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Solar Panels And Inverter For Off Grid.

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Good morning folks,


I am planning an off grid excursion to a CCC meet next week and i need some solar advice,


What i have at the moment is an 80w roof mounted panel which is really only there for battery top up over winter months, I also have 150w freestanding panels and a 2. 5kw to 5. 0kw pure sinewave inverter and a spare 115ah battery.


My plan is to set up the freestanding panels to the battery and inverter and then take 230v from the inverter as required via the two 3 pin sockets as and when required.


My fridge and hot water would then need to be run on gas and my lighting would be from the leisure battery.


My big question is. ..................


Could i use the 3 pin outlet from the inverter and plug it direct to the van ( as if it were fed from a site bollard )????


My thinking is that then my 230v system in the van would be live and so would feed the fridge and be used for a spot of tv and maybe even supply the hot water too.


Does this set up sound good or bad? All the relevant cables on the inverter are of the correct spec i believe and has an 80a inline fuse between the battery and the inverter.


Any advice on this would be very much appreciated,

BMW X5 followed by a 2014 Lunar Delta RS

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I did suspect a drop in efficiency to be honest, I was more worried about any potential damage being caused to the van wiring.

BMW X5 followed by a 2014 Lunar Delta RS

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I can't see there being a problem with the 230v van wiring because it's protected by MCBs and you say the inverter is pure sine wave, so no nasty spikes, and it's quite powerful.


The issue will be with your water heater, in terms of running the battery down.


A 1 kw water heater uses 1000 watthours per hour.

Your 230 watt solar panels will produce upto 1500 watthours per day at this time of year, so leaving aside the losses in the inverter this will give upto 1. 5 hours use of the water heater per day, but there will be other demands like lighting, fridge, TV, water pump etc.

The 115Ah battery stores 1380 watthours of energy (115 x 12v) but you don't discharge this below 50% so you have 690 watthours available for the duration of the stay, which isn't much. You might want to consider turning off the battery charger because this intoduces more energy losses.


A useful reference is http://www. campingandcaravanningclub. co. uk/helpandadvice/technicalhelp/power/solar-power/

Land Rover is now back towing.

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When you explain it like that it makes sense, I think the tv and phone chargers etc will be enough for the inverter, Fridge and hot water will be run on gas, Lighting will run off the leisure battery.


Thank you for your input.

BMW X5 followed by a 2014 Lunar Delta RS

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We use a 12 v TV . ....... Lots of flat screen TV's are actually 12 v they just come with a lead with a transformer to plug in to the 240 mains. We just plug ours into the 12 v supply instead using an appropriate lead it. Works fine.


We have an 80W portable solar panel ( a 2 x 40W suitcase affair) and use gas for the fridge and hot water.

2007 Bailey Series 5 Senator Arizona (4 berth, rear bathroom, side dinette) towed by a 57 Kia Sorento XS Auto with Kumho KL17 tyres, Reich Mover, Kampa Rally 390, Caravan Tyres : GT Radial Maxmiler CX 185/80 R14 102R.


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Water & Heating & Fridge on Gas.


You are OK to plug the caravan into the inverter, however, the caravan electronics will try and use that mains feed to attempt to charge the internal caravan battery, so some of your power will be inefficiently being used to do that.


If you want the convenience of the van mains systems, sockets etc, then I would plug the caravan into the inverter tactically - IE when you want to use something on mains in the caravan, such as the TV or microwave. When finished I would switch the inverter off.


I would advise against simply plugging the van into the inverter and leaving the van mains feed on 24hrs.




Edited by SteveMilner

Olympus II 620-6 & Mitsubishi Shogun

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I feel you are heading for a big disappointment in that the inverter you have is way out of sync with your battery storage capacity.

This does not mean it will not work but only for the briefest of time.

An inverter of the size you have will IMO have quite a heavy "quiescent load" [ie parasitic load it drains simply before doing anything], so watching TV that in itself might need 30 odd Watts could be pulling much more from the battery. If the TV is an AC unit requiring an inverter then the inverter should be sized for the job not, not 80 to 100 times over-sized.


The 115 Ah battery is usable for about 50% of its rated capacity when new and fit, so let us say 58 Ah worth. That at 12. 6 volts equates to 0. 731 kW hour. Not a lot there to be clapping a 2. 5 plus kW device onto.


Solar is fine but not for the high loads like running fridges and heating water; for the TV get the right sized inverter.

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What you want to do is reasonable but inefficient. However, you seem to be overestimating what the solar panel and battery can do by quite a margin.


Keep the fridge and heating on gas, TV and phone chargers on 12v, and all should work. Keep inverter use to the bare minimum, turning it off when not in use, do not try to charge the battery from the inverter.

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As others have said, use gas for water heating and fridge, any heating is best on gas where possible when using battery power and not EHU.


Your solar panels seem the right size for your 12v usage, lights, pump, chargers, and even a smaller TV inverter as has been mentioned.


A 5kW peak inverter must be a bit of a beast and if it was 100% efficient would take a battery killing 416A at full load, you say the cables are correct spec and include a 80A fuse, well 80A @ 12V is only 960W of power !, If its a 24V inverter, its still not even 2kW. 400A cables would be very thick and heavy. Definitely think about a smaller inverter :)


There is nothing wrong with feeding the inverter output mains into the caravan 230VAC 16A input though, just isolate if you can the battery charger and don't use the water heater and fridge etc on mains.


I have 300W of solar on the roof and I can add a 1. 5kW pure sine inverter and extra battery, if on a stay I want AC for the microwave and hairdryer. To do this I connect the inverter and extra battery with 16mm2 cables and a anderson connector to the van batt and then they live beneath the existing van batt housing in a Kampa 'storage' draught skirt storage pod, the battery parallel link cable and mains cable are short and I plug mains into the normal caravan 16A input. In the van fusebox I open the breaker that feeds the charger, fire, fridge and water heater leaving just the sockets powered. The inverter is remotely switched on when AC is needed.

2007 Bailey Ranger 620/6

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if you do go a head with this id recommend a second battery in parallel to share the load. Id also turn the inverter off what your not using it as it will empty the battery even without a draw.

2010 Lunar Delta Ti pulled by a 2012 Volvo XC60 D3 AWD remapped to 210bhp & 501Nm

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