starting off small but turning into more

[redbank]

Hello All,

I tried doing research using the stickies and other topics that may lead to an answer but it seems like nothing jumps out at me like....this is the answer.

I have a small cabin used on the weekends, we have been off the grid for 15+ years. It started out as a deep cycle battery that I would haul back and fourth and had a few 12v rv lights. I then upgraded to a goal zero package (small panel, lights and a small battery) it was at Costco's and has served us well for about 10 years. But recently, we need more because the Coleman instantaneous water heater we use for quick showers is fading.

I didn't want to just replace the Coleman unit with another one, if you are unfamiliar with them they are self contained unit that has a small battery to pressurize the water to make hot water. I wanted to have a water system that would be using power from a source that I can recharge using solar. Doing some searching on another forum I figured buying a bigger panel with a controller would be nice and then I could run more lights and my instantaneous hot water system.

My initial goal
1. Have a 12 volt system at the cabin
2. Run a 12v water pump to pressurize my shower system
3. Run about 10 12v led lights, not all lights will be on constantly
4. have the availability for the system to grow

future goal - would be nice to have a composting toilet inside the cabin for those cold nights, looking at one that requires a 12v fan that would need to run while I am there

My initial purchase
1. 100 watt solar panel
2. 30-100A MPPT inexpensive charge controller
3. 105Ah AGM 12v battery
4. a couple USB charge ports (charge phones)
5. 10 12v light sockets with pull chain on and off switch
6. 10w and 35w 12v led light bulbs
7. 250' of 12/2 low voltage wire
8. fuse block

Starting out I introduced myself in the welcome forum and kinda spilled my basic plan and received a recommendation and decided to act on it. I was told only having one panel may not be enough to properly charge my battery and so I ordered another 100w panel. Well this has created a can of worms because my initial order didn't arrive on time, when I emailed them they said the supplier was having problems. So about a week later I received my panel and thought great, well a few days after that I had another one show and now three weeks later another showed up. So now I have 4 100w panels. Trying to read and figure out can they work with my controller or would it be too much for my battery, or thinking if I purchase another battery can I start using bigger draws on my system like buying and inverter and running a fridge, microwave, coffee pot etc. I know I have to figure out the math but honestly it becomes confusing when you are just getting into this. Any help would be appreciated.

[Mike90250]

If I found myself with 4, 100 w panels, I'd do the following for a 12V system

buy a 30A MPPT charge controller (opinions vary about brands)
Wire 2 panels in series, and aim SE
Wire the other 2 panels in series and aim SW This will spread you solar harvest over a wider period of daylight, instead of centered around noon
Use two 6V 200ah golf cart batteries wired in series, creating a 12V 200ah bank

This would not be enough of a system to run a fridge. You could use a mod sine wave inverter to run a small coffee pot for 10 min after the sun is up and on the panels
It is enough to keep several LED lights on, shower pump and electrics for a propane water heater (would need a PSW inverter, not a MSW)

[redbank]

If I found myself with 4, 100 w panels, I'd do the following for a 12V system

buy a 30A MPPT charge controller (opinions vary about brands)
Wire 2 panels in series, and aim SE
Wire the other 2 panels in series and aim SW This will spread you solar harvest over a wider period of daylight, instead of centered around noon
Use two 6V 200ah golf cart batteries wired in series, creating a 12V 200ah bank

This would not be enough of a system to run a fridge. You could use a mod sine wave inverter to run a small coffee pot for 10 min after the sun is up and on the panels
It is enough to keep several LED lights on, shower pump and electrics for a propane water heater (would need a PSW inverter, not a MSW)

Thank you for your response. I already have a 30A MPPT and it is cheap, I didn't realize how important they can be but for now it works and will be upgrading.

Why can't I wire all four panels in series and place them in different directions?

I looked at golf cart batteries but the ones I could find need vented and I intend to keep the battery inside the cabin so that is why I opted for a 105ah agm battery.

The 12v water pump is already wired to my fuse block which the system works. https://camplux.com/camplux-1-6-gpm-...gm-water-pump/ this is the pump. Why would I need an inverter?

I see you mention MSW and PSW inverters and they can become costly, it appears my system will not be big enough to run the appliances and I really wasn't going for that but the four panels had me thinking.

I guess about my only other wish is having an inverter so that I could charge my dewalt 20v battery, so I will need to look at what size and type of inverter I will need.

[Mike90250]

Any panels wired in series, need to be aimed in the same direction. Power will be limited to the least illuminated panel

Panels wired in parallel, can face any direction, all will contribute what they can

Generally, with a MPPT controller. you need 1.3x max battery voltage, from the array, to insure the MPPT will work. There are some occasions where MPPT can work without much voltage overhead, but the reason to use MPPT is to have higher panel voltage for distance and thin wires, and convert at Controller to lower voltage high amps with thick expensive copper.

And MPPT controllers have input voltage limits. small controllers are often 50V, medium ones, 150V, large ones, up to 600V input from PV arrays.

Charging small devices, some tool chargers REQUIRE pure sine wave, some don't . Weigh the cost of replacing a fried charger, with the higher cost of PSW inverter.
Rule of thumb - if the charger is heavy, it has a transformer and needs PSW. If lightweight, it's a switching power supply and can often manage with modified sine wave. And you will find many exceptions.. But PSW never fries things. (If operating correctly)

[Ho jo]

Ive used a 4 100 watt 30 amp mppt system. Like mikes description. For 3 years now
when the sun is out.
I use a $75 300 watt psw inverter for charging phones. tool batteries and
3=4 hours per day of 32 led tv.

At night I switch to 12 volt DC only
12 LEDs a 12 volt water pump.
hwh and lp fridge silinoid.

[SunEagle]

Ive used a 4 100 watt 30 amp mppt system. Like mikes description. For 3 years now
when the sun is out.
I use a $75 300 watt psw inverter for charging phones. tool batteries and
3=4 hours per day of 32 led tv.

At night I switch to 12 volt DC only
12 LEDs a 12 volt water pump.
hwh and lp fridge silinoid.

I guess my question is what do you do when the sun isn't shining? The panels are now useless and the battery is heavily discharged.

[Ho jo]

Push the genstart button on the remote.

[redbank]

[QUOTE=Mike90250;n418646]Any panels wired in series, need to be aimed in the same direction. Power will be limited to the least illuminated panel

If I understand you, 4 panels wired in series will be just as effective as 2 wired in series because one of the 4 could not be getting its share of light therefore restricting the others from charging the battery..

[Mike90250]

If I understand you, 4 panels wired in series will be just as effective as 2 wired in series because one of the 4 could not be getting its share of light therefore restricting the others from charging the battery..

No, first, 4 in series is likely to overvoltage your controller @ 80V

But if you have 4 in series, and shade one, the bypass diodes in the shaded panel are supposed to allow the other 3 panels to work, at the expense of cooking the bypass diodes in the shaded panel. So relying on bypass diodes to solve a known problem, is poor practice and eventually, you will be looking for replacement diodes.

[SunEagle]

Push the genstart button on the remote.

Makes sense to me. Thanks

[redbank]

[QUOTE=Mike90250;n418674]

No, first, 4 in series is likely to overvoltage your controller @ 80V



I have looked at the specs of the controller (actually have two). One shows max voltage of input at 18v. One panel spec says max open circuit voltage (Voc) 23.2v and the max power point voltage (vMPP) 18.54. So one panel is actually too big for this controller?

My other controller I have shows max input voltage 42v, so I could run two panels with this controller safely.

If I took your advice and wired two panels in series and face them SE and the other two SW what would be the best way to switch between the two panels? I am assuming I need to create some sort of switch before it reaches the controller so I can limit the max voltage these panels will provide.

Appreciate the input as it is slowly making sense.

[Ho jo]

With Max input controller voltage of 42.
Using 23.2 voc panels x 2 in series 46.4
Seems your only choice is all panels in
parallel. Or a higher voltage controller.

[Mike90250]

With your charge controller, you can only parallel panels.
Then I would parallel all 4 panels, face 2 SE and face 2 SW
It's unlikely you would exceed more than 30A with this configuration, so a 30A PWM controller should work. 40A would be absolutely safe

[PNPmacnab]

At that open circuit voltage for the controller, it is probably a FAKE MPPT. You said it was cheap. I like camp systems because they get you so close to the energy where you have to actually plan the use. I turn excess PV into hot water and run what I can directly from solar panels. The other day my hot water tanks had turned off, did a load of dishes in the dishwasher with heated dry, did two loads of laundry with high capacity LG washer running off solar panels, Fridge does not run at night so it has to recover in the morning and the battery gets charged. Also run a pump. All this and before noon. The battery is only a car battery. Amazing what you can do when you get creative and ditch big black box systems.

[ewarnerusa]

...If I took your advice and wired two panels in series and face them SE and the other two SW what would be the best way to switch between the two panels? I am assuming I need to create some sort of switch before it reaches the controller so I can limit the max voltage these panels will provide.

Appreciate the input as it is slowly making sense.

You won't be switching between anything. They are all connected all the time. Your panels are like buckets collecting rainwater, you're just trying to arrange them to collect the most cumulative harvest throughout a day.