Buying Fireflys and Solbian - can someone check my math?

[markcoulter]

Originally Posted by lordgeoff

A €50 12V fridge with a cigarette lighter socket from Lidl will keep a few things cool for you........ICE is a PITA.

The only good thing about the solid state coolers is that they are cheap. They only cool to 17c below ambient temperature so are of marginal use in the tropics. They don’t hold all that much and they use 96 amp-hours per day (4 amps x 24 hours).
Adding a compressor conversion kit to the ice box would add a third or less to the power consumption, keep the food at the proper temperature, and add room in the cooler (Ice takes up a lot of space).

[rbrentp]

4p buys my opinion as well. Also been looking at Fireflys, and if all testimonials are true, they take no damage at 90% discharge. So two should provide capacity based on your adjusted numbers and not hit.

Others will chime in but I have always been told the smallest of the solar panels limits the amp output. A matched pair would be better.

Don't know how you intend to mount them, but if I calculated the dimensions properly they are close to a meter square and a pair of the 100 watt Renologys might fit in that space. They should provide about 14 amps per hour (assuming a 12 volt system.) With sunshine on them 10 hours a day, you are at 140 replacement amps per day which should handle everything you listed, except at night, heavy overcast, shade, etc.

Math says if you want to be engine independent you need 300 watts of solar.

While weight difference between the SXP and the Ren for three panels is about 33 lbs. Not much on a lead bottomed boat and half of a third battery.

My boat has 400 watts, an amp draw about 50 above yours (fridge) and will have three Fireflys. They replace 8 Trojan golf cart batteries with more usable capacity and 180 pounds less weight. A question is: do you have room for more solar?

[patprice]

My done very quickly thoughts based on the total of 125.84 appearing very high...

Amp calc for 24 hours at passage:
Interior LEDs - 4 lights at .3 amp hours each x 3 hours = 3.6 (Why 4? And .3 each light is high.
Nature's Head fan - 24 hours - 3.84 (Not needed)
Caframo fans - 2 fans at .54 amp hours each x 24 hours max - 25.92
Miscellaneous charing - 5 amps (Not needed)
chartplotter - .99 x 12 hours (assume standby for the other 12) - 11.88 (No comment)
Wind instrument/display - 1 amp x 24 hours = 24 (1 amp? Anyway turn off mostly)
LED Nav lights - .6 x 12 hours = 7.2 (Mine 0.35 amps)
Tri color LED - .3 x 12 = 3.6 (Duplication)
VHF - .55 on standby x 24 = 13.2 (??)
VHF AIS receiver - .9 x 24 = 21.6 ??
compass light - .5 x 12 hours = 6 (Does anyone use a compass anymore with self steering)
total = ??

[mitiempo]

Originally Posted by rbrentp

.......a pair of the 100 watt Renogys might fit in that space. They should provide about 14 amps per hour (assuming a 12 volt system.) With sunshine on them 10 hours a day, you are at 140 replacement amps per day which should handle everything you listed, except at night, heavy overcast, shade, etc.


My boat has 400 watts, an amp draw about 50 above yours (fridge) and will have three Fireflys. They replace 8 Trojan golf cart batteries with more usable capacity and 180 pounds less weight.

10 hours a day at full output is not possible. Figure 5 hours @ full output in temperate climes and 6 hours @ full output in the tropics.

[StuM]

Originally Posted by rbrentp

Don't know how you intend to mount them, but if I calculated the dimensions properly they are close to a meter square and a pair of the 100 watt Renologys might fit in that space. They should provide about 14 amps per hour (assuming a 12 volt system.) With sunshine on them 10 hours a day, you are at 140 replacement amps per day which should handle everything you listed, except at night, heavy overcast, shade, etc.

That would be 14 Amps (not "per hour") at peak insolation (i.e. around noon if panels are perpendicular to the sun). Most of the day, the incident angle means a much lower output even in direct sunlight. In the OP's location 4-5 hours full power equivalent is a reasonable estimate, so it would be more like 60 replacement Amp hours (not amps) per day.

My boat has 400 watts, an amp draw about 50 above yours (fridge) and will have three Fireflys. They replace 8 Trojan golf cart batteries with more usable capacity and 180 pounds less weight. A question is: do you have room for more solar?

Presumably, that should be 50 more Amp hours per day. An extra 50 Amp draw would consume another 1,200 Amp hours per day

[zboss]

Originally Posted by dwedeking2

I would think fan usage while under sail would be minimal. I never felt the need to run fans unless I was becalmed.

We run ours on passage... we don’t sail with and ports or hatched open so it can get stuffy. That’s not fun for the off watch crew.

Ours pretty much run 365 days a year.

Originally Posted by mitiempo

10 hours a day at full output is not possible. Figure 5 hours @ full output in temperate climes and 6 hours @ full output in the tropics.

It’s 4to 4.5 for temperate and 5 for tropical during the winter, which is what I think you are supposed to base sun hours on. This also doesn’t take into account shading caused by rigging or other obstructions.

Plus he should expect to almost never reach 100% full. 80% is a good target... then he also needs to take into account round trip inefficiencies. So add 10% or so for amps needed.

So... going between 80% full and 40% full gives him about 88 amp hours he can expect to get out of the batteries without shortening battery life or spending a huge amount of effort/money/time getting above 80%

We just bought 3 firefly batteries have just gone through this calculation as well. We are ordering two more batteries.

We have 610 watts of solar and a 400 watt wind and we struggled to keep pace with our energy usage on alt power alone. For raining days or weeks we still have to run the generator.

[jhulmer]

Originally Posted by Cthoops

Thanks to Rapanui for the comment on the amps for the wind instrument/display. I found a big error in my original calculation which brings it down to 3.6 amps vs. the 24 that I had. Between that and w32honu's comment on the LED Nav lights vs. tri-color, I was able to bring the 24 hour passage calculation down to 98.24 before making any adjustments for the Caframo fan useage or the AIS receiver not always receiving. The numbers are looking a lot better. I'd edit my original post, but I can't anymore so I changed it in the quote above.

I really appreciate the comments I've had on this. I wouldn't have caught these errors otherwise.

Where are the pumps? bilge, freshwater, shower sump?

[Sea Life]

We Just finished our second full time year cruising the tropics, some thoughts for you....

It is a lot cloudier then expected, often several days ina row, then full sun for a few. Make sure the panels have a very high low light output.

Everything cost a lot more, if you can get it. So adding anything once you leave the US, is going to cost dearly. Shipping rates are high from the US, and customs can be as well. Maybe install fridge now, and just don’t use it?

I’m in the put in as much battery as you can afford and will fit. Never have I wished I had less capacity on any boat

[Cthoops]

Originally Posted by jhulmer

Where are the pumps? bilge, freshwater, shower sump?

No shower sump or freshwater pump (we have a footpump in the galley and a handpump in the head). We do have a bilge pump which is activated so infrequently that it's not worth adding into daily calculations.

[Sailmonkey]

Our last 48 hour passage consumed a grand total of 120ah. That’s with refrigeration, autopilot display on, iPad charging, tricolor, 3 fans on almost the whole time etc. the total consumption is somewhat skewed because we have solar, put it was obscured for most of the time.

What I’m trying to say is your consumption estimate is high for 24 hours.

[Dougtiff]

Consider a water tow, i have been using one for year's, when i change boat's, i always keep the tow, now there are tows that attach to the boat, not intrusive, doesn't impact the speed.

[Cthoops]

Thanks so much to everyone for their input. Working through the math and taking into account the suggestions that were made was invaluable. I found a few errors, made several adjustments to the passage calculations, and rethought the solar panel sizes to have two of the same vs. one large and one small.

We're going to go with the two Firefly's (I ordered them yesterday) and two 138 watt Solbians. The panels will easily keep us topped off while at anchor and will also cover our useage while on passage assuming it's not a cloudy day.

Nine months and twenty days to go! Thanks again.