solar panel usage data

Things 12V and 24V
Whimsical
Posts: 370
Joined: Sat Apr 28, 2007 8:01 pm
Location: Fremantle W.A.

solar panel usage data

Post by Whimsical » Fri Jan 27, 2012 9:53 pm

Thought i might put up a bit of data i have from my 1590 watt panels. I have 5 Sunpower 318 W panels mounted at 20 degrees on the roof. As my intended cruisng area is near the equator and the panels will be flat i am hoping i will get similar results. I will have 3 of these panels on the boat for for 954W.
In winter i was getting about 4 to 8,000 watthours. Now it is summer i get 11,000 on a bright hot cloudless day and 6,000 on a very hot very dark cloud covered day like today was.
Allowing for only 3 panels and an 85% efficiency for the charge controller this gives 226 to 415A/H per day. Bloody happy if i get that :D. As my panels are not near any shading hopefully i won't lose a lot but time will tell.
Supposedly the Sunpower panels are better than most at converting low angle light so my data may not be transferable to other brands. If feeding lead acid batts would have to allow for about 15% less delivered to the batts.

Mike

Trev
Posts: 160
Joined: Thu Jan 15, 2009 2:56 am
Location: Moruya NSW

Re: solar panel usage data

Post by Trev » Sun Jan 29, 2012 7:52 am

Whimsical wrote:I have 5 Sunpower 318 W panels mounted at 20 degrees on the roof
Hi Mike,
You bring up a interesting point that has been worrying me about mounting my solar panels. The only area I have to mount my panels is on the saloon/cockpit roof but this area is, for arguments sake, flat. I see this is less than ideal, in fact 1/2 the panels will be facing away from the sun slightly am and pm, because of the curvature of the cabin top.
How do you think this will affect power production?
Trev

44c
Posts: 1148
Joined: Tue Aug 08, 2006 5:08 am
Location: Hervey Bay, Qld

Re: solar panel usage data

Post by 44c » Sun Jan 29, 2012 9:03 am

Whimsical wrote:Allowing for only 3 panels and an 85% efficiency for the charge controller this gives 226 to 415A/H per day. Bloody happy if i get that :D. As my panels are not near any shading hopefully i won't lose a lot but time will tell.
Supposedly the Sunpower panels are better than most at converting low angle light so my data may not be transferable to other brands. If feeding lead acid batts would have to allow for about 15% less delivered to the batts.

Mike
Probably be wise not to expect 226 to 415 a/h every day. Boats don't sit still, and even with your rig you'll still get shading at times.

We have 600 watts, and the best I've seen was around 250 a/h in a day.

Still, if you have a reasonably efficient boat, and you're not trying to run aircon, you should have plenty of power nearly all the time.

Whimsical
Posts: 370
Joined: Sat Apr 28, 2007 8:01 pm
Location: Fremantle W.A.

Re: solar panel usage data

Post by Whimsical » Sun Jan 29, 2012 12:41 pm

Trev
Mounting them flat will obviously cost u some performance but how much is hard to say, the further south u are the more u would lose. I have no data to support it but i think the angle of the sun to the earth has more influence than the angle of the panels. At the moment i don't see much change as the sun goes through about 30 or 40 degrees in the middle of the day but i haven't collected much data about that. Will be able to answer this better when the panels go on the boat. On clear days i think u would lose a greater percentage than u would on cloudy days as the clouds make a nice diffuser. The further north I head the less influence the flat panels will have.
What prompted me to post was how surprised I was at the amount i still get on heavily overcast days, i was expecting a lot less. The other day had very dark solid cover all day. When i collected the No's they were still 55% of a clear day.

44c
Your No's equates well to mine percentage wise but what i am more interested in is what do u get on a day with solid dark cloud cover. Scale the panels and your consumption to take care of those days and u don't have to worry about the good days.

Mike

44c
Posts: 1148
Joined: Tue Aug 08, 2006 5:08 am
Location: Hervey Bay, Qld

Re: solar panel usage data

Post by 44c » Sun Jan 29, 2012 2:28 pm

A really crappy, raining all day, type of day, we might only get around 30-40 amp/hours. :shock:

But at least we don't need the watermaker then.

Jim
Posts: 691
Joined: Fri May 19, 2006 8:25 am
Location: Cairns

Re: solar panel usage data

Post by Jim » Tue Jan 31, 2012 5:55 pm

My solar panels, 2 x 24 volt x 250w don't seem to be doing very much. The most I have seen is a combined input of 8 amps and that is rare, it is usually 6 point something. To me who knows SFA about electrickery that doesn't seem to be anywhere near enough. Any ideas?? and if so KISS.
When I am on the boat the batteries, 510ah, are usually around the low to high 12v area, which depending on who you talk to is nearly flat. I never have any doubts about starting the motors with low voltage as they are just small outboards and they don't require much in the way of battery life to fire them up.
Jim.

Smooth Cruiser
Posts: 583
Joined: Thu May 11, 2006 1:51 am
Location: Brisbane

Re: solar panel usage data

Post by Smooth Cruiser » Tue Jan 31, 2012 11:04 pm

Jim - need to know the voltage at the point the current measurement is being made too. Solar panels themselves put out about 18V, a 12V system has them in parallel and the regulator drops the voltage to around 14.5V for charging the batteries. In your 24V solar system the cells are in series so the solar regulator sees about 36V on the inlet side and then drops this to around 14.5V again for charging. (Unless your battery bank is 24V which I don't think it is?)

So the typical 6A you see if measured before the regulator (36V) is equivalent to 216 watts (6*36) which is pretty good out of 250W panels. However if this 6A is measured post regulator it is only 87W (6x14.5) which isn't so good!

If your batteries are lead acid then the highest you will see with no charging happening is around 12.6V. Other types of batteries will see higher voltages. While charging you should be seeing up to about 13.7V measured. So your voltage numbers do look pretty low - if you have a multimeter then hook this up directly to the battery terminals and see how the reading compares to your panel. It may be that you have significant voltage drop between the batteries and the voltmeter.

mahnamahna
Posts: 580
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

Re: solar panel usage data

Post by mahnamahna » Wed Feb 01, 2012 11:08 am

Please dont stop there Smooth. What would cause such a loss between panels and regulator? Wrong cable size for example? If so what cable size ought to be used. What if anything else would cause this loss. Whilst you are addressing Jim's problems, the rest of us will also learn from it. Cheers. Paul

Smooth Cruiser
Posts: 583
Joined: Thu May 11, 2006 1:51 am
Location: Brisbane

Re: solar panel usage data

Post by Smooth Cruiser » Wed Feb 01, 2012 12:10 pm

I was first going to see if there was a voltage drop in the meter before trying to diagnose the problem!! But yes it could be too small a cable size somewhere along the line, the meter could be in parallel with some of the load, the meter itself could be faulty, if analog the needle may need adjusting and I'm sure there could be many other causes IF this is the issue.

There are plenty of tables and guides available online and in books to select the correct cable size for the current that will be seen, but within reason the bigger the better!

mahnamahna
Posts: 580
Joined: Wed Aug 02, 2006 4:48 pm
Location: Gosford NSW

Re: solar panel usage data

Post by mahnamahna » Wed Feb 01, 2012 8:53 pm

Smooth, Please excuse my ignorance, like others here Electricity is a dark art. If the solar panels I am looking to import work out (being tested at the moment) they are so cheap, and I have so much roof real estate, that I am going to put 6 x 180 watt panels up there. Am I better off joining them up there and sending all that load down one big cable or sending each panels wiring down individually and then joining them just before the regulator. Sending over 1000 watts @ 18v down one wire, isnt that about 60 amps and is that wire going to be as thick as say and power extension cord? Or will it be thicker than that? The wires that come out of the panels now are about that thickness so sending 6 of them down will need either multiple routes or a really big conduit.

Or is 1kw just going to be way over powered? The way my uneducated mind thinks, is that if I can put them up there then I am not likely to ever exceed their feed, in usage. Does it work that way. Am thinking on having 400amp hour lifepo4 battery bank, maybe 600AH (but cant afford the extra 200AH yet). Will have outboards so they only charge at 15amps. Will probably have one of those Honda 2000 petrol gennies for emergencies or for when we want to use the convection microwave to roast. I have a 200 litre Isotherm fridge/freezer not sure what it draws yet, it depends on ambient temp I think but it has a danfoss 50 compressor which I believe are pretty good, I will have the usual array of electronics including radar, plotter, sounder and ais, 19in lcd tv with dvd player, laptops (cant imagine life without internet!), led lighting throughout, and will be buying a watermaker, probably an 80e Katydyn, makes about 12 litres an hour and uses about 8amps an hour. Will probably want to run that every second day.

Post Reply