New system design

photonboy

Solar Friends,

i am designing a new off grid system for a place I am building in Colorado.  We may only be at the cabin a total of 6 weeks per year over the next 5 years; after 5 years, I anticipate spending more like 3-4 months per year.  I am fortunate to have an assortment of 12v inverters, charge controllers, 12v batteries, and panels around my place from screwing around over the last few years, and I was going to try to make these items work until we started spending more time at the cabin.  I was planning eventually to go to a 48V system, and was going to wire the system to account for building capacity in the the future.  

I found what seems to be a good local deal on some  Sunpower X-22 360 panels and was tempted to buy.  If i purchased the right mppt charge controller, like the outback flexmax, could i use these panels as a way to build the system slowly and use the 12v inverters/ batteries I have laying around?  I am ultimately trying to avoid purchasing a bunch of batteries that would have minimum usage over the next 5 years.

Appreciate all the comments.  

Chris

mike95490

5 years is calendar life for many batteries, idle or not. So go with the cheapies, learn how your system plays together, and you will be needing fresh batteries in 5 years.

My thoughts, wire a 12V system and plan on using inverter to get "grid" power into the house to run the lights and stuff (maybe not the microwave) and lay out space for a 48V bank

Is there going to be any inspections or building code requirements ?

What about water, well pump, sewage pump, any 240V appliances

photonboy

Mike,

This is exactly what I was thinking in terms of a 12V system.  I was going to wire it to code, and then breakout select circuits to run on one of the 3 inverters that I have.  I will charge my cistern in my crawl space with a generator and use a 12V pump for my domestic water; my sewage is gravity fed.  

Keeping in the 5 year transition theme, and to fill time, I have built a 12V load center for DC loads.  Per suggestion of the group, I will move these items to AC or convert back to DC when I have the “real” system in place.

I am having a hard time finding opinions about panels in Off grid systems.......that is, is it silly to purchase these 360W panels for my temporary 12V inverter application.  If I bought the panels, I would wire them in parallel for both  my 12V and future 48V system.  Purchasing these panels now would be a permanent solution for my needs in the future rather than cobbling nominally 12V panels together for the short term and changing out.   This is off course all predicated on having a flexible charge controller.

Appreciate the feedback.

Chris 

mike95490

Many of the larger (40A + ) MPPT charge controllers, will work at both 12V and 48V (Morningstar 60A MPPT, Midnight Classic)

 If you are able to manhandle the large 300+ watt panels, I'd say go for it.  You are going to get them eventually, prices are about as low as ever and no realistic breakthroughs in pricing on the horizon.   To use the 300w, you will need a MPPT controller anyway.

littleharbor2

You will need to series wire at least two panels at a time for your 48 volt system. Pwm controllers are cheap but you might as well buy an MPPT controller once unless you want a PWM for a small 12 volt aux. system to power your water pumps and any other small 12 volt loads.

Photowhit

The  Sunpower X-22 360 has  vmp  of round 60v and a VOC of  around 70.  This  will  make your plans difficult. 3 would work for a 112 volt system, but 3 wouldn't  work  for a 48   volt system, with the  FM80.  The  VOC will rise in extream  cold  and  likely push past the 150v  absolute  max in your cabin.  While a single panel  is really too  low a VMP  to charge a  48  volt  system. Might look t a  Midnite  Classic  150  charge  controller   with  a max  of  150 +  system voltage (150+48)

Estragon

Following on with the thought that you will want to put panels in strings of 2 or more for 48v bank, you'll want to be sure the mppt has a suitably high max voltage. 

I'm guessing the 360w panel may be 72 cell with Voc in the mid-high 40s?   Many controllers handle strings of 150v or more, but some are lower.  A 100v max controller, for example, might be problematic assuming it gets cold there.

littleharbor2

Estragon said:

Following on with the thought that you will want to put panels in strings of 2 or more for 48v bank, you'll want to be sure the mppt has a suitably high max voltage. 

I'm guessing the 360w panel may be 72 cell with Voc in the mid-high 40s?   Many controllers handle strings of 150v or more, but some are lower.  A 100v max controller, for example, might be problematic assuming it gets cold there.

The Sunpower panels he is talking about are 96 cell panels, hence the high Vmp. and Voc.

  SPR-X22-360  360 W  Rated Voltage (Vmpp)   59.1 V  Rated Current (Impp)   6.09 A  Open-Circuit Voltage (Voc)   69.5 V  

Estragon

I hadn't seen Photowhit post - that is high.  +1 on looking at a controller with >150v max.  

mike95490

Magnum Energy PT-100 MPPT goes up to 200V, I've installed them, and they have done well.

BB.

If your power needs are "smaller" (say 1,200 Watts or less), then a 12 volt system is probably a good way to go (300 Watt inverter, 2-4 6 volt @ 200 AH golf cart batteries, etc.) and use a genset (and AC transfer switch) for charging/running larger AC loads (Honda euXX00i family stuff or similar)... I would not plan on having too many dedicated 12 VDC loads. If they are close to the battery bank, then using cigarette lighter plug adapters (cell phone charger, laptop/tablet charger,some 12 Volt LED lighting, etc.) can work OK, and maybe even kept later (24/48 to 12 volt DC to DC downconverters for a few amps).

Otherwise, wire everything up for 120 VAC and just pick energy efficient appliances and lighting.

Another question is security... Keep the system small(er) so that if there is any theft down the road, it will not be the worst thing in the world. Putting any expensive hardware in a remote location is always a difficult issue.

-Bill