Solar Assisted Refrigerated Delivery Truck

I have an Econoline van which has 1000 watts (4X250), a Renogy Tracer controller, Tripp Lite inverter and a marine charger for nighttime charging, and an 8X35ah battery array. I plugged a pair of freezers, 20 and 22 cubic feet into the inverter. It is pretty reliable, you can run all day, the freezers take about 3000 watts per day, though the system is a bit like cinderalla's coach, gotta be plugged in by about 8PM in the winter. In summer, the system usually collects enough during the day to run until the sun next comes up, though I make a point of plugging in the charger every night or when at home base. I've had an interesting time making it work. We mounted the panels on a ladder rack that came with the van, with some tubular steel additions welded on. The 900 lb capacity of the freezers, and inability to raise the freezer lids all the way limits its usefulness. This is our Mark 1 'Man the Van' an we view it as a proof of concept.
We are envisionong two more improved models. Our next step, having avoided the problem of freezing the whole truck by just using commercial freezers, is to build a 24 volt freezer unit, to avoid the inefficiencies of the inverter and the duplicate freezer units, is to use polyurethene spray foam to insulate the freezer box and build a 24 volt freezer. The freezer build is in progress, the compressor being adapted from a 24V air conditioner unit. The freezer part has a lot of questions, we think it will keep 240 cf frozen but we don't have a proof of concept on this part.

I have a bill of sale in progress for a fairly late model 16-foot box truck. The roof will carry 5 X 325 watt 24V modules in the 16 X 7 foot roof, we are going to freeze about 240 cubic feet in an 8 foot length of the truck, leaving the other 8 feet for various ambient cargo and equipment.
The power demand of the freezer unit is basically 625 watts for the compressor, 200 watts for fans and etc., complicated by the 1800 watt inductive surge on startup and the fact that the system runs about a third of the time due to thermostat action. We expect daily power consumption to be in the area of 6000 to 8000 watts, this depending on the season. The availability of more sun power when we need more cooling and what we call the 'parasol effect' where the panels block out about 20% of the heat on hot days runs in our favor, and our experience with Mark 1 leads us to believe that we will have enough power.
We've specced 5 X Suniva OPT 325-72-4-100 325W Mono SLV/WHT Solar Panels, a couple of Renogy Tracer 1000 W controllers, a pair of 225 AH lead acid batteries, a Tripp Lite inverter for occasional AC use, a yet-to-be decided 24 volt charger and various breakers and switches.
The one area we have had trouble with is the charger, we burned up a bunch of Powermax units and settled on a big marine charger in the end. We're inclined to err on the side of caution with the chargers and go for another unit with a big transformer in it. We think the smart chargers get confused when the solar power cuts when the sun comes up.
Anyone got any helpful suggestions on what we should be doing?

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Re: converting my van...

    Welcome to the forum Sausage Guy!

    Wonder what you are trucking around. ;) Sounds delicious.

    First, just to get the units right... You typed 3,000 Watts -- But I am guessing 3,000 Watt*Hours of energy usage:
    • 125 Watt average load * 24 hours = 3,000 Watt*Hours per day
    And that sounds pretty reasonable. ~1.5 kWH per day per freezer. In hot weather, can be worse, in cold weather it will be better.

    If you put the food in "pre-chilled", that will greatly reduce the freezer run-time. I assume you are not keeping the meat frozen, but just near 32F? Or what?

    If you need another charger sometime--Look at the Iota brand. They are pretty simple and reliable.

    http://www.solar-electric.com/batteries-meters-accessories/bach2/bach1.html

    So--Lets look at this piece by piece.

    First the cooling system... You want it to be as efficient as possible. Besides insulation and such--The circulating fan motors being outside the cool box would help (200 Watts of motor will put >200 Watts of heat into the cool box--And need the refrigeration to pull it out. Put the motors outside the cool box, reduce heat load from the fan substantially.

    Next, loads... 1,800 Watt inductive surge... A little mixing of units. 1,800 Watts is "power" -- And that would be how much current*voltage you pull from the battery bank. 1,800 VA (volts * amps) is a mix of power and inductive load. If this is a 24 VDC system (DC motors?), then there is no real inductive load--Unless this is an AC compressor driving by a DC to AC inverter?

    Anyway--Quick sizing of the battery bank. The minimum battery bank to supply an 1,800 Watt starting load (may be >>1,800 VA inductive, which means a larger inverter, but not battery bank):
    • 1,800 Watts * 1/0.85 inverter eff * 2.5 maximum surge current for flooded cell battery * 1/24 volt battery bank = 220 AH @ 24 volt battery bank minimum
    Next, assume your system runs 50% duty cycle, and I would suggest a maximum of 25% discharge for nominal operation:
    • 825 Watt load * 0.50 duty cycle * 10 hours per shift = 4,125 Watt*Hours per shift (excluding parked/charging--perhaps even compressor turned off?)
    • 825 Watt load * 0.50 duty cycle * 10 hours per shift * 1/0.85 inverter eff * 1/0.25 maximum battery discharge * 1/24 volt battery bank = 809 AH @ 24 volt battery bank
    This is assuming a 10 hour work day, that you still need cooling in bad weather/truck parked in shaded area/for longer battery life and to allow for "issues" (warm items put in truck to cool), etc.

    If you use 6 volt @ 220 AH golf cart type batteries, that would be ~16 golf cart batteries (4 in series by 4 parallel strings)--A pretty large amount of lead (and acid) to haul around. If you wanted to save weight/costs and cut things a little closer, you could try 8 batteries (or other mix of batteries--just giving you an idea of size of battery bank).

    I understand the interest in solar--But perhaps you would like to look at a Marine Alternator system for your truck:

    http://www.balmar.net/

    Should help extend the work day of the truck without having to get it back for 12 hours on charge.

    For the solar side... 5x 325 Watts of solar panels for Memphis TN. Using PV Watts to figure out hours of sun per day for array mounted horizontal (zero degrees of tilt):



    Month
    Solar Radiation
    (kWh/m 2/day)


    1
    2.55


    2
    3.36


    3
    4.52


    4
    5.60


    5
    6.18



    6
    6.65


    7
    6.62


    8
    6.22


    9
    4.65


    10
    4.11


    11
    2.74


    12
    2.21


    Year
    4.63



    Using 4 hours of sun as a "break even" value:
    • 5 panels * 325 Watts per panel * 0.52 system eff * 4 hours of sun per day = 3,380 Watt*Hours of 120 VAC of solar power per ~8 months of the year typical minimum.
    However, with an actively driving truck, building/power line/trees/power poles/etc. shading will dramitically reduce solar power output during times not getting full, shade fee, sun.

    Anyway--A little math behind my questions about your usage.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Re: converting my van...

    By the way, I have moved to its own thread. It will be easier to keep everything in one place about your project/needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Solar Expert Posts: 9,571 ✭✭✭✭✭
    Re: converting my van...

    While you drive the truck, you could have a chiller compressor running to a freeze plate in the ice boxes. The boating folks use those quite a bit, build a cabinet, foam in the mass and then while the engine runs, you are driving that plate super cold, reliving the load on the electrics. look up Sea Freeze, Sea Frost and Technautics
    How do cold plates work?
    Cold plates are stainless steel tanks mounted inside of refrigeration or freezer units. These plates contain networks of refrigeration tubing surrounded by a low temperature liquid solution that freezes quickly. Our objective is to make sure this solution freezes fast while you have surplus power available. While running your generator or engine for one to two hours a day (heating water, cooking food, charging batteries, etc.), you are simultaneously freezing your cold plates. A good cold plate system will save money normally spent on battery replacements or running your generator needlessly.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Sausage_GuySausage_Guy Registered Users Posts: 4
    Re: Solar Assisted Refrigerated Delivery Truck

    BB: thank you for the long and detailed response. Much food for thought there. I was hoping for such erudite responses when I posted my original article. I signed a bill of sale for the new truck and am about to sink most of my remaining cash into the Mark 2 truck,

    Firstly, my sausages are very fine indeed, and I also carry a few other producer's product. Lots of great artisanal and farm product out there that can't get to market.
    I am mostly using the truck for otr use, have been going to Atlanta and New Orleans regularly for about 6 months now. I'm still going through the math, thanks for laying it out so fine.
    We actually plan to add a 24 volt alternator to the setup providing my mechanic can fit it in, but we are looking at an alternator designed for bulldozers, a lot cheaper than anything with 'marine' in the name. We plan to use it as a backup in case solar and battery give out and plug-in is not available.

    The economics of mobile solar are quite a bit different to land-based solar. This is because gas and diesel are (still) so expensive compared to mains AC. Assuming we take 2 or 3 units of AC at night, it costs less than 50 cents (electricity is cheap here) to run the reefer per day, compared to about 10 gallons of gas for a conventional engine-powered reefer for otr, where the internal combustion power source has to run 24 hours. I assume that the economics of running an alternator would be similar. I estimate I have saved about $1700 over the last 6 months from using the combination of solar and mains AC power, and it would have been more at last year's gas prices. This is esentially because internal combustion engines have an efficiency of less than 20%, the wasted energy disappearing as excess heat in the engine and as friction in the rest of the machinery. It seems to me that the payback period for mobile solar is potentially a lot less than land-based installations.

    I am very conservative with my temperatures. I run my freezers in the 0 to 5 degree range. For complicated reasons to do with Boyle's law, that my refrigeration guy has tried to explain many times, refrigeration equipment actually works harder the higher the temperature. Running at zero requires less energy than 31 degrees. The drive-in freezer at the warehouse runs at minus 3 to minus 10 F, so when we load up the new product is colder than the freezers, and this helps. We also try to minimize opening and closing the freezers. And I never park in the shade :) if possible.

    One of my big worries is a van breakdown. I would have to find a mechanic who would plug the van in while working around. And there is a fullrange of similar headaches.

    If I expect a hard day, rainy with little light, I usually max out the freezers overnight and get them down to minus 10 or so, and then I can get to noon before the freezers take any power. Still, I have had solar give up the ghost in mid-afternoon on really bad days. The upside of this is that it takes up to 6 hours for the zero-degree freezers to get up to where I get worried and I can get 400 miles to a plug-in in that time. The upside to not much solar is that I don't need much cooling either.

    At the same time, in mid-winter, I make sure that I am at a place where I can plug in by 8 PM or so. Sort of a cinderella thing.

    As I did not put my current unit into service until September, I have limited experience of summer, and, as I am reluctant to risk temperature-deviating my stock, I have been plugging it in at night. The system was new at that time, but one night I let the system run off battery power until 7 AM, when it conked out. I was waking up every couple of hours to check it and I was totally knackered the next day, so I have not repeated the test. In mid September I saw the solar panels still generating past 8 PM. It is one of our obectives to have the system run all night on the solar power generated during the day. When I am out of town I stay in hotels where I know I am allowed to plug in at night, or RV parks where they always have power available.

    For the new build, I plan on using 3 inches of closed cell binary polyurethane foam for insulation, with an r-value over 20. This is about 3 times the insulation in our current commercial freezers, so if I do a good job of sealing the door, I'd expect the load to last upwards of 12 hours without any power, during winter.

    Before we built 'Man the Van' mark 1, everyone who we talked to in the reefer business was dubious. Factors in our favor were when we needed most cooling, there was more sun to provide the energy. Also, the thermodynamics dudes neglected what we call the 'parasol effect'. The solar panels on the roof absorb or reflect about 20% of the sun's energy, so the system has less work to do, and this is also the hardest part of the work for a freezer compressor.

    The bad news is that we don't think we can freeze any more than half the space under the solar panels, in the new truck. We'd like to be able to freeze the whole vehicle, but there are numerous applications (e.g. food distributors who have a combination of ambient products like dish detergent and frozen items), where the whole cargo space is not frozen. And our version 3 will be based on a pickup truck, in the style of a slide-in camper top, where there will be extra panel space above. We have efficiencies of about 50% over our mark 1 in the current development, so we might be able to the whole cargo area frozen eventually.

    The major obstacle to widespread adoption of solar for mobile refrigeration are more commercial than technical. Businesses are reluctant to risk possibly millions of dollars of frozen food on an unproven technology. Our aim is to prove that the system is actually more reliable than conventional reefers. As we have three redundant power sources (solar, AC and alternator backup) compared to a single source in a conventional reefer we think that we will be able to prove this actuarily when we have enough data. Making it past the equinox was a major deal for us, when we get to the summer solstice we will be able to complete the data picture.

    You might say we could get the same effect by having more batteries, and, we agree, that would probably be cheaper for hardware on the front end. But if we charged up on mains power, we're using fossil fuel in coal-burning power stations, and solar is renewable and free. We believe the investment in free solar, leveraged by the excess cost of energy from portable gasoline or diesel, will pay off short term.

    The not-directly-economic consequences are also considerable in my business. Basically, solar is cool. I have pulled up at a restaurant, within a few minutes the entire kitchen staff were having the van tour, and the chef was ordering sausages before he even tasted them. I have tripled my business with the help of 'Man the Van' which is the main reason why I need to build a bigger van so soon. Doubtless, if solar powered reefers were more common, the 'wow' effect would diminish, but this generation of chefs, especially the farm-to-table guys actually like the idea that their ingredients have had renewable inputs, and this includes the logistics of getting it from the farm into the kitchen.

    We are in an industry that appreciates green stuff and understands sustainability and the husbanding of resources, and they think about their carbon foodprint.

    By the way, conventional reefers are expensive to maintain, requiring specialized factory service every 1000 to 3000 hours. As you know, solar panels last 25 years without service, all you'd have to do with a solar reefer is replace the batteries every few years. Our current prototype, based on a used Ford Econoline, cost about 10K to convert, about a third the cost of a conventional reefer conversion. Cheaper to build, maintain and run. I am a businessman, I respond to bottom line considerations, and that is why I am investing in mark 2 less than 6 months after mark 1. I want more of the same. Even though it has been frustrating and even scary at times :) My customers call me the mad sausage scientist.

    Finally, next time you roll on the slab, look at all those 18-wheeler reefers in the slow lane. Each of them uses up to 40 gallons of diesel per day keeping the load frozen. Wouldn't it be cool if, in 20 years or so, they were all running on a roof-full of solar panels? We think it's possible and we plan to market our mark 3 version to micro food distributors.

    Bill, thank you for all the info. I am digesting the math and it is very helpful. I had forgotten about the inductive surge from a DC motor being much less than AC. One of our freezers was losing a lot to excessive firing up. And apologies for the wrong units, I should know better than that.

    By the way, I love your forum. I found the definitive answer to one of our most vexatious problems, a succession of busted AC chargers, and there is a wealth of other info in there. A wonderful resource, you are doing good work curating it.

    Attachment not found.

    Here's a pic of Man the Van mark 1, parked at a hotel in Atlanta on one of its early road trips. Anyone know of another commercial, road-going solar powered reefer? I am claiming to be the first and no-one has been able to contradict me. Man the Van 1 has complete 20,000 miles OTR and not temperature-deviated a single sausage. Mark 2 will be better.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Solar Assisted Refrigerated Delivery Truck

    Have a read of this article... It's not what I was after as there is a commercially made fiberglass cab-over model that is plentiful up here in BC, just cant remember the name right now. Lots of technical info in the article that may help...http://www.for.gov.bc.ca/hfd/pubs/Docs/Frr/Frr123.pdf

    aslo this article on a solar powered 'bus' might give you some ideas. Note the size of his array closely... 10 panels...http://www.bostonmagazine.com/news/blog/2014/11/14/vecna-cto-solar-powered-vw-bus/
     
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  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Re: Solar Assisted Refrigerated Delivery Truck

    Watt and Watt*Hours---It is a very common mistake--Made that many times myself even after years of doing this:
    • Watts ~ Miles per Hour (a "rate" of usage vs time)
    • Watt*Hours ~ Miles Driven (an "amount" used/driven/etc.)
    • Volts * Amps = Watts
    • Volts * Amps * Hours = Watt*Hours
    • Amps
    • Amps * Hours = Amp*Hours
    So--it is sort of "reverse" of the units we are are used to.

    Three things to focus on...

    1) Insulation--It is obviously a choice between between thickness (and cost) insulation, and available cargo volume... More insulation, less cubic feet available for paying load.

    2) Efficiency of the Compressor system... There are losses in any system... Belt drive from an electric/diesel motor, vs a diesel electric generator and electric compressor... Conversion from 12/24/48 volt battery bus to electric motor power, etc. A company that specializes in truck refrigeration systems would be much better than I at estimating the cost/energy consumption of different solutions.

    3) Choice of fuel/energy sources/etc. (using grid for over night/truck stop and 460 VAC refer AC bus), vs XX VDC battery bus (and losses of the batteries from 80-98% efficiency, 80-90% AC to DC battery charging eff, 85% DC to AC inverter efficiency, etc... One of the big killers for off grid solar is the conversion losses easily add up to ~52% overall efficiency (typical worst case)... You can get 10%-20% improvement--But it does come at a cost.

    You spoke of using 40 Gallons of Diesel per day for a Refer truck... It looks like there are those that do ~10-30 gallons per day--But that probably depends on load temperature (36F vs 0F) and outdoor temperatures.

    Just to pick a point for some back of the envelope calculations... A 15 GPD Diesel can generate pretty easily:

    7 kWH per gallon of diesel * 15 gallons of diesel per day = 105 kWH er day

    A pure off grid system, using typical worst case numbers, would need:

    105,000 WH per day * 1/1,000 WH per sqmeter * 1/0.18 solar panel eff * 1/0.52 system eff * 1/5 hours of sun per day = 224 sq meters of solar panel
    117 sq meter * 10.7639 ft per meter = 12,411 sq feet
    1,259 sq ft / 9 foot wide trailer = 268 feet of trailer roof worth of solar panels

    Assuming that is a 40 to 80 foot Refer????

    So--From an order of magnitude issue, it would appear that we need a much more efficient refrigeration compressor+cold space insulation to even begin to power the refer from solar panels. And if you an improve the compressor/cold space efficiency--Then the diesel costs would go down too by a similar amount.

    Anyway--I think the math is approximately correct. And what would be helpful is "accurate" estimate of power needs. Once we have that, we can be a bit more helpful in designing a system with solar assist and estimate how much help it would be.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Sausage_GuySausage_Guy Registered Users Posts: 4
    Bill: we're making various efficiencies over our prototype. One is using 24 volt everything and DC compressors and fans to eliminate inverter conversion loss, which we agree is vital. We're going to use 3 inches of polyurethane closed cell foam with an r-value around 20. And running as cold as possible, less than zero, also makes the refrigeration more efficient. We are in the process of building the refrigeration unit and we will get some consumption estimates soon. We also managed to squeeze in 60 extra watts on the roof by going from 5 X 325 watt panels to 6 285 watt panels, and we are carefully planning our cable runs to minimize loss, with triple zero gauge, 6 gauge and 10 gauge wires throughout and careful layout of components. Our take on conventional reefer tech is that it is basically 1950s technology and can be more efficient. We also have a lot of operational experience with our current van. Our new truck is much lower than an 18 wheeler and we are only refrigerating half the space, so we have reduced the whole-trailer freezing problem to about 30% the size. We are willing to cheat by superfreezing at night off AC, having a second cascaded compressor and having an alternator assist as needed, and Ed, our refrigeration expert thinks it is doable.
  • BB.BB. Super Moderators, Administrators Posts: 32,601 admin
    Sounds like a plan SG. The "hard part" is the refrigeration, insulation, and high efficiency. The easy part is to plug in the numbers for XYZ Solar + Batteries = Power generated.

    I undestand that Inverters are something you want to get away from... However, the average inverter is 85% or better efficient. And a DC refrigeration compressor already (most likely) has an internal inverter anyway (look up VFD or variable frequency drive).

    Try several paper designs first--Don't make any design choices until you have looked at the overall picture. It can surprise you.

    Having a good refer guy is going to be worth his weight in diesel! I will be very interested to see his designs as they go forward.

    Off grid Air Conditioning is a close second to Refrigerators and Well Pumps. Pretty close to what you are doing--Just doing it mobile.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Sausage_GuySausage_Guy Registered Users Posts: 4
    BB. wrote: »
    Re: Solar Assisted Refrigerated Delivery Truck

    Watt and Watt*Hours---It is a very common mistake--Made that many times myself even after years of doing this:
    • Watts ~ Miles per Hour (a "rate" of usage vs time)
    • Watt*Hours ~ Miles Driven (an "amount" used/driven/etc.)
    • Volts * Amps = Watts
    • Volts * Amps * Hours = Watt*Hours
    • Amps
    • Amps * Hours = Amp*Hours

    So--it is sort of "reverse" of the units we are are used to.

    Three things to focus on...

    1) Insulation--It is obviously a choice between between thickness (and cost) insulation, and available cargo volume... More insulation, less cubic feet available for paying load.

    2) Efficiency of the Compressor system... There are losses in any system... Belt drive from an electric/diesel motor, vs a diesel electric generator and electric compressor... Conversion from 12/24/48 volt battery bus to electric motor power, etc. A company that specializes in truck refrigeration systems would be much better than I at estimating the cost/energy consumption of different solutions.

    3) Choice of fuel/energy sources/etc. (using grid for over night/truck stop and 460 VAC refer AC bus), vs XX VDC battery bus (and losses of the batteries from 80-98% efficiency, 80-90% AC to DC battery charging eff, 85% DC to AC inverter efficiency, etc... One of the big killers for off grid solar is the conversion losses easily add up to ~52% overall efficiency (typical worst case)... You can get 10%-20% improvement--But it does come at a cost.

    You spoke of using 40 Gallons of Diesel per day for a Refer truck... It looks like there are those that do ~10-30 gallons per day--But that probably depends on load temperature (36F vs 0F) and outdoor temperatures.

    Just to pick a point for some back of the envelope calculations... A 15 GPD Diesel can generate pretty easily:

    7 kWH per gallon of diesel * 15 gallons of diesel per day = 105 kWH er day

    A pure off grid system, using typical worst case numbers, would need:

    105,000 WH per day * 1/1,000 WH per sqmeter * 1/0.18 solar panel eff * 1/0.52 system eff * 1/5 hours of sun per day = 224 sq meters of solar panel
    117 sq meter * 10.7639 ft per meter = 12,411 sq feet
    1,259 sq ft / 9 foot wide trailer = 268 feet of trailer roof worth of solar panels

    Assuming that is a 40 to 80 foot Refer????

    So--From an order of magnitude issue, it would appear that we need a much more efficient refrigeration compressor+cold space insulation to even begin to power the refer from solar panels. And if you an improve the compressor/cold space efficiency--Then the diesel costs would go down too by a similar amount.

    Anyway--I think the math is approximately correct. And what would be helpful is "accurate" estimate of power needs. Once we have that, we can be a bit more helpful in designing a system with solar assist and estimate how much help it would be.

    -Bill

    I agree, and we will need much more efficiencies to freeze an 18 wheeler. On reviewing the efficiency figures for various types of reefers, it seems that the 18 wheeler fleet is pretty efficient as these things go. But at the smaller end of the market - like the engine driven Thermo King V300 which is seen on panel vans like my (mark 1) Econoline I figure they use 4.5 gallons of gas (using their figures) for a 7-hour daily cycle - like a local delivery route, plus a half-gallon per hour when idling, probably three more hours per day, plus some more during the compressor duty cycle during the idle time. The idle time would be when the driver gets lunch or is parked at a customer unloading. These reefers are especially inefficient when the doors are open because the cold falls out the door. For a 10-hour day, assuming the reefer is either empty or plugged in the remaining 14 hours, probably about 7 gallons. But if you are on the road, the extra 14 hours idle time will cost another 7 gallons, plus extra used during the duty cycle - the 16 or 17 gallons per day means that the system is awful inefficient and expensive to run. If 18-wheeler performance was equalled, it would be closer to a gallon or two. We think this is because of design decisions made for build economy and operational convenience. Smaller box reefers and panel vans will be our initial target market. Food distributors typically run a mixed configuration with freezers and ambient cargo anyway. Also, there are no moving parts in solar power generation and the conventional reefers need a lot of maintenance.

    After chewing on your previous advice, we added another 200 AH of sealed lead acid batteries to our Mark 1 solar reefer and got a huge qualitative jump in performance. It is basically turnkey now - even in days of constant rain it will reliably run until midnight, whereas before it needed constant on the road tweaking. In fact, today, on a sunny South Louisiana run our solar controller hit 29 volts and went into an overvoltage mode around midday, and it did not turn on again until about 4 PM when the voltage went under 25, with the battery bank indicating over 90% charged. Never seen so many bars on the battery icon on our Renogy meter. We are now figuring out how to harvest this lost energy, we are thinking of running the freezer down to a very low temperature, maybe -30 or so, when the battery voltage gets near 29, and storing the excess that way. Or some way of running the voltage under 29 and 'resetting' the controller so it forgets it was in overvoltage mode. Or more batteries. Given the 71% additional panels we have on the new truck, and our unit only needing about 30% more power, we think that energy budget on the new truck won't be much of a problem. In April, for a theoretical maximum of 42 amps (1000W @ 24V) I have been seeing long periods of over 30 amps being generated in the hours around midday, and amperages in the teens for multi-hour extended periods. We made it through the winter and it looks like summer will be a breeze.

    We are very disenchanted with the binary closed cell propylene spray foam insulation. It is a dog to work with, highly toxic in application and awful hard to trim even with the studs, and expensive. We think next time we will get 4 X 8 X 3/4" closed cell foam panels and laminate them into the freezer walls to a depth of 3 3/4 inches, stud depth. Probably build the freezer panels outside the truck and assemble them later. The insulation held us up for weeks, we only recently got that done. Aerogel would be very nice but probably cost prohibitive. Just buying the foam in this form at the local hardware store would also be about half the cost and a lot less work. Chalk that one down to experience.

    At this point we have a bunch of sub-assemblies to install to complete the build and we have 4 guys lined up to get it finished next week. Then we'll be able to charge the refrigerant lines and power it up.

    You are also right about the compressor having a sort of inverter in it, but best we can tell from the schematics, this is for control purposes and it only 'inverts' a small amount of the available energy. The compressor itself seems to run at 24 volts DC. We'll be able to find out more when we power things up.

    Fascinated by Tesla's still upcoming announcement of solar batteries. We don't have good numbers, but at the quoted $300 per KWh it still seems about twice as expensive as regular lead acid. We paid about 750 for 450 AH (at 12V) batteries, the equivalent Teslas would seem to cost $1500. Of course, for mobile the weight savings might be worth the extra dough, but Elon will have to come up with a raft of reasons for land based users, who basically don't care about the weight, to shell out the extra. My take on the Tesla is that it might well be Tesla marketing their batteries for solar use just to get the volume up and avail of economies of scale. You can already get cheap Li Ion batteries from China if you want to hassle with Ali Baba and wait 3 months to get them shipped on a slow boat from China.. We didn't, and we were also unsure of their performance and quality. I think Elon was banking on a breakthrough technology for his batteries and despite research on Li Ion Phosphate and Li with metal air, I think they concluded that they will have to open up with basically regular Li Ion and have to find some way to compete with the Chinese. So we are not holding our breath waiting for Musk's big announcement but wll be looking at things like weight savings, performance and battery life after the announcement.
    We are also concerned about the recyclability of Li Ion. This is still problematic, but lead acid batteries in the US are completely recycled, lead, acid and plastic. We are not sure that Li Ion is actually better for the environment, and when you factor in the energy used in its manufacture and shipping it all over the universe from mine to refinery to processor, maybe lead acid is still a contendor. Until we get a real breakthrough in the technology at least, notwithstanding what Elon and his crew would have us think.
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    re
    Until we get a real breakthrough in the technology at least, notwithstanding what Elon and his crew would have us think.

    Like most technologies, a 'teething period' is needed and we haven't gone through that yet, maybe in another 5 - 10 years... the Kitty Hawk comes to mind, yes it did fly but not for long...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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