Solar Panels and LiFePO batteries

[neil1967]

I am looking to replace my Trojan Lead Acid batteries (390AH) with between 200-300AH of LiFePO. I appreciate that I will have to change my engine and shore power charging arrangements, but for the time being, this question is about installing solar panels to charge the batteries. I am intending to fit 2 x 175W panels at the stern, on the guard rails (I don't have/want an arch), one on each side. Given the possibility of shading, my presumption is that I am better to fit the two panels in parallel? If so, am I better using 2 MPPT controllers, one for each panel (eg Victron Smart Solar 75/15) or one larger controller (Victron 100/30)? There will be around 5-6m of cable between each of the panels and the controller (s). Grateful for thoughts/experiences

 

[Trident]

With two in parallel its fine to use one MPPT rated to the total input
The Victron are good as are the Renogy controllers; with the added bonus of LifePo4 settings (and custom) and a screen to see what's going on. Also a lot less expensive than Victron for a possibly better product. As an aside they also do a combined MPPT and DC DC charger which would kill two birds with one stone with regard to your other charging system (alternator)

 

[neil1967]

With two in parallel its fine to use one MPPT rated to the total input
The Victron are good as are the Renogy controllers; with the added bonus of LifePo4 settings (and custom) and a screen to see what's going on. Also a lot less expensive than Victron for a possibly better product. As an aside they also do a combined MPPT and DC DC charger which would kill two birds with one stone with regard to your other charging system (alternator)

That Renogy combined B2B and MPPT controller looks really interesting - thanks for pointing it out.

 

[geem]

I am looking to replace my Trojan Lead Acid batteries (390AH) with between 200-300AH of LiFePO. I appreciate that I will have to change my engine and shore power charging arrangements, but for the time being, this question is about installing solar panels to charge the batteries. I am intending to fit 2 x 175W panels at the stern, on the guard rails (I don't have/want an arch), one on each side. Given the possibility of shading, my presumption is that I am better to fit the two panels in parallel? If so, am I better using 2 MPPT controllers, one for each panel (eg Victron Smart Solar 75/15) or one larger controller (Victron 100/30)? There will be around 5-6m of cable between each of the panels and the controller (s). Grateful for thoughts/experiences

Have you considered a pair of smaller panels on each side? Say 2x100w. This would allow you to run these pairs in series. It will give you circa 40v at the MPPT controller. Your cable sizes can be a lot smaller, like 1/4 of the cross section. It's the set up I have and it works well. My panels are also mounted on the guardrail. 2 pairs of 180w panels giving 720w in total

 

[GHA]

One point vaguely relevant, victron smartsolar regulators say in the manual that for the regulator to turn on the solar panel voltage needs to be 5v above the battery voltage. It's been said on here before that this is a good reason to run panels in series, you get more power as the regulator turns on earlier in the morning. Just tried it with a power supply simulating a solar panel. With battery voltage at 13.74v it took 40mA to push the voltage on the solar input up to 18.77V when the regulator turned on. No point running in series to get more power in the morning, takes very little light to push the voltage up enough to turn on the regulator.
Other reasons for series may well make sense for your setup, but if someone say go in series to get power earlier in the morning they are mistaken.

 

[Poey50]

I am looking to replace my Trojan Lead Acid batteries (390AH) with between 200-300AH of LiFePO. I appreciate that I will have to change my engine and shore power charging arrangements, but for the time being, this question is about installing solar panels to charge the batteries. I am intending to fit 2 x 175W panels at the stern, on the guard rails (I don't have/want an arch), one on each side. Given the possibility of shading, my presumption is that I am better to fit the two panels in parallel? If so, am I better using 2 MPPT controllers, one for each panel (eg Victron Smart Solar 75/15) or one larger controller (Victron 100/30)? There will be around 5-6m of cable between each of the panels and the controller (s). Grateful for thoughts/experiences

On our 32 footer I have limited solar consisting of 2 x 80 watt panels in a batwing configuration (same as yours). I also have a 30 watt panel on a hatch garage to which I can attach a 100 watt roving panel at anchor. To maximise the solar harvesting I have a separate MPPT controller for each of the two wings and another for hatch + solar. That plus the lithium pack is as good as it gets for a small array, IMO. As GHA mentions, I don't see any noticeable delay in the controllers coming onstream in the morning.

 

[neil1967]

With two in parallel its fine to use one MPPT rated to the total input
The Victron are good as are the Renogy controllers; with the added bonus of LifePo4 settings (and custom) and a screen to see what's going on. Also a lot less expensive than Victron for a possibly better product. As an aside they also do a combined MPPT and DC DC charger which would kill two birds with one stone with regard to your other charging system (alternator)

Having considered this more, I think that having a single device that handles both the Solar and Alternator charging would be tempting fate - if it were to fail on a voyage there would be no way of charging the batteries - at least with separate B2B and MPPT controllers, one or other could be used if the other failed. Also I noted that when an MPPT input is totally absent (eg at night) then the whole capacity of the B2B is available to the Alternator, so with the 50Amp version, when sunlight is available the Alternator and the MPPT are allocated 25A ea, but in the absence of a solar input the Alternator gets 50A, which is no good if you are relying on the B2B to restrict the max current flow and hence protect the alternator from overheating. It does look like a good bit of kit, but perhaps better suited to an RV than a boat. Thanks again though - most interesting.

 

[roaringgirl]

I had solar wings for a while. I wired them in parallel to a single MPPT rated enough to take them both at full power. I reasoned that one would almost always be partially shaded.

It turned out I was completely right and we never saw the full power of both panels and normally only reasonable output from one of them. Had we wired in series I suspect the average yield would have been significantly lower due to partial shading.

 

[geem]

I had solar wings for a while. I wired them in parallel to a single MPPT rated enough to take them both at full power. I reasoned that one would almost always be partially shaded.

It turned out I was completely right and we never saw the full power of both panels and normally only reasonable output from one of them. Had we wired in series I suspect the average yield would have been significantly lower due to partial shading.

The idea is to wire up a pair on each side in series then wire up the two series pairs in parallel. Compared to horizontal panels on an arch I think we get more output. When sailing we can angle the panels so at least half the bank points at the sun. Not possible if the boat is heeled away from the sun with fixed horizontal panels on an arch.
We have been tilting panels down this week at anchor to catch the early morning sun and late afternoon sun. The batteries were in float by 1100 this morning due to the extra input. I don't normally tilt them down but I have been getting out at 0600 for a run whilst it's a little cooler. It seemed like a good idea?

 

[noelex]

I am intending to fit 2 x 175W panels at the stern, on the guard rails (I don't have/want an arch), one on each side. Given the possibility of shading, my presumption is that I am better to fit the two panels in parallel? If so, am I better using 2 MPPT controllers, one for each panel (eg Victron Smart Solar 75/15) or one larger controller (Victron 100/30)? There will be around 5-6m of cable between each of the panels and the controller (s). Grateful for thoughts/experiences

With one panel on the port side and one on the starboard side the best solution is two solar controllers. One tracking the Vmp of port panel and one for the starboard panel.

In many conditions the voltage or the current produced by a panel on the port vs the starboard side will be significantly different which makes parallel or series connection less efficient. The cost of two smaller controllers is often not enormously different from one larger controller and there is added benefit of redundancy.

 

[roaringgirl]

Ultimately, we moved away from that system because the panels, even when stowed were too vulnerable to damage by my bad parking, or other boats coming alongside us.

 

[Mait]

I would use 4 panels. Connect 2 panels in series on port side and the other 2 in series on starboard side. Then use separate MPPT controllers for them.
This is what I am planning to do on my OE36. The stern and shape of the boat and will not favor a solar arch and there's not much deck space available for solar.
A question for those who have had solar panels on guard rails, are they really that vulnerable? I am thinking of 100...120W each side.

 

[geem]

I would use 4 panels. Connect 2 panels in series on port side and the other 2 in series on starboard side. Then use separate MPPT controllers for them.
This is what I am planning to do on my OE36. The stern and shape of the boat and will not favor a solar arch and there's not much deck space available for solar.
A question for those who have had solar panels on guard rails, are they really that vulnerable? I am thinking of 100...120W each side.

I think it depends on the boat and how you intend to use it. We very rarely go in marinas but when we have done we tilt the panels vertically. We have 2x180w panels on each side.
We are currently anchored in Falmouth Harbour Antigua. We have a 55ft Tayana anchored to one side of us with 2 panels on each side and a 51ft Najad with two panels on each side. There are plenty of other yachts here that have panels on the guard wires.

 

[roaringgirl]

We had them for a year. I broke one while it was lowered when rafting up to another boat, a taxi boat in the Galapagos broke another. The third was broken by a boat swinging into us at anchor.

 

[geem]

We had them for a year. I broke one while it was lowered when rafting up to another boat, a taxi boat in the Galapagos broke another. The third was broken by a boat swinging into us at anchor.

Sounds like you had some bad luck. We have had them on the guardwires on two boats since 2003. Never broken one. We are careful. Extra fenders by the panels in a marina. If we are anchored in a tight anchorage we fold them down at night.

 

[Travelling Westerly]

I would use 4 panels. Connect 2 panels in series on port side and the other 2 in series on starboard side. Then use separate MPPT controllers for them.
This is what I am planning to do on my OE36. The stern and shape of the boat and will not favor a solar arch and there's not much deck space available for solar.
A question for those who have had solar panels on guard rails, are they really that vulnerable? I am thinking of 100...120W each side.

I have x2 100w panels in series on port and starboard hand rails, then both series connected into a parallel connection into one MPPT. Similar set up to yours except I use a single Victron 100/50 MPPT.

Two things I did to minimise any possible damage, I converted the guard wires into hard rails, fitted NOA mounts to the rails and panels which allow me to put the panels into a horizontal position and slide the panels inboard. I then put a big ball fender between the panels. They are big so really protect the panels.

 

[roaringgirl]

We have hard rails. Reflecting on it, we could have avoided some of the damage by configuring the panels to fold vertical on the *inboard* side instead of the outboard side of the rails.

If you have no other option, I wouldn't let the risk of damage stop you, a 140w solid panel is cheap as chips these days, and if you're not in the Galapagos, it's easy to replace.

 

[geem]

We have hard rails. Reflecting on it, we could have avoided some of the damage by configuring the panels to fold vertical on the *inboard* side instead of the outboard side of the rails.

If you have no other option, I wouldn't let the risk of damage stop you, a 140w solid panel is cheap as chips these days, and if you're not in the Galapagos, it's easy to replace.

I paid $140US each for 180w panels in Bonaire in 2019. Compared to a wind turbine they are incredible value