School bus solar system

kdruva

Hello all! So I have to apologize in advance if this question has already been asked/answered but I have searched and been unable to find an answer! I'm converting a school bus into an RV and we are going to try to make it so we can go days at a time without being plugged in and I just have a couple questions. We're not huge power users, we have a cell phone and laptop each to charge sometimes, a 32 inch LED TV and a Playstation 4 for the conveniences. For everything else, we're thinking smaller 120v fridge, toaster oven to be used very rarely, then just a little water boiler to make coffee/tea in a press rather than an actual coffee machine. Other than that, just a 4 LED lights throughout the bus and the 12v clean water pump for sink/shower water. So my plan is to have Six 6v 220ah batteries wired with three wired in parallel to get to 660ah and then two of those banks to reach a total of 12v at 660ah. I will have 3 160w solar panels (that I recieved with the bus) and then a Morningstar 45amp MPPT Charge controller to charge the batteries. On the inverter side, I'm thinking a Samlex 3,000 watt 12 inverter/charger (high wattage rating so I can expand in the future without buying another inverter) and then have that go to a breaker panel. First off, I just want to ask if that all sounds reasonable for the demands or if I need more Solar and/or a larger battery bank for those needs. Second, the thing that has been throwing me off is with this system, how does the grounding work on the whole system. Do I ground the DC and AC to the vehicle chassis when there is the original vehicle 12v system using the chassis already? Thanks in advance

Aguarancher

First you need to define your loads, what each item will req. in a 24 hr period. What are the full specs on you solar panels. It appears with your current wants and needs you would be better off with a 24v system "input to inverter"..

littleharbor2

Try to find alternative water heating/cooking sources, ie; Propane. There are plenty of propane powered small appliances, search the internet. Bass pro shops, Sportsmans Guide and Harbor freight are good sources. If you're only needing to dry camp part time you might even consider a propane/120 volt AC RV fridge.  You can run it off propane when away and off "shore power" when available. My point being you will need much less charging and battery capacity if you don't use electricity to heat and cool.

kdruva

So if I leave out the fridge and oven, does that seem like the right amount of power and solar capability? Its really not like we watch much tv or game much haha the whole point of this is to get out and live a mpre disconnected life. That being said, maybe a movie night every so often and some gaming sometimes!

Photowhit

Lots of odds and ends. What other forms of charging will you have for the battery bank? The array isn't large enough to provide reasonable charging on sunny days.

12 volt systems are difficult for reasonable wire sizing, a 3000 watt inverter would not be recommended on a 12 volt system, please consider a 24 or 48 volt systems.

I would rather 'float' a system on a vehicle rather than a frame ground. A frame ground can create some dangerous situations.

kdruva

The charging system will still be 480 watts of solar into a Morningstar Charge controller thrn into the battery bank. So then with 6 of those 6v batteries, how would I get to 24v? Or do I need to do 8 batteries? Haha sorry my brain is starting to hurt with all this but I definitely wanna know exactly my setup before I purchase anything. And thanks for the float thought that is good to know!

westbranch

yes 8 needed for  2 parallel strings of 24V...  wait , you are just starting to get into the thick of planning...

kdruva

Haha oh I know! Very much planning involved! But I love it, just have to figure out a couple things. What is the huge benefit to 24v? Seems like I would have add so much extra equipment to run 12v stuff with a different setup like the water pump and lighting and stuff.

mike95490

How much driving will you do in the bus, 30 min driving, the alternator can stuff a full days worth of solar into the batteries

If you need more than 1,000 w of AC, then you need to think about a 24V system, not 12V     Running a 3Kw inverter to power a light or 3 is very wasteful.   You may want to put larger loads on a large inverter that is only turned on when needed.  Small loads on the small inverter - much less standby losses.

kdruva

So how about something like this, 480 watts solar > MPPT charge controller > 8 6v 225ah batteries for 24v@900ah. Then either a 2,200 watt Samlex 24v Inverter/charger or 4000w. The main reason for the large inverter would be so that at some point, I can add in a roof AC unit down the road without having to purchase a new inverter. Then I would use an insulated terminal bus bar to create a floating ground instead of chassis. For my 12v stuff, just a Samlex 23amp 24v to 12v converter. I'll probably honestly expand the solar panels to be closer to 1000w. Its a full size bus so I have the roof real estate to do it. I just want to avoid buying too low of gear for when I want to expand for some more power if I need to.

kdruva

Also, one other thing is the 3 solar panels that I already have are 12v. Are those going to be able to be used to charge a 24v system? Not sure if the Morningstar MPPT is able to convert that or not?

mcgivor

Use a smaller inverter, building for AC in the future is a mistake, my opinion, AC would require a larger inverter yes, but would also require a large array to support it, ponder this for a while, do some calculations, consider the space available, the battery requiments and so forth and if it is feasable, build a system for it with its own inverter, that can be turned off when not required, thereby not taxing the battery on idle, the smaller unit will take a lot less less to run continously.   

littleharbor2

Those 8 batteries will give you 450 Ah @ 24 volts.
Air conditioning is definitely out of the question. There isn't enough real estate on your roof, no matter how big your bus is.

kdruva

Hmm alright haha lots to think of here. And ohh yeah ok I get the Ah number there now my bad. So maybe I will just stick to a 12v setup. Use a 2000watt inverter/charger because that allows for at least some expansion. If I leave AC for just when I'm plugged in, then I really just need it for TV, Playstation, phone and laptop chargers, and the occasional 2 cup hot water boiler. I should be good with six 6v batteries to get to 660ah and then call it a day...

westbranch

Please read this, anything more than 2 strings/batteries is a recipe for poor charging of on or more of the 3...
http://www.smartgauge.co.uk/batt_con.html

mike95490

kdruva said:

Hmm alright haha lots to think of here. And ohh yeah ok I get the Ah number there now my bad. So maybe I will just stick to a 12v setup. Use a 2000watt inverter/charger because that allows for at least some expansion. If I leave AC for just when I'm plugged in, then I really just need it for TV, Playstation, phone and laptop chargers, and the occasional 2 cup hot water boiler. I should be good with six 6v batteries to get to 660ah and then call it a day...

Get a nice efficient 12V 300-500W inverter to run the day-day stuff.  Wire your water boiler to a cheap 1500W mod sine inverter that you only turn on for the 4 minutes to boil water. 
If you have lots of power (you don't with the roof area you have)  you can afford to idle a large inverter, but it will suck your batteries down while it idles.

Estragon

+1 on Mike's two inverter thought. Something like a Morningstar 300w pure sine wave inverter will play nice with electronics. Big PSW inverters are expensive and such a fair bit of power just being on. Using a cheap square wave inverter should be fine for a resistive load like your water boiler, but may not play well with other stuff.

kdruva

Appreciate the help guys!

Iceni John

You don't say how big your bus is.   My somewhat glib suggestion when folk ask how much solar to put on their RV or bus is simple  -  as much as will fit!   The reasons are many:

1.   When have you ever heard about anyone with an RV or bus conversion complaining they have too much of anything?   Too much water, too big poo or grey tanks, too much space or storage, too much electrical capacity?   No, I thought not.

2.   PV is still cheap.   Grid-tie panels are well under a dollar a watt, so why not buy more for that price?   At some point PV prices will rise again.

3.   Panels on an RV or bus will probably not be as well aligned towards the sun most of the time as panels on a house or purpose-built array, so you'll need more panels than otherwise to generate the same amount of usable power.   Plus, you may be parked under trees or in the shade, so you'll need more panels to compensate for that.

4.   Everybody's electrical needs increase with time.   What you think is an adequate amount of power now may be inadequate in a few years as you get more things that use power.   After all, who would have foreseen thirty years ago the current addiction to cell phones and all their needed chargers, or the prevalence of power-hungry electronica throughout our lives?

5.   You've probably got enough space on your roof for at least a thousand watts of panels, and maybe more than that.   Why not just carpet the whole darn roof with panels in that case?   Too much is never enough!   Besides, you want to try to charge your batteries at the upper end of the recommended 5 to 13% charge rate, so having more panels rather than fewer will help you do that.

6.   PV panels shade a bus roof very effectively in hot weather to noticeably lower interior temperatures by reducing heatload on the roof itself.   With panels as cheap as they are now, it wouldn't cost you much less to just make a simple double roof like old Land Rovers had, or like MCI made for their MC5 buses that were used in Saudi Arabia  -  for not much more money you can have a tropical roof that also produces power.

That's my entirely unscientific way of deciding how much power to have!   I've got 2,040 watts of panels on my bus's roof, and they occupy only 22 feet of roof space, leaving plenty more room for two eventual solar water-heating panels.

John

oil pan 4

If the panels lay flat only expect to get around 50% of name plate capacity on an mppt charge controller in winter.

Iceni John

oil pan 4 said:

If the panels lay flat only expect to get around 50% of name plate capacity on an mppt charge controller in winter.

And this is why it's so important to have tiltable panels on an RV or bus roof.   Some folk have made 2-axis tilts, but that's not easy on a vehicle roof.   My panels can lay 21 degrees down against the roof (but still with a few inches of air gap under them), or level, or 21 degrees up (good for Southern California summers), or 33 degrees up, or 45 degrees up (good for winter as far north as I'll ever be).   I still want to get usable harvest even during winter, and in the summer I may actually have more PV than I'll need.   We'll see.

John

oil pan 4

Get more then you know you will need and I bet it will be just enough