Power Creation and Using it Up

[Dame.n.Jess]

We are currently fitting our boat out to live aboard. My question is around power creation and realistic timelines for usage. We have fitted two 100w panels over the stern and I am in the process of buying and mounting 8 trojan 6v deep cycle batteries. Essentailly I want plenty of reserve power, I will fit led lights thru-out and we are only powering two laptops and two cell phones + the normal nav lights sounder gps etc. No fridge, No autopilot.

Any thoughts on actual performance based off similar systems.

Damien

[noelex 77]

With 200w of solar and no fridge you should have enough power ( only just in the depths of winter, but a heathy excess for most of the year) in Sydney or more northern lattitudes.

[Factor]

You should pi55 it in, as long as you are careful. I have two 120 watt panels, a fridge freezer autopilot instruments alectric windlass etc etc. And I keep up fairly well

[capt_douglas]

Originally Posted by Dame.n.Jess

We are currently fitting our boat out to live aboard. My question is around power creation and realistic timelines for usage. We have fitted two 100w panels over the stern and I am in the process of buying and mounting 8 trojan 6v deep cycle batteries. Essentailly I want plenty of reserve power, I will fit led lights thru-out and we are only powering two laptops and two cell phones + the normal nav lights sounder gps etc. No fridge, No autopilot.

Any thoughts on actual performance based off similar systems.

Damien

Power usage always seem to exceed the power generation, at least in my experience.

With no fridge and autopilot you've eliminated two high usage items. However I'd suggest the following:

1. Find out the exact usage of the items you have onboard (power draw, time used). That'll give you a good idea of the power requirements. Don't forget to leave some room for future additions (fans, fresh water pump, more lights, etc). Low discharge levels will actually give you longer power time compared to a heavy drain. If you use an inverter for the cell phones or computer, make sure you account for the inefficiency of the power conversion.
2. You probably want a 4x capacity to load. That way, you've got reserve capacity for those short/wet/cloudy days when the solar panels aren't working as well.
3. Two 100W solar panels will give you about 150W/day total. There is a 20% efficiency conversion loss when charging batteries.
4. You also want to be aware that the deeper the discharge cycle of your batteries and the longer you keep batteries at a low charge, the shorter the life.
5. I like the Trojan batteries (mine were 105AH ones) so assuming 100A/battery/bank you'd have 400AH of capacity.
6. If you keep the total load on the batteries to about 100AH/day (150AHx0.8=120AH) you should be fine. This way, you could supply more than you use; great when you drew a bit too much power the day before. It might be good to invest in some kind of smart battery monitoring system so you have a good idea of the condition of your battery capacity.
7. You can gain some more charge power by keeping the panels clean, giving them a clear look at the sky, and rotate them with the sun.
8. Be serious about turning off what you're not using. You'd be surprised at the power you can waste by leaving the laptop plugged in, the anchor light on, or that fan running.
9. Check the fluid levels in the batteries weekly. If the level falls too low, you can warp the plates and reduce the load capacity of the battery.

I still find it magical to leave the boat in the morning with a negative charge load on the monitoring system only to return to find the discharge in the single negative digit, or much nicer, 0 on the display. It wasn't free but it was clean and quiet.

[noelex 77]

Good advice from Capt Douglas, although I didnt quite follow 3 and 6

Originally Posted by capt_douglas

3. Two 100W solar panels will give you about 150W/day total. There is a 20% efficiency conversion loss when charging batteries.

6. If you keep the total load on the batteries to about 100AH/day (150AHx0.8=120AH) you should be fine. This way, you could supply more than you use; great when you drew a bit too much power the day before. It might be good to invest in some kind of smart battery monitoring system so you have a good idea of the condition of your battery capacity.

Based on my rather limited sailing around Sydney with 200w of solar you will get about 70AHR a day in summer and 35AHrs in winter.

[djmarchand]

A good rule of thumb is that 100 watts of solar panels produce 33 amphours of stored energy at low lattitudes in the winter or high lattitudes in the summer on a sunny day.

David