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Wednesday, April 17, 2013

How It Works: Off-Grid Solar Electric

Purpose.  Provide all electrical power with no tie to grid.

How It Works Summary.  Photovoltaic panels convert sunlight to DC electricity which is stored in battery bank and converted to 110V AC for usage.  Gas-powered generator backup.

Cost.  $30,000 including installation.  Also received large tax credit.    Battery replacement in 7 to 10 years biggest anticipated future cost.    We have no electric bill and never will.

System Components

12 Photovoltaic (PV)  Solar Panels each capable of producing 250 watts DC max for a total of 3000 watts DC max.  Actual wattage depends upon amount of sunlight which is a function of solar veiling (trees, structures, clouds, fog, snow, rain, ice..) and solar angle.  No trees and structures veil our panels.  Angle impact changes throughout the day, peaking at noon and falling to zero  between sunrise and sunset.   Angle impact changes throughout the year,  maximized on summer solstice and minimized on winter solstice. 

16 Deep Cycle Batteries each capable of storing 2500 watt hours for a total of 40,000 watt hours.   Batteries must be kept above 50% capacity (20,000 watt hours).    Battery depletion rate is roughly proportional to amount of electricity used.  Since our home typically draws only 100 watts at given time of day, the batteries store 4 days of electricity.  Upon hitting the end of useful life, our lead-acid batteries will be 90% recycled.

Tractor-powered PTO Generator capable of producing 6000 AC watts to recharge batteries before they fall below 50% capacity.   With generator plugged into 60amp AC service outlet and attached to PTO, diesel-fueled tractor is manually started and run 4 hours to recharge depleted battery bank. 

110V AC Electric Panel.   Like any home is USA, provides 110V AC power to outlets and fixtures. 

Multi-function Invertor.  Outback FlexpowerOne intelligently charges batteries from either the DC solar panels or the AC generator.  Draws DC power from batteries, converts to AC and routes through electric panel to provide home power.    Monitors and displays amount of solar-generated power, battery capacity and amount of power house is drawing. 


Maintenance.  Monitor battery capacity and recharge with generator (when approaching 50%).  Replenish water in battery cells (every 3 months).    Start battery equalization program (every 3 months).  Scrape snow off solar panels (as needed). 

Report Card.   Warm Season = A.   Cold Season =  A-.    (See blog post for details).

Biggest Challenge.  Can we get away from the house for a week?  Yes from February through October.  November through January remains uncertain.  (See blog post fordetails).

Biggest Success Factor.  Low power house (100 watts typical).  No AC, dishwasher, clothes dryer, or microwave.  100% LED lighting.  Ultra-efficient fridge and freezer.   Water pump is shallow not deep-well.    No toilet flushing power.   LP gas stove. 

Enabling The Connection.    Behaving like any plant, solar panels make transparent the amazing power of the sun.  Like the Land, off-grid  solar electric follows the seasonal cycle of scarcity and abundance, conserving energy in winter and joyfully “wasting” power in the summer. 


  1. This blog is really very informative and I would like to see some more blogs on this topic as I want to learn about different kinds of batteries for my engineering study. | | deep cycle battery by Aussie Batteries Solar | deep cycle batteries by Aussie Batteries Solar

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