Merged LiFeYPO4 1000Ah Winston prismatic cells and all electric galley...

[hzcruiser]

Originally Posted by CatNewBee

Thanks.

Well talking about the project has some benefits, it is a review of what you have done when discussing it with others, and sometimes you even learn from other solutions or think about side effects by the upcomming questions, so you can improve your system. Its a win-win...

It sure is beneficial to a lot of people, unless you get into endless discussions where both sides are adamant they are "right"...


As a comment from my end, and I haven't analysed every bit of information you gave: It seems you've designed your LFP storage (I don't always add the Y) to come up to 100% SOC every average day?



That would almost be like storing them at 100% for extended periods. From my understanding, LFPs shouldn't be kept at or close to 100% SOC (and neither at or below 10%) in order to maximise their lifespan.


In that scenario, wouldn't it be ideal if you could tell your BMS to generally keep the LFPs at x to y percent (e.g. 50-60%) and when you know there are a few days of less sunshine coming up you tell your system to maximise storage?



Well, "ideal" would be if your system pulls down the weather forecast itself and makes that decision, also including your average consumption during the last x days... but that's for the next release.

[CatNewBee]

I consider 100% SOC at 3.55V and not at real 100% SOCat 3.65V, it is around 95% and healthy, the Absorption voltage at the MPPT is set to 14.35V that translates to this value on the cells if you subtract the voltage drops on the way. this voltage stays for 30 minutes to allow some balancing, then the Voltage drops to FLOAT 13.6 at the controller, in reality this are 13.4V at the battery, it is around a cell voltage of 3.35V, there is no charge until the battery reaches this value.

Also there is a constant discharge of around 15A, the consumed energy until solar contribtes to the board consumption is another 50Ah. The battery stays the day to safe 90% SOC to the pont, where the sun goes down, then the battery slowly discharges to 80%
on the next morning. There is no point in time the battery is at real 100% SOC.

50% SOC is meant for long-time storage only and not for daily usage. Shallow cycles extend the life expectancy of any battery, ant the battery is there to be used and not to contribute to the weight of the vessel only..

I expect 5000+ Cycles with this use pattern or at least 10-15 years battery life in daily use.
Of course any system can fail at any time, but under regular circumstances I will be fine.

[CatNewBee]

Originally Posted by hzcruiser

....

Well, "ideal" would be if your system pulls down the weather forecast itself and makes that decision, also including your average consumption during the last x days... but that's for the next release.

Well there is a ideal solution of the differnd kind. Just buy a LFP of the half size, then use and abuse it with full charges, when it dies after 10 years, buy another one, then hopefully more reliable, smaller, lighter and cheaper than today.

Batteries are consumable products. Dont put too much effort to safe their life instead of using them as long as they last. (the engeneers point of view, the academic would object obviously)

[CatNewBee]

Here a screenshot from the Victrom MPPT controller,
you can see, what Energy was harvested and how long it took to charge the battery, until the MPPT goes to float, also the battery min/max voltages during the day.

on the max voltage you must subtract 0.2V, because it is is the Voltage when the controller is charging in absorption, and there is a voltage drop between the output and the battery. The low voltage is measured on heavy loads by induction cooktop, oven or espresso machine, that pull the voltage down a little while running.

More interesting are the values of peak energy, they only once hit 1400W, else they stay around 1000W, this is due to shading from the boom (one panel always shaded) and cloudy weather.

But this 4 days show, that the system can produce 4-5kWh per day on cloudy days and over 6 when the sun is shining. Always, when there is a float phase on the diagramm, there was excess energy, that the system has not harvested due to full batteries and lack of demand.

So pretty good I guess...[emoji108]

[CatNewBee]

Today fixed the water heater, 40l took 120Ah to heat up until the boiler switches off.
Because it was cloudy all day long - only 3.3kWh harvested and the water heater on top, I probably will end up with -300Ah or SOC 75%. Not that bad.

Will see what tomorrow brings.

[rpmbnsf]

Great information, thanks for sharing so much in such an exact way!

I'm especially interested in your plans to run one small AC unit off your system.

[CatNewBee]

Well, the A/C will be tested when I am back in the water end of june I hope. I am still on the dry refitting her, but live on board and use everything possible without shore power, even all the power-tools to get an idea of my power needs.

I will continue posting how far the 1000Ah battery and my solar can keep me off-grid.

So the generator test and the A/C stuff must wait for now.

There are 4 A/C units on board, all the same size. I have no idea yet how much power they need, however, the generator has 9kVA, and I assume they will not use all of it. My guess is, they will probably draw approx. 1.5kW each and this can easy be provided by the inverter.

[CatNewBee]

The water heater is really a power hog.

It takes 110A and needs 1h 20min to heat 40l of water, that translates to almost 150Ah for hot water (it is a 1200W / 220V unit). Will see how to handle this on the way. Probably run it only when the solar goes to absorption or maybe earlier, when SOC goes over 95% at the end of charging...

[john61ct]

Don't you have diesel?

[CatNewBee]

For what?

I dont want to run the engine or a generator only to make warm water. The sun is (until now) 4 free... [emoji1] [emoji108] and it keeps the SOC below 100%.

[CatNewBee]

[CatNewBee]

[john61ct]

Sure if it turns out you have surplus electric from solar, just I would not design that as the primary source.

But usually hot water is a waste byproduct of burning dino juice anyway.

Living in cold dark climate I'd have Webasto-style for boosting, as well as space heat distribution (hydronic)

[CatNewBee]

I am still testing, what my setup is capable to do. Today up to now 7kWh, still charging with 40A (its almost 6pm here...), used / charged 530Ah, the battery can swallow another 90Ah until full...

A webasto is a nice furnance. I have only the A/C units and use a dyson blower/heater if necessary in the spring / autumn. Can run it easy from the LFP..

[rpmbnsf]

I wonder if it would be beneficial to set up some kind of solar water heating system, mate to the back side of the solar panels. help keep the solar cells cooler (more efficient) and you get free hot water. set up a temp switch to shut off when water reaches a certain temp.