What output can I realistically expect from a solar panel?

seanfoster

seanfoster

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Hi All,

I've been calculating my typical daily usage from my battery bank, in theory it's around 80A/h per day, although I'll have to see what it is in real life!
The biggest drain is my Waeco portable fridge coolbox which draws 4 amps.

I will be on a fore and aft mooring on the Hamble (first time I've been on it) so will be relying on solar to charge my house batteries (I have an outboard which will only really have enough guts to charge it's starter battery).

I'm looking at a 100,130 or 150W panel which the manufacturers give a max output of around 6,8 and 9 amps respectively.
As the cost between the sizes are pretty minimal (£80, £110 and £135 looking around on ebay) the physical size is the biggest factor, I will be stern mounting but would like to stow it away when needed.

Can anyone tell me from their experience what I could realistically achieve from these panels, I would be looking really at summer figures, and for the most time the panel will be mounted in a south facing direction, angled slightly to give best performance.

I've estimated figures based on 2/3rds of the manufacturers outputs based on 12 hours per day, this gives me 47, 63 and 71 amps for the 100,130 and 150W panels, is this optimistic?

Any advice would be appreciated!
 
seanfoster said:
Can anyone tell me from their experience what I could realistically achieve from these panels, I would be looking really at summer figures, and for the most time the panel will be mounted in a south facing direction, angled slightly to give best performance.
Click to expand...

According to the remote monitor for my controller, the most my 2 x 50W panels has ever given is 4.1A.

I would recommend buying the biggest panels you can physically fit.
 
As Jumble Duck says it is the physical size for the boat that should be the deciding factor. Bigger the better. If your fridge is a compressor type then it should cycle and draw 4 amps for perhaps 30% of the time so reducing your load. If it is one of those Peltier electronic fridges then throw it away. You will not be able to feed it from solar power.
I am not familiar with UK sunshine so I can't really give advice (sun here is generally regarded as too much in summer). However my guess is that the 150w panel if you can mount it facing the sun will do you OK if you don't ask too much of the (compressor) fridge thermostat. good luck olewill
 
On the East Coast of England our single 80W panel gives us around a realistic 10-15 amps per day averaged out across the summer, which is enough to keep the 220aH batteries in good shape when nobody is aboard, if you were wanting to be solar reliant whist on passage you would need a good deal more to produce your desired 80aH. You may find it more practical to look at ways of reducing your consumption before in vesting in large numbers of solar panels.
 
Thanks for your replies, it's good to know what people are getting in a real world scenario.

My Waeco coolbox is a compressor type, I have,'t used it yet so I was assuming 12 hours per day running at 4 amps, so with the advice that it runs a 30% of the time I can reduce my daily consumption to 60 A/h.
I have LEDs in every fitting inside and outside.
I will mainly be weekend cruising with a few weeks over the summer, so the batteries will be full up during the week.
I think a 150w panel would be the way to go!
 
12 hours per day is a tad optimistic, I'd be looking at say 6 - 8 hrs on average during the summer. I've got 2 x 100 W panels and it keeps my domestic size fridge freezer going (I leave it switched on permanently) as well as charging the batteries. The max input I've seen is about 9 amps on a really sunny day, but in Dartmouth they can be few and far between.............
 
FWIW, there is a rule of thumb that says a panel will give about 25 percent of its wattage in Ah's. This is as a monthly average for May - August in mid/northern European latitudes. Based on this your 150 w panel would produce 37 Ah/day – though more on a sunny day.
 
William_H said:
If it is one of those Peltier electronic fridges then throw it away. You will not be able to feed it from solar power
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Why do people persist in posting such misinformation?

Our Peltier fridge consumes barely 1A on the Eco setting and that's good enough on all but the hottest days

I haven't analysed the duty cycle (be interesting to do so) but it's certainly in the same ball park overall as a compressor fridge

Now I grant that it isn't a huge fridge (it's not bad for a twenty seven footer though) and also that in tropical rather than temperate climes it might struggle but there is nothing inherently wrong with Peltier fridges in the right application if properly installed
 
Waeco

seanfoster said:
Thanks for your replies, it's good to know what people are getting in a real world scenario.

My Waeco coolbox is a compressor type, I have,'t used it yet so I was assuming 12 hours per day running at 4 amps, so with the advice that it runs a 30% of the time I can reduce my daily consumption to 60 A/h.
I have LEDs in every fitting inside and outside.
I will mainly be weekend cruising with a few weeks over the summer, so the batteries will be full up during the week.
I think a 150w panel would be the way to go!
Click to expand...
We found that the Waeco could be turned off overnight even in the med and stuff was still nice and cool in the morning. A reflective insulated cover pad (windscreen cover I think) also helps if sun can get on it.
I'd love a Waeco but too expensive for me this year. I'll have to stick with my halfords peltier with added insulation for now.
 
WE're on a mid river mooring on the Hamble with a single 60w Panel fixed to the deck. Peak output I have seen is 3.1 A. Makers claim it will give 20Ah on a sunny day in these latitudes with an MPPT controller 17Ah with a PWM.

Best advice is to fit as much as you can but before you go shelling out hundreds it's worth looking at your realistic use.

Are you going to be spending weeks on end on the hook? In which case self sufficiency via Solar is vital.

If it's a more typical Use the Boat Friday to Monday then work interspersed with the occasional week or two then solar is less vital. Assuming your batteries coped with your usual cruise pattern and that that is not going to change then the only think that is different is that you will want to top your batteries up from say 50% charged on Sunday evening to 100% by say early afternoon on a Friday. Call it 5 days. You donlt say how big your domestic bank is but If the ask is to recharge 100Ah out of a 200 Ah domestic bank then you will need panels capable of replacing 20Ah a day. 100W should do that comfortably but if you can fit bigger then no harm at all in doing do.
 
For weekends you should take the coolbox home and make sure it is as cold as you can get it before leaving home. If driving any distance, keep it cold on your car's 12v system. Just doing this will mean you will save a lot of battery capacity by not having to get the coolbox cold. Thne only run the fridge for several short periods during the day, making sure you keep it closed for as much time as possible. Possibly instal a electronic thermometer to let you see the exact temperature at a glance, and then judge when you need to run it. Constant opening and closing of the coolbox will raise the internal temperature, so train your crew to only open if necessary. Then switch off overnight for a peaceful nights sleep.

For holdays, follow the above advice but make sure you vist a marina every few days to hook up to the mains to fully charge your batteries and cool your coolbox.

Hope this advice helps.
 
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I think Waeco quote an actual consumption of about 35Ah per 24hrs for an average sized fridge (about 80L) so I think your estimate of about 60 is a bit high.

You can reduce its consumption by taping some 25mm Kingspan or Celotex to the sides, top and back (if you have room in your installation) with aluminium tape.

I did this to our 85L Isotherm fridge, which uses the same Danfoss BD35 compressor, and together with the Webasto Smart energy controller find that overnight the fridge only uses 5Ah.
The 150w solar panel I fitted to the sunroof adequately keeps up with the fridge and all other consumption (water pump, shower pump, radio, vacuum cleaner, lighting etc) without a problem.
 
Erbas said:
Why do people persist in posting such misinformation?

Our Peltier fridge consumes barely 1A on the Eco setting and that's good enough on all but the hottest days

I haven't analysed the duty cycle (be interesting to do so) but it's certainly in the same ball park overall as a compressor fridge

Now I grant that it isn't a huge fridge (it's not bad for a twenty seven footer though) and also that in tropical rather than temperate climes it might struggle but there is nothing inherently wrong with Peltier fridges in the right application if properly installed
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Sorry Erbas. I am really pleased you find the peltier fridge useful. I am also pleased that you find the current consumption reasonable. I guess the real answer to the recomendation for peltier type fridges is a variable quantity. yes my statement was just a throw away line and generality but my experience is obviously biased being from sub tropical zone. However I think many others on this forum operating in UK have been dissapointed in peltier results. good luck olewill
 
The key with Peltier systems is effective cooling of the hot side of the plate. Unless the heat is effectively dissipated the system won't work efficiently

And, of course, Peltier systems are best suited to smaller installations and cool boxes. Once you get to small domestic fridge size and upwards a compressor system wins hands down
 
jac said:
WE're on a mid river mooring on the Hamble with a single 60w Panel fixed to the deck. Peak output I have seen is 3.1 A. Makers claim it will give 20Ah on a sunny day in these latitudes with an MPPT controller 17Ah with a PWM.

Best advice is to fit as much as you can but before you go shelling out hundreds it's worth looking at your realistic use.

.
Click to expand...

I'm glad you brought up the difference between PWM and MPPT controllers, I wasn't aware of the difference, but after doing some background reading, watching youtube etc I think an MPPT controller is pretty much a must have if you want to squeeze everything you can from a solar panel set up.

Based on the advice here, I'm going for a 150w mono panel with a 20A MPPT controller (not one of the many 'fake' ones on ebay for under £30!), the whole lot will be around £180 and hopefully should last for years, lets just see what I can achieve from this!
 
If the OP swapped the Waeco peltier coolbox for compressor driven one or switched it off at night he could save 24ahr/day. I always try to look at minimising the demand rather than maximising the production.
The important thing is to get the energy audit as close as possible and try to verify this by live measurements. The 'fit as many panels as you can' argument is not very helpful I feel. It may be better to fit two smaller panels from a shading point of view (some say) there's little economy of scale and 2x40w will cost about the same as 1x80w.
 
I find that this model works reasonably well and have used it in several locations. Actual daily output seemed to be reasonably close to the forecast from 2012-2014.
http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php

It shows that a boat in Hamble area would get following average daily Ah in each month from an unshaded 100W panel lying flat on deck.
Jan 4
Feb 9
Mar 17
Apr 26
May 30
Jun 33
Jul 31
Aug 26
Sep 19
Oct 11
Nov 6
Dec 3

So around 46Ah/day would be reasonable from a 150W panel during months May-July. That would leave a shortfall of 34Ah/day if you are using 80Ah/day. It would actually be worse as recharging is not anywhere near 100% efficient. As you don't have a big alternator, I'd guess that 300W would just keep up with usage.

Output from my panels in Galicia and the med. don't approach figures you are hoping for. I'd need to look out data from last year but think I got equivalent of 70Ah/day from 150W at best in Algarve last year. More like 65Ah/day on average in peak months.
 
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Re: Waeco

I have two 150 watt solar panels mounted horizontaly. On a sunny day spring and autumn I get about 15 amps during the middle part of the day. In high summer up to 20 amps and on a overcast winters day it can fall to 1 amp.


Martin
 
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