mppt vs pwm

brulaz wrote:

BFL13 wrote:
"...boondocking, I appreciate being able to set the float higher (13.6V) so MPPT kicks in earlier at a higher voltage."

I missed that. Confusion over the set point for when the controller kicks back into Bulk and the setting for the Float voltage

When you set the Absorption Stage (the controller might call it Float) at 14.4 or whatever, which the controller maintains, the voltage does not drift down to 13.2 and then kick back into Bulk. It would only get down to that if you ran some loads for long enough and then it would kick in the MPPT and start over same as in the morning.

Exactly. The Rogue is different. Your MPPT kicks in at 13.2V, the Rogue kicks in at whatever the FLoat voltage is set for. In my case, 13.6V when boon docking. And I've set my absorption stage to kick in at 14.8V instead of the 14.4V in your example.

So if the loads (and low sun) initially keep battery voltage below 14.8V, the Rogue will be in MPPT mode all that time. If the loads are lower or the sun is better, when 14.8V is reached the Rogue switches to Absorb and maintains 14.8V for a set time period or until the battery charge current drops to a set point. If the sun goes behind a cloud or the loads increase so that the voltage falls below 14.8 again (0.2V below the set point), the Rogue goes into MPPT again. And so on.

If however the Absorb voltage (14.8V) can be maintained over the set time period, the Roque then stops charging (Full mode) and allows the battery voltage to fall to the Float voltage (13.6V) and then tries to maintain that indefinitely. If it cannot maintain 13.6V, it switches to MPPT and the whole cycle restarts as long as there is light and watts available from the solar panels.

If you like, both Absorb and Float modes can be disabled, so the Rogue will use MPPT up to the Absorb set point (14.8V), then stop charging (Full mode) until the battery voltage drifts down to the Float setpoint (13.6V) when MPPT starts again. Repeat as long as there is sufficient sunshine.

Anyway, by adjusting these setpoints, you can have as much or as little of the MPPT mode as you or your batteries would like.

If you disable Absorb and can set your Float voltage to 14.8 as well, then it seems the Rogue would get to 14.8 in Bulk, then stay in MPPT doing Float at 14.8 till dark?

I would like that in my situation. Smk would have fits, because he doesn't like any more time in the 14s than minimum needs, but that is because he has a million kilowatts of solar and gets to Vabs by 8am. :)

"If you cover the roof with panels you will be making your own shade."

Provided the panels are well above the roof and well ventilated. Otherwise it would be much like the heat build up that occurs in an attic. Just running an attic fan, and no a/c, can lower house temperature significantly.

I'm looking into actually harvesting this solar heat for winter under-floor hydronic heating. There are solar panels available with built in heat exchangers/collectors. In summer, the heat would be exhausted to the outdoors using a fan/heater core combination.

Your logic is nonsense. Not worth bring up. No one in their right mind will use a 72 cell panel in a 12V pwm system.

The same rules apply when comparing 400W 36 cell panels using pwm and 400W 72 cell panels using mppt. The difference in gain will be on average only 5%.

lorelec wrote:

Salvo wrote:


I see no real advantage when using a higher Vmp. Temperature still reduces power by the same amount. 90's thinking still apply.

The difference between Vmp and battery voltage is directly proportional to the gain you would expect to see an MPPT controller provide. The greater the difference, the greater the advantage will be for MPPT over PWM.

nevermind, a misread post

BFL13 wrote:
"...boondocking, I appreciate being able to set the float higher (13.6V) so MPPT kicks in earlier at a higher voltage."

I missed that. Confusion over the set point for when the controller kicks back into Bulk and the setting for the Float voltage

When you set the Absorption Stage (the controller might call it Float) at 14.4 or whatever, which the controller maintains, the voltage does not drift down to 13.2 and then kick back into Bulk. It would only get down to that if you ran some loads for long enough and then it would kick in the MPPT and start over same as in the morning.

Exactly. The Rogue is different. Your MPPT kicks in at 13.2V, the Rogue kicks in at whatever the FLoat voltage is set for. In my case, 13.6V when boon docking. And I've set my absorption stage to kick in at 14.8V instead of the 14.4V in your example.

So if the loads (and low sun) initially keep battery voltage below 14.8V, the Rogue will be in MPPT mode all that time. If the loads are lower or the sun is better, when 14.8V is reached the Rogue switches to Absorb and maintains 14.8V for a set time period or until the battery charge current drops to a set point. If the sun goes behind a cloud or the loads increase so that the voltage falls below 14.8 again (0.2V below the set point), the Rogue goes into MPPT again. And so on.

If however the Absorb voltage (14.8V) can be maintained over the set time period, the Roque then stops charging (Full mode) and allows the battery voltage to fall to the Float voltage (13.6V) and then tries to maintain that indefinitely. If it cannot maintain 13.6V, it switches to MPPT and the whole cycle restarts as long as there is light and watts available from the solar panels.

If you like, both Absorb and Float modes can be disabled, so the Rogue will use MPPT up to the Absorb set point (14.8V), then stop charging (Full mode) until the battery voltage drifts down to the Float setpoint (13.6V) when MPPT starts again. Repeat as long as there is sufficient sunshine.

Anyway, by adjusting these setpoints, you can have as much or as little of the MPPT mode as you or your batteries would like.

If you cover the roof with panels you will be making your own shade.
My air conditioner seems to perform better in hot sunny conditions such as Ely or Las Vegas in 110+ heat in full sun.

Roof area is probably the only integer that can interfere with my cheapskate nature. Higher energy density per square foot can be costly. Down here, SHADY parking for RV's is a must. In one park I suffered 104F interior temperatures awaiting someone to pull out that had a shady site. Within 10 minutes of them leaving I had moved. Interior temps dropped to 82F. No hookups. This really tosses a coconut into the gears of the viability of solar panels.

Price it is. What is strange here lately is that a few years ago it was the MPPT controller needed for 24v panels being so expensive that made 12v the way to go.

Prices in your area can be much different so YMMV (a lot!)

Last year and still on here is that the 24s are way cheaper than the 12s and you can get an MPPT controller (Eco-Worthy or Tracer) at little more than than a PWM controller. Here, eg, the 250w is the same price as the 150w

http://www.wegosolar.com/categories.php?category=Solar-Panels

So I have a Hanwha 230w panel that cost $260 last year and a $102 Eco-W for $362. Two 12s would be about $450 and the controller $35 for $475. Going 24v and MPPT in this case was $113 cheaper.

To me the issue is purely one of finances. Useable amperage versus total cost of the array. If a higher voltage panel with MPPT is cheaper then I'll take that path. If I camp in the middle of a grove of redwoods, ten acres of panels and a controller the size of a washing machine ain't gonna cut it. Neither is assuming the panels are going to do much in Port Alberni or for 6 months at a stretch at the south pole.

lorelec wrote:
The 17v Vmp --> 12v battery scenario is old news,

stinking thinking