Re: How much Solar?


Scott SV Tengah
 

Hi everyone,

In FP and Hawaii, we were averaging 5500-6000wh per day. Most I've seen is a handful of days approaching 7000wh. As Mark mentioned, we have a lifepo4 bank (2.5 years now) and that makes a huge difference as you can see when you compare my data to Porter's with similar solar output and similar environmental conditions. I'm sure you all see that once you take a lead battery above 80%, the charge acceptance drops like a rock. And worse, you're supposed to keep lead at high SOC to prevent sulfation so a lot of your solar output will be wasted. With my bank, the full output of the solar (or the 200amps of AC-powered charging) is taken up by the batteries until the upper 90% SOC. And I try to keep the batteries between say 50-80% to maximize longevity, so literally every watt is being put into the batteries.

Another thing that Mark didn't mention, but makes a huge difference is that lifepo4 charging is much more efficient than lead charging. With lead, you lose about 20-30% of your the charge current through inefficiencies. read: heat. With lifepo4 over 2.5 years I'm losing about 2-3%, based on the cumulative data on kWh in compared to kWh out that is provided by my Victron MPPT.

Billy - I suspect something is wrong with your battery monitor? We have 450ah and with 2 fridges and a freezer running, we drop about 8% overnight or 36AH. Not sure if you have water cooled fridges on the 55, but the homemade Frankenstein brushless pump (detailed in another post) has reduced power consumption considerably. Freezer is colder, too! You also stated that you figure about 5kw a day, which should be 5000/25.6v = 195AH, which sounds more realistic. Or are you running other items that we're not? In any event, I don't think your 750w on gel will be enough to eliminate genset usage most days if you are anything like us. 2 fridges plus a freezer and computers on, electric kettle, microwave and plus, the admiral has gotten addicted to Ozark, so the TV is on quite a bit. :) That said, we also run the water maker off our batteries and the 2.2kw scuba compressor if the batteries get too full. But I still suspect 750w on gel won't be enough.

Dan - have you considered adding more AC-based charging capacity? If you have to run the genset, since you have lithium, which can accept high currents, might as well add as much charging capacity to reduce genset runtimes. Your calculated figures on $/hr for genset usage frightened me into looking at more solar! And it's not just the money, I am consciously trying to reduce ongoing maintenance. With our 200amps charging capacity, on the rare instances we run the genset, it's almost always for less than an hour. I suggest rewiring that water heater. We do, in fact, run the water heater on battery/inverter. Our heater is only 700w and I run it for say 20 minutes prior to each shower, which gives me just enough hot water for 2 people.

Eric - no need to add extra ventilation, at least on our passage berth mounted batteries. I have monitored individual battery temps via bluetooth and they rarely get above 30c. They only get hot (40c or so) when I'm running AC-based chargers at 200amps and try to take them to 90%+ in order to balance out the batteries and help the battery monitor reset.

Justin - do you have the hardtop panels on a separate MPPT? Once you get on your boat, I am really really curious to know how many AH you get out of them, compared to your aft panels. Another boat we met in FP has 2kw of solar on their decks and they produce about the same kWH per day as we do with only 960w of arch mounted solar. Much of that inefficiency is probably related to shading, but if you look at the specs on most panels, the power output drops about 0.3-0.5% PER degree C increase over 25degC. I measured the panel temps on mine and it's not much above ambient since they get cooled by the breeze blowing underneath them. I would love to add them but it would be a lot of brain damage for me, so I want to make sure it's worth the effort or maybe I just accept I'll have to run the genset every few weeks.  

Ken is very right with the weight balance issue! I am sick of scrubbing the port side gelcoat! 

At the end of the day, energy is like money - the more you have, the more you use!


--
Scott 
2007 A54 #69
SV Tengah
http://www.svtengah.com

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