Five Letters Re: My Home Energy Backup System

As a solar power contractor/installer, I can tell you that David L.’s power plan is a solid one.
One thing he left out was the 30% Federal Tax Credit (not just a deduction) offered against the cost of residential renewable energy systems, including of course solar.

A synopsis of the Federal tax credit as well as all available state credits (some huge) is online at the Database of State Renewables & Efficiency (DSIRE).

Also, Eco Business Links keeps an updated listing of the lowest available prices on solar panels, inverters, and both on and off grid systems. 
230 Watt panels like David used can be had for less than $350 these days, thanks to a glut in the panel market. (There was no “Green Jobs” revolution [as had been promised]). – Bo in The Sunny South


I thought that this was an excellent persuasive essay on sustaining power in bad situations, and in carefully budgeting critical items. 

My thoughts on scaling these ideas up or down are as follows:

If you work around computers, most companies throw away UPS systems, which can vary from 200 to 3,000 watts. The gel cell batteries inside are all that goes bad 95% of the time. By soldering extension leads to the battery wires, you can hook up external 12, 24, or 48 volt batteries as appropriate. You now have a battery charger that will keep your batteries from going bad (sulfating), and when power goes out, you have 120V.  Best of all, “free leads to redundant.” Make sure you can turn the UPS on with no 120V power applied. Real solar power inverters are much more efficient, but cost $2,000 and up.

Running an inexpensive inverter 24 hours a day will take a lot of your solar systems output. My $200 48V 3000W APC brand UPS takes 80W from the batteries with no load, so that would be 2 kwh over 24 hours. Instead, consider wiring your retreat with a 12V bus. For lighting. LED auto bulbs are inexpensive and widely available. This can also power your security DVR and monitor (new ones are 12V) and perhaps a 12V laptop and router. We use a 12V RV pump to feed domestic water from a tank as a well backup. Keep your loads light, with heavy loads close to the battery, and size your wiring and fuse everything appropriately. 12V DC refrigerator/ freezer  units are now available or $400 or so and are a good option, with mine pulling about 60 watts at 12V. You might be able to find good salvage yard 12V batteries and parallel them.

If you are in the hot humid south, I highly recommend mini-split air conditioners and heat pumps. They have energy efficiencies up into the 26 SEER range, are very quiet, and can air condition (and heat) the core of a home, much as a woodstove does in the wintertime. They rectify the incoming AC power to run an electronic variable speed compressor drive, so the compressor has low starting current and throttles back in operation. They are very quiet, inexpensive compared to central A/C, and easy to install. If you install one yourself, make sure you use a 2 stage vacuum pump, the R410A compressors seem picky. Carefully check for leaks, the high side pressure is 600 lbs/ sq. in. I look forward to 48 volt DC units which soon will be available.

I second the recommendation on the Outback FlexMax charge controller. I have tried the inexpensive Chinese controllers, they are not MPPT as advertised. The American controllers are the standard of the world, buy one, unless you are building a tiny system. When you buy solar panels, search for the lowest cost per watt. The range of prices is extreme, and you might want two sets–in case of EMP or hail damage. – J.M. in Oklahoma

That was an excellent article by David L. on his backup power system. I run a very similar system but also have hydro power except in the summer. The hydro is set up to match the 48 volt 390 Amp Hour battery bank and connects directly to the batteries. The Outback will manage any excess power through a load dump. The Magnum inverter operates just like his setup and gives the ability to limit power available for battery charge vs. shore power. So I have no problem running the small Honda generator at the same time the charge controller is feeding photovoltaic (PV) panel power to the batteries. Hydro running at the same time is also not a problem.

I’d like to add that for those wanting a similar setup using made in USA products to look at Magnum Energy Inverters, and Midnight Solar Charge Controllers. I have no connection with either company other than as an end user. I believe Mastervolt is/was a Dutch Company bought out by a US company, but the Combi Inverters are made in China. They seem to have an excellent reputation in the Marine/Yacht market, but I don’t believe the Combi inverters are rated or UL listed for use in the US. It doesn’t mean much unless you are dealing with a code inspector. For those interested in escaping via sail power Mastervolt has some very interesting hybrid electric propulsion systems that charge batteries while you sail and give some limited propulsion when you are out of wind.

For long time system life I advise people to look into Edison type nickel iron batteries. They are reputed to last a long time and can be rebuilt easily. The main drawback seems to be higher internal resistance which may limit charge/discharge rates, but that may fit in well with the small generator/small load concept.  I have not tried them yet but intend to investigate further.

One other point. This should not come as a surprise to anyone, but here in the nanny state of Kalifornia, it is illegal to run your little Honda or Yamaha generator on propane. So is looking at a steelhead trout like he might taste good. Next they will outlaw flat sheets and double sided mattresses–wait they already did that. I can only say that the positives outweigh the negatives here. I have unlimited gravity fed water, abundant fish and game, the conveniences of the city at the front door, wilderness at the back door, fantastic soil and growing conditions, and I won’t need to chop much of the unlimited firewood for winter. The only problem here is that everything is illegal, unless you want to grow pot, then everything is ok and you won’t be bothered. The felons held in the Supermax prison at the fairly close Pelican Bay don’t bother as much as the ones held in Sacramento or DC.

Stepping off my soapbox, I’ll just mention that a nice upgrade to David L.’s system would be to spend perhaps another $1,200 to go up to the Honda 3000 with automatic electric/remote start capability. You can then add a module to the Outback charge controller or Magnum inverter to give you an automatic generator start capability. This capability fits in well if you are running off a large propane tank, but makes less sense if you run off a small fuel tank. Stand-alone automatic generator start modules are also available. – Chris B.


I read David L.’s well written paper on home power generation with considerable interest as it parallels our system/development/needs.  There are only two items I would question:  First – Why all the concern over an 11 cubic foot refrigerator running long term?  David does not share with us the total number of stomachs that might be sharing this refrigerator, but with just two people the freezer section (assuming a 2 to 1 refrigerator to freezer ratio) of only four cubic feet will be empty very soon.  This, and the fact that any vertical system designed to ‘made cold’ suffers a nearly 100% air exchange every time the door is opened.  Having lived through the Columbus Day Storm in Portland, Oregon and being without power in the heart of the city for over three weeks drives this point home with me, and probably dates me also! 

Our solution is to have two medium size chest freezer units.  One of them is about 13 cubic feet and the other is 16 cubic feet.  Both units are run packed as full as possible, even if we have to fill up unused space with gallon water jugs as air is one of the hardest things to [keep] cool.  Next, the units, which are normally set cold for veggies and very cold for meats, are both re-set to just veggie cold.  That will still keep the meat well frozen for several months.  It is just that freezer burn will happen sooner and, in a grid down situation this factor drops way down the list.  Being chest units we only loose around 10% of the cold air when we open a lid, and we only open one lid, and only once per day.  Our system is to re-distribute the meats and veggies more evenly for a grid-down.  We will only eat out of the smaller unit until it is empty, then re-fill it from the larger unit, replacing the cubic feet removed from the larger with the gallon water bottles (a good source of non-contaminated water if you filled them correctly in the first place.)  As you can see, with this system we will be running both units at first, then only running the small unit when the large one is emptied.  We still retain the ability to chill out large cuts of meat, as in elk hindquarters, etc. as they become available which in our area can be quite often. 

Second – David does not share with us his location.  We live in the Oregon High Desert area with the expected wide temperature swings from day to night.  While we have a couple of small window unit air conditioning units we are agreed they will not normally be run and reserved only for use at our medical teams’ discretion.  (Yes, I have verified our generating abilities include starting amp loads).  – CentOre


Hi Jim,
I just wanted to comment on David L.’s article on his energy back up system. He states that:

 “I don’t run the solar charge controller and the inverter/AC-charger at the same time so as to not cause a conflict between the two chargers. “

There should be no conflict when running the FlexMax charge controller and the inverter charger at the same time. I do it all the time with my system especially if it is very cloudy and I want more power or to charge the batteries. The charge controller and the inverter when charging produce DC power not AC where there would be synchronization problems to deal with. – Tim K.

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