Just another newbie with solar component sizing questions for a van

[ruiz.manuel94]

Hi there, I know another newbie that wants solar in his van and has no clue...

In reality, I have done a lot of research but am having a little trouble putting all the information together to decide what components to buy, since apparently everything is interconnected and I have to make all the decisions simultaneously, so I would love to hear from some of you because I am lost.

Note: My van used to be an ambulance, and it already has an inverter, and I don´t know the specs of it since they are not printed on it.


MY DESIRED SYSTEM OVERVIEW:
-LiFePO4 DIY battery (Only thing I actually have, 4s 12V 230 ah)
-Solar charging
-Shore charging
-120V AC loads:

• Tiny Mini Fridge (running from the inverter with a relay to turn it on and off using a temperature controller, like this setup )
• Charge two laptops
• 600W nutribullet (can leave this out if too expensive to include, but would be nice)

-12 V DC loads:

• LED lights
• Charging phones
• Small water pump

BMS: What max current BMS do I need? what I know:
-Separate port BMS have low charging max current, but that is okay since apparently you can connect the battery directly to the MPPT charger, according to something I read around here. But is this also true for the shore charger?
-Discharge max current depends on the loads I plan to apply, but I am clueless about this. I guess my max load would be the fridge cycle? How to calculate current for the fridge?
-What is the current of a 600W nutribullet running on an inverter?

Panels: How many watts? (probably can only fit two standard size panels)
-Most van setups have about 200W panels. How do I calculate the current that panels will generate given their voltage and wattage?
-Should I connect them in series or in parallel?

Solar charger:
-The max voltage should be above the voltage of my panel setup
-The higher the amps the faster the charge? or more like the higher the amps the more panels I can have?
-What do we think of a charger like this one.

Shore charger:
-The larger the charger current the faster I can charge my battery. Is that right? Can I bypass the BMS?
-What is a good cheap charger?

Is there such a thing as a dual solar/shore charger? Maybe I could save a buck if such thing existed but I am guessing it doesn't

I am gonna stop there since these are already too many questions.

Would appreciate any kind of guidance.

I would like to add that I am trying to cut costs wherever possible, building the cheapest system but also ensuring it works good and is safe.

 

[rmaddy]

First thing. Watts = Volts x Amps. Or Amps = Watts / Volts. Or Volts = Watts / Amps. If you know two of the values, the third is simple to calculate.

You need details on the inverter. So much of the system design depends on knowing these details. Mainly you need to know its size, in watts. It will determine many wire size choices and fuse size choices. It will determine whether the nutribullet can be used or not. It will determine what size BMS you need.

Don't use the inverter to charge your laptop. Use the 12V DC directly. Add a standard 12V plug to your system just like you have in your car. Then you can charge your laptop and phone and other gadgets using standard car charging accessories. Much more efficient. No sense on going from DC to AC and back to DC to charge that stuff.

If you can, get a 12V fridge. Again, it will be far more efficient.

There are no "standard sized solar panels". 100W panels are generally close in size with each other. 400W panels are generally close in size with each other. But 400W panels are much larger than 100W panels. And of course there are many sizes in between. You need to figure out the physical size you have to work with and figure out how much solar you need and then figure out what will actually fit.

Don't start looking at specific solar charge controllers yet. You have to figure out all of the numbers first.

The first real step is to do a proper energy audit so you have a good understanding of how much power you really need. From those numbers you can start working out how much battery you need, what size inverter will work, and how much solar is needed. Then you can move on to more and more specific details. Don't buy anything until you have everything figured out or your will end up with the wrong stuff and waste time and money.

System Energy Audit and Sizing Spread Sheet

To get the spreadsheet, click on the orange Button in the upper right of this page. This sheet is intended to help you plan your system. Fill it out down to the last decimal place, look at the results..... and then make your best guess;)...

diysolarforum.com

 

[ruiz.manuel94]

Awesome, thanks for all that info.

So I filled everything out and this are my results:




So what I understand is:
-I should check my inverter to see that it is at least 800 watts (I am assuming it is, since it is HUGE and must have been used for intense ambulance stuff)
-My 230 amp hour battery is more than enough
-I need a BMS with minimum 77amp discharge and min 33 amp charge
-The solar charger needs to be around 33 amp? (not sure about this one)
-400 W solar array is good to start.
-What about the shore power charger???

 

[rmaddy]

If you came up with 811W for the inverter I would expect a much larger value for the surge watts. Anything with a motor or compressor will have a big, brief startup surge. Your 600W nutribullet might need 1200W to startup (I have no idea what the actual surge would be). Hopefully your inverter is 1500W or more.

Your BMS should be able to handle the full size of your inverter. If it turns out to be a 2000W inverter, for example, then you would want a BMS that can handle 2000W / 12V / 0.85 = 200A. You could get away with a 150A BMS but you would only be able to use 1500W.

If you use 400W of solar on at 12V system that's up to 33A. Since you'll never (very rarely) get a full 100% out of solar panels then a SCC that supports 30A output current would work fine. Based on the chosen panels, the Voc, and the panel arrangement, you also need to consider the max input voltage of the SCC.

For shore power you need an appropriate charger that will take the 120V at 30A (or 50A) and convert it to 14+ volts. It should be a charger that can properly handle charging LiFePO4 batteries. You will also need an automatic transfer switch. I know little about these two items since in my system I have an inverter with a built-in charger and transfer switch. It's possible your inverter has this as well which would make things a lot simpler. Check if there is an AC-in in addition to the AC-out and DC-in connections.

 

[ianganderton]

You haven’t mentioned where you are in the world

Your BMS will need to cope with your inverter. Max size for a 12V battery is realistically 2000W

2000W / 12V = 166A + any 12V loads

Size things at max 200A (BMS, wiring and fuses)

Your solar requirements will depend where you are. I recommend understanding what your worst case scenario is (usually winter) and planning around that.

For winter a DC to DC charger might be needed

 

[ianganderton]

My vans system is

200Ah 12V Lifepo4 battery with 200A BMS
2000W Epever inverter
480W (4x120W) solar (max I can fit in the roof)
Epever 40A Tracer AN

I’m based in NZ and the system is sized for use year round here

 

[ruiz.manuel94]

Thanks a lot for your responses, really. I am beginning to understand this.

2000W / 12V / 0.85 = 200A

is the .85 the inverter efficiency?

It's possible your inverter has this as well which would make things a lot simpler

I know that there is a 120V inlet right next to the gas inlet (on the outside of the van) and when you plug that in, the inverter is bypassed and now the 120 V outlets go directly to the shore power. So I guess that is what an ATS does, based on what I found on google.

As for the charger I am not sure. There is a small 12V battery that I don´t know how the system charges or what it is for.

You haven’t mentioned where you are in the world

I am in Mexico, but will be travelling all over the continent, avoiding winter too far north or south.

For winter a DC to DC charger might be needed

You mean to charge with the alternator?

 

[ianganderton]

Thanks a lot for your responses, really. I am beginning to understand this.


is the .85 the inverter efficiency?

I know that there is a 120V inlet right next to the gas inlet (on the outside of the van) and when you plug that in, the inverter is bypassed and now the 120 V outlets go directly to the shore power. So I guess that is what an ATS does, based on what I found on google.

As for the charger I am not sure. There is a small 12V battery that I don´t know how the system charges or what it is for.


I am in Mexico, but will be travelling all over the continent, avoiding winter too far north or south.


You mean to charge with the alternator?

Yes DC to DC is for the alternator.

Best and simplest is to charge with solar but when there is no sun or enough space for solar then dc to dc is a good option for supplemental charging

This is my favourite calculator for solar irradiance. You’ve used 4 which is quite high for some places in winter

Solar Irradiance Calculator

www.solarelectricityhandbook.com

 

[Isaac-1]

Renogy does offer this combination DC-DC charger / MPPT solar controller which also acts (sort of ) as a battery isolator and charging source for the engine starting battery when the house battery is fully charged, the only real downside is it is limited to 25VDC max solar input so you must use 12V style solar panels wired in parallel not larger higher voltage residential panels, or wire panels in series, though with a roof area as small a van this not a big limitation, on top of this you would only need a shore power charger/converter the size and type would depend on if you expect to need to do fast charging when you have shore /generator power or not