small solar panel system

[rogerc]

i had a 100W flexible fixed panel that got water damage after 3 years. and want to replace it. i would like a 50-100% increase in battery charge. i do a 6-8 week cruise in the summer and occasional  long weekend cruises  between April and October (Inclusive).
initially i thought of getting a slightly larger panel with tilting mounting, but I'm beginning to think 2 fixed panels would do the same for a similar cost. i stuck my original panel which seemed good but water got under it and eventually all the paint became a soggy mess and the panel failed. I'm not keen on drilling & screwing to the roof as water might get through, so thinking of magnets. and I'm wondering about whether to have them connected serially or in parallel. parallel seems better for summer and serial for winter. and i want to avoid too many connections and keep it simple.

i would welcome suggestions on the best panels and mounting systems and connections.

[David Mack]

I mounted my rigid panel using these mounts, glued to the cabin roof with stixall, and then screwed through the mounts into the panel frame with self tappers. The large base gives plenty of area for the glue to stick. They hold the panel high enough to allow for the roof curvature. And there are no projecting corners or other bits for ropes to get caught on.

Edited September 11, 2021 by David Mack

[Kendorr]

Same happened to my 100W flexible panel, I bought a 160W rigid panel which covered almost exactly the same space, this one

 

https://www.ebay.co.uk/itm/124454982088?var=425329918427

 

I also used the same mounts as David, and simply plugged into the wiring that I already had fitted.

[ditchcrawler]

On 10/09/2021 at 11:23, rogerc said:

i had a 100W flexible fixed panel that got water damage after 3 years. and want to replace it. i would like a 50-100% increase in battery charge. i do a 6-8 week cruise in the summer and occasional  long weekend cruises  between April and October (Inclusive).
initially i thought of getting a slightly larger panel with tilting mounting, but I'm beginning to think 2 fixed panels would do the same for a similar cost. i stuck my original panel which seemed good but water got under it and eventually all the paint became a soggy mess and the panel failed. I'm not keen on drilling & screwing to the roof as water might get through, so thinking of magnets. and I'm wondering about whether to have them connected serially or in parallel. parallel seems better for summer and serial for winter. and i want to avoid too many connections and keep it simple.

i would welcome suggestions on the best panels and mounting systems and connections.

I have 2 small panels that I fitted rubber door stops to as feet and they just sit on my roof, no fixings at all 

[robtheplod]

28 minutes ago, ditchcrawler said:

I have 2 small panels that I fitted rubber door stops to as feet and they just sit on my roof, no fixings at all 

Do you get nervous when its windy?

[ditchcrawler]

1 hour ago, robtheplod said:

Do you get nervous when its windy?

I did at first but they have withstood all the gales and storms so far

[booke23]

5 hours ago, David Mack said:

I mounted my rigid panel using these mounts, glued to the cabin roof with stixall, and then screwed through the mounts into the panel frame with self tappers. The large base gives plenty of area for the glue to stick. They hold the panel high enough to allow for the roof curvature. And there are no projecting corners or other bits for ropes to get caught on.

 

These look fantastic. Where did you get them from @David Mack?

 

I have 2 rigid panels on high and over complex aluminium frames (previous owner had them fitted). They sit far too high, are non tiltable, don't look that good and I'm always getting the centre line snagged in them. I'm very much in the 'keep it simple' camp and your mounts look excellent. 

[Kendorr]

Got mine off ebay

 

https://www.ebay.co.uk/itm/154415903757

 

1 hour ago, booke23 said:

Where did you get them from

 

[David Mack]

2 hours ago, booke23 said:

These look fantastic. Where did you get them from @David Mack?

 

I got mine from Bimble Solar, but I have also seen them on ebay and elsewhere.

https://www.bimblesolar.com/extras/mounting/solar-abs-mount-kit

Edited September 11, 2021 by David Mack

[rogerc]

thanks very much for the suggestions particularly for the brackets.
does anyone have any views on whether serial or parallel connection is better.

also what % of the rated out put you get in winter and summer  at midday and a couple of hours before sunset?

[Tony Brooks]

7 hours ago, rogerc said:

thanks very much for the suggestions particularly for the brackets.
does anyone have any views on whether serial or parallel connection is better.

also what % of the rated out put you get in winter and summer  at midday and a couple of hours before sunset?

 

I doubt anyone can answer your last question because you don't specify the cloud cover, but expect and absolute maximum of 50% in high summer and all but zero % in winter. Assume no solar output Octoberish to Aprilish.

[The Welsh Cruiser]

My experience over 7 years was that I could achieve around 60% of the stated output during high summer. During the winter it was down to around 5%, and that was just for an hour or so either side of midday, on a clear day.    

[Jen-in-Wellies]

1 hour ago, Tony Brooks said:

 

I doubt anyone can answer your last question because you don't specify the cloud cover, but expect and absolute maximum of 50% in high summer and all but zero % in winter. Assume no solar output Octoberish to Aprilish.

I'll have a go! Use average figures for solar irradiance that reaches the horizontal ground.

There is data on-line for solar radiation reaching the ground by location and month. Here is one.

http://www.efficientenergysaving.co.uk/solar-irradiance-calculator.html

Enter your location to nearest city. It assumes horizontal panels. You'll get the average amount of solar energy in kWhrs each day for each month. Multiplying that by the area of your panels and their efficiency should give you the kWhrs each day. Divide by 12 and multiply by 1000 will give Ahrs each day. For where I live, it gives 4.51kWhr's per m^2 per day in June and 0.51 in December. I've got 1.58m^2 of panels. Note this is an estimate of the actual silicon area, not just the length and width of the frame. Assuming 12% efficiency (old panels and I forget to clean the dust off them!) of converting sunlight in to electricity, I get around 71Ahrs in June and 8Ahrs in December each day. Numbers that fit in with my experience well. In Summer I don't quite keep up with consumption, so need some engine running. In winter it is a tiny fraction of a typical days consumption of around 100Ahrs.

 

It is a different approach from the one boaters usually use of taking the rated Watt output of the panels, Halving that for summer average output, then dividing the summer number by ten for winter, but the numbers come out very similar.

 

Jen

Edited September 13, 2021 by Jen-in-Wellies

[David Mack]

9 hours ago, rogerc said:

what % of the rated out put you get in winter

No numbers, but since fitting a single 185W panel I found found that even in the depths of winter it provides enough power to counteract the self discharge of the batteries, when the boat is not in use. Not much help for a liveaboard, but a distinct benefit for a boat that can spend weeks unused during the winter (especially during a pandemic).

[Tony Brooks]

5 minutes ago, David Mack said:

No numbers, but since fitting a single 185W panel I found found that even in the depths of winter it provides enough power to counteract the self discharge of the batteries, when the boat is not in use. Not much help for a liveaboard, but a distinct benefit for a boat that can spend weeks unused during the winter (especially during a pandemic).

 

Agreed, even a 65 watt panel did that for me.

[IanD]

8 hours ago, Tony Brooks said:

 

I doubt anyone can answer your last question because you don't specify the cloud cover, but expect and absolute maximum of 50% in high summer and all but zero % in winter. Assume no solar output Octoberish to Aprilish.

Take the panel peak power rating, the average energy per day in summer will be about 3x this according to the panel yield calculators -- try this (use your location in the UK):

 

https://mppt.victronenergy.com/?locale=en#

 

So for a 160W panel you could expect an *average* of 0.5kWh/day in summer -- more on a bright sunny day, less on a cloudy one. This drops off rapidly before April and after August.

Edited September 13, 2021 by IanD

[ditchcrawler]

13 hours ago, David Mack said:

No numbers, but since fitting a single 185W panel I found found that even in the depths of winter it provides enough power to counteract the self discharge of the batteries, when the boat is not in use. Not much help for a liveaboard, but a distinct benefit for a boat that can spend weeks unused during the winter (especially during a pandemic).

Thats what mine does

[rogerc]

On 11/09/2021 at 12:39, David Mack said:

I mounted my rigid panel using these mounts, glued to the cabin roof with stixall, and then screwed through the mounts into the panel frame with self tappers. The large base gives plenty of area for the glue to stick. They hold the panel high enough to allow for the roof curvature. And there are no projecting corners or other bits for ropes to get caught on.

 

[rogerc]

1 minute ago, rogerc said:

here do you get stixall? i searched the web and couldn't find it i tried screwfix and tool store but no luck 
i have some Grip fill max which is not solvent based and supposedly suitable for  metal and can be painted over. is it suitable??

 

[rogerc]

i have a PWM controller. does the same current from the panel flow to the battery but at a lower voltage and so lower power?

[David Mack]

 

https://www.toolstation.com/stixall-adhesive-sealant/p77137

 

[PeterF]

Here's my self installed 3 x 100W panels with the plastic mounts, I did not use the corner ones just the straight ones even at the corners. Because of the roof curvature, the corner ones stand more proud than the straight ones, so using the straight ones keeps the panels lower and gives better contact between the panels and the supports. I did this even though the roof curvature is quite shallow on this boat. I glued the supports down with Sikaflex, similar to Stixall and used self tappers for holding the panels down to the supports.

 

Edited October 4, 2021 by PeterF
forgot the photo

[PeterF]

7 hours ago, rogerc said:

i have a PWM controller. does the same current from the panel flow to the battery but at a lower voltage and so lower power?

A PWM controller can be thought of in simple terms as letting the panel run at the battery voltage and have the same current flowing into the battery as exiting the panels and loose some of the potential power. As an example, if the panel could run at 21V and generate 5A = 105W, the PWM controller would let 5A flow into the battery at the battery voltage of 14V = 70W, a potential loss of about 30% of the power. An MPPT controller has voltage conversion electronics so that the panel can be run at a different voltage to the battery and the power transferred more efficiently. The controller also keeps the panel voltage at its most efficient. For example, if the panel is most efficient at 21V and makes 5A = 105W, then the battery at 14V will received 7.5A = 105W, although due to efficiency losses it may only receive 100 to 103W depending on how good the controller is.

 

I do not think that PWM controllers should be used with panels in series for 12V systems as all the extra voltage will be lost.

[Alan de Enfield]

9 hours ago, rogerc said:

i have a PWM controller. does the same current from the panel flow to the battery but at a lower voltage and so lower power?

 

Test show that you will get ~30% more 'power' from an MPPT controller than from a PWM.

 

The MPPT costs more but it really does extend your solar collecting period.

 

Be very wary of buying MPPT controllers from Ebay (even English sounding named companies) they are simply PWM controllers labelled MPPT.

 

Edit to add Link :

 

MPPT Charge Controllers (bimblesolar.com)

 

PWM vs MPPT Charge Controller Test

We often get asked about the actual difference you get between an MPPT and a PWM controller so we setup a side by side test using our Yingli part used panels onto 2 separate 12V batteries, 1 with a PWM controller and one with our tracer MPPT. Panels were set-up side by side angled south.

With early March sun the MPPT was giving 3.7A into the batteries while the PWM gave 2.5A which was 32% lower than the MPPT.

In cloudy conditions the MPPT was giving 1A when the PWM was giving 0.8A (20% lower with PWM)

Both charged the batteries well, but 20%-32% more power was gained by using the MPPT.

Edited October 4, 2021 by Alan de Enfield

[ditchcrawler]

9 hours ago, Alan de Enfield said:

 

 

PWM vs MPPT Charge Controller Test

We often get asked about the actual difference you get between an MPPT and a PWM controller so we setup a side by side test using our Yingli part used panels onto 2 separate 12V batteries, 1 with a PWM controller and one with our tracer MPPT. Panels were set-up side by side angled south.

With early March sun the MPPT was giving 3.7A into the batteries while the PWM gave 2.5A which was 32% lower than the MPPT.

In cloudy conditions the MPPT was giving 1A when the PWM was giving 0.8A (20% lower with PWM)

Both charged the batteries well, but 20%-32% more power was gained by using the MPPT.

But what were the panel voltages.?