2kw solar setup, comments appreciated.

maan · February 2014

Hello, I have 8 Grape solar panels , Pmax=250 watts, Vmp=30.7v, Voc=37.7v, Imp=8.15A, Isc=8.72A. Midnite Classic 200. Silent inverter/charger 4000watts, 24 volt. Battery bank: Trojen 1680 AH @ 24v. Mdnite 4 strings combiner box to be purchased, will be expanding solar Array in near future. present design: #of modules in series 4; # of parallel strings 2. This will give me PV array current of 16.4 amps, VMP of 122.8 volts, VOC of 150.8. Solar panels will be installed on the roof facing true south, in Cincinnati, Ohio at an altitude of 39 degree at a fixed angle year round of a 51 degree angle. Will be using 6 guage wire to keep losses below or at 5%, Solar panels to charge controller distance about 50 feet. Any comments on this configuration is appreciated. Thank you in advance.

More info on the inverter:

• 4000 watt output power, 24 Volts
• Pure sine wave output
• 2.5X surge capability
• 120V or 240V generator input
• Intelligent multi-stage battery charger with battery protection
• Cost effective all in one design – User interface, generator start controller, DC disconnect breaker, DC current shunt, AC disconnect breaker, cabinet enclosure, all included.
Onboard Breaker and Shunt
• Built in 250 amp breaker — no external box to mount or wire, resulting in a cleaner and quicker installation.
• 40 amp dual pole breaker for generator input included.
• Shunt included internally for charge control and data logging.

Onboard Charger

• Charger is totally separate and independent of the inverter providing a truly uninteruptable power supply.
• Intelligent multi-stage charging to protect batteries from overcharging. Low and high temperature compensation.
• Continuous output up to 136 amps to assure fast charging.
• Charger receives either 120 or 240 VAC input.

Any comments on this configuration is appreciated.

Cariboocoot · February 2014

Re: 2kw solar setup, comments appreciated.

Welcome to the forum.

You say you have a 1680 Amp hour 24 Volt battery bank? That is a lot of battery. Normally you'd want to have 168 Amps of peak current available, and that isn't going to flow through one 80 Amp MidNite Classic nor will it be provided by eight 250 Watt panels (2kW array). In fact you could expect a bit over 60 Amps from that array on a 24 Volt system, which is <4% charge rate. If those numbers are correct that is not going to work without a lot of generator run time.

So my first question is: why the big battery bank?
At 25% DOD that 1680 Amp hours will provide about 8.5 kW hours AC. Rather a lot for an off-grid system.

There is no way that 2kW of PV will recharge that much battery, so either you need to shrink the battery capacity and/or load demand or expand the array.

Another question about that battery bank is what it is made up of and how it is wired. If you really need that much stored capacity you should be using a 48 Volt system.

maan · February 2014

Re: 2kw solar setup, comments appreciated.

Thanks for responding. As I stated i will be adding more solar arra, another 1000 watts of array or most likely a wind turbine genrator 2000 watts, 24 volts with another midnite controller. The battery bank consists of 4 L16P, 6 volts Trojan batteries @ 24 volts. The Present inverter is 24v, not compatible with the 48v battery bank, however should be able to handle more solar array or wind turbie.

vtmaps · February 2014

Re: 2kw solar setup, comments appreciated.

maan wrote: »

Battery bank: Trojen 1680 AH @ 24v.

maan wrote: »

The battery bank consists of 4 L16P, 6 volts Trojan batteries @ 24 volts.

Welcome to the forum.

I think your battery bank is 420 ah at 24 volts. By most rules-of-thumb you have enough solar panel to charge those batteries.

I think you are getting near the limits of your Classic 200 with 2000 watts of array. How much more do you intend to add?

Also, by running your panels four in series on a 24 volt system, you are making your Classic less efficient. A combination of high input voltage and high power throughput means that your classic may run fairly hot.

I would prefer to see your panels configured as four parallel strings, with 2 panels in series per string. With a 50 ft distance between the combiner and the controller, you would see a 2.1% voltage drop over 50 ft of #6 cable.

btw, if you do that you might want to trade your Classic 200 for a Classic 150 which can handle more power than the Classic 200.

--vtMaps

maan · February 2014

Re: 2kw solar setup, comments appreciated.

This system is to supply a two family home, I know that I will have to add a second midnite controller if i'm to add more array of 1000watt or 2000 watt wind turbibe to this system. four 6v Batteries 420 AH each @ 24v bank. Thabks for your comment.

zoneblue · February 2014

Re: 2kw solar setup, comments appreciated.

Not necessarily, thats the advantage of 48v, one controller can run 4kw+. As Coot says at that power level you do need to step up to 48V, and its a good time to get a better quality name brand inverter. Ebay the other one, good inverters are absolutely critical to off grid life.

re CL200, the point of those higher voltage controllers is for long array cables, and longer series pv strings is the point. As vt points out for normal cables the CL150 and shorter strings is the right choice.

Cariboocoot · February 2014

Re: 2kw solar setup, comments appreciated.

I think vtmaps has correctly ascertained a root problem in that the OP added both the Amp hours and the Voltage of each battery to come up with the capacity. I was suspicious about this and asked for clarification on the battery bank configuration as a result.

So now it appears the solar array could recharge the battery bank as it is only 420 Amp hours @ 24 Volt not (4X) 1680.

But that shifts to a new potential problem: insufficient battery capacity to supply the needs of a two family home. At that point we need to know the actual Watt hours daily use, and without that number everyone (including the OP) is just guessing.

Right now I'm guessing it still won't work, but for a different reason.

maan · February 2014

Re: 2kw solar setup, comments appreciated.

My bad, I did add up both amp and voltage. I will add a second bank in paralle with this initial bank. Heat, dryer and range is on natural gas, will be operating lighting and 2-laptop computers and a fridgerator. very conservative, meaning you will not find a room with lights on and no one in it. keep in mind we are still on the grid, this is a backup. We do not want to tie it to the grid. we will be adding no less than a 1000 watts more to the system with a second midnite. It isn't cheap to build a 3kw/4kw at once. Together we ar using 456KWH, this is a 12 average, 456kwh/30days = 15.2kwh/day. What is the maximum battery AH that it could handle at the present time, can I add 420Ah in parallel to bring the battery bank to 840AH @ 24 Volt?

Cariboocoot · February 2014

Re: 2kw solar setup, comments appreciated.

maan wrote: »

My bad, I did add up both amp and voltage. I will add a second bank in paralle with this initial bank. Heat, dryer and range is on natural gas, will be operating lighting and 2-laptop computers and a fridgerator. very conservative, meaning you will not find a room with lights on and no one in it. keep in mind we are still on the grid, this is a backup. We do not want to tie it to the grid. we will be adding no less than a 1000 watts more to the system with a second midnite. It isn't cheap to build a 3kw/4kw at once. Together we ar using 456KWH, this is a 12 average, 456kwh/30days = 15.2kwh/day. What is the maximum battery AH that it could handle at the present time, can I add 420Ah in parallel to bring the battery bank to 840AH @ 24 Volt?

Okay let's go with that 15 kW hours per day number. That's about the same as my on-grid house here, so it's definitely possible.

Off grid that's a lot of power: 15,000 / 48 Volts = 312.5 Amp hours used, meaning a minimum 625 Amp hours @ 48 Volts (at 50% DOD which is pretty much the maximum). On a 24 Volt system multiply the capacity by two. And those are just rough numbers.

You can definitely parallel another string of 420 Amp hour batteries to the first one. That will give you 840 Amp hours @ 24 Volts. That would still "max out" an 80 Amp charge controller under normal circumstances and necessitate about 2500 Watts of panel to supply it.

What you would get from that at 25% DOD would be roughly (840 /4 * 24 * 0.85) 4.2 kW hours AC per day. Think of that as 1/4 what you are using now.

So is this back-up for emergency purposes or is it the start of a "take everything off grid" plan?

maan · February 2014

Re: 2kw solar setup, comments appreciated.

Thanks for responding. It is a back-uo system, I just don't want to tie it to the grid. I will order two more panels 250 watts each to add to the 2kw i have now. Is 1/0 (0 Gauge) AWG Battery Terminal Cables 3/8 Copper Lugs good enough before i order it from wind and sun? Which generator do you recommend? In the next few months I will be adding wind turbine to this system, what do you recommend? I'm gathering all components for the solar, all i need now is wiring and the combiner box. I see the 6 string midnite at wind & solar, but not the pre wired combiner box.

Cariboocoot · February 2014

Re: 2kw solar setup, comments appreciated.

Two things go in to sizing inverter cables: current draw and distance (to prevent Voltage drop over distance you sometimes use larger cable). We know a 4kW 24 Volt inverter will draw 167 Amps nominally at full power. 1/0 is good for about 200 Amps under most circumstances so it would work, especially if you don't expect to run near full power (people rarely do) and do not have really long distances (greater than 10 feet, which isn't a good idea anyway).

As for generators, I'm very fond of the inverter-generators from Honda. The Yamaha version have plenty of fans too. That inverter has two pole 40 Amp breaker for gen input, and that's a lot of power: 9.6kW on 240 VAC, 4.8kW on 120 VAC. You probably don't need that much generator, so there is some question as to how the charger in that inverter works. If it can't be "programmed down" you could have trouble. Read through the manual and see what it says about programming the charger. "Up to 136 Amps" is a huge amount of power @ 24 Volts (over 3kW) and with the power factor involved ... well it looks like they planned on people using a 5kW genset with this.

I don't recommend wind turbines at all. Small wind is fraught with fraud and poor quality and it's a gambler's game even if you have a site with steady wind and a 50' tower to mount it on. No way am I sticking my neck out on wind power. Seems the build-it yourself crowd do better than the commercial ones.

Contact NAWS directly about the combiner box question. I'm pretty sure there is a six panel MNPV6-MC4 pre-wired unit, even if it isn't shown.

vtmaps · February 2014

Re: 2kw solar setup, comments appreciated.

Cariboocoot wrote: »

I'm pretty sure there is a six panel MNPV6-MC4 pre-wired unit, even if it isn't shown.

The prewired combiners with MC4 connectors that are in the catalog have fuses. Fuses take up more space than circuit breakers. Six breakers fit in the same space as four fuses.

boB or Ryan (on this forum) indicated that they will be happy to make up a prewired combiner with breakers and MC4 connectors.

--vtMaps

Cariboocoot · February 2014

Re: 2kw solar setup, comments appreciated.

vtmaps wrote: »

The prewired combiners with MC4 connectors that are in the catalog have fuses. Fuses take up more space than circuit breakers. Six breakers fit in the same space as four fuses.

boB or Ryan (on this forum) indicated that they will be happy to make up a prewired combiner with breakers and MC4 connectors.

--vtMaps

I thought so!

Darn good way to go, too.

maan · February 2014

Re: 2kw solar setup, comments appreciated.

The manual states Gen Max Output (default is 3000W which sis presently the maximun available from te charger). 0 to 5000w in 500w increments; set the size of the generator to limit the charger if needed. I belive i should be ok with Honda eu2000.

maan · February 2014

Re: 2kw solar setup, comments appreciated.

will be calling them tomorrow. thanks

2kw solar setup, comments appreciated.

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