Power management

[dohenyboy]

How about something simple as covering it with a blankie at night? If you have a top loading box, some thick batt insulation sewn inside a vinyl pillowcase.


Sent from an undisclosed location on the high seas or from the lounge chair by the pool, you decide.

[tomfl]

Lets not get too deep into my setup. It is a box I added insulation to and a Frigoboat D50 with the nice card that starts up at 25% for the first 5 min, then to 50%, for the next 5 min, and then to 75% for the next 5 min, and finally to 100%. I also use a couple of sheets of the silver bubble wrap mylar on top of the top loading box to minimize loss and have double rubber seals under the lid. Also have a sheet of the silver mylar bubble wrap inside on top and also on top of the freezer. The mylar bubble wrap on top is in two pieces so I only open one side when going in the box. I have an Engel in the cockpit I keep drinks, milk, and yogurt in and open several times a day. The big box is normally only opened maybe five times a week.

What I am trying to do is come up with the most efficient way to manage power, not deal with a power shortage. I run my Honda 2000 once a week more to maintain the gas engine than to charge the batteries. Last time I did it just to charge the batteries was when there was rain/clouds for four days straight.

[hellosailor]

Let me see if I'm the only one a bit confused here. (That's my job, after all, to lead the confused by example.)

You have excess power during the day, and currently dump electrical power during the day.

And what you want to do is store that as "thermal power "(i.e. extra cooling capacity) in your ice box overnight.

Did I get that right?

And there's some reason you'd prefer to store thermal power, instead of using something terribly conventional like a battery to store the electrical power you're dumping right now?

Seems like either way, you're producing more in every 24-hour cycle than you can use, even if you stored it as cooling, you'd have to either dump the extra cooling, or turn the boat and anchorage into an ice floe as that built up.

Or, start selling power to the neighbors.

[tomfl]

Originally Posted by hellosailor

Let me see if I'm the only one a bit confused here. (That's my job, after all, to lead the confused by example.)

You have excess power during the day, and currently dump electrical power during the day.

And what you want to do is store that as "thermal power "(i.e. extra cooling capacity) in your ice box overnight.

Did I get that right?

And there's some reason you'd prefer to store thermal power, instead of using something terribly conventional like a battery to store the electrical power you're dumping right now?

Seems like either way, you're producing more in every 24-hour cycle than you can use, even if you stored it as cooling, you'd have to either dump the extra cooling, or turn the boat and anchorage into an ice floe as that built up.

Or, start selling power to the neighbors.

That may be one way of looking at it.

Adding batteries is certainly one option.

But even if the cost and extra wiring and what ever is ignored I have a catamaran and you know how much extra weight is a no no.

What I am trying to figure out is the best way to manage the extra watts my solar panels produce in the sunlight hours to keep the fridge cool at night.

Quite frankly the few hundred dollars for two or four more batteries is not as big an issue as where to put them and how much the extra weight would change the performance of my boat. Or even if there is enough room for four more batteries because just adding two would probably cause the boat to tilt to one side.

[hellosailor]

Tom, you can't say that battery weight is an issue, unless you've already cut that 3/4 by going to lithium batteries. (G)

Seriously, though, that's the best way to get the lead out, even if no one is certain of whether you'll need a BMS or other complications. And that would allow you to increase capacity and reduce weight at the same time. Batteries allow for much higher power density than ice, I think.

That, or you buy large blocks of blue goo, or some other phase change media, and freeze it down during the day. No adjustments needed, it will soak up power as it freezes down, and that should prevent (delay) the box from running at night. No weight reduction though, that stuff has weight.

[tomfl]

Originally Posted by hellosailor

Tom, you can't say that battery weight is an issue, unless you've already cut that 3/4 by going to lithium batteries. (G)

Seriously, though, that's the best way to get the lead out, even if no one is certain of whether you'll need a BMS or other complications. And that would allow you to increase capacity and reduce weight at the same time. Batteries allow for much higher power density than ice, I think.

That, or you buy large blocks of blue goo, or some other phase change media, and freeze it down during the day. No adjustments needed, it will soak up power as it freezes down, and that should prevent (delay) the box from running at night. No weight reduction though, that stuff has weight.

Already have the blue stuff that freezes just below the freezer.

Realistically I am not going to have anything but flooded batteries.

My guess would be that batteries do have higher power density than ice but I suspect frozen blue stuff inside the fridge, especially with good insulation would have good power density. Good point though

[hellosailor]

Well, if you can find out how may BTUs those blue goos eat, you can always compare to the watt-hours your batteries can take.
BTU to watts (W) conversion calculator
As they say, the rest is all simple math left to the reader.

[SV THIRD DAY]

Tom..
I think I see what you want...to use some of those extra amps you have during the day to store that power in your freezer rather than expand your battery bank.

A real easy way to do that with the system you have is to fill a container or two of 25% water and 75% antifreeze and place it in the freezer. Your freezer can freeze it up during the day when you have the "extra power to spare". Then at night to not use as much refrigeration power, put a 12v timer on the refrigerator circut to turn it off for a few hours at night and let the frozen containers help keep your box cold. Just play a bit with how many containers, of what size and volume and then how long you can turn your sytem off for at night. Or here's another recommendation, come to the realization that once your system is tuned up and running properly...forget about it and go enjoy yourself! Don't stress over the extra 10 or 20AH your system will use at night because you have the ability to easily put that back during the day without generator runing right?

Seriously, you only need to run your Honda 1hr/week and at that just to run the engine...why are we even having this conversation? Let go of the need to over-engineer things and always be tweaking things. You are in the 5% group of cruisers that have enough solar to carry their boat so it's time to relax and enjoy it!

On a serious note (which is very hard for me), you are describing one of the advantages of a Eutectic Holding Plate system. Which has the ability to store excess electrical power available during the day or when motoring in the holding plate rather than in your batteries. You don't have that ability with a rolled alumunium evaporation plate since it has no hold over capacity. So the frozen containers of water/antifreeze can help give you the "Holding Plate Affect". But heck from your energy usage profile I say you have a great energy ballance and set-up. Time to take off the tin foil, let go and enjoy it!

[Ex-Calif]

WHy dind't I think of that - Oh wait I did - LOL.

Look how about this - just get a timer. Don't futz with ice bags or plates.

Just shut the reefer off from say 3am - 6am and see hat happens. Measure morning temp and see what you lost.

You celarly don't want frozen food thawing and freezing every night but 3 hours off with decent insulation might save a few amps. But as others have pointed out - cooler at night so duty cycle is already less etc...

There's no free lunch here - it's either a heat transfer problem or electrical storage problem. It's all energy, baby...

[Dsanduril]

If you can keep your fridge at the desired temperature with your proposed cycle then there is no doubt (particularly with flooded batteries) that running the fridge while the solar is generating will save you big on total energy.

Two parts to that:

1. battery inefficiency - look at all the info here about Peukert's, LA charge efficiencies, etc. In the best world you can take out 85-90% of the energy you put into LA batteries. The rest goes into the inefficiency of the charge/discharge cycle and just heats your battery. If you run the fridge at night you have to go through that cycle. On the other hand, if you can run the fridge down during the day, and the power goes straight from the solar to the fridge then you get to bypass the charge/discharge cycle (energy gain ~12.5%)
   
2. compressor efficiency - Look at the efficiency curves for most of the compressors we use in marine refrigeration - they prefer to run at a higher voltage, which is something that is naturally available when the solar is generating (efficiency gain ~2-4%).

All of that becomes much (much) less if you switch to LiFePO4, the charge/discharge cycle is way more efficient, and the voltage drop during the discharge cycle is much less. But if you're stuck with LA it is always better to run your equipment (fridge, watermaker, whatever) while the power is being generated so you don't have to pass through the charge/discharge cycle. That of course assumes you can actually switch the equipment usage to times when the solar is charging (can't really change the running light hours to coincide with solar charging )

[kmacdonald]

You need a watermaker to use the extra power generated. You will have to cary less water so you will reduce weight. A win win situation. May I suggest a Spectra Watermaker.

[Ex-Calif]

Originally Posted by kmacdonald

You need a watermaker to use the extra power generated. You will have to cary less water so you will reduce weight. A win win situation. May I suggest a Spectra Watermaker.

Bottle it and sell it!
Get an ice maker and sell ice!
Get the right plugs and charge other people's boats!

Tom's the only guy on CF complaining of having too much energy - LOL!

(PS - Suggest you switch all your LED lighting to incandescent ASAP)

[kmacdonald]

Originally Posted by Ex-Calif

Bottle it and sell it!
Get an ice maker and sell ice!
Get the right plugs and charge other people's boats!

Tom's the only guy on CF complaining of having too much energy - LOL!

(PS - Suggest you switch all your LED lighting to incandescent ASAP)

He sure is. Bless his heart!!!!

[Ex-Calif]

Originally Posted by kmacdonald

He sure is. Bless his heart!!!!

I'm really liking the bottled water idea - Tom could call it "Marine Water" - For the serious cruiser! It's loaded with dihydrogen oxide for peak sailing performance!

Sell it for 2X Perrier to credit card sailors.

[noelex 77]

I don't see anything wrong with what Tomfl is suggesting.

Whenever your solar controller is regulating you are throwing away power. No matter how big a battery bank you have there will be times where your solar system is regulating. It is sensible to try and make use of this power if possible.

The fridge/freezer and watermaker are the two biggest power consumers. Lowering the temperature of fridge, adding warm goods that will need to cooled down (like drinks) and or freezing bottles of water will all help store that excess power. The watermaker can be run longer.

Other smaller devices can also be used to make use of the excess power such as backing up the computer on days when there is excess power. There are lots of other examples.

These techniques will give you more usable power and/or a longer battery life. This applies regardless of the size of your battery bank, providing your system reaches the point of regulating.

Whether it is worth the trouble to do this is another matter. Most people don't bother at times of the year when power is abundant, but start incorporating these practices when power is marginal.