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Monday, January 28, 2019

Solar power backup - my dirty little secret

When I tell people that I have a solar powered home they tend to assume that I have battery backup for power outages.  I don't.  I have a grid intertied system, so any excess power I generate gets fed into the grid for which I get a credit under net metering rules.  In essence the grid is my storage, because I can use up that credit in the fall and winter.  When the power fails my solar power system shuts down to prevent my power from back feeding into the grid and harming line workers (this is a federally mandated safety system).   

By not having a battery I have to use a different strategy to survive the winter storm power outages that average 3 days each year here in rural Maine.  Some outages have run over 7 days, while other are just a few hours.  I need power to run my home based business, well pump, heating systems, refrigerator etc.



Since my solar power system is not designed to incorporate battery backup, I decided to install an automatic home backup generator that runs on propane.  This generator starts up in 15 seconds and powers my whole property - house and workshop. Yes, I'm burning fossil fuel to generate power!  But the cost performance trade-offs made sense at the time.  

My 5kW Generac generator only cost me about $2500 in 2009 from Home Depot and has 700 hours on it as of January 2019.  I installed it myself and do most of the basic maintenance, but also pay for maintenance and repairs as needed.  The cost of installing a large battery bank would have been more than double my modest investment.  Lead acid batteries need frequent maintenance and replacement every 5-7 years and the cost just did not make sense to me.  Batteries also have a very finite amount of energy storage lasting maybe a day or so without recharging whereas the stored propane in my tanks can provide power for almost 2 weeks if needed.

After every snow storm, the first thing I do is clear the solar panels and collectors - even if the power did not go out.  If the power did go out, the generator turns on with in 15 seconds.  I want to get as much free solar energy as possible.  So I have a long snow rake that I use to remove all the snow - usually in the morning before the sun hits the panels.
time-laps video fo snow clearing
Click the image to see a time-lapse video of me clearing the snow on my property and solar panels in February 2018. 
There has been a change in the solar industry in the last year or so.  They are now offering home battery backups - whether or not you have solar power.  This is due the the plunging costs of large batteries like those use in electric vehicles.  Enphase, the company that makes the microinverters that I use have introduced just such a system, and there are many others like the Tesla PowerwallClick here for details about the Enphase battery system.  And click here to read an informative blog post from Energy Sage about Tesla Powerwall cost realities.  At some point I hope to install a system like this, but for now it is beyond my means.

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