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Solar - what to buy?


Richard10002

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Further to the thread where I believe I've killed my Trojan T105s, I'm going to take Petes advice and get more solar. I've had a bit of a search, but remain a bit confused :(

 

I've currently got a 100W panel through a 10A PWM controller. My plan is to get a couple of 165W panels and a 40A MPPT controller from Bimble, and see how things go with the Trojans. I'll fit the MPPT in the same place as the current PWM, and use the existing wires to the batteries. I've got a Smartguage and a NASA BM2 for monitoring the batteries.

Do I need to buy anything on top of the panels, the controller, and some cable? Bimble offer a meter for about £25, but I'm not sure what it does http://www.bimblesolar.com/offgrid/mppt/MT50-meter 

Can I include the existing 100W panel in the system?

Do I connect in series, or parallel, and what is the difference in terms of how things are connected?

Anything else I need to know?

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You may find your existing controller to battery cables are not thick enough.

I would keep existing and link to starter battery if you don't cruise much, and fit new cables for the new system, wiring the panels in series for best results.

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if you want to use the existing 100W panel, I suggest you buy 3 more the same, wire all 3 in series.  The MPPT controller will thrive on that.

I suggest you buy the proper cable bayonet connectors for the solar panel cabling, and a switch to isolate the batteries from the MPPT.

Edited by Murflynn
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The meter is worth having. It was overcast today and the meter said it was pushing 0.5 amps into the battery, the BM2 said that it was charging at 0.1 amps as the only thing that was running at the time was the heating pump, which on a slow speed, uses 0.4 amps so it really helps to keep an eye on what is going on, even at low current usage.

i do need to get more panels though I think I can get another 200 or so watts on my controller

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if the 165 watt panels are house panels they will chuck out 36 ish volts and 2 can be wired in series or parallel, series gives less volt drop and they will provide power in lower light levels.  Shade will have a greater effect in series, as if one part of one panel is shades it will reduce the total power out, wired in parallel shade on one part of one panel will only affect that panel the other one carries on full tilt.

The 100 watt panel will probably be 18 ish volts and a lower current so cannot be used with the 36 volt 165's but could be retained and used with the pwm controller to keep your starter well topped up.

You can only connect panels is series if the current output is similar between panels and you will get the lower value as your max current, the total volts will add up and must not exceed the controllers max. You can only wire panels in parallel if the output voltages are the same, the output currents will add up together.

If the 165 watt panels are the same volts as the 100 you could put the whole lot in parallel but then you could have over 25 amps on the cable and the standard 6 mm squared cable would have a volt drop of .75 volts for a 10 meter run and you are not likely to get less with 3 panels. If like mine the panels are at the front and the controller at the rear 8 meters from the nearest panel the volt drop would be over 2 volts which is ridiculous.  Remember the cable run is the total of the  +ve and -ve lengths

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On 12/03/2017 at 20:55, Bewildered said:

The meter is worth having. It was overcast today and the meter said it was pushing 0.5 amps into the battery, the BM2 said that it was charging at 0.1 amps as the only thing that was running at the time was the heating pump, which on a slow speed, uses 0.4 amps so it really helps to keep an eye on what is going on, even at low current usage.

i do need to get more panels though I think I can get another 200 or so watts on my controller

 

I agree. Mine confirms how little the solar is contributing (i.e. 0.1a = feck all) during Dec Jan and Feb, and how MUCH it contributes the other nine months.

Peeps who claim 5A from 250w of solar in December are simply kidding themselves, and you.

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5 hours ago, Mike the Boilerman said:

 

I agree. Mine confirms how little the solar is contributing (i.e. 0.1a = feck all) during Dec Jan and Feb, and how MUCH it contributes the other nine months.

Peeps who claim 5A from 250w of solar in December are simply kidding themselves, and you.

Luckily, I neither kid myself, or listen to you on this one.

a good cold sunny day in December can give you a suprising decent return, mine certainly allows me to keep the fridge going all year round when I'm not on the boat ....something I didn't do for the first few years on the boat. . 

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it will make a huge difference in the winter if the panels are tilted up to face the sun.  theoretically, on a cool day with a clear sky and the panel at 90 degrees to the sun, you should get the greatest output even when compared to a hot sunny day.

when the sun is low in the sky there will be much less radiation density on a horizontal panel.

  • Greenie 1
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On 13/03/2017 at 06:18, matty40s said:

Luckily, I neither kid myself, or listen to you on this one.

a good cold sunny day in December can give you a suprising decent return, mine certainly allows me to keep the fridge going all year round when I'm not on the boat ....something I didn't do for the first few years on the boat. . 

 

Well you would say that, as someone who sells them for a living. How many "good cold sunny" days do we get each December? Whenever I peer at my Tracer controller in the three winter months and see 0.1a or 0.2a it's usually grey, dull and often raining outside. Compouinded by the fact there are 8 hours of daylight and 16 hours of darkness rather than the other way around in summer. 

But I think murflynn above puts his finger on the difference. My panels are flat on the roof and the sun in December is only at an average of about 10 degrees above the horizon in winter so I have very little 'presented area' to the right bit of sky. But if if your panels are tipped to face the sun on all these bright sunny days you get around your way in December, I'm not surprised you claim a higher output than I get.

Could you tell the board how many panels and what type and power they are please that keep your fridge running all winter? And if your panels are flat on the roof or tilted please? Many thanks.

(I've never been able to keep my fridge on all winter on either boat without trashing the batteries.) 

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Reading between the lines Richard already has a 100W 18V panels and is planning on a couple of 165W 36V panels which will be hard to mix and match with the existing.

So I'd prefer to leave the existing install as is and install the new panels and MPPT along side. Tracer do at least a couple of ranges (A and BN series) with programmable output voltage:

www.epsolarpv.com/en/index.php/Product/index/id/95/am_id/134

The cable size between panels and MPPT isn't so critical so 4mm2 will be fine, being the minimum size for domestic solar cable. But if 6mm2 can be had for the same price, why not?

For the cable between MPPT and batts best use the fuse and cable size recommended in the MPPT manual, failing that the 'amps divided by three' rule of thumb will do for cable size if the MPPT is reasonably near the batts.

Identical panels can be put in series provided the max (open circuit) voltage is around 20% below the max input of the MPPT, best not to cut things too fine there.

For 310W of panels a 20A MPPT should just scrape by for a 12V system, though of course a bigger one will allow some room for future expansion. At a very rough guess I'd expect 310W should more or less cover 70Ah to 100Ah of daily use on a 12V system in high summer and around 60Ah on most days of spring/autumn.

Out of interest when the Trojans are equalised at the recommended voltage, what current do they take?

Edited by smileypete
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5 hours ago, Mike the Boilerman said:

 

Could you tell the board how many panels and what type and power they are please that keep your fridge running all winter? And if your panels are flat on the roof or tilted please? Many thanks.

(I've never been able to keep my fridge on all winter on either boat without trashing the batteries.) 

We have 1kw of panels for the winter wired in series to a Tracer 40A MPPT controller. This will just keep up with our fridge use if away for a few days, and we return to batteries at 100% on smartgauge. Everything turned off except fridge and bilge pump. 

Doesn't do much for any of our other electric usage when on board though, and I assume the fridge uses a lot less without opening and shutting the door. Also of course much colder on boat when we're away in winter. 

Oh and I believe our Trojan’s are also pretty much trashed after one winter despite trying or hardest to equalise and charge fully when we could.

Tom

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1 hour ago, Tom and Bex said:

We have 1kw of panels for the winter wired in series to a Tracer 40A MPPT controller.

Do you re configure them for summer use? The reason  I ask, is that I had 1kw of panels through a 60A MPPT and thought I was pushing my luck with it. I think they were connected series-parralel iirc. 

Edited by rusty69
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46 minutes ago, Tom and Bex said:

We have 1kw of panels for the winter wired in series to a Tracer 40A MPPT controller.

 

Really? How many panels is that though?

I have six panels to get to 560w so you have perhaps 10?

Ten is series at 28v each would be generating soem seriously dangerous DV voltage as well as vastly exceeding the maximum input voltage specified by your Tracer.

Or maybe you have just four of those enormous 250w household panels...

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2 hours ago, Tom and Bex said:

We have 1kw of panels for the winter wired in series to a Tracer 40A MPPT controller. This will just keep up with our fridge use if away for a few days, and we return to batteries at 100% on smartgauge. Everything turned off except fridge and bilge pump.

what horror of a fridge are you running?

I get the same as you are describing from 180w of solar using one of the waeco coolmatic fridges.

edit: I'm a dummy, I didn't spot that this was winter usage.... I would struggle in deep winter (mid February - mid November is fine though).

Edited by Jess--
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