Solar Panel Question?

[Dougal]

Thinking about this: http://www.sunstore.co.uk/12v-100w-Monocrystalline-Solar-Panel.html

 

[VicS]

I don't know WHAT to expect from them. ............. do manufacturers measure the output in different ways?

There are standard test conditions defining the irradiance level, the solar spectrum and the module temperature.

The manufacturer's tech specs should refer to the test conditions,

The watts output quoted is always the maximum power output (P_MAX) under the test conditions

 

[Mistroma]

There are standard test conditions defining the irradiance level, the solar spectrum and the module temperature.

The manufacturer's tech specs should refer to the test conditions,

The watts output quoted is always the maximum power output (P_MAX) under the test conditions

Yes, panels will never give the rated output. It's really only useful for comparing different panels using data derived from a standard test method.

This website is a useful tool to estimate realistic solar panel output in an average year.
http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php

The model asks for panel size as kWp and output is daily average kWh. You can enter small panel sizes as fractions of a kW but it's easier to ignore the "k" part and assume panel size is W and output results are in Wh. Model will say daily output from a 100kWp installation might be 30kWh but you just read is as 100Wp and Wh respectively.

Assuming OPs boat is in Brittany he could expect following daily Ah from a 100W rigid panel lying flat on deck and not shaded:
May 29.2 (average Ah/day)
June 31.2
July 29.6
August 25.2

Obviously accuracy isn't good enough to forecast actual to a decimal place. However, I've found forecasts to be pretty good over past 3 years and would be confident in expecting around 29-30Ah per day at best for most of the summer for each well sited 100W panel. Shading will obviously reduce the output but the figures are a good guide if sited sensibly.

It might be worth considering 2x50W panels rather than 1x100W to either reduce impact of any shading or allow serial connection feeding an MPPT controller (plus some redundancy in event of panel failure.

 

[RichardS]

Why do you bother to do that if you have a decent regulator?

I do the same as a small panel is all that's needed to keep my batteries fully charged during the winter season when the boat is closed up.

You could leave the large panel/s connected through a regulator but all the additional power is not required and it just feels like more of a fire risk if anything should malfunction.

Richard

 

[Mistroma]

I do the same as a small panel is all that's needed to keep my batteries fully charged during the winter season when the boat is closed up.

You could leave the large panel/s connected through a regulator but all the additional power is not required and it just feels like more of a fire risk if anything should malfunction.

Richard

I do the same for similar reasons. Main panels will produce many times the output needed to keep the batteries at float, so lots of excess not going to batteries. Nil risk of damage to the main panels in winter gales and they are easy to remove for storage.

 

[William_H]

As said the first question for solar power is just how will you mount them on the boat and this how big a panel can I fit? Panels are usually sold as being designed for a 12v battery charge so produce 20v no load. They are also described as max current ie at short circuit situation. (no they are not damaged by shorting.) So generally a 10 watt panel will give about .5 amps by dividing 20volts into 10watts. The 20v max output is to ansure that at low light levels you have enough voltage to push some current into a near charged 12v battery.
Now using an MPPT controller throws that theory out the window by converting provided voltage to that which is required to charge the battery. So in producing 14v from 20v input some more current can be supplied.
Those large panels used on buildings for PV systems are usually 40 volts no load at 180 to 200 watts.They can be very cheap to buy new and may be found Second hand from house wrecking people. But the problem is they are very big for a small boat. he 40v is not a problem with an MPPT controller which still converts to 14v for the battery.
good luck olewill

 

[ip485]

I started from the premise i wanted enough solar to be energy independent. Dont kid yourself, if you want to run a fridge, freezer, lighting an autopilot with a bit to spare its a lot. I opted for 1,000 watts in three domestic panels with a controller and 800 amps of house battery. More by luck than judgement in the uk it just about copes in all conditions with 2 panels on the arch and one on the deck. This may not be your aim but if it is i wanted to give you are realistic idea of an acheivable goal that will make you energy sufficient.

 

[Mistroma]

I believed the OP had a 32' boat and only used it for 6 months each year. I assume that you need 1kW as you have a much larger boat and live on her winter and summer. That would explain your need for 1kW panels and you should have a surplus during the summer months. Is that correct?

OP said he wanted basic information and I thought likely output per 100Wp panel during summer would be useful. Details of your system might put it into perspective for him.

 

[TQA]

Cheap non marine panels do not do well in the marine environment. Connections turn to green slime in 18 months.

Cheap semi flexible panels delaminate and suffer major output losses in 2 or 3 years.

My hard frame Kyoceras seem to be to be close to original output at 8 years.

 

[vyv_cox]

Why do you bother to do that if you have a decent regulator?

Because once the batteries are fully charged the excess current is dissipated as heat, into a finned radiator inside the regulator. In Greek sunshine, even in autumn and spring, the regulator becomes very warm and just might lead to the unthinkable problem.

 

[Tim Good]

I do the same for similar reasons. Main panels will produce many times the output needed to keep the batteries at float, so lots of excess not going to batteries. Nil risk of damage to the main panels in winter gales and they are easy to remove for storage.

Because once the batteries are fully charged the excess current is dissipated as heat, into a finned radiator inside the regulator. In Greek sunshine, even in autumn and spring, the regulator becomes very warm and just might lead to the unthinkable problem.

Fair point. I wonder if i simply laid a sheet of removable black lino flooring over 3/4 of the panel that would basiclaly do the same and remove some of that risk you talk about.

I suppose long term you would want to stress some cells more thn others but you could easily do the left one year and right the next over the layup period.

 

[Triassic]

My boat came with a solar panel fitted horizontally across the aft deck behind the cockpit. It's a rigid affair in a frame measuring about 3'x4' and I believe it's rated in the region of 65w, and it looks quite old. I have a fairly modest power need, running just a radio, chart plotter and a small Waeco fridge box plus occasionally the tiller pilot and LED lighting. I've yet to have a problem with the single 100a/hr battery running down although I have just fitted a BM1 meter to see how close I am cutting things..... I do have the capability of charging from the outboard if I really have to, but I don't generally as it interferes with the instruments (something else I must get round to sorting some time!).

It's my first experience of solar panels and I must say to date I've been really impressed, however I'm aware I'm not sailing right around the clock (I've done the odd night passage but then I've not been draining the battery during the day). My rationale for getting the meter was to see how marginal things are so that I can consider fitting a second battery and additional panel if needed. Some great advice and links on here, thanks.

 

[vyv_cox]

Fair point. I wonder if i simply laid a sheet of removable black lino flooring over 3/4 of the panel that would basiclaly do the same and remove some of that risk you talk about.

I suppose long term you would want to stress some cells more thn others but you could easily do the left one year and right the next over the layup period.

Yes, I think that's a satisfactory solution. I left the boat and came home last August, covering the larger panel with a cloth, well tied on. Achieved the same result as changing to the 38 watt panel on deck. That's my original one, 15 years old now, still working OK.

Greek fishermen cover anything that needs protection from the sun with old carpet, heavy enough to stay in place and completely opaque. Probably keeps some of the heat off as well.

 

[JumbleDuck]

Because once the batteries are fully charged the excess current is dissipated as heat ...

Wouldn't the regulator just disconnect the panels in that case? I can't see any advantage in drawing power from them in order to dissipate it as heat elsewhere.

 

[VicS]

Because once the batteries are fully charged the excess current is dissipated as heat, into a finned radiator inside the regulator. In Greek sunshine, even in autumn and spring, the regulator becomes very warm and just might lead to the unthinkable problem.

Wouldn't the regulator just disconnect the panels in that case? I can't see any advantage in drawing power from them in order to dissipate it as heat elsewhere.

I'm surprised if the regulator gets that hot, pretty warm maybe but not as hot as it would if all the excess energy is dumped and dissipated as heat.

For solar panels you have a choice of:

• A simple on/off regulator that disconnects the panel from the battery when the battery voltage reaches a certain figure and reconnects when the volts fall to some lower figure. ( actual values should be in the spec)
• A pulse width modulated (PWM) regulator which breaks the charging into a series of pulses of diminishing duration as the battery becomes charged. Better because the battery is always maintained at max state of charge.
• A maximum power point tracking regulator (MPPT) that maintains the panel volts at the voltage corresponding max power output during the charging stage but then uses PWM control as the battery becomes charged. Better still because it is maximising the power output from the solar panel

It is the older wind charger controllers that dump all the excess power into a shunt resistance which becomes hot as a result.

 

[Twister_Ken]

May I butt in? I have a 36w pV panel. It is connected via a Phocos charge controller rated either at 4 or 10 amps (impossible to tell without taking the controller off, the products look identical front view). http://www.phocos.com/products/cm-series-4-10a for mfg's www.

Am I right in suspecting that my pV panel at best will produce 36w/12v = 3 amps? If so, if I wish to connect more pV capacity and I have the 4amp version, I'd need to upsize the controller?

Excuse the basic questions, but I'm electrically dyslexic.

 

[JumbleDuck]

May I butt in? I have a 36w pV panel. It is connected via a Phocos charge controller rated either at 4 or 10 amps (impossible to tell without taking the controller off, the products look identical front view). http://www.phocos.com/products/cm-series-4-10a for mfg's www.

Am I right in suspecting that my pV panel at best will produce 36w/12v = 3 amps? If so, if I wish to connect more pV capacity and I have the 4amp version, I'd need to upsize the controller?

Excuse the basic questions, but I'm electrically dyslexic.

Manufacturers generally come up with a power rating by using open circuit volts (normally about 20V) x short circuit amps, so in your case I would expect a maximum current of 36W/20V = 1.8A. You should be OK to double your power, but any more and you'll be overstretching the 4A version. Incidentally, a little googling suggests that you can find out which one you have by looking at the back:

 

[Twister_Ken]

Ah yes, but to do that I've got disconnect and unmount the damn thing!

 

[VicS]

May I butt in? I have a 36w pV panel. It is connected via a Phocos charge controller rated either at 4 or 10 amps (impossible to tell without taking the controller off, the products look identical front view). http://www.phocos.com/products/cm-series-4-10a for mfg's www.

Am I right in suspecting that my pV panel at best will produce 36w/12v = 3 amps? If so, if I wish to connect more pV capacity and I have the 4amp version, I'd need to upsize the controller?

Excuse the basic questions, but I'm electrically dyslexic.

No

36 watts is the maximum power it can produce under standard test conditions ( Probably an irradiance of 1000W/m² and a panel temp of 25C)

The panel terminal volts at max power ( V_PMAX) will probably be of the order of 16 or 17 volts . . . .( the panel manufacturers tech spec should state a value for V_PMAX)


The amps at P_MAX will be 36 divided by V_PMAX ie about 2.2 amps. (dont forget at standard irradiance level) and should be quoted in the tech spec

The Tech spec should also tell you the max current (I_MAX)under short circuit conditions. which will be only marginally greater than I_PMAX

 

[ghostlymoron]

I think the pre-occupation with adjusting the tilt angle to follow the sun is also mis-placed unless you're going to adjust them every hour.

I had two Rutland 913 WG managed by a HRDX Controller. I sold one WG and fitted two 80W panels on my wheelhouse roof-fixed & flat. Generally speaking I get at least 2x the output from one panel as I did from the Rutland. Winter days usually .5-1 amp summer days 2-5amps. I think the effect of partial shading is overstated from many people, from my experience with my panels. I can be seeing 4 amps from a particular panel and then shade half of it and I would then see a proportional decrease in current say 2 amps not the dramatic reduction some seem to think. I am pleased I kept one Rutland (modest output but well engineered and so quiet) for those wet windy days which we still get in Uk summers.