A/C that runs off a battery...

[Be Free]

I crunched a lot of numbers trying to get my "X" to be self-sustaining off grid with my preferred electrical budget (and that did not include an air conditioner). I just could not come up with enough "real estate" to mount the required solar panels without significantly compromising the aesthetics or performance of the boat. I finally settled on a small inverter generator and (eventually) a much smaller solar array.

I already have 242 pounds of lead acid batteries under the aft dinette seat and it does cause a noticeable list to starboard. I offset most of it by storing heavier items under the port settee and galley.

Realistically, at your latitude 600W of solar will generate about 3000W per day on average. That does not take into account any losses due to shading from the sails, boom, or mast. Those losses be significant if you are not very careful about where you place your solar panels and on a boat as small as ours the choices are very limited.

When you are doing your energy budget, don't forget to subtract the power that you are using during the day from the power generated by the panels.

[Tomfoolery]

Realistically, at your latitude 600W of solar will generate about 3000W per day on average.

For another data point, I've never seen more than 15A or so from the 300W of solar panels on the roof of my van, in Houston in summer on a clear day. At 13.6V, that should produce about 22A, but panels are never actually used in the same conditions as whatever reference standard is used for rating them (including the pixie dust factor).

So 15A for 6 hours, which is fudged to include lower solar incidence in the morning and evening but more time than the middle 6 hours, is 90Ah. That's more than enough to keep up with my 2-door 12V compressor fridge/freezer (2.4A averaged for 58Ah over a 24 hour period) and the usual parasitic loads running all night. The 600Ah battery SOC can drop over time if it's cloudy, when I'm only getting 3-4A at mid-day, but a sunny day or two will bring it back up with everything still running.

A/C will run for hours on the battery, or all night if it can cycle, but solar has no chance of bringing that back up for the next day. It would take most of a week of sun to bring it up from a low SOC, with no loads on it.

[Be Free]

I was working mostly from memory in my last post. Looking up the actual numbers, Jacksonville would be more like 2.34kWh on average (1.42-3.15).

Tom, you should be able to make around 0.894kWh on average from your 300W panels (0.281-1.46). How do those figures line up with your actual experience?

[Tomfoolery]

I was working mostly from memory in my last post. Looking up the actual numbers, Jacksonville would be more like 2.34kWh on average (1.42-3.15).

Tom, you should be able to make around 0.894kWh on average from your 300W panels (0.281-1.46). How do those figures line up with your actual experience?

What are those numbers in parentheses? KWh/day/m^2?

I’ve never really tracked it I’m afraid. I plug in when traveling but when I can’t, I just leave everything running and let the battery carry the day. The van has a second alternator (280A Nations alternator) just for the house battery, so it’s charging when driving, too. But I’m guessing 15A at 13.4V for 6 hours (WAG at the average) is about 1kWh per day, give or take.

[Be Free]

I was working mostly from memory in my last post. Looking up the actual numbers, Jacksonville would be more like 2.34kWh on average (1.42-3.15).

Tom, you should be able to make around 0.894kWh on average from your 300W panels (0.281-1.46). How do those figures line up with your actual experience?

What are those numbers in parentheses? KWh/day/m^2?

I’ve never really tracked it I’m afraid. I plug in when traveling but when I can’t, I just leave everything running and let the battery carry the day. The van has a second alternator (280A Nations alternator) just for the house battery, so it’s charging when driving, too. But I’m guessing 15A at 13.4V for 6 hours (WAG at the average) is about 1kWh per day, give or take.

Max and Min kWh per day over the course of the year for your location based on 300W panels. Max for your location should be in July and Min in December. For Jacksonville it would be June and December.

I'd say that 894kWh falls somewhere pretty close to "about 1kWh give or take". It's nice when theory and reality are at least on speaking terms.

"In theory there is no difference between theory and practice; in practice there almost always is."

[Tomfoolery]

I was working mostly from memory in my last post. Looking up the actual numbers, Jacksonville would be more like 2.34kWh on average (1.42-3.15).

Tom, you should be able to make around 0.894kWh on average from your 300W panels (0.281-1.46). How do those figures line up with your actual experience?

What are those numbers in parentheses? KWh/day/m^2?

I’ve never really tracked it I’m afraid. I plug in when traveling but when I can’t, I just leave everything running and let the battery carry the day. The van has a second alternator (280A Nations alternator) just for the house battery, so it’s charging when driving, too. But I’m guessing 15A at 13.4V for 6 hours (WAG at the average) is about 1kWh per day, give or take.

Max and Min kWh per day over the course of the year for your location based on 300W panels. Max for your location should be in July and Min in December. For Jacksonville it would be June and December.

I'd say that 894kWh falls somewhere pretty close to "about 1kWh give or take". It's nice when theory and reality are at least on speaking terms.

"In theory there is no difference between theory and practice; in practice there almost always is."

Yes it is. I know for fact that the panels top out at 15A or so* in strong sun in summer in Houston TX. The rest is a guess as I’m compacting a full day of sun, which is shaped something like half a sine wave or even a bell curve as it tapers off at each end. It’s obviously not 6 hours of full sun like it’s high noon with nothing before or after, so I’m sure the error on my part is significant. It’s a little disappointing that the best those panels do is 2/3 of what they’re rated for though, but it is what it is.

*One of the three panels wasn’t even connected since the van was built, as I found out when playing with the plugs on the roof trying to figure out why I was only getting 10A from 300W of panels. One panel didn’t make any difference when disconnected, and I found the leads buried inside the cabinet with the electric controls. The standard array on that model was 200W from two panels, and the third was included with the ‘no generator but big LiFePO4 battery with second alternator’ option. Needless to say, I was pretty happy to find those fat leads just tucked away, as it explained to some degree why the performance was so anemic.

[OverEasy]

Hi Tomfoolery

Sounds like a nice power package for your van!

We are contemplating upgrading our tow vehicle in a year or two.

One aspect is is we were to consider doing “The Loop” it would be incrementally…. Going a distance then renting a car one way to retrieve the tow vehicle and trailer then back to where the boat was left off at… Then back home for southern sailing of the winter season… and then tow back to where we left off the year before… etc.

Might take three or four cycles to complete “The Loop” that way but it wouldn’t ever be a race in the first place.

But a larger van type tow vehicle would make the transiting with some level of accommodations would make it a lot more enjoyable. I believe I saw some pictures of your van refurbishment a while back but can’t seem to surface the postings. I recall some nice innovations were being made. Do your recall the thread?

Any suggestions on what might make a good van tow vehicle? Ford? Dodge? Chevy?

Best Regards,
Over Easy

[Tomfoolery]

I believe I saw some pictures of your van refurbishment a while back but can’t seem to surface the postings. I recall some nice innovations were being made. Do your recall the thread?

Found it. viewtopic.php?f=11&t=27874&p=344383 (page 2) Not my renovations, though - that's the (mostly) factory package. I've been making some improvements over time, one of which was an air suspension on the rear axle. Still rides like a truck back there, but now it's a much softer truck.

All of the Sprinter vans are capable tow vehicles. BOAT tows with an older series T1N van with shorter wheelbase and 5 cylinder diesel. There is supposedly now a gasoline version, too. But for interior space, you really need the high roof version though the 144" (shorter) wheel base is fine, as are single rear tires (2500 vs 3500).

I don't know if Ford is even making the standard E-series vans any more, as I believe they're being replaced with the Transit vans. Many Class B RVs are currently built on the Transit. I believe some Class Cs are too, though they're mostly using Sprinters for those.

The Dodge RAM vans are front wheel drive. They are super popular for Class B units, but I don't know how they tow.

Chevy is almost out of the RV biz at this point. They're the only full-sized old-school vans still being made I believe.

Edit: Oh, yeah - the title is A/C that runs off a battery. The A/C in the van does run off the battery, for several hours on a sunny day, or all night when it can cycle.

[OverEasy]

Thanks!

[Be Free]

Tom,
It sounds like you have three 100w panels. Are they connected in series or parallel? Which solar controller(s) are you using? What is the Vmp (optimum operating voltage) on your panels? I can probably tell you why you are only getting 15A out the them if you can answer those questions.

I suspect that you have them hooked up in parallel. Most 100W panels will put out a little over 5A under optimal conditions so 15A for three panels in parallel would be expected.

[Tomfoolery]

It's a Go Power system. Probably the 200W system with a 100W expansion kit, since 200W is the standard with this model van. The control panel in the web site looks a little different, but the solar panels are the same.

And yes, they're wired in parallel. With the PWM control, I don't think wiring in series would help, and the combiner cable on the roof connects them in parallel by default.

https://gpelectric.com/products/200-wat ... -flex-kit/

https://gpelectric.com/products/solar-f ... expansion/

I had to add ring terminals to the second pair of conductors that was buried in the wall insulation, and land them on the terminals on the controller, also in parallel.

It's possible the two panels that were originally connected went over 10A once or twice that I saw, but 10A sticks in my head. The web site states 11.36A, which has got to be at the equator at high noon.

[Be Free]

With a PWM controller you are limited to the optimum operating current (in the vicinity of 5.3A for a 100W panel). Even an MPPT controller would not do you much good on a 100W panel unless the panels were wired in series. You need to get the voltage well above the battery voltage before the MPPT controller can work its magic.

It sounds to me like you are running well within expected parameters. You may be able to close to 16A out of them under ideal conditions.

[Jimmyt]

And if you want to hit it with a big hammer....

[NiceAft]

I don't know how you found that Jimmy, but thumbs up.

[Be Free]

It's impressive and a step in the right direction. You will still need a large LiFePO4 (lithium) battery bank to feed it and more solar that we can carry to keep it charged. I really like the fact that it is a heat pump and will heat as well as cool.

Billy Box and a 2Kw inverter generator still looks like the best option for me.