Solar for Sailboats -- microMPPT

[OceanSeaSpray]

The other thing when it comes to the test from Compass Marine is that conditions were just about as good as they get for a MPPT application. The test was done in Maine, in spring, on a rainy day:

1. The panels were cold (watercooled actually!), which maximised the gap between the battery voltage and the voltage at maximum power point (the panels used had Vmp=17.7V in standard conditions, 25degC).
2. The sky was overcast and output was rather average, which meant staying away from both the high load and very low load situations where efficiency problems are usually found.

In these near-perfect conditions, he couldn't tell which MPPT controller was better (unsurprisingly) and measured 20% gain. Ok, that's not bad at all, but now transfer the whole setup down to the tropics, run the panels hot and the MPPT converter at high current and you would find that most if not all of that 20% advantage has vanished, because a 36-cell panel is actually a pretty good match for a 12V system in hot sunny areas, and 33 cells is better in colder climates or if efficiency in overcast conditions is the objective.


In the tropics with well matched panels, the only gain you often get from MPPT is in the morning, when the light is at an angle and before things heat up. It is too small and hardly worth the cost of a good controller. Buy a crappy MPPT controller and you can very easily be worse off than with simple PWM.

[nimblemotors]

I got my circuit boards back from fabrication and did an initial test today.
Hooked up a 50 watt solar panel to the miniMPPT and used a little motor as a load. Could adjust the load by just gripping the motor shaft.

The good news is the circuit board works, and was getting about 25 watts max from the panel, consistent 29v output under varied loads.
When I hooked the motor up directly to the panel, it would only get about 12 watts max.
The chinese solar panel was not too impressive, but it was late afternoon.

Will be doing some more tests tomorrow.

[nimblemotors]

A little more testing today. This time I hooked up a 12v lead acid battery to the 50 watt panel directly, and it was charging it at about ~2 amps, ~15v,
which is still only ~30 watts. Rather disappointing for the panel.
I hooked up the miniMPPT and another 12v battery in series, and got ~1.2 amps at ~28v only ~33 watts. A little better, but not 50 watts.

I took some pics of these tests, but with my old cflash camera, and my cf reader doesn't work, my sweety took my newer camera to Jamaica today,
so doesn't look like I can upload pics until she gets back.

The next test is having two panels in parallel with the MPPT,
and shade one panel and show that it still contributes current.

Also wanted to say this 50 watt panel gets very hot in the sun,
really quite hot to handle with bare hands, and it isn't even hot here today, maybe 80F.
It really should be no problem to get some solar hot water from them.

[OceanSeaSpray]

Jack, good on you for getting behind the gear and testing. To clarify the results, what are the specs of your solar panel?


Regards,


Eric

[nimblemotors]

Originally Posted by OceanSeaSpray

Jack, good on you for getting behind the gear and testing. To clarify the results, what are the specs of your solar panel?


Regards,


Eric

Essentially the same as this:

50 Watts 12 Volts Monocrystalline Bendable PV Solar Panel for RV, Boat, and Cabin | Renogy Store

Or this:
Semi Flexible Bendable 50W 50 Watt Lightweight Solar Panel 12V Battery Off Grid | eBay

I pulled out my old video camera and it should work to get some pics online.

[Sea Frog]

Originally Posted by OceanSeaSpray

Multijunction GaAs cells already reach >40% efficiency, so twice that of the old monocrystalline technology we are using.

I could not locate any product I could buy. Seems this is very much in it's infance and no commercial products are available yet.

[nimblemotors]

Originally Posted by Sea Frog

I could not locate any product I could buy. Seems this is very much in it's infance and no commercial products are available yet.

They are available, used where size and weight are of ultimate importance, such as space satellites. If you have to ask what they cost, you can't afford them..

[nimblemotors]

I redid the tests yesterday with a camera that works (for upload).
Direct to battery, 2.0 amps, via the mppt 2.2 amps from the panel.

And the last pic shows just a little shadow on the corner of the panel drops the current from 2.0 to 1.5 amps.

[Fog Bank]

Love what you're doing. Keep up the good work!

[hellosailor]

A cursory glance at the chip's data sheet says it is only a BOOST converter, so if the panel exceeding 12V out (which most nominal 12v panels do) any excess voltage would be thrown out rather than converted to amperage?

And that these require a CVCC charger in addition, that they can feed a battery or charger, but they lack any provision for changing to output power in the typical bulk/absorbtion/float modes.

Did I miss something, or this just a one-trick pony that would have to be integrated into a more complex yet unfinished system?

[nimblemotors]

So here are two identical panels in parallel connected to a 12v battery. With no shade, you can see one is charging at 44ma, the other at 77ma (just variation in quality, these are brand new 1.5 watt panels just pulled them out of their shipping boxes today, but I bought them over 10 years ago.)

When one is shaded, it drops to 8-15ma, and the other one is unaffected.
Similarly when the other one is shaded, it has no effect on the other.
When both shaded, both are toast.

Each panel has a blocking diode, which allows them to connect in parallel and not effect each other, otherwise unshaded one would 'charge' the shaded one.

So clearly this shows having panels in parallel is what you want to handle shading.

[nimblemotors]

There is no 'wasted' voltage, this boost dc-dc is 97% efficient.

As I posted earlier, it is NOT a battery charger, it is a MPPT boost dc-dc converter that takes a '12v' panel and boosts it to a '24v' output.
It can be put inside the junction box, or just connected right next to the output of the panel. This gives you a '24v' output bus for all panels.
The 24v bus wire goes inside the boat where it connects to a battery charger.

The battery charger does not need to be mppt, a pwm charger is fine,
anything off-the-shelf will do. Just needs to work with '24v' input.

Originally Posted by hellosailor

A cursory glance at the chip's data sheet says it is only a BOOST converter, so if the panel exceeding 12V out (which most nominal 12v panels do) any excess voltage would be thrown out rather than converted to amperage?

And that these require a CVCC charger in addition, that they can feed a battery or charger, but they lack any provision for changing to output power in the typical bulk/absorbtion/float modes.

Did I miss something, or this just a one-trick pony that would have to be integrated into a more complex yet unfinished system?

[nimblemotors]

I hooked up the mppt to these little panels and got a little boost to 47ma and 80ma, the board is not really designed for such low current.
It did improve a lot when they were shaded, but hard to really say if the shading was the same as before.

Here is a pic of the board, sorry so fuzzy, this camera is an 'old one'.

[barnakiel]

Originally Posted by nimblemotors

That is a good question.

(...)

So you need only a single battery charger that gets the 24v input.
This can be a cheaper 'PWM charger' for lead acid, or any charger that will take 24v input.

OK, what about the output voltage then?

Your statement does not seem to be the case of cheap PWM controllers that are set for 12 Volt system: they do seem to be locked in only one voltage.

You may be talking about cheap 24 Volt solar chargers for 24 Volt (batt bank at 24 Volt) wired boats. Is this so?

I have seen cheap 24 to 12 Volt MPPT controlers (24 panels in side, 12 Volt batteries out side) but I have not seen cheap PWM controllers of this type.

I may be talking gibberish and if this is the case PLS disregard my post.

I love what you are doing but I cannot decode if/how this could work on a 12 Volt wired boat.

b.

[nimblemotors]

I see what you mean, the pwm battery chargers are not actual dc-dc converters. So you would need a charger that is a dc-dc, which the mppt chargers will do. The good news is it doesn't need to really be mppt,
so the chinese mppt that are not really mppt should work, or a real mppt battery charger is good too.

I'm also working on the 'magic' charger for lithium, I would not bother to create one for lead acid. On electric-boat-forum.com I document a simple charger, about $30 in parts.

Originally Posted by barnakiel

OK, what about the output voltage then?

Your statement does not seem to be the case of cheap PWM controllers that are set for 12 Volt system: they do seem to be locked in only one voltage.

You may be talking about cheap 24 Volt solar chargers for 24 Volt (batt bank at 24 Volt) wired boats. Is this so?

I have seen cheap 24 to 12 Volt MPPT controlers (24 panels in side, 12 Volt batteries out side) but I have not seen cheap PWM controllers of this type.

I may be talking gibberish and if this is the case PLS disregard my post.

I love what you are doing but I cannot decode if/how this could work on a 12 Volt wired boat.

b.