Best solar panels for the buck

[prroots]

If I'm reading that correctly it looks like you are getting up to around 280 watts. I'm think that isn't bad if the panels are not perfectly orientated towards the sun.

That would equate to somewhere in the neighborhood of 23 amps at 12 volts. We were usually getting about 9-12 amps during the mid-day out of 180 watts, so I feel you are doing well. We were still in bulk charge, but the battery was voltage was still up there. I don't think we ever had our batteries much under 60%. As the batteries started to top off the amps went down as they should. I think that the state of battery charge at any moment is going to throw a curve ball into the whole deal.

Interesting what you are doing. I don't have the patience for it . I just put as many panels up there as I can find space for and live with the results :cry:,

Thanks. We had a nice clear sky prior to and following midday; first time since panels were installed. We saw a peak of 304 watts at 12:45 PM while in the parallel mode. Yup, the panels were horizontal without shading. We wanted to establish that data point before continuing with additional testing. Now we know that series vs parallel is a wash under unshaded conditions. We had to turn everything on to keep the batteries from going into absorption mode
Pete

 

[Sumner]

Even 260 watt average for 6 hours a day will get you close to the Ah you were shooting for I believe,

Sum

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[prroots]

Even 260 watt average for 6 hours a day will get you close to the Ah you were shooting for I believe,
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Thanks. The problem is that we haven't seen a clear day like today in quite some time
:cry:
Pete

 

[Sumner]

Thanks. The problem is that we haven't seen a clear day like today in quite some time
:cry:
Pete

Can't blame the panels for that . Bring the boat to the 4-corners....we have sun almost every day , of course there isn't much water here because of it ,

Sum

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[prroots]

Even 260 watt average for 6 hours a day will get you close to the Ah you were shooting for I believe,

Thanks. I have a resource as referenced above that states for my present location:

Clear sky average on horizontal surface in February 5.17 kWh/m2/day (clear sky = < 10% cloud cover)

If I divide that by 1 kW/m2, I get 5.17 hours/day of equivalent irradiance at 1000 kW/m2. If I then derate my panels for temperature from 210 to 200 watts I get:

2 panels X 200 watts/panel * 5.17 hours / 12.5 volts = 165 Ah
​

Today I collected 126 Ah, but the early morning until around 10:30 was quite overcast so maybe I'm not too far off.
Pete

 

[Ron20324]

Morningstar has advised me to wire the panels in series. not, then parallel is preferred. Series has the following advantages overall:
Better overcast performance, Earlier collection in day, Later collection in day, Better performance under light shading...

As mentioned earlier, I would love to find a treatise on parallel vs series. It's certainly not the case where one is preferred in all cases.
Pete

I'm glad you got into the series/parallel info. When I put in my 2 panels, I just assumed parallel was the thing to do, and ran a cable to each panel from the controller. However, when later looking at the Morningstar picture, I saw they had them in series. I pondered the situation and figured when the sun was low in the sky and one panel's output (say 12.6) dropped below the battery voltage, it would stop charging. If you wired in series, then you'd have maybe 25.2 from the panels, so the charge would continue later into the day and start earlier in the morning.

I figure a DPDT switch would do the transfer between series/parallel, but I think using 2, SPDT, switches would allow you to take one of the 2 panels off line. I'm looking for a 50-volt DC switch. Pete, I'd like to hear your transfer setup.

Ron

 

[prroots]

I'm glad you got into the series/parallel info. When I put in my 2 panels, I just assumed parallel was the thing to do, and ran a cable to each panel from the controller. However, when later looking at the Morningstar picture, I saw they had them in series. I pondered the situation and figured when the sun was low in the sky and one panel's output (say 12.6) dropped below the battery voltage, it would stop charging. If you wired in series, then you'd have maybe 25.2 from the panels, so the charge would continue later into the day and start earlier in the morning.

I figure a DPDT switch would do the transfer between series/parallel, but I think using 2, SPDT, switches would allow you to take one of the 2 panels off line. I'm looking for a 50-volt DC switch. Pete, I'd like to hear your transfer setup.

Ron

Yes, I believe you are right; in series mode you will have more overhead compared to battery voltage to charge panel during low light conditions. I assume your panels are nominal 12 Volts. My panels are nominal 18 Volts so I would probably have adequate overhead margin even wired in parallel.

In my case the panels are adjacent so a single duplex cable runs from controller to a junction box located under the panels. In the box is a small terminal strip. The panel wiring and the duplex cable connect with terminal lugs. It takes me a moment or two to switch between parallel and serial by simply moving wires around on the terminal strip. I'm hoping to make my final decision soon in which case there will not be a long-term need to switch back and forth
Pete

 

[Bill Roosa]

All of this discussion with shading, parallel vs series, losses ..... is why there is a move afoot to wire the individual cells in parallel (avoiding the shading issue and bypass diodes) and have a 0.6 volt panel that is mpp regulated (maximizing power out) then boost convert the voltage to whatever you like (solutions for home AC power inverters and RVs with DC battery systems.
One panel to rule them all and in the sunshine bind them ;-)

 

[sea_casper]

230 Watt Solar Panel

http://www.theinverterstore.com has a 230 watt panel for $300 + shipping.

230 Watt Solar Panel

 

[prroots]

http://www.theinverterstore.com has a 230 watt panel for $300 + shipping.

230 Watt Solar Panel

I paid < $1/watt for my 210 watt panels. Shipping from West to East coast was $120 for both panels.
Pete

 

[Sumner]

I paid < $1/watt for my 210 watt panels. Shipping from West to East coast was $120 for both panels.
Pete

Yep and they have 80's on sale now for $99 each and I thought I got a good deal at $159 last spring :cry:. I've been starting to think that these are like computers....once you buy one quit looking at the price until you need the next one.

I think next fall we are going to seriously think about a lot of panels for the house. They are starting to look awful cost effective and we get a lot of sun here,

Sum

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[Kestle]

I am still learning this stuff, so could someone explain to me how a PV system prioritizes power from the panels, versus the batteries? At first glance it seems like the unit with the most power output would have priority, so usually the batteries, or is there equipment that direct power from the panel and supplement with the batteries as needed?

Jeff

 

[Bill Roosa]

It is all done by voltage. If the panels are putting out 18 volts and the controler is feeding that to the batteries then the contoller continues to route solar power to the batteries which get drained. As the panel voltage falls to 10 volts the controller cannot pump power to the batteries and the batteries take up the load.
think of the batteries as a wide spot in the circuit. If something else has greater than battery voltage that source provides the power.

 

[prroots]

Today we oriented the boat so that the stern faced North which causes shading by wind generator and radar radome. The day was partly cloudy which really confused the results as clouds passed in front of the sun. In the graph you an see when it's in parallel or series by looking at the array voltage. Also the transitions are indicated by the power dropping to zero. Can anyone make sense of it?
Pete

 

[Stu Jackson]

Pete, great information, but without knowing when you changed from parallel to series, how can we help?

 

[sea_casper]

Parallel

Can anyone make sense of it?
Pete

On average it appears parallel is yielding more power, and your controller is efficient.

 

[prroots]

On average it appears parallel is yielding more power, and your controller is efficient.

Thanks. I tend to agree. I need to repeat the test under clear sky since the partly cloudy condition really obscured things.
Pete

 

[prroots]

Pete, great information, but without knowing when you changed from parallel to series, how can we help?

I explained that in my post.
Pete

 

[Maine Sail]

Pete,

It looks as if today parallel beat series in terms of current to the bank. Of course this is impossible to confirm without more data gathering sich as Ah's returned during series & parallel time frames. From my experience it all depends on the type of shade, coverage and where you panel maker placed the bypass diodes etc. etc..

Keep testing and you'll eventually find what performs best on your installation. I've not yet found the ultimate answer for the series/parallel conundrum. Tomorrow series could win, just the way solar rolls sometimes..

 

[prroots]

Pete,

It looks as if today parallel beat series in terms of current to the bank. Of course this is impossible to confirm without more data gathering sich as Ah's returned during series & parallel time frames. From my experience it all depends on the type of shade, coverage and where you panel maker placed the bypass diodes etc. etc..

Keep testing and you'll eventually find what performs best on your installation. I've not yet found the ultimate answer for the series/parallel conundrum. Tomorrow series could win, just the way solar rolls sometimes..

Thanks. Yes, I agree. I'll keep testing and hopefully get a clear sky day before long to better distinguish the differences. Did you happen to notice the voltage steps near the center of time line while in series mode? Apparently strings were cutting in and out leading to several different discrete steps; interesting to see it in real life!
Pete