Solar Panel Output verse rating

[StuM]

Originally Posted by rom

cos(3° + 26°) = 0.87 and you have it the picture you just posted

Edit: Isn't there something wrong with the way this link calculates resulting intensity as a function of air mass ?? Make air mass 1 (by selecting -3° latitude) and still the intensity is lowered ! This conflicts with direct radiation given here Calculation of Solar Insolation | PVEducation and also conflicts with the definition of solar intensity given here https://en.wikipedia.org/wiki/Air_mass_(solar_energy)

OK, I see that 87% is the intermediate figure of .871 in the previous link calculations.

We have discrepancies for several reasons.

We are mixing direct and total insolation. The figures in the calculator we have been using are for Direct Radiation. Your first link gives figures for Total Insolation including Diffuse Radiation which is about 10% higher.

AMx is used in two different ways:
1. To define the solar spectrum (the spectrum changes are various wavelengths are filtered out in the atmosphere to different extents)

2. To define the atmospheric attenuation of radiation. (the longer the path through the atmosphere, the more direct radiation is lost through absorption and scattering).

The AM1.5 spectrum is used for STC of solar panels. AM1.5 attentuation doesn't come into testing.

AM1.x attenuation is used to determine the reduction in actual radiation intensity based on the atmospheric path of the suns ray from the Top Of Atmosphere solar constant figure of 1353W.

My Conclusion:

Based on all the information from the various posts, it would appear that the 10% extra insolation when you include diffuse radiation is pretty well offset by the 10% loss of efficiency due to temperature effects etc.

Consequently, the final Smodule figure in the calculator is a realistic factor to use when determining the likely maximum output in normal use from a solar panel which is rated to output a specified number of Watts when it is at 25°C and 1000W/m² of radiation of an AM1.5 spectrum are directed at it for a short period of time.

I stand by the expectation of less than 80% of rated output today in Palm Beach.

[rom]

Originally Posted by StuM

The AM1.5 spectrum is used for STC of solar panels. AM1.5 attentuation doesn't come into testing.

AM1.x attenuation is used to determine the reduction in actual radiation intensity based on the atmospheric path of the suns ray from the Top Of Atmosphere solar constant figure of 1353W.

AM is clearly in the favor a Palm Beach now that the sun is almost at the equator, but it is already taken into account in the 1023W/m2 figure that I am using from the first link, so right, nothing to add. However, STC at AM1.5 takes the highest value of the range because they are testing in ""rural aerosol loading" i.e. clean air conditions", cf. https://en.wikipedia.org/wiki/Air_mass_(solar_energy). That is they are expecting 1000W/m2 where the average should be 930W/m2.
So we could as well use the highest figure at sea ! to which you might argue "are we really at sea in Palm Beach" ?

Well, here is a real life experience: I am currently at 14.5°N, so based on your calculations I should not get anything better than roughly 85% ? I am however getting 95% of STC rating, and I have achieved a steady 110% the other day.
cos (3 + 14.5) = 0.95

[a64pilot]

I'm still trying to understand the two year payback as opposed to running the generator.
I figure ownership and operating costs for my generator to be as a guess of $2.50 an hour.
based on an assumed lifespan of 6000 hours and a cost of $6,000 = $1 an hour
Fuel $1 and hour and maintenance .50c an hour. Rough guess really, but close I bet.
So how the heck do you correlate that to Solar?

[newhaul]

Originally Posted by a64pilot

I'm still trying to understand the two year payback as opposed to running the generator.
I figure ownership and operating costs for my generator to be as a guess of $2.50 an hour.
based on an assumed lifespan of 6000 hours and a cost of $6,000 = $1 an hour
Fuel $1 and hour and maintenance .50c an hour. Rough guess really, but close I bet.
So how the heck do you correlate that to Solar?

That part is simple. The only missing part is how many hours you run the genny per day. Say you run for 4 hours that is 10 bucks per day . Solar would save you that ten bucks. The other missing link is the cost of the solar array.
Say 3k bucks so the array in this instance wod pay for itself in 300 days (money saved not using genny . (Actual would depend on individual numbers plugged in where they need to be.)

[masonc]

Originally Posted by a64pilot

I'm still trying to understand the two year payback as opposed to running the generator.
I figure ownership and operating costs for my generator to be as a guess of $2.50 an hour.
based on an assumed lifespan of 6000 hours and a cost of $6,000 = $1 an hour
Fuel $1 and hour and maintenance .50c an hour. Rough guess really, but close I bet.
So how the heck do you correlate that to Solar?

Solar doesn't make noise.
Solar doesn't need fuel - not always easy to get.
Doesn't need a human to start the generator, keeps working basically forever.
Extremely reliable.

[a64pilot]

So what does a 1KW array supposed to cost?
I know about what I paid, but that was low.

To me trying to make a $$ decision on Solar Vs Generator is a lot like trying to decide on a cost basis, sail or motor?

I went with as much Solar as I could fit, and a generator to fill in the shortfalls, ideally I'd never run the thing, but I know for me that is not realistic.

[rom]

I did some more testing today, result here in pictures.

The picture where the left (port) array shows 705W while the starboard array shows 734W is the result of a test conducted when both arrays were steady around 700W. I cooled down the starboard array with some fresh water. I touched the back of the array and it was indeed way colder than the other one. No measurements though, this is as far I went today. To be taken with a grain of salt though as the sky started to get cloudy here and there and the ouput started varying. I shall try that again.

The second picture showing 750+ on both array was taken about 10 minutes later at a moment where the sun seemed to be at its max. Both array were at about the same temperature then.

Both arrays are made of two panels in parallel, cf. picture for specs. I did measure amps & volts at the input of the MPPT controler (victron 150/60) and found it to be accurate.

All that today at 14°28' N 60°52' W; 1 pm local time.

Stu, that is 14% above STC rating at the best time of the day, what's your take on this ?

[newhaul]

Originally Posted by a64pilot

So what does a 1KW array supposed to cost?
I know about what I paid, but that was low.

To me trying to make a $$ decision on Solar Vs Generator is a lot like trying to decide on a cost basis, sail or motor?

I went with as much Solar as I could fit, and a generator to fill in the shortfalls, ideally I'd never run the thing, but I know for me that is not realistic.

Mm ok so for you it would pay for itself at the rate of $1.50 per hour that you dont need to run the genset. So devide the cost of your array by 1.5 and that w ok ll give you the payoff point for the array. Then it will be an aditional 4000 hours to recoupe the cost of the genset. After that point it would be like money in the bank.

[Paul L]

Originally Posted by newhaul

You do realise.my boat is a 24ft islander right?
Attachment 143030

No, I wasn't. I have seen plenty of small cruising boats with a panel oriented as you have plus one on each lifeline. That would would be max. And the additional windage does effect your windward performance.

[newhaul]

Originally Posted by Paul L

No, I wasn't. I have seen plenty of small cruising boats with a panel oriented as you have plus one on each lifeline. That would would be max. And the additional windage does effect your windward performance.

The affects are mitigated to a major extent by proper mounting .
When properly mounted and adjusted there in no noticeable adverse effect. (At least my customers haven't told me of any issues.)

[Paul L]

Originally Posted by newhaul

The affects are mitigated to a major extent by proper mounting .
When properly mounted and adjusted there in no noticeable adverse effect. (At least my customers haven't told me of any issues.)

Sure, as long as the boat doesn't heal.

[newhaul]

Originally Posted by Paul L

Sure, as long as the boat doesn't heal.

Heal means readjust panels no problem its easy .

[Paul L]

Originally Posted by newhaul

Heal means readjust panels no problem its easy .

Sure, on the flat Puget Sound, what happens offshore.
There is no free lunch.

[newhaul]

Originally Posted by Paul L

Sure, on the flat Puget Sound, what happens offshore.
There is no free lunch.

Loo offshore you are on the same tack.for a lot lon than in the puget sound. So makes adjusting even easier you dont need to change angles every hour or.two.

[Paul L]

Originally Posted by newhaul

Loo offshore you are on the same tack.for a lot lon than in the puget sound. So makes adjusting even easier you dont need to change angles every hour or.two.

And you think this will set the panels so they don't present windage? The boat is moving all around with seas and the wind is gusting around. With adjustable panels most people adjust them for the Sun, not the windage.

Enough of a discussion for me. Have it any way you wish.