new solar system-advice please

[WhiteSuit]

Calling all you solar experts out there. I have searched all the threads I can find on the forum in order to come up with my soon to be purchased scheme. I would value your real world advice.

I run a 12volt system with 4 x 110Ah leisure bank. I am reasonably frugal on electric usage with one exception, a 1600Watt inverter running a 240 volt AAA fridge. According to my BMV gauge this uses about 12 amps when running with 0.2 draw when off. I have all LED lights throughout the boat, use a small LED tv maybe a couple of hours at most and regular pump usage. Main heat source does not use any current but occasionally use the Mikuni fired central heating for short periods when it is not cold enough for the Bubble stove. I am looking to be almost self sufficient from spring to Autumn.

I am looking at 2 x 150Watt Bosch 18 volt mono panels wired in series to a Tracer 30amp MPPT controller with a fuse in the positive feed to battery. These are as big as I can fit on the roof and still walk around them.

These panels come with 5 metres of 4mm cabling with MC4 connectors. Is this cable big enough? If it is am I right in thinking I can remove the back of the junction box and direct connect the cable between the panels. This would mean I would not have to buy any further cable. I would still be able to disconnect panels by covering with cloth and disconnecting one of MC4s.

In the real world use I plan to put these too should I look at building a tilt or tilt and turn system to follow the sun? I am intending to mount them on shallow roof boxes for which I can have a hinged lid to face one side of the boat. I also have brackets which would point them to the other side. This will be cheap and easy to design although I was thinking of adding a swivel to fully follow the sun. Am I going to get sufficient benefit for the extra work?

Again in the real world, is the Tracer going to increase my output sufficiently over the cost of a PWM controller? Could I reduce the size (& cost) of the panels and still achieve my aim.

 

What size fuse would you advise between controller and batteries?

 

Thank you in advance

 

Mark

[b0atman]

What is your fridge width ?

[WhiteSuit]

Full size under counter domestic. I am intending to vent it better to improve efficiency. Suck some cold air up from the bilges as it is rather tightly fitted

[ROBDEN]

WOOooosh!!

[WhiteSuit]

Lovely dog Robden, first I've seen with 3 pairs of ears

[Jess--]

with your battery bank (4 x 110AH) I would say you have a usable capacity of 220AH (going further would be discharging the batteries too far and could risk shortening their life), your panels will deliver between 20 and 25A under full sun (depending on battery voltage) so using a guessed average of 21A it will take around 10 1/2 hours of direct summer sun to fully recharge your batteries (with no other loads) with spring or autumn sun I would suggest that you could easily double the amount of time needed.

 

with sun tracking you have to try and work out what percentage increase you will get by tracking, in the summer there will be very little, early spring / late autumn you could gain a lot BUT you could also lose a lot by leaving the panels in the wrong position while you went out for a few hours (is the extra work worth the small overall gain?)

 

I can't comment on PWM vs MPT (Tracer) as I only have experience with tracer.

 

fuse size (between batts and controller), voltage will be 12-15v with 300w available, this gives a theoretical max current of 25A (assuming the full 300w into almost dead batteries), I would say a safe fuse to use would be 30A

[WhiteSuit]

Thank you Jess--

Currently my gauge will show, during a typical 24 hrs moored in summer, a drop from 100% SOC to 70 or 75%SOC. I realize these figures are not necessarily that accurate but that would suggest 6-7 hours of good sun would top up allowing for the slower charge as the batteries 'fill up'. Are my simplistic sums somewhere near the mark?

I know there is nothing worse than pointing the panels in the wrong direction so I can reasonably plan to leave them flat if not around to alter them.

I had an extremely simple system on my old boat of propping the panels up with a stool!

[rusty69]

We have a similar energy requirement to yours. With 2 x 250w panels in series and an MPPT controller, we manage from spring to Autumn. Our panels are flat mounted on the roof.

Edited January 21, 2016 by rusty69

[peterboat]

yes the mppt controller is worth the extra cost also as your panels will be in series the cables are big enough. my panels are flat on my last boat they were tilted and in the winter the tilt was worth the effort for the extra power. in this boat i have a gennie so make up the missing 200 amps with that

[ROBDEN]

Lovely dog Robden, first I've seen with 3 pairs of ears

Thanks but you should see HIS other end.

[KJT]

I have a similar setup to the one you are planning. 4 x 100 watt panels mounted on two pitched roof boxes. The panels tilt but do not turn. I have found it is certainly worth tilting the panels to increase efficiency but in my installation it is not possible to turn them due the size of the panels and design of the boxes. When they were first installed I used a PWM controller. After about a year I replaced it with a Tracer 30 AMP MPPT controller. It certainly increased the overall output. I did observe two things regarding the two different controllers though. Firstly, if you don't align the panels equally, the output seemed to be LESS with the MPPT than with the PWM. I think this might be something to do with the panels output not being equal and confusing the software. Secondly, the panels do seem to perform better in lower light conditions than with the PWM.

 

Ken

Edited January 22, 2016 by NB Ellisiana

[WhiteSuit]

Ken

Interesting, I've heard the differential between panels has something to do with the diodes fitted, presumably cheaper panels cut costs there. It's been raised in relation to shading. One of the reasons I raised the question of which controller

Very neat and tidy set up. Do you have problems with some bridge holes?

[KJT]

Ken

Interesting, I've heard the differential between panels has something to do with the diodes fitted, presumably cheaper panels cut costs there. It's been raised in relation to shading. One of the reasons I raised the question of which controller

Very neat and tidy set up. Do you have problems with some bridge holes?

Shading will be a problem with whatever panels you have, but I understand the issue with MPPT controllers is if all the panels are not producing the same output, for whatever reason, being shade or differing angles, then the algorithms used in controller software get confused and the output is affected. I am sure someone who knows what they are talking about will be along shortly to explain why, exactly, but it is certainly something I have noticed.

As for the clearance for bridges, and tunnels, so far I haven't had any issue. A couple of very low bridges on the Basingstoke only had about an inch to spare, but so far, no problem, and we cruise extensively every summer. They are quite easily removable though, so if push came to shove, then I would just have to remove them for any very low bridge.

 

Ken

[Stilllearning]

Am I the only person that thought this was about the possible new planet that as been deduced to exist?

[Afloat]

Nope, had the same thought yesterday!!

[WhiteSuit]

K-9 with the extra ears!!!

[Mat B]

WOOooosh!!

XKCD

[Peter Reed]

What is your fridge width ?

What colour is your fridge?

[ROBDEN]

XKCD

Got me there. XKCD??

[rgreg]

I am considering installing the flexible adhesive solar panels. Has anybody had any negative experience of these?

[Top cat]

I have no first hand experience of that type but if you compare the specs you will see that they usually cost more per W delivered and need a greater panel area for the same power as flat types. They also tend to be more adversly affected by high temperatures being bonded to a hot roof. Also you wont be able to get the small gains in efficiency but pointing them at the sun.

 

A lot will depend on how important their perceived benefits are.

 

I've heard secondhand reports of corrosion under them and some are not as resilient to being walked on as some might hope. Im sure people with first hand knowledge will chime in soon.

 

Top Cat

[Graham.m]

Whitesuit from what I have read the difference between panels being laid flat and set at the optimum angle to the sun, which varies through the year is about 15% overall. In the summer when the sun is high flat panels can be ahead.

 

One problem with individually mounted angled panels is getting them to the same angle. Otherwise as you have noted it can upset some controllers

 

 

My panels are flat mounted and seem to perform OK

[Mat B]

Got me there. XKCD??

Whoosh

[ROBDEN]

Whoosh

Nope! Still got me.