Solar for Sailboats -- microMPPT

[OceanSeaSpray]

Jack,


Ok I got specs for your Renogy panel:


Maximum Power: 50W
Optimum Operating Voltage (Vmp): 17.6V Open-Circuit Voltage (Voc): 21.6V
Optimum Operating Current (Imp): 2.84A Short-Circuit Current (Isc): 3.05A



This is a 36-cell panel, so it is going to be awfully close to its maximum power point in full sun without doing anything in a 12V system.


On the other hand, it looks like you went ahead with SPV1020 MPPT boost converter boards. Those are only going to deliver benefits if the battery voltage is higher, in which case direct connection to the battery doesn't compare.


The setup that would make the most sense for your experiment would be:
1/ Two 50W panels in series charging two 12V batteries in series directly
2/ Two 50W panels in parallel into the MPPT board charging two 12V batteries in series directly


Then you could show that shading is much worse on setup 1 and only reduces output on setup 2. In both cases I wouldn't expect much difference without shading if the panels are warm.


Your MPPT boards are only good for 24V systems using lower voltage panels, unless you can source panels with very low voltage. Taking it to the limit you could split the solar panel into small sections and boost each one up to battery voltage in parallel (that is what the SPV1020 was designed for), but who is going to make you special solar panels with multiple outputs and what is the gain going to be compared to sticking a bypass diode under each cell and down-converting with a buck? Hardly anything for a high cost and high complexity.


Note that bypass diodes only come into the picture if you shade part of a panel, or a whole panel in a series configuration. They allow the current to flow over the shaded part. If you are in parallel and shade a panel, you lose it and the other one carries on and the bypass diodes don't come into play.

[barnakiel]

Chinese MPPT stear clear ;-)

I have seen tests and cheap Chinese MPPT clones did not deliver.

I think if MPPT at all then quality.

b.

[nimblemotors]

So I've been looking into making solar panels, and put up a poll to ask what is more important, price, size, or weight.

I would use very thin glass instead of plastic for the 'top sheet'.
The thinner the glass, the more it costs, but it weighs less.

The size I'm looking at is approximately 19 inches by 16 inches.

This size panel can use different cells that would yeild about 50 watts or 35 watts, the higher watts will cost more.

The rare material cost to make these panels is about $50-ish
The biggest expense is actually making them and the machine needed.

Just a totally rough number would be minimum $15,000 to justify the trouble, or a quantity of 150 panels at $100 each.

That seems like a do-able number, and in fact totally cheap in my view, why anyone would bother, well I'm just a crazy man building a million dollar solar powered boat for $25,000.

[nimblemotors]

I went and bought another CF reader, so can use my better camera.
Tested another 50 Watt SunPower cell solar panel I had custom made which basically it brings out the wires for 4 cells, which when connected in series gives you 16 cells in series or 8v output.

I use the MPPT to output 24v, and feed that into a DC-DC converter that outputs 12v, and that is connected to a 50 watt lamp bulb.

The first picture shows this gets 2.50 amps through the bulb, better than the 12v panel, which connected directly to the bulb was getting 2.38 amps.

I then shaded the panel, and still get 2.32 amps.

I then went to combine both panels together, and got 3.5 amps, until I realized the DC-DC is rated only 3 amps, and it shuts off when > 3 amps.
While figured what to do next, the clouds came in, so no more testing today.

I got the kickstarter setup for the boards, waiting for approval.

[s/v Beth]

Jack, if you really want to make something we need, a mppt/ inverter/battery charger combo would do the trick. I have seen some really nice ones that get the power from either solar or 110, pure sine wave it, or put it into bats. But all expensive (1.5 k and up) I need one for my house and my boat.

[Albro359]

I find all this to-ing and fro-ing about MPPT and PWM and matching panels to batteries quite interesting....maybe....
On my previous boat, DIVA, I had two 130W 21V panels in parallel with a chinese MPPT controller to charge my 12V house bank, and it worked very well....this controller included a 3-stage programmable charging system, bulk, absorb, float....
My current boat ELYSE has 3 x 200W 36V panels wired in series with diodes across each one and connected to ...again another Chinese MPPT controller with built in 3 stage charger to our 24V 660Ah house bank...and it works very well...

Look at the pic of the controller display


104.9V@3.0A = 314.7W coming into the MPPT
27.8V@11.2A = 311.4W going out of the MPPT to the battery bank

Not much waste there !

I verified these currents and voltages with my clamp current meter and multimeter, so I know this thing reads correctly.

AND the fact that it is a 3-stage charger it will charge my batteries correctly unlike the other systems discussed here.

My vote is for MPPT everytime.....

[nimblemotors]

Are you saying you don't need shade tolerant hot water generating solar panels and/or MPPT controllers, or that you need a cheaper inverter/charger?
There are plenty of inverter/chargers available, seems like everyone makes one. I am making an inverter/charger for lithium batteries. This is all a hobby basically, so if I don't need it myself, I'm not going to work on it.

Originally Posted by s/v Beth

Jack, if you really want to make something we need, a mppt/ inverter/battery charger combo would do the trick. I have seen some really nice ones that get the power from either solar or 110, pure sine wave it, or put it into bats. But all expensive (1.5 k and up) I need one for my house and my boat.

[nimblemotors]

Kickstarter approved and now launched.

https://www.kickstarter.com/projects...lar-controller

[s/v Beth]

I am interested Jack. How would this work. I will have 4 of those panels you mentioned in the front. What advantages to hook them into a micro MPPT and then hook them into a MPPT down below? Why not just have some diodes to keep them from bleeding off wattage, and then down to a MPPT and onto the battery?

[nimblemotors]

When you have panels in parallel, they need to have the same voltage.
When a panel is shaded it will put out less voltage.
The microMPPT makes sure all panels output 24v even if shaded.
A diode will just prevent a shaded panel from actually drawing current from the other panels.

I will demonstrate this effect once the sun is shining again and I can get back to testing. So far I've shown that
1. The circuit board actually works.
2. It increases the output of a panel compared to not having it.
3. Panels in parallel put out more current when shaded than when in series.


I also note that diodes consume power, they lower the output voltage by .4v usually, more when the current is higher. A panel with the microMPPT board doesn't actually need a diode anymore since this is done by the circuit board, the diode is consuming less power because the voltage drop is at 24v and the current is lower than with the direct 12v output.

And finally, you have 24v running in the wires to the inside charger instead of 12v, so the wire can be smaller or less loss in the cables than 12v.
The board can actually output up to 40v, but I think 24v is good enough and is safer than even higher voltage.

Originally Posted by s/v Beth

I am interested Jack. How would this work. I will have 4 of those panels you mentioned in the front. What advantages to hook them into a micro MPPT and then hook them into a MPPT down below? Why not just have some diodes to keep them from bleeding off wattage, and then down to a MPPT and onto the battery?

[seandepagnier]

Originally Posted by Dsanduril

[*] Water cooling - We've played with this a fair amount, on paper it sounds like a good idea, but you actually need a huge quantity of water. Most panels operate ~20-25C above ambient (and your Sunpower cells will be at the lower end of that range). In order to get a useful electrical boost you want to reduce that operating temperature by ~10C, which leaves you with a maximum heat increase on the water side of ~10C

So... couldn't you pump lots of water to get maximum power output, or pump less water to get maximum water temperature?

Originally Posted by OceanSeaSpray

The annoying thing at the moment is that the solar cell industry is driven by the cost-per-watt figure: space in land installations is usually plentiful. For us on yachts, higher efficiency would make a big difference, but that market is rather small in comparison...

Yes, but as it is, I already have plenty of power and space from 15% efficient panels.

Originally Posted by OceanSeaSpray

What you lose from shading depends on the construction of the panel, not so much the cells themselves. The best panel should have one ideal bypass diode over each cell, so you never lose more than what is actually shaded. You can actually find some with one Schottky diode over each cell, but most panels have a couple of diodes only and shading losses come in huge steps instead of very gradually.

I wonder how well this works... They do make "ideal" diodes which are basically a mosfet with very low on resistance (higher gate capacitance maybe but we don't care about high frequency) that automatically switches to act like a diode. They make drop-in replacements for diodes, or you could build this type of circuitry into the panel.

The other option is to have a lot more cells in the panel and wire them in multiple strings in parallel. I have some 50 watt panels like this that are broken into 2 strings and they are already more shade tolerant, but this usually reduces power per area.

Originally Posted by nimblemotors

So I've been looking into making solar panels, and put up a poll to ask what is more important, price, size, or weight.

I would use very thin glass instead of plastic for the 'top sheet'.
The thinner the glass, the more it costs, but it weighs less.

Wouldn't thinner glass break easier from wave strikes?

[d4raffy]

OK - will give this a go.
My Victron MPPT needs PV at VBat +5v to start.
I have 4 x 50 watt 12v small panels on my guard rails and had to series 2 up to ensure voltage.
So this way I can parallel the lot ? And will help with partial shading.
If I have this right ?

Kick Started


Sent from my iPad using Cruisers Sailing Forum

[nimblemotors]

Yep, you got that right, put all in parallel with '24v' (actually 29v) to the charger.

Originally Posted by d4raffy

OK - will give this a go.
My Victron MPPT needs PV at VBat +5v to start.
I have 4 x 50 watt 12v small panels on my guard rails and had to series 2 up to ensure voltage.
So this way I can parallel the lot ? And will help with partial shading.
If I have this right ?

Kick Started


Sent from my iPad using Cruisers Sailing Forum

[OceanSeaSpray]

Just a thought: I think you would have met a lot more success making a board based on the LT8490 chip instead. It would be a lot more usable than a MPPT circuit that is generating a voltage that is in fact not particularly desirable on board and then requires further conversion again.

The LT8490 can take anything between 6V and 80V and convert it to battery voltage, either up or down. The current capacity depends on the MOSFETs you use with it.