Electric system, total beginner

[Éric Bouvéron]

Bonjour,

I plan to put a battery and have it maintained with a solar panel.

I understand that  + goes to + an - goes to -, but am I correct with that design? In fact, is it possible to plug the enegy wires charging the battery via the solar panel together with the "output" wires going to the electric panel for repartition?

Thank you for your answers,

Éric

[boatsmith]

that should do it

[Éric Bouvéron]

Thanks Boatsmith

boatsmith said:

that should do it

[Bart]

Do use a voltage controller beteren the solar pannel and the battery. Even small, 5 watt, pannels can cook a battery dry.
Ofthen they have an output as wel, witch protects the battery from draining.

Regards Bart

[Éric Bouvéron]

Thank you Bart.

So the diode doesn't block the current in the battery? I thought it was an anti-return system. If I put a voltage controller, do I need the diode? 

[Budget Boater]

The diode prevents the battery from draining when the sun it not out. Most solar panels have the diode built into them now.

The voltage controller/voltage regulator/solar charge contoller, controls the voltage coming out of the panel into the battery, preventing the battery from being overcharged and boiling. Most solar panels will put out a voltage that is too high, which will damage your battery.

Éric Bouvéron said:

Thank you Bart.

So the diode doesn't block the current in the battery? I thought it was an anti-return system. If I put a voltage controller, do I need the diode? 

[Ricardo Aráoz]

So the voltage regulator actually throws away part of the electricity generated by the solar panel because your battery won't be able to absorb it. Then it seems plausible to think that having too big a solar panel is a total waste of space and money. Which size would you recommend and why?

Thanks

[Éric Bouvéron]

Thanks Budget Boater. Will take care of that. 

[Budget Boater]

The most common voltage regulator used for solar charging is a Pulse Width Modulated (PWM) regulator. They only control the voltage. If your solar panel is rated at 4.0A output at 18VDC in direct sunlight, the regulator will only allow a set voltage (14.1V for gel, 14.5 AGM, 14.6 Flooded) into the battery and the maximum amperage the solar panel can put out. You cannot put excess voltage into your batteries or they will be destroyed, along with other sensitive electronics that might be connected to the batteries.

As your battery reaches a full charge, it will regulate the amount of amperage it allows in, regardless of the size of solar panel or voltage regulator functions.

Newer style Maximum Power Point Tracking (MPPT) controllers will (put very simply) recycle the excess voltage into usable power. Read this article:

https://www.solar-electric.com/learning-center/batteries-and-chargi...

So, for a small system, a PWM regulator will work fine. For larger systems, the extra money spent on a MPPT controller will more than pay for itself.

Sizing has to do with estimated load on the system. This goes for your battery bank and your primary charging source(s).

To size a system you first need to determine the total average daily load you will have. This is the most important thing to do. Without knowing how much power you are using on a daily basis, you cannot properly size your system.

• Let's say that you determine your average daily load to be 100Ah.

• Because you do not want to cycle your batteries more than 50% before recharging, and you would want extra time in the event that your charging system cannot do its job (sun blocked, alternator belt broken, wind generator fell in the ocean, etc.) your battery bank should be at least 4X your average daily load, so 400Ah. This allows for two full days of battery bank usage before the bank reaches 50% capacity and needs to be recharged. However, under any normal circumstance, you will recharge your bank daily.

• Batteries do not accept incoming current at face value. There are inefficiencies in the system. It is normal to calculate 20%. Your average daily load is 100Ah, but you will need to replace 120Ah. With solar or wind, you will also want to account for cloudy days. This is usually calculated at 30%. So you will want a solar array with a 156Ah capacity in your average location.

• South Florida has 5.5 hours per day of full sunlight (if no clouds are in the sky). So you would take the 156Ah per day requirement and divide that by 5.5 to get the size of array you would need, which in this case is 28.4Ah (or 340W solar array.)

Ricardo Aráoz said:

So the voltage regulator actually throws away part of the electricity generated by the solar panel because your battery won't be able to absorb it. Then it seems plausible to think that having too big a solar panel is a total waste of space and money. Which size would you recommend and why?

Thanks

[Andy Best-Dunkley]

Thanks, this is a very clear description of how to work this all out!