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

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Posted by dermotmcdonnell on April 17, 2006, 9:03 pm
 


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 Im 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:

www.realgoods.com/renew/shop/product.cfm/dp/1200/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 Murphys Law)? Anyone done this already?

Any and all advice welcome.

TIA, Dermot.


Posted by dermotmcdonnell on April 17, 2006, 9:34 pm
 


The link should be:

http://www.realgoods.com/renew/shop/product.cfm/dp/1200/sd/1204/ts/1025078

Sorry!


Posted by dermotmcdonnell on April 18, 2006, 12:31 pm
 

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 its 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


Posted by Colin Wilson on April 18, 2006, 10:15 pm
 


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


Posted by Colin Wilson on April 17, 2006, 10:26 pm
 


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)

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