Alternative to spending lots on solar

[tundranurse1]

We are planning to get an Arctic Fox 25W travel trailer. It has 180watts of solar on the roof, WiFi booster and two 6 volt deep cycle batteries. It also has a plug in for portable solar.
We don’t particularly want to spend more on a big solar set up.
We will have propane furnace and fridge & stove top coffee pot, IPad and phones to charge.
My question is we don’t run anything but CPAP, and possibly get a 12 volt tv for evening, would it be possible to use a solar generator to run the tv in the evening and CPAP at night? The tv only uses 45 watts.

[SLOweather]

I'm not quite clear on the advantages of what you are trying to do. You don't want to "spend more on a big solar set up", yet a "solar generator" is nothing more than one or more solar panels (which you are already wired for, anyway), and more batteries and an inverter in a spiffy case. Some of the "solar generators" I looked at, you need to buy the solar panels separately, too.


It seems to me that for the same or less money, you can add some portable panels, and a small inverter (if you don't already have one) to your existing setup.

[TajMahal]

Surf on Craigslist for solar panels. I picked up 2 330 watt panels for $175 each. Deals are out there if you know where and how to look. Good Luck

[drdarrin]

If your batteries are golf cart batteries, they are good for about 230 amp hours. Unless you want to replace them regularly, only about 20% of that is available for you to use each day, so about 46 amp hours.

Your tv uses 4 amps per hour. How long do you plan on using it? 4 times hours of use subtracted from 46.

Your CPAP uses how many amps? Times hours subtracted from the above.

Lights and parasitic loads draw how many amps? Times hours and subtract again.
You see how this works?

Once you figure out how much you consume, you’ll have to figure out if your one panel can replace it.

I suspect you’re going to need to add two more batteries and another panel but that’s only a guess.

[Mark_K5LXP]

Not sure where drdarrin came up with the 20% Ah figure but is correct about figuring time and power which generally works for both discharging (negative Ah) and charging (positive Ah). An ideal system will have enough battery to run the stuff you want as long as you need it, and enough solar panel to replenish that charge over your typical solar day. Complicating factors are unexpected loads and clouds or shade which can be accommodated somewhat through design margin but this would go beyond your desire to keep things from getting "big".

More solar won't hurt but you need to find out how many amps the controller you have can accommodate, and what the capacity of the portable inlet is. My take on it would be to come up with a realistic load estimate (device amps times hours) for a 24 hour period and see how close you are with the panel you have. That will tell you if you're just a panel or two short or if what you'd need crosses the "big" threshold.

Something solar users figure out in a hurry is every watt not used is about 1.25 watts you don't need to generate and store. So deciding up front just what you "need" to have vs what you "want" to have can make a big difference in solar system size and complexity.

Mark B.
Albuquerque, NM

[1bigmess]

The 12 Volt Side of Life

The 12volt Side of Life (Part 1)

[C.Martin]

Originally Posted by tundranurse1

We are planning to get an Arctic Fox 25W travel trailer. It has 180watts of solar on the roof, WiFi booster and two 6 volt deep cycle batteries. It also has a plug in for portable solar.
We don’t particularly want to spend more on a big solar set up.
We will have propane furnace and fridge & stove top coffee pot, IPad and phones to charge.
My question is we don’t run anything but CPAP, and possibly get a 12 volt tv for evening, would it be possible to use a solar generator to run the tv in the evening and CPAP at night? The tv only uses 45 watts.

There’s no such thing as ONLY when it comes to 12v power use. Fridge, Hot Water Heater control boards, fans, room lights, tank level monitor, LP detector, Water Pump,...

If you plan on living off grid...having a battery monitor is most helpful. You can do a proving run and tally up your actual aH usages. Then make a better informed decision of how much battery storage you need...and then how much solar it requires to get the batteries charged up each day.

I believe doing it properly the first time will save you money in the long term.

[astrocamper]

I would start with a Victron BMV-712. Monitor a few days of off grid use. It will tell you how much power you are using and how well the solar is keeping the batteries charged up.

It's great that you already have 180 watts of solar. I use a BIPAP AutoSV but I use it with a 12 volt cable so I don't need to leave my inverter on overnight.

My first small trailer started with 160 watts of solar and I later upgraded to 240 watts total so I could also run an Engel DC freezer. I was powering a pair of Trojan 6 volt T105 batteries for 220 amp-hours of total capacity.

I was powering an Engel freezer, astronomy equipment, laptops, phones, lighting, furnace, fantastic fan and a little light use of a 1000 watt inverter to power a blender and vacuum cleaner. My batteries were still doing great after 8 years when I sold it. I bought an Arctic Fox 22G to replace the small trailer and installed a much larger LiFePO4 battery bank, 2200 watt PSW inverter and 985 watts of solar.

My point is with wise power management your existing solar may do pretty well. You may want more solar or a generator when you use your trailer in the colder months with less solar hours and more furnace use.

If you like how the solar works but need more consider adding a panel that you could set out for the day. Your trailer already has an SAE (ZAMP) connector. You can buy the ZAMP portable kit or do one on your own for a bit less. Home Depot sells Grape Solar 180 watt panels on sale for about $215. You could use it as a portable panel and buy a Victron Energy SmartSolar 100/20 MPPT controller for $158. You would also need a disconnect switch and circuit breaker/disconnect and some cables between the panel, controller and batteries.

[HaRVey 74.5]

The 180W panel yours came with is probably a Grape Solar, which would be good as adding to your exising, you want to match (just like for batteries). Your factory solar controller is probably a GoPower PWM30 (my friend just bought the same Artic Fox and came with the same setup), which can handle up to 400W of solar. So buy one more panel and mount it next to the existing one and simply disonnet one lead and connect the new panel in series.
And for golf cart batteries, you can repeatedly discharge and recharge them 50% ~600 times (or cycles). As with all batteries, maintenance is critical.

[PbdBlue]

Originally Posted by HaRVey 74.5

T So buy one more panel and mount it next to the existing one and simply disonnet one lead and connect the new panel in series.

Do not connect the new panel in series. With a PWM controller the panels must be wired in parallel.

[astrocamper]

Parallel is correct. You can buy MC4 splitters pairs on Amazon. You will also need to buy mounting Z brackets for attaching panels to roof.

[drdarrin]

Originally Posted by Mark_K5LXP

Not sure where drdarrin came up with the 20% Ah figure but is correct about figuring time and power which generally works for both discharging (negative Ah) and charging (positive Ah). An ideal system will have enough battery to run the stuff you want as long as you need it, and enough solar panel to replenish that charge over your typical solar day. Complicating factors are unexpected loads and clouds or shade which can be accommodated somewhat through design margin but this would go beyond your desire to keep things from getting "big".

More solar won't hurt but you need to find out how many amps the controller you have can accommodate, and what the capacity of the portable inlet is. My take on it would be to come up with a realistic load estimate (device amps times hours) for a 24 hour period and see how close you are with the panel you have. That will tell you if you're just a panel or two short or if what you'd need crosses the "big" threshold.

Something solar users figure out in a hurry is every watt not used is about 1.25 watts you don't need to generate and store. So deciding up front just what you "need" to have vs what you "want" to have can make a big difference in solar system size and complexity.

Mark B.
Albuquerque, NM

This is where I come up with the 20% figure, if you don’t want to replace your batteries regularly.



I prefer to get 5-10 years out of my lead acid batteries instead of 1.5-2.5 years but the choice is yours. Then there is the issue of getting them fully recharged with a single 160W panel. If you discharge to 50%, ergo use 1400W, you’ll need 11-12 hours of full sun to recharge them.

[Mark_K5LXP]

Originally Posted by drdarrin

This is where I come up with the 20% figure, if you don’t want to replace your batteries regularly.

The ubiquitous cycle life graph. Missing from the graph is amp hours delivered. Amp hours are what runs your stuff, not cycles. Apply amp hours to that cycle life graph and you will see that DOD doesn't have the impact on service life you might think. Service life -- dollars per delivered Ah -- is what counts, not years in service.

I prefer to get 5-10 years out of my lead acid batteries instead of 1.5-2.5 years

20% DOD is 3300 cycles, a cycle every day for nearly 10 years. Maybe in an off-grid solar application you might make a case for this kind of use cycle but GC-2 style batteries won't last that long, their composition doesn't support it. So you'd be recycling them before they're used up. Now, if your goal is to make them last 4-5 years, then you can apply what is your actual cyclic use and DOD. Conservatively this is at least 50% DOD or more, not 20%. The most efficient use of a battery is to use up it's amp hour capacity before the calendar takes it away from you. That only happens with deeper cycles. That's not to say you don't recharge when you can but in just about any portable operation you can name, depth of discharge is not a predominant factor in battery cost per Ah. It's not about making batteries last as "long as possible", it's getting all the Ah you paid for. Whether you hit that limit in 2 years or the limit of 4-5 years the $ per Ah is the same.

Mark B.
Albuquerque, NM

[Big Dreamer]

180 watts isn't a bad start however with that Cpap I would install two more golf cart battery's. Furnace, tv and cpap will add up and you don't want to get below 50% state of charge. I'm running 400 watts on the roof, I have 200 watts portable in the basement if I need them. I run my fridge off 120 Volt ac inverter and heating water with a 300 watt 12 Volt dc element and the control systems are set up to ensure charged battery's when we go to bed and switch to propane.