Solar - Upgrade or replace outright?
The new-to-us coach has a small solar panel system. I would like to upgrade it to the point where I could reasonably hope to capture 50 or 60 amp-hours per day in light conditions that are less than ...
Forum Discussion
Empty Nest, Soon wrote:
Which is most important for avoiding loss: Minimizing the cable run between panels and controller? Minimizing the cable run between controller and battery bank? Or simply minimizing the total cable run?
I assume that it would be better to locate the controller closer to the battery bank and have a greater percentage of the total run at the higher voltage between panels and controller?
Wayne
1) No, not "simply minimizing the total cable run". Cables before and after the controller are different things.
Your planned 300-400W new array will be either a pair of 12V panels in parallel, or a pair of 200W in series. There are pros and cons to each scenario. With 12V panels in parallel you will need a thicker cable than with 24V in series, but controller can be cheap PWM type. With 24V panels in series the install will be easier, and it's easy to go up to 480W and higher (see below), though controller will have to be MPPT type, they are more expensive.
Wiring 24V panels in series is easy. This will let you avoid a messy rooftop junction box and will also raise your voltage to ~60V, 8A. At this current the resistance losses are negligible, so the length of cable from panels to controller is not important. Order a 75 of 100ft length of MC 4 cable gauge 10 or 8, cut it (approximately) in half, connect MC4 ends to panel pigtails and bare ends to controller. Done.
(You will also need a few ft length of MC4 cable between the two panels).
2) After MPPT conversion you will have 20-25A at 13V on the controller output. At this current it makes A LOT of sense minimizing the cable run from controller to battery. And maximize the cable gauge. Try keeping the voltage drop in this section within 2%. Here is the Voltage drop calculator. Enter one-way length of cable, not total 2 leads.
When you will start shopping for 24V panels, you will find that 200W, 220W and 250W are same size and weight, and the price difference between 200W and 250W is negligible. Don't know about your area, but in South West 2*240W array will keep your house batteries full on most days without running a generator. The only thing that you can't have on solar, is a fulltime air conditioner. Everything else is manageable with 450-480W. If your plans are living offgrid for weeks at a time - maximize the wattage, install 3*250W in series if there is enough space.
Controllers with 24V panels.
Up to 450-480W I would not look any further than Rogue MPPT 3048. They include voltage sense cable - to adjust the voltage drop between controller and battery, and remote temperature sensor. You won't find a cheaper 30A MPPT with these features and this quality.
With 700-750W you can get either Morningstar TS 45, or TS 60: TS 45, TS 60. Either one will handle it.
