[RE-wrenches] DC, or not DC, Dat is Da question (Two Load Questions)

[Larry Crutcher, Starlight Solar Power Systems]

Why would one specify DC voltage appliances or lighting for off grid systems today when we have sub-buck-a-Watt PV solar power?  If you have space, you can make the added power that conventional AC appliances draw for very low cost. It could even be argued that the cost for DC items, wiring, distribution gear and labor will cost much more than simply adding more PV solar and staying all AC.

I don't like wasting resources and I understand old school thinking when PV modules were very expensive, but with high efficiency AC appliances and low cost inverters and PV modules, does it still make any sense? Shine some light on my thinking.

Larry Crutcher
Starlight Solar Power Systems





On Dec 10, 2012, at 9:12 PM, Allan Sindelar wrote:

Wrenches,
We still try to encourage prospective off grid customers to do a full load analysis as an initial step in the system design process. To the point:

1) What is a good watt-hours/day figure to use for a typical, modern, new, carefully chosen, fairly large conventional AC chest freezer, if kept in a heated indoor location? Assume 65 degrees and seldom opened.

I will encourage that the freezer be located in a shaded, protected outdoor location, in order to greatly reduce winter energy consumption, but I need a good base figure to work with. 

The proposed system will most likely be 48Vnom, so a Sundanzer or similar DC freezer is out.

2) Same question for a ceiling fan, for general slow circulation of winter heat. The energystar.gov list gives relative cfm efficiency but not wattages. Is 55W still a good figure to use as a default?


I have attached a condensed energystar.gov list for the freezers, but wonder what other off grid Wrenches typically use. Also, I'm not sure that Wrenches posts allow attachments, so this may not appear with my message.

Thank you,
Allan
-- 
Allan Sindelar
Allan at positiveenergysolar.com
NABCEP Certified Photovoltaic Installer
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder and Chief Technology Officer
Positive Energy, Inc.
3209 Richards Lane (note new address)
Santa Fe, New Mexico 87507
505 424-1112
www.positiveenergysolar.com



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