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Old 03-22-2020, 06:41 PM   #1
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Building my own Solar Panels - Let's see if I can do it!

Goal: Build my own solar panels to install on my RV roof


Today my solar cells arrived!
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They measure 4 X 5 inches apiece
Power per cell = 4.5 Watts
Total quantity is 100 pieces.

Subscribe to follow along as I build my first one!
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Old 03-22-2020, 08:19 PM   #2
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Out of curiosity, how much did they cost you? There's going to be a lot of other materials here, and I got my Axitec panels for a little over 60 cents a watt, about $220 for 340 watts at 45 volts.

I think it would be cool to have the random shape of the top of the RV covered, but in my case at least, I don't seem to have the total capacity of capture for that much. Cool project though!
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Old 03-22-2020, 11:25 PM   #3
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Out of curiosity, how much did they cost you?
About a dollar a cell.
If I wanted used or broken cells, they would have been alot cheaper.


I'm still deciding how big to make the first panel.
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Old 03-22-2020, 11:29 PM   #4
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Originally Posted by geordi View Post

I think it would be cool to have the random shape of the top of the RV covered, but in my case at least, I don't seem to have the total capacity of capture for that much. Cool project though!
Just want to make sure I am not misunderstanding! Are you saying it would be cool to build 1 huge solar panel that covers most of the RV?
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Old 03-23-2020, 09:19 AM   #5
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Just want to make sure I am not misunderstanding! Are you saying it would be cool to build 1 huge solar panel that covers most of the RV?
That's the general idea, but I don't know that I'd have every cell connected to every other - just b/c of the issues with shading. But if there was a way to group them in strings that ended up with an intelligent wiring scheme... Maybe?

But here's the thing: You have to have enough battery for the power to have somewhere to go. Even with full sun, if I'm not pulling the batteries down, my 4+ kWh of possible daily collection might only be 200 watts if there's no place for the power to go.
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Old 03-23-2020, 09:36 AM   #6
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Originally Posted by geordi View Post
That's the general idea, but I don't know that I'd have every cell connected to every other - just b/c of the issues with shading. But if there was a way to group them in strings that ended up with an intelligent wiring scheme... Maybe?



But here's the thing: You have to have enough battery for the power to have somewhere to go. Even with full sun, if I'm not pulling the batteries down, my 4+ kWh of possible daily collection might only be 200 watts if there's no place for the power to go.
Hmmm, I have never considered making 1 or 2 extremely large panels. I was planning on making 300-400 watt panels.

What are the advantages of making super large panels? Compared with the disadvantages would it outweigh the advantages? You mentioned mitigating it with the way the cells are wired into an intelligent wiring scheme. Do you have an example off the top of your head?

My goal is to have a large lithium battery bank as well. My lifestyle once I hit the road will require lots of power, given that I will at a minimum be running the AC 24/7.
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Old 03-23-2020, 05:07 PM   #7
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Are these raw wafers? The challenges before you are mechanical, thermal, electrical and environmental.

Consider the frame of a commercial solar panel product. It's rigid to minimize flexing. The glazing passes the most amount of useful light and protects the wafers from impact. They're waterprooof. They both conduct and dissipate heat. The electrical configuration - series/parallel and number of cells will be secondary to installing them in such a way they work and stay that way for very long.

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Old 03-23-2020, 05:19 PM   #8
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Are these raw wafers? The challenges before you are mechanical, thermal, electrical and environmental.

Consider the frame of a commercial solar panel product. It's rigid to minimize flexing. The glazing passes the most amount of useful light and protects the wafers from impact. They're waterprooof. They both conduct and dissipate heat. The electrical configuration - series/parallel and number of cells will be secondary to installing them in such a way they work and stay that way for very long.

Mark B.
Albuquerque, NM
I am up for the challenge! If I fail, then I'll be a good example of what NOT to do.
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Old 03-23-2020, 08:05 PM   #9
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In addition to the suggestions about protecting the cells mentioned above, the wiring becomes a consideration based on your end controller and how much battery storage you will have.

Wanting the AC running 24/7 is admirable... BUT you likely won't be able to store even CLOSE to that much power even if you had the solar to generate it per day!

This is the math, and I think you will find the math on the cost will quickly outstrip a generator or full hookup somewhere:

The BEST most efficient AC system I've seen is a mini-split system. These aren't designed for RVs, so right away you will be rolling your own. They are inverter systems so the compressors can soft-start and use a lot less power than standard systems. But they still are using almost as much power as a microwave oven - around 800 watts. Impressively, this is about HALF of the power that just ONE standard RV roof AC unit uses. So factoring on the best-case scenario (and really - that is only about a 10k BTU unit, in true summer it will NOT be enough to keep an interior cool, especially when you have to be in the sun for the solar to work!).....

800 watts per hour at 120 volts is 19,200 watts per day - 19 kWh!
At 120 volts, that is drawing a continuous 6 amps, or roughly around 73 amps (with losses) out of a 12V battery system. Continuously. To power this off of an inverter like a Magnasyne 2812, you would need significant battery capacity. My array is 8 GC2 flooded batteries, for a total of 880 amp-hours of capacity, of which 440 is usable if I want to keep them above 50% state of charge for their protection. Lithium doesn't have that limitation, but at a MINIMUM you would need 1800 amp-hours of 12V batteries for just ONE DAY of running that perfect-scenario AC.

Costco just ended a sale on 12v lithium batteries, I don't know what the regular price is, but the sale was $700 for a 100-amp battery. Here's where the road ends. For JUST ONE DAY of all-battery-power on lithium - with NO CONSIDERATION of space or weight or wires or anything else, JUST buying the batteries... $126,000.

This is under PERFECT conditions, and not even thinking about the cost of charging those batteries back up. Also this is ONLY running the AC, and sucking the batteries to near-zero daily, which isn't good for them either. They would need to be replaced after somewhere between 500 and 1000 cycles.... Which means that 126k is being spent every year or so.

Now let's look at the power replacement. To charge the batteries back up AND provide enough power to simultaneously run the AC, you would need double the power - or more.

Calculating power from solar is "how much can I get before the sun isn't positioned right anymore" and relies on some fudging. You aren't going to get 10 hours of useful solar even though the sun is up 12 hours each day. You SHOULD get about 7 hours but saying that you only get 5 is more reasonable for sizing the system to your expectations.

So 5 hours of sunlight. To replace 19,000 watts of power, AND supply 5 hours of 800 watts at the same time. That's a grand total of 23,000 watts under perfect conditions to capture in 5 hours each day. Its possible.... BUT you will need at least a 4600 watt array, and (because of losses) probably more like about 5kw. That will mean a possible daily capture of around 25,000 watts, which SHOULD be sufficient for replacing what you would be using from those batteries.

eyes watering yet? Now we have to talk about the solar array sizing.....

Considering that a 340 watt panel is roughly 40x80 inches or 3200 square inches or 22 square feet - you would need 15 panels of that size to capture the 5kw of sunlight. Assuming NO OTHER roof furniture of any kind and zero spacing, that's 3 more panels than could (in theory) fit on the FULL LENGTH of my 40' RV. Two panels sit almost the full width side to side on my roof, and one is front-to-back. The ENTIRE roof could only hold 12 of them if there was nothing else up there - and you'd need another 10 feet of length.
My RV needs BOTH roof AC units in the heat of a Georgia summer, and one of those is a 15k BTU unit - nearly 50% again the size of the example I listed above, and since mine are made by Carrier (no longer manufactured) they are also more power efficient than a Coleman unit, but the big one STILL needs 11 amps running all the time at 120V. To use two AC units... EVERYTHING ELSE DOUBLES. Including the cost of all those batteries.

It is a great dream but it's just not possible.
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Old 03-24-2020, 07:42 AM   #10
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Geordi
how about the fact that the ac unit would not run for 24 hours, some would probably only run actually about 6 hours a day in mild temps? How would that figure in your calculations.
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Old 03-24-2020, 07:47 AM   #11
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Thank you so much for the input!!! I really do appreciate it.

Quote:
Originally Posted by geordi View Post
Wanting the AC running 24/7 is admirable... BUT you likely won't be able to store even CLOSE to that much power even if you had the solar to generate...
I've been researching this for the past 6 months and believe running the A/C 24/7 off of solar is possible.

My experementation will answer this challenge in the end. I'm open that this could be a massive fail, however I am keeping optimistic with the modifications from my research.

My success or failure documented on this forum will be a good example for others!

I'm more than willing to be the forum's guinea pig.



Quote:
Originally Posted by geordi View Post
The BEST most efficient AC system I've seen is a mini-split system. These aren't designed for RVs, so right away you will be rolling your own. They are inverter systems so the compressors can soft-start and use a lot less power than standard systems. But they still are using almost as much power as a microwave oven - around 800 watts. Impressively, this is about HALF of the power that just ONE standard RV roof AC unit uses. So factoring on the best-case scenario (and really - that is only about a 10k BTU unit, in true summer it will NOT be enough to keep an interior cool, especially when you have to be in the sun for the solar to work!).....
Yes, I will be removing both inefficient rooftop A/Cs and will be installing a multi-zone minisplit that is around 25-30 SEER. That will increase the cooling efficiency as you have explained and it will also free up alot of room on the roof.

I plan on having one unit in the bedroom and one unit in the mid-section. I'm not 100% certain at this point if I can have different BTU outputs per unit with the multi-zone. If so, I would like around 5000 BTU in the bedroom and either a 9000 or 12000 BTU in the mid-coach section. I'm looking at a few diffent models of mini-splits with the high SEER ratings so the exact choice is not determined just yet.

Keep in mind that as part of my current coach gutting/remodel, I am re-insulating the ENTIRE coach to a significantly better R-value than the existing pathetic factory standard installed, to also include improving all windows.
This will definitely impact the amount of power required to cool the interior.

Also keep in mind the research shows that once a minisplit has reached the desired interior temperature, with eco-mode it will not run continuously with the factory specified watts output. It will in fact be lower. It will use much less power to maintain the existing temperature. So the actual watts per hour used is much less. Combine that with my vastly improved insulation, it is fair to predict my power used will be significantly less. We will find out for certain when I document it this year.

David aka Goneboondocking demonstrated this with a full year of using his mini-split in his Class C.

Part 1: https://youtu.be/wbXXRoN7Tyw

Part 2 update: https://youtu.be/rjVIxqTHahY


Quote:
Now let's look at the power replacement.
My plan is to build a lithium powerwall in the coach. More details will be forthcoming, but as of now, I'll be putting together lithium battery cells myself so the costs will be down for the power storage. The estimate as of now with the materials I have calculates to about $150 per 24 Volts/50 Amp Hours put together. Ill post more details on it once I focus on that project.

Quote:
eyes watering yet? Now we have to talk about the solar array sizing.....

Considering that a 340 watt panel is roughly 40x80 inches or 3200 square inches or 22 square feet - you would need 15 panels of that size to capture the 5kw of sunlight. Assuming NO OTHER roof furniture of any kind and zero spacing, that's 3 more panels than could (in theory) fit on the FULL LENGTH of my 40' RV. Two panels sit almost the full width side to side on my roof, and one is front-to-back. The ENTIRE roof could only hold 12 of them if there was nothing else up there - and you'd need another 10 feet of length.
Panel placement. As you know, this is one of the focuses of this particular thread besides the details of putting together the panels.

I'm not terribly worried about roof space for the panels. I have almost 40 feet available minus necessary vents and the 2 fantastic fans. As said earlier, I'm removing both A/Cs which free up a large amount of space. I'm also removing the rooftop antenna since I do not watch television.
The only item I'm debating about keeping is the bathroom skylight. I'm not sure if I want it or not. If I remove it, that will give me more space as well.

I am open to the idea of placing additional panels on the ground if needed.


Quote:
It is a great dream but it's just not possible.
I am a dreamer for sure. But do not tell me it can't be done because it motivates me to make it happen, lol.

This could all fall flat on its face come the summer when we see how it does. Whatever the results, it will be a good experement.

I'm always open to suggestions and criticism. They will help to improve the project.

Please continue to share your thoughts, I do look forward to them.

Cari Beth
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Old 03-24-2020, 09:00 AM   #12
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I salute you sir.
To Geordi. You are no doubt correct. I didn't check your figures but they sound about right.

However as I remember from history, the Wright Bros were told it wouldn't work.Richard Pearce was told the same. No doubt many others have been told the same.
So live the dream my friend. Keep us informed as it sounds like a great project.
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Old 03-24-2020, 09:13 AM   #13
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I'm not terribly worried about roof space for the panels. I have almost 40 feet available minus necessary vents and the 2 fantastic fans. As said earlier, I'm removing both A/Cs which free up a large amount of space. I'm also removing the rooftop antenna since I do not watch television.
The only item I'm debating about keeping is the bathroom skylight. I'm not sure if I want it or not. If I remove it, that will give me more space as well.

I am open to the idea of placing additional panels on the ground if needed.


Cari Beth
I just left my bath skylight in place and went over it.

It actually made it better. You are not in the bath to look at the stars and the solar heat gain was so bad I had to keep an insulated cover on the inside during the day anyway.

With the panel just above, I have nice natural light from around the edges and no more heat gain
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Old 03-24-2020, 09:15 AM   #14
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I know the AC systems won't be at full burn all the time, but the total power usage will definitely depend on the size of the system and the insulation. So those are somewhat unknowable at this point. Starting from the point of use though is good for planning your needs - b/c there's always the fridge and microwave, the water heater, water pump, computer, and anything else you have that has a plug to add to the power needs.

If you know which AC unit you are interested in purchasing, the specs for that (and any other electrical device) will say how many amps or watts they use, which will give you the other number. Watts equals volts times amps. Volts and amps can vary opposite each other, Watts never change. If you calculate the AC based on the rating sticker and a duty cycle of around 60% (maybe more in really hot summer) that should give you an idea of what it will need.

Building your own lithium array - I'm intrigued. Personally I would go for a 12v system, that will result in less conversions for the power used since RV things are already designed for 12v power.

With insulating - GOOD. RVs are usually terribly insulated, and far from airtight to begin with. Double pane glass will help a LOT - go with the framed windows rather than frameless, they seal better.

Since you are building a lot of this now, build it from the usage devices first - then you can measure the actual power used and know what you need to build for power generation. On mounting the panels / elements - I mounted mine above the roof, they are separated from the coach so that I'm not heating up my roof with the sunlight that I'm capturing.
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