What Questions To Ask, Lessons Learned, What You'd Do Differently

ryan112ryan · December 2014

I'm about to pull the trigger on my new solar panel system, signing this Friday. I'm hiring a company to install it because I don't have the skills to do it myself. 2.25kw system, fully off grid. I live in a tiny house, so I double checked the math and it seems to check out for what I'll need. I've checked references, The Better Bureau has them in good standing, google searches found good reviews, no red flags. My interactions with them have been very good too.

My question is, what questions do I need to ask before I sign?
What would you have done differently with your solar setup?
What were the lessons you've learned?
What do I need to watch out for?

Details of system:
2.25kW Solar PV System w/ Battery Backup

(9) Canadian Solar CS-6p 250 Watt Poly Black Frame
(1) Schneider SW 4024
(1) Schneider MPPT 60 Charge Controller
(8 ) Trojan L-16 6v 370 AH Flooded Lead Acid Batteries
(1) Schneider System Control Panel
(1) Midnight Sp;ar E-Panel
(1) Midnight Solar MNPV 80AMP Dinrail Breaker
(2) Midnight Solar Surge Protection Device AC/DC

Loads are a

Mini Split - 800w max variable motor at 6 hours
Bar fridge 90w variable motor at 8 hours
10 LED lights 5W each at 5 hours
Laptop 45 W at 4 hours
Cellphone 5 w at 8 hours
router 30 w at 24 hours
Fan 40 w at 1 hour

Total watt hours maximum per day 6,500
Max peak load at one time 1060

All are 110V and motors are variable motors so there is no motor lock out/ramp up spikes

DanS26 · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

The experts here on this forum will tell you if you have a good design...but they will have know more information about your loads.

But from a financial standpoint..... it appears you have purchased all the parts and you just want an install. If labor is more than the parts then you might want to get a few more quotes. If you have not obtained competitive quotes, that is risky. Need at least 4 or 5 quotes.

Cariboocoot · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

Welcome to the forum.

Yeah ... okay, off-grid doesn't use the same rules as grid-tie. We don't think in terms of array size but rather load capacity, as in Watt hours per day. So let's see how your equipment measures up.

ryan112ryan wrote: »

Details of system:
2.25kW Solar PV System w/ Battery Backup
(9) Canadian Solar CS-6p 250 Watt Poly Black Frame

(1) Schneider SW 4024

(1) Schneider MPPT 60 Charge Controller

(8 ) Trojan L-16 6v 370 AH Flooded Lead Acid Batteries

(1) Schneider System Control Panel

(1) Midnight Sp;ar E-Panel

(1) Midnight Solar MNPV 80AMP Dinrail Breaker

(2) Midnight Solar Surge Protection Device AC/DC

Eight 370 Amp hour 6 Volt batteries on a 24 Volt system is two parallel strings totaling 740 Amp hours. That is quite large and is capable of up to about 7.5 kW hours AC at 50% DOD. Half that with the DOD limited to 25% which is usually what you go for.

Now about that array. Nine panels means you get three strings of three in series. Probably it would be better with strings of two which gives you high enough Vmp for a 24 Volt system without reducing charge controller efficiency.

Now here's the bad news: 2250 Watts will produce about 72 Amps peak current, which is a tad light for 740 Amp hours of battery. They are really going to want that 10% charge rate, or more. If you could include a tenth panel and have five strings of two in series it will work better.

I would not pick the Schneider SW 4024 nor the Schneider MPPT 60 controller if I were you. Get a Midnight Classic 150 controller at least, as the Schneider won't even handle the expected current. You also should have a combiner box for those panels; a six string one it looks like.

Others will no doubt have additional suggestions.

AuricTech · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

Besides a hydrometer to check the specific gravity of your batteries' electrolyte (specific gravity is the gold standard for determining state of charge for flooded lead-acid batteries), I would suggest adding a battery monitor to your system. Our host offers the Schneider Electric Conext Battery Monitor that would be compatible with the other Schneider Electric components you've listed in your planned system. Another good battery monitor is the Bogart Engineering TriMetric series.

zoneblue · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

ryan112ryan wrote: »

I'm about to pull the trigger on my new solar panel system,...

[*](9) Canadian Solar CS-6p 250 Watt Poly Black Frame

9 x 250W= 2250Wp.= 2250W/24V = 90A. Thats a slightly messy amount, for controllers which come in 60/80A intervals. Midnite classic could handle that at a squeak those with its 90 amp rating. As Coot said, 9 is an odd number, an even number would be more flexible for 24V systems.

[*](1) Schneider SW 4024

This is a 24v only inverter. For 2.2kWp solar you are pretty close to the limit at what you can do well with 24v, and a 48V system might be a better bet for you. This means going to Outback, Magnum or SMA for the inverter, or going up to the XW if staying with Scheider. What we really need to know is what are your daily laod demands.

[*](1) Schneider MPPT 60 Charge Controller

There are those here who like scheider gear, but most of us, i think its fair to say are midnite snobs. Do some reading and youll see what a remarkable bit of kit it is. The scnieder controller reportedly runs cool and efficiently, however the SW has a truly awful idle tare draw, worst in its class. Combox is getting a reasonable rap, and intergration is one of their strong points.

[*](8 ) Trojan L-16 6v 370 AH Flooded Lead Acid Batteries

As Coot said, new system, try to avoid parallel batterys. 48V equals instant solution. One string, and pretty much any of the CCs will power that array at 48V, because its on 35 amps charging current.

[*](1) Schneider System Control Panel

See above combox is a better solution than the SCP. Better monitoring. Scheiders guys will know, i dont think you need them both.

[*](1) Midnight Sp;ar E-Panel
[*](1) Midnight Solar MNPV 80AMP Dinrail Breaker
[*](2) Midnight Solar Surge Protection Device AC/DC

All good stuff there. Suggest you take a bit of a look at Outback inverters. One thing to watch is to be wary of using the DIN rail breakers on the charge controller. They arent rated for reverse polarity which you need there. Use the panel mount versions.

We like to do numbers here, and that all starts from your load expectations, and sunshine hours.

offgrid me · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

What racking are they using?

ryan112ryan · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

Loads are a

Mini Split - 800w max variable motor at 6 hours
Bar fridge 90w variable motor at 8 hours
10 LED lights 5W each at 5 hours
Laptop 45 W at 4 hours
Cellphone 5 w at 8 hours
router 30 w at 24 hours
Fan 40 w at 1 hour

stove and water heater are gas, no oven or dryer

Total watt hours maximum per day 6,500
Max peak load at one time 1060

All are 110V and motors are variable motors so there is no motor lock out/ramp up spikes

ryan112ryan · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

I'll be building the racking with plans they're providing.

Cariboocoot · December 2014

Re: What Questions To Ask, Lessons Learned, What You'd Do Differently

With a 6.5 kW hour per day load demand you will be better off with a 48 Volt system.

Basic math:
6500 Watt hours AC = 7650 Watt hours DC. 7650 / 48 = 160 Amp hours. 160 * 4 (for 25% DOD) = 640 Amp hours @ 48 Volts. Pretty big capacity battery bank. If some of the power can be counted on as running opportunity loads (i.e. direct from panels during the day when the batteries are full) you could reduce the battery capacity some. Otherwise:

64 Amps peak charging current * 48 Volts / 0.77 efficiency = 3990 Watt array. That would be sixteen of those 250 Watt panels for 4kW array.

What it looks like if you run 370 Amp hours (the proposed batteries) @ 48 Volts:

25% DOD: about 3.7 kW hours AC
50% DOD: about 7.5 kW hours AC
Array size needed: 2500 Watts (ten of the 250 Watt panels which isn't going to work well on 48 Volts because you need three in series to have minimum Vmp for a 48 Volt system).
Battery life will be shortened by deeper DOD.

You could change the batteries to the 390 Amp hour L16's like these Crown's (better than Trojans in my opinion) http://www.solar-electric.com/batteries-meters-accessories/batteries/crdecyinba1/stdecyba/cr395amdecyb.html
That would give you a little more leeway: 7.9 kW hours AC at 50% DOD.

An array of twelve of those 250 Watt panels would be four parallel strings of three in series (90 Vmp) for 3kW total which would be more than adequate for that size bank at 48 Amps.

Yes, I know: back and forth with the numbers to try to find something that meets all the needs including budget.

What Questions To Ask, Lessons Learned, What You'd Do Differently

Comments

Categories