Solar crunch time! Please review my plan.

[Chilepalace]

I would like begin my first post with a big thank you to all who have shared their knowledge and experience on this forum. Without that, I probably wouldn't be entering the solar jungle!

I hope you will take a look at my plan,(will try to keep it short), and alert me to any big mistakes I am about to make.

The rig: 27' 5er, 2 Trojan T-105 batteries. Lots of dry camping, however our power needs are minimal. No plans for a large inverter or power hungry appliances. LED's already installed. Usually camp in warm, sunny places, often at 11,000ft. elevation.

The equipment:
Solar Cynergy 300W kit from Solarblvd. $415/free shipping.
Includes:
2 150W mono panels
Solar Cynergy 20amp controller(probably not use).
40' of 10Ga. cable w/mc4 connectors, 2 mc4 Y connectors.
8 'Z' brackets(won't use).

Trimetric SC2030 controller kit from solarseller.com. $340 w/shipping.
Includes:
30amp PWM Controller and 2030RV monitor.
500amp shunt.
Monitor wiring harness and temp. sensor w/connectors.

Battery cables,fuses, disconnects, panel mounting hardware: <$200? So maybe do this for just under $1000. Worth it?

My main questions for all of you:
Is the above controller & monitor a good choice for my system?
Would an MPPT controller justify the extra cost? I have been trying to research the Tracer 4215Bn with Mt50 remote monitor. Haven't had any luck finding adequate info.(or suppliers) on these units.

Wire size: Approx. 12' run from panels to controller, is 10 ga. supplied in the kit adequate? 4' controller to batteries, 4ga. welding cable OK?

Thank you for any comments/suggestions you care to share.

[pianotuna]

Hi Reed,

Are these -30 C LI batteries available to the great unwashed (i.e. ME)?

Are they "safe" like the LiPo cells you are using?

My RV has to endure -30 from November to March with occasional dips to -40. Even with loads of solar I doubt that the bank could be kept warm without shore power.

[reed_cundiff]

Pianotuna - as we have posted ad nauseum, we went to LFP two years ago but we do not have the extreme cold that you have. NASA uses a type of lithium battery that will charge at -30 C and Manzanita Micro has told us that the CALB cells they use will safely charge at far below 0 C which is the limit for certain LFP formulae. We left rig for three months at son's place in mountains of NM and it did go down to -10 to -15 F (- 23 to -26 C) and left battery suite connected. There is no noticeable decrease in capacity. We do have enough battery capacity that we could put electric heaters and insulation around the batteries and keep them above 0 C. We have replaced all bulbs with LEDs except for the main storage area of 5th wheel (Basement as my wife calls it). There are four x 40 W incandescent lamps in the basement. We have left two of them running on battery on cold nights to keep pipes from freezing and that only gave us a -1kW-hr deficit. Probably only require a one 40 W incandescent plus insulation to keep the forward bay (battery suite) above freezing. However, we choose to go south when it gets cold.

Reed and Elaine

[BFL13]

pianotuna wrote:
Hi Reed,

I don't always agree with BFL13, but I have a LOT of respect for the tests he has done for all of us. I'd be proud to call him a friend.

reed cundiff wrote:
Well at least folks are being polite here, something that does not always happen on other fora.

Reed and Elaine
Solar autonomous for two years and delighted.

PT, you are cute too! 🙂

Looking at Surrettes--wow, bring money! 😞

http://www.wegosolar.com/brands.php?brand=Surrette

[pianotuna]

Hi Reed,

I don't always agree with BFL13, but I have a LOT of respect for the tests he has done for all of us. I'd be proud to call him a friend.

reed cundiff wrote:
Well at least folks are being polite here, something that does not always happen on other fora.

Reed and Elaine
Solar autonomous for two years and delighted.

[pianotuna]

Hi BFL13,

Mostly I agree.

A larger bank will not cause the user to use more amp-hours for say running the microwave per day. But running a microwave on a 200 amp-hour bank is going to consume more amp-hours. The choice then, is either a larger bank (not always possible), or more wattage per 100 amp-hours to try to mitigate the "too small" capacity. That is what I mean when I say discharging is not linear. It depends on the size of the load. In my case the load is 1561 watts and that shows up as about 170 amps. The 400 watt coffee maker draws only 54 amps.

I believe in setting the battery bank size based on an energy audit. There are some variables such as frequency of use. When I was using the RV 50 nights per year I could get by with a smaller solar "farm", and by having a medium large battery bank I could do a week long trip without shore power or any generator use (no air conditioning, but all cooking and water heating done electrically). The goal was to have the RV behave as if it were on shore power 100% of the time. During storage, the solar panels would return the bank to bursting full for the next trip. It is true that I did rely on the alternator to do a lot of the "heavy lifting".

Now that I full time, my energy needs are no longer entirely met by solar, and the distance I travel is actually smaller. I could use a thousand watts of panels.

From May 1, 2009 to Oct 1, 2013 I did 125 deep cycles. Since then I've done a further 300 cycles. My batteries are showing their age. Last fall, they would still draw 125 amps from the Magnum inverter charger. Now they do not get near that number. The posts are showing evidence of corrosion, and the solar never gets down to the 1 amp level, so it really is time to replace them.

Because of my need to recharge in extreme cold, I've decided that AGM is the only sensible alternative. I think I can fit in four L-16 Surrette 400 amp-hour six volt jars. Some careful measuring will have to be done.

[reed_cundiff]

Well at least folks are being polite here, something that does not always happen on other fora.

Reed and Elaine
Solar autonomous for two years and delighted.

[BFL13]

Hard to tell for sure, but it looks like PT is starting with the battery bank size requirement and then moving to the solar requirement to match the size of the bank.

I am saying the solar requirement is independent of the battery bank size requirement. But both requirements start with the daily AH usage figure.

PT says to start with an audit and get that usage figure, and I agree.

Now you need some batteries and you want to go no lower than 50% SOC daily and you want to get back to 100% daily. I agree.

So whatever recharging method you use, you want to replace the daily usage daily ending up will full batteries. With solar as the recharging method, that means getting to 100% before dark and not getting below 50% overnight until the sun comes out next day and you start recharging again. I think PT would agree.

So my point is that the solar has to replace that daily AH usage daily and that you can figure out how much of a solar set-up you need to do that. I think PT would agree. BUT I am saying that has nothing to do with how many batteries you have, which is a separate subject but is also related to the daily AH usage so you don't drop below 50% overnight.

It doesn't matter if your daily usage is all microwave from inverter or all LED lights left on all day, an AH is an AH, and the daily AH figure we are starting with includes everything. So it doesn't make any difference to the solar requirement just how you use up the AHs.

I did say the battery bank size required can be affected by whether you have solar. But the solar requirement is a separate thing, only relating to replacing that daily AH usage.

So with that background, I will insert replies to PT's quote below, but just for the record, and there is no need for anybody else to follow it unless you are bored! 🙂 If PT wants to respond, then he will have the last word here so we don't keep spinning our wheels.

pianotuna wrote:
Hi BFL13,

No I'm not saying that at all. A small bank needs more wattage because there is a much greater chance that it will dip below 50% state of charge.
-------------
The premise is that the two batt bank will be at 50% starting its recharge, so this is a deflection change of subject, not a response
-------------------

What I have consistently said is that as battery bank capacity rises the solar wattage per 100 amp-hours can be lower and may approach but not be below 60 watts per 100 amp-hours.
---------------
It is incorrect to say it "can" be lower. It is not some kind of choice. It IS lower if the bank is bigger while the solar amount remains the same at the AH required to replace daily usage
----------------

I have also consistently said that 150 watts per 100 amp-hours is a reasonable maximum wattage, because above 85% state of charge that is as much as the jars will accept.
--------------------
The premise is that the solar will replace the daily AH so it is understood the battery acceptance rate vs SOC at the voltage concerned will allow that recharge to 100%. So if that is the maximum per battery then that's fine, but not in dispute anyway
-----------------

Charging is not linear. Neither is discharging.
---------------

The standard V looking graph of that shows that the recharge is not linear for AH vs SOC and has that SG sag line too. BUT the discharge side shows a linear drop of SOC and SG. I don't understand what exactly PT is saying or where it fits in here
-----------------

If an inverter is going to be used or the user is a full time RV'er, then they may benefit from maxing out all available unshaded space, and they should ignore the 150 watt suggestion. They should NOT ignore the 60 watts per 100, unless they use bank switching (I do use it).
-----------------
It doesn't matter what the AH usage is composed of, inverters or LED lights. An AH is an AH and the daily AH usage from whatever cause is what we start with.

I am not including the battery requirement to be equalized as a solar requirement. PT keeps sliding that in as though the only way to equalize is with solar, so you must have enough solar to do that too.

I am saying the solar requirement is to replace the daily AH usage to get back to 100%. You don't need to equalize to get back to 100. Yesterday I got back to full baseline SG 100% before dark on solar alone with the last few hours of daylight in Float at 14.4 volts. (with 255W on a 458AH bank)

BFL13 wrote:
So now you are saying the four batts will need more amps (and so a higher wattage array) than the two batts to cover the "higher" losses to do the same AH in the same time. This is a 180 in your story!

[pianotuna]

Hi BFL13,

No I'm not saying that at all. A small bank needs more wattage because there is a much greater chance that it will dip below 50% state of charge.

What I have consistently said is that as battery bank capacity rises the solar wattage per 100 amp-hours can be lower and may approach but not be below 60 watts per 100 amp-hours.

I have also consistently said that 150 watts per 100 amp-hours is a reasonable maximum wattage, because above 85% state of charge that is as much as the jars will accept.

Charging is not linear. Neither is discharging.

If an inverter is going to be used or the user is a full time RV'er, then they may benefit from maxing out all available unshaded space, and they should ignore the 150 watt suggestion. They should NOT ignore the 60 watts per 100, unless they use bank switching (I do use it).

BFL13 wrote:
So now you are saying the four batts will need more amps (and so a higher wattage array) than the two batts to cover the "higher" losses to do the same AH in the same time. This is a 180 in your story!

[Fisherguy]

.... just trying to learn, been reading a lotta solar threads the last few days. 😉

[BFL13]

Fisherguy wrote:
(This is starting to remind me of those infamous hotly contested converter threads...) :B

Ha! If you are still reading this stuff, it is obvious that there is something weird about you, not about PT and me. 🙂

[Fisherguy]

(This is starting to remind me of those infamous hotly contested converter threads...) :B

[BFL13]

pianotuna wrote:
Hi BFL13,

No, the four battery bank will require more amp-hours to get to 100%.

You already know this from the generator days. No one does 90% to 100% using a generator because it is not cost effective because the charge tapers.

Since above 85% there will be no more than about 12.5 amps per 100 amp-hours going in. As the bank gets closer and closer to 100% there will be more and more loss. The loss may be around double for four jars vs two jars.

Whether that makes a difference in 'real life' situations or not I could not say without a careful experiment.

BFL13 wrote:
Each needs the same AH to get to 100%. Assuming the solar can do that many AH that day, the time is the same, the AH is the same, so the amps must be the same.

Same amps, same size solar array.

So now you are saying the four batts will need more amps (and so a higher wattage array) than the two batts to cover the "higher" losses to do the same AH in the same time. This is a 180 in your story!

However, the acceptance rate in absolute amps (twice the amps actually) of the four batts is higher at high SOC than the acceptance rate of two batts at the same SOC and voltage, and with half the charging rate, the four batts will get to a higher SOC before tapering, and they started at 75% instead of 50% so IMO there will be no difference to get to 100. A lab test to show what really happens would be good though! 🙂

The assumption is the solar amps will be at least the acceptance rate all the time to 100% in both cases. But against that is the controller itself dropping to Float voltage up in SOC somewhere, that costs you amps delivered that the batteries might still take. Let's assume the controller will stay at Vabs to 100% SOC in both cases, to remove that side-issue.

(My Eco-Worthy controller will not co-operate in that. It drops to Float voltage as soon as it reaches Vabs, so I set Float as close to my Vabs setting as it will go to get longer in the day at the higher amps. IMO it would still be a wash even with that controller)

[pianotuna]

Hi BFL13,

No, the four battery bank will require more amp-hours to get to 100%.

You already know this from the generator days. No one does 90% to 100% using a generator because it is not cost effective because the charge tapers.

Since above 85% there will be no more than about 12.5 amps per 100 amp-hours going in. As the bank gets closer and closer to 100% there will be more and more loss. The loss may be around double for four jars vs two jars.

Whether that makes a difference in 'real life' situations or not I could not say without a careful experiment.

BFL13 wrote:
Each needs the same AH to get to 100%. Assuming the solar can do that many AH that day, the time is the same, the AH is the same, so the amps must be the same.

Same amps, same size solar array.

[BFL13]

pianotuna wrote:
Hi BFL13,


You need more wattage with a tiny bank because the depth of discharge is going to be greater.....

Descriptive vs prescriptive again. The charging rate IS higher on the smaller bank accepting the same amps but you don't need more array to be at the same amps.

The two batt bank will be at 50% and the four batt bank will be at 75% going in.

Each needs the same AH to get to 100%. Assuming the solar can do that many AH that day, the time is the same, the AH is the same, so the amps must be the same.

Same amps, same size solar array.

[pianotuna]

Hi,

The bare minimum for being able to equalize is around 60 watt of panels per 100 amp-hours of storage.