Building new Off Grid Home in Panama

Re: Bulding new Off Grid Home in Panama

Cariboocoot wrote: »

Another way of looking at it:

Largest solar charge controller you can get is basically 80 Amps @ any nominal Voltage.
10% rule of thumb limits battery bank size to 800 Amp hours (+/- a bit).
400 usable maximum Amp hours @ 24 Volts = 9.6 kW hours stored power.
400 usable maximum Amp hours @ 48 Volts = 19.2 kW hours stored power.

That is not saying you can't have multiple charge controllers and really large battery banks, it's just one way to look at the available equipment and make a choice.

At some point you simply have to make a judgement call.

Cariboocoot - at 48 volts would I not have 200AH usable which would give me 200 * 48 = 9.6kW hours stored power, the same as a 24V system?

The one good thing about the 24V system is that adding another string of batteries can be done relatively inexpensively - get them from Panama City, getting more panels and such into Panama is not quite as straight forward - not impossible though.

You are right, at some point a decision will be made. I do appreciate yours, and everyones input.

Cheers

Ernest

Re: Bulding new Off Grid Home in Panama

solar_dave wrote: »

Here is a nice way to setup a wireless repeater.
http://www.geeks.com/details.asp?invtid=NU-644-202-0005&cat=NET

I have 2 of these, one one the TED and one on my media computer.

Looked at the unit, quite nice, compact and price is good. Will review again.

Cheers

Ernest

Re: Bulding new Off Grid Home in Panama

Have done some more data mining on this site. More information than I can ever assimilate; however, it brings up some interesting issues that I need to resolve. Also using the formulas I have found in the various posts. Don’t poke too many holes in my logic, don’t want the ship to take on too much water before it even sets sail.

This is a long rant; however, I trust that for those of you who do read it, that I have logically put my thoughts on paper so to speak.

First thing is the requirement for 100AH per kW of inverter, with one poster saying a minimum of at least 80%. I notice from signature blocks that several people have 400 or so AH battery banks connected to an XW6048 (the price difference between an XW4024 and XW6048 is ~$600.00). I expect this is the total AHs for the battery bank and not the 50% draw down rate. I would expect that “rules of thumb” have been further tweaked as people have been off grid longer and technology has developed. In this instance I would say that Generator Support is one of the new paradigms that in the past was not available. I would also submit that companies are developing and producing new equipment, and designing into firmware/software new protocols that make solar power systems more effective and efficient..

I have sourced US battery L16 420AH for my system. No special reason, just that these are available here in Panama, I have not found other brands such as Rolls or Trojan of this size here at this time.

For myself, if I were to go with a 48V system, and having sourced US battery L16 with 420 AH at the 20 Hr rate. This gives me a workable AH of 210 for the battery bank that is ~7560 watt hours of power (210AH * 48V * .75 system efficiency). Having done my load analysis and separated it into daytime and night time loads with each being approximately equal at ~3200 watt hrs. The battery bank I have sized would easily handle the night time loads and give me capacity for getting going in the morning.

The temperatures here in Las Uvas, Panama are such that the system will be operating somewhere in between STC and NOTC values. I will be using the NOCT rating values for my calculations. I am also using the sizing tool and using both STC and NOCT values to compare sizing issues. Another reason for using the NOCT rating values is that Photowit recommended it and after reflecting on his suggestion, and that it made sense, I am doing just that. This drops the panel rating to 229 watts at 45 deg C. Where we live it averages 30ish on the celsius scale year round, so in this case it would be prudent to use the NOCT ratings. We also have an annual daily average of 3.5 hrs of sunlight.

Using this as the basis for the array size, for a battery bank of 420 AH with a 50% usable amount of 210 AH, I would need an array size of:

210AH*57.6V charging*1/0.77 panel+controller derating*0.05 rate of charge (ROC) = 785 watt array minimum
210AH*57.6V charging*1/0.77 panel+controller derating*0.10 rate of charge (ROC) = 1570 watt array nominal
210AH*57.6V charging*1/0.77 panel+controller derating*0.13 rate of charge (ROC) = 2042 watt array maximum

Taking into consideration that we will be disconnected from the grid, the solar array should be able to replenish the battery bank and provide power for daytime loads of ~3200 watt hrs.

I will need 9 of the 305W panels at an NOCT of 229W for this array size. I would be able to use a single controller and have 3 panels in series with 3 parallel strings.

The array size based on the NOCT rating of 229W would be 2061 watts. Charging current from this array would be:

2061W*.77/57.6V= 27.55 amps (dividing by system voltage of 48V = 33.06 amps)

The 13% charging rate on a 420AH – 50% usable of 210AH is 27.3 amps. This array size would provide adequate charging for the battery bank size. This array size would also meet the requirement to equalize the batteries through the CC if needed, on a good day of course.

With this in mind, and the sentiment that the array should be sized to deal with battery bank charging and daytime loads, installing 12 panels at 229W would give me an array of 2748 watts. Charging current from an array of this size would be:

2748W*0.77/57.6V 48=36.38 amps (divided by system voltage of 48V = 44 Amps)

This would provide additional current for daytime loads.

Adding a supplemental, smaller array of 6 panels configured as 3 panels in series with two parallel strings would give an array size of 1374W (NOCT rating of 229W per panel). This would provide additional charging current or current for daytime loads of:

1374*0.77/57.6V= 18.36 amps (divided by system voltage of 48V = 22.04 amps).

Of course all this is based on the perfect day, but we all know this is rare and often not the case. For us here it does happen to fit about a 4 1/2 month window from mid December to end April; however, it is the wet season that needs to be addressed with the array and battery bank sizing.

I have been watching with interest, the weather of late and we have had some days where the sun never peeked through the cloud cover and it rained. With this in mind, the extra solar panels, in my opinion will be needed. I also get an extra CC for redundancy.

I have also been thinking about how to figure out what the batteries consume for charging and what the loads consume. I expect that taking the amps coming from the CCs and what the inverter is pumping out to the loads and doing the math, I should be able to determine what went where and how much.

I have been discussing a 48V system so far, but have not ruled out a 24V system. In this case, I submit the following charging rates for a 420 AH battery bank – 50% usable at 210 AH:

210AH*28.8V charging*1/0.77 panel+controller derating*0.05 rate of charge (ROC) = 392 watt array minimum
210AH*28.8V charging*1/0.77 panel+controller derating*0.10 rate of charge (ROC) = 856 watt array nominal
210AH*28.8V charging*1/0.77 panel+controller derating*0.13 rate of charge (ROC) = 1113 watt array maximum

For charging, this would give me (using the max array size for 13% xharging):

1113W*.77/28.8V= 29.75 amps (divided by system voltage of 24V = 35.7 Amps) – more than adequate to recharge the batteries, and provide for house loads during the day.

I would need a solar array of :

1113W/229W panels= 4.86 panels, let’s round it up to 5 Panels.

Since this 24V system mentioned above deals with a single string of 4-L16 batteries with a 20Hr rating of 420AH – 50% usable at 210AH, I would need to have a second string of 4-L16 420 AH batteries to give me the required watt hours per day, because a single string would only be able to provide power for night time loads and be drawn down to 50% SOC.

Using this new battery bank size of 840 AH – 50% usable of 420AH, I would need an array sizing of:

420AH*28.8V charging*1/0.77 panel+controller derating*0.05 rate of charge (ROC) = 785 watt array minimum
420AH*28.8V charging*1/0.77 panel+controller derating*0.10 rate of charge (ROC) = 1570 watt array nominal
420AH*28.8V charging*1/0.77 panel+controller derating*0.13 rate of charge (ROC) = 2042 watt array maximum

Using the array for a 13% charging rate I get:

2042W*.77/28.8V= 54.6 amps (divided by system voltage of 24 = 65.5 amps)

The 13% charging rate for a 420AH battery bank on a 24V system is 54.6 amps. From the above there is sufficient charging current being supplied from a 2042 watt array.

It is also an array size of 9 panels. Using the CC sizing tool from MidNite Solar indicates that at the 305W STC rating for the Helios panels, an array of 6 panels, 3 in series with two parallel strings, or 2 panels in series with 4 parallel strings can be accommodated by one Classic 150 controller. This is short of the 9 panel requirement for the 13% charging rate for an 840AH battery bank – 420AH usable at 50%.

The best array sizing and configuration for this size battery bank would be two small arrays at 1830W (panel at 305 STC rating) – 1374W (panel at 229W NOCT
Rating).

Each array would provide charging amps at the 229W NOTC rating of:

1374W*.77/28.8V= 36.74 amps (divided by system voltage 24V = 44.08amps)

The combination of the two smaller arrays should provide adequate charging amperage and current for daytime loads.

Adding to this, I intend to get a generator capable of being used for Generator Support. Have not found a Honda dealer as yet, but I am still looking.

Getting to the inverters, should the loads grow, and having a 24V system, there is the possibility of having to either upgrade to a 48V system, or put in a second 24V inverter (same kind).

I mentioned above that there is not a lot of price difference between the XW4024 and the XW6048 - ~$420.00. The XW4024 is ~$2479.00 and the XW6048 is~$2897.00. (I’m expecting NorthGuy to chime in here regarding 100AH, etc.).

Having to upgrade and install a second XW4024 would entail an additional cost of ~$2479.00 plus ancillary items. Installing an XW6048 with a battery bank of 420AH does not fit the “rule of thumb”, but it does fit a cost perspective. The XW4548 fits in the middle at ~$2689.00. Upgrading to a 48V system in the future is also an additional cost as well, and here in Panama, selling used solar system equipment is not as easy as up north.

Reviewing our requirements, and what we could have to provide for ourselves in the future, the only real issue we have is the need for AC. We will not be putting in a well system (we are having a backup water system at 12 or 24 volts – TBD). Other than AC requirements, there are no big draws on the system. I am actively perusing forums and the web to find something that will fit the bill.

The AC split systems we had installed in another house use 4 amps on high. I know this from seeing the fluke meter when it was installed. Still too much draw on the system. May have to have a separate panel for the AC units, having two installed, one for each bedroom. Having said this, power consumption for this unit is:

220V*4 amps=880 watts

As we get more acclimatized, we are starting to raise the temperature on the AC units in the house we are renting. Our new house will also have security grates over all windows and doors, and as such, will allow us to leave our windows open at night.

Operating 1 AC unit for two hours would consume 1.76 kWh and seriously dip into the next day reserves. Operating two when company comes calling throws all game plans out the window.

The AC question is still up in the air, and it is also required when there is no power being produced from the solar array. More work on this to be done.

Lots of information out of my head, but need to do this. Decision time is coming.

Cheers

Ernest

Re: Bulding new Off Grid Home in Panama

BB. wrote: »

I think that this derating/sizing parameter is a typo:



I would replace them all with "1" (1/0.77) and everything else is OK (including the answers)--Same copy and paste error in the rest.



-Bill

Bill

Originally had it as "1/0.77" and thought I had made a mistake so I changed it. Was looking at a lot of info and it was getting late.

Cheers

Ernest

Re: Building new Off Grid Home in Panama

jeffkruse wrote: »

I think it was mentioned before but just in case it wasn’t.

After a certain period of time you should not add batteries to existing batteries (IE: and another bank after 2 years).

So unless you plan on adding the third bank within a year don’t consider adding a bank an option.

I would also get lots of clouds in the afternoons her in Puerto Rico. I very slightly oriented my panels to favor the morning sun. With 2K of panels I would avg 8KWH/Day in the summer.

Thanks. It has been mentioned and I did know this. Good to be reminded. Have thought a lot about the orientation of the array(s). If I put all panels on the front roof area, I will capture all of the morning sun and be good up to 2 to 3 in the afternoon.

Cheers

Ernest