How to add a small generator to Conext SW 4024 - DC coupled system

Welcome to the forum PondWater,

Sorry you have not had any replies yet... I do not know much about the details of inverter AGS integration to answer that question... However, you do need to start measuring your daily loads and solar harvest to get a handle on the system. And, some questions:

• Are you close enough to the cabins to (for example) come by and start a genset every couple of days (as needed during bad weather/heavy usage)? My personal suggestion is to keep systems "simple". Adding genset+AGS adds complexity, more maintenance, and more ways things can go wrong. And finding a "cheap" AGS compatible genset is not usually easy (genset needs low oil, temperature, crank/no start, AC voltage/frequency, etc. alarms), AGS interface (start/stop/starter/alarms/etc.)... Noise/smoke, fuel, fire safety (many a broken fuel line has burned down a generator shed/home).
• Do you have ability for remote monitoring (Internet/WIFI/Radio/hardwire/land line)?
• Are you OK with adding solar panels... I will "do some math" below--But you are probably correct that you have way too few solar panels--Plus--Adding solar panels vs adding AGS+Genset can be a good answer.
• That your cabins are only rented for 2-3 Days a week is probably a saving grace here... That gives your system 4-5 days to recharge--Not a great design, but cost effective.
• Storing Lead Acid batteries in winter is usually a good thing--Get the batteries fully charged before putting things to bed, turn off master breakers (don't want inverter idling during winter running batteries dead), possibly adding a small vertical array (free of snow) to keep battery bank trickle charged during winter can help too.
• Could you move array farther from trees? It is certainly doable to move/enlarge an array hundreds of feet from cabins. Solar panels need full sun... Shading and even just a few leaves/dappled shade here and there will kill array output (50% or more losses is easy with even a cord/rope/etc. shadow across array).

Your batteries are 8x Flooded Cell Lead Acid (FLA) and 6 volts @ 200 AH (20 hour discharge rate). We use rules of thumbs here to quickly get to a "working" system design. The numbers are not carved in stone, and can be deviated from based on your needs--But they are a good way to a reliable system design.

https://www.rollsbattery.com/battery/s6-gc2-hc/

In your case, you have a "weekend cabin" system. And they are rentals, so it can be very difficult to do any sort of consistent energy conservation plan. For you, LED lighting and a fixed water pumping need--Works for you. Guest come in and plug in hair driers, laptops, computers, kids with games, leave lights on, etc... And the system is supplying way more energy than you may have planned.

For off grid solar power systems--They are, by design, way over-sized for day to day usage. Yes, they will produced 2-4x more energy than you need in the middle of summer--But towards late fall/early spring (or winter--If full time), little sun/shading from hills/trees/etc.--The system is struggling to provide even the minimum amount of energy needed.

First, for sizing the solar array based purely on battery bank size/capacity. 5% rate of charge can work for a weekend/sunny weather system. 10% Rate of charge is usually the minimum/nominal required by the battery manufacturers for FLA deep cycle batteries. 13%-20% rate of charge can be OK for more heavily used systems (>13% rate of charge, make sure the solar charger has a "remote battery temperature sensor" on the battery bank for proper/safe charging at higher charging current.

• your bank is 400 AH @ 24 volts (4 series * 2 parallel strings of batteries)
• your array is 2x 280 Watts = 560 Watts
• 400 AH * 29.0 volts charging * 1/0.77 solar panel+charge controller deratings * 0.05 rate of charge = 753 Watt array minimum
• 400 AH * 29.0 volts charging * 1/0.77 solar panel+charge controller deratings * 0.10 rate of charge = 1,506 Watt array nominal
• 400 AH * 29.0 volts charging * 1/0.77 solar panel+charge controller deratings * 0.13 rate of charge = 1,958 Watt array "typical" cost effective maximum

The above numbers are just stakes in the sand... And are rough numbers... Any "number" within 10% of the above is "close enough" to identical for solar--I just carry the full numbers from equation to equation so you can follow my math (and catch any errors/typos I may make ).

Next--Size how much energy per day/over night would the system battery bank be able to supply (i.e., no-sun cloudy/stormy weather). Generally a good starting place is 2 days of stored energy and 50% maximum planned discharge (for longer battery life)... In your case--That would work out to 25% (1/4) of bank capacity per day (2 days = 50% discharge)--And a buffer of another 30% capacity for 50% to 20% state of charge (SoC) for maximum usage (don't take bank below 20% SoC ever--And get recharged back >75% SoC "quickly").

• 400 AH * 24 Volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 2,040 WH per day
• 2,040 WH per day / 2 cabins = 1,020 WH per day per cabin

That is a relatively small amount of capacity... 500-1,000 WH per day is LED lighting, cell phone charging, limited laptop/tablet computer charging, and a little bit of water pumping (your lift pump and even running a 4,000 Watt AC inverter--are pretty heavy loads here).

24 hour per day loads, even small ones, can be pretty significant on smaller systems. Your AC inverter has an 11 Watt load in "search mode" (off until over something like 10 Watts AC load turned on) and 29 Watts just "on" (no load/tare loss):

• 11 Watts * 24 hours per day = 260 WH per day "search mode"
• 260 WH / 2,040 WH = 13% battery draw per day in "search mode"
• 29 Watts * 24 hours per day = 696 WH per day "on" no load draw
• 696 WH / 2,040 WH = 34% battery draw per day in "on" no load mode

In this case, just turning the inverter "off" when cabins are empty is an energy saver here... And if running inverter "on" (vs "search mode") when cabins are occupied--Draws a fair amount of power (1/3rd of your daily battery budget). Over sized AC inverters can be a big energy hog for smaller systems (not saying yours is over sized--But it is largish).

And for a 400 AH battery bank, the recommended AC inverter maximum size would be around 2,000 Watts for a 400 AH @ 24 volt battery bank. And around 1,000-2,000 Watt AC inverter would "match" the cabilities of your battery bank "better". Your 600 Watt (?) gray water pump (one per cabin) is also a load of "concern" (could you setup drains to one pump to reduce possibility of 2x600 Watt load at same time? Or possibly use relays to allow only one pump to run at a time (of course, more chances for failure).

Next--Sizing the solar array based on your energy needs... Assuming fixed array tilted south, Augusta Maine:
http://www.solarelectricityhandbook.com/solar-irradiance.html

Augusta
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 46° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.28	4.07	4.63	4.59	4.50	4.64
Jul	Aug	Sep	Oct	Nov	Dec
4.69	4.80	4.39	3.60	2.68	2.58

Say 3.0 hours of sun "non-winter" day (long term average):

• 2,040 WH per day (based on battery capacity) * 1/0.52 off grid AC power system eff * 1/3.0 hours of sun per day = 1,308 Watt array "Nov/Jan" break even usage

You do not have a lot of sun anyway--And add some shading from trees (big issue with trees--They tend to grow/leaf out over time--And a good possibility that shading will grow--So you may need to address trees/shading/t  location/tree trimming at some point).

I don't know your actual "winter shutdown" dates--Or how much shading you have--But for a rental, you probably would want to only use something like 65% to 50% of the predicted system capacity (bad weather, some shading) --- And/or plan on running a genset:

• 1,308 Watt array "break even" / 0.65 base load "fudge factor" = 2,012  array adjusted for base load requirement and "some shading"

Anyway--A lot here. And lots of assumptions. This will give you some ideas of what you can do to reduce loads (turn off inverter/run in search mode)... Possibly switching to 24 VDC LED lights (pretty available these days) so you can run cabin lightning without running AC inverter (save inverter losses). Even simple stuff like using "mechanical twist timers" for lighting (so people don't turn lights on then leave for day and such) can help too.

Get a Kill-a-Watt type energy meter to better measure your actual loads:

https://www.amazon.com/s?k=kill+a+watt+meter&ref=nb_sb_noss

Or even some sort of energy monitor in cabin/at your place so that everyone is better informed about actual energy usage (you want to keep the battery bank "happy" for longer life).

After you have gone through all the above stuff--You may still need to visit the "generator solution" and its issues (finding a smallish auto start genset, fuel storage and type--propane vs gasoline vs diesel--And even location--Put generator at "top of hill" or your residence--if applicable and run AC line to cabins/battery system).

Your thoughts?

-Bill