# I want help before I buy any more stuff.

flash
Registered Users Posts:

**8**✭
Here is my plan for an off grid emergency back up power that provides 1600 watts per day.

Morning Star 45 amp HTTP charge controller. (Will buy soon but open to ideas)

3 Grape 250 watt panels – 8 A at 30 volts. (May buy these but open to ideas)

4 EverStart 12 volt batteries (I have 2 already). (Other battery options next time.)

Ames 1240/3100 watt inverter. (I have now)

Coleman Powermate 5,000 watt generator. (Will sell this and get a Honda later)

What is your opinion of this set up?

Where and what fuses do I need?

Am I better off with pairs of panels so I can wire up to 2 in series? I’m asking because I have to put the panels in two locations.

Your suggestions and comments would be appreciated.

Morning Star 45 amp HTTP charge controller. (Will buy soon but open to ideas)

3 Grape 250 watt panels – 8 A at 30 volts. (May buy these but open to ideas)

4 EverStart 12 volt batteries (I have 2 already). (Other battery options next time.)

Ames 1240/3100 watt inverter. (I have now)

Coleman Powermate 5,000 watt generator. (Will sell this and get a Honda later)

What is your opinion of this set up?

Where and what fuses do I need?

Am I better off with pairs of panels so I can wire up to 2 in series? I’m asking because I have to put the panels in two locations.

Your suggestions and comments would be appreciated.

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## Comments

5,400✭✭✭✭Welcome,

A couple of quick thoughts, more to come I'm sure.

First, are looking for 1500 peak watts or 1500 WH/day?

Second, I don't think your battery choice is very good. I don't believe these are true deep cycle batteries. I encourage you to read the following:

http://www.batteryfaq.org/

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

My rule of thumb for off grid sizing is this (understand that all calcs and hardware choices stem from the loads!), take the name plate rating of the PV, divide in 1/2 to account for all cumulative system loses, then multiply that by 4 to account for the AVERAGE NUMBER OF HOURS OF GOOD SUN one can realistically expect, per day, on an annual basis.

So 500 watts of PV might look like this,,,500/2=250*4=1000 WH/day

I would further add, your choice of inverter is way too big for your battery bank.

Enough to chew on for now,, keep in touch, and once again welcome to the forum,

Tony

8✭Tony thanks for your response:

I need 1600 watts per day.

Batteries: I now realize the marine batteries are not the best for this use but I have two already so my thought was to buy two more and make the best of it. The setup will be fully charged most of the time and used only for emergencies. When the EverStart batteries are done I'll get something else.

Charge Controller: I thought with 3 panels at 8 amps and 30 volts in parallel (because of seperate loactions) that would be 24 amps in. There is a chance I may add a fourth panel to that would be 32 amps in. Did I figure that correctly? What size charge controller would you recommend?

I'm in Southern California and about one mile in from the ocean. The panels will be mounted facing south and I estimate 6 hrs of good sun each day. So: 750/2 = 375 x 6 = 2250. Four hours would be 1400.

I very open to suggestins.

Charlie

5,400✭✭✭✭Once again,, is that 1600 watts (peak) or 1600 watt/hours?

Do also realize that you may have 6 hours of sun,, but have you factored in, cloudy days, foggy days, partly cloudy days,seasona changes etc? Do a PV watts calc. For you location to get a better idea of your likely insolation.

http://www.nrel.gov/rredc/pvwatts/grid.html

Also realize the 8 Amps is probably a best case scenario, you are likely to get somewhat less.

Like I said before, all design and hardware considerations come from the load calcs. Work backwards from your (assumed) 1600 WH daily load to figure out how much battery, then how much PV, and then what size controller.

Just as an FYI, we live f I'll time with 400 watts of PV, using 450 ah of batteries, and we use, on a daily basis, 5-800 WH, about half off hat I assume your loads are likely to be.

Tony

8✭Hi Tony:

It's 1600 watt/hours per day. I think of them as just so many watts to use. Like I could use 100 watts for 16 hours, or 200 watts for 8 hours etc.

I went to the nrel site as you suggested and on an average its 5.46 Kwh/m2/day. I'm not sure what that means.

The four batteries I have in mind have 460 AH total. To supply these batteries in a 12 volt setup, 12 x 46 /.77 = 716 watts for the panel capacity. The panels have 750 watts total, so 750 x 4 hrs x .50 = 1433 watt/hrs At 6 hrs it comes to 2250 watt/hrs. It looks like I'm in the ballpark with the panel size.

It is informative that your system is about half of what I attempting.

Charlie

30,936adminIt is actually 1,600 Watt

*Hours (times, not divide) per day. Many times just typed WattHours, WH, AmpHours, AH, etc...-Bill

3,738✭✭✭✭I think it should be watthours, not watt/hours. --vtMaps

119✭✭Charlie

A couple of quick things. First you should think about a second charge controller for two reasons: You should not have panels from two different locations going to one controller, it will confuse the mppt function, second that controller is not big enough for the panels you have proposed. In a perfect world those panels could produce over 60amp and anything over 45amp would be lost power. The other problem I have with your setup is that you would have 4 parallel strings of batteries. Anything more than 3 strings is just asking for trouble. You are cutting it a little close on panel and will probably only be able to harvest about 1500 wh per day so during an extended outage you will be deficit charging and will slowly kill the batteries. Just my two cents.

Ned

5,400✭✭✭✭Got it,, I nevr put two and too together with the / as a symbol for division. An old habit I will try to break, as I do it often.

Tony

3,738✭✭✭✭If you multiply "A" times "C" (AC) you get alternating current. If you divide "A" by "C" (A/C) you get air conditioning. go figure. --vtMaps

5,400✭✭✭✭I wonder what would happen. If you divided DC/A/C? You would you get,,, oh never mind!

Tony

170✭✭✭✭✭a popular classic rock band that uses the same beat all the time

8✭The learning curve continues.

I would like to determine how much good sun I can expect to get. I went to the nrel site and plugged in my zip and the average solar radiation per month is 5.46 kWh/m2/day, with a low of 4.21 in January and a high of 6.29 in August. How do these numbers relate to hours of good sun?

On cloudy days I plan to use a generator because otherwise the system size doubles or triples.

Charlie

5,400✭✭✭✭First, search around the P watts sites and versions. You can plug in your location, array size and orientation etc,ad will come up with a pretty good average per day, per month. On a second note,, you should consider how much autonomy you need or want for cloudy days. Counting on running the genny may turn quite expensive over time, so design accordingly.

Tony

30,936adminUsing PV Watts for Los Angeles, with fixed 1 kW array, tilted at latitude and 0.77 derating for grid tied solar (use 0.52 derating for typical off grid solar power):

Basically, the "hours of sun" per day is equal to 1.0 kWh/m^2/day... (i.e.., ~X.X hours of noon time equivalent sun stretched out over a ~10-12 hour day of sun light).

Or:

-Bill