Best solar panels for the buck

[prroots]

As a mini-update, my two solar panels have arrived from SolarBlvd. It turns out they are a Photowatt model PW2050-210 panel rated at 210 watts apiece as shown here:
http://www.photowatt.com/documents/produits/PW2050_EN.pdf

Our fabricator is now constructing the aluminum frame. On Monday he is scheduled to weld the stainless steel support structure to our existing dinghy davits. In the meantime, I have completed the installation of our Morningstar TriStar MPPT 45 solar controller. I especially like the RS232 link back to laptop. It allows me to:

• Monitor or log any combination of many many variables
• Setup custom profiles
• Update firmware as required

As a glitch, the PC monitoring software has difficulty connecting to the controller ie, it is intermittent. Morningstar tech support stated that this is not correct and they will send me a free replacement controller and return label for the existing one. Can't beat that for support
Pete

 

[Maine Sail]

As a glitch, the PC monitoring software has difficulty connecting to the controller ie, it is intermittent. Morningstar tech support stated that this is not correct and they will send me a free replacement controller and return label for the existing one. Can't beat that for support
Pete

One reason why I generally recommend a charge controller from a reputable company...

 

[prroots]

I'm really happy I stepped up and didn't skimp on the charge controller
Pete

 

[prroots]

Can anyone recommend some type of flexible conduit to protect our AWG 8/2 (conductor) wire from the UV? The cable itself is flat and about 5/8" wide. Thanks
Pete

 

[Sumner]

Can anyone recommend some type of flexible conduit to protect our AWG 8/2 (conductor) wire from the UV? The cable itself is flat and about 5/8" wide. Thanks
Pete

I would look at the cheap corrugated stuff at an auto parts store. Cheap and easy to replace and comes in different dia. and colors,

Sum

[FONT=Arial, sans-serif]Our Endeavour 37[/FONT]

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[prroots]

I would look at the cheap coragated stuff at an auto parts store. Cheap and easy to replace and comes in diffferent dia.

S

Thanks. Just got panels mounted today and wiring almost finished
Pete

 

[prroots]

I found a nice thin-walled, white bilge pump hose to use to cover my AWG 8/2 wire. it fit perfectly.
Pete

 

[thinwater]

This type of product works great on flat surfaces.

Can anyone recommend some type of flexible conduit to protect our AWG 8/2 (conductor) wire from the UV? The cable itself is flat and about 5/8" wide. Thanks
Pete

It can almost disappear on the white gelcoat.
http://www.homedepot.com/h_d1/N-5yc...splay?langId=-1&storeId=10051&catalogId=10053
It's self-adhesive, though you could add screws on the inside. It snaps open for service.

If this is too small (it would be big enough for 2 #8 wires, but not a #8 cable), electrical supply houses have more sizes and more products for running exposed wire on a wall.

 

[prroots]

I've used the Morningstar TriStar MPPT 45 to monitor solar collection. As mentioned, I have a total of 420 watts in two 210 watt panels. Using a rule of thumb here in Florida that average Ah/day is equal to 1/3 of wattage I would expect something close to 140 Ah/day. Instead I've collected between 60 and 73 Ah over the last 3 days. I've shown a graph from the controller of the output power which corresponds to 73 Ah collected. Does anyone have experience with collected solar here in Florida this time of year. Admittedly, the last 3 days have mostly been pretty overcast.
Pete

 

[Maine Sail]

I've used the Morningstar TriStar MPPT 45 to monitor solar collection. As mentioned, I have a total of 420 watts in two 210 watt panels. Using a rule of thumb here in Florida that average Ah/day is equal to 1/3 of wattage I would expect something close to 140 Ah/day. Instead I've collected between 60 and 73 Ah over the last 3 days. I've shown a graph from the controller of the output power which corresponds to 73 Ah collected. Does anyone have experience with collected solar here in Florida this time of year. Admittedly, the last 3 days have mostly been pretty overcast.
Pete

The rule of thumb I find most accurate is max panel current X 5 . Up in the North max panel current X 4 - 4.5.. What is the max current you've seen your panels produce? Know that, and multiply by 5 and you be pretty close. If those are 24V panels you'll need to base this off the MPPT conversion max amperage..

Also keep shading in mind...

 

[Sumner]

... Using a rule of thumb here in Florida that average Ah/day is equal to 1/3 of wattage I would expect something close to 140 Ah/day. Instead I've collected between 60 and 73 Ah over the last 3 days..

If you go back to the first page on this thread and my post there I felt we were averaging 43-50 Ah/day from 180 watts of panels and that was in March to May when the days were a fair amount longer than now. The panels were flat all day with no shading. That would of been about 1/4 of wattage, but I've never seen that formula before.

I've used (watts/12) X (.4 to .5) X 6 (HR). Using that I get about 45 Ah/day for our 180 watts, which is pretty close to what I think we got. Don't ask me where I came up with that formula. I think I saw some one else give it or maybe I just made it up :cry:.

For you that would be (420/12) X .4 X 6 = 84 Ah. I thought those panels were discounted since they were suppose to be about 200 watts each. With that (400/12) X .4 X 6 = 80 Ah which might not be too far off if it was overcast and considering day length now.

I'll bet you get more in a month or so, but maybe not near the 140 that you are hoping for. I'm hoping that we average 90 to 100 Ah/day with the 480 watts we are putting on the Endeavour,

Sum

[FONT=Arial, sans-serif]Our Endeavour 37[/FONT]

[FONT=Arial, sans-serif]Our Trips to Utah, Idaho, Canada, Florida[/FONT]

[FONT=Arial, sans-serif]Our MacGregor S Pages[/FONT]

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[prroots]

If you go back to the first page on this thread and my post there I felt we were averaging 43-50 Ah/day from 180 watts of panels and that was in March to May when the days were a fair amount longer than now. The panels were flat all day with no shading. That would of been about 1/4 of wattage, but I've never seen that formula before.

I've used (watts/12) X (.4 to .5) X 6 (HR). Using that I get about 45 Ah/day for our 180 watts, which is pretty close to what I think we got. Don't ask me where I came up with that formula. I think I saw some one else give it or maybe I just made it up :cry:.

For you that would be (420/12) X .4 X 6 = 84 Ah. I thought those panels were discounted since they were suppose to be about 200 watts each. With that (400/12) X .4 X 6 = 80 Ah which might not be too far off if it was overcast and considering day length now.

Thanks. Well, guess my estimates were very optimistic:cry: The panels were very highly discounted, but due to a mistake by the OEM I ended up getting A grade panels. These 2 panels were sold to Solar Blvd by Photowatt as part of a shipment of 10. Eight were B grade which they apparently sold on eBay. These last two tested out at spec and Solar Blvd sold them to me.
Pete

 

[prroots]

I would like to know how to test solar panels to see if they live up to their ratings. Is this impossible without somehow simulating the standard solar insolation? Maybe there is a resource to see what the solar insolation is at my location and somehow ratio it?
Pete

 

[Sumner]

Thanks. Well, guess my estimates were very optimistic:cry: ...

I'll bet you see more when you have more sun and more hours. Panels actually put out max. when they are cooler, like in the winter, but have to be angled perfectly and since the days are short you aren't going to get as much. I'll bet you start to see a difference once we get into late March and on into the summer with the longer days.

I try and remember that the panel is going to spec out when it is 90 degrees or close to it to the sun. Our panels are never at 90 degrees and only close to it for a couple hours mid day. Not sure if I've seen your boat or not, but do you have a bimini and if so are more panels above it an option

I was going to put 4 above the bimini and 2 above the davits, but figured out how to have all 6 above the bimini, although 2 will extend a slight ways behind it. I think we could still put some over the davits if needed.

The Endeavour is a lot bigger than our Mac, but we are trying to live the same on it with about the same power requirements. The frig will be 1 cubic foot larger and have a little over 1/2 cu. ft. freezer so will probably consume more electricity than...

http://purplesagetradingpost.com/sumner/macgregor2/inside-22.html

... the frig we use on the Mac, but I'm hoping that with more insulation it won't use too much more. The rest of our power needs should stay the same. Nothing 110 on the boat except a small....

http://purplesagetradingpost.com/sumner/FL-spring-2011/FL-Spring-11-10.html

...pure sine wave inverter that gets used every once in a while to charge the batteries for ...

...the power tools and a few other batteries.

We will have a Honda 2000 onboard with a charger, but sure hope to not use it except for maybe the sewing machine and possibly a power tool if needed.

Good luck and let us see a graph in a month or so. Also the mount came out nice looking. What did you end up doing for the rotation and locking it at an angle? I'd like to see pictures of that area,

Sum

[FONT=Arial, sans-serif]Our Endeavour 37[/FONT]

[FONT=Arial, sans-serif]Our Trips to Utah, Idaho, Canada, Florida[/FONT]

[FONT=Arial, sans-serif]Our MacGregor S Pages[/FONT]

[FONT=Arial, sans-serif]Mac-Venture Links[/FONT]

 

[prroots]

I found a pretty simple off-grid solar calculator at:

http://www.altestore.com/store/calculators/off_grid_calculator/
​

For variables I entered:

12 Volt battery system
0 days backup
Miami, FL -> 4.5 sun hours
50 F minimum temperature
​

I then varied the daily energy usage until the answered equaled the actual 420 watts of solar panels and came up with the 1450 watt-hrs/day or 118 Ah/day (based on 12.25 Volts). This is about double what I've actually experienced in the last 3 days. Comments?
Pete

 

[Sumner]

How are you measuring the amperage? Are the panels connected to the house bank of batteries? Are the batteries way down? If the controller isn't in bulk charge mode with the batteries discharged you aren't really going to know what the panels are capable of since the charger is cutting back. At least that is my experience,

Sum

[FONT=Arial, sans-serif]Our Endeavour 37[/FONT]

[FONT=Arial, sans-serif]Our Trips to Utah, Idaho, Canada, Florida[/FONT]

[FONT=Arial, sans-serif]Our MacGregor S Pages[/FONT]

[FONT=Arial, sans-serif]Mac-Venture Links[/FONT]

 

[prroots]

How are you measuring the amperage? Are the panels connected to the house bank of batteries? Are the batteries way down? If the controller isn't in bulk charge mode with the batteries discharged you aren't really going to know what the panels are capable of since the charger is cutting back. At least that is my experience,

Thanks. The Morningstar TriStar MPPT 45 Controller is monitoring about 15+ variables at both its input and output. One of the variables is collected energy at its output in Ah. The batteries were at about 12.2 Volts and, therefore, the controller was in bulk charge mode.
Pete

 

[prroots]

Further to the above, at some point I can turn off all DC loads and any other charging sources and compare the built-in monitoring of the controller with my Victron BMV-600 battery monitor. This will help me determine the accuracy of the controller. I do know that it's battery voltage readings almost exactly match the Victron's. Both the controller and Victron use a voltage sense wire to determine battery Voltage independent of current.

I continue to be very impressed with this controller and highly recommend it.
Pete

 

[Bill Roosa]

Hey Prroots
The only way to test panels is to run some, well tests. A variable load is required so you can measure the voltage and amps for a given solar input. The manufacturer may or may not have the IV curves and without those you would have nothing to compare except max output watts/volts/amps. Max output is of course only going to happen under a full sun so that kinda limits the times of your testing unless you can reorient the panel to make it orthogonal to the incoming light.
The procedure is to measure both volts and amps for a number of different load resistances (under a constant illumination) then plot the current vs. the voltage.
Alternately you can just use the battery monitor to access the panels input in AH and compare that to what you would expect given your specific set up as you did.
Things to account for:
Panels not aimed at the sun (horizontal?). P(actualAtSolarNoon) = P(maxRating)*sin(latitude-solar altitude), note this is power not energy. Since it is winter and the suns altitude is a negative number now you are probably only going to be able to get 50% output at best till the sun is higher in the sky or you tilt the panels toward the sun.
Panels not at standard temp, hotter is worse
Shading of the panels during parts of the day (this is a real killer as even a small amount of shading will basically kill the panels output. Cheap panels do not have bypass diodes to handle this situation.)
Long wiring runs, high resistance connections, basically the voltage drop between the panel proper and the batteries.

Just for my own edification, what is your AH consumption / day?

 

[prroots]

Hey Prroots
The only way to test panels is to run some, well tests. A variable load is required so you can measure the voltage and amps for a given solar input. The manufacturer may or may not have the IV curves and without those you would have nothing to compare except max output watts/volts/amps. Max output is of course only going to happen under a full sun so that kinda limits the times of your testing unless you can reorient the panel to make it orthogonal to the incoming light.
The procedure is to measure both volts and amps for a number of different load resistances (under a constant illumination) then plot the current vs. the voltage.
Alternately you can just use the battery monitor to access the panels input in AH and compare that to what you would expect given your specific set up as you did.
Things to account for:
Panels not aimed at the sun (horizontal?). P(actualAtSolarNoon) = P(maxRating)*sin(latitude-solar altitude), note this is power not energy. Since it is winter and the suns altitude is a negative number now you are probably only going to be able to get 50% output at best till the sun is higher in the sky or you tilt the panels toward the sun.
Panels not at standard temp, hotter is worse
Shading of the panels during parts of the day (this is a real killer as even a small amount of shading will basically kill the panels output. Cheap panels do not have bypass diodes to handle this situation.)
Long wiring runs, high resistance connections, basically the voltage drop between the panel proper and the batteries.

Just for my own edification, what is your AH consumption / day?

Thanks. I've attached the IV curves for my 210 watt Photowatt PW2050-210 panels. I currently estimate a daily load between 110 and 140 Ah. I can tilt the panels and estimate the temperature, but at the moment I don't know how to estimate the irradiance in kW/m2. Not sure why a variable load is required. Why not just measure an instantaneous voltage and current and see if it falls on the manufacturer's IV curve? That by itself would satisfy me. My charge controller automatically sets voltage and current to achieve maximum power output. This should be close to the knee of the curve. For comparison with the IV curve, I probably need to divide voltage in half since the two panels are in series. It seems that the next step is to find irradiance values based upon geographical location, month of the year, and time of day.

Update: I may have answered my own question. I have located a source of solar irradiance based on time of year and geographical location here:

http://eosweb.larc.nasa.gov/cgi-bin/sse/grid.cgi?email=
​

Once I put in my location and month, it gave me an average midday irradiance on a horizontal surface of 0.56 kW/m2 which I can now enter onto IV curve. Using the right hand curve with 0.56 kW/m2, we get a maximum power of about 105 watts. I would expect temperature to derate that by approximately 10% which gives us approximately 95 watts (or twice that for two panels). This is definitely something I can test for by averaging the instantaneous watts around midday over several days in a row.
Pete