Sizing Amps use and charging when solar is not available

WinkerVan

New Member
I am new to the sight and I am in the middle of a DIY design and buildout of a 350HD 2019 Transit Van. I will have several sources of power including 375-400 watts of solar, 300 lithium amh, 3500 watt (7000 peak) pure sine inverter, shore power (with charger) and engine alternator recharging (250 amp alternator). The buildout will NOT include propane. The buildout will be all 12v and 120v. The problem I anticipate is limited solar power, as I live in Ohio and most of my travel will be September-May. I am stuck in Ohio the entire summer due to work! I will treat any solar power as a bonus when traveling the winter in States other than FL, TX, NM and AZ. While skiing CO and UT I will assume that I have shore power most all nights.

NOTE: I AM RECEPTIVE TO CONSTRUCTIVE ADVICE ON ALL ASPECTS OF THIS ENERGY/POWER SYSTEM BUILDOUT.

Buildout will contain lots of energy sucking devises, including the following:

1. Lots of 12v LED lights and USB and 12v charging ports (75 watts/6 amps)- high use
2. 120v Electric only refrigerator (1000 watts/8 amps) - on full time
3. 120v computer use/recharging (45 watts/1.5 amps)-high use
4. 120v microwave (750 watts/6.2 amps)- limited use
5. 120v coffee maker (1000 watts/8 amps)- very limited use
6. 12v Fantastic fan (30 watts/2.5 amps)- high use
7. 120v Induction cook top(1500 watt/12 amp)- limited use
8.120v Tankless water heater (1800/16 amps) or 4 gall tank water heater (1500 watts/12.5 amps)- limited use/showers and dish washing
9. 120v Limited use space heater (2400 watts/20 amps)- when needed/high use, with option to run engine heater
10. 12v Water pump (90 watts/7.5 amps)- moderate use
11. 12v Smoke/Carbon dioxide detector (5 watts/.5 amps)-on full time

I know, any question about available power has about 100 variables, so I will keep it simple. As some devises are much more important then others I will assume that the coffee maker and induction cook top use can be limited to when shore power is available. I also assume driving at 2200RPM will be a primary source of recharging the lithium batteries when shore power in not available.

In order of importance the important 12v items are the lights/usb charging ports, water pump and fantastic fan.

In order of importance the important 120v items are the refrigerator, computer recharging, water heater and microwave. Space heater will be important in 5-6 hour stretches from time to time while the van is parked in a parking lot while I am skiing/snow shoeing, etc. I just need to keep it warm enough so that my water heater and waterlines do not freeze.

I will also assume that certain combinations of simultaneous device use will need to be avoided. With the assumption that the refrigerator, detector, lights are in use, I should not attempt to operate more then one of the following: the microwave, water heater or space heater.

First Question: I have assumed the amount of energy generated by the solar panels will not impact the size of the inverter I need. I assume that the size of the inverter needed depends on the estimated "draw" or simultaneous use of watts. If I estimate that I could be drawing 2900 watts of power I need at least a 3500 watt inverter. While simultaneous draws of up to 3000 watts on the 3500 watt inverted would be less then 30 minute period is it safe? Is the inverter large enough to handle the draw. Anything watts I get from my solar panels will extend my battery life. I have not made this purchase yet, but i am ready to.

Second Question: The way I have may roof rack laid out i think i have maximized my solar panels. I have room for 3 panels. Is there anything or any new solar panel technology that will allow me to get more out of 3 panels in the September-May time frame, other then to hope for lots of sunshine?

Third Question: Will all that being said, I am have a difficult time determining/estimating just how efficient or inefficient the tankless water heater will be verses a standard 4 gallon tank water heater. Either type of water heater would be operated by a power switch verses being on demand all the time and it would only be switch on in preparation of use. The tankless using 16 amps might be on for 10 minutes to take a shower once a day and on for 5 minutes 2-3 times a day to wash dishes and wash up. The 4 gallon tank using 12.5 amps might be on for 15-20 minutes heating up for a 10 minute shower and 15-20 minutes heating up a second time once a day to wash dishes and wash up. Which set up, a tankless or tank water heater would be more efficient under the described circumstances. I have not made this purchase yet, but i am ready to.

Any thoughts would be appreciated.
 

FilterGuy

What, me worry?
Welcome!!

I have not made this purchase yet, but i am ready to.
Do not buy anything till you have a complete design. Otherwise you are likely to end up regretting some of your purchases.

Buildout will contain lots of energy sucking devises, including the following:

You have a good start on understanding your needs, but you need to flesh it out a bit more to get a better handle on system sizing. The way I do it is with this spreadsheet:


If you take the time to work through this, you will have a much clearer view of your situation.


First Question: I have assumed the amount of energy generated by the solar panels will not impact the size of the inverter I need. I assume that the size of the inverter needed depends on the estimated "draw" or simultaneous use of watts. If I estimate that I could be drawing 2900 watts of power I need at least a 3500 watt inverter. While simultaneous draws of up to 3000 watts on the 3500 watt inverted would be less then 30 minute period is it safe? Is the inverter large enough to handle the draw. Anything watts I get from my solar panels will extend my battery life. I have not made this purchase yet, but i am ready to.

Correct, inverter sizing is about your load. Not about your generation.
Yes, a 3000W draw on a 3500W inverter for 30 min should be fine...... but 1750 Wh is a lot to use in just 1/2hour.

Second Question: The way I have may roof rack laid out i think i have maximized my solar panels. I have room for 3 panels. Is there anything or any new solar panel technology that will allow me to get more out of 3 panels in the September-May time frame, other then to hope for lots of sunshine?
Not a lot new beyond MPPT charge controllers. All you can do is buy the highest wattage panels you can fit.
One common problem with RV systems is that it is hard to control shading. Consequently, you want wire the panels in parallel in order to minimize the shading impact. You also want to look for panels that have multiple bypass diodes in order to minimize the impact.

If you want to squeeze every last electron out of the panels.... put a separate MPPT controller on each panel.... but that gets pricey.

BTW: A lot of people are able to pretty much live off of solar in van conversions. You might be surprised how much of your needs will be met by the solar. (You might also want to change the induction stove to an LP stove)

Third Question: Will all that being said, I am have a difficult time determining/estimating just how efficient or inefficient the tankless water heater will be verses a standard 4 gallon tank water heater. Either type of water heater would be operated by a power switch verses being on demand all the time and it would only be switch on in preparation of use. The tankless using 16 amps might be on for 10 minutes to take a shower once a day and on for 5 minutes 2-3 times a day to wash dishes and wash up. The 4 gallon tank using 12.5 amps might be on for 15-20 minutes heating up for a 10 minute shower and 15-20 minutes heating up a second time once a day to wash dishes and wash up. Which set up, a tankless or tank water heater would be more efficient under the described circumstances. I have not made this purchase yet, but i am ready to.

Lets do the math.
Tankless:
10 min for shower + 5*3 minutes other times: Total of 25Min
16A x 120V = 1920W
1920W * 25min / 60min/hr = 800Wh

Tank
20 min + 20 Min = 40min total
12.5A x 120V = 1500W
1500W * 40min/60 min/hr = 1000Wh

Based on your numbers, the tankless would be better.
 

Mr.Michael

New Member
Tank: warm up the water when energy is available i.e. when your batteries are full make hot water.

Heating the van for freeze protection? Just heat the tank with a 12V silicone pad, 120W or so to 45F and all is good. I successfully used a pad recycled from my stock driver seat. It is about 12x12, flexible with 2 wires.

In my van I use a $120 diesel heater because it seemed cheaper than buying huge batteries. Specifically in winter you get maybe 6 hours of good sun, so your heater runs most of the time on battery. It will be difficult to run a heater the remaining 18h unless plugged in.

My rule of thumb is to mostly worry about permanent loads. As crazy as it sounds my wireless router consumes as much on a daily bases as my coffee maker that only runs 5 minutes each morning.
 
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