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Forum Index : Solar : Caravan Solar System
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Dinosaur Guru  Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All I am evaluating what system to put on our Caravan roof. It is 5650 x 2300, although the area where I want to put the panels is 1500 x 2300. After looking at the possible usage, I decided to stick completely with 12vdc, and not use an Inverter for 240vac. The lights are all led, the fridge is a 15 Amp 12 vdc when it is cooling. Even the telly is 12 vdc. Intending to put 2 x 70ah deep cycle batteries (cause I already have two new ones), and looking at 3 x 200 Watt panels. Cost per Watt is about $1.80 On the Caravanners forum there is heated debate (and I mean heated) http://caravanersforum.com/viewtopic.php?f=2&t=20693 about the merits of a 24 vdc system with pwm system or mppt. There is a document published by the manufacturer http://www.morningstarcorp.com/en/support/item.cfm?ItemId=42 6 that discusses the merits of their system. Graphs in that document appear to support a panel with a 13 Vmp if you are charging a 12 volt battery system.I can appreciate that with 24vdc, the cable sizes can be smaller, but if that is the only benefit then I am steering towards 13Vmp panels and a pwm controller. I also want to use a pic such as the Maximite to constantly record currents of each device, and current from the panels.Saving these in an Excel format for graphing. But the reason for posting is that need a wider opinion on the merits of such a system. Any comments appreciated. Regards Regards Hervey Bay Qld. |
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norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
I`d go with the voltage that your vehicle is, you state your refrigerator draws 15amp whilst cooling. I assume you are using a 3way fridge, thus a 12v electric element powers the unit whilst on battery. I suggest you upgrade to a 12v/24v compressor driven refrigerator this will cut your draw for refrigeration by more than 2 thirds or below 5amp (12v) whilst operating. By doing this the area you have for panels will give sufficient power under sunny conditions even allowing for some clouds and you`ll have colder beer. By keeping the system at same voltage as vehicle you can also be charging whilst underway without too much electronics. PWM or MPPT on a caravan system, there would be little difference on a system of this size(my opinion) and that comment will probably be contested on this forum too. There are many agruements for MPPT but the gain would not be significient enough to warrant the extra cost nor the added complexity thus the reliability. We come from the land downunder. Vic |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All Vic, after just having paid $37k for the van, I am not about to throw the fridge. Having said that, I have no idea what a replacement fridge would cost. However, I noted that the fridge does not use a thermostat when on 12vdc, in other words, it draws 15 amps 24/7. But on 240 vac it uses the thermostat, so it may be worth adding a small inverter to run it of 240vac. At least it will cut out when at temp, and the savings in amps should more then offset the conversion losses in the inverter. Regards Regards Hervey Bay Qld. |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Can understand your reluctance there but if your travelling into Northern Aussie, you`ll appreciate the ability of compressor driven refrigeration to keep foodstuff colder. If you go the way of using an inverter perhaps a 240v fridge would be the answer, they are much cheaper than their 12/24v cousins. But they will consume more power but still no where near the consumption of your existing fridge. Seems like I`ve added to your evaluation rather than helped, that is the nature of solar. Get it right and you`ll have no dramas, wrong and plenty of dramas. We come from the land downunder. Vic |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All Vic, it is all about getting my eyes opened. I have decided to buy a cheap power meter, and connect the fridge through it. Then whilst I am on the grid, evaluate with actual kwh figures what it is going to take. Then I can convert to dc amps and see if I am any better off. I have googled standard fridges and $500 gets you a reasonable unit.(that will fit in the hole) Regards Regards Hervey Bay Qld. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
dinosaur, I can give you a ballpark figure for comparison, the midsized danfoss compressor (not the new variable speed ones) chews 5.2 Amps when it first starts then settles down to 3.5 Amps at 12 volts. on a 290 litre fridge/freezer it runs for 10 hours a day freezer -20C fridge 3.5C to 5.6C, so this fridge draws 220 watts overnight . It uses exactly the same 12/24/240V controller as the little car fridges. On the subject of panels I am not sure you will find a 12volt 200watt panel,its probably two smaller panels paired on a frame. a 12v panel should have a Vmp around 17V to 22V. All 200w panels I have seen are 24 volt ones these have a Vmp of 35v to 45v. you wont be able to use a Pulse Width Modulation controller with 24 Volt panels and have a 12v battery bank. You must match the panels voltage to the batteries. there are some MPPT controllers that reduce higher voltage to lower but the conversion losses down to 12 volt are significant and if you drive them hard the mosfets get warm. i would say you could lose 10 -15% on a < 500Watt system. I good quality 30 amp PWM controller with a monthly battery equalisation setting and 400watts of panel would give you heaps of margin, I use the prostar 30, seems OK. 15 Amps at 12.6 volts for 24 hours is 4.5 KW, you only have 800 watts of available battery storage (50%)before damage starts, it will need some real creative thinking to get the existing fridge to work. run it with a timer perhaps??? gas??? hope this helps yahoo I'm confused, no wait... maybe I'm not... |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All Yahoo, many thanks for your response. The figures you showed is the reason why I want to run this fridge on 240vac as a trial. It is a three way fridge, so gas is an option, but not sure what the cost would be. Because the thermostat is in the circuit on 240vac, it should cut in /out as it reaches temp. This means less power then on 12 vdc. You are right about the panels, I was looking at the 24v ones, so the closest for 12 v is 120 Watt. The cost of replacing the fridge with a compressor fridge is prohibitive, as I am already adding close to $1500 for panels and controller. Regards Regards Hervey Bay Qld. |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
The newer Danfoss compressors(2 sizes) are even more efficient and as Yahoo says has the advantage of variable speed. It is the way to go if operating with solar although costly. Should have fridgies down your way that can replace the 240v comp with a Danfoss, find one that specialises in low voltage and insist on having a small cooling fan placed in compressor compartment in such away its air flow "pulls" the air across the compressor "blowing" through the condenser before it exits outside through the existing vents on the caravan. My Prostar(late 80`s vintage) served us well in our travels, just check with the newer version they have voltage,amperage etc readouts and perhaps there is one out there does logging. The Dingo from Plasmatronics(MPPT) has logging and is built with caravans in mind and may be the way to go. Anyhow Happy Caravanning Just read your reply to Yahoo, the thermostat on 240v will very seldom cycle in our warm climates. Absorption refrigeration has its uses but does not align to well with solar. We come from the land downunder. Vic |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Yeah, that's the problem there is no compressor its an ammonia loop and a heater like the old KERO fridge, just without the soot. From memory the large house gas fridges get more than 4 months from a 45 Kg bottle, I think you should do 4 weeks from a 9Kg LP bottle, about 0.3 kg per day, thats less than $1 per day. If you supplement that with a bit of 240 Vac when you can get it, it works out fairly cheap and there is no large capital outlay up front. NB disregard my monthly equalization recommendation if you don't have wet lead acid batteries, I just assumed. Its all about cold beer, frozen schnitzels, full batteries and no stress. How you get there doesn't really matter as long as it works  I'm confused, no wait... maybe I'm not... |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Have a small 3way fridge(one taken from caravan) in a fishing hut used to keep mainly vegetables cool, it consumes around the 1 lb of gas (20days from a 20lb cylinder)a day, same ballpark figure as Yahoo`s. I do not knock absorption refrigeration, it has its applications. Just feel without taking capital costs into too much consideration, low voltage compressors(chiefly Danfoss) are the way to go when considering solar powering caravans. In household solar systems 240v seems currently the way to go, initially it wasn`t in solars infant days, and solar is probably only just starting to get its teeth. Keep us posted Dinosaur, am interested to see how it pans out for you, enjoy travelling Aussie it is a magic experience. As Yahoo says its about cold beer etc and low hastle. We come from the land downunder. Vic |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
If it's a brand new van and the fridge hasn't been used the builder may consider a swap for a smallish fee, if you tell them you made a mistake and apply large amounts of charm. 
I think the 12v circuit on the absorption fridge is a bit of a bodge job its only meant for running from the alternator while your driving, even then that silicon chip latching relay here may be needed to stop the power hungry thing killing the batteries. I went to a yard auction for a caravan re-fitter last month, there were 5 very new looking absorption fridges sold, I bet they replaced them with compressor models. Vic, I totally agree with you observation on 240 Volt but I wonder if that is more a lack of choice available. I have looked hard for the new Elcold and Vestfrost freezer models in Oz without a lot of luck so far. the vestfrost SW 321C is a 240 Volt 300 litre chest freezer rated at 550 watt-hrs/day. surprise, surprise, its driven by a low voltage variable speed danfoss compressor, I haven't found any genuine 240 compressor models under 1Kwh/day..... yet. I'm trying to think of something witty and entertaining to end this post with but I got nuthin! cheers yahoo I'm confused, no wait... maybe I'm not... |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All Taken your advise and shopped around for 12 Fridges. Best I can find (for the size we need) is a HDC-161 Weaco So I added up my wattages and have some questions. Wattages: Fridge 2.2Ah/h what does that mean ? 2.2 Amps x 12 vdc = 26.4 Watt Manufacturer claims 38% duty cycle for above 32 degree C Ambient. So my list Fridge 242 Watt = 38% of 24 Hrs Fridge Fan 34 Watt = 100 % of 24 Hrs (1.4 Watt = 56m3 /Hr @ 29db) Lights 42 Watt = 5 Hrs / 24 Hrs (4 x 2.1 Watt) TV 122 Watt = 3.5 Hrs/24 Hrs (35 Watt TV) Water Pump 30 Watt = 0.35 Hrs /24 Hrs (84 Watt x 20 Min) ??? Total = 470 Watt Cooking / Hot Water is Gas, and washing machine / Micro wave will work only when generator is run ie: max 1 Hr per day every 3 or so days only. Amongs you solar guru's what solar panel capacity do I need, and have I calculated it correctly ? Regards EDIT: Just had a call back from Fridge manufacturer and it appears that the fridge draws 2.2 Amps averaged over a whole day at + 32 degree ambient. So will adjust the calcs. Regards Hervey Bay Qld. |
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| Barry T Coles Senior Member  Joined: 30/07/2009 Location: AustraliaPosts: 109 |
Hi Dinosaur I think youl be pretty happy with the perfomance of the Weaco. I've got the 35 litre one & can run that in freezer mode overnight on the car battery (about 14 hours) & still have no problems starting the car in the morning. The overnight temp would never get below 20 deg C at the time of the year when we are travelling. Cheers Barry I need to learn from the mistakes of others. I dont have the time to make them all myself. |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
I assume the 2.2Ah/h is 2.2 amp/hr that figure would be already taking into account the 38% duty cycle. Better to work with an average current draw of 5 amps a duty cycle of at least 50%. That gives us 5ampsx12voltsx12hours(50%of 24hr)=720watthrs. Now a 200watt cell with say a 8hr sunny day will give you around 200x5=1000watthrs. The 5 is a ballpark figure I`ve found to be approx spot on.(that`ll get a giggle from the purests). If you wish to save a little, start with 200watt of panels ,with 400watt ample, with a generator as back up on the days the TV programs are tops and you go over your allocated hours use, especially with all those microwave TV meals. Main thing is you`ll have cold beer and a magic time, look I`m getting envious chuck me in and I`ll ensure the system works A1, change your tyres, get the firewood and keep the fridge loaded. 
You will not need the fridge fan as the Waeco has a fan forced condenser,and no I`m not sponsered by Danfoss but they just are the BEST. Whoops Barry got in while I was writing scared the Irish out of me. 
We come from the land downunder. Vic |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All look I`m getting envious chuck me in and I`ll ensure the system works A1, change your tyres, get the firewood and keep the fridge loaded. As long as you are prepared to sleep on the mat outside the door. 
I have been looking at my weights as well, and have concluded that 4 x 120Watt panels will give me insurance for weeks of cloudy weather.They weigh 15kg each, so that is 60kg. That is also 4 x 6.67 = 26 Amps. Any suggestions on a suitable controller ? I thought the Dingo was a bit expensive. Regards Regards Hervey Bay Qld. |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
The Dingo does seem a little pricey, but remember it has logging. Personally I`ve never used a Plasmatronic product but they have a good name. The Prostar worked around OZ twice for me and is still a goer, the newer models have digital readouts. My solar household uses a Outback, American made but I don`t believe they make any for mobile use. Too many options but half the fun`s researching and purchasing. I`ll supply me own mat even We come from the land downunder. Vic |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I would have a look at the GSL30A Programmable MPPT Solar Charger, Rockby have it for $390 then you can use the cheaper 24v or grid panels. They have a cheaper model but I don't think it does gel or agm ??. They also have a remote lcd panel option if you want it later. I haven't installed one so  
I cant do serious calculations with the image of norcold ocky-strapping his favorite jason recliner to your roof rack. You will have to give me some time on that. I'm confused, no wait... maybe I'm not... |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All Yahoo2 you have raised an issue which was hotly debated on the caravanners Forum. It is the issue of efficiency, when using 24 v panels with a MPPT controller to charge a 12 vdc battery system. From all the hot headedness  I still havent made up my mind if there is an issue.
That is the sad thing about some forum's, ego's are sometimes the driving force and not facts. Ideally I would put 24 v panels in. Regards Regards Hervey Bay Qld. |
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| norcold Guru Joined: 06/02/2011 Location: AustraliaPosts: 670 |
Dinosaur, I`m probably a bit ancient in regards to any debate about PWM vs MPPT on caravans it is usual to have the panels flat or near so with the pitch of the roof. Inefficiency here, so add an extra panel, no issue really. When I started out they were $20 /watt now getting close to $1/watt. Just add another panel and enjoy. Yahoo2 probably didn`t notice that on the left side of that recliner was a hidden door that revealed a little drink fridge. So I`m hoping you`ll go with the extra panel and I`ll sneak a little wiring in when your elsewhere. Anyhow there`s room up here for 2 Recliners Yahoo2. We come from the land downunder. Vic |
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| Dinosaur Guru Joined: 12/08/2011 Location: AustraliaPosts: 311 |
Hi All Thanks for the advise, sounds like you guys need to get away and enjoy the outdoors a bit. Personally we are winding up our company by June and hitting the road for at least 18 months. So have till June to get all the bits fitted and a few test runs. Regards Regards Hervey Bay Qld. |
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