One more thing, need to add the power requirements that your inverter will use. I just purchased an inverter that uses appx 1900 watts per 24 hour period. Yes, it is a 220 volt larger model than you will be using but you do have to factor the power requirements for the inverter at an idle with no draw x a 24 hour period and add that to your power requirements.
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- Thread starter The_Kobayashi_Vroom
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The_Kobayashi_Vroom
New Member
MisterSandals
Participation Medalist
True, you may be purchasing a larger inverter that a 6000 watt 220 volt setup that I have, very possible. I was just making a statement that all power requirements need to be accounted for, even the power the inverter uses. All inverters change one energy to another. In this case, it is changing DC current from DC battery storage to AC current to be used by AC appliances.How do I know that yours will be larger than mine if I don't know what mine will be yet? I never would have thought of adding the inverter. Thank you. I am assuming (based on what you all taught me last night) that it is DC since it is wired and not plugged in?
The_Kobayashi_Vroom
New Member
Ok! I have added an inverter, and then added back in the things I would really want and not necessarily need. I also put the window AC on there. What do I learn from these updated numbers? @FilterGuy @Rednecktek @rmaddy
Thank you all so much!
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Rednecktek
Solar Wizard
Well, it looks like you're going to need a 8Kw inverter if you decide you want to run it all at once (worst case scenario) but could easily get away with a 6Kw. Most good 6Kw inverters call for a 48v battery because at 12v the fuse becomes a flamethrower.
It also tells you that you're going to need 243 amp hours of battery to run that load for an hour, 485 for 2 hours and so on. Due to mass you're going to have to run Lithium to not burst your shocks carrying that much battery around, and you're going to have to be creative on where you sleep because that's a LOT of volume. Worst case scenario. You'll need to change the "Nominal Voltage" entry to 48v and see what it does to the numbers.
In the grand scheme of things your DC stuff is about 50Ah @ 48v and using a buck transformer to kick that down to the normal 12v.
The solar power required to feed that is insane, 6Kw worth of panels and 3 days no load to recharge the batteries.
So, that gives you worst case scenario. Now you start looking at your budget and whittling down what you can save where, and try to plan out as close to your "Worst Case" as your budget, space, and patience allow. This is where the math magic comes in because you're not going to run the hair dryer for 24 hours, and the water heater shouldn't need 24 hours to heat up the tank and so on. The biggest offender is of course the AirCon and you might want to think about a small dual-fuel generator to run that on while you're parked or something to take the load off the system.
12VoltInstalls
life passes by too quickly to not live in freedom
The thing about the hair dryer: little things a) make life good and b) it’s gonna get used for what? 3-4 minutes a day? So it will be high demand for a low amount of time. Factor for it, sure, but it’s not a crises like an air fryer or an AC- and some AC like minisplits ain’t a crises either.
The_Kobayashi_Vroom
New Member
Oh I was def going to go lithium. Also, our bus is pretty big.
I think that is really good advice. Right now we have about $4,000 saved for the system we will end up building and of course, we don't need to live in it until 2025, when our youngest graduates from high school!
It does appear that it changed quite a few numbers - but I don't know if it was an improvement or not. ?
The_Kobayashi_Vroom
New Member
No none of them are important,... I had removed all of them but then was suggested to make a worst case scenario so I added them back in. We are also VERY well insulated so hopefully that really does help with summer heat. Also, the hairdryer doesn't make sense to anyone who doesn't have curly hair - it's more like 20 minutes every 3 days to diffuse it - but again, it's not a necessity other than when I want to try to look fancy. ?
Rednecktek
Solar Wizard
The biggest change was going from 600 amps feeding the inverter to 150 amps which is a MUCH smaller and safer wire to work with. You also went from 2430Ah to 600Ah which is going to be easier to pack into the bus. Yes, it's the same watt-hours, but if you can source 48v Lith packs rather than having to worry about if your 4 12v lith packs will play in series and parallel with each other makes life MUCH easier to plan for. One of the oddities of Lith packs is different brands will or will not connect up in series, will or will not connect up in parallel, will or will not connect up in series-parallel, and getting them to all play well with each other is a pain in the ass.
And believe me, I understand how the niceties of life can make a BIG difference. When I first power audited my camp I spent a lot of time figuring out the maximum size AirCon my little generator would feed, and you better believe I made room for the little ice maker and coffee pot! Life Savers!!!
The biggest reason to have you do the Worst Case is to find the size of the inverter you'll need. Knowing that worst case you'll want a 6Kw or 8Kw inverter saves you a lot of time and money if you can skip the 2Kw-not big enough-4Kw - still need more - 6Kw and bigger rewire steps and just shoot for the top now. The cost savings from the smaller inverters you didn't have to buy will add up FAST! It also helps plan out the battery layout for starters and for future growth. If you just get 1 big 48v battery now it'll get you going, but if you know you'll eventually want 4 or 6 of them then you can plan the space/racking/bolting that those 4 or 6 will eventually need and only weld the racking together once. AKA Future-Proofing.
The rackmount Gyll's (or whatever the new name is) are pretty much going to be the sweet spot for durability, reliability, and a plannable form factor. The price should only come down over the next few years and AFAIK they parallel up nicely to each other.
The_Kobayashi_Vroom
New Member
How do I know how many solar panels I need? Do I look at the full load watts on that table? I have no idea how you get to 6000w on top of a school bus. Maybe that's not what I need and I'm mistaken? If I do a 48W system, does that mean I have to have 48 W solar panels? It sounds like it'd be an obvious answer, but still want to ask that!The biggest change was going from 600 amps feeding the inverter to 150 amps which is a MUCH smaller and safer wire to work with. You also went from 2430Ah to 600Ah which is going to be easier to pack into the bus. Yes, it's the same watt-hours, but if you can source 48v Lith packs rather than having to worry about if your 4 12v lith packs will play in series and parallel with each other makes life MUCH easier to plan for. One of the oddities of Lith packs is different brands will or will not connect up in series, will or will not connect up in parallel, will or will not connect up in series-parallel, and getting them to all play well with each other is a pain in the ass.
And believe me, I understand how the niceties of life can make a BIG difference. When I first power audited my camp I spent a lot of time figuring out the maximum size AirCon my little generator would feed, and you better believe I made room for the little ice maker and coffee pot! Life Savers!!!
The biggest reason to have you do the Worst Case is to find the size of the inverter you'll need. Knowing that worst case you'll want a 6Kw or 8Kw inverter saves you a lot of time and money if you can skip the 2Kw-not big enough-4Kw - still need more - 6Kw and bigger rewire steps and just shoot for the top now. The cost savings from the smaller inverters you didn't have to buy will add up FAST! It also helps plan out the battery layout for starters and for future growth. If you just get 1 big 48v battery now it'll get you going, but if you know you'll eventually want 4 or 6 of them then you can plan the space/racking/bolting that those 4 or 6 will eventually need and only weld the racking together once. AKA Future-Proofing.
The rackmount Gyll's (or whatever the new name is) are pretty much going to be the sweet spot for durability, reliability, and a plannable form factor. The price should only come down over the next few years and AFAIK they parallel up nicely to each other.
Just FYI, in 2 inverters, 9 solar panels, 2 controllers, 12 batteries, fuses, wire and other essential connection pieces, I have in the neighborhood of 15,000+ in my systems. That is 14,400 watt hours in batteries, 9000 watts of DC inverters and 2745 watts in solar panels, feeding 60 amps of AC power. This was with purchasing used solar panels.
The_Kobayashi_Vroom
New Member
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
The solar panels need to be large enough to replace the Whrs used by the system. So if you use an average of 13000Wh/day, the panels need to produce an average of 13000Wh/day.
If every day was sunny and you get the full wattage every day, then you only need to divide the daily usage by the insolation number for your area.
(The Insolation number is the number of effective full hours of sun). Lets assume your insolation number is 5. The panels would need to be 13000/5 = 2600W.
However, the sound does not shine every day. Consequently, there has to be enough extra wattage to make up for lost generation on cloudy dayw.
So, if you get no power for a day and you want to make up for that in one day, then the panels have to be large enough to replace the daily usage *and* replace the energy from the previous cloudy day. (2600 x 2 = 5200W). However, if you are willing to accept it will take 2 days to make up for the lost day, then the panels only have to make up for 1/2 of the lost energy of the previous day. (2600 + 2600/2 = 3900W)
The spreadsheet assumes the batteries start from empty and must be recharged in the "Number of days to recharge while under load", So, the size of the batteries comes into play. If the batteries are 20KWh, it will take more to charge them to full than if the are 10KWH
NOTE: The spreadsheet assumes there will be zero production on cloudy days. This is perhaps overly conservative because there will be some amount of production.
Once the Wattage of the array is figured out, calculating the number of panels starts with a simple division. If you have 300W panels and need 6000W then 6000W/300W/Panel = 20. However, panels almost never produce at their rated wattage. Consequently, to be sure to hit the needed production, it should be assumed about 20% more panels are needed... so in this example, it would be 4 extra panels for a total of 24.
Note: As you saw with the fan, the actual usage of almost all devices is less than the actual usage. Sometimes by a lot. Consequently, the spreadsheet you have developed is probably indicating more usage than will actually happen. The way the spreadsheet works is that this gets amplified while calculating battery sizes and then amplified again when calculating the solar wattage needed. Unfortunately, I don't know of a good way to compensate for this other than actually measuring the usage of each device.
This does not mean the spreadsheet is useless. It gives you worst-case sizing and that is a very valuable thing to know. It also helps you understand where the big energy users are and that helps you make decisions around what you will use or not.
You might not be able to without getting into complex slide-out racks or hand-deployed ground panels. Unless you have an alternate source of power, this becomes the limiting factor of the system. Now comes the difficult task of scaling back the rest of the system accordingly.... but at least you go into the project with proper expectations.
Note: You mentioned that eventually the bus will be parked and not traveling. That makes the idea of ground-mount panels more practical.
One idea is to make a patio area just outside the bus with panels overhead providing shade.
The_Kobayashi_Vroom
New Member
Yes - that is the whole idea we have.... just makes sense to travel if we have the means to do it - and then also have a better idea for sure where we want to buy land. We are definitely thinking east.... like Vermont... but I probably should visit there first
I have definitely said we could have ground panels (of course I have said it with basically zero knowledge) but having them provide shade is such a great idea. When I made a copy of the spreadsheet - and took the non-necessities off - and kept it as a 48v system, it reduced the W-Hrs down to just under 7k as opposed to 13k. It's amazing to think that those things almost double the needs of the bus (of course in a worst-case scenario)
I did the math on those numbers and it comes out to 12 - 300 watt panels (including the 1.5 days to make up for and the 20% more). I still don't know if I can fit 12 panels on top of the bus. Maybe 10? If I went up to 400 watt (I googled and it seems that is a thing), then I would need 8..... So maybe if that is possible I go for more conservative - and 8 - 400w panels and then plan on ground panels when we land in a spot permanently.
BTW I am a STEM Educator at a children's museum and I promise to take all you all have taught me and after I have this down - make a science program for little kids so they can at least start off ahead of where I have at age 39 LOL.
MisterSandals
Participation Medalist
How long and wide is the bus? What fixtures/vents/etc are on the roof?
You can get the dimensions of a couple different panels and play Tetris on top to get an idea of what size works best.
Making a couple cardboard life size panel pieces will help as will painters tape.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
That is fantastic!!! I love it when people pay it forward!!!
The_Kobayashi_Vroom
New Member
I believe it is a 35 ft. - flat nose and maybe 8 feet wide. I don't have it here in front of me. Right now it is just the 2 emergency hatches. My husband wants to put two skylights in though, 1 over our bed, and 1 in the shower. Those are not there yet. Our Maxxfan will be inserted into the center of the front hatch, and I believe that the shower skylight is going to take out the 2nd hatch. So I guess I will take the area of the roof of the bus and subtract the area of both skylights and the 1 hatch that will have to home our fan. Then we will have to have a flue for the cubic mini stove... so that has to come out the top, but I think everything else will come out the sides.
MisterSandals
Participation Medalist
You should definitely make a plan with all this in mind if you want to maximise solar panel acreage.
12VoltInstalls
life passes by too quickly to not live in freedom
That and new hampshire- and not just in summer lol
What region are you now? The winters here are a little rough at times…
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