Techno-babble redux

A friend wanted a summary of what our off-the-grid electrical system was.  So, I wrote him.  Sal said, “You should make a blog of it!’

“But I have said all this before!”

“Not so succinctly.  Do it!”

So, here goes: the system is: batteries, cable, inverter/charger, charge controller, relay and a tower (of sorts).

Batteries first – I have 12 of them. All the same size.  All the same age.  12 volts.  200 amps each.  8D’s are the designation.  Of the cheaper class, L-16’s are better.  Mine are very cheap at $150.00 each and they will live for about 7 years.  Surettes are expensive and will last 20.  But everyone ruins their first (and usually second) batch of batteries so go cheap for the first few years while you learn their ‘nature’ and the situation in which they live and function.

Batteries are almost sentient.  And they are eccentric to say the least.  My 12 are divided in 3 groups of 4.  Each group of four is wired in series to give 48 volts at 200 amp-hours. Then the three groups are wired in parallel to give 48 volts at 600 amp-hours. At our rate of usage, that will give us 3-4 days without a charge (from sun or generator).  Longer if we stayed with just lighting-only but we have screens and computers and all sorts of little ‘drains’ (like cell phone and computer batteries and such).

Cable is Teck.  Armoured.  Heavy.  Oversize because the array is placed in the optimum location (100 feet from the house) and we don’t want ‘voltage drop’.  Buy a size or two heavier than you think you will need.  That gives ‘capacity’ in case you add panels later.  Cable is expensive but two cables is dumb.  Ask me how I know that…  Better to go BIG the first time.
The same is true for the cable connectors on the batteries.  Spend time and money on that.  Those connectors are a huge deal.  Those little cables would ideally be bolted on rather than ‘slipped on’ like a car battery terminal because bad connections are the biggest drains in the system. Bolt-on hard bars is best.
I have 2100 watts of power on my array.  The array is about 120-150 sft.  It consists of a steel rack that sits on top of three scaffolds stacked to make about 15 feet in height.  This height pretty much eliminates any effect from tree cover.  If you are much further north, you may wish to go to four levels ’cause the sun is lower in the sky.  You can go higher but, after four levels you need to add additional stays.  I only have stays at the top of mine.  Any higher and I’d mid-stay, too.
My array is made up of 8 x 80 watt BP panels (640 watts) from the first few years and then 6 x 240 watt panels (1440) I added last year.  I combined the first generation system with the second.  You’d be more efficient, of course, going 240 watt panels from the start.
3000 watts in total is likely ideal for most modest OTG cabins.  I can’t see a minimal home of 1200 sft or less needing more unless you were driving electrical appliances (ours are propane except for the one-time uses like a toaster or an iron).  It is the fridge and freezer that drain you.  24/7/365.
I have two charge controllers.  The 640 watts go into an old-style PWM (pulse wave modulation) charger and the power feeds go into battery group #3 (the back end).  My MPPT charger is part of the OUTBACK ‘system’ that includes the inverter.  That takes the newer 1440 watt source and feeds that power into battery group #1 (the front end of the battery assembly).  This is a bit unusual. Most people prefer to use just one charge controller but I had two so I did it ‘my’ way.  Turns out that ‘my way’ is considered a little better (by the local techies) because the wave lengths of the chargers are slightly different and that seems to be a good thing.  I had no idea.  I just tried it and found out later from the techies that they are discovering it is better.  Luck plays a role in all of this.
OUTBACK is the best and most expensive inverter.  Plus it is the most confusing to figure out. The manual is complete gibberish.  Mine is 2500 or 3000 watts (either – can’t remember) and that is enough for me.  It basically means it can supply 20/25 amp service at 120 volts.  Typically normal houses have 100 amp service or nowadays 200 amp service.  But we OTG’ers are good at 25.  Some people go for two of them to get 50 amp service but then everything else has to be more as well.  Our house is wired conventionally with a 120v system.  .
I went 48 volts because 48 volt systems are the best – technically.  But now I would recommend 24 volt systems because Surettes can be configured cheaper in 24 volt systems than 48.  Plus there are more ‘minor’ accessories at 24 volts than 48 (like supplemental chargers).  A good (the only good one for OUTBACK, actually) supplemental charger (with genset use) is IOTA.
The relay device I use to shunt from one genset to the other depending on which one  is in use.  Total cost of the ‘system’ is likely around $12,000 – to $15,000 – for the parts.  It cost me more because some of the components were more expensive ten years ago.  Panels are cheaper.  Cable is more expensive.  That estimate does not count genset (ONLY consider Honda or Yamaha or diesel.  5000 – 7500 watt genset is enough). And that was me ‘scrounging’ steel for the array, making everything myself and doing everything myself.  I also got good deals on batteries.  You can do a good system for $15,000 if you scrounge a bit and do a lot yourself.  And you could easily spend $25K or more to duplicate the system we have by ‘doing it right’ and getting assistance.
There are some pics in the gallery alongside the blog.

6 thoughts on “Techno-babble redux

    • Me, too. I hope Elon Musk invents better batteries but don’t count on them being cheaper. Elon/Tesla Motors didn’t get rich by giving it away. Fortunately the Chinese are pumping out PV for their masses and their masses aren’t rich so that helps our masses. And the Chinese steal technology so they may eventually put out a cheaper Tesla battery. Still…as of today…I don’t think you can do a system like mine much less expensively (well, you could screw up fewer times, I suppose. Each screw up costs to fix).


    • I hope so but, of course, it is all still in a stat of flux. PV is ‘moving’, going ‘mainstream’ more and more. If it were me (and it is!) I would try to stretch my current battery bank as long as I can. BIG Li-ion batteries are the next to hit the market. They’ll rival Surettes. Thin-film will make it’s debut in such a way that your roof will be the ‘panel’. That will be a huge boost…..and a new way of roof building. And they are going to have to make good inverters (OUTBACK) more user friendly. Geeks take a few months learning Outback and non-geeks NEVER get it.


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