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Solar upgrade


Foggy66
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We currently have 3x100W Lensun flexible solar panels which are mounted on magnets to give a small air gap underneath. They’re about 5 years years old and I’m considering upgrading to frame mounted panels on tilting brackets for all the obvious reasons.

In the recent sunny weather the panels have been maxing out at around 7 or 8 amps which seems low given that they’re in full sun all day. 

What would I expect to get from framed panels angled towards the sun?

 

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1 hour ago, Foggy66 said:

We currently have 3x100W Lensun flexible solar panels which are mounted on magnets to give a small air gap underneath. They’re about 5 years years old and I’m considering upgrading to frame mounted panels on tilting brackets for all the obvious reasons.

In the recent sunny weather the panels have been maxing out at around 7 or 8 amps which seems low given that they’re in full sun all day. 

What would I expect to get from framed panels angled towards the sun?

 

 

Do you mean 7 or 8 Amps from each, or total? (I'm guessing the latter, so between 2 and 3 Amps each).

 

FWIW I have 2 x 300w framed panels, 1 is flat and 1 a bit tilted towards the sun, and have been getting up to around a total of 20A max over the past couple of weeks. I think I have had a max of 72Ah a day so far this year.

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If the batteries are well charged and you aren't drawing power to run something, then that will limit the current from the panels. You need to compare a similar state of battery discharge, or better, compare the current in to a dummy load.

Jen

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2 hours ago, Richard10002 said:

 

Do you mean 7 or 8 Amps from each, or total? (I'm guessing the latter, so between 2 and 3 Amps each).

 

FWIW I have 2 x 300w framed panels, 1 is flat and 1 a bit tilted towards the sun, and have been getting up to around a total of 20A max over the past couple of weeks. I think I have had a max of 72Ah a day so far this year.

Yes the 7 amps is in total and when the batteries are discharged to around 60% 

I have capacity in the MPPT controller to add a 4th 100W panel but if I’m not getting much from them it’s probably not worth the expense. 

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In UK you will get max just over 50% of your panels rated output on a good day , tilting may add 20-30 % depending .. on a good day , Most people expect too much from small panels on boats . The old adage of you cannot ever have too much solar in UK rings true , I have 1630 watts on my narrowboat and that is like being plugged into shoreline from Feb to Nov and most of what I need in Dec and Jan with just the occasionally gennie run every couple weeks to make sure the batteries are getting a true 100% charge . I am off grid moored and dont cruise much until summer . so if you do cruise more you will not need as much , but a few small 100watt panels will always disappoint in UK climate IMO . I doubt you will see a huge improvement by swapping flexies to framed even tilted unless you up the wattage quite a bit . 

 

Now if you are like Will Prowse and lived in Vegas , then 300 watts would be give you 300 watts or more all day but not at 52 degress latitude unfortunately 

 

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We've just had two 355w panels installed in series and this is our first week out cruising with them. So far according to the Victron app the peak watts we have had is 399w.

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17 hours ago, RufusR said:

In UK you will get max just over 50% of your panels rated output on a good day , tilting may add 20-30 % depending .. on a good day , Most people expect too much from small panels on boats . The old adage of you cannot ever have too much solar in UK rings true , I have 1630 watts on my narrowboat and that is like being plugged into shoreline from Feb to Nov and most of what I need in Dec and Jan with just the occasionally gennie run every couple weeks to make sure the batteries are getting a true 100% charge . I am off grid moored and dont cruise much until summer . so if you do cruise more you will not need as much , but a few small 100watt panels will always disappoint in UK climate IMO . I doubt you will see a huge improvement by swapping flexies to framed even tilted unless you up the wattage quite a bit . 

 

Now if you are like Will Prowse and lived in Vegas , then 300 watts would be give you 300 watts or more all day but not at 52 degress latitude unfortunately 

 

Your estimate of 50% max is way too conservative, many of us get way more than that.

I have 3 x 180w panels in parallel to give a theoretical 540 watts.

My panels are laid flat so with the sun at its current declination of 12 degrees north I did not expect too much in the way of efficiency. 

However I have been surprised to recently see a figure of 29.8 amps going to my batteries which were at 75% charge status,

So I reckon I am already getting 66% of maximum theoretical solar power and the sun still has a lot further to go up.

Quite pleased to be totally solar whilst moored at this time of year, even with the washing machine, tv, microwave and other electrical items in regular use.

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50% is an average across the day every day  , You may see the odd spike but unless you get that number constantly for 8 hours or so then it wont help charge your batteries any faster 

 

 

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4 hours ago, RufusR said:

50% is an average across the day every day  , You may see the odd spike but unless you get that number constantly for 8 hours or so then it wont help charge your batteries any faster 

 

 

 

 

Eggsactly - next day when its overcast and raining and you get 25% of theoretical output you still need to take that into account.

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7 hours ago, RufusR said:

50% is an average across the day every day  , You may see the odd spike but unless you get that number constantly for 8 hours or so then it wont help charge your batteries any faster 

 

 

Obviously I appreciate that fact in respect of averages over time however it is not what you said.

 

"In the UK you will get max just over 50% of your panels rated output on a good day....."

 

So, with the sun still relatively low in the sky and me already getting 66% can I assume that it was indeed a 'good day' or will there be even better ones?

 

Your figure of "just over 50%" is proven too conservative unless of course you are counting a day as 24 hours, in which case the hours of darkness might mess with the averages somewhat.

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On 21/04/2021 at 18:02, Rob-M said:

We've just had two 355w panels installed in series and this is our first week out cruising with them. So far according to the Victron app the peak watts we have had is 399w.

You will do better with them in parallel, partial shading on one panel will limit the current from the pair, in parallel only the one shaded is affected.  The common theory that they will do better early and late is a myth until the panel is producing over 90% of its volts the current is in the milliamp range so next to nkthing. By the time they are producing useable power they are at full voltage. 

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13 hours ago, Detling said:

You will do better with them in parallel, partial shading on one panel will limit the current from the pair, in parallel only the one shaded is affected.  The common theory that they will do better early and late is a myth until the panel is producing over 90% of its volts the current is in the milliamp range so next to nkthing. By the time they are producing useable power they are at full voltage. 

The advantage of series is the losses in the cable are reduced, or for the same loss as a parallel installation thinner cables can be used, which adds up for a solar farm, but for a ‘one-off’ boat installation the cable cost is a tiny percentage of the total cost.  So always use thick cables.

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I found that parallel reduced the voltage between panels and controller, allowing me to fit a switch that could cope with 48V, but not 70V, (or something like that). Another benefit was to do with shading. I think the Amps increased, but the cable I was using could cope with the higher amps, so all was good.

 

Not everyone wants a switch between panels and controller, but I did :) 

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2 hours ago, Rob-M said:

We have the panels at the front of the roof and cable running to the stern so went for series because of the long cable run.

Our panels are also at the front of the boat but I just went for higher voltage panels in parallel. I can switch mine to series at the panels by swapping plugs but it would be dangerously close to the controllers limit of 92v  on a bright sunny day.

  • Greenie 1
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All mine are in parallel, i have trees which shade between 11 and 2 so parallel gives more power during that time , as said on a boat cable lengths are not long enough to make a difference unless you are using 12 volt panels , my opinion is don’t , they are too expensive and too low voltage unless series connecting , victron mppt for example doesn’t even turn on until 5 volts over battery voltage it’s all too tight imo , give yourself some headroom , 24 volt panels much better with an mppt , reserve 12 volt for pwm controllers . 

 

 

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47 minutes ago, RufusR said:

All mine are in parallel, i have trees which shade between 11 and 2 so parallel gives more power during that time , as said on a boat cable lengths are not long enough to make a difference unless you are using 12 volt panels , my opinion is don’t , they are too expensive and too low voltage unless series connecting , victron mppt for example doesn’t even turn on until 5 volts over battery voltage it’s all too tight imo , give yourself some headroom , 24 volt panels much better with an mppt , reserve 12 volt for pwm controllers . 

 

 

 

 

Mine is 120v and I've been getting 105-109v for the last couple of days, but only 'fractions' of an amp (about 3 amps @ 13v) as the 1200Ah battery bank is fully charged.

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