Brain dump for some simple water pump/solar systems.
all this stuff is from Amazon.ca, just to illustrate. You can sub in whatever you want from any other source
SIMPLE Series vs Parallel circuits
Series - Voltage of each part adds up. Parts are wired + to - to + to -….putting all devices (batts/solar) in a single string. Amperage stays the same (at the level of the lowest amperage device in the string)
Parallel - Voltage stays the same, Amperage adds up. Parts are wired so that all the + are wired together…and all the - are wired together
The higher the amperage, the heavier gauge wire must be used so that it doesn’t overheat/melt/catch fire/etc.
The higher the voltage the further the wiring can run with thinner wire (less costly)
Watts = Volts x Amps
Solar Panels
Common solar panels are either Mono or Poly Crystalline. Mono is more efficient, but more expensive.
max voltage ~22V
max amps ~5.8A
max watts ~ 100W
doesn’t quite add up (w=v x a)…because all panels are inefficient
So (theory), if you connect 2 of these panels in series and they get full sun, the pair will produce 44V and 5.8A. (255W but really 200W).
if you connected 2 of these in parallel…you’ll get 22V and 11.6A.
To figure out how much power you’ll produce…guestimate how many hours of sun the panels will get…and then knock 50% off…because the panels are inefficient, the sun won’t always be directly 90deg to the panel face, it’ll be a bit cloudy, etc….
Batteries
LiFePO4 (lithium iron phosphate) are WAY better than Lead Acid (lead plates & sulphuric acid….what you have in your car to start the engine/etc)
LiPO (Lithium polymer….this is the main batt in your hybrid) is more sensitive and dangerous than LiFePO4.
LiFePO4 are super light in comparison, smaller then LA for comparable power, don’t hold a memory (when you partial charge), live for many more cycles, have built in protection for over discharge/under discharge/etc…
Measured in Voltage (e.g. a 12v battery) and Amp Hours (AH…how many amps it can discharge for an hour). So you’ll see a 12v 50AH battery…it’ll be the size of a lunch box and one of the kids can pick it up. You’ll see a 12V 100AH battery…about 2/3rds the size of a car battery and less than half the weight. 12v 200ah….quite big, but easy to lift…but I would be barely capable of picking up a 200ah lead acid battery by myself (or at least I wouldn’t want to).
Batteries store power…so think of how many amps a battery or battery bank have
Similar to solar panels…the can be wired in series or parallel. Same thing happens with Voltage and Amperage.
Pumps
Submersible where the whole pump sits underwater….or dry (sits on the ground out of the well/water source and has an intake/suction hose that draws water)
Like all electrical devices…they need a given voltage and draw a given range of amperage to operate. All electric motors will “surge” and draw more power (watts) when they start up…then less as they keep running.
Lift - all pumps will have some sort of Lift rating. How many gallons/liters per minute to what height. That’s theoretically straight up from the pump. Dry pumps will also have a draw/suction rating…how far down can it suck up water. Again…theoretically straight down from the pump.
Pumps need to be primed (filled with water). They’re not good at pumping air. Water cools the pump to keep parts from burning up or wearing out.
Submersible - stay cool in the water…aways primed. Cons…can’t see it to check things
Dry - can see the pump…some will “self prime” (that just means that they can run dry for a bit until water is sucked in)
Some of the pumps that you’ll see if you search for 12v water pump on amazon
Diaphram - cheap…high pressure…ok for running for shorter periods…small (most are 10mm) fittings…ok for spraying stuff…they would likely not last long pushing large volumes of water (e.g. 4.5L/min)…noisy
Transfer - cheapish…most connect direct to a battery with alligator clips…not great for lift…decent flow rates (e.g. 330Gallons/hour…a third of an IBC tote in an hour….a 55gallon drum in about 20min)…many are garden hose fittings
cheap submirsible - usually used connected direct to battery….dropped into water source (e.g. pond/pool/water tank). Can run off of smaller <50AH batteries. 10M head (i.e. lift). I used one of these for the well…not enough lift for me and burned out after one season.
Deep well pump - made for bigger lifts (40M). 2300L/H. This is what we use…about 20min it’ll fill 1/5th of an IBC tote pushing 1000ft and up to the top of our water tower through a 1’ pipe. These can be run horizontal/vertical.
Keeping crud out of the pump is key….so arranging the intake so that it doesn’t draw in sand/silt/algae/twigs/leaves/etc is key. In a shallow setup…a 5 gallon bucket with slits cut into it all around packed with coarse rock will help. In a deeper setup….a PVC pipe with slits cut in below the water line but above the pump/off the bottom of the well…and the pump dropped into it…will work.
Stopping the pump from running dry is key….in a lake, no big worry (vs a well)
How much power does the pump need….it’ll run at 12v and draw ~16a ( so approx 200W)
Those panels are putting out ~5.8a…so you’d need at min 3x of them to supply the pump if they’re wired in parallel.
So….you can power it just off of solar panels, but as the sun won’t be optimal all the time the panels might not put out their theoretical max. Too little power and the pump might not even turn on. Say each of those 100W panels are only putting out 70W….so you’d need 3x of them just to start the pump…and if the sun isn’t optimal, you’d need more panels. That gets expensive.
Instead…use 1 or 2 panels (just makes charging the battery faster to keep up with use) to charge a battery. A PWM controller is super cheap (~$20)….an MPPT charger is much more efficient but more expensive. The controller will take solar power and charge the battery (or battery bank). The pump will draw from the battery to power the pump. If the battery holds 100Amps…and the pump uses 16A…then the pump can run for approx 5 hours before the battery is completely dead (prob way too much water). If you used a 50AH battery…then you’ve got about 2hr of battery power for the pump to run…(prob plenty).
With a charge controller, you’re less concerned if the panels will power the pump….because the battery acts as a power reserve/buffer that supplies the pump. The panels just charge the battery.
BUT…do what if you hit 2 or three days of cloudy weather? Maybe you need that battery power reserve to run the pump for those days…maybe not.
Maybe you want to run the pump more than once a day or for longer….so you might need more solar panels to charge the battery faster so it’s recharged quicker and ready for the next usage. It’s a balancing act.
Note- controllers are rated for a given amount of Voltage and Amperage from the solar panels…so if the controller is 40v/10a…you can’t wire up a bunch of solar panels that output 70v, it’ll kill the controller.
Good news is that many controllers have a 12V load capability…that means you can connect a 12v device (load) directly to the controller and there’ll be settings in the controller when to turn on/off that load.
So depending on the controller capabilities you can:
Take a solar panel, wire to a controller
Wire a battery to the controller
Wire the pump to the load of the controller and set it to pump on a schedule
Put the pump into the water (lake)
From the pump in the water, I’d put in a spring loaded (not flapper) check valve right after the pump (like a foot or so after it)….maybe another somewhere along the run if its a long one (I only have 2 in my 1000ft run). Use as big of a line as you can (I used 1” pvc/pe pipe that matched the output of the pump) to minimize drag. A 1” pipe will sit low enough so as not to get hit by the lawn mower….and easy to slit a trench to sink it.
Once at your target spot…simple drip pipe (none pressure) works well…you can make a ring loop of perforated hose around each tree…or just run it along the line of trees as best suits your needs.
In the winter….pull the pump out of the water.
So…
deep well pump - $170
1"' PE hose 200ft - guess $100
check valve/hose clamps/etc - guess $50
100w solar panel - $100
MPPT controller - $80
50ah LiFePO4 battery - $250
Total - $750 + prob some misc wire/etc
Or….just run a couple of long garden hoses (~$60-100/100ft) from the outside tap of the house to some drip hose around the trees and turn it on each day for an hour…..