School bus solar system

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 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