More power-Bigger panel or another battery?

[Outnabout]

Putting this out there for group thinking. In place I have a 100ah Lithium SOK and a 160w panel on roof and a 100w portable panel. Victron 100/30 solar controller and Smartshunt.

My draws are a 12v fridge (~3.0amps when cycling), furnace when cold, lights, and phone charging. I have plenty of power when sun is available but parked and with minimal sun and only moving a 100w panel around to catch rays I start to get low after a couple days. Hot days also cause more fridge cycling.

I want to add more capacity so am thinking of adding another 100ah Lithium in parallel.

Any advice? Bigger panel on roof, say 300-400w (heavier to pop up) or go with additional battery in parallel?

Thanks in advance. I always appreciate the feedback I get on this forum. Cheers. Tom

 

[pvstoy]

Based on your own thought that getting low after a couple of days... you would need more storage (battery). That will extend your supply longer when solar is not getting you back up when solar is not working.

Having more storage will take longer to get you up to 100 percent, but more solar will get you back faster with cost and weight on roof.

When solar is not working due to weather, having the alternator ability to get you some charge back in the existing 100 amhr battery while stationary can extend your stay.

 

[Vic Harder]

Tom, it depends on your usage patterns and charging availability. More battery means more days without charging at all or minimally. More solar means faster recovery of SOC. I sized my system for 3 days of use without any charging, and enough solar so I can recover from a low SOC to full in a single day.

For commercial installs that are designed to recharge fully every day (if possible) the rule of thumb is 2x the AH of the batteries is what you need in solar watts. So, 100AH lithium battery needs 200W of solar panels. And if you are in the trees/shade/far north, then the solar array needs to be upscaled to accommodate that.

I have 330W of solar (and yup, that's 40-45# on the front of the roof) and 200AH of battery. We use an induction cooktop and that is by far our biggest draw. I'd like to have 700W of solar to help keep up the SOC.... so far I haven't been able to source a panel of that power yet. I can get 550W for about $280 in Canadian Funny Money, but am holding out.

 

[Jon R]

My thinking was similar to above when sizing my system for Pacific Northwest use, with the addition of sizing my DC to DC charger so I can get a day’s worth of energy (40 ah for me) from less than 90 minutes of driving. I have 400 watts of panels on the roof (helps on our cloudy days) with a Victron MPPT 30 amp charger, a 30 amp DC to DC charger, and a 200 ah battery. I pretty much don’t have to think about electrical power when camping, which I like.

Note that if you are buying a DC to DC charger today the Victron Orion XS 50 amp charger is probably the one to buy, even if you dial it back to 30 amps for wire size or alternator capacity reasons.

If I had your current setup and only had the budget/desire to make one improvement right now, I’d increase my battery storage because it adds the most versatility and is probably an easier project. Whether I added solar panels next or added truck charging next would depend on your camping areas and stay lengths as Vic said.

 

[Outnabout]

Thanks so much for the feedback. Everything mentioned is what I had been tossing around but wanted some experienced users to chime in. I think I will go additional battery as it would be the easiest fix for now and then most likely a bigger panel down the line to more quickly regain a full charge. The DCDC makes a lot of sense from the standpoint of quickly charging while driving. I have really considered this but I don’t want to delve into wire changes, cost, etc. In my mind, however feeble, it seems to complicate my system and give me one more thing to worry about.

Thanks again!

 

[rando]

I would vote for more battery in your situation - and maybe a DC-DC charger. The beauty of the DC-DC charger is that you don't need to upsize the wire - the charger makes up for to the voltage drop in the wire (to a point).

We have a similar setup - 150 ah lithium battery, 160w panel on the roof and a 100W portable. In the sunny rockies and south west, this has worked great and we have never had an issue with low power. It is rare that we need the portable, which is good as we are rarely at the camper during the day, but it is key when the only option is to park the camper in the shade.

 

[rubberlegs]

Your power uses sound similar to ours, except we've recently added an electric blankie. My wife loves the blankie! (50w, so three hours usage is about 10% of battery capacity). We also have a 100ah SOK lithium battery. But we only have a single 100W, 5 lb, flex panel and a 30a DC-DC charger. The solar panel gets tossed on the roof or on the windshield. Sometimes it goes on the ground somewhere.

The SOK battery we bought 2 years ago has a useless State of Charge feature -- on ours it's just plain wrong. Maybe all you need is a shunt which is more accurate. We got this inexpensive one: Amazon.com. I've heard the newer batteries have a better BMS, but still isn't very accurate for SOC. Our SOK SOC sucks, yuk yuk!

Our battery SOC was rarely below 80% on our recent 5-week trip, although we spend most of the daytime out hiking. We can last 3 days without solar in cool weather. If we drive 2-3 hours every 3 days, the only value of solar is to save a little gasoline. If I recall, fully charging our battery would be something like 0.15 gallons of gas (don't quote me!). But it's fun to use solar.

 

[CPT Davenport]

I run 175watts on the roof with 206ah SOK lithium. We camp a lot in the winter/off season. 3 days in the rain and still not below 50%. The 4th and 5 day goes fast but I still have not been out of power. Same draws as you. 30% SOC has been our all time low.

Cool weather camping the fridge gets a break but the heater runs more but with a lower draw.

Hot summer I have found it makes a quite noticeable difference to park so the
fridge is on the shady side of the truck.

I think adding another 100ah will help you a lot. I have a DCDC charger but have not hooked it up for the same reasons as you. Haven’t had the gumption to swap out to a larger wire size.

We also have a 130w folding panel but rarely need it.

 

[Outnabout]

I run 175watts on the roof with 206ah SOK lithium. We camp a lot in the winter/off season. 3 days in the rain and still not below 50%. The 4th and 5 day goes fast but I still have not been out of power. Same draws as you. 30% SOC has been our all time low.

Cool weather camping the fridge gets a break but the heater runs more but with a lower draw.

Hot summer I have found it makes a quite noticeable difference to park so the
fridge is on the shady side of the truck.

I think adding another 100ah will help you a lot. I have a DCDC charger but have not hooked it up for the same reasons as you. Haven’t had the gumption to swap out to a larger wire size.

We also have a 130w folding panel but rarely need it.

I ordered the extra battery today. I have noticed the same as you have. Heater takes extra in cold weather, frig doesn’t work as hard and summer is a big draw on the feig because of heat. I think the extra 100ah will be a good addition for me.

 

[JHanson]

The biggest mistake you can make with a solar power system is to have more battery than panel. Your batteries need to reach full voltage each day—or as near to it as possible—to ensure full battery life. We learned this living almost 15 years completely off-grid, in addition to having PV panels on our 70-series Land Cruiser and our three Four Wheel Campers.

 

[rando]

The biggest mistake you can make with a solar power system is to have more battery than panel. Your batteries need to reach full voltage each day—or as near to it as possible—to ensure full battery life. We learned this living almost 15 years completely off-grid, in addition to having PV panels on our 70-series Land Cruiser and our three Four Wheel Campers.

One of the big advantages of LiFePO4 batteries is that they are not impacted by partial charges, and actually prefer siting at a partial state of charge. With lithium there is much less of a penalty both from charging and weight perspective to oversizing.

 

[Starbrightsteve]

I think another 100 watts on the roof and another battery will help to minimize power issues. But relying on the truck engine as backup will be the last resort.

I have 8900 watts in my backyard. Yesterday (clouds and rain) I made 2 kilowatts of power. On a good sunny day I make 50-55. No engine for backup I use the grid.

 

[CPT Davenport]

The biggest mistake you can make with a solar power system is to have more battery than panel. Your batteries need to reach full voltage each day—or as near to it as possible—to ensure full battery life. We learned this living almost 15 years completely off-grid, in addition to having PV panels on our 70-series Land Cruiser and our three Four Wheel Campers.

of the big advantages of LiFePO4 batteries is that they are not impacted by partial charges, and actually prefer siting at a partial state of charge. With lithium there is much less of a penalty both from charging and weight perspective to oversizing.

Hi Jonathan, just wondering what type of battery your need for daily charging to full capacity was with.

 

[JHanson]

Hi Jonathan, just wondering what type of battery your need for daily charging to full capacity was with.

My comment referred to AGM batteries (or flooded-cell of course). As Rando wrote, LiFePO4 batteries have a different regimen. I still prefer enough PV input to fully charge any system I have, then let the DC/DC controller manage it.

 

[ckent323]

I concur with J Hanson, You want a Solar system that is sized to fully recharge your battery bank everyday, ideally with a little margin (a bit more power than your power usage calculations indicate that you need.

If you have not calculated your daily power consumption needs based on the seasons you camp and the devices you use I suggest doing that exercise first.

Amps Per Day Spreadsheet

Star 152 came up with this spreadsheet to calculate amp use per day. Pretty cool! The file uses default values for his camper - update as needed. Amps Per Day Spreadsheet

www.wanderthewest.com

I always recommend installing the largest single rigid panel that will fit on your camper roof. It will be lighter and cheaper for the power it produces than any combination of smaller wattage rigid solar panels. In most cases it should provide all the power you need and provide a little margin in the event of cloudy days.

A 360W to 380W panel will fit on many camper roofs. It is important that you have a controller that can handle the higher voltage and current of the larger panels, which produce around 36v - 48v and around 10A. If you have an older solar controller for a smaller panel you may need to replace it.

A rigid 360 watt, 60 cell panel will weight about 40 pounds. By comparison 160W panels weigh about 24 pounds.

I bought a new LG 360 W residential panel in 2018 for just under $300 as I recall. I do not know what current prices are.

Panels up to around 500W are available but their dimensions may be too large for most camper roofs.

I hope this is helpful.

Craig

 

[Outnabout]

I concur with J Hanson, You want a Solar system that is sized to fully recharge your battery bank everyday, ideally with a little margin (a bit more power than your power usage calculations indicate that you need.

If you have not calculated your daily power consumption needs based on the seasons you camp and the devices you use I suggest doing that exercise first.

Amps Per Day Spreadsheet

Star 152 came up with this spreadsheet to calculate amp use per day. Pretty cool! The file uses default values for his camper - update as needed. Amps Per Day Spreadsheet

www.wanderthewest.com

I always recommend installing the largest single rigid panel that will fit on your camper roof. It will be lighter and cheaper for the power it produces than any combination of smaller wattage rigid solar panels. In most cases it should provide all the power you need and provide a little margin in the event of cloudy days.

A 360W to 380W panel will fit on many camper roofs. It is important that you have a controller that can handle the higher voltage and current of the larger panels, which produce around 36v - 48v and around 10A. If you have an older solar controller for a smaller panel you may need to replace it.

A rigid 360 watt, 60 cell panel will weight about 40 pounds. By comparison 160W panels weigh about 24 pounds.

I bought a new LG 360 W residential panel in 2018 for just under $300 as I recall. I do not know what current prices are.

Panels up to around 500W are available but their dimensions may be too large for most camper roofs.

I hope this is helpful.

Craig

Thanks Craig. I have been looking around for a panel in the range you mention. I wasn’t sure if the higher voltage they produce would be compatible with my system. I am used to seeing open voltage of around 20v on the panels I have. I have a Victron 100/30 MPPT controller and I believe it handles the voltages you mention. Thanks again for chiming in.
Tom

 

[Jon R]

With a LiFePO4 battery, you are free to operate the battery like your phone battery and charge to the extent you can when you can. This allows you to size the battery, solar charging system, and truck alternator charging parts of your system according to your needs.

How many days do you want to be able to camp in the trees or in dark winter without solar input and without running your truck or a generator? This multiplied by your daily energy use can dictate minimum battery size.

What is your daily energy use? If you want to be able to camp in the open with no electric-energy-driven time limits, your solar system should be able add back at least this much energy to the battery on the worst case solar day you want to cover (cloudy October or March day at 45 degrees latitude was my design point). This can size your solar system.

How quickly do you want to be able to recover one day or two days of energy by running your truck? Use this to select your DC to DC charger option and wiring, of course also limited by your alternator excess capacity. Less than 90 minutes driving to recover a day’s worth of energy with a 30 amp charger was good enough for me.

 

[ckent323]

Tom,

Yes, the Victron 100/30 will handle 100V and 30A.

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-100-30-&-100-50-EN.pdf

Best,

Craig