Solar powered freezer. Lancaster - the Amazon!

[Danny T]

Hello,

About a year ago I was finally convinced of 12v fridges, and made the leap from an inefficient 3-way to a 12v fridge-freezer for my off-grid narrowboat on the Lancaster Canal.

 

I am now needing to keeping stuff frozen in the Brazilian Amazon in a (different) small boat! 12v fridges/freezers are not easy to get hold of here, and so I think I will have to buy the smallest and most-efficient freezer that I can find, and an inverter.

 

Some examples of small freezers that I can find locally are 127 or 180W, and will run on either 110 or 220 V (which are the standard Brazilian mains voltages). I have also found local inverters between 750 - 3000 W (I assume the 750W will be fine for a 180W freezer?).

 

However, I don't understand how to do a power audit when an inverter is involved! I am trying to work out how many solar panels and batteries I will need to keep the freezer running all day. Note - I will be able to plug the freezer into the mains to get it down to temperature initially, but will then be relying entirely on the solar panels in remote areas to keep the contents frozen.

 

I hope it's ok to post this boaty but not UK-canal questions here! I imagine that canal folk will have experiences that are applicable to this situation!

 

Thanks in advance for any help.

 

Danny

 

 

 

[booke23]

It's a bit tricky to work out without local knowledge. 

It's hot in the Amazon so the most efficient freezer is a must. Say you get the 127W version, and assume it has to run 75% of the time to maintain temperature in the hot conditions. That's 8 amps/hr at 12 volts. Say 9 when you factor in inverter losses. So 216AH every 24 hrs. So you need a solar array that can generate at least this during the hours of daylight and probably 400ah of battery capacity.

If you can get a lot of direct sunlight 500w will probably be ok (30 amps in full sun in that part of the world), but maybe double that to be safe.....after all it does rain at times in a rainforest. Will you have an alternate source of power? (boat engine for instance)

My guesstimates are very pessimistic. The freezer probably won't draw as much as much in real life, but not many of us have run one in a tropical rainforest so who knows!

[agg221]

I was on the Colombian Amazon about this time two years ago (seems like a lifetime away!) and to be honest I would rather be back there right now, so am somewhat envious.

 

Not only was it hot, it was -incredibly- hot, all the time, all night long, and 100% humidity too. I think you will give any fridge a serious workout. I would think the above figures are not pessimistic. If anything they may be optimistic - it may well run more than 75% of the time.

 

Alec

[rogeriko]

The most important thing you must do is to completely insulate the freezer with about 100mm of Kingspan or similar hard insulation. the more the merrier. If you had perfect insulation the compressor would hardly run at all. The insulation has to be glued on so no air can circulate between the freezer and the insulation. Leave a hole where the compressor is and the hot pipework must be outside the inulation of course.

[Jen-in-Wellies]

8 hours ago, rogeriko said:

The most important thing you must do is to completely insulate the freezer with about 100mm of Kingspan or similar hard insulation. the more the merrier. If you had perfect insulation the compressor would hardly run at all. The insulation has to be glued on so no air can circulate between the freezer and the insulation. Leave a hole where the compressor is and the hot pipework must be outside the inulation of course.

Also, ensure there is good air flow over the evaporator coils, or plate, which will most likely be at the rear, or side of the freezer. This will carry the heat away that is being shunted from the inside to the outside of the freezer.

If you use a mains freezer, then using a local version of one of these can find the average power consumption, which won't be the same as what is likely in the freezer literature and on the plate. Finding the number of kWhrs consumed by day, then convert to amp.hours at 12V by multiplying by 100.  You need enough solar panels to provide in excess of this every day, or you will run the batteries flat and ruin them. The AmpHours per day from solar panels will depend very much on local conditions, which will need measuring. Cloud cover will affect this a lot. Season likely not as much, compared with the UK. Again, real world measurements are going to be needed, or find some one local who has already done this. You need the total Amp.Hours you can get over an average for the year in 24 hours, so nothing at night and lots during the middle of the day.

There will be some measurement and maths involved in doing this right and ensuring the freezer doesn't conk out after a few days. Hard to help more as most of us on the forum are unfamiliar with the conditions where you are.

Jen

Edited January 21, 2022 by Jen-in-Wellies

[magnetman]

A compressor cool box is worth considering. I use a 15L one of these as a freezer set at -16'C. 

No idea how good it would be in a hot climate or if it's available there. Does not look very well insulated but you could probably put it in a box of insulation material provided air flow is arranged. 

 

 

 

 

 

[Danny T]

Great tips, thanks! Even with lack of experience in the local conditions your insight is useful.

 

The idea to further insulate the freezer is a great one - I'll do that. I also thought that keeping it full of ice packs could help? Just remove an ice pack every time I need to put more stuff in it (because I will be filling the freezer, not emptying it).

 

The calcs that you have given me make it look quite tricky - but not impossible. Day length remains a pretty constant 12 hours all year here (6am-6pm), and unfortunately I will probably not have the option to charge from the boat engine, as I think I will be using a longtail outboard. But I could get my hands on a generator.

 

With a little more research I have found that I can get 12v freezers in Brazil - and like the UK they are twice the price of mains! But maybe that would be a good option? The problem being that I can't use mains electricity to get it down to temperature, nor top it up if I have a genny.

 

A compressor cool box is an interesting idea. I can get my hands on them here, but most are just for cooling and not freezing - I'll keep researching!

 

Thanks again!

[Slim]

An off the wall suggestion. Some years ago a friend had a lumpy water yacht with a freezer. It.'s heat exchanger was water cooled. It kept us in frozen food (and ice cubes) on the trip down to Gibraltar and beyond. No more details not least the temperature of the Amazon.

 

Just found out that the average temp of the Amazon is 30 c so maybe a non starter😄

Edited January 21, 2022 by Slim

[BEngo]

If you buy a 12 V freezer all you need to get it down to temperature is a small 12 V  battery  and a Brazilian mains voltage battery charger.  The 12 V battery is really only there to keep the charger voltage down to a level the freezer is OK with. You should be able to get away with a simple (cheap)  charger as you will not be leaving the battery on charge without the freezer running.

 

Or just sit the freezer in the shade and  connect it to a solar panel in the sun. When it is cold move it to the boat.  The Danfoss BD365K compressor is designed to run off a solar panel, according to the data sheets.  Not tried it.

 

Filling with chilly packs is a good idea.  They will not reduce the total electric consumption by much but they will mean the freezer runs less frequently and might go all night without running.

Try to turn the freezer thermostat down during the day  when the sun is shining, and up at night.  That way you get things as cold as possible before you are running on battery.

 

N

[booke23]

1 hour ago, Danny T said:

Great tips, thanks! Even with lack of experience in the local conditions your insight is useful.

 

The idea to further insulate the freezer is a great one - I'll do that. I also thought that keeping it full of ice packs could help? Just remove an ice pack every time I need to put more stuff in it (because I will be filling the freezer, not emptying it).

 

The calcs that you have given me make it look quite tricky - but not impossible. Day length remains a pretty constant 12 hours all year here (6am-6pm), and unfortunately I will probably not have the option to charge from the boat engine, as I think I will be using a longtail outboard. But I could get my hands on a generator.

 

With a little more research I have found that I can get 12v freezers in Brazil - and like the UK they are twice the price of mains! But maybe that would be a good option? The problem being that I can't use mains electricity to get it down to temperature, nor top it up if I have a genny.

 

A compressor cool box is an interesting idea. I can get my hands on them here, but most are just for cooling and not freezing - I'll keep researching!

 

Thanks again!

 

Good luck with it.

 

As mentioned the next step would be to actually run a freezer there (in a non air conditioned room) with a watt meter attached to see what power it will actually use. There are a few things in your favour.......constant day length, good hours of sunshine and as you're on the equator the sun will be 90 degrees above the horizon at midday, so solar panels will get close to actually producing their rated output (potentially 40 amps on a 500W system). Lithium batteries are worth exploring too. 

[Alan de Enfield]

Is the Amazon not shaded by a few trees (some 390,000,000 apparently) ?

That could affect any solar output

[booke23]

23 minutes ago, Alan de Enfield said:

Is the Amazon not shaded by a few trees (some 390,000,000 apparently) ?

That could affect any solar output

 

Yeah but they don't grow on the water! 

Edited January 21, 2022 by booke23

[Jen-in-Wellies]

3 hours ago, Alan de Enfield said:

Is the Amazon not shaded by a few trees (some 390,000,000 apparently) ?

That could affect any solar output

Not for much longer!

[agg221]

10 hours ago, Jen-in-Wellies said:

Also, ensure there is good air flow over the evaporator coils, or plate, which will most likely be at the rear, or side of the freezer. This will carry the heat away that is being shunted from the inside to the outside of the freezer.

If you use a mains freezer, then using a local version of one of these can find the average power consumption, which won't be the same as what is likely in the freezer literature and on the plate. Finding the number of kWhrs consumed by day, then convert to amp.hours at 12V by multiplying by 100.  You need enough solar panels to provide in excess of this every day, or you will run the batteries flat and ruin them. The AmpHours per day from solar panels will depend very much on local conditions, which will need measuring. Cloud cover will affect this a lot. Season likely not as much, compared with the UK. Again, real world measurements are going to be needed, or find some one local who has already done this. You need the total Amp.Hours you can get over an average for the year in 24 hours, so nothing at night and lots during the middle of the day.

There will be some measurement and maths involved in doing this right and ensuring the freezer doesn't conk out after a few days. Hard to help more as most of us on the forum are unfamiliar with the conditions where you are.

Jen

My concerns were that the very high temperature would reduce the temperature differential between the coils/plate and the air, reducing cooling efficiency, and that the 100% RH would effectively prevent evaporative cooling. It really didn't get much better at night either (but at least the freezer won't care about the mosquitos!) - do you think that would be an issue?

 

To the OP - biological specimen collection? Anything interesting?

 

Alec

[Jen-in-Wellies]

29 minutes ago, agg221 said:

My concerns were that the very high temperature would reduce the temperature differential between the coils/plate and the air, reducing cooling efficiency, and that the 100% RH would effectively prevent evaporative cooling. It really didn't get much better at night either (but at least the freezer won't care about the mosquitos!) - do you think that would be an issue?

 

To the OP - biological specimen collection? Anything interesting?

 

Alec

The 100%RH won't affect a conventional compressor freezer. The evaporation is happening within the sealed refrigeration system. There won't be evaporation from the outside of the coils/plates. The reduced temperature differential will have an effect. However, if a freezer is being sold as a freezer locally, then it should still be capable of freezing. It will have to work harder to do it and consume more energy than one in the UK, but will still function.

Edited January 21, 2022 by Jen-in-Wellies

[booke23]

On 21/01/2022 at 20:07, agg221 said:

To the OP - biological specimen collection? Anything interesting?

Maybe he really likes Birds Eye fish fingers, and wants a large stockpile. I hear they are quite unobtainable in the rain forest! 

 

"Only the best for the captn's table!"

[Danny T]

On 21/01/2022 at 12:01, booke23 said:

 

Yeah but they don't grow on the water! 

😂  Indeed!!

[Danny T]

Considering the past comments, it seems important to get a freezer that is designed for/ tried and tested in the Amazon. Which possibly puts me off the 12V option (which will probably come from Southeast Brazil), and instead steers me towards just getting an A+ efficiency standard freezer from the local equivalent of Currys! (+ inverter)

 

Thanks very much for all the tips - I will get some more local advice now, and tell you what I discover!

[Danny T]

On 21/01/2022 at 16:22, Jen-in-Wellies said:

To the OP - biological specimen collection? Anything interesting?

Yes - I am work at a Brazilian Sustainable Development Institute with fishing, hunting and food security. I'm going to be collecting small off-cuts of what local people catch, and analyzing them for lots of things, including mercury content (very toxic for consumers!). Most communities only have a few hours of electricity every evening via a diesel generator, so I want to be able to rock up in my little self-sufficient freezer boat! Shame I can't get my narrowboat over here...

[Tony Brooks]

A word of warning that may or may not be relevant. A compressor cool box will have to have an evaporator and as they tend to be somewhat less robust it may well be built into the side of the outer case like some modern fridges. Probably not a good idea to add extra insulation to that part but extra insulation inside should be fine, so possibly a larger unit to give you the space.

[Tracy D'arth]

Some modern fridges and freezers have the condenser coils inside the side panels of the cabinet, no good if you want to add external insulation. Could you arrange water cooling of the condenser coils, well painted to stop corrosion?

[Tony Brooks]

Just now, Tracy D'arth said:

Some modern fridges and freezers have the condenser coils inside the side panels of the cabinet, no good if you want to add external insulation. Could you arrange water cooling of the condenser coils, well painted to stop corrosion?

snap

[agg221]

15 minutes ago, Danny T said:

Yes - I am work at a Brazilian Sustainable Development Institute with fishing, hunting and food security. I'm going to be collecting small off-cuts of what local people catch, and analyzing them for lots of things, including mercury content (very toxic for consumers!). Most communities only have a few hours of electricity every evening via a diesel generator, so I want to be able to rock up in my little self-sufficient freezer boat! Shame I can't get my narrowboat over here...

A very worthwhile exercise. I have some sense of what it may be like, having spent a night by the shores of Lake Tarapoto. The generator goes on from 7pm to 8pm. Then there is nothing but dark and rainforest for miles. It felt like a very fine balance - my being there (largely as a tourist but with a secondary interest in a potential R&D project) generated income which gave them the ability to buy items which they couldn't grow or extract from the forest or river, but too many people being there would cause a fundamental change away from something the residents are completely happy with. At the moment, they are in control - the choice to build a hut for visitors, and to feed them, is entirely theirs, and the impact our presence had was completely within their control, both numbers and what we did (going out onto the lake at night looking for caymans with a local guide, who proceeded to get into the water and catch them with his bare hands, bring them over to the canoe and then when we had seen them, let them swim off again was certainly an experience!) but it did feel like there was the potential to impose, or erode the way the whole ecosystem of the place worked.

 

I would love to go back though!

 

Alec

[markeymark]

i spent many years as a logistician working with cold-chain for vaccines in Africa. what I learnt from that was that if you apply a demand-side management approach to any problem as opposed to supply -side management you will save money and effort. What this could mean in your situation is this; what is the minimum amount of energy i would need to USE to fulfill my objective? This is not just the solar power output but the time that you need to use it. E.G how long is the longest time away from your base when you need to use the freezer? if you do a logistics plan then could you stop at places with 220V and use that power to top up your freezer, store specimens etc  and REDUCE the energy that you need. whilst travelling?  How long does the specimen need to be in the freezer? can you do on-site analysis and REDUCE the needs of using the freezer? can you use an AC/DC model for flexibility so that you can switch energy sources as required? How often will you be going to the lab with your specimens and so how do you mange that more efficiently? I find that supply-side requires a larger input and expense and a good logistics plan based on minimalism works better. If you are in a long boat then how about building the insulation into the boat so that you can drop the freezer/cooler box into it and use  the smallest freezer/cooler so as to save space,  weight and power use. good luck

[Jen-in-Wellies]

11 hours ago, markeymark said:

i spent many years as a logistician working with cold-chain for vaccines in Africa. what I learnt from that was that if you apply a demand-side management approach to any problem as opposed to supply -side management you will save money and effort. What this could mean in your situation is this; what is the minimum amount of energy i would need to USE to fulfill my objective? This is not just the solar power output but the time that you need to use it. E.G how long is the longest time away from your base when you need to use the freezer? if you do a logistics plan then could you stop at places with 220V and use that power to top up your freezer, store specimens etc  and REDUCE the energy that you need. whilst travelling?  How long does the specimen need to be in the freezer? can you do on-site analysis and REDUCE the needs of using the freezer? can you use an AC/DC model for flexibility so that you can switch energy sources as required? How often will you be going to the lab with your specimens and so how do you mange that more efficiently? I find that supply-side requires a larger input and expense and a good logistics plan based on minimalism works better. If you are in a long boat then how about building the insulation into the boat so that you can drop the freezer/cooler box into it and use  the smallest freezer/cooler so as to save space,  weight and power use. good luck

A good way of thinking about the problem. Against this is the risk from any delays, or the non-availability of an expected generator, or mains supply. Especially towards the end of a trip, when all the samples from the session are at risk. Only the OP can decide the appropriate balance.