Post by Mike Harding on Oct 24, 2024 12:33:45 GMT 10
24th October 2024
An overview of my caravan solar system, installed one year ago.
My system is rather different to how these things are normally done because I wanted a 24 or 48 volt system rather than the usual 12 volt. Most modern caravan solar systems are simply upgrades from the original lead acid battery to a lithium battery and more solar panels on the roof and maybe replacement of the solar controller. This is, sort of, OK and usually works well enough for caravan holidays but will struggle for long off-grid trips into forested areas or in winter with a run of poor weather.
A big problem is that 12 volts (12V) is a terrible choice for caravan power and is only used today for historical reasons and the reality that virtually all caravan accessories are 12V.
A quick, basic lesson about electricity:
Current (in amps) = power divided by voltage so if we have a light globe in our 12V caravan which is rated as 24 watts it requires 24W / 12V = 2 amps. And if we have a microwave rated at 1200W it will require 100A which is a lot of current. However if we increase the supply voltage to 24V we'll only need 50A for that microwave. For technical reasons the lower we can make the current in our caravan system the better it will work and the more reliable it will be. And, frankly, with the significant currents needed at 12V for large appliances I get a little worried by the fire risk.
As my caravan is natively 12V the prospect of changing the entire van to 24V did not appeal, it would be a significant and expensive task. Instead what I decided was to run the whole van from 240V just as I would in a caravan park but in this case the 240V was to originate from a lithium battery pack.
Thus my system comprises eight 202Ah lithium (LiFePO4) cells in series to produce about 25V, these feed a 2kW 24V to 240V inverter and the output from the inverter plugs into the mains input on the outside of my van, as would be the case in a caravan park. A further advantage to doing this is I can easily swap the van from the battery to a generator or mains.
In addition a Victron 100V/30A MPPT solar controller takes an input from four 200W free-standing solar panels and converts that to 24V in order to charge the lithium cells (battery). The system is protected by a 65A circuit breaker. A Victron SmartShunt provides Bluetooth information regarding what the system is doing - as does the MPPT controller.
The solar panels are wired series/parallel - ie. two panels in series produce about 80V at 5A and the other two panels are also wired in series then the two pairs are connected in parallel at the caravan thus producing about 80V at 10A or 800W. In practice I've never seen them produce more than 700W. Wiring the panels this way has the significant advantage that I can use long leads (so low power loss in the cables) to position the panels and minimise tree shade. Each solar panel is about 1500mm x 800mm and weighs 15kg. I have made simple legs for them from rectangular aluminium tube, each leg has three holes in order the panel angle may be varied to suit the time of year and/or geographical location - this is worth about 11% extra sun energy.
In effect all I have done is create a battery pack charged by solar and connected to an inverter to produce 240V. Such an item could be used to provide power or emergency power in any situation. The cells (see picture) are located directly over the caravan axle which is ideal. The solar controller and inverter are located under the bench seat and require about 1m of cable from the battery thus minimising power loss as this is the only cable with high current.
In regard to the photograph of the cells:
The large red item at the bottom is the battery management system (BMS) which ensures the lithium cells are kept within their electrical tolerances.
The thing with the two gold blocks and two black wires is the Victron SmartShunt.
The orange box to its right is the cell balancer.
The 65A circuit breaker is just peaking out to the right of the vertical white batten.
-----
That's the system - how well does it work?
The battery provides about 5kWh of energy - the average four bed suburban house uses about 20kWh of energy per day - varies wildly depending upon how many teenagers you're burdened with :)
For one person living in a caravan who has a basic knowledge of energy consumption 5kWh is quite adequate for most of Australia most of the time. I run a microwave and/or (never together) an air fryer frequently, each draws about 1300W (55A at 25V). Yesterday (because it hasn't run since last year) I ran the air conditioner for about one hour to give it some exercise.
Soon I'll change from a three-way fridge to a 240V compressor fridge, this will consume a maximum of around 1kWh per day, adding my Starlink system and miscellaneous consumption into that will see me using about 2kWh of energy per day. This, of course, needs to be replaced by the solar panels which means they need to see about 500W of sun for four hours per day. I think this will generally be OK but when camped in the forest in Victoria in winter I may need to run a small generator a couple of times a week - or get more panels... but it's a bit more complicated than that.
-----
Cost:
Cells, BMS and balancer about A$2100
Solar controller and shunt about A$400
Inverter A$200 (may change to Victron at A$1200)
Panels A$120 (used domestic roof panels)
Sundry A$150
Self installed
Total = about A$3000
-----
Issues:
The OEM caravan battery charger uses a lot of power, wastes it, so that was put onto a $10 Bunnings timer and only operates for two hours in the middle of the day. I've not had problems with it since.
The solar system produces some RF noise, which will only be a problem to Amateur Radio operators and perhaps AM radio listeners, but it's not too bad.
After one year I cannot see any wear issues on the cells and expect them to last ten years, maybe more.
Freestanding solar panels are much better suited to long stays; setting up and taking down is a pain. However the battery readily copes with unpowered stays of three or four days and the generator can be used for recharge if essential.
There is some inherent power waste in my system ie. solar energy is converted to 24V then to 240V and with some, items, then to 12V, each of these steps wastes energy but combined I doubt it comes to 5% of my overall energy use.
It is critical to ensure the system you design has enough battery capacity for your needs as it's very difficult to increase the capacity of an existing system rather one has to, pretty much, throw away the current cells and buy a whole set of new ones. Spend a bit extra and buy more battery capacity than you need is my very strong advice.
-----
Conclusion:
This system works very well. Increasing voltage to 24V or 48V is close to essential for a long term reliable system in my opinion.
The LiFePO4 cells are ideal for this situation with their ability to accept high charge rates and deliver high power across flat voltage discharge curves. Lifetime on these cells is nowadays looking excellent. NB. This type of lithium cells does not have a propensity to burst into flames when it's bored! :)
For A$3k this was money well spent. I am now totally grid independent and except in the worst of conditions don't even need the generator.
I would have preferred a 48V system but the caravan storage area for the additional cells was too much for me.
If I ever sell the caravan it would be an easy task to remove the entire system and install it in a new van.
-----
-----
It's worth mentioning how I use a generator to charge the 24V lithium battery bank.
The first thing not to do is buy an expensive 24V lithium battery charger because you already have one - your MPPT solar controller is a sophisticated battery charger all it needs is a power source - anything from about 35V to 100V will do. To this end, from eBay for A$140, I bought a quality 240V, 320W, 48V industrial power supply. The solar panels are unplugged, the power supply is plugged into the generator and its output plugged into the MPPT controller. The MPPT controller is set to use a maximum of 11A battery charge current so as not to overload the power supply and the batteries charge at about 300W. Easy, safe and cheap :)
I also have a few 12V batteries for portable use around camp for stuff such as pumping water, running the diesel heater and sometimes my Amateur Radio when sitting by the campfire. To charge these I use a second Victron MPPT solar controller (100V/20A bought on special for A$100!). This controller is only connected to the solar panels when the main batteries are fully charged and its output used to charge which ever of my 12V batteries needs it. Again this system works very well.
Additionally I have a 10W, 18V solar panel which is occasionally connected directly to my 4WD battery - no solar controller - if the vehicle is not being used regularly.
-----
That's it - I'll update the thread if I think I have anything worthwhile to add. Feel free to ask questions.
An overview of my caravan solar system, installed one year ago.
My system is rather different to how these things are normally done because I wanted a 24 or 48 volt system rather than the usual 12 volt. Most modern caravan solar systems are simply upgrades from the original lead acid battery to a lithium battery and more solar panels on the roof and maybe replacement of the solar controller. This is, sort of, OK and usually works well enough for caravan holidays but will struggle for long off-grid trips into forested areas or in winter with a run of poor weather.
A big problem is that 12 volts (12V) is a terrible choice for caravan power and is only used today for historical reasons and the reality that virtually all caravan accessories are 12V.
A quick, basic lesson about electricity:
Current (in amps) = power divided by voltage so if we have a light globe in our 12V caravan which is rated as 24 watts it requires 24W / 12V = 2 amps. And if we have a microwave rated at 1200W it will require 100A which is a lot of current. However if we increase the supply voltage to 24V we'll only need 50A for that microwave. For technical reasons the lower we can make the current in our caravan system the better it will work and the more reliable it will be. And, frankly, with the significant currents needed at 12V for large appliances I get a little worried by the fire risk.
As my caravan is natively 12V the prospect of changing the entire van to 24V did not appeal, it would be a significant and expensive task. Instead what I decided was to run the whole van from 240V just as I would in a caravan park but in this case the 240V was to originate from a lithium battery pack.
Thus my system comprises eight 202Ah lithium (LiFePO4) cells in series to produce about 25V, these feed a 2kW 24V to 240V inverter and the output from the inverter plugs into the mains input on the outside of my van, as would be the case in a caravan park. A further advantage to doing this is I can easily swap the van from the battery to a generator or mains.
In addition a Victron 100V/30A MPPT solar controller takes an input from four 200W free-standing solar panels and converts that to 24V in order to charge the lithium cells (battery). The system is protected by a 65A circuit breaker. A Victron SmartShunt provides Bluetooth information regarding what the system is doing - as does the MPPT controller.
The solar panels are wired series/parallel - ie. two panels in series produce about 80V at 5A and the other two panels are also wired in series then the two pairs are connected in parallel at the caravan thus producing about 80V at 10A or 800W. In practice I've never seen them produce more than 700W. Wiring the panels this way has the significant advantage that I can use long leads (so low power loss in the cables) to position the panels and minimise tree shade. Each solar panel is about 1500mm x 800mm and weighs 15kg. I have made simple legs for them from rectangular aluminium tube, each leg has three holes in order the panel angle may be varied to suit the time of year and/or geographical location - this is worth about 11% extra sun energy.
In effect all I have done is create a battery pack charged by solar and connected to an inverter to produce 240V. Such an item could be used to provide power or emergency power in any situation. The cells (see picture) are located directly over the caravan axle which is ideal. The solar controller and inverter are located under the bench seat and require about 1m of cable from the battery thus minimising power loss as this is the only cable with high current.
In regard to the photograph of the cells:
The large red item at the bottom is the battery management system (BMS) which ensures the lithium cells are kept within their electrical tolerances.
The thing with the two gold blocks and two black wires is the Victron SmartShunt.
The orange box to its right is the cell balancer.
The 65A circuit breaker is just peaking out to the right of the vertical white batten.
-----
That's the system - how well does it work?
The battery provides about 5kWh of energy - the average four bed suburban house uses about 20kWh of energy per day - varies wildly depending upon how many teenagers you're burdened with :)
For one person living in a caravan who has a basic knowledge of energy consumption 5kWh is quite adequate for most of Australia most of the time. I run a microwave and/or (never together) an air fryer frequently, each draws about 1300W (55A at 25V). Yesterday (because it hasn't run since last year) I ran the air conditioner for about one hour to give it some exercise.
Soon I'll change from a three-way fridge to a 240V compressor fridge, this will consume a maximum of around 1kWh per day, adding my Starlink system and miscellaneous consumption into that will see me using about 2kWh of energy per day. This, of course, needs to be replaced by the solar panels which means they need to see about 500W of sun for four hours per day. I think this will generally be OK but when camped in the forest in Victoria in winter I may need to run a small generator a couple of times a week - or get more panels... but it's a bit more complicated than that.
-----
Cost:
Cells, BMS and balancer about A$2100
Solar controller and shunt about A$400
Inverter A$200 (may change to Victron at A$1200)
Panels A$120 (used domestic roof panels)
Sundry A$150
Self installed
Total = about A$3000
-----
Issues:
The OEM caravan battery charger uses a lot of power, wastes it, so that was put onto a $10 Bunnings timer and only operates for two hours in the middle of the day. I've not had problems with it since.
The solar system produces some RF noise, which will only be a problem to Amateur Radio operators and perhaps AM radio listeners, but it's not too bad.
After one year I cannot see any wear issues on the cells and expect them to last ten years, maybe more.
Freestanding solar panels are much better suited to long stays; setting up and taking down is a pain. However the battery readily copes with unpowered stays of three or four days and the generator can be used for recharge if essential.
There is some inherent power waste in my system ie. solar energy is converted to 24V then to 240V and with some, items, then to 12V, each of these steps wastes energy but combined I doubt it comes to 5% of my overall energy use.
It is critical to ensure the system you design has enough battery capacity for your needs as it's very difficult to increase the capacity of an existing system rather one has to, pretty much, throw away the current cells and buy a whole set of new ones. Spend a bit extra and buy more battery capacity than you need is my very strong advice.
-----
Conclusion:
This system works very well. Increasing voltage to 24V or 48V is close to essential for a long term reliable system in my opinion.
The LiFePO4 cells are ideal for this situation with their ability to accept high charge rates and deliver high power across flat voltage discharge curves. Lifetime on these cells is nowadays looking excellent. NB. This type of lithium cells does not have a propensity to burst into flames when it's bored! :)
For A$3k this was money well spent. I am now totally grid independent and except in the worst of conditions don't even need the generator.
I would have preferred a 48V system but the caravan storage area for the additional cells was too much for me.
If I ever sell the caravan it would be an easy task to remove the entire system and install it in a new van.
-----
-----
It's worth mentioning how I use a generator to charge the 24V lithium battery bank.
The first thing not to do is buy an expensive 24V lithium battery charger because you already have one - your MPPT solar controller is a sophisticated battery charger all it needs is a power source - anything from about 35V to 100V will do. To this end, from eBay for A$140, I bought a quality 240V, 320W, 48V industrial power supply. The solar panels are unplugged, the power supply is plugged into the generator and its output plugged into the MPPT controller. The MPPT controller is set to use a maximum of 11A battery charge current so as not to overload the power supply and the batteries charge at about 300W. Easy, safe and cheap :)
I also have a few 12V batteries for portable use around camp for stuff such as pumping water, running the diesel heater and sometimes my Amateur Radio when sitting by the campfire. To charge these I use a second Victron MPPT solar controller (100V/20A bought on special for A$100!). This controller is only connected to the solar panels when the main batteries are fully charged and its output used to charge which ever of my 12V batteries needs it. Again this system works very well.
Additionally I have a 10W, 18V solar panel which is occasionally connected directly to my 4WD battery - no solar controller - if the vehicle is not being used regularly.
-----
That's it - I'll update the thread if I think I have anything worthwhile to add. Feel free to ask questions.
