Solar design help for DC powered boat lift

It appears to be 24 volts for the motors (and the battery bank)... And it says 12 volts for lighting.

Which is a question... How do they generate the 12 volt power. Is there a 24 to 12 volt down converter, or do they just take 12 volts off the 24 volt battery bank (not usually a good method--Can unbalance the two 12 volt batteries).

-Bill

Are you looking at 4x charging setups or 1x charging setup charging all 4 batteries (can you wire from one panel to 4x batteries)?

-Bill

PS: What voltage are the battery banks (12 or 24 volt)? Just want to confirm (specifications say both 12 volts for lighting and 24 volts for lift).

Just one post that answers the questions for everyone is fine.

Based on battery capacity, 5% to 13%+ rate of charge. 5% can work for sunny season/light usage. 10%+ is really recommended for best battery life.

• 2x12volt in series = 24 volt
• 2x 22 AH (at 24 volt) strings in parallel = 44 AH @ 24 volts
• 44 AH * 29.0 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 69 Watt array minimum
• 44 AH * 29.0 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 137 Watt array nominal
• 44 AH * 29.0 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 178 Watt array "typical cost effective maximum"

And then there is sizing the array based on your daily loads and hours of sun for your location.

• 100 Amps * 0.03 hours (aka 2 minute cycle) * 1/2 cycle per day (once every 2 days) * 24 volts = 36 WattHours per day

Solar energy for Nashville Tn, array, facing south:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Nashville
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 54° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.00	3.51	4.38	5.02	5.04	5.13
Jul	Aug	Sep	Oct	Nov	Dec
5.22	5.14	5.13	4.70	3.52	2.87

Worst case is 2.87 hours (long term average sun) for December:

• 36 WH per day * 1/0.52 off grid system eff * 1/2.87 hours of sun per day (Dec) = 24 Watt array "December breakeven"

I would suggest a minimum of 2x "predicted harvest" to account for bad weather and extra cycles during nice weather... Or 2x24=48 Watt panel minimum.

And if we go back to what 5% minimum rate of charge = 69 Watt minimum array (recommended for better battery health) with 137 Watt array also being a good choice (best for battery charging).

• 69 watt / 29.0 volts charging = 2.4 Amps charging current

You are looking at something a little "different' for a solar power system... A relatively low power 24 volt charging system. You either need a "12 volt" solar panel (Vmp~18 volts) and ~69 Watts (suggested) and a "boost type" charge controller:

https://sunforgellc.com/gvb-8/ (something like $170 -- not cheap)

With a ~69 Watt array

Or get a standard PWM Solar Charge Controller (pulse width modulated) which are much less expensive and 2x Vmp~18 volts ~35 Watt solar panels in series (for a ~70 Watt Vmp~36 volt solar array).

The actual size of the array at ~69 Watts minimum is just that, you could go as high as 180 Watt array (two ~90 Watt panels in series) just fine... Just depends on what you can get for a reasonable price.

https://www.solar-electric.com/residential/solar-panels.html?p=3&product_list_order=watts

Smaller solar panels tend to be more expensive--So do a couple configurations (including cost of shipping, if shipped) to see what works out best for your.

I suggest "glass" based crystalline panels (mono or poly) as having the best life... However they are glass and if you have vandalism issues, then possibly a flexible panel may be a better choice (but they last probably 2-7 years vs 20+ years for glass).

-Bill

Guessing this is the Harbor Freight kit you are asking about?

https://www.harborfreight.com/100-watt-solar-panel-kit-63585.html
In my humble opinion, I would not use Amorphous panels (or at least these panels). They have a history of failing in 6 months to a year (or at least dramatic loss in output). Crystalline (the round/squarish black or "fractured blue" looking cells) last much longer under a glass face.

The other question we have dodged for the moment... I don't know anything about the controller and wiring of your system.

You have two choices--You feed "unregulated" solar panel power (around Vmp~36 volts, but realistically from zero volts (night) to 45-50 VDC -- Voc Voltage open circuit) and there is a "charge controller/regulator already in the system to charge the batteries--OR you feed (more or less) regulated 28.8 volts (if those are sealed/AGM batteries) directly to the battery buses (no switches, no downstream regulator, diodes, etc.--Must be directly connected to batteries).

And most solar charge controllers must connect directly to the live battery bus so they can power their internal electronics and measure the battery voltage (to make charging decisions). And you connect the solar panels last (powering a solar charge controller from solar panels and no battery connection can confuse or even damage the solar charge controller).

Do you have any information on what the Charging Input to your boat lift system is/requires? You can post a link to the system/manual if you have one available (links are OK when directly asking/answering questions--We try to avoid "free advertising" since our forum host who pays the bills is a solar retailer/wholesaler).

-Bill