Newbie at decision time...

miksu

Hi guys,
I'm looking for advice on my equipment list. I'll be burning 8000 watts a day, every day (security lighting situation) The outfit I contacted designed a system to include the following. (9) Astronergy 250w panels, Morningstar TristarTS-60 60 amp controller, Colek ST series 250 w 48volt Pure Sine Wave Inverter,Midnite MNPV-3 Combiner,MidniteMNDC175 Mini Disconnect. Being new at this I'm looking for some tech support regarding this setup. Thanks for any advice. Mike

Cariboocoot

Re: Newbie at decision time...

Welcome to the forum.

Okay, we'll assume that's 8 kW hours per day. That's pretty hefty off-grid.

2250 Watt array is capable of 4680 Watt hours per day, based on a 4 hour sun minimum and standard 52% over-all system efficiency. Big problem right there.

No mention of battery bank size, which is essential. 8kW hours AC would require a minimum of about 390 Amp hours @ 48 Volts. That would want about 2430 Watts of array for recharging. That would be at 50% DOD. For 25% the numbers double: 780 Amp hours @ 48 Volts and 4860 Watt array. That array could manage 10 kW hours per day as per above.

It looks like the array is a bit undersized either way.

I presume that's a Cotek 250 Watt 48 Volt inverter? That seems highly unusual: 48 Volt inverters tend to be over 2kW.

Really need to know what battery bank has been sized and what depth of discharge is expected.

miksu

Re: Newbie at decision time...

Thanks for the reply. The battery bank is designed using 8 (6volt) with 800 amp hrs. I was told not to exceed 50% discharge and this was used as worst case scenario. As far as the inverter goes (oops) I left off one 0. Should be 2500 watt. Thanks Mike

Cariboocoot

Re: Newbie at decision time...

I can't think of a 6 Volt battery that's 800 Amp hours. You need eight of them just to get 48 Volts.
To recharge that much battery you want a 10% peak charge current, which would be 80 Amps. The 60 Amp TriStar will fall short in this duty. You should also have like 5kW of array to supply that current. That 2250 Watt array will supply about 36 Amps max, which would be only 4.5% peak charge rate, which is below the recommended minimum 5%.

miksu

Re: Newbie at decision time...

Thanks for your patience, I'm on a pretty steep learning curve here! I'm not sure where the designer came up with an 800 amp hr requirement. I've run some numbers and maybe you can tell me if i'm doing this right. 1000 watts x 8 hrs per day =8000 watts per day. With a 50%DOD I would be looking for a16000 watt hr. application. 16,000 watt hrs./ 48 volts =333 amp hrs. battery bank. Does this make more sense? Mike

Cariboocoot

Re: Newbie at decision time...

More like 370 Amp hours @ 48 Volts.
Here's why:

8 kW hours AC. Conversion efficiency of the inverter: 90%. You now have 8888 kW hours DC. Inverter consumption in 24 hours: 480 Watt hours (@ 48 Volts means another 10 Amp hours). 8898 Watt hours / 48 Volts = 185 Amp hours. X2 for 50% DOD = 370 Amp hour 48 Volt battery. I picked 390 in Post #2 because I was thinking of certain L16 batteries which happen to be 390 Amp hours.

And that would be easier to recharge too.
39 Amps @ 48 Volts = 1872 Watts, less typical 77% efficiency derating = 2431 Watt array. Round up to the nearest available size.

By the way, with that size array and battery bank it would probably be worthwhile to use an MPPT type 60 Amp controller. The TriStar comes in two versions. On the whole, though, an Outback FM60 is a better deal (has a built-in meter): http://www.solar-electric.com/oupofl60mpso.html

miksu

Re: Newbie at decision time...

Thanks very much for your time and help. I guess I'll go back to the drawing board and pass on some of this info to the designer. Any other recommendations you might have would sure be appreciated. Thanks again. Mike

Skippy

Re: Newbie at decision time...

I have been looking into some outdoor security lighting for around my house as well .... what kind of lighting units are you running ? Might be a bit cheaper to switch to low power - high tech lights, than to purchase a large solar system too run the old stuff. . .

Just a thought.

BB.

Re: Newbie at decision time...

Currently I am running Costco LED based motion detector lighting. Much less power than the old 100+ watt pair of flood lamps.

And motion detector lighting, in my opinion, is better than using an "on all night" security light. The lights turning on startle and attract attention of neighbors. The on all night seem to just light the stuff you don't want stolen.

I am on grid--So, these are AC powered lights. I have not taken one apart to see if they could be supplied by DC or not (seems like DC conversion is possible).

You can also purchase kits and modules (IR, microwave, etc.) that could be wired up for your own sensor system/control.

-Bill