Using a DC Water Heating Element as a Dump Load for a Renewable Power system.

[dermotmcdonnell]

I want to use a DC Water Heating Element as a Dump Load for a 48v/30amp small wind turbine and/or photovoltaic set-up. Say I=B4m looking at an absolute maximum power output of 1.4kW. I would like the power to go straight from the renewable system to an immersion hot water tank DC water heating element. This would save a lot of expensive electronics and it should also minimise power losses. There are some very good, cheap, small wind turbines in this power range available. I want to install this for my mother and she lives in a very windy area in the West of Ireland so the pay back time should be short.

As Mike Dodd has pointed out such DC Water Heater Elements are available here:

Is this safe to do or will I fry the wind turbine generator? What kind of life times do DC water heating elements have? Do I need another fail-safe dump load and the associated electronics (probably, I suspect, to avoid Murphy=B4s Law)? Anyone done this already?

Any and all advice welcome.

TIA, Dermot.

[dermotmcdonnell]

The link should be:

[Colin Wilson]

Out of interest, since you`re talking about

[sam]

If it is to be 'interconnected back to the mains network' then why not use that as the dump load?

When the batteries are fully charged, and the hot water is fully heated, then the surplus can go back to the grid?

Can you tell me what sort of system YOU'RE using?

Cheers,

[sam]

Nah, I don't think you'll fry the generator with the DC load. If the turbine can't supply full power to the element, it will just turn slower or not at all.

Actually, I don't think you really need any dump load with this sort of system. All that will happen is that the solar cells will get hot and the turbine will spin at a rapid rate. Perhaps a mechanical arrangement to turn the turbine out of the wind if it starts spinning too fast.

Cheers,

[meow2222]

have you calculated payback time?

DC heater element casings last the same as ac, and casing failure is common cause of end of life. The element itself will be more robust than mains ones.

NT

[dermotmcdonnell]

Thanks you for your help and interest.

What I will do is connect the small wind turbine directly to the water heating element in the immersion water heating tank- no batteries, inverter, charge controller, etc. Cheaper and less power lost that way which means faster payback time.

Not using any kind of protection system (dont know what G83/1 is). The turbine furls nicely in high wind but keeps producing power :)

Pay Back time quick calcation: Mean Wind Energy where my mum lives

600w/sq.m. (see map ref below), Turbine efficiency 35%, Blade radius 1=2E045m =3D> energy capture area 3.43sq.m, cost of electricity in Ireland 14.45 c/kWh (incl vat @13.5%), cost of small wind turbine incl shipping and mounting pole 2100e (incl VAT @21%), DC heater element and wire, 100e (incl VAT).

Govt subsidy/grant for renewables in: Ireland - 0%, UK circa 1000stg, Spain - 50% etc

Total costs:

2200e (about1475 sterling - VAT is lower in the UK)

Annual power saving:

0=2E6kw/sq.m*3.43sq.m*0.35%eff*24hrs*365day*0.1445eu=3D950e (655stg)

Payback time: about 2.3yrs without incl costs of capital and assuming electricity costs do not change. If your govt gives a subsidy for renewables then it=B4s a no brainer even in a medium/low wind area. I also expect power costs to rise over the next few years.

Wind Maps:

[Colin Wilson]

I`m not, hence the question - although I do have an interest in how it all hangs together (or not !)

[Colin Wilson]

If you`re not looking to "export" any excess generation capacity it won`t apply to you afaik - although if you plan to hook it up to your existing wiring so that it may potentially backfeed onto the mains network it probably would apply :-} ?!? but depending on location and who your supplier and / or network operator is, different rules may apply.

One of the first hits in google gives...