Help me put together a simple solar system for my car

[drabina]

I want to build a small (1 panel) solar system for my car. The goal is to run a portable refrigerator. I am currently using a power station but while it has a built in MPPT controller that supports solar charging, it cannot charge and discharge at the same time. So here is what I think I need:

One 100W solar panel - most likely will go with Renogy at about $100 with brackets
PWM or another inexpensive controller - was looking at Renogy Wanderer 10A PWM controller
50Ah LiFePO4 battery - I have no idea which one to pick
Fuses - again, no idea what sizes and how many
Cables - gauge?

The refrigerator will be directly connected to the battery as it runs on 12V and will be the only thing that's powered by the system. When if runs, it draws about 46W. There is a built-in battery voltage monitor and can turn itself off when a certain low voltage is detected. There are 3 settings (high, medium, low) that correspond to certain voltage values (don't remember what they are off the top of my head).

There is a limitation of just one 100W panel as there is no space on the roof for more and I can fit only panel that's up to 42in x 22in. I would like to go with 50Ah battery because that's what I have in my power station and works fine. Even if I could squeeze 100Ah battery, I am not sure if one 100W panel would be able to charge it.

Could somebody help me out by checking if I am not missing anything? Also what battery would you recommend and what wire gauges and fuses should I use for this system? I am also open for recommendation on a different panel or solar controller if there is something better than the one I picked.

 

[42OhmsPA]

Let's first discuss how you are going to securely mount the panel to the roof so it doesn't turn into a potential deatharray at highway speeds.
Would you be better off charging from the vehicle while your in motion and deploying the panel when stationary?

Other than that your on the right path. I would think 12awg and 20a fuses would be fine in this application.

 

[pollenface]

Don't use an inexpensive PWM controller for a Lifepo4 battery, you will shorten it's life dramatically (I know because I did it).

IMO, you are better off using a programmable mppt controller which can be set up to charge Lifepo4 correctly or a DC-DC charger with MPPT input which is Lifepo4 compatible.

 

[OffGridForGood]

Don't use an inexpensive PWM controller for a Lifepo4 battery, you will shorten it's life dramatically (I know because I did it).

IMO, you are better off using a programmable mppt controller which can be set up to charge Lifepo4 correctly or a DC-DC charger with MPPT input which is Lifepo4 compatible.

Ditto (agree)
Lucky thing, some dude named "Will Prowse" has a pretty good YT video on just this topic! 12v low cost SCC compared: from 4-years ago, but still relavant to OP's situation.
youtube.com/watch?v=kF_cVEYxj3E

I would look at ways to use your existing battery (just solving the charging problem with a dedicated MPP SCC) but that is me. For a separate small 12v 50Ah low cost LiFePO4 battery, it seems like the Chins or the Ampere-Time would be suitable options, maybe someone else has other suggestions...I have never purchased one of these types of batteries and make the above suggestions based purely on Will's review videos.

100W panel allow 15% over = 115W
115/12v = 10A
I would use wire and fuses of 15A (ie 2C-14AWG wire, 15A inline MC-4 fuse)

 

[drabina]

Thanks for all the replies.

I watched the video and honestly, unless I am missing something, I didn't get an impression that MPPT is that much better than PWM. Besides the issues with wire terminals and ease of programming (which I probably won't do for 1 panel and 1 battery system), the difference was only about 1-2 Watts or so when there was some cloud coverage. The video was actually very informative but I think I am going to stick with the Renogy PWM instead of spending 6x or more for MPPT.

Thank you for the battery recommendation. I was actually looking at the Chins batteries and also Li Time. Both companies have $200 50Ah batteries. The whole system is going to be used during warmer months (May till September) and I will remove it from the car for the winter. As to the mounting, I can secure the panel to the roof rack I have. I have recovery boards and other stuff mounted for over a year and nothing flew away so I think I can do a pretty good job here.

The power station I have (BigBlue CellPowa 500) supports pass thru while charging from 120V outlet and 12V car system (outputs on DC only) but I was told by the manufacturer that it doesn't support charging via solar and discharge at the same time. I am still confused how the battery knows what type of charging is connected to it but I can only assume that manufacturer knows better. If there is a way to have the solar panel connected to the power station and be able to draw power from the 12V outlet at the same time, that would be great. I just don't know how to approach this.

One more question. Would it make sense to go with 100Ah battery instead of 50Ah if I would only run one 100W panel? Or the 100Ah battery is too much for just one panel and I would never be able to fully charge the battery in a reasonable time?

 

[OffGridForGood]

The point about the MPPT is better control over battery charging, not more watts.
Like Pollenface, I have ruined a perfectly good (expensive) battery using a cheap PWM charger, hope you learn from our mistakes.
A 100W PV is likely going to give you 70-80W at best, I assume it will be mounted flat on the roof, not at an ideal angle.
50Ah battery x 12v nominal is "about" 600Wh
charging at 70 W per above PV on the car roof could take over 8-hours, a 100Ah battery double this time.

If I were working on this assignment, I would open up the power station and look at how I could connect the new SCC directly to the battery, rather than buying another battery. There could be electronics that will not function correctly doing this (ie coulomb counter, SOC display etc) or you may not be comfortable doing this, in which case, don't.

 

[Rednecktek]

The 100ah battery (and they're making smaller form factor ones now) buys you more time in krappy weather. Doesn't hurt and if you can get a DC-DC charger involved you can charge it from your car to help the panel out.

A PWM controller will be fine as long as you make sure it's got settings for LFP and doesn't require you to program a USR profile. MPPT is a bit overkill for a single panel.

 

[pollenface]

I didn't get an impression that MPPT is that much better than PWM

It needs to be programmable to some degree to correctly charge a Lifepo4 battery.

 

[drabina]

Thanks again guys. Any recommendations on a SCC that would work better than the cheap PWM Renogy? If the MPPT is that much better, I could spend up to $100 on one. The only requirement would be small size. I can't fit anything like Renogy Rover which is 9" tall. The max I could fit is up to 6" tall. Or maybe there are kits that include solar panel, SCC and all the required wiring you could recommend?

Also, with the DC to DC charger that would charge the battery while I am driving, could that be connected at the same time with solar panel or would I have to have a switch that determines if the charging is via solar or DC to DC charger? Sometimes we do drive to a location that's 2 or more hours away and I think car's alternator would charge the batter faster than the solar panel.

As to modifying the power station I have, I don't want to do it. I will keep it as a portable power that we can use in a tent to charge devices.

 

[OffGridForGood]

Typical Car Alternator output 100A 14vdc ie 1400W (like 14 x your one PV on a good day!)
Do a search on the forum this has been discussed several times, generally DC-DC on it's own fuse to the battery, plus a switch or relay.
I expect @Rednecktek to make a suitable recommendation for your SCC, which may be a PWM (with LiFePO4- appropriate settings).

 

[Rednecktek]

The Wanderer isn't a bad choice as long as you get the Li version, and the 30a gives you some room later if you decide to parallel in a ground deployed array or the like. If you wanted a super cheap MPPT that still does the LFP profile, I've used this little 10a unit in my heater and it seems to do the job according to the BMS.

Renogy makes a DC-DC converter that has a built in MPPT as well which might be the best of both worlds in your case but it is a bit pricy and I'm striking out finding something comparable that has the MPPT built in. It would charge from the running vehicle AND solar panels at the same time.

@Will Prowse did a video on it a while back, but I don't know if he's seen anything that does the same thing from a different vendor that might be cheaper.

 

[SamDeleted]

Would you be better off charging from the vehicle while your in motion and deploying the panel when stationary?

That's what I'd do , DC-DC charger is a much simpler solution

 

[drabina]

I was looking at the DC to DC chargers to which I can also hookup solar panels. Unfortunately, the price $200+ is a bit much for the simple system I want to build. Also, we usually drive up to 2 hours one way and have the car parked for the rest of the day. For a longer drives, I can always switch the refrigerator to my power station which I can charge from 12V car system. Then I could swap to the 50Ah house battery that's charged via solar.

 

[NuraMustafa]

Thank for sharing.

 

[HarryN]

There is some distance between what you would like to work and what will work.

If your expectation is that a 100 watt mono renogy panel + 50 amp-hr of LiFe battery will be sufficient to run the refrigerator and keep it less than 40 F reliably - then this will for sure not work. 100 amp-hr is really just barely enough if you have a lot of charging power.

I help people with mobile power systems - mostly to run these kinds of refrigerators and this just isn't enough.

The re-start of charging is also not so automatic like you are imagining when it shuts off due to low voltage. This is a manual re-start process.

___________

One strategy would be to run the refrigerator at 50 - 60 F instead of 35 F. This will still keep your drinks cooler than they would be in the car normally and use a lot less power. It is quite refreshing to drink water at 60 F vs 100 + F from inside of a car.

__________

As far as the controller, it only makes sense to buy an MPPT controller if you have a 24 volt panel or panel array.

Don't be tricked into buying a renogy mppt controller no matter what.
_________--

If you need the temperature of the fridge to stay below 40 F, then that one panel is really only able to reliably supply ~ 1/3 of the needed power.

If you want more power, then perhaps look at if there is a place to plug into the grid sometimes and add a 120 volt charger.

 

[drabina]

If your expectation is that a 100 watt mono renogy panel + 50 amp-hr of LiFe battery will be sufficient to run the refrigerator and keep it less than 40 F reliably - then this will for sure not work. 100 amp-hr is really just barely enough if you have a lot of charging power.

If you need the temperature of the fridge to stay below 40 F, then that one panel is really only able to reliably supply ~ 1/3 of the needed power.

Maybe when you look at the raw numbers, that's true. But in my case, with the 50Ah power station I have, I cool all the stuff at home (in the refrigerator), then set the car fridge to 36F, drive 1-2 hours and leave the car for 8 hours or more in the sun. Two weeks ago, the battery was down to 30% after that time as it was pretty hot. Last Sunday, the same setup and time and my battery was at about 50% at the end of the day. So even if the 100W panel would take over 8 hours to fully charge, then it should supply enough power to the battery so I may loose less than 25% of the storage during the day. If that's true, then the setup would work for me. That unless I am missing something obvious.

Could you elaborate on what you meant by manually restarting the charging process?

 

[GravelRider]

Maybe when you look at the raw numbers, that's true. But in my case, with the 50Ah power station I have, I cool all the stuff at home (in the refrigerator), then set the car fridge to 36F, drive 1-2 hours and leave the car for 8 hours or more in the sun. Two weeks ago, the battery was down to 30% after that time as it was pretty hot. Last Sunday, the same setup and time and my battery was at about 50% at the end of the day. So even if the 100W panel would take over 8 hours to fully charge, then it should supply enough power to the battery so I may loose less than 25% of the storage during the day. If that's true, then the setup would work for me. That unless I am missing something obvious.

Could you elaborate on what you meant by manually restarting the charging process?

How many days are you planning on being out at a time? In your real world testing, you've used between 25 and 35 Ah per day. If you're only planning on staying out for a weekend, why mess with solar at all? Just get a 100 Ah battery, and you'll have 3-4 days of cooling, without the work, cost, and space of solar, then charge the battery at home to use for your next outing.

 

[HarryN]

If your goal is to:
- Use solar to charge up the battery during the week
- Run it at it's highest temperature during the week.
- Put in cold items and turn it down on Friday
- Use it over a 2 - 3 day weekend

That is viable with the 100 watt panel + 100 amp-hr battery that you are talking about.

________

A good viable controller for you is the bogart pwm pwm controller. Just buy the sc2030 controller - don't need any of the other stuff. Yes I know it looks ugly but it works and is easy to use.

A simple fuse block for example a blue sea 5025 or 5026 if you have space.

Some 15 amp ATO type fuses just like are in many cars and boats all over the place.

10 awg wire if you can.

Run everything through that fuse block and you should be fine.


If you need to add more stuff over time:
- More solar charging power in the future, you can add more solar panels easily though that controller
- More batteries - just attach them to that that fuse block
- More types of chargers or charging methods - attach them through that fuse block
- More loads - same thing - attach them to the fuse block

 

[Tdcampbe]

I can confirm that the system you’re describing is a little undersized depending on how long you wanna stay out.

I have 200w on top of my truck that runs a 55qt fridge and various other things in the truck but the fridge is the only “constant”. 100ah battery I built and a Victron 75|15 controlling the whole thing. I used to have only 100w and it couldn’t keep up in the summer months at all. The battery would eventually drain after about 3 days. I stay out in the middle of nowhere for weeks at a time and have absolutely no issues now. My battery will recharge everyday in the sun and I can go about 5 days without sun before im dead.

If you’re only looking for a day or 2, no need to mess with solar at all. Spend the money you woulda spent on panels and mppt on a 100ah battery and you’ll go 3-4 days. If you want longer, learn from my mistake and go bigger to begin with.

 

[drabina]

A weekend outing is my goal. Usually, me and my kids, we go for one full day (6am till 6pm). The fridge is portable so it doesn't stay in the car unless we prepare for a daytrip. All I need is to have enough battery left in case we stay overnight or for those super hot summer days or when kids want to charge their R/C cars. Just hoping that the panel will provide enough juice to run the fridge so the charged battery is not used too much.

I could get a bigger power station (1000W+) but those are fairly expensive. Cheaper to add one solar panel and 50Ah battery. Unfortunately, there is space for just one panel on the roof of my car. As far as 100Ah battery (not a power station), then I do not want to deal with moving the battery in and out of the car for charging. Looking for somewhat permanent solution. The car is parked outside so Mon-Fri it could charge the battery so it is ready for the weekend. Plus my current 50Ah power station can be used as a backup.

I hope that clarifies some things.