Can somebody go over this build and make certain I'm not missing anything.

Re: Can somebody go over this build and make certain I'm not missing anything.

Jchell,

Is this an RV, "work trailer", or moving a fixed system from place to place?

If you are going to be "up north", some method to tilt the array for winter is going to be important.

Power usage--You could be looking at 1.5 kWH per day pretty easily (laptop and router, satellite?--can easily push close to 1 kWH or more if used a lot during the day).

Since we don't really have loads--And assuming this is going to be a reasonably full time off grid power system, using our nominal rules of thumbs--See how it looks (note, for an RV, battery may be 1/2 the size because of weight/size limitations--which does limit life and surge capacity somewhat--But 1/2 the battery buying 2x as often--the costs will be similar--AGMs have very good surge, so that is in your "favor").

Starting with 250 AH @ 24 volt battery bank. 2 days of storage, 50% maximum discharge:

• 250 AH * 24 volts * 0.85 AC inverter eff * 1/2 days * 0.50 max discharge =1,275 Watt*Hours per day nominal

So, the battery bank is a bit on the small size--For what I would recommend for a full time/off grid system... For a portable system, it is probably what you have to live with.

Charging current of 5-13% rate of charge--10%+ is "very nice" for full time off grid:

• 250 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 942 Watt array

6x 280 Watt of panels (?) = 1,680 Watt array

You could support, pretty easily (with power left over) for a larger battery bank:

• 1,680 Watt * 1/29 volts charging * 0.77 panel+controller derating * 1/0.10 rate of charge = 446 AH @ 29 volt battery bank

To size a battery bank for 2 days of off grid and 50% maximum discharge--A "nominal" average discharge rate of 20 hours:

• 250 AH * 24 volts * 1/20 hour discharge * 0.85 inverter eff = 255 Watt AC "nominal" average load
• 250 AH * 24 volts * 1/8 hour discharge * 0.85 inverter eff = 638 Watt AC "nominal" maximum load
• 250 AH * 24 volts * 1/5 hour discharge * 0.85 inverter eff = 1,020 Watt AC maximum short term continuous load
• 250 AH * 24 volts * 1/2.5 hour discharge * 0.85 inverter eff = 2,040 Watt AC max surge load

The above are for Flooded Cell batteries--AGMs can do "better"--But there is really no reason to push the above limits most times--It requires much heavier cabling and is stressful on the batteries.

And then there is how much average daily power you can "expect" from your solar array. Assuming a minimum of 4 hours of sun (typical 9 months minimum, may not be true in coastal Washington state):

1,680 Watt array * 0.52 AC system derating * 4 hours of sun = 3,494 Watt*Hours of 120 VAC per "sunny" day

If you use ~1,275 Watt*Hours (fix because of 12/24 volt error) at night, that leaves you a lot of "extra power" you can use during the day (computer/work hours/etc.)... So, you do have a question of day/night split of power. For off grid homes, typically power usage is very low during the day (out working) and peaks in the evening... 24 hour loads (like fridge) and office loads (computers/network/printer) during the day can "play" with battery sizing assumptions.

One reason to not assume "daytime" power loads is that if you need to work during the day and cannot shutdown during bad weather or run a genset (like putting off clothes washing, water pumping, etc.) as you would do for a residence.

Which brings us to a genset--Assuming somewhere around 10 to 20% nominal charging current and worst case battery charger design (Iota's are not very generator friendly):

• 250 AH * 29 volts * 0.10 rate of charge * 1/0.80 charger eff * 1/0.80 light duty genset derating = 1,122 VA rated genset for ~25 amp @ 24 volt charger
• 250 AH * 29 volts * 0.20 rate of charge * 1/0.80 charger eff * 1/0.80 light duty genset derating = 2,266 VA rated genset for ~50 amp @ 24 volt charger

The first one is just about the limit for a Honda eu2000i genset... (check with Iota retailer to make sure OK with smaller genset)

If you go with a "larger" battery bank, it does make the charger/generator bigger:

• 446 AH * 29 volts * 0.10 rate of charge * 1/0.80 charger eff * 1/0.80 light duty genset derating = 2,021 VA rated genset for ~45 amp @ 24 volt charger
• 446 AH * 29 volts * 0.20 rate of charge * 1/0.80 charger eff * 1/0.80 light duty genset derating = 4,042 VA rated genset for ~90 amp @ 24 volt charger

If you want to keep with a smaller Honda eu2000i genset and an Iota type charger, you are probably looking at a 20 amp @ 24 volt charger--Probably a bit on the small size for

Anyway--The paper side of the system design/capabilities. You could also look at "Generator Support" capable Inverter/Chargers too--Would make the whole backup generator (and possible grid power) much more transparent and support larger loads when needed (if needed).

-Bill

Re: Can somebody go over this build and make certain I'm not missing anything.

If only my mistakes were so "rare"--I like to think of them as "well done".

Off to fixing the post. Thank you Photowhit.

-Bill "I show my work" B.

Re: Can somebody go over this build and make certain I'm not missing anything.

The 1,000 watt inverter is just on the ragged edge of running a refrigerator/freezer... 1,200 to 1,500 watt minimum should run just about any full size energy star rated fridge/freezer.

If you know the 1kW inverter you are looking at will run a fridge--Then ignore me--Just a generic warning.

-Bill