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´m 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 he

http://www.realgoods.com/renew/shop/.../sd/1204/ts/10...

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´s Law)? Anyone done this already?

Any and all advice welcome.

TIA, Dermot.

The link should be:

http://www.realgoods.com/renew/shop/...204/ts/1025078

Sorry!

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=3Fm looking at an
absolute maximum power output of 1.4kW

Out of interest, since you`re talking about 3.5kw output, can you tell
me what protection system you`re using ? (G83/1 applies I think, but i`m
not sure whether you`re looking to interconnect back to the mains
network)

Colin Wilson wrote:
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=3Fm looking at an
absolute maximum power output of 1.4kW


Out of interest, since you`re talking about 3.5kw output, can you tell
me what protection system you`re using ? (G83/1 applies I think, but i`m
not sure whether you`re looking to interconnect back to the mains
network)

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,

dermotmcdonnell wrote:

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´s Law)? Anyone done this already?


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,

dermotmcdonnell wrote:

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´m 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.

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

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
1.045m = 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:
0.6kw/sq.m*3.43sq.m*0.35%eff*24hrs*365day*0.1445eu=950e (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´s a no brainer even in a medium/low wind area. I
also expect power costs to rise over the next few years.

Wind Maps: http://www.awstruewind.com/inner/windmaps/Ireland.htm

Out of interest, since you`re talking about 3.5kw output, can you tell
me what protection system you`re using ? (G83/1 applies I think, but i`m
not sure whether you`re looking to interconnect back to the mains
network)
Can you tell me what sort of system YOU'RE using?

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

Not using any kind of protection system (dont know what G83/1 is)

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...

http://www.actionrenewables.org/grid.htm