Solar panels question!!!

[The Rockwood Colony]

HELLO!

Somebody I know bought a pallet of solar panels. He has 7 left over and I have the opportunity to buy them all for $1400 and I think I could talk him down a bit but I'm not sure how much power we need and have no clue if they are what anyone else would have selected for their own bus. They are 40"x65"x1.5". The brand names are Yingli and Vikram. They each put out 250 watts, 24 volts, and 8.9 amps.

We have a 40 ft. school bus and want enough power to never need shore power... ever. Even with A/C running for all daylight hours. Is 1,750 watts enough? Any good links to resources that could explain this better? When I searched on here for solar panels it just came up with random stuff so I am sorry if there are other threads that will answer all of my questions. If so please let me know how to find them. Thanks!!!!

[lucasd]

1,750 watts could be plenty for everything but the AC. AC is expensive in terms of wattage, but some people pull it off.

If you're having trouble finding topical threads on this or any other subject, just do a Google search using the "site:skoolie.net" parameter. That will pull only threads from this forum and may help you find what you want better than the built in search function.

[MarkyDee]

You have the right energy input, so just make sure you have the correct storage, i.e. batteries. If you are wanting to run A/C, you'll probably have to go with Lithium Iron Phosphate batteries to get the energy density you need. Otherwise your rear-end will be dragging because of "all the lead in the back" (i.e. you'll be too heavy with lead-acid batteries)....


Yea, my wife hates my jokes, too.

[The Rockwood Colony]

Ok, thanks guys! Has anyone ever heard of these brands? Would $1200 for all of them be a good deal? Or is there other brands you'd reccommend that i could get the same amount of watts or more for a better deal with better quality? Sorry, it's just that there is like 700 brands. Brain tornado.

[lucasd]

Anything under a dollar per rated watt of output tends to look pretty good in terms of cost, unless you find a special local deal or mail order in large quantities.

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[pengyou]

Do they come with inverters and controllers? Sometimes it's cheaper to buy the set together, panels, controllers and bms. Also, that way you know everything matches. I'm guessing the person who is selling these either added his to an existing installation or bought a whole set and these were extras - he keeps the controller etc.

You also need to check the warranty.

The cheapest way to go for batteries might be to get a reconditioned hybrid pack and have the pack rewired for lower voltages.

[john61ct]

You can run all the A/C you like off a bus roof full of solar.

Long as its during peak solar conditions, maybe 4-5 hours a day at best.

A huge battery bank may add 2-3 more hours.

Altogether probably $6+k, likely more doing it right.

Or get a portable generator.

[rossfree]

Descent price. Less than a dollar per watt. I have 500 watts of solar. Two panels. Four golf cart batteries, charge controller, inverter, battery monitor and more.

I can run a small 5000 btu Wally World AC while the sun shines and generally use only a small amount of additional power from the batteries if they're fully charged for three or four hours. But it won't touch the BTU's required to cool my short six window bus. Further, it will slowly drain my batteries to my imposed limit of 80% charge more or less.

While the sun shines on 1700 watts of panels you can probably expect to power a good 1200 watts of equipment but the batteries will be required to even the power out as the clouds float by. If you want your battery bank to last longer than one or two years you need to limit the discharge to 75 - 80% of full charge. Discharging the batteries further takes a hard hit on longevity.

There's a lot to understand around solar but I love it! If you include some frugality and get a good understanding of the strengths and limitations you can really use it to its hidden potential. Lots of bad information out there. Read read read. And then read some more.

You can cover your bus with solar but I don't believe you will ever be able to run full time AC to any comfortable level without boarding up all your windows and insulating the crap out of it.

Still... I can draw a curtain across the bus and cool the sleeping area for a few hours for a midday snooze. . And that's frugal!

Best of luck!

Ross

[lucasd]

Originally Posted by rossfree

You can cover your bus with solar but I don't believe you will ever be able to run full time AC to any comfortable level without boarding up all your windows and insulating the crap out of it.

Of course, by covering the roof with solar panels and leaving that gap between the underside of the panels and the top of the roof, you do block some of the heat that would have transferred into the bus. I'm debating a way to take that a step further with a shade cloth deployment system.

Some old-school military camo netting stretched out into high flying canopies on either side of a bus could keep a lot of direct heat/sun from being absorbed. Using netting instead of canvas would make it a lot lighter, and it would keep the shade cloth from being so much of a wind hazard. It wouldn't keep any rain off, of course, but that wouldn't really be the point. Just stopping the side of the bus from being a big heat sink could help a lot.

Ok, maybe not actual camo colored netting... that might attract random paramilitary groups or cause salvation army stores to mysteriously appear in the vicinity. Maybe use the white kind.

[john61ct]

Originally Posted by rossfree

Further, it will slowly drain my batteries to my imposed limit of 80% charge more or less.
...
If you want your battery bank to last longer than one or two years you need to limit the discharge to 75 - 80% of full charge. Discharging the batteries further takes a hard hit on longevity.

Not relevant to your overall point, but a good quality deep cycling bank is designed to go down to 50%.

It is always true that it will last many more cycles of lifetime if you cycle it more shallow, but then you are paying double and carrying a lot more weight.

[Twigg]

Passive cooling and insulation are the best way to address AC, and keep the requirements reasonable.

Painting the roof a brilliant white, adding 3" of insulation and parking under the shade cloth you suggest would keep the interior temperature way down. You might then be decently comfortable without AC, or maybe a small window unit in say, the rear bedroom, would give you a retreat when you needed it.

[Iceni John]

I have eight grid-tie panels totaling just over 2kW, and I plan on using a 12K mini-split A/C from them. With enough power, anything's possible!

John

[Twigg]

Originally Posted by Iceni John

I have eight grid-tie panels totaling just over 2kW, and I plan on using a 12K mini-split A/C from them. With enough power, anything's possible!

John

Don't put the shade cloth over the panels

Sounds like you have a good system.

[john61ct]

Originally Posted by Iceni John

I have eight grid-tie panels totaling just over 2kW, and I plan on using a 12K mini-split A/C from them.

Yep that's getting there. Mounted on the roof, or portable?

Do you plan on running off batteries, or only while you're parked out in the hot sun?

How big a bank?

Let us know how it actually works in practice

[rossfree]

Originally Posted by john61ct

Not relevant to your overall point, but a good quality deep cycling bank is designed to go down to 50%.

You can John, but should you? Let's agree to disagree.

Ross

[Iceni John]

Originally Posted by john61ct

Yep that's getting there. Mounted on the roof, or portable?

Do you plan on running off batteries, or only while you're parked out in the hot sun?

How big a bank?

Let us know how it actually works in practice

All the panels are individually tiltable for maximum solar harvest, and are hinged to a central walkway that runs between my two roof hatches. I will have two separate 12V battery banks totaling about 900aH, and most things will run directly from 12VDC. For everything else I have a Magnum 2000W sine-wave inverter/charger, and I'll probably buy a smaller second inverter just for the fridger. I plan on having three days' sufficiency if the sun doesn't shine, and only then I would use the generator to Bulk charge the batteries back up to about 80%.

John

[john61ct]

Originally Posted by rossfree

You can John, but should you?

Well if you're buying your bank as 12V batteries from big box retail, you might well make them last a little longer that way. That alone shows you haven't done your research.

That's really throwing money away and carrying a lot of dead lead, compared to a proper bank that can easily last for eight years or more if properly taken care of. Including 50% DoD as is standard in the DC electrical world.

If you actually use 300AH per day, you would really prefer carrying around the weight of a 1500AH bank rather than 600AH? Not to mention 2.5x the up-front cost?

Buying cheap batteries is costing you a lot more money over time.

[rossfree]

I was trying to avoid mud slinging John. Battery companies would like you to believe that discharging them to 50% SOC is fine but in practice your beating the hell out of the your batteries. But do it your way John. Really!



Ross

[Twigg]

Originally Posted by rossfree

I was trying to avoid mud slinging John. Battery companies would like you to believe that discharging them to 50% SOC is fine but in practice your beating the hell out of the your batteries. But do it your way John. Really!



Ross

I like to protect my stuff, so I'd be interested in any literature or testing that showed that it would be more economical in the long term, to restrict the discharge to 20%

[pengyou]

Originally Posted by Twigg

I like to protect my stuff, so I'd be interested in any literature or testing that showed that it would be more economical in the long term, to restrict the discharge to 20%

When you say "down 20%" are you saying deplete until only 20% is left? Just checking.