Tristar TS-45 vs Tristar TS-MMPT-45 for a Off-Grid Small Cabin

Re: Tristar TS-45 vs Tristar TS-MMPT-45 for a Off-Grid Small Cabin

Welcome to the forum!

Looking at each point:

hmarkvitz wrote: »

First of all, greetings to all. I have a question about solar panels and charge controllers that don't have an answer. I am hoping anybody with knowledge can help me find an answer to it. My family started to build a small cabin in my country here in the Caribbean. It is a hot and sunny place so we decided to go for a off-grid solar system since there is no electrical source at this place. I am currently using (4) Astroenergy 285 watt panels to produce electricity.

The Astroenergy panels you link to are Vmp~35 volts--Which is find for use with a PWM type charge controller.

I am using a Trace 2.0kw power inverter and an 8 battery system.

What are the batteries? (type, volts per battery, AH per battery, etc.). I am not a big fan of paralleling batteries, but if you must, follow the recommendations from the Smartgauge web site.

Also, because batteries can output scary amounts of current into a dead short--You should use Fuses/Breakers on each cable/wire that leaves the + battery bus (to protect down stream wiring against shorts). If you have parallel battery banks, you should have a fuse or breaker per parallel battery connection.

I was looking at buying the charge controller and stumbled upon two good choices. First of all, let me make clear what I will be using in this cabin. We have 3 light bulbs, 1 radio, 1 small fridge, 2 outside 50w lamps, and a 32 inch lcd.

The small fridge is the "killer"... Small refrigerators use almost as much power as full size (efficient) refrigerators... (maybe 820 WH per day for small fridge vs 1,000-1,200 WH per day for a full sized fridge).

See if you can get a Kill-a-Watt type meter to measure your AC electric loads (don't know if you need a 120 VAC or 230 VAC meter for your location).

If you need just refrigeration (vs fridge/freezer) a converted chest freezer can use as little as 250 WH per day (wives tend not to like chest freezers because of poor access to food--be warned).

I saw the Tristar TS-45 controller and the same Tristar TS-45 with MPPT. I want to know if it is necessary to spend 266 more dollars for the MPPT controller. What are the differences in efficiency? Is it worth it for a system rated at 1140 watts? Any help would be appreciated.

MPPT controllers can pull more energy (not a huge amount--maybe 10-25%) out of solar panels in sub freezing weather--But that is probably not an issue for your location--So that would not be reason to buy in your case.

The two-three reasons that may make a MPPT more interesting to you... First, if you have a long wire run from the solar array to the battery shed--You can put two (or possibly) three solar panels in series and run 70 to 105 volt Vmp-array voltage... That will allow you to use much smaller diameter wire and/or install the array 100' (30 meters) or more from the battery bank.

Another reason, you can put two panels in series--This will give you a bit more "head room" for Vmp-array-hot vs Vbattery-charging-cold (hot panels depress Vmp, cool/cold batteries need higher charging voltages).

Since you are on a semi-tropical island with moderate temperatures (vs high desert with very high daytime temps, and very low over night temps), again, this is probably not a driver for spending extra money at your installation.

Lastly, MPPT controllers tend to have more data/logging information (larger memory, large controllers can even have Ethernet connections) and other options. Also, MPPT controllers can be "over paneled" and they will safely/reliably limit their output current to rated maximum (PWM controllers will not--can over heat/shutdown with "extra larger" solar array).

So--distance from array to battery bank and ultimate solar array size (vs controller current rating) are the two points I would focus on.

Both TS family controllers support remote battery temperature sensors (I would suggest buying the option). And both controllers support remote battery voltage sensing (extra "volt meter" wires from controller to battery bus)--Also a very good idea and well worth installing (accurate battery voltage readings usually gives you a bit faster recharging times).

There are more choices for MPPT controllers in the 60 amp or larger range... But not many other in the 45 amp range....

Another option I would suggest is a Battery Monitor (Victron is another good brand)--Batteries are the "heart" of your off grid system--And about the only thing you can damage through poor operational practices (under/over charging, not checking water levels, not using distilled water, etc.). A battery monitor makes it much easier for spouse/kids/guests to see what is happening and you can give simple instructions like (conserve power if less than 75% of bank capacity, start generator/call you if battery bank is below 50% of state of charge, turn off all loads if approaching 20% SOC as bank will be damaged/ruined, etc.).

-Bill