Time to get serious designing my off-grid home solution

Hey Travis,
I have a few misc. thoughts - in no particular order.

1) Internally (here at altE) we've become increasingly convinced that the new Midnite Solar lightning arrestors will provide better lightning protection for your system versus the traditional lightning arrestors. Check out the video on our spec page:

http://www.altestore.com/store/Enclosures-Electrical-Safety/Lightning-Protection/Midnite-Solar-Solar-Surge-Protection-Device-115V/p9546/

Another plus to them, is basically if they somehow do get fried, the manufacturer will actually replace them during the warranty period (and inexpensively after the warranty). Where as with the Delta lightning arrestors, they are more like fuses - they are expected to "pop" to absorb a nearby lightning strike. Once it's popped - time to get a new one.

2) A lot of the installers that buy from us really like the Soladeck combiner box that can be installed right on to shingled roofs. Makes roof penetration and combiner box mounting easier. It's designed more for high voltage systems, but could be used with lower voltage systems as well.

http://www.altestore.com/store/Enclosures-Electrical-Safety/Electrical-Enclosures/Combiner-Pass-Through-Boxes/Soladeck-DC-Combiner-Box-600VDC-120A/p9517/

3) Again for lightning protection, but in this case for your wind turbines, I learned a trick from a former NASA physicist to get charge to dissipate more quickly on your turbine tower and decrease it building up enough to discharge as a lightning strike. It's a little difficult to describe but here goes... Basically you make a kind of ball out of frayed out wires (say 10-12 AWG) all clamped together at one end and connect it to off of the side of the mounting pole if it's grounded or have it run to ground. The concept is that the increased surface area, and sharp edges of of all this cut copper wire will more easily discharge into the air than just the tower itself.

I know once customer of ours in a very lightning prone tropical location did this and they've not had lightning fry anything since (they did before).

4) Consider using an MPPT solar charge controller so that you put more of your solar panels in series, use smaller wire size and get overall higher performance out of your whole system. The one I'm considering for my house right now is Midnite Solar's Classic - right now it's the only controller that provides arc fault protection.

http://www.altestore.com/store/Charge-Controllers/Solar-Charge-Controllers/MPPT-Solar-Charge-Controllers/Midnite-Solar-Charge-Controllers/c1180/

5) In terms of mounting, I personally prefer the IronRidge XRS rail system because it requires fewer attachment points on your roof than other manufacturers seem to require - reducing your time on the roof and fewer potential holes in your roof means fewer potential points for leaking down the road too.

What voltage are you thinking of running your battery bank at? And what are you thinking for total power output of your inverter(s)?

I have a lightning arrestor on my garage system, so I'll have to remember to add it to the "shopping list" I'm creating for The Big Project as well.  At what point(s) would I put them?  On my garage system (4 sets of 2, 12v/125w modules) I have all the PV juice going to one combiner inside, and the lightning arrestor is mounted there.

I plan on using 48v batteries going to a pair of Xantrex inverters.  As for PV voltage, I'm using 24v on the garage.  Using MPPT chargers, I can go higher, so I still have some deciding to do.  I plan on building in some redundancy, so I won't be going near 600v for the PV modules.  The distance for the wiring will only be from the 1-story roof to the basement, so I shouldn't have to go too big with wire size.
Will do.  I like my C40 for my garage, but the MPPT chargers allow a lot more flexibility with PV input power.

I'll probably be building my own mounting solution.  I'm familiar with working with metals.  The roof is corrugated metal, and I'll be running grounds at all four corners of the building.


48v battery pack.  I'm running 24v in the garage, and it handles the loads I have there well.  For the house, I'll put two of Xantrex's bigger offgrid/gridtie inverters together for 220vac.  I'm going to try to assemble a preliminary list over the weekend.

My recommendations:

1) Don't mount your turbines to your structure.  Use a separate pole mount.  Also, rather than three small turbines (lots of moving parts) mounted low to the ground (much less wind), consider a larger turbine mounted on a taller tower.  I'm fond of my Bergey XL.1.

2) Choose a high-quality, long-lasting (and warrantied), deep-cycle battery bank.  I like Rolls-Surrette.  Also, opt for independently switched parallel banks in case you need to replace one or more batteries or perform maintenance.  This way you can keep power flowing to your house while one bank is offline.  This adds redundancy and reliability.  If you only want to buy one bank for now, pre-wire it to add a second or third in parallel later.

3) Run extra wires between your shed and your house now rather than trying to feed extra ones later.  E.g. you may want to run CAT-6 wire to send system data to a computer in the house.  Or coax for security camera feeds.  Or you may want to have an independent inverter for your well pump or other large load.  You may also want to (and I HIGHLY recommend to) run some DC loads in your house directly.  Pull all of these wires at the same time even if you don't use some of them yet.

4) Put lightning protection on your indoor breaker panels, because lightning can strike the ground between your shed and your house and overload your house circuits.  Also make sure to have a surge protector on your inverters.  Over-amperage protection (breakers) is not enough.

5) Don't put off the backup generator but don't go overboard on it either.  You don't need to run your whole house with it, just charge your battery bank.  A camping-sized propane generator ought to be sufficient.  Mine puts out just over 1kW, which is as much as my wind turbine is rated at top speed.  That's plenty to charge up the batteries.  The batteries themselves handle surge loads.  I.e. you may be running your 1kW generator to charge your batteries for an hour, and during that time, your well pump may pull 2kW for 3 minutes.  No problem.  You don't need a 2kW generator for that.

6) Opt for propane rather than diesel or gasoline for your generator.  Propane does not need stabilizers to keep for a long time, it cannot spill on the ground, and it doesn't gum up engines that may not run for 6-12 months between uses. 

7) Make sure to vent your battery boxes to the outside, store extra distilled water at all times (unless using AGM or gel batteries), and install freeze protection inside.  While charged batteries can go below freezing and be OK, they won't hold their charge as long and won't charge up as fully.  It's actually more efficient to leave a 20-40 watt light bulb on in there than to let the batteries freeze.  You'll have more usable power that way.  I have two CFL light bulbs (about 20W each) on a little thermostat cube which turns them on below 40.  My space is only about 5'x5' though -- you may need more heat than that unless focused near your batteries.  I would avoid heat tape or space heaters because of the hydrogen.

8 ) If using regular flooded batteries, buy water miser caps to reduce the number of times you need to top them up.

9) Make sure to size all of your wires big enough and use fuses where appropriate.

10) Be safe at all times.  Make sure someone knows you're working on electric before you start so they can check up on you.

    I am planning to take the biggest part of my house off grid. I have four windturbines and 4.2kw of solar. I have left my bank at 12 volts and have a 2250 ah battery bank. I have multiple out backs going to a hub and mate for the solar and the wind turbines have their own charge controller with a dump load.

  I've been told that a higher voltage system would be a better way to go, but I can walk into any parts store or r.v. dealership and walk away with 12 volt items I need for the house.

  i'll be hard wiring a aims 5000/10000 watt pure sine wave inverter into a separate braker box. I will put a disconnect between the braker box and inverter and one between the regular braker box so I can switch back and forth if need be.

  our next home will be totally off grid on a 12 volt system. I know it can be done. I set up a 12 volt system for a friend of mine. he has one outback and is running four 200 watt panels to charge 10 6 volt Duracell golf cart batteries. he has propane to run his frig, stove and water heater. if it storms for 6 days straight he will trip the braker between his braker box and inverter. then he'll turn on the braker and start up his genny. after one day of charging in low light conditions he is charged back up fully and ready for another six days of rain. if the sky is clear and sunny, he has all the power he needs to run everything in his home. he runs the lights, tv , ceiling fans, microwave, computers what ever he needs. he just watches how long he runs the larger stuff like the micro wave or power tools. other than that he is ready to go all the time.