Another look at Solar Powered refrigeration on sailboats

[john61ct]

Originally Posted by valhalla360

I think back in the day when many cruisers charged by running the engine an hour or two per day, cold plate systems made sense. The battery bank couldn't accept as much power as the motor could generate, so you went a bit smaller on the alternator and put in an engine driven compressor to use up some of the excess power that was available from the motor that was already running...this is actually much closer to "free" power as the incremental amount of fuel used was negligible.



With modern solar charging over many hours and modern compressor based fridges that are drastically more efficient compared to 20-30yrs ago, there just isn't the advantage to using an exotic system.

But if that engine running daily is actually still part of the routine, then holding plates can still make sense.

[Q Xopa]

Originally Posted by valhalla360

Where is this free energy coming from?

You need an energy storage system with both systems...it's just a battery vs holding plate storing the energy. Both require the box, insulation, compressor, etc...but the cold plate trades battery for cold plate. You can take that same "free" energy and put it in a battery for later use.

Efficiency might be better but we've reached the point where it's not hard to run a compressor based fridge on a typical cruising boat.

Yeh ok sure, as you correctly say nothing is 'free'.

Correct you do need to buy Cold plates, batteries, solar panels, diesel engine with alternators or EU220i's etc.

However what I more correctly should have said is 'on going' costs as opposed to initial capital costs.

Ie diesel, gasoline, etc costs us money.
Sunshine to produce PV solar power doesnt cost.

However as John correctly says if your motoring anyway, you're spending that money anyway for another purpose, so you can sneak in some 'free', nay 'already spent', money.

Of course I appreciate semantics as much as anyone.

[john61ct]

And I very carefully stated, "relatively free".

With even solar capital investment needs to get amortized into your per-month or per-AH accounting.

[Q Xopa]

Originally Posted by john61ct

And I very carefully stated, "relatively free".

With even solar capital investment needs to get amortized into your per-month or per-AH accounting.

'Amortized'. Sounds suspiciously like an accounting principle.

Wasn't someone warning about thread drift a few posts ago?

[Richard Kollmann]

I am glad to see the real facts are coming out on solar power for refrigeration that relieves stress on a boat's DC power grid. Hopefully it is now understood that not one unit in these ice box conversion refrigeration units can within its self create energy. Energy for a boats refrigerator comes from the Sun or wind or Hydrocarbon fuel. Energy can be stored in batteries with less loss than storing it in ICE. Process energy that comes from refrigeration cooling is disposed of by a well designed condenser and how and where condenser warm air is discharged. If more people would spend more time on condenser heat disposal their worries about energy consumption would actually be reduced.

There are advantages and disadvantages with the two types of evaporators. For the average pleasure boater most seem to prefer the utility variations of standard evaporators. Water boats">Blue Water boats with surplus energy can take advantage of eutectic evaporator plates. In the US several companies who in the past sold eutectic plate systems for small 12 volt compressors have stopped marketing them. Most boater's want more than a single temperature small space refrigerator.

[Q Xopa]

Originally Posted by Richard Kollmann

I am glad to see the real facts are coming out on solar power for refrigeration that relieves stress on a boat's DC power grid. Hopefully it is now understood that not one unit in these ice box conversion refrigeration units can within its self create energy. Energy for a boats refrigerator comes from the Sun or wind or Hydrocarbon fuel. Energy can be stored in batteries with less loss than storing it in ICE. Process energy that comes from refrigeration cooling is disposed of by a well designed condenser and how and where condenser warm air is discharged. If more people would spend more time on condenser heat disposal their worries about energy consumption would actually be reduced.

There are advantages and disadvantages with the two types of evaporators. For the average pleasure boater most seem to prefer the utility variations of standard evaporators. Blue Water boats with surplus energy can take advantage of eutectic evaporator plates. In the US several companies who in the past sold eutectic plate systems for small 12 volt compressors have stopped marketing them. Most boater's want more than a single temperature small space refrigerator.

Did I miss someine pushing the line that Cold plates create energy?

As for batteries storing energy more efficiently yes maybe.

However I would argue that if you can store 'free' energy, or energy that would have otherwise been wasted ie Solar when your batts are already topped off, I would be up for it.

Also if that inefficient energy storage, like Cold plates, was a lot cheaper and easier to maintain than batteries, I would also be sorely tempted.

[valhalla360]

Originally Posted by a64pilot

I guess I’m playing both sides of the fence, cause I don’t see what is exotic about a tank full of largely water. All a cold plate system is, is a thin plate evaporator placed into a water tank.
Only true downside I see is loss of box space.

Exotic in the sense that outside older long distance cruising boats, they are rare...and becoming more so as modern marine fridges have closed the gap on efficiency.

[valhalla360]

Originally Posted by Q Xopa

Yeh ok sure, as you correctly say nothing is 'free'.

Correct you do need to buy Cold plates, batteries, solar panels, diesel engine with alternators or EU220i's etc.

However what I more correctly should have said is 'on going' costs as opposed to initial capital costs.

Ie diesel, gasoline, etc costs us money.
Sunshine to produce PV solar power doesnt cost.

However as John correctly says if your motoring anyway, you're spending that money anyway for another purpose, so you can sneak in some 'free', nay 'already spent', money.

Of course I appreciate semantics as much as anyone.

If you are talking running a diesel specifically to power the compressor vs you are already running the diesel either to motor somewhere or to charge the battery bank anyway, throwing a motor driven compressor in the mix will burn so little fuel that you probably can't measure it.

But if you are talking about solar with holding plate vs solar with battery bank, if you ignore capital costs, the daily operating costs are about the same. (of course if we are conducting a true analysis, it should be life cycle cost that we consider not capital or operating)

[newhaul]

Originally Posted by a64pilot

I guess I’m playing both sides of the fence, cause I don’t see what is exotic about a tank full of largely water. All a cold plate system is, is a thin plate evaporator placed into a water tank.
Only true downside I see is loss of box space.

well in the system I'm installing ( technautics) the plate I am looking at will be approx 12x24x1 is 288 cubic inches ( there are 1728 in a cf)
the solution is a mixture of food grade antifreeze and water. The plate inside as I am to understand looks more like a small radiator or transmission cooler.
(Don't know about other systems) and how they are built.
With my Lfp and 400 watts solar I will be able to run the fridge primarily off of the solar in the afternoons once the battery is fully charged.

[Q Xopa]

Originally Posted by valhalla360

If you are talking running a diesel specifically to power the compressor vs you are already running the diesel either to motor somewhere or to charge the battery bank anyway, throwing a motor driven compressor in the mix will burn so little fuel that you probably can't measure it.

But if you are talking about solar with holding plate vs solar with battery bank, if you ignore capital costs, the daily operating costs are about the same. (of course if we are conducting a true analysis, it should be life cycle cost that we consider not capital or operating)

Ok, I agree with everything you say. Im also not opposed to batteries.

However Im not sure of exactly what you are trying to say?

The thread is "Solar powered Refrigeration". Perhaps Im wrong but I take this to mean not using Batteries or generators to power it.

So your mention of batteries is probably correct, but not what I thought this thread is meant to be about?

Anyway seeing you are talking batteries, I havent done any numbers like you may have but I would be supprised if the life cycle cost of comparable Batteries to Cold Plates for a similar BTUs/day system would be similar. I would think Cold plate cycle life costs would be less. Im up for being proven wrong here.

The only way I can envisage having shot at a refrigeration system functioning adequately without using battery, is using Cold plates.

I am not a refrigeration expert like many here, but I cant see how an evaporator plate system can practically stay cool outside solar production hours. Maybe very good insulation? (tongue in cheek).

[valhalla360]

Originally Posted by Q Xopa

The thread is "Solar powered Refrigeration". Perhaps Im wrong but I take this to mean not using Batteries or generators to power it.

Can you run a holding plate on direct solar? Sure...but without discussing and comparing to the alternatives, what's the point?

[Q Xopa]

Originally Posted by valhalla360

Can you run a holding plate on direct solar? Sure...but without discussing and comparing to the alternatives, what's the point?

Ok sure.
So do you have any data to back up your alterative of how comparable battery Life cycle cost is to Cold plates?

[ramblinrod]

Originally Posted by valhalla360

Can you run a holding plate on direct solar? Sure...but without discussing and comparing to the alternatives, what's the point?

I too, don't really understand what we are trying to accomplish here.

A cruising boat typically has a house bank.

Why wouldn't one wish to connect the refrigeration system to it, so that if the sun isn't shining when the box temp comes up, the compressor can still run to keep the beer cold and cubes frozen?

There's no point in arguing if one technically can do something, when in practice, they just shouldn't. ;-)

[valhalla360]

Originally Posted by Q Xopa

Ok sure.
So do you have any data to back up your alterative of how comparable battery Life cycle cost is to Cold plates?

Nope, I don't but I can tell you with certainty...there is no such thing as "free power". Several of the posts from various posters talk about free power.

As most already have a solar/battery bank system, you need to break out the incremental costs to buy and maintain it compared to the incremental costs to buy and maintain a solar/cold plate system to get a true comparison.

Personally, had a cold plate on the last boat...didn't care for it, so unless there is a major benefit that can be shown, I going steer away from them on future boats.

[Q Xopa]

Originally Posted by valhalla360

Nope, I don't but I can tell you with certainty...there is no such thing as "free power". Several of the posts from various posters talk about free power.

As most already have a solar/battery bank system, you need to break out the incremental costs to buy and maintain it compared to the incremental costs to buy and maintain a solar/cold plate system to get a true comparison.

Personally, had a cold plate on the last boat...didn't care for it, so unless there is a major benefit that can be shown, I going steer away from them on future boats.

Sure.

Again agreed no such thing as free anything. I guess Solar power when your batteries are topped off could be termed more correctly already paid for.

So I guess to keep everyone happy, lets say "already paid for" or "cheaper". Can everybody live with those terms?

Yes also agree its not a question if it can be done. I think most agree it can. So I guess the more correct way to ask this is "should we", or "is it viable".

So we have some 'nays', noted.

I dont know the answers but Im here to hopefully get some. So far we got some strong opinions.

Anyway carry on.