Off Grid Beach Lot System

Re: Off Grid Beach Lot System

Welcome to the forum.

That's some pretty big off grid power need! Do you have a number for maximum draw at any given time? Would a 6 kW Xantrex unit handle it? In other words, everything that will be running at once draws no more than 6000 Watts. This can be dicey with AC and water handling pumps, all of which have big start-up surge draws and can come on whenever they need to.

As far as I know, SMA doesn't make battery-based inverters. Therefor the only way to use them is with the SunnyIsland option. Nice, but an expensive way to go for off grid only power. If we had that max power figure there's probably some other suggestions that might help keep the costs down. Assuming you want to keep the costs down. Haven't met anyone yet who didn't!

One example system for your needs (not a specific recommendation):
XW 6048
Parallel banks of eight L16's (320 Amp hours, 6 Volts) for 640 Amp hours @ 48 Volts
4 kW - 5 kW of array (could be problematic in the tropical heat - requires more panels)
Two charge controllers (to handle a peak charge current of over 60 Amps using Xantrex system)

That would meet the 15 kW hour demand using up to 50% of the battery capacity. You'll need some type of generator for a back up charge source too, because even in paradise the sun doesn't shine every day. At least you should have above average hours of sun when it does shine!

Beyond that it's hard to be more specific without more specifics.

Re: Off Grid Beach Lot System

I recommend Trojans as a kind of default, not because they're the best choice for every application. Almost a kind of industry standard. There's nothing wrong with SunExtenders, except that being AGM's they cost more per Amp hour than a FLA battery like the Trojan. Usually he flooded battery is better to start with because they are more forgiving of mistakes. Over charge an AGM and it's done. One battery I do not recommend is Surrette; they used to be top-of-the-line but lately there have been many problems with them shipping dead/defective batteries. So far they've been good about replacing, but who wants the problem in the first place? For a premium priced battery their quality is slipping.

Rule #1 of off-grid power is reduce the loads as much as possible. Electric appliances? If that includes anything that heats look for an alternative. Heating is murder on electric. Burn dried coconut husks if you have to.

The way the system works over-all is that the power is supplied by the batteries which are recharged by the solar panels. There comes a time during the recharge cycle when the batteries will be in "Float" stage, at which point they are fully recharged and you're not making use of the panels' full output capacity. This is the time to switch on those heavy loads, as the panels will supply much or all of the power needed to run them without draining the batteries. Saving battery capacity for when the sun doesn't shine. This is called "load shifting" and can add significantly to your system's over-all power.

Is it possible you'd hit the Xantrex's 12kW surge? I don't know. There are too many possibilities of what you'd plug in and turn on all at once. I run the whole off-grid set-up with 3.6 kW inverter and it never comes close to capacity. It runs an electric 'frige, computer/satellite modem/phone/office equipment, lights, water & septic pump, and even microwave. But what devices you run and for how long and when makes a difference. I use about 2.4 kW hours per day, and the peak load is managed to be under 2 kW (don't confuse Watts with Watt hours) by switching the water pump and septic pump on a controlled basis. The water pump draw 850 Watts running, with a start-up surge well over that but only runs for 6 minutes a day. Run at full sun, it uses nothing much from the batteries and the water is stored in a large pressure tank for use as needed. The septic pump is 1 HP and draws a staggering 1.2 kW - but runs less than 1 minute per day. Again; on during "float" and the batteries stay happy.

Since batteries are the heart of an off-grid system I suggest you read through the battery FAQ's to start getting familiar with them: http://www.windsun.com/Batteries/Battery_FAQ.htm

And for terminology the Glossary: http://forum.solar-electric.com/showthread.php?t=6136

There's tons of info in the forum FAQ too, for independent reading and consultation: http://forum.solar-electric.com/forumdisplay.php?f=14