Matching solar panels to batteries to consumption

[Adelie]

Originally Posted by Sauntress

The existing panel (and it is one panel, not two) is, to judge by the dimensions a Unisolar MBC-262 which would have been installed in the early 1990's. The owner's manual, which I still have says
Rated Power (Wp) 11,
Voltage Typ Max Pwr (V) 15.60
Current Typ Max Pwr (A) .70
There is more, but presumably that is enough for information purposes, I hope. I have printed and read through, several times, your (Adelle) long and learned explanation and realise that the more I think I understand, the less I actually understand. Thus I am in the hands of the experts. I also printed the Article by Richard Perez "Lead-Acid Battery State of Charge vs. Voltage which will make nice bed-time reading.
And yes you have answered my question. But I confess I am confused. Both you and Mitiempo now seem to be saying that if I convert all to LED (which I will certainly do) I could almost get by on the existing Unisolar panel. Or could do if I added a 40 watt panel. Is that right?

I will get hold of a digital voltmeter
The batteries are "maintenance free rechargeable sealed Lead-Acid.

Yes we agree that the existing panel will almost get get you by if you change to all LED.

I thought about it a bit longer and looked up daylight hours for the Med, or more accurately I looked up latitude and checked daylight hours at that latitude and realized that in the Med night in the middle of the winter is on the order of 14-14.5hr long.

So revising the load assumptions to reflect this your daily demand will be on the order of [0.2a (tricolor) + 0.02a (compass)]*14.5hr + 1 a-hr (chart table) = 0.22*14.5 + 1 = 3.19+ 1 = 4.19 a-hr/night.
Let's fudge the rule of thumb for panel output down to 20% to account for the short days:

4.19a-hr / 20% --> 20.95w. A 20w panel would let you scrape by having changed the nav and compass bulbs to LED but not the chart table and being careful about chart table use.

Get a 30w panel and keep the existing one stored away for help during cloudy periods.

I recommend "Boatowner's Illustrated Electrical Handbook, 2nd Ed." by Charlie Wing as an excellent source for info on batteries and electrical systems. It will show you how to calculate a lot of this yourself and how to do the wiring to ABYC standards. ABYC standards don't carry any weight in the EU but I can't imagine the EU is significantly more stringent on this than the US.

I am just finishing reading the 1st edition copyright 1993 which has some dated material so. The 2nd ed is 2006.

[thomm225]

You can make things as complicated or as simple as you want in electronics.

Many times my battery "monitor" is my autopilot. I can hear when it's running slower than normal.

Another is my inverter which will alarm when the batteries are getting low. I run a fan at night from the inverter during the warm months and when I had a battery dying the alarm would sound around 3 am. No more fan for that night.

Then there are the lights or the readout on your controller.

If you have a meter, you can check the voltage on panel side of your controller. When it's starts to climb upwards of 16, 17, 18-20 volts you know you batteries are nearing full charge

[newhaul]

One last.from me on all this . The controller I sugested has a digital battery meter built into it and I have found it to be fairly accurate . Over the long term . For simple installs.