Any tips on my setup?

[Wrybread]

> However, if the Voc is really that high, forget what I said about needing a 4th panel. You could support a 24 V battery with the three panels in parallel, more efficient overall and less expensive wiring.

Converting the battery bank to 24 volts is a really good idea and gracefully handles a lot of the issues. It's easy enough to get a 24v inverter, but the rest of my RV runs on 12 volt, so I'd probably just use a step down transformer, which is easy enough. Only one thing pulls a lot of power, which is the furnace blower (80 watts!), but I could easily do without that since I mostly use a portable Buddy Heater since it's so much more efficient.

I think my plan of attack will be to connect the 2 panels in parallel for now. They're flat mounted and unlikely to exceed 520 watts, though its definitely something to watch for. I'd love to keep the 3rd panel up there so I can switch it on during cloudy periods (and to piss off SunKing), so if there's enough room I'll probably do that too.

And if it looks like that system won't work, I can convert the battery bank to 24 volts and go from there, or consider upgrading the charge controller.

[sensij]

I think you would be better using all 3 panels, even if you stay at 12 V. Don't let the 520 W bogey scare you... look closely at the Page 10 Sunking linked. 520 W is the max charge power... in other words, that is the 40 A output spec translated to the input charge power, accounting for the efficiency of the CC. Even if your panels would be capable of producing more than that, the mppt system will pull the operating point away from the maximum, to stay within the 40 A output limit (as described in the preceding paragraph on page 9). In that same table on page 10, you can see that the max installed PV array power for the 12 V setup is listed as 1560 W, which is simply 3X the array charging power rating, although Voc and Isc limits might come into play as well as you approach that maximum.

By increasing the your array size, you are increasing the number of hours the batteries can be charged at 40 A. Your batteries will thank you later.

[-TX-]

Yeah, I don't understand the math. How does 1.9kWh (PV) minus 14% inefficiencies equal 7 kWh of radiation in July, for example, when we get sun for 10 hours a day?

Seems very conservative. Which is good in a sense, but still....

kWh.png

[J.P.M.]

Yeah, I don't understand the math. How does 1.9kWh (PV) minus 14% inefficiencies equal 7 kWh of radiation in July, for example, when we get sun for 10 hours a day?

Seems very conservative. Which is good in a sense, but still....

kWh.png

FWIW, see my 03/07,1:08 P.M. comment.

[sensij]

The solar radiation column is displayed in units of insolation. Many people are more familiar with the term "sun hours", but the values are the same. The insolation isn't affected by array size. Read the help files for more information.

For an off grid application, losses will be more than 14%, the AC energy it suggests will be available using the default loss factor is way too optimistic.

[SunEagle]

Because while the sun may be up for 10 hours a day your panels are only producing for 7.03 hours a day on average. A solar pv panel needs to have the sun light hitting it more than just at a glancing angle to produce close to it's nameplate wattage. If you look at a graph you will see a "hump" as the sun comes up with the peak around Noon. If the panel produced full output as soon as the sun hit it the graph would look like a rectangle.

[-TX-]

'On average', gotcha. So if I travel to an off grid site knowing the sky will be clear for the days required of me I should expect better output.

[sensij]

'On average', gotcha. So if I travel to an off grid site knowing the sky will be clear for the days required of me I should expect better output.

This interpretation of the word "average" is part of what made my post yesterday objectionable. No, your understanding and expectations are not aligned with what the model is showing.

respectfully, if you have questions about pvwatts, it might be to start a new thread. This one has enough confusion in it already.

[-TX-]

Link? couldn't find that post

[Wrybread]

I think you would be better using all 3 panels, even if you stay at 12 V. Don't let the 520 W bogey scare you... look closely at the Page 10 Sunking linked. 520 W is the max charge power... in other words, that is the 40 A output spec translated to the input charge power, accounting for the efficiency of the CC. Even if your panels would be capable of producing more than that, the mppt system will pull the operating point away from the maximum, to stay within the 40 A output limit (as described in the preceding paragraph on page 9). In that same table on page 10, you can see that the max installed PV array power for the 12 V setup is listed as 1560 W, which is simply 3X the array charging power rating, although Voc and Isc limits might come into play as well as you approach that maximum.

By increasing the your array size, you are increasing the number of hours the batteries can be charged at 40 A. Your batteries will thank you later.

Thanks, fantastically good to know.

[Sunking]

Thanks, fantastically good to know.

It is a fools trap you have fallen for. Yes you can over power any MPPT controller to get a few more minutes of Sun Hours. But that is a FOOLS GAME. It is not a bad thing for a Grid Tied System, but throwing away money on a battery system. Also asking for over heating and equipment failures.

At very best if you parked in a Walmart Parking lot with no shade issues on a hot summer day will give you 5 Sun Hours with 0 degree tilt. With a 600 watt panel connected to a 40 amp controller only harvest you 1700 watt hours. However with a 50 amp controller that same 600 watt panel generates 2000 watt hours. You screwed yourself out of 15% of power. Add that 3rd panel with your 40 amp controller, sure it will work, you get 2000 watt hours. Use the 80 amp controller with 900 watts of panels and you harvest 3000 watt hours. You just screwed yourself out of 33% of your power. Then you compound your mistake connecting the panels in parallel screwing yourself again out of more power lost on wiring, and spending a lot more on wiring and hardware than you had to. All because your equipment is not compatible with each other. .

For someone who claims to be an expert with 20 years experience, you have not learned anything other than how to throw away your money on incompatible equipment. I would stop bragging if I were you, and start listening.

What is amazing is all you have to do to fix yourself is get rid of that POS controller you have and buy 1 compatible with your panels.

[Sunking]

Yeah, I don't understand the math. How does 1.9kWh (PV) minus 14% inefficiencies equal 7 kWh of radiation in July, for example, when we get sun for 10 hours a day?]

Because you do not understand 10 hours day light does not equal 10 Sun Hours. Kwh / M^2 / Day = Sun Hours. Additionally you cannot compare a Grid Tied System with a Battery System. With a battery system you use December sun hours and a 66% efficiency with MPPT or 50% with PWM. Stick around, in 1 week here you have learned more in the last 20 years.

[Wrybread]

If someone made a browser plugin that blocked all posts from SunKing, this forum would benefit greatly.

As I said about 50 times, I'm well aware of the drawbacks of flat mounting my panels, and wiring them in parallel, but for an RV setup with the equipment I have, I have to do it. I haven't "screwed myself" out of anything, and you using that language over and over exposes you for the argumentative troll that you are.

I'm through even reading your alarmist and overly dramatic "advice", and certainly done responding to you. Look at your posts from yesterday for example (not just to me, they were all over this forum, some so hostile that they were deleted by the mods), every single one of them is hostile and full of misinformation and reading comprehension fails, and failure to grasp that sometimes people have to work with the equipment they have at hand (not to mention budget).

[SunEagle]

If someone made a browser plugin that blocked all posts from SunKing, this forum would benefit greatly.

As I said about 50 times, I'm well aware of the drawbacks of flat mounting my panels, and wiring them in parallel, but for an RV setup with the equipment I have, I have to do it. I haven't "screwed myself" out of anything, and you using that language over and over exposes you for the argumentative troll that you are.

I'm through even reading your alarmist and overly dramatic "advice", and certainly done responding to you. Look at your posts from yesterday for example (not just to me, they were all over this forum, some so hostile that they were deleted by the mods), every single one of them is hostile and full of misinformation and reading comprehension fails, and failure to grasp that sometimes people have to work with the equipment they have at hand (not to mention budget).

You do have the ability to "mute" anyone that posts on this forum so you will not see their posts or have to respond to them. That is your choice.

[Sunking]

As I said about 50 times, I'm well aware of the drawbacks of flat mounting my panels, and wiring them in parallel, but for an RV setup with the equipment I have, I have to do it. I haven't "screwed myself" out of anything, and you using that language over and over exposes you for the argumentative troll that you are.

I have told you 50 times Flat Mounting Panels is not your problem. Never did I ever say it was a problem I am typing slowly so you understand. The problem is your equipment incapability and it all revolves around your Charge Controller. Wiring panels in parallel was antiquated 20 years ago with MPPT Controllers. Two of your 300 watt panels wired in series exceeds the 100 Voc input of your controller. Hear that.

Battery systems are best constructed with 200 and in some cases 250 watt panels because the Voc is low enough that allows you to at least wire 2 panels in series on 50 amp and less controllers. If you had 200 or 250 watt panels you could use your controler. Of th e12 volt controllers out there 200 and 250 watt panels fit nicely with 80, 60, 40, and 20 amp controllers. You should know why. Well here is your clue with a 12 volt battery the max power rating vs current is:

250 watts @ 20 amps
500 watts @ 40 amps
750 watts @ 60 amps
1000 watts @ 80 amps.

300 watts is not a common denominator. Additionally the charge controller manufactures Voc input is designed with 200 and 250 watt panels in mind although those rule of thumbs go away with high voltage controllers of 200 to 600 volts. Why High Voltage? Because it works better and smart money. At 48 volt battery you can wire 10 panels in series and limit parallel string to 2. That means a much more efficient system with a lot lower installation cost because you use a lot less wire. much smaller wire, no fuses or combiners.

Bottom line here is if you get rid of the POS controller, all your problems are gone with the minor exception of using 300 watt panels do not fit well, but can be made to work as long as you do not use a PRIME NUMBER of panels like 3, 5, 7, 11, 13, 17, 19.....

So am I being hard on you and others. Yep when you claim to be an expert of 20 years and do not know the basic fundamentals and cannot understand simple concepts. Grow some skin and balls. Bottom line here is you do not understand the technology or what you are doing causing you embarrassment claiming to be an expert. I called you out. Your low ball budget is costing you more to do it right and you only get half arse results screwing yourself.

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