System Design...so far...need to know if this makes sense

[Slider]

I think I understand most of this but need some help, here is the background info:

5 month summer cottage, just need a solar system for CFL lighting only. Average sun insolation factor is 5.2 average over those 5 months – May to Sept. My calculations are below based on the information from this site, great info, love the site!

Questions:
1. As far as the solar panels themselves. I need panels for 346 watts on a 48v system. How many and what size panels are required here? Do I need 4 x 12v panels for a 48v system? I was hoping to just buy 2 panels @245w to make 490w total...which covers the 346 watts I need. I am confused on the panels and the min/max charging...

2. Charge Controller – on a 48v system, I only need cc to handle 7.2amps. I assume a 20amp MPPT is more than enough and this will still let me run up to 960w of panels if I wanted to. Is this correct thinking?

3. Batteries - I have some used AGM batteries to start with - 8 x 12v64ah. What configuration and size of batteries to you recommend when I have to purchase new ones? I hope to get this summer out of what I have been given for free.


Total wh/day = 1200
1200 watt/hours x 1.5 = 1800 watts per day
1800 / 5.2 = 346 watts

1200 x 5 days = 6000wh
6000wh / 48v = 125 amp hours
Battery Bank (I have 8 batteries given to me – 12v 64ah)
12v-64AH AGM batteries
2 strings of 4 batteries, each string @48V and 64AH x2 = 48V 128AH

Inverter
48 volt 1500 watt inverter (any recommendations??)

Charge Controller
346w / 48v = 7.2 amps
20 amp Charge Controller is enough. @48v, could go up to 960 watts of panels

Thanks for you help....Kent

[inetdog]

Questions:
1. As far as the solar panels themselves. I need panels for 346 watts on a 48v system. How many and what size panels are required here? Do I need 4 x 12v panels for a 48v system? I was hoping to just buy 2 panels @245w to make 490w total...which covers the 346 watts I need. I am confused on the panels and the min/max charging...
You need to be sure that the voltage of the panels in series is high enough to reach the input range of your MPPT controller. At a minimum the total voltage will have tyo be higher than 60 volts for a 48 volt battery system.

2. Charge Controller – on a 48v system, I only need cc to handle 7.2amps. I assume a 20amp MPPT is more than enough and this will still let me run up to 960w of panels if I wanted to. Is this correct thinking?
Yes.

3. Batteries - I have some used AGM batteries to start with - 8 x 12v64ah. What configuration and size of batteries to you recommend when I have to purchase new ones? I hope to get this summer out of what I have been given for free.

I will leave this question for someone else.

Thanks for you help....Kent

See bold answers inline.

[Sunking]

I think I understand most of this but need some help, here is the background info:

5 month summer cottage, just need a solar system for CFL lighting only. Average sun insolation factor is 5.2 average over those 5 months – May to Sept. My calculations are below based on the information from this site, great info, love the site!

Questions:
1. As far as the solar panels themselves. I need panels for 346 watts on a 48v system. How many and what size panels are required here? Do I need 4 x 12v panels for a 48v system? I was hoping to just buy 2 panels @245w to make 490w total...which covers the 346 watts I need. I am confused on the panels and the min/max charging...

2. Charge Controller – on a 48v system, I only need cc to handle 7.2amps. I assume a 20amp MPPT is more than enough and this will still let me run up to 960w of panels if I wanted to. Is this correct thinking?

3. Batteries - I have some used AGM batteries to start with - 8 x 12v64ah. What configuration and size of batteries to you recommend when I have to purchase new ones? I hope to get this summer out of what I have been given for free.


Total wh/day = 1200
1200 watt/hours x 1.5 = 1800 watts per day
1800 / 5.2 = 346 watts

1200 x 5 days = 6000wh
6000wh / 48v = 125 amp hours
Battery Bank (I have 8 batteries given to me – 12v 64ah)
12v-64AH AGM batteries
2 strings of 4 batteries, each string @48V and 64AH x2 = 48V 128AH

Inverter
48 volt 1500 watt inverter (any recommendations??)

Charge Controller
346w / 48v = 7.2 amps
20 amp Charge Controller is enough. @48v, could go up to 960 watts of panels

Thanks for you help....Kent

OK you have made a few mistakes. For a battery system you do not use Average isolation over period of time. You use the lowest shortest day for the period of time.

For a 1200 wh system 48 volts is not really necessary. If all you are using is CFL lights you can use 12 volts and no inverter is required if you use 12 volt CFL's. However having 120 VAC is often needed just in case. I would consider 24 volt battery with an inverter.

From what you have stated so far a 1500 watt inverter is way too large. Inverters are are based on maximum connected load that is likely to be turned on at one time. With only 1200 wayy hours per day, there is no way you will ever need a 1500 watt inverter. Basically the inverter wil be no larger than your solar panel wattage. Watt Hours = Watts x Hours. Think about that? how long does a 1500 watt load need to be on to burn 1200 WH? Give you a hint. 1200 wh / 1500 w = Hours. Less than 1 hour maybe? I hardly doubt you will have 1200 watts of CFL's connected used less than an hour each day.

Lat thing in the world you want to do is use parallel strings of batteries. If you need 128 AH buy at least 128 AH batteries.

As for panels assuming you are going to use a MPPT charge controller you will use Grid Tied Panels, no tbattery panels. Wattage depends on what battery voltage you run and total wattage needed. But basically if you need 400 watts, then total panel wattage required is a minimum of 400 watts. Not rocket science as wattage adds. The trick is what battery voltage and charge controller you select. Th etotal panel voltage needs to be about 20 volts for every 12 volt of battery.

So you need to go back to the drawing board and start all over.

[Sunking]

For grins and giggles to humor myself assuming you actually have only 4 sun hours, 1200 watt hours days use, 24 volt system, and 150 watt connected load all you need is:

Panel wattage = 450 watts
MPPT Charge Controller = 20 amps minimum.
24 volt Battery Capacity = 250 AH.
Inverter = 300 watts.

To go 12 volt system all that changes is battery capacity to 500 AH and CC to 40 amps.

[Naptown]

Here's my 2 cents
Build a 24V system with the batteries you have. (four parallel strings of two in series ) This will kill the batteries fairly quickly but they were free right?
Get panels with a Vmp of 30 or more 2 in series
Get a 30A mppt controller
Buy 24V dc CFL lamps (they are available but cost more than the home center 120V AC bulbs)
Get a 24V inverter of your choice.
When it comes time to replace your batteries buy 6V batteries and put them in series to get 24V at the desired AH rating.

[Slider]

OK you have made a few mistakes. For a battery system you do not use Average isolation over period of time. You use the lowest shortest day for the period of time.

For a 1200 wh system 48 volts is not really necessary. If all you are using is CFL lights you can use 12 volts and no inverter is required if you use 12 volt CFL's. However having 120 VAC is often needed just in case. I would consider 24 volt battery with an inverter.

From what you have stated so far a 1500 watt inverter is way too large. Inverters are are based on maximum connected load that is likely to be turned on at one time. With only 1200 wayy hours per day, there is no way you will ever need a 1500 watt inverter. Basically the inverter wil be no larger than your solar panel wattage. Watt Hours = Watts x Hours. Think about that? how long does a 1500 watt load need to be on to burn 1200 WH? Give you a hint. 1200 wh / 1500 w = Hours. Less than 1 hour maybe? I hardly doubt you will have 1200 watts of CFL's connected used less than an hour each day.

Lat thing in the world you want to do is use parallel strings of batteries. If you need 128 AH buy at least 128 AH batteries.

As for panels assuming you are going to use a MPPT charge controller you will use Grid Tied Panels, no tbattery panels. Wattage depends on what battery voltage you run and total wattage needed. But basically if you need 400 watts, then total panel wattage required is a minimum of 400 watts. Not rocket science as wattage adds. The trick is what battery voltage and charge controller you select. Th etotal panel voltage needs to be about 20 volts for every 12 volt of battery.

So you need to go back to the drawing board and start all over.

Thanks Sunking...ok, starting to make more sense. I figured the 48v was better, even though its a small system. 24v does make more sense and gives me more choice on the inverters. There is a fair distance from where the panels will be mounted and the batteries will sit, say 150 feet. Does that make a difference whether to go 48v or 24v?

You're right...just calculated the lights that would be on at once and its about 400 watts only. So a 500watt inverted would be cheaper and more efficient I would assume.

[Naptown]

Thanks Sunking...ok, starting to make more sense. I figured the 48v was better, even though its a small system. 24v does make more sense and gives me more choice on the inverters. There is a fair distance from where the panels will be mounted and the batteries will sit, say 150 feet. Does that make a difference whether to go 48v or 24v?

You're right...just calculated the lights that would be on at once and its about 400 watts only. So a 500watt inverted would be cheaper and more efficient I would assume.

Use higher voltage panels with an MPPT controller to reduce losses in the run from panels to CC.
This must be a large cottage to have 400W of CFL lights running at once. They are generally 15W which would mean you would have 26 on at once?

[Slider]

Here's my 2 cents
Build a 24V system with the batteries you have. (four parallel strings of two in series ) This will kill the batteries fairly quickly but they were free right?
Get panels with a Vmp of 30 or more 2 in series
Get a 30A mppt controller
Buy 24V dc CFL lamps (they are available but cost more than the home center 120V AC bulbs)
Get a 24V inverter of your choice.
When it comes time to replace your batteries buy 6V batteries and put them in series to get 24V at the desired AH rating.

Thanks Naptown....seems 24v is the way to go. I can hook up the batteries as you suggest, perfect. Now the reason for the inverter and not using 24v dc CFL's is that the cottage as already been wired for 120v, and we currently use a generator/inverter when we want the lights on. So the inverter must stay.

ok, so a couple of 245w panels with a Vmp of 30 or more in series will work. Good, that makes more sense. I had really only read about the watt requirement and not heard about needing 20v of panel for every 12v volt of battery.

[Slider]

Use higher voltage panels with an MPPT controller to reduce losses in the run from panels to CC.
This must be a large cottage to have 400W of CFL lights running at once. They are generally 15W which would mean you would have 26 on at once?

Yes, that's about right. Some are the 23w/100w CFL's, and there are chandeler types lights in the mainroom with 5 bulbs in each x 2. Then there are 5 path lights to get to the outhouse... Oh, and always a couple of cell phones charging....that is in there too..

[bonaire]

Are led lights a consideration here for the OP? Seems to make sense to cut usage further to allow more runtime or cut system size.

[inetdog]

Are led lights a consideration here for the OP? Seems to make sense to cut usage further to allow more runtime or cut system size.

LEDs are not going to be much if any improvement over good CFLs unless you are able to run them directly off DC.
They have advantages (which are also disadvantages) over CFLs in that they deliver their light primarily in one direction.
A T5 fluorescent with good electronics will be more efficient in terms of total light output than either LED or CFL with current technology.

[russ]

Do any of the suppliers list the power factor for CFL type lamps now? I haven't checked in a while but it used to be hard to get.

For any off-grid system that does count as you are the supplier. For grid connect it doesn't matter to you.

[johngalt]

Are led lights a consideration here for the OP? Seems to make sense to cut usage further to allow more runtime or cut system size.

Here is a 12 volt LED lamp I made out of PVC and flexible LED strips. I plan to make the same thing in 24v or 48v if I can get the LEDs.



Testing inside my battery closet



12v 50/50 LED/PVC homemade bulb



This light pulls about half an amp at 12 volts and puts out about the same lumens as a 60 watt incandescent bulb.

Disregard the printing on the PVC. I haven't painted it yet.

Lamp Shade = $15
PVC Pipe and fittings = $5
6" PVC Drain (base) = $10
Toggle Switch = $5
Wire and LEDs = $5

Satisfaction = Priceless

[inetdog]

Satisfaction = Priceless

Looks very nice! A lot better design and aesthetics than most commercial LED lamps I have seen. Most of them are really not suited to a table lamp like that.

[Wy_White_Wolf]

I think I understand most of this but need some help, here is the background info:

5 month summer cottage, just need a solar system for CFL lighting only. Average sun insolation factor is 5.2 average over those 5 months – May to Sept. My calculations are below based on the information from this site, great info, love the site!
....

You need to use the lowest month the system will be used instead of the average for the 5 months. Worst case.

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