Solar Air Conditioner

"Does the KWH rating of PFP batteries reflect total KWH, or usable (available) KWH (70% of total capacity)? Also, did you have to get a special solar controller or was the Morningstar folks able to reprogram your controller with LFP voltage curves?"

Chip

The 9.6 kW-hrs is total energy storage, we can safely use 80% DOD for several thousand cycles (according to work done by Liberty Coaches) so we have just under 8 kW-hrs of usable energy. Our older son (as noted in earlier posts) has been in solar for almost 30 years as a researcher and first licensed solar/alternative energy contractor in New Mexico(has BS in electro-mechanical engineering and is a licensed master electrician). As noted elsewhere he designed and fabricated the panels and low voltage (under 1000 V probaby)for a 1.8 megawatt system for the power company near Las Vegas, NM. He did the reprogramming required for LFP voltage curves along with Manzanita industries. The Manzanita batteries came with internal battery management system that seems to work well (after 13 months with no hiccups)

I think our plan is to put a much smaller a/c unit into our bedroom that would (750 W) that would cool that room for sleeping. The outside temperature was in mid-90s today and we kept the 34' fifth wheel down to low to mid 80s which is quite comfortable. A single a/c unit is insufficient when it gets above 105 and we do not plan to go anywhere like that again. The Fantastic-Fans and the smaller 12V fans we plug into the 12V outlets make life quite livable. If it gets over 100, we go to much higher elevations, and we primarily boondock at dispersed camping in BLM/NF areas. We are currently "mootchdocking" for several days on the street visiting my cousin in Missoula, MT. We have not hooked up - and of course cannot open the slides on the street. City and neighbors are happy.

But we shall look into the 48 V DC heat pump. If it does use 1/3rd the wattage, it would be most affordable at $1.8K

We see no reason to add LFP batteries since 256 pounds is quite enough. The front bay is rated at around 400# so it could be done within frame, pin weight and pickup rear axle loadings.

I can send you photos of system via e-mail if you like since I have not figured out how to attach photos to this forum

Reed and Elaine

Reed, since you are already at 48v it seems that adding a high efficiency 12,000 BTU mini-split 48v DC heat pump (actually an AC and an efficient heater) that uses only 1/3rd the wattage of your conventional rooftop ac unit at only $1,800 would be more cost effective than adding enough LFP batteries to triple your roof unit's runtime.

Does the KWH rating of PFP batteries reflect total KWH, or usable (available) KWH (70% of total capacity)? Also, did you have to get a special solar controller or was the Morningstar folks able to reprogram your controller with LFP voltage curves?

Almot, I see your point that their minimal system might provide 10 hours of cooling on day one (as you are starting with full batteries), but what about day two, (as you are starting day two with depleted batteries)? You would definately need more battery capacity and more solar power than that for continuous 10hr/day usage. Perhaps they are counting on the AC's 500w draw being reduced significantly as the inside temperature drops during the evening hours and the AC compressor scales back its output - to say 6,000 BTU or lower. I'm sure that a lot would depend on the load placed on the AC (which will vary widely) to determine its actual current draw and battery run time.

Chip

"...In reality, 30ft trailer - meaning 30ft box - will have room for 6*250W solar, not 2,000W. There should be clearance from roof structures, sides, front cap, and enough space to walk between all this if you need to inspect the roof and/or service the panels. Unless you cover the side walls with folding panels that you would have to fold/unfold every time, getting 2,000W on a 30ft box is going to be difficult..."

As noted in earlier post, we have 1420 W of solar on a 34’ 5th wheel and could have put another 700 W if had we so chosen. We have obtained over 1300 W to controller at mid-day in summer. There are definitive power losses in the system as is expected to battery suite and then from battery suite through inverters.I just went on roof to check and 3 more 235 W panels could be installed. We would have to remove the TV aerial but we don't watch TV anyway (we are generally not in coverage)

"Also, 4*6V batts is a lot of batteries for some RVs, and RV-oriented lithiums in infant stage yet"

As noted in earlier posts, we have 9.6 kW-hours of lithium-iron-phosphate and it has worked extremely well for a year. LFP is beyond infant stage and into advanced development since Liberty Coaches has been installing on all their $2M Liberty Ladies for the last two years. This is much like the ads in Scientific America 50 years ago when GE was making fun of solid state devices (transistors then) by noting that valve technology was quite developed and we should never need anything more advanced.

Son Cary noted we have room for another 4.9 kW-hours of LFP in the bay. We do not think this is necessary and choose not to do such. 14.5 kW-hour and 24 kW-hour lithium suites are available.The latter is about 500#. The prices are going down.

We do run the a/c several times a day when it does get hot. We choose not to run it continually since we are a bit OCD about going far down on DOD.

Ron Jones was the first that we know of to incorporate LFP which he did on his motorhome(400 amp-hours I believe).
Reed and Elaine

Sushidog, 2,000W solar on 30ft trailer is just a math.

In reality, 30ft trailer - meaning 30ft box - will have room for 6*250W solar, not 2,000W. There should be clearance from roof structures, sides, front cap, and enough space to walk between all this if you need to inspect the roof and/or service the panels. Unless you cover the side walls with folding panels that you would have to fold/unfold every time, getting 2,000W on a 30ft box is going to be difficult.

Also, there are many 20ft and 24ft rigs out there, and those will only have room for 700W or 1000W.

Also, the retailer's estimates of solar harvest are a bit optimistic. I couldn't find any data on the A/C current on their website, but from what they say about 5 hours of run from 4*6V batts, it comes to 45AH per hour @12V. Harvesting 500-600 AH a day required to run the 1,200 BTU A/C for 10 hours and other loads - with 1,000W solar panel I wouldn't count on that. (Or - 1.5 times that much with 1,500W panel). There will be days when there will be hot but not sunny enough to harvest even 400 AH. Not to mention that harvesting is one thing and putting it into battery is another.

Also, I feel a bit of sales pitch here. They say - A/C 10 hours in daytime (with their smallest system), and 5 hours from battery after dark. Wait a minute - 10 hours A/C plus other loads is ALREADY what the solar can harvest under perfect conditions, so where those extra 5 hours will come from? You need to put that 5 hours worth of energy back in battery next day, but the solar is already taxed up to the limit.

Also, 4*6V batts is a lot of batteries for some RVs, and RV-oriented lithiums in infant stage yet.

Also, running 48V system for 48V A/C and battery charging won't let you use the excess of solar energy without it going into battery first, when you have such an excess. Technically possible, with some 48V inverter to run 110V devices, and some DC-DC converters to run the remaining 12V devices. A bit of pain and losses. IMO, this retailer didn't think that far.

As Sushidog notes, going to higher voltages ameliorates a lot of problems

"...Wiring it at 48 volts, the amperage drops to 1/4 of what it would be for a 12v system. The wire size required drops too, making the wiring weight and expense 1/4 of what it would be for a similar wattage 12v system.." Son

Our son designed and fabricated our system so that the six 235 W panels are ganged in two series of 3 each so that they go to controller at around 90 V. The LFP batteries (each of 4 cells) are ganged in series to be a nominal 48 V (54.6V float) after going through controller etc. Having the panels in series requires that we try to find a "camping" spot that gives us solar for several hours each day.

Son has been in solar for 23 years after 6 years of research at New Mexico State University's Alternative Energy Labs. He just completed the contract for a 1.6 megawatt system for power company. He is off grid with 7 kW in mountains above Las Vegas, New Mexico; our daughter has 7 kW in Las Cruces; NM and brother-in-law has around 3kW in Albuquerque.

Our 1.42 kW solar and 9.6 kW-hour LFP combination is good for up to 4 hours with the 15,000BTU Dometic system (a power hog) with 50% DOD. We generally just run for an hour or so to get the temperature down to 85 and then let it recharge to -1000 kW-hours or so. As Almot noted regarding our earlier post, the 12V fan and Fantastic-fans make things quite livable with interior temperatures below 90 (provided the humidity is low.

We do have a Morningstar TS-MPPT-45 which is quite sufficient for 1300 W at 90 V. If we were to go to 2 kW solar, we might go to a TS-60 but the 45 should be sufficient at 90 V.

We have had the Lithium Iron Phosphate (LiFePO4) battery suite for 13 months now and have had zero problems. The suite is about 9.6 kW-hours and weighs 256 lbs. Prices have dropped quite a bit in the last year. One poster noted that a 14 kW-hr system was going for around $4.5k and a 24 kW-hr system was going for around $7k. Tesla may be selling 50 to 80 kW-hr suites (about 1000#)
Reed and Elaine

Almot wrote:

sushidog wrote:
What's wrong with the Morningstar TS-MPPT-45 and TS-MPPT-60 charge controllers?

Nothing is particularly wrong with TS 45 or TS 60. Don't know whether Outback 60 would work better, but TS 60 is a good machine.

But they don't offer TS 45 or TS 60 with their 1000W system. They offer some unspecified PWM controller. A lot of beefy cable to run in RV.

They do offer TS 45 with 1500W solar, but 1500W won't fit on the roof of most RVs.

Besides, TS 45 is way too small for any of their systems. 1000W array needs at least 60A controller, not to mention larger arrays. They have very unusual approach to solar design. Not meant for RV.

Thanks for the reply.

Yes a TS45 is too small if you're only running it at 12v, as it will only handle 600 watts at 12v. But according to Morningstar's specs http://www.morningstarcorp.com/wp-content/uploads/2014/02/TSMPPTdsEng.pdf it will handle 2,400 watts at 48volts (what is needed to run this air conditioner). Wiring it at 48 volts, the amperage drops to 1/4 of what it would be for a 12v system. The wire size required drops too, making the wiring weight and expense 1/4 of what it would be for a similar wattage 12v system. Frankly I'm amazed that most solar systems don't run at higher voltages to save system resources. You can always draw 12v out of a 48 volt battery bank using 6-12v batteries to run your 12v appliances.

As far as roof acreage goes, let's do the math: a typical TT is 8ft x 30ft or 240 sq ft. Let's subtract 40 sq ft for the single ac (your solar AC is a mini-split design that will rest on your trailer tongue and won't protrude through the roof) This still gives you about 200 sq feet or available area for solar panels. Your typical 250 watt solar panel is nominally 40" x 65" or 18sq ft. Lets say that you place 2 panels side by side so their long axis is the same as the TT. this means that together, they would be 80" wide (less than the 96" width of the TT) and 65" (5 1/2 ft long). So 6 panels making up 1500 watts would occupy 195 inches of trailer length (16' 3") of that 30 ft long roof. 2000 watts would occupy less than 22 ft of roof space allowing you an 8 ft x 8ft area for protrusions (and their shadows), like an ac unit, roof vent and such. That's a little tight, but still doable. Then you can always mount solar panels on a fold our rack to the side of your TT, as I've seen some do, if you really need more than 2,000 watts of solar power.

At 44lbs each, plus wiring, you probably won't want to add more than 2,000 watts of panels (352lbs)to your roof anyway. Of course all this weight up top, raising your center of gravity will be offest by 500lbs (8-6v golf cart batteries) down low. Again, we're talking about a huge system. I think most folks might at least start with a 1,000 watt system (176lbs on the roof) and 4-12v deep cycle batteries (about 300lbs with controller and maybe another 30-35lbs of wiring) making the total minimum system weigh in at around 530lbs (plus the weight of the solar ac, which will be offset by the loss of the second roof mounted ac unit that it replaces - removing 85-90lbs off the roof too.)

Will there be unforseen problems to solve? Certainly, just like when folks install Lithium batteries in their RVs. But any new concept has these challenges. I'll bet it won't be long before installed systems like this become options on higher end units specifically marketed to the boondocking crowd. Of course I'm sure they'll be pricy, especially at first. Well at least there's the 30% second home tax credit you can get till 2016 - but you have to pay income taxes to get the tax rebate, which leaves out a lot of full-timers and retirees who would benefit the most from something like this.

Chip

sushidog wrote:
What's wrong with the Morningstar TS-MPPT-45 and TS-MPPT-60 charge controllers?

Nothing is particularly wrong with TS 45 or TS 60. Don't know whether Outback 60 would work better, but TS 60 is a good machine.

But they don't offer TS 45 or TS 60 with their 1000W system. They offer some unspecified PWM controller. A lot of beefy cable to run in RV.

They do offer TS 45 with 1500W solar, but 1500W won't fit on the roof of most RVs.

Besides, TS 45 is way too small for any of their systems. 1000W array needs at least 60A controller, not to mention larger arrays. They have very unusual approach to solar design. Not meant for RV.

Almot wrote:

sushidog wrote:
Of course you could always get the real thing like this:

http://www.hotspotenergy.com/DC-air-conditioner/DC-AC-Complete-Systems.php

Those are not designed with RV in mind. Wrong controller.

OK, please educate me. What's wrong with the Morningstar TS-MPPT-45 and TS-MPPT-60 charge controllers? I thought they were top of the line. What do you recommend to charge the 48V battery bank necessary to run one of these ACs off of solar panels?

Chip

sushidog wrote:
Of course you could always get the real thing like this:

http://www.hotspotenergy.com/DC-air-conditioner/DC-AC-Complete-Systems.php

Those are not designed with RV in mind. Wrong controller.

Funny video.

There are swamp coolers, they work, and the smallest one would draw upwards of 10A @12V. So it is not entirely impossible to run it 24 hours a day on solar and batteries, though you would have to have +800W total panel area. There is also a matter of all those gallons of water evaporating in your room.

A/C is nearly impossible to run on solar in RV. Not with two $10 controllers for sure. Golden HVAC knows what he is talking about, and I used his recommendations while making and attaching panel brackets. But the math and physics don't favor a "solar A/C". You can get solar parts cheap, yes. Good parts cost more, though. Typical cost - with good parts - is about $2 per watt including panles, cotroller, hardware etc, and labor is mostly DIY, no special mechanical skills required.

For just lights, fans, pumps, LP fridge, TV - a 500 solar is enough in all but extremely rainy climate zones. $1000 in parts, few weeks of thinking (subject to a particular person's ability to think :) ), a week of doing.

With added 110V devices like microwave, coffee maker, toaster - 700W-900W solar. You can cook on propane, make coffee in French Press, and probably won't die if left without toasts for a month or two, so there isn't really much need to have 900W.

For A/C, and considering all other devices of your RV, you would need a panel area bigger than your RV roof. Don Pianotuna here is "thinking" - so far - of running A/C off solar, and I know that his thinking ability is pretty substantial, but don't see solar A/C yet.

As mentioned by Reed and Elaine, 12V fans and powered vents like Fan-Tastic will help with cooling a lot, but there are limits to what they can do.