double the efficiency of the photovoltaic panels then there is not the loss with the inverter. Some heat would be provided on overcast days compared with none at all with a photovoltaic panel (unless it is hugely oversized, ie. several times bigger than the roof).

I think you have this the wrong way round; solar PV works on daylight whilst the tubes work on radiated heat.
It would only produce 3Kw from around March to September, and then not in the early morning or evening on most of those days.

TimBuckTeeth

Surprisingly the vacuum tube panels produce heat output on all but the dullest of winter days as sufficient infra-red passes through the clouds.
Where the photovoltaic panels are producing 500W due to a dull day the output would cut off if the immersion is connected, giving no heat output at all, but the vacuum-tube panel would be heating the tank, albeit at a slow rate.