We have been working on our list of winter projects while we are not sailing. One of the more complicated items on the list is figuring out the solar panels. We have to figure out how much power we need, which solar panels to buy, what equipment we need to go with them and where and how to attach them. George spent a few weeks investigating how much power we need. He listed all the items on the boat that draw power, how many amps each item used per hour then estimated how hours a day each item was on. He totaled them up and came up with 150 amps while sailing and anchoring and 218 amps when sailing 24 hours a day. We don't currently have a monitor to tell us what we actually draw so these numbers are just estimates.
I have been practically no help with this project because I have had a mental block against all things electrical. No matter how many times it has been explained to me, I haven't been able to understand it. Until this week, that is. A member of the fantastic Facebook group, Women Who Sail, asked a question about electricity on a boat. Holly Scott, another member of the group and owner of Charlie's Charts www.charliescharts.com, wrote a very simple explanation in response. I finally understood. Holly gave me permission to publish her explanation here.
Everything uses some juice. Batteries hold juice. Look on your batteries and see if you can find a sticker that says something like 120 AH or amp hours. Add them all together on your house batteries. Amps are like measuring cups for electricity. Maybe a lightbulb draws 1 amp. That means that in one hour, it will use up 1 amp from the batteries. 10 hours = 10 amps etc. Some things list the watts they use. It's just another measuring thing, but not much help cuz you have to convert them to amps. sigh. Here's how: watts divided by 12 (12 volts - some folks have 24 volts and other weird things) equals amps. So a 75 watt bulb draws 6.25 amps if it's on for an hour. Yikes!!! Add up the amps for all the stuff you use. Running lights might be on for 12 hours, but your fridge might cycle on and off and only use 7 amps in an hour. You will have to pay attention to how long things are turned on. Auto pilots use a lot and so do SSB radios when you are transmitting. There should be a label on each light, pump, fridge, whatever - that states how much juice it uses. Convert them all to amps and add them up. To be safe, round fractions up. So lets say that your total is 80 amps in 24 hours. And your battery bank, all together holds 360 amps. You can only use half the amp hours in the batteries or it screws up the batteries, so you have 180 amps to work with. Woo Hoo! Your batteries can manage that! Now, how do you put amps back in the batteries? Run the engine, solar, battery charger if you are plugged into a dock etc. What size alternator is on your engine? 50 amps, 80? Look and see. Alternators charge fast when you first turn on the engine, but then taper off so you don't fry the batteries. Run the engine hard for about 20 minutes, then slow it down and charge them up! Solar panels are rated in watts. A 100 watt panel would crank out 8.3 amps every hour in perfect conditions, but not for more than maybe 4 or 5 hours every day, depending on where you are. You still need to come up with 50 more amps…. does that make sense? There is a doohickey called a Link Monitor, which you can install and it tells you how much you are using, how much you already used, how much you need back and how fast you are charging. I put one in and LOVE it. No more worries. Totally worth the time and $. There's a bunch of other technical stuff, but that's the basics of what you need to know to figure this all out. It's kinda fun if you don't get freaked out. Smile and good luck!!!
I love this explanation. I now finally understand the difference between a watt and an amp. Holly's website is a great resource for sailors. I bought a cruisers siphon there as a gift for George and plan to return to the site for other great cruising gear.
We have a battery bank with 360 amp hours. As Holly mentioned above, we can draw down 180 amp hours without damaging the batteries. If we use 150 amps in 24 hours while we are sailing and anchoring we will get through a little more than a day without having to recharge the batteries.
We plan to buy flexible solar panels and install them on our bimini using either zippers or Velcro. Measuring the bimini was a fairly easy task and it looks like we will have plenty of room to install four panels measuring approximately 21"x41".
If we purchase four 100 watt solar panels we will be able to recharge our batteries up to 166 amps per day. That is 100 watts/12 volts=8.3 amps per panel. Multiply by 4 panels=33.2 amps per hour for the set. Multiply 33.2 amps by 5 for the number of hours of sunlight adequate enough to charge the panels each day and we get 166 amps per day under ideal conditions. That doesn't quite get us to what we need but it helps a lot and is a good place to start.
We are considering purchasing a set of four 100 watt
Renogy solar panels from Amazon. These are available at a very good price for flexible solar panels and the controllers and wiring we will need for the installation are included. I have learned from other Women Who Sail that you can sew right through the edges of the panels so I am thinking I can sew Velcro on the top of the bimini and also on the edges of the solar panels to attach them to the bimini. Drena Jacinta Galarza sent a link to her
blog post explaining how she attached hers using Velcro. We think they look very nice.
So, that is where we are on this particular winter project. Stay tuned...
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