Three-way fridge or compressor for off-grid?

Hi Trek’n_Teach,

Having had and used both types of fridges, I would choose a Compressor fridge over an Absorption fridge every time. Whilst the latest Absorption fridges are more efficient than the older models, a compressor fridge is still more efficient at doing the job than an absorption fridge. That is why we no longer have absorption fridges in our homes.

The drawback of course is that you need a certain amount of battery capacity, and recharging capacity to keep them running. Depending on a few variables, the average compressor fridge can use between 70 and 120 amps per day. This means that you will need at least a 100 AmpHr (possibly even 200 AmpHr) deep cycle battery just for the fridge. Then you will need enough solar capacity to keep the battery charged, and a DC/DC Charger.

The rule of thumb for battery capacity and solar capacity is 2 for 1 ie, for every battery amp you have, you need double the watts of solar capacity. In simple terms, if you have a 100 AmpHr battery, you need 200 watts of solar capacity. This rule of thumb has been debated by some stating that you only need to be able to put back in what you are taking out. This might sound logical, however it does not take into account that you need to recharge the battery at the same time that it is continuing to discharge, and that there is really only about 4 to 6 hours of optimal solar charging conditions. So in that 4 to 6 hours, you need to fully recharge your battery and keep it there for as long as possible.

Of course, then you have the issue of how do you charge the battery when there is not enough sunlight, you then need a supplemental means of charging. This could be as simple as running your vehicle to put charge back into the batteries, or having a portable generator. The next issue is weight, batteries and solar panels will add weight to your rig. Whilst LiFePo4 batteries weigh less than other deep cycle batteries, extra batteries and solar panels will be make your rig heavier.

Whilst you do not have the issue of needing enough battery and solar capacity with an absorption fridge, you still need to watch how much LPG you have. Depending on a few variables, the average absorption fridge can go through a 9 Kg gas bottle in as little as a fortnight. You then need to ensure you have a spare bottle, or access to somewhere that can refill your bottles. If you like being remote, and off grid for extended periods of time, this may pose a problem.

As an aside, if you read or are a member of a caravan forum, you will find that there are more questions regarding issues with absorption fridges than pretty much all other questions combined, certainly more than questions with issues around compressor fridges. There are also many more people ditching their absorption fridge for a compressor fridge, than the other way around.

I am certain you will get people stating the opposite to what I have said, that they would never have a compressor fridge, but that is the beauty of a free society where people can have a difference of opinion.

Macca.

Not much.

The energy requirements of any fridge is about how often you open it, what you put into it and how much energy goes through the walls (which is about the quality of the insulation and dependent on the difference in temperature between the inside and the outside). If you choose the right fridge, it is often easy to add lots more quality insulation which will substantially reduce its energy requirement. It is typically easier to do that effectively with a compressor fridge and especially if it has a remote compressor.

The other benefits of a compressor fridge is the requirement for a big hole in the side of the van that can fill up with dust is no longer required and your gas requirement will be significantly reduced allowing you to reduce the size (and weight of bottles) of the gas you need to carry.
Compressor fridges are also not affected by parking on a slope.

With a good solar system, you can "fill up" with electricity in the bush for free. You can't fill up with gas, and if you drive somewhere to find some, it may be quite expensive.
Cheers,
Peter
OKA196 motorhome

I installed a Thetford T2175c in daughters tandem caravan, great Frig/Freezer with lower power usage, suggest you should have at least a 100 Amp Lithium Battery and Solar on the roof to meet your needs, if off grid fill up the roof with solar as much as possible, but leave room for the Sat Dish.

https://www.thetford.com.au/product/t2175c-compressor-refrigerator-175l/

https://www.youtube.com/watch?v=wVKwkklKC6M

Trek'n_Teach
I agree with Peter above and regard insulation added to any fridge will enhance it's performance and lessen the energy use.
Depending on size, the compressor has to run to cater for use pattern. Always closed = good, often open or warm stuff added not so good. You will know that already but a compressor fridge will cool it quicker than a gas fridge will.
Depending on the "actual" current draw while running, ( best to find that out before buying one) so any calculations for battery and solar requirements can be more accurately calculated. The energy used during a warm night up north in OZ might find the fridge running longer cycle times. Cold weather much less. The maximum has to be considered.
People talk of watts of panels, but before buying any panel you need assurance that, in full sun, it delivers close to the claimed watts, or you are not going to get returns which you think it will achieve. No rule of thumbs, because they vary in size.
Consider using panels in series. You are going to require an MPPT regulator which will accept higher voltage from panels. This allows early starting of meaningful charge to batteries and in low cloud days too. The MPPT taking advantage of far greater panel voltage than the battery it is overcoming, will convert the solar harvest to the best amount of charge to battery. Cable size from panel to MPPT charger, and to battery, is important to achieve the full benefit.
There is more to consider in the whole package though!

You need to look at what length of time you generally go camping for off grid be it a day or a week etc and other items like interior lights water pump etc that use power. If you cook with gas or electricity then you can talk to someone about what battery capacity you need and solar requirements. I would always get more batteries than needed so you don't fall short.

Regardless of the numbers of batteries you need to be able to charge them otherwise all you do is have 2 flat batteries instead of one.

With today’s technology and how cost effective electrical setups can be I wouldn’t even consider a gas fridge. Compressor fridges are the most common for a reason

Trek_n_Teach
I for one, am interested as to what decision you arrived at to solve your fridge problem?