My Solar Installation: Flex Panels, Magnet Mounts, Water Heater Load Dump

[socalrider]

Hey all,

Thought there might be some interest in the way I've set up my solar after pulling my genset. This might not work for everyone, but I think it will do quite well for our use case: SoCal cruising with kids in good weather for a few weeks to a month at a time.

I have four Renogy 175kW flex panels mounted to my bimini fabric via magnets mounted to the panel grommets, paired to magnets on the bottom of the fabric.

The fused output goes via 8ga cable to a Renogy 60A charge controller to top off my 6Vx6x222aH 12V golf cart bank via 4ga cable.

I found on my last trip to Catalina that even 2 of these panels had my batteries topped off before noon. I bought four in anticipation of a water maker, but either way I have far more solar than I require, even in somewhat cloudy spring weather.

After doing tons of research on water heating to supplement our engine clarifier loop, I decided that given all this excess solar the easiest, safest & cheapest path would be to use my excess PV output to heat water. Intuitively this seemed crazy, but I think it'll work. Here's how I'm going to do it:

I got a 12VDC 700W dual element heater (can drop to 350W if I want) that should swap directly into my existing 6gal Whale 1500W AC heater. I also got a DC 140F thermostat (you can't use the AC thermostat) which will also be an easy swap.

To control the element, I got a mechanical relay, and finally a simple digital controller which can set the relay to turn on when battery voltage reaches a certain set point, and off again after a period of time *or* when battery voltage drops to a second set point.

This last piece will probably take some tinkering to coordinate with the Renogy charge controller set point; I can always bypass and switch the heater on manually if necessary (e.g. around noon when my batteries are full).

700W will heat 6 gallons of water from 68F to 140F in about 90 minutes. We're pretty frugal with water, though that could change if we end up with hot water and a water maker!

Total cost for the DC/solar heater components: about $100 shipped. I'll need to get a 60A fuse too. This seems way better than messing around with a diesel heater given that we don't really need cabin heat here. Hopefully this is helpful - I'll update if there's interest once I get it fully installed.

 

[Comodave]

Interesting setup. Good job.

 

[boathealer]

I had a similar thought process, and was wrestling with what to do. My solar would typically charge our batteries up by noon also, and the rest of the day was being "wasted".

We have 1400W of flexible solar and 1600Ah (800@50%) of house batteries. Solar is split into 4 banks, with 4 MPPT controllers. (pic)

The first thing I did was change the 50lb, 120V, 24V-thruster/windlass bank charger to a 5lb 12V-24V true charger, with the 12V supplied from the house bank.

Next, I switched our dinghy over to full electric with a 2kW motor and 24V, 75Ah lithium dinghy "bank". Charged with 12V-to-24V lithium charger, with the 12V supplied from the house bank.

Next was the water heater. I had all the same thought process - all kinds of 12V heating elements, switching algorithms, etc.

When my 240V, 1500W, 20gal water heater went out, I had an epiphany. I bought a 120V, 750W, 11gal Isotemp water heater and connected it to the inverter circuits. This would draw 60-70A from the 12V house bank when running. My thought was when the batteries were full around noon, I would just flip the water heater breaker on for an hour or so, and then let the solar charge the batteries back up (partially supplying power during heating also).

This arrangement seems to work well. I had a chance to try it out a few days ago at anchor. A solar "diary" of one day is below:

---

1st week of April, North Florida
Bow facing east most of the time
72deg daytime, full sun, 55deg night
Static boat loads average 8 to 14A @12V, 24/7 in current climate (refer, computers, USB, etc.)
--
Day 1/1:00pm: Anchor down - 100%SOC
Day 1/6:00pm: Induction cooking range and microwave ~20min each. TV.
Day 1/9:00pm: Bed, 95%SOC
Day 2/7:00am: 88%SOC
Day 2/7:15am: Coffee maker and short microwave time, 87%SOC
Day 2/11:30am: Lunch bread toast 85%SOC, charging showing +23A after loads
Day 2/12:30pm: 90%SOC, charging showing +40A after loads
Day 2/2:30pm 100%SOC, charging showing +17A after loads
Day 2/2:30pm Turned on water heater, discharging showing -42A after solar input (72A total consumption)
Day 2/3:30pm Turned water heater off, 98%SOC, charging showing +37A after loads
Day 2/5:00pm 100%SOC, 20A consumption, charging showing +4A after loads

Actual watts output per Victron BT link shows 890W+1130W+840W+2210W=5070Wh produced for all of Day 2. (pic)

This approximates an average 70+A per hour from 11pm to 5pm for the day/conditions above.

---

 

[koliver]

Do I see you eliminating a $20,000 genset by installing a pair of solar panels, a DC heating element for your water heater and a fuse, wire, etc. all for a boat buck?
Pretty nice! quiet too.

 

[boathealer]

I have four Renogy 175kW flex panels mounted to my bimini fabric via magnets mounted to the panel grommets, paired to magnets on the bottom of the fabric.

Surely you mean 175W, not 175kW per panel!!

 

[socalrider]

Surely you mean 175W, not 175kW per panel!!

You got me! Yes of course 175W. Unless they are the new cold fusion reactor panels

 

[socalrider]

Do I see you eliminating a $20,000 genset by installing a pair of solar panels, a DC heating element for your water heater and a fuse, wire, etc. all for a boat buck?
Pretty nice! quiet too.

Exactly! Lots more space in the engine room, and I sold the generator for 3x the cost of the new stuff. See, you *can* make money messing around on boats!

 

[CaptTom]

Exactly! Lots more space in the engine room, and I sold the generator for 3x the cost of the new stuff. See, you *can* make money messing around on boats!

I'm following this thread closely, thanks!!!

Doing some measurements now, but it looks like I have room on the Bimini for 4-6 panels if I use the magnetic mounts.

I may even check into running my water heater off the inverter if it turns out I have power to spare.

Dumb question though: Do I need a dedicated MPTT controller for each panel?

 

[socalrider]

Dumb question though: Do I need a dedicated MPTT controller for each panel?

No you don't. If all your panels are on your bimini and you're not likely to get shading, you can probably run them all in series to get the voltage up & keep your amperage down (that's what I did and why I only need 8ga for the long run down to my charge controller, but 4ga for the short run at 12V to my battery bank. Just make sure the controller you pick can handle the combined max voltage of your panels, and also the amperage output to your batteries.

If shading is a concern there are other options.

 

[SteveK]

Side question. Noted that direct DC does not have the conversion loss from using an inverter. Just wondering if that option was eliminated. Charge battery while inverter heats water.

 

[socalrider]

Side question. Noted that direct DC does not have the conversion loss from using an inverter. Just wondering if that option was eliminated. Charge battery while inverter heats water.

I thought about it briefly - but I couldn't see the sense in spending $300 min on a 2kW inverter and losing 10% efficiency versus $35 on a DC heating element & thermostat. If I had another good use for the AC power or already had an inverter onboard I may have gone that route. If it's close to a toss-up I like not having any AC on the boat to keep things simple & the cost of a wiring mixup relatively low.

Edit: another consideration was that 700W = 56A, versus 1500W/90% efficiency = 133A. That's a serious draw on the battery pack, even with 40-50A of peak solar going in. I'd rather a lower draw for a longer period of time to absorb the excess solar & not cycle the pack. I chose the dual element DC coil so that I could experiment with using it at 350W (28A) so that I'd have a longer period of time over which to harvest the excess solar while the batteries are charging.

The way the controller works, I'll have a high voltage set point to turn the element on when the batteries are fully charged (e.g. 14.4V), and then turn off when the batteries are able to accept charge again (e.g. 13V? not sure of this yet). If I switch on an inverter and it drains 100A from my pack, the voltage will drop way down (e.g. 12.3), and it'll be trickier to control. I'm sure you could do it, but I think the concept might work best when the dump load resistor (heating element) is sized at or below the PV array peak output so you're not discharging the battery to heat water.

 

[SteveK]

I thought about it briefly - but I couldn't see the sense in spending $300 min on a 2kW inverter and losing 10% efficiency versus $35 on a DC heating element & thermostat. If I had another good use for the AC power or already had an inverter onboard I may have gone that route. If it's close to a toss-up I like not having any AC on the boat to keep things simple & the cost of a wiring mixup relatively low.

Oh you did the right thing. I made the assumption everyone has an inverter, my bad.

 

[Chuck in WA]

Thanks very much for posting this Socalrider. And for the hyperlinks. I'm in a similar situation as I'd rather pull out my old rusty/leaky generator that won't start rather than throw $$ at it, so I'll be following your thread also. With propane for cooking and no air conditioning, I hope to go all solar. The question of the hot water heater had me stumped (short of running an engine just to heat water). While I do have an inverter, it seems unappealing to put such a load on it for the reasons you describe above, and I think your solution is great. I hope you're able to make your system as "hands-off" as possible - meaning when the batteries are topped, the extra energy goes to work heating the water automatically without user input. How cool!
Please continue to update as you fiddle with it (and pics are always great too)!!

Edit - I wouldn't mind keeping my AC element in the hot water heater for a fast heat when I'm plugged in. I wonder if it's possible to do both somehow?

 

[socalrider]

Please continue to update as you fiddle with it (and pics are always great too)!!

Edit - I wouldn't mind keeping my AC element in the hot water heater for a fast heat when I'm plugged in. I wonder if it's possible to do both somehow?

Will do - glad you appreciated the post. I probably won't have it fully dialed in for another month or two, but it'll be fully proven out over the summer & I'll report back.

If you want to keep the AC option & already have an inverter on board I'd consider using it - if you have or could find a dual element heating element (2x750W instead of 1x1500W probably) you could switch it to half power while on solar and back to 1500W on shore power. Or just swap the element down to 750W or so - you could set up the same control system I've got where the solar "charges" the water heater via the inverter once battery voltage hits a certain set point. If your water heater has two heating elements you could make a dual voltage system work, but otherwise I'm not sure how to do it easily.

 

[Bud]

Nice system and design. My only concern for myself would be the loss of redudancy with mutiple sources to charge and operate items. I also would be concerned with wiring the solar panels in series. Allthough the installation is easier with smaller wire, if one cell or one panel goes open you lose all solar output. If you wire them in parallel yes you have to use heavier wire but one panel can go out and you would still have the other panels producing. Same with any shadowing.
Having said that, I only have a small two panel solar system in place and I am looking to go to a 6 panel system on a hard top. So my comments are somewhat theoretical.

Bud

 

[socalrider]

Nice system and design. My only concern for myself would be the loss of redudancy with mutiple sources to charge and operate items. I also would be concerned with wiring the solar panels in series. Allthough the installation is easier with smaller wire, if one cell or one panel goes open you lose all solar output. If you wire them in parallel yes you have to use heavier wire but one panel can go out and you would still have the other panels producing. Same with any shadowing.
Having said that, I only have a small two panel solar system in place and I am looking to go to a 6 panel system on a hard top. So my comments are somewhat theoretical.

Bud

Thanks Bud,

The panels are all connected using MC4 connectors (https://en.m.wikipedia.org/wiki/MC4_connector)

If a panel goes out, it’s trivially easy to pull the plugs and re-connect to its neighbors, removing it from the string. So I don’t see any loss in redundancy with the series wiring versus parallel. You could get more redundancy if you had multiple charge controllers I suppose - though in a pinch you could even wire a panel straight into the battery bank. These are really reliable solid state devices compared to rotating machinery. And I still have two alternators as well.

 

[Bud]

On my vessel I have a VHF antenna and a mast that could throw a shadow across a panel. If they were in parrallel a shadow across one panel does not stop all output of the solar system.
As far as isolating a bad or damaged panel I do not beleive my wiring on my hardtop will be as flexible as yours is on your bimini. I would be concerned about having enough excess wire to reach around the bad panel to the good one. For those reasons for me it would be easier to just run heavier wire and wire them in parralel.

Bud

 

[JimW]

Hey all,



Thought there might be some interest in the way I've set up my solar after pulling my genset. This might not work for everyone, but I think it will do quite well for our use case: SoCal cruising with kids in good weather for a few weeks to a month at a time.



I have four Renogy 175kW flex panels mounted to my bimini fabric via magnets mounted to the panel grommets, paired to magnets on the bottom of the fabric.



The fused output goes via 8ga cable to a Renogy 60A charge controller to top off my 6Vx6x222aH 12V golf cart bank via 4ga cable.



I found on my last trip to Catalina that even 2 of these panels had my batteries topped off before noon. I bought four in anticipation of a water maker, but either way I have far more solar than I require, even in somewhat cloudy spring weather.



After doing tons of research on water heating to supplement our engine clarifier loop, I decided that given all this excess solar the easiest, safest & cheapest path would be to use my excess PV output to heat water. Intuitively this seemed crazy, but I think it'll work. Here's how I'm going to do it:



I got a 12VDC 700W dual element heater (can drop to 350W if I want) that should swap directly into my existing 6gal Whale 1500W AC heater. I also got a DC 140F thermostat (you can't use the AC thermostat) which will also be an easy swap.



To control the element, I got a mechanical relay, and finally a simple digital controller which can set the relay to turn on when battery voltage reaches a certain set point, and off again after a period of time *or* when battery voltage drops to a second set point.



This last piece will probably take some tinkering to coordinate with the Renogy charge controller set point; I can always bypass and switch the heater on manually if necessary (e.g. around noon when my batteries are full).



700W will heat 6 gallons of water from 68F to 140F in about 90 minutes. We're pretty frugal with water, though that could change if we end up with hot water and a water maker!



Total cost for the DC/solar heater components: about $100 shipped. I'll need to get a 60A fuse too. This seems way better than messing around with a diesel heater given that we don't really need cabin heat here. Hopefully this is helpful - I'll update if there's interest once I get it fully installed.

Great post, thank you . . . considering similar setup with the flexible panels on the bimini w/magnets to secure . . . Goal would be to be a backup to charge house bank (2 Odyssey AGM PC 1800’s +/- 400ah, soon to add a 3rd), to limit generator usage later converting to more solar, 1st step . . .

 

[fryedaze]

Do you think the magnets will hold in a 65 knot wind? I like the idea but would be concerned that wind could get under it.

 

[dhays]

Do you think the magnets will hold in a 65 knot wind? I like the idea but would be concerned that wind could get under it.

I would think that the whole point of using magnets is that the panels would be easy to take down, along with the Bimini, when severe weather forecast.

 

[fryedaze]

I would think that the whole point of using magnets is that the panels would be easy to take down, along with the Bimini, when severe weather forecast.

I was thinking about that straight line storm that hits 50-60 kts. I have been in two. Both came out of no where, not forecasted and gone in 20 minutes.

 

[socalrider]

I was thinking about that straight line storm that hits 50-60 kts. I have been in two. Both came out of no where, not forecasted and gone in 20 minutes.

We don’t get weather like that out here. In 60kt winds I’m pretty sure my Bimini frame would tear off the flybridge, solar or no. I’d pull the panels and the sunbrella down if I was expecting more than 30 I think - that happens maybe 1-3x per year here and is forecast days in advance.

FYI I’m in Sta Barbara now after a week in Sta Cruz Island from San Diego. Enjoying the town for a few days and then down to Catalina for a month. Wonderful time - panels are doing great and hot water system is working as well. Doesn’t make a ton of hot water but enough to make life significantly nicer. Having a watermaker is amazing.

 

[Codger2]

The panels are all connected using MC4 connectors (https://en.m.wikipedia.org/wiki/MC4_connector)

If a panel goes out, it’s trivially easy to pull the plugs and re-connect to its neighbors, removing it from the string. So I don’t see any loss in redundancy with the series wiring versus parallel. You could get more redundancy if you had multiple charge controllers I suppose - though in a pinch you could even wire a panel straight into the battery bank. These are really reliable solid state devices compared to rotating machinery. And I still have two alternators as well.

I am also in San Diego and am "fascinated" with your set up! My boat is a 22' Duffy with 16-6v AGM batteries. I also have a 1200 watt inverter that powers the TV, coffee maker & future micro wave. I fantasized about covering the entire Surrey top with flex panels but have not pulled the trigger because of wanting to keep the canvas top and not wanting to put holes in it! Your approach (magnets) sounds perfect for my installation.

The boat is powered by a 48v motor that gives me 5.5-6 knots of speed.
My goal for solar power is to extend the range as & I never sleep on board.
(I have a head but no births over 6' in length.)



Please PM me if I could come to your slip to see your set up. It sounds like you have covered all my concerns.


BTW, my top is made of welded SS and is 15' X 9'. It should suffice for holding 5 or 6 panels?

 

[socalrider]

I am also in San Diego and am "fascinated" with your set up! My boat is a 22' Duffy with 16-6v AGM batteries. I also have a 1200 watt inverter that powers the TV, coffee maker & future micro wave. I fantasized about covering the entire Surrey top with flex panels but have not pulled the trigger because of wanting to keep the canvas top and not wanting to put holes in it! Your approach (magnets) sounds perfect for my installation.

The boat is powered by a 48v motor that gives me 5.5-6 knots of speed.
My goal for solar power is to extend the range as & I never sleep on board.
(I have a head but no births over 6' in length.)

Please PM me if I could come to your slip to see your set up. It sounds like you have covered all my concerns.

BTW, my top is made of welded SS and is 15' X 9'. It should suffice for holding 5 or 6 panels?

Happy to show you the setup - I’m on a mooring in America’s Cup Harbor, but out cruising through August.

I’m sure your Bimini frame can handle it - the panels weigh next to nothing. I’d just check the specs to make sure you find panels which fit well between the Bimini frame bars.

 

[GoneFarrell]

Conger,
Here's another mounting idea. I built wood stringers that run between the frame tubes because the grommets on the panels never line up with tube frame. Hung the stringers with rubber lined hose/tube clamps. Put grommets in the bimini for fasteners. Tested to 42 knots last week.

 

[Codger2]

Conger,
Here's another mounting idea. I built wood stringers that run between the frame tubes because the grommets on the panels never line up with tube frame. Hung the stringers with rubber lined hose/tube clamps. Put grommets in the bimini for fasteners. Tested to 42 knots last week.

Thanks, GF! I'm adding some shots of the underside of my surrey top so that you can see the grid pattern. It's unlike most biminis.


BTW, Did you use magnets for attaching the solar panels?

 

[GoneFarrell]

I thru bolted to the stringers with 1/4-20 pan heads, put grommets in the bimini fabric.
I leave it up all summer so it has to survive whatever the straits throw at it when I'm away from the boat

If/when you lay panels on the bimini you will get an idea of the sag factor. Your local weather may allow magnets. Me I have to deal with gales and puddling under panels.

 

[socalrider]

I thru bolted to the stringers with 1/4-20 pan heads, put grommets in the bimini fabric.
I leave it up all summer so it has to survive whatever the straits throw at it when I'm away from the boat

If/when you lay panels on the bimini you will get an idea of the sag factor. Your local weather may allow magnets. Me I have to deal with gales and puddling under panels.

Sounds like the right solution for you. In an ideal world I’d have a hardtop with rigid panels, but that would be a pretty significant project - the magnets are a great way to inexpensively experiment with solar and figure out how much you really need (and if solar will be enough to get rid of the generator, as it has been for me).

 

[chriscritchett]

First, thanks for this thread! Second, how have the magnets held up rust-wise?

I’m about to try this with a single panel on my upper Bimini, maybe add another one eventually, and am just curious if the magnets want to be painted(?) to avoid bleeding later on? I know the say they’re corrosion resistant, but salt air is salt air.

You don’t have a whole lot of time on them yet, but I’d love to hear your comments.
Thanks again.

 

[socalrider]

First, thanks for this thread! Second, how have the magnets held up rust-wise?

I’m about to try this with a single panel on my upper Bimini, maybe add another one eventually, and am just curious if the magnets want to be painted(?) to avoid bleeding later on? I know the say they’re corrosion resistant, but salt air is salt air.

You don’t have a whole lot of time on them yet, but I’d love to hear your comments.
Thanks again.

I have 14 months on them now - there's just a touch of corrosion on one of the magnets. I guess you could paint them if you like; I don't think I'll bother.

We're nearing the end of six weeks cruising the Channel Islands from San Diego to Santa Cruz Island, Santa Barbara, and Catalina. It's been absolutely fantastic & we are extremely happy with this setup. Having a watermaker & hot water is a real game changer, and we've had between 7-9 people on the boat for weeks on end. We've never come close to running our batteries low. You can't get unlimited hot water with this setup, but it's a huge step up from no hot water unless the engine's been on. Highly recommended for our use case where we can get by without a generator.

I do think that whenever I need to replace the bimini, I'll go ahead and have some grommets and reinforcing fabric put in (or possibly go with a hardtop solution with integrated PV). The magnets so far have been flawless and a great way to get the panels up to start understanding how they work. I do think about them when it gets windy though, and all things equal I'd rather have a mechanical fastening holding them on.