another solar question, beating the dead horse

[aronhk_md]

Ok, so in searching I have found lots of talk about solar being great for topping off batteries, but usually insufficient to power anything with substance, like refrigerators or A/C. The usual statements are that for the average user, its not possible to have enough juice produced to make it happen with the number of panels the average boat can reasonably carry.

So I say, ok...makes sense. Takes lots of room and lots of panels.

I have lots of room on my deck canopies. So would you folks mind carrying me through an exercise in "what if?"

*An average small home fridge uses 10 amps on 120v.
*An average home 8000 BTU A/C unit uses 7.5 amps on 120v (I think marine reverse cycle A/C is more efficient but haven't researched it yet completely, just going off the fact that instead of using 90 degree ambient air for your heat sink you are using cooler water)

Lets take a solar array hooked to a bank of 12v batteries. I don't understand the conversion from 10 amps at 120v to what the draw would be through an inverter at 12v DC on those batteries. Can anyone explain that for me? With today's panels, how many panels would be needed, and how much surface area?

What I'm wondering is.........what WOULD it take to run that fridge? Or the A/C? Not necessarily together. I am assuming you would want to match the current draw of what you are using to what you are producing, though I imagine if you came close you'd slowly drain the batteries and that would not be good.

Honestly just looking at the stuff on ebay and conversations about it here leads me to confusion as far as how many panels can be hooked together, run by a single controller, what type of panels, etc. Not sure where to go to research it more carefully even since there is SO much info out there.

 

[deckofficer]

Looking at your deck canopies from your avatar I would say you have plenty to power a fully electric galley along with A/C. The biggest draw would be A/C, so lets crunch some numbers there. 12,500 btu will draw around 1500 watts and depending on outside temp could cycle 50% for 10 hours per day. 7500 w-hr on the A/C, and no more then 2500 w-hr for everything else including electric cooking and fridge and freezer. I set every load on the high side to show max draw. 2000 watts of solar that would fit on your boat's canopies coupled with a large battery bank would make you self sufficient. If you stay with a 12 volt bank for inverter loads I would go with LiFePO4 cells instead of lead acid, which sags under load.

At 90% conversion efficiency a 10 amp load at 120 VAC would draw from a 12 volt battery 110 amps.

 

[aronhk_md]

So you are saying that a 2000 w system on 12 volt would run a 12,500 BTU A/C unit, a fridge, and most of everything else in the galley with occasional use? Something like a 3000w inverter would be needed I guess? Does producing and drawing that much energy through the batteries shorten the life of the batteries?

Also, what kind of controller would that require? So far rthe HD controllers I see for example by Tristar only control 60 amps...which equates to 720w at 12v.

What size battery bank would be needed?

 

[deckofficer]

I think the largest 12 VDC input inverter is 4000 watts cont, surge 8000 watts. Most inverters this size are 48 VDC input, so the amp draw on the battery bank is 1/4 of a 12 volt battery bank. Lets say your A/C is running at the same time you use your microwave and coffee maker. That comes to 3900 watts, so at 90% efficiency of the inverter would draw close to 400 amps, and any lead acid battery would experience serious voltage sag along with de-rating of a-hr capacity due to the Peukert effect. This is why for such a large system at 12 volts, lithium cells are the way to go, almost nil Peukert, and minimum voltage sag. If you feel more comfortable with lead acid instead of LiFePO4, then I would go with a 48 volt bank to feed a 48 volt inverter. A good choice would be (24) 700 a-hr 2 volt AGM cells in series. This would give you 33.6 Kw-hr bank which is large, but you could go with a 17 Kw-hr LiFePO4 bank and have the same usable a-hr with 4 times more cycle life.

Starting load of an A/C can be twice the running load.

 

[aronhk_md]

Which Li cells would be needed and how many? Don't you need special lithium chargers and controllers too?

 

[deckofficer]

I have used Winston LiFePO4 cells. I don't use any BMS (battery management system) but I did perform a bottom to top balance of my cells in parallel before putting them in service. The only thing I use is a cell logger with digital readout and high and low cell alarm. You could assemble a LiFePO4 700 a-hr 12 volt battery that would have more usable capacity than a 1400 a-hr lead acid bank for $2240 here Balqon - Advanced Transportation Solution

Charge cells to 3.55 volts (14.2 Volts for 4 in series) and don't allow them to discharge below 3.0 volts (12 volts).

 

[deckofficer]

The reason you can use a much smaller a-hr rated LiFePO4 battery vs lead acid is how these two different batteries get their advertised rating. With lead acid for decades it has been calculated on a 20 hour rate to completely drained. So on a 100 a-hr lead acid, that is 5 amp draw for 20 hours. LiFePO4 use a brutal 1 hour rate and stop when the battery is 80% discharged instead of the 100% discharge for a LA rating. LA should not be discharged deeper than 50% for it to give 500 cycles, while a LiFePO4 can be discharged to 80% for 2000 cycles.

If you discharge a LA at a 1C load (100 amps for a 100 a-hr battery), then the Peukert effect would de-rate that 100 a-hr battery to about 30 a-hr at best.

Big difference between LA and LiFePO4. It has only been the last year that due to major price drops of LiFePO4 cells, they have become the least expensive battery option when you factor cycle life. I've used all types of batteries in the electric vehicles, and now that I've used LiFePO4 I will never go back to lead. Lead is dead.

 

[aronhk_md]

Without some sort of battery management system I cant imagine knowing when the cells have reached their charge threshold. It would require frequent checking, and THEN turning on the charging system when it gets there, no? Or do you allow the system to charge WHILE using the current to power stuff on board? Doesn't Li also require a special charger?

 

[deckofficer]

With your solar you can enter bulk and float voltages into the MPPT controller. Due to the high charge acceptance of LiFePO4 you will need to reduce the output of an engine driven alternator. On a LA bank, the surface charge helps to cut down on charge rate, but a 80% DOD LiFePO4 bank will pull whatever the alternator will put out without taper so after a period of time the alternator that has thermal protection will back itself off. I mentioned above that a cell logger with high and low alarms will notify you with an alarm that one cell has slipped below 3.0 volts. For charging, if you set the solar controller and alternator for 14.2 volts, there won't be a chance of any single cell going over 4.0 volts. For everything you might want to ever know about the care and feeding of these cells, here is a 2800 post thread just on LiFePO4 cells for house banks. LiFePO4 Batteries: Discussion Thread for Those Using Them as House Banks - Cruisers & Sailing Forums

 

[deckofficer]

BTW member rjtrane just upped the ante on his boat, going with (16) 1000 a-hr Winston cells for a 48 volt 1000 a-hr bank. He not only has a fully electric galley, A/C, electric heated hot water, he also has diesel-electric propulsion, thus the big bank. He is also running 6 Kw of solar, whereas I mentioned for your needs of A/C and electric galley, 2 Kw of solar would fit on your canopies and do the job for you of no gen set run time while on the hook.

 

[Insequent]

I have just installed 7 x 260 W panels on my boat, and removed a 7.5 kW and a 2 kW generator. So far I have seen the solar putting 60 A into the battery bank in recent weeks in Puget Sound. When I get to somewhere with more sunshine, or sun angle higher in the sky, I expect to easily double that.

In due course I'll collect some data for analysis, but initial thoughts are that I have plenty for LED lighting, DC refrigeration and assorted electrical stuff. But not enough to run an electric range/oven or airconditioner - i dont have, or want, those things, so no problem.

 

[deckofficer]

1820 watts of solar is a nice array. Get out of the PNW and with your efficient lighting and fridge you should be able to run the A/C and electric kitchen appliances.

 

[FF]

*An average small home fridge uses 10 amps on 120v.

50% to 90% of the time!

*An average home 8000 BTU A/C unit uses 7.5 amps on 120v (I think marine reverse cycle A/C is more efficient but haven't researched it yet completely, just going off the fact that instead of using 90 degree ambient air for your heat sink you are using cooler water)

The first solution is always to trash the home cheapo equipment for far more efficient alt energy gear.

A better fridge like a Sun Frost may require 1/2 to 1/5 the energy of a house reefer.

Thicker insulation , no need for heat to defrost internal thin insulation and a more efficient compressor all help.

There are 12 Truck air cond, built for battery operation.

The use of water cooling does make any refrigeration/air cond slightly (5%-10%?) more efficient , BUT the main use is to get the heat out of the boat.

You will still need a Honda for those days when there is not 12 hours of sun shine..

A simple cost analysis may show you are spending $50 to save $4.00 worth of fuel per hour..

 

[aronhk_md]

Thanks guys....this is just an exercise in "what if" as I mentioned. Sure, it might be cheaper to run a generator in the short run, but what if you are living aboard? With the price of solar panels coming down to less than $1 per kw, its not so far fetched to put together a 2000 kw system for under $4000 (not including batteries). Even a new Honda 2000 generator is $1000, and to run it all the time costs money.

If you are on the grid while plugged in, that costs money.

Its an interesting exercise in "what if" to see what it would take to be self sufficient part of the time, even if it turns out "not worth it". Most of the time in these threads its left at that, rather than actually tallying up what it would take in equipment to make it work. In other words FF....actually DOING that cost analysis. As an exercise if nothing else.

Now I do realize its not sunny every day. And there are months in our seasons here in the northeast where the days are short. But I do wonder what my local marina would say if I asked them about feeding back into the grid on sunny days. (lol, yes I know its probably not possible even though they have metered slips)

 

[motion30]

that seems like a high current draw for small 120 volt fridge

 

[aronhk_md]

You may be right. I just did a search to see if I could find average draw for a home type fridge. FF....I do realize there are much more efficient appliances out there too. Good stuff. Just tried doing the setup without going to "best of the best" scenario.

So its sounding to me like a 2000 kw system with Lipo batteries could be assembled for around $6000? Doing it all oneself that is. It would be able to run at least some A/C, a fridge and some other on demand galley equipment as needed. I'm sure for the average user it would have no problem with LED lights on board, and probably a computer. Maybe an LED tv?

So....you'd be able to power those items on sunny days in your region. Less so on winter days obviously due to the angle of the sun. My guess is too, if you used "best of the best" equipment, you might be able to get away with less power.....say 1600 kw?

 

[Phil Fill]

One big factor is you are in Delaware. Take a walk around and see how many solar panel there are. In the PNW, not many and if there are to charge the batteries.

 

[deckofficer]

Just a few corrections. The average home fridge consumes 180 watts when running which is 1.5 amps at 120 volts, not 10 amps. I quoted a 2 Kw solar array (2000 watts) not 2000 Kw (2,000,000 watts).

 

[Underway]

I spent much of this week speaking with the technical staff of several large insurance companies about the confusing and potentially dangerous situation that is developing for Lithium batteries amongst do-it-yourself boaters. Every one of them is extremely concerned with the "wild west" (their words) information scenario that is developing in the marine community... primarily via boating web sites. ABYC is in the loop and I suggested that they step up their efforts to clarify design, component certification, installation, monitoring, maintenance, and inspection criteria for a minimum acceptable system. I have also alerted the Coast Guard Engineering and Boating Safety offices to the potential safety scenario that is clearly developing. I specifically requested that both ABYC and the Coast Guard conduct a serious engineering assessment of the Greenline boats that are being imported. Awards in the categories of design innovation and eco-friendly are nice, but the important categories are performance, safety, and quality. Greenline might set the example for the industry...good or bad. Information in these threads is heavy on performance potential and light on safety. The word cavalier comes to mind.

 

[deckofficer]

skidgear,

And as a kid you were the hall monitor, right? I don't know of anyone using any other lithium battery for a house bank other than the perfectly safe LiFePO4 chemistry. We give up some energy density with these cells over lithium ion, but have no thermal issues. Yet you felt it was your duty to cast doubt over all lithium battery installations? Politicians use scare tactics for their agenda, what is your agenda?

 

[Underway]

skidgear,

And as a kid you were the hall monitor, right? I don't know of anyone using any other lithium battery for a house bank other than the perfectly safe LiFePO4 chemistry. We give up some energy density with these cells over lithium ion, but have no thermal issues. Yet you felt it was your duty to cast doubt over all lithium battery installations? Politicians use scare tactics for their agenda, what is your agenda?

No need for the offensive wise guy antics. My discussions with them were specifically about LifePo4 battery technology. My agenda is safety.

 

[deckofficer]

I'm not being a wise guy. You are just what the insurance companies love, a reason to not pay a claim. Should I or any of my friends have a claim unrelated to our house batteries, you have just provided a means of claim denial. For what reason have you spent a week doing this? Did you even bother to research all the safety tests preformed on LiFePO4 cells? Or are you just an alarmists that gets excited easily by Boeing's issues with their lithium batteries which BTW are NOT LiFePO4 cells?

 

[twistedtree]

I think you guys may be overly optimistic on the power draw calculations, especially for AC. If you run the AC 24x7 then once the boat is cooled down you might be able to keep it cool with a 50% duty cycle 24 hrs a day. If you only run it 10hrs per day, I think you will get more like 100% duty cycle as it works to cool the boat down. Also, 12k BTU doesn't seem like much AC for a 54' boat. If you take a look at your AC units you should be able to see what they collectively draw, and from your current use perhaps you can get a sense of the duty cycle.

In general AC is a brutal load on solar/batteries. Electric cook tops are too, but they tend to only run for 15-30 minutes or something in that range (no pun intended), but AC is relentless. Your fridge and other loads should be manageable with solar, especially if you get yourself changed over to LED lighting.

There are tables where you can look up the equivalent number of hours of full sun light for different parts of the country. For DE, I'd guess it's around 5 hrs. That number takes into account weather patterns and expected shading over the course of a year. You could get weeks of clear skies, but you could also get weeks of overcast. The 5hrs is what it all averages out to. If you are only powering in the summer, then you will get bteer numbers since the 5hrs also accounts for seasonal variation.

Anyway, with 5hrs of equivalent full sun a day, that means that 2kW worth of panels will produce 10kW-hrs of energy per day. But that assumes you can capture 100% of that energy, and you usually can't. As batteries become charged they accept a slower and slower charge which means available power is being forfeited. I'd probably de-rate everything by 80%, yielding 8kW-hrs produced per day. That's still pretty good power, but I think you are going to be hard pressed to get very satisfactory AC performance out of it. Maybe if all you cool is your stateroom at night? That's probably what DeckOfficer is envisioning.

 

[Underway]

I'm not being a wise guy. You are just what the insurance companies love, a reason to not pay a claim. Should I or any of my friends have a claim unrelated to our house batteries, you have just provided a means of claim denial. For what reason have you spent a week doing this? Did you even bother to research all the safety tests preformed on LiFePO4 cells? Or are you just an alarmists that gets excited easily by Boeing's issues with their lithium batteries which BTW are NOT LiFePO4 cells?

More attacks. I am very aware of the differences in chemistry, as were the insurance companies, ABYC, and the Coast Guard. They don't share your enthusiasm in the safety area.

 

[deckofficer]

twistedtree,

Good points. As to A/C usage, go the zone approach where during the day only the main cabin is cooled, at night if needed, berths only. Reuben cools his entire cat trawler in Florida from his solar array. The charge acceptance of LiFePO4 is much greater than lead acid, so with a MPPT solar controller you will harvest most all of the solar energy produced if feeding a LiFePO4 bank. Many of us are doing that now, because of the large price drops of these cells this last year. Just on the Cruiser's Forum I know of 8 boaters that have switch from LA to LiFePO4 when Balqon had their clearance sale. They all are amazed at the difference in a-hr rating, low voltage sag under heavy inverter load, nil Peukert effect, and charge acceptance. The biggest one of course is a 400 a-hr LiFePO4 bank is giving more usable a-hr than the 800 a-hr lead bank that was replaced. As to cycle life, even the early adopters haven't reached any where near the advertised life, though they have passed the life of the best LA's they have ever had by a factor of 3.

 

[deckofficer]

More attacks. I am very aware of the differences in chemistry, as were the insurance companies, ABYC, and the Coast Guard.

So, what was their response to LiFePO4 cells? Since you stated they have concerns, combined with the fact all the boaters I know that switched from LA to lithium chose LiFePO4, it still begs the question, why were they concerned at all?

 

[Ebaugh]

I spent much of this week speaking with the technical staff of several large insurance companies about the confusing and potentially dangerous situation that is developing for Lithium batteries amongst do-it-yourself boaters. Every one of them is extremely concerned with the "wild west" (their words) information scenario that is developing in the marine community... primarily via boating web sites. ABYC is in the loop and I suggested that they step up their efforts to clarify design, component certification, installation, monitoring, maintenance, and inspection criteria for a minimum acceptable system. I have also alerted the Coast Guard Engineering and Boating Safety offices to the potential safety scenario that is clearly developing. I specifically requested that both ABYC and the Coast Guard conduct a serious engineering assessment of the Greenline boats that are being imported. Awards in the categories of design innovation and eco-friendly are nice, but the important categories are performance, safety, and quality. Greenline might set the example for the industry...good or bad. Information in these threads is heavy on performance potential and light on safety. The word cavalier comes to mind.

The problem is no one in the alphabet soup you mentioned has much practical experience with lithium phosphate in marine applications. Really no one does yet. Genasun, Mastervolt and Victron have products, but the installed base is small. The collective DIY installed base is probably even smaller. If you know of incidents related to marine LFP installs please share them, and we can worry about the safety together. Boeing's problems and the earlier laptop fires were for cells with significantly different characteristics than what is being used for marine. Don't take my word for it, read this:

http://www.electrochem.org/dl/interface/sum/sum12/sum12_p037_044.pdf

It's clearly stated there that LiFePO4 cells are the safest available. That does not mean some unique precautions are not justified, but I don't think it's a looming safety crisis. If you do some homework, and I have. Have you?

 

[deckofficer]

An informed man of reason, Ebaugh thank you.

 

[sunchaser]

Politicians use scare tactics for their agenda, what is your agenda?

It all depends on whose ox is getting gored.

For many years I was involved with providing fuel in the nuclear fuel cycle. A big concern is/was spent fuel. Harry Reid lobbied correctly (IMHO of course) and hard for building a nuclear waste repository at Yucca Mtn Nevada. However once he saw the light of Senate leadership, political correctness and the Democrat party platform he flip flopped and this wonderful now built facility is shut down. Guess which State's leaders told Harry to tow the line, hint it is known as the left coast

When it comes to energy, everybody has an opinion and fewer still have the facts whether for Li batteries, coal or nuclear. On a different thread I had mentioned CA has not recently allowed any power plants to be built, I left out the word coal - lucky for me I guess as coal burning emits CO2, as do I. So instead CA builds gas plants emitting ---??? But, CA is quite content to import gas from elsewhere while letting its economic savior, the oil and gas rich Monterrey Basin, lie largely untouched due to "concerns."

So Bob, welcome to "not everyone loves my mode of energy" debate.

 

[deckofficer]

We will get to the point of understanding that the sun provides all the energy we need for our modern lives, hopefully sooner than later. Full time cruising is a perfect example to bring this point home, as it is the sun that creates the winds for propulsion, and the electricity for all our needs. Even hydro is really solar, think about it. Future historians will remember this era as the fossil fuel era, providing we make the switch away from fossil fuel so that there is a future.