DC heat [RE-wrenches]

Todd Cory, Mt. Shasta Energy Services toddcory at finestplanet.com
Wed Nov 23 09:27:46 PST 2005


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Around here we have abundant sunshine for 7 to 8 months. Our grid tied 
3.2 kW PV system banked a utility surplus of 1700 kWh last summer which 
we are now "spending" to heat our home with the heat pump.

I also used to cringe at the thought of using solar PV for heating, but 
with a grid tied system, on a yearly net metered schedule, one can bank 
power all summer, when solar works well and energy use is low, to offset 
the winter months when the situation reverses... solar is minimal and 
energy uses (ie: heating) is high.

Generally, heat pump efficiency is compared with resistance electric 
being 100% efficient. With that as the basis, a heat pump that delivers 
double the btu's /kWh is 200% efficient. Triple the btu's is 300% 
efficient. At around 45 degrees our unit (COP 3.08) is 300% efficient. 
This drops to about 225% at 20 degrees F. Still WAY better than 
resistance electric.

So yes, solar electric heating is not only doable but a reasonable way 
to avoid fossil fool use. This avoids the issues of embedded energy and 
whether the grid will remain a usable energy bank for the foreseeable 
future. With peak oil looming, the reliability of the electrical grid 
(IMO) is in question.

Todd


Hugh wrote:

> At 10:59 am -0800 22/11/05, Ian Woofenden wrote:
>
>> Hi David and others,
>>
>> Off-list for this terminology discussion.
>>
>> I love saying that resistance heat is 100% efficient, 'cause it 
>> shakes up people's perceptions from the old days, when resistance 
>> heat on RE was out of the question.
>>
>> But I wonder if or when we'll come to a new paradigm in this 
>> terminology. Heat pumps are 200 to 400% efficient if we use the 
>> present definition as a standard. And how efficient is passive solar 
>> heat compared to resistance heating via PV?
>
>
>
> Efficiency is just a comparison of ins and out.  I mostly use it for 
> energy so we can measure energy fed into a machine and compare it to 
> the useful energy coming out.  In the case of an electric heater, we 
> get 100% out as useful heat.  In the case of a heat pump we have 
> multiple energy sources - electricity and low grade heat coming in - 
> and we have higher temperature heat coming out.  It cannot be more 
> than 100% efficient, but it gives us a lot more heat for the same 
> electricity.
>
> I cringe a the idea of using PV generated electricity for heating 
> because it is much more efficient use of materials and money to 
> produce heat by solar collector (water heating etc).  Here I am 
> talking costs in versus result or even the environmental impact of the 
> product (embodied energy) versus result.
>
> And yet electric heaters are commonplace still, and any PV that is fed 
> into the grid will be used in part for heating.  Electricity must be 
> too cheap!
>
> As for terminology, efficiency can be used for many different 
> variables, although I normally use it for energy.  But of course the 
> energy around us is almost unlimited, so we have to consider whether 
> efficiency is important, based on the quality of the energy that we 
> are using and its cost.
>

-- 
Todd Cory
KE6SXS
toddcory at finestplanet.com
Mt. Shasta Energy Services
License C-10 # 811428 
P.O. Box 689
Mt. Shasta, CA. 96067
(530) 926-1079

http://www.lifeaftertheoilcrash.net/

"To announce that there must be no criticism of the president,
or that we are to stand by the president, right or wrong, is
not only unpatriotic and servile, but also treasonable to
the American public." - Theodore Roosevelt, 1918


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