Introductory Post: My Small Off-Grid backup

[Garret]

Hi Everyone,

Thought it might show my DYI off-grid backup PV system.  This is my first post anywhere with attachments, so may have to try again.

So far I have fabricated my own top of pole mounting for 6 of 9 Solarworld-SW275 W panels.  It is adjustable in altitude and azimuth.  Current angle 26 degrees for winter.  There are 2-strings of 3 panels in series (93 v).  Even though it is a 24 v system, I elected to series 3-panels to keep the voltage drop to <2% (100 ft run; 6AWG Cu).  I will shortly have 3 additional panels on another 6 panel mount that I will connect along with the rest.  The midnight planner tool limits me to 9 panels.  However, I will eventually over-panel to 12, because it is very unlikely I will ever see the nameplate output here in western Pennsylvania where gloom is the norm.  There are days with 0.0 KWh-hr energy harvested.  I realize it is wintertime, but can't see it getting that much better.  We only get about 100 days that the sun shines at all. Clear days are far between.

Been up and running for ~3 weeks now.  Very disappointing.  Can't harvest more than 1 kWh-hr on most days, pathetic.  Enough to run LED lighting that I installed throughout the house, but no continuous loads larger that about 200 w for more that a couple of hours.  One day 4.4 KWh-hr with manual tracking (wow?).  OK as a backup for intermittent critical circuits in the house, but too small to compete with a generator or other real source of power.

Had to disable the Arc Fault in Classic 150 because whenever well pump kicks on, fault occurs regardless of settings.

My biggest regret is not getting a 48 v system.  My 24 V requires DOUBLE 4-0 copper (+) and (-) battery cables and have to parallel strings of batteries to get needed capacity.  Also Magnum inverter 4000 W in 24 V model vs 4400 in 48 V and less efficient overall.  Don't make the same mistake I did. 

[dgd]

That's a nice neat system, looks well planned and constructed.
With such low daily kWH I would not just over panel by an extra three PVs but perhaps by six so that on poor days you get the daily kWh up to 2 to 3.
In fine weather then you can possibly look at switching out some panels or diverting their output elsewhere, maybe water heating.

With the overall capacity of your system I'm not sure the cost of going 48v would have been very economic, more batteries vs an extra, maybe, 400w of inverter output.

Dgd

[xsnrg]

I really like your mount Garret, well done.   Hopefully you can tell a little more about what you did?

[Garret]

Thank you for the encouraging comments.  Sometimes, I realize I'm my own worst critic.  I just had higher expectations after all the effort and expense.  I am a firm believer in renewable energy.  It is a large part of what I do at work.  Losing my dependency on electrical grid power is for me the final frontier.  I currently fuel a car, truck, two tractors and a generator on homemade biodiesel and comfortably heat my home (along with unlimited domestic hot water) with a clean-burning gasification-type outdoor wood furnace.  I think we all fantasize about the day we call the electric utility company and request a disconnect.  I'm determined to see that day.

I read a post somewhere on here about the concept of virtual tracking, that is, installing two separate arrays pointing in their own optimal direction to reduce peak combined power (that may exceed normal design limits), but normalize overall energy production throughout the day.  That will be my strategy for over-paneling.

I could not find any drawings on the Web for a well-constructed top-of-pole mount, so I gleaned what info I could from manufacturers Websites and YouTube videos.  The attached images show more details of the mounting head design I conjured up.  As it turns out, a 5" sch. 40 pipe fits snugly into a 6'x6" 3/16"-walled square tube.  That is the basis for the bearing surface that supports the mounting.  The whole array is very rigid and sturdy, but can be slewed with one finger and gravity holds it in place.  Same goes for changing inclination.  Also well-balanced.  My welds aren't the prettiest; nothing a grinder can't fix.

Third photo shows the 4-0 battery cables routed through a 2" sch.40 rigid plastic conduit into the ME mini-panel.  It is a tight and difficult operation, especially pulling the two negative cables past the delicate shunt circuit board to attach to the (-) inverter input.  A 48 V system would have only required a single 4-0 cable.

[shawn_1976]

Garret

I have ta similar system at home. At first I had no loads turned on and was getting less than 1KW per day. Then I thought about it, if I am not using the amps it will not produce the amps. Now I pull about 5 KwH per day from the system and it keeps up fine.

[freegirl]

With the overall capacity of your system I'm not sure the cost of going 48v would have been very economic, more batteries vs an extra, maybe, 400w of inverter output.

If you are there, could you kindly elaborate on this comment? I am newbie getting ready to buy 48v. Maybe send a private if off topic. ;>

[zoneblue]

The downsides of 48V are few, roughly:
- if your system isnt big enough to justify the common battery sizes in 48V. For say the common 370AH L16, thats 18kWh and 1.8kWp array. Smaller arrays need smaller batterys hence unless you want to use  or can get smaller batteries 24V is often a better choice below that.
- if you have any 12 or 24V loads having a lower voltage bank makes that easier. (but DC converters largely solve that now).
- you tend not to be able to get small inverters at 48V. Sometimes a smaller inverter has its place for its low tare.

Thats about it. Dont be shy about starting your own threads, (rather than scattering your stuff about). Check out NAWs too.

[smanners]

Is it windy where you live?

I'm fortunate as we get lots of sun and good steady windy days upwards of 50kmh so I have solar and a turbine.

Nice setup you have.

[Jacotenente]

48v is really the way to go...however, I think 24v gives you a little bit of flexibility. Mine is 24v (Outback Power VFX 3524). I only power my 120v side of the house...the 240v stuff...meh.