My complete Off Grid system- Montague Township, Canada,

Cariboocoot wrote: »

Welcome to the forum, eh?

What you can expect from 800 Amp hours @ 48 Volts: about 4800 Watt hours per day @ 25% DOD. So the question is: is that enough? An A/C unit (window shaker) will pull 500 Watts and run half the time: 6 kW hours. Oops.

Sixteen 310 Watt panels is 4960 Watts. Based on that you'd have enough to recharge that much battery, but realistically for end-to-end efficiency you've got perhaps 10 kW hours AC per day.

Your inverter size depends on how much you need to run at any one time.

As always you should start by coming up with a realistic daily Watt hour need and plan from there. Without that magic number there's no point in picking any equipment at all. You can start with existing electric bills and measuring wit a Kill-A-Watt meter any and all things you have now that you expect to run there. It will give you something to go on.

Of course it is going to be said: why off grid? It is definitely not economical. Grid-tie may be far more practical for you.

SolInvictus wrote: »

With the Conext XW-MPPT80-600 charge controller's maximum of 600 V, you could put 8 PV panels in series to make two series strings. That way you buy only 2 parallel MC-4 connectors, do not need series fuses and can probably use smaller gauge wire. Because its MPPT range is 195 VDC to 510 VDC, 4 PV panels in series only gets the V_oc to 181.7 VDC while the V_mp will be even lower which are both outside of the specifications.

With sixteen 310 W PV panels, you will lose some power because the charge controller's output is limited to 80 A.

16 * 310 W * .85 (efficiency) / 48 V = 87.8 A

16 * 310 W * .85 / 57.6 V = 73.2 A

The 80 A output occurs when the battery voltage is 52.7 V. It is a judgement call.

It is best to have only one or two series strings in a battery array because it minimizes wiring and makes it easier to balance the voltages. You could use fewer batteries with a higher capacity to achieve that.

Is there some reason why you want to mount them on a 2x8 (wooden?) pole instead of on the roof of the garage/workshop? Unless you need the pole for dual axes tracking, cantilever mounts always require strong components. I doubt that a 2x8 would be strong enough in cantilever (7.25"² * 1.5" * f_b / (8' * 72) = .137 f_b at best). It would probably wobble and snap in the 2" nominal direction with only moderate wind. A ground mount rack would probably be less expensive and more durable. Concrete, concrete blocks, anchor bolts and EMT would be reasonably cheap.

We can not check the size of your battery array nor PV panels without having a detailed accounting of your electrical loads and how long you plan to run them. Does the propane furnace have an electric fan to circulate the air through a central ducting system? Since you have not built your house yet, you could design it to use less electricity. There are wall mounted, ductless propane heaters available. Two or four of them located strategically around the house could be adequate. Perhaps a wood stove?

Cariboocoot wrote: »

Well if we take 200 Amp hours * nominal 48 Volts we get 9.6 kW hours so I guess I slipped a digit on that first calc. After AC conversion and not including inverter consumption you should have about 8kW hours to work with. So this is looking better.

A/C could still be murder on this, depending on how much has to be allotted for everything else. Usually refrigeration takes up a substantial amount.

Don't work from maximum sun hours on long days because you need to know the minimum amount of energy you can count on. There's some curious factors that will come in to play: hot temps will reduce panel Voltage and thus power, and even though the days get long the amount of equivalent direct sun on the panels doesn't increase linearly (especially not with fixed arrays).

Then there is the fact the sun does not shine every day. That one can be killer, especially in our Northern climes. But that is why you allocated for a generator.

Problem with battery-based system is that the efficiency isn't very good due to the losses incurred from having to put power in to and take it out of batteries. When you can make use of panel power during the day after the batteries are charged you gain efficiency, but it is not always convenient to turn things on midday.

As such my original end-to-end estimate of 10 kW hours per day should be thought of as a minimum for sunny days. This will handle your <9kW hours daily load estimate. My main point is to be very sure of the accuracy of that number because it will make or break the system. If you have only 2 Hours of good sun on the panels that 'harvest' number will be cut in half. How much do you want to have to run the generator? The auto gen start may be a good feature here, and btw you can also use the XW with gen support to handle really large loads if needed (parallel output of inverter & generator).

Xantrex equipment is not quite the wonderful stuff some may have you believe. If you search the forum for threads about the XW6048 you will see it has numerous bugs and a few operating quirks. Fortunately you will also find a lot of the solutions and workarounds too.

(Okay: corrected over 30 typos in this post; it must be getting late.)

I would bet that if you did a random survey and asked people what the most expensive thing is about living off-grid that you would not get the right answer from most folks. It is batteries. Not solar panels, or inverters, or controllers, or generators, or fuel in the generators. Batteries.

Sandia Labs did a study a few years back on off-grid deep-cycle batteries related to DoD and battery life using Rolls-Surrette batteries. They determined that the amount of usable energy gotten out of a battery over its life is greater if you deep cycle it vs shallow cycle it. I'm sure the study could be googled up for those who are interested. So people who buy extra battery capacity to prevent cycling them below 70-80% SOC are actually spending more money over the long term on batteries than those who deep cycle them to 50% and replace them more often.

Where generator support in an off-grid inverter comes in, is allowing you to buy the bare minimum in battery capacity to run your normal daily loads and let the generator help with the big stuff instead of just throwing more batteries and solar panels at the problem. Many folks consider it the "pinnacle" of off-grid to not have to run their generator. In reality, that generator fuel is a lot cheaper than the extra battery (and RE generating) capacity it takes to never run the generator.

In most off-grid homes the normal loads are pretty light, and the heavy draw stuff is very intermittent. Instead of spending the extra money on batteries and multiple inverters to meet the peak demand, generator support is a lot cheaper. So it not only saves you money on batteries, it also saves you money on extra (or bigger) inverter equipment.

And the last thing it allows you to do is save money on generator fuel. Too many off-grid people have a 10, 12 or 14 (and some even over 20) kW generator on a XW6048 inverter or similar. This is ridiculous. The generator should not be any bigger than required to get either maximum charging amps from the inverter, or C/10 charge rate for your battery bank, whichever is smaller. Running a 8 or 10 kW generator to charge batteries with a 6 kW inverter is like using a semi to haul an armload of wood. Inverters that only have generator pass-thru support are limited to either what the inverter can run, or what the generator can run. And that means if you want to power a 6 kW load with a 4 kW inverter you need a 6 kW generator, and you have to run that 6 kW generator for charging when you only need 3,500 watts to max out the charger in the inverter. With gen support you can save the gen fuel and run your 3,500 watt generator for battery charging, and still power that 6 kW load with ease.

These are all the reasons why, to my way of thinking, an inverter that does not have generator support in it is not a real off-grid inverter. I know way too many off-grid people who have over-sized their generator because they got Outback FX-series inverters and need to power an occasional heavy load that only the generator can run.
--
Chris