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Old 21-11-2017, 13:55   #1
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Resurrect old solar install

I am needing to do something to increase my solar charging as it isn't keeping up adequately. The existing system:
(4) 75 watt Siemens panels
(2) 90 watt Kyocera panels
Wired in parallel, through a Morningstar PS-30M charge controller
580 amp-hour AGM battery bank
No wind generation.

I currently estimate I use 200 amp hours daily at anchor, and 300 amp hours daily while underway.

I am wondering if rewiring the panels in series through a new MPPT controller would be beneficial enough to make it worth it, or should I just add one more large panel and separate controller? I have space for another 300 watts on my dinghy davits.

Realistically I see 20-22 amps peak charging now, in Alaska, and saw around 28 amps peak in Seattle. We are headed to the tropics so I'm sure the charge will grow, but I'm unsure how much. I am also concerned my charge controller is undersized.

Any guidance would be appreciated.
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Old 21-11-2017, 14:44   #2
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Re: Resurrect old solar install

If it were me I would add a big panel or 2 ( 24 volt in the 300 watt range ) running its own mppt to add charging capability. (The current controller is just about at its limit now.)
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Old 21-11-2017, 15:12   #3
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Re: Resurrect old solar install

Don't put them in series. Get a little shade on one, and the whole string's output is dramatically reduced.

You have almost 500 watts solar, but your usage is a bit high for that amount.
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Old 21-11-2017, 15:26   #4
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Re: Resurrect old solar install

And investigate watt-trimming possibilities. All LED lighting? Gas solenoid? Refrigeration?

Saving watts is often cheaper than generating them and storing them.
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Old 21-11-2017, 15:43   #5
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Re: Resurrect old solar install

Add as much solar as you can fit and use MPPT controllers.
Ensure that the panels are not shaded at all and keep them clean.
As you go south you'll get more direct sun but the ambient temperature goes up driving up your refrigeration loads. Also further south it may be more humid which reduces the strength of the sun on the panels.
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Old 21-11-2017, 16:48   #6
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Re: Resurrect old solar install

For my daily draw, I'm not sure how much I can reasonably cut. Lights are all LED, cabin lights are alpenglow.

My major power users are a pair of fridges- both pretty efficient, one is technautics coolblue with 3" of foam, the other is a small front load dometic, combined draw around 50-60 ah per day. Also is the little wonder 12v water maker, 6A for 6gal an hour, and the autopilot underway as it is a catamaran.

I wonder if a mppt controller would help push me over the edge with my existing panels? The existing is pretty close to maxed out as has been said, and is PWM.

It is a possible option to turn off my front load fridge, but is not ideal as the big one is under a bunk and hard to access.
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Old 21-11-2017, 17:44   #7
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Re: Resurrect old solar install

Quote:
Originally Posted by Excalibur5 View Post
For my daily draw, I'm not sure how much I can reasonably cut. Lights are all LED, cabin lights are alpenglow.

My major power users are a pair of fridges- both pretty efficient, one is technautics coolblue with 3" of foam, the other is a small front load dometic, combined draw around 50-60 ah per day. Also is the little wonder 12v water maker, 6A for 6gal an hour, and the autopilot underway as it is a catamaran.

I wonder if a mppt controller would help push me over the edge with my existing panels? The existing is pretty close to maxed out as has been said, and is PWM.

It is a possible option to turn off my front load fridge, but is not ideal as the big one is under a bunk and hard to access.
the biggest thing you can do here is increase the insulation on the cool blue fridge to at least 5 inches ( that alone will get you in the green so to speak.)
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Old 21-11-2017, 17:58   #8
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Re: Resurrect old solar install

Quote:
Originally Posted by Excalibur5 View Post
For my daily draw, I'm not sure how much I can reasonably cut. Lights are all LED, cabin lights are alpenglow.

My major power users are a pair of fridges- both pretty efficient, one is technautics coolblue with 3" of foam, the other is a small front load dometic, combined draw around 50-60 ah per day. Also is the little wonder 12v water maker, 6A for 6gal an hour, and the autopilot underway as it is a catamaran.

I wonder if a mppt controller would help push me over the edge with my existing panels? The existing is pretty close to maxed out as has been said, and is PWM.

It is a possible option to turn off my front load fridge, but is not ideal as the big one is under a bunk and hard to access.
An MPPT controller will certainly help and they are cheap enough these days. In fact, in your case it may make sense to put 2 MPPT controllers in. 1 controller for the old 75W panels and 1 controller for the 2 90W controllers (as long as all the panels are matched).

As to shading.. I have found that its WAY overblown about panels in series (if you have bypass diodes). Since you are on a cat, shading should be quite reduced anyway..

On my cat, I have 1 bank of 4 old Shell solar 75W panels in series (today they peaked at 312W, pretty good for 16 year old panels). Our second bank is 2 150W Renogy panels in series (peaked at 318 today). Our third bank is 2 100W "Amazon Cheapies" in series (only peaked at 172W today). Each of these banks is hooked to a Victron MPPT controller. We have a final 4th bank of a single 100W panel hooked to a cheapie Chinese MTTP (peaked at 88W today).


Your daily draw is almost exactly the same as mine (yesterday we did 208AH). Down here in the Caribbean we hit 14.8V by about noon (still not fully charged, but close). After that we plug in all our toys (2 laptops, kids games and tablets, ect).

I hope that helps you a bit.. I always find "real world" numbers mean so much more then anyones "theory".
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Old 21-11-2017, 22:56   #9
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Re: Resurrect old solar install

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Originally Posted by travellerw View Post
....Down here in the Caribbean we hit 14.8V by about noon (still not fully charged, but close).......
WOW... I thought everybody here on this excellent forum knows that reaching 14.8v is nowhere near fully charged - fact not theory!

You are probably only 80% charged and need to sit at this absorption voltage for maybe 4 hours or more (depending on battery capacity) before the solar charge controllers drop to float. That also isn't fully charged - maybe only 95%. This last 5% can take longer than the number of hours of sunshine left in the day.

80% charged has only reached 60% of your useable capacity. 95% charged means you are still up to only 90% on your useable capacity. Useable capacity figures are more enlightening than the actual SOC battery capacity.

It's worth repeating again and again that getting back to a REAL 100% at least every 1-2 weeks extends the life of the batteries.
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Old 21-11-2017, 23:59   #10
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Re: Resurrect old solar install

get a 2nd controller and run each type of panel through it's own controller. I wouldn't have put different panels in parallel.

ideally you'd have 5 controllers. but try 2 and see what happens. do you track how much ah your solar produces daily? (ie shunt / monitor on solar controller)

just noticed your not MPPT. get 2 new MTTP controls and run each panel type in parallel to it's own controller

those panels are pretty small each though, and may have low peak voltage for an MPPT. you'd have to find specs.
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Old 22-11-2017, 00:55   #11
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Re: Resurrect old solar install

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Originally Posted by sailinglegend View Post
WOW... I thought everybody here on this excellent forum knows that reaching 14.8v is nowhere near fully charged - fact not theory!

You are probably only 80% charged and need to sit at this absorption voltage for maybe 4 hours or more (depending on battery capacity) before the solar charge controllers drop to float. That also isn't fully charged - maybe only 95%. This last 5% can take longer than the number of hours of sunshine left in the day.

80% charged has only reached 60% of your useable capacity. 95% charged means you are still up to only 90% on your useable capacity. Useable capacity figures are more enlightening than the actual SOC battery capacity.

It's worth repeating again and again that getting back to a REAL 100% at least every 1-2 weeks extends the life of the batteries.
ok so enlighten us
Btw 14.7 is full according to trojan for 12v Fla batteries.
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Old 22-11-2017, 02:28   #12
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Re: Resurrect old solar install

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ok so enlighten us
Btw 14.7 is full according to trojan for 12v Fla batteries.
I think you will find that that is a misunderstanding of what Trojan say.

You can't tell a battery's state of charge by what voltage it is receiving during charging, that is purely a function of the charge controller. You can only tell the SOC by a combination of charging voltage and current acceptance.

14.7/14.8 is the charging voltage, not the "battery voltage". A FLA will be only be full (or close to it) when the charging voltage is at that level and the batteries are only accepting a small charge current - which will be several hours after the charge voltage first reaches that level.

Assuming a 3 stage "smart charger' (bulk, absorption and float), hitting 14.8 just means that charging has reached the end of the first (bulk) charging stage and is switching to the second (absorption) stage.

As Sailinglegend says, that will generally be at around 80% SOC and getting up to 95% or more will take several hours.
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Old 22-11-2017, 02:45   #13
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Re: Resurrect old solar install

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I think you will find that that is a misunderstanding of what Trojan say.

You can't tell a battery's state of charge by what voltage it is receiving during charging, that is purely a function of the charge controller. You can only tell the SOC by a combination of charging voltage and current acceptance.

14.7/14.8 is the charging voltage, not the "battery voltage". A FLA will be only be full (or close to it) when the charging voltage is at that level and the batteries are only accepting a small charge current - which will be several hours after the charge voltage first reaches that level.

Assuming a 3 stage "smart charger' (bulk, absorption and float), hitting 14.8 just means that charging has reached the end of the first (bulk) charging stage and is switching to the second (absorption) stage.

As Sailinglegend says, that will generally be at around 80% SOC and getting up to 95% or more will take several hours.
here is one for ya .
I consider my bank to be charged when at 14.7 it is only accepting a .4amp charge ( 440 ah bank) realistically only about 400ah real world. ( Fla )
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Old 22-11-2017, 02:46   #14
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Re: Resurrect old solar install

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WOW... I thought everybody here on this excellent forum knows that reaching 14.8v is nowhere near fully charged - fact not theory!

You are probably only 80% charged and need to sit at this absorption voltage for maybe 4 hours or more (depending on battery capacity) before the solar charge controllers drop to float. That also isn't fully charged - maybe only 95%. This last 5% can take longer than the number of hours of sunshine left in the day.

80% charged has only reached 60% of your useable capacity. 95% charged means you are still up to only 90% on your useable capacity. Useable capacity figures are more enlightening than the actual SOC battery capacity.

It's worth repeating again and again that getting back to a REAL 100% at least every 1-2 weeks extends the life of the batteries.
I guess I should have worded that better. Since he was asking about solar and MPPT I didn't feel it necessary to launch into a battery charge thread.

Once I hit 14.8 I pretty much know I'm no longer using all the capacity of my 4 solar banks. At that point I can begin plugging in our other gear to use that excess capacity. As long as the sun shines strong, more and more of that capacity is available as the batteries charge current tails off. That was the point I was trying to make.
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Old 22-11-2017, 02:52   #15
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Re: Resurrect old solar install

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As long as the sun shines strong, more and more of that capacity is available as the batteries charge current tails off. That was the point I was trying to make.
Actually I think that is a very good point, if the batteries limited by how much they can absorb by mid day then use the surplus power elsewhere.
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