Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

thompsdw · June 2014

Hello everyone, very nice forum but I couldn't find the answer to the question I have. I recently purchased the following equipment:

Instapark ZJ-02 100w Monocrystaline Panel
Sunforce 60032 30a Digital Charge Controller

The intent was to charge a bank of 3 batteries - 1 start battery and 2 house batteries wired in parallel. All batteries are 12 volt due to the "boat".

I usually do better homework, but I am afraid I might have screwed up this one. I was subsequently told by Sunforce after installation that you cannot charge multiple batteries with a single panel and controller. I certainly understand that the controller would be confused by having that many batteries connected and "what is happening" at the battery.

So here is what I did - I disconnected the house battery from the controller and left the 2 house batteries (wired in parallel). The system seems to work fine now as it views the house batteries as one big battery (the batteries are exact matches). Comes up to voltage and floats.

So, here come the questions. Given that the system is installed - can I leave it on the house batteries and put another system on the starting battery? Is there some other solution (is there a charge controller that works on 2 battery banks?) that I can implement given I have "sunk" the cost of the current system?

Thanks in advance.

jcheil · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

thompsdw wrote: »

The intent was to charge a bank of 3 batteries

We need to know the Ah rating of the batteries.

However, be advised that a single 100w panel is likely not going to be able to "charge" that bank - it will only be able to produce enough power to "maintain" that bank - unless they are very small batteries.

thompsdw · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

jcheil wrote: »

We need to know the Ah rating of the batteries.

I would only like to charge the 2 house batteries. They are right at 100 Ah's each. What I am thinking is to leave it as is to maintain the batteries, add a second panel and charge controller for the starting battery. I would also install a charger for the house batteries if they are deeply discharged.

BB. · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

Here is a controller family designed to charge two different battery banks (good but not cheap):

SunSaver Dual Battery 25 Amp 12 Volt Solar Charge Controller
SunSaver Dual Battery 25 Amp 12 Volt Solar Charge Controller With Digital Meter

To charge 200 AH of 12 volt deep cycle type batteries from solar, we recommend 5% to 13% rate of charge:

200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 188 Watt array minimum
200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 377 Watt array nominal
200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 490 Watt "cost effective" maximum array

And to "Float" the battery bank, a minimum of 1% rate of charge:

200 AH * 14.5 volts * 1/0.77 derate * 0.01 rate of charge = 38 watt array to "float" battery bank (with charge controller)

In the end, it depends on what you are trying to do... If you use the engine to keep the bank mostly charged, weekend use, etc... a 5% rate of charge minimum can be OK.

If you are living long term on the boat, don't want to use the generator/boat motor too much--Then the 10%+ is a better solution.

Of course, it depends on how well the panel catches sunlight (i.e., sail boats, boats at anchor, etc.) can be less than optimum for solar charging.

And, how much power do you plan on using--You have two choices--Build out the system you can fit/afford/works and that is the amount of power you have available--Or you start with your loads and design a system to meet your needs. In either case, extreme conservation will be your friend (it usually costs more to generate power than it does to conserve).

Solar also depends on the angle of the panels, where it is installed, and seasonal usage (summer vs winter), etc... But if you assume an average of 4 hours of day during 6-9 sunny months of the year. A couple examples of the "solar math" for a 100 watt panel:

100 Watt array * 0.52 AC system efficiency * 4 hours of sun = 208 Watt*Hours per day (120 VAC inverter)
100 Watt array * 0.61 DC system eff * 4 hours of sun * 1/12 volt system = 20 AH per day @ 12 volts

-Bill

jcheil · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

thompsdw wrote: »

I would only like to charge the 2 house batteries. They are right at 100 Ah's each. What I am thinking is to leave it as is to maintain the batteries, add a second panel and charge controller for the starting battery. I would also install a charger for the house batteries if they are deeply discharged.

So 200ah total.

The problem is that you need around a 10% charge rate to get any kind of effective charging abilities.
That would roughly be 20amps of charging current. That single 100w panel you have, "at best; in perfect conditions" will only put out 5 or 6 amps; and depending on where you are, that would only be for a handful of hours each day. So if you were only using 20-30 ah per day, you might "get by" but any more than that and you will fail to get them back up to 100% each day. But it will certainly work to "keep' them charged while they are not being used.

I'm sure the experts here can chime in and give you a more exact set of numbers.

draines · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

BB. wrote: »

To charge 200 AH of 12 volt deep cycle type batteries from solar, we recommend 5% to 13% rate of charge:
200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 188 Watt array minimum

200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 377 Watt array nominal

200 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 490 Watt "cost effective" maximum array

Not to hijack a thread....but BB, can you break this down for the beginner? I see you respond with very similar calcs in a lot of forums...so I imagine it's important for me to understand it?
Namely the rerating values and the rate of charge % origination.
Thanks in advance!

BB. · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

Sure Draines,

Most people assume that solar panels are sized to meet their load needs--And that is certainly true....

However, "we" (many folks on the forum) recommend that a person also size the solar array based on the size of the battery bank too... For many reasons, the "optimal" charging rate for a battery bank is around 5% to 13% rate of charge for a solar power system (you can go upwards of 20-25% rate of charge on a lead acid battery bank--But for solar panels--It gets sort of "expensive" to over panel that much).

In the olden days--Solar panels were very expensive and lead acid batteries were cheap. So for people that had problems with not enough solar power at their cabins/homes, many folks suggested adding more batteries to their bank and that would solve their running out of power problems.

In practice that made their problems worse... The cabin owner now had a 2x or larger battery bank that was 2x more expensive and started sulfating/producing less average power (from solar array) than before--Because they really simply needed more generation power (solar panels and/or generator run-time+fuel).

Today--Batteries are expensive and solar panels are cheap--So adding more panels is not the problem it used to be (panels were $10-20 per watt, now are ~$1-$2 per watt). And we can "afford" to go back and look at the overall power needs and create a "balanced" system. One with a "just large enough" battery bank for 2 days or so of energy storage (no-sun, plus 50% maximum discharge for longer battery life) and enough solar panel to meet both needs--The 5-13% rate of charge for battery bank health and a large enough array to meet the daily power needs (based on location, season, aka amount of sunlight per day).

5% -- Usually the minimum recomended rate of charge for a lead acid battery... Below this, battery chemistry can have problems, takes many days to recharge, and battery self discharge can use much of the solar array's output energy. You need ~2.5 to 5% rate of charge to properly "equalize" a battery bank. At 5% and below rate of charge, you need to babysit your loads to make sure your batteries are kept "happy" (try not to discharge below 50% state of charge, and get back over 90% state of charge several times per week).

10% -- Usually a good fit for most people. Battery bank is charged correctly/quickly. And usually if you do the "balanced" system design math, the solar array + battery bank will meet load requirements for a full off time cabin/home/RV very nicely. If you have some daytime loads (computer, office, water pumping, etc.)--This is a nice size array that lets you run your loads without too much baby sitting. Some battery vendors recommend 10% rate of charge as their minimum charging current.

13% -- More than this, most people have the battery bank charged by noon--and are simply wasting energy. And if you go >~13% rate of charge, you really need a charge controller with remote battery temperature sensor to prevent battery thermal run-away (boiling dry, starting fire/explosion).

The 0.77 or 77% derating--Solar panels are rated for ~75F degree operation of their cells. Works great in a lap/factory test--However, for real life, the sun heats up the cells by upwards of 30C/54F over ambient air temperature. This reduces their output voltage/power to ~81% or so of Marketing Spec. Add losses for controller/dust on panels/aging--77% of rated output is a good starting point for sizing the system.

The rest, is battery bank AH capacity and charging voltage (~14.5 volt charging vs 12 volt battery bank). Just another "fudge factor" that works well for me... I try to conservatively size the system so that, worst case, it will perform as expected. In cooler climates, others will use ~82% or a bit higher for their deratings--Your choice.

Does this help?

-Bill

RCinFLA · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

The batteries you describe sound like size 27 or 30 marine batteries. They are likely lead-calcium alloy plate construction which have a much lower leakage then true deep cycle lead-antimony alloy plates battery. It only takes approximately 0.1 to 0.3 amps to maintain a float charge for a 100 AH battery of this type, assuming the battery is in good condition. You should try to accomplish at least 1 amp for float maintenance per battery since you only have 3 to 5 hours of reasonable sun exposure time to replace the capacity loss by self discharge leakage. Again this only accomplishes float maintenance on a lead-calcium battery.

If you are trying to recharge a partially depleted battery you need the 5 to 15% AH in amps from the solar panel to make any reasonable headway on recharging.

AuricTech · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

BB. wrote: »

<<snip>>

The rest, is battery bank AH capacity and charging voltage (~14.5 volt charging vs 12 volt battery bank). Just another "fudge factor" that works well for me... I try to conservatively size the system so that, worst case, it will perform as expected. In cooler climates, others will use ~82% or a bit higher for their deratings--Your choice.

Does this help?

-Bill

Am I correct in assuming that the charging voltage in your 12-volt equation scales with increases in battery bank voltage, such that a nominal 24V battery bank would use ~29 volts for charging and a nominal 48V battery bank would use ~58 volts for charging? If so, am I further correct in assuming that achieving such charging voltages at the battery bank would require ~17 volts / ~34 volts / ~68 volts at the PV array (higher if using an MPPT controller with GT panels, of course), so as to allow for voltage losses in the system? (My forum search-jitsu is not yet strong enough for me to find your equations for battery banks of voltages higher than 12V....

)

BB. · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

Yep--That is the way it works... Technically, usually 17.5 to 18.6 volts is typical Vmp for a "12 volt panel".

By the way a good way to search the forum (or limit your searches to any specific website) with Google is to use the "site:" tag... I.e.,:

solar rule of thumbs site:forum.solar-electric.com

You can also use "quotes" to search for exact spelling, and "+" to make sure something is in the results and "-" to remove a word from the results.

-Bill

thompsdw · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

So I am wondering if the best solution for me is to add a second 100w panel, buy the duo charger, and use the two panels to charge the house batteries. If the starting battery gets low, I can use the house batteries to start the boat. My panel uses HQRP fittings. I assume I can tee into the existing panel in some way and use the single 50' line set to put the additional charge to the duo. The HQRP wire I am using is good for 12 AWG, Voltage: 600/1000V.

TucsonAZ · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

One thing I noticed nobody has pointed out, make sure if you're hooked up to two batteries in parallel that you've done your connections properly (positive connected to one battery and the negative connected to the other) and they're of the same type/age otherwise you will shorten their life.

I would do this to keep things simple and somebody correct me if I'm wrong. Convert everything to watts, you have 200ah @12v or [200AH*12V=] 2,400 watt*hours, of that you can use 1,200 WH of it without causing yourself issues. That would mean in Southern Arizona with a PWM charge controller you would be getting 80% of what your panels are rated for times 5 hours per day (at best) so with your 100w panel you'll be getting 400 wattsb*hours per day. In your case with 1,200 available watt*hours, on the best of days you would need 300watts of solar panels.

If I were you, I would add at least one or two more panels and call it good enough, if you're going over 400 watts, I would readjust your thinking, use what you have for the single battery and buy grid tie panels with an MPPT charge controller as your main system.

[correct energy usage to Watt*Hours. Watts is a rate like miles per hour and Watt*Hours is and amount like miles driven. -Bill B]

vtmaps · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

TucsonAZ wrote: »

I would do this to keep things simple and somebody correct me if I'm wrong. Convert everything to watts, you have 200ah @12v or 2,400 watts, of that you can use 1,200 of it without causing yourself issues.

amps is a rate of charge movement. multiply it by time and you get an amount of charge (amphours)

an amount of charge multiplied by volts is an amount of energy (watthours)

The energy that a battery stores is measured in watthours

200 ah X 12 volts = 2400 watthours of energy storage

solar panels produce energy at a certain rate, measured in watts

a panel producing 100 watts for 4 hours produces 400 watthours of energy

--vtMaps

BB. · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

For TucsonAZ, I corrected the post to Watt*Hours.

Also, don't forget losses... It is unfortunate--But the average off grid power system and good components/design/usage is, overall, only ~52% efficient from Panel "Marketing" Ratings to actual Watt*Hour of AC power used at the load.

So, a typically minimum sunny day of 4 hours of "noon time equivalent sun" on a 100 Watt panel would be:

100 Watt array * 0.52 AC system eff * 4 hours of early spring/late summer day = 208 WH of AC power from the inverter per day

Panels are approximately 81% eff based on their "marketing rating. MPPT charge controller is ~95% eff. Flooded cell lead acid batteries are ~80% efficient. And the AC inverter is ~85% efficient. Multiply all those together and get ~52% end to end efficiency.

It is a pain--But it is the math/engineering. You can do a bit better (with component selection, how the system is operated, keeping panels very clean, etc.)--But the above is conservative enough that most everyone will at least meet the above production predictions.

Panels mounted flat to an RV roof--Collect more sun during the 6 months of summer in the American south... Toward the northern boarder/Canada, the mounted flat to roof becomes a real issue with a less summer production and a lot less winter production.

Making tilting panels is a pain for RV's--But for for folks that winter camp/especially up north--Should seriously think about what to do about winter usage (more fuel for a genset, vs panel mounting/tilting/stowing for travel).

You can use PV Watts or SolarElectricHandbook to see how much panel tilt will affect your production.

-Bill

TucsonAZ · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

To the OP, I didn't notice where you lived and BB makes a good point as it could really impact your choices. On a 500ah bank I'm installing 1,380 watts of solar which would be overkill in Tucson where I live but I will be traveling with it and spending time in the PNW so I've sized accordingly. There are days I may be able to run any and everything while the sun is still up and there may be days I seriously struggle. One thought is to have a panel you can chase the sun with, meaning, it isn't permanently attached and you're able to point it right at the sun, moving it a few times throughout the day.

Good luck and don't get yourself overwhelmed! Nice work on diving in!

thompsdw · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

Is there any negative to using a higher watt panel like a 250watt in my application? In that case I could use the 100w for the starting battery and a 250watt panel would get me over the 5% charging threshold on the two house batteries. I don't know how to predict the sun at my location. Because it is a boat, they must be fixed panels. I am just going to have to make a stab at it and hope it works well.

Cariboocoot · June 2014

Re: Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

thompsdw wrote: »

Is there any negative to using a higher watt panel like a 250watt in my application? In that case I could use the 100w for the starting battery and a 250watt panel would get me over the 5% charging threshold on the two house batteries. I don't know how to predict the sun at my location. Because it is a boat, they must be fixed panels. I am just going to have to make a stab at it and hope it works well.

You would need an MPPT type charger to make full use of the 250 Watt panel's power.

Newbie Needs a Little Help on Solar Charging of Batteries on Houseboat

Comments

Categories