Energy Audit

Mike B1026 · Jan 21, 2012

My case is similar to yours. I went with 2 AGM's (don't have to be AGM's) and went with a 20w solar panel. A controller is recommend. I also found the 20w panel gives me a bit more cruising range. I also have a ventilation fan that runs 24hrs 7day a week. (draw .08a) VHF, GPS, instruments, auto tiller pilot, fan. I usually run off one battery the first day, then switch to the second one the next day (first still has some reserve and panel is charging it while using the second battery) Third day I still have power without having to head to a marina for power.

I developed a solar panel that attaches easily to a railing and easily adjustable. I plan on putting them in production soon.

Benny17441 · Jan 21, 2012

A controller is recommended as it will prevent battery power from leaking back into the panel at night.

Ron20324 · Jan 21, 2012

The "Boatowner's Illustrated Electrical Handbook" offers that if your panel is less than .5 percent (in amps) of the battery Ah rating, you do not need a controller. (2 amps panel in a 400-ah bank).

West says 1.5 percent. (1.5 amp panel on a 100- amp battery.)

Maine Sail · Jan 21, 2012

Squidd said:
Looking to "power up" my boat, buy batteries and thinking solar charger but not sure how to do an energy audit when I'm not sure what my usage is goin gto be...?

Weekend crusier, sitting on trailer at marina during the week so not alot of "shore power" to charge off of unless I spend the night in a transient slip...(which I probably will do one night a weekend)

No TV no AC, probably no heater (unless is slip) only "major" usage is I will have a 12 v 75 watt coffee maker for a pot or two in the morning...

A french press might be a good energy saver..

Squidd said:
Other than that not much draw, beside anchor light one maybe two nights, 10 watt deck light occasionally and basic interior lights... and VHF while crusing and weather reports at night.

Listening to the VHF is low draw. The lighting will be your biggie and cold be +/- 10 Ah's per day.

Squidd said:
I have a pull start outboard so no starter battery needed, so was thinking one (maybe two ??) average size deepcycle batterys and a 10 watt solar panel to recharge during the week (might be two weeks between weekends)...

If you can fit a couple of deep cycle group 27's you'll have about 180 +/- Ah's depending upon brand. A 10W solar panel is a "maintainer" not a "charger"...

Squidd said:
My impression is with that low a panel a regulator/controler was not neccessary, but I don't want to cook the batterys but I do want them charged up for the weekend excursion...

A general rule is that any panel that does not need a charge controller is also a panel that is not a charger but rather one that basically maintains your state of charge and not much more.

A 10W monocrystaline rigid panel can put out roughly 0.55A. At an average of abuot 5 hours per day at max output (usually less if panels can't be "aimed") you'll get about 2.75Ah's returned per day, at best. If you're using 10 Ah's per day, which is quite light with incandescent bulbs and a 75W coffee maker, you're still consuming 3X the energy than you're putting back per day.

Squidd said:
Am I in the ballpark or am I missing some commonly used appliances that I should add to audit...?

When shopping for panels look at the (Max Power Current / lmp) rating and multiply that times 5. That is roughly what the panel can return in optimum conditions per day.

With a 180Ah bank down 30 Ah's (roughly 84% state of charge) it would take you 10.9 sunny clear days to get back to full. Though this is straight math and does not account for charge inefficiencies, parasitic loads and natural self discharge. In reality you're looking at about 12+ days to get back to full from an 84% state of charge. That is a panel which is far to small for weekending...

Joe Diver · Jan 21, 2012

One of the best things I've done to my boat is replace all the cabin lights with LED's. I have 5 lights in the cabin. The previous incandescent bulbs would draw 1.4 aH each...the new LED's are brighter and draw .09 aH each. I can light the whole boat for less than half the cost of 1 incandescent bulb.

Bill Roosa · Jan 21, 2012

Check the downloads section. there is a spreadsheet the takes a lot of the toil out of dong and energy budget.

Merlin Clark · Jan 22, 2012

How did you get it to work Squidd?

DannyS · Jan 22, 2012

Squidd, get rid of the coffee maker. I had one, used it once and it drained the battery to the point that I couldn't start the engine (long time ago, different boat with only one battery and me being very "green" about my energy setup). Get a percolator. I love making coffee and enjoy the ritual every morning on board.

Steve Dion · Jan 22, 2012

DannyS said:
Squidd, get rid of the coffee maker. Get a percolator. I love making coffee and enjoy the ritual every morning on board.

A melitta works well. Get an insulated caraf and it will keep your coffee hot for several hours.

Stu Jackson · Jan 22, 2012

Do a search on coffee on this board or any other one, and you'll have enough to read for weeks.

Merlin Clark · Jan 23, 2012

Thanks.
I'd also vote for the french press. A Marine buddy gave me a plastic one when my crew was at Camp Babylon and it made the best coffee...all I'd had for weeks was the crap from the mess hall and that was usually limited to one cup due to the traffic.
Wally World has one for 20 bucks http://www.walmart.com/ip/Mr.-Coffee-French-Press/14968038?findingMethod=rr