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[aprssig] Shack backup power

Bob Bruninga bruninga at usna.edu
Sun Sep 11 20:08:16 UTC 2011


>  … please tell this to the grid-tied people among
> the 2 million who went without power in the 
> American SouthWest recently or among the millions
> in the NorthEast after Irene.
>
> Yes, Bob, in a perfect world untroubled by extremes 
> of weather, grid-tied makes sense, but if we learned 
> any lessons from this recent bout with Ma Nature we 
> would start taking greater account of outages.

Bryan, good point.  everyone should consider their emergency backup plans (independent of their economic energy plans). 

Grid-tie makes ECONOMICAL ENERGY sense by a factor of 3 to 1 over battery storage systems.  Grid-tie Solar systems this year are delivering economical energy at 7 cents/KWH, cheaper than coal.  This economy is available 99+% of the time.  

But you are correct to point out that grid-tie also has NOTHING to do with emergency power.  That is a separae problem and separate solution like for everyone else.  The power needed to keep the refrigerators and freezers going for 3 days is only about a dollar.  A 1 kw generator and a can of gas is hard to beat for economy. 

For those with grid-tie solar as a daily source of energy, I agree, a pair (or two) of golf cart batteries (not a whole house ton of batteries) and a 1200W inverter should be able to keep the refrigerator/freezer and enough lights going indefinately.  Though 2400W would be more luxurious so that one did not have to worry about when the wellpump, freezer and refrigerator all need power at once.

My caution, was not to be sold a whole-house system of batteries at 10 times that cost, when a much smaller emergency system is possible.  Unless again, one cares more for comfort than about economics.
  
>On Jun 4, 2011, at 4:58 PM, Bob Bruninga wrote:
>
>> For a shack system [or any battery storage system],
>> designed about one's average operating load, 
>> on any day when one does not fully use the [batteries]
>> to that average, then all excess solar energy is 
>> also wasted, because the batteries have no room 
>> for today's excess solar power.. (Generally).
>> 
>> That's why grid-tie wins hands down.  Every penny 
>> of solar energy is credited to you no matter how 
>> or when you use it.[99.8% of the time].




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