Solar - Permanent mount or portable?

obiwancanoli wrote:
Pianotuna,

It would also be interesting to learn if there's a means of tilting the roof panels from the ground, since climbing on the roof at my age probably isn't the safest approach, but then, securing these panels would seem to require a hands-on approach. Still cogitating this dilemma...

As for the batteries, I'm definitely leaning toward two 200Ah Li's, though I have room for the four wet cells that will come out. Others have suggested keeping all batteries at the same size and Ah...

What I'm needing more clarity on is the panel voltage, why higher might be better, how it would function with existing panels which operate at lower voltage. Mono vs. polycrystalline is also not clear to me, though a little research will solve that... some of which, by the way, suggests an MPPT Controller north of 80 amps for the panel wattage I envision...

For tilting look at linear actuators. But it still comes down to cost per watt--and panels with fixed mounting are cheaper. It definitely will be cheaper to add another panel than to have actuators on each panel.

There have been studies done on manual tilt. On average the RV'er gives up on that after only seven times. It is simply too much effort for the better solar harvest.

I live in a windy Province. Securing portable panels would not be easy, and having them blow away is really a concern.

Great decision on 2 200 amp-hour jars. Now if I could only entice you to SiO2..... LOL

Here are some ideas on higher panel voltage.

1. lowers cost of wire and lowers transmission losses.

2. charging, at least in theory, should start earlier and end later in the day. I do get charging 30 minutes after sunrise, and there is a similar shorter time at the end of the day

3. a 17 volt MPPT (nominal 12 volt) will move to PWM mode sooner. If input voltage is double that, then the unit will stay in MPPT mode longer and won't move to PWM until the battery bank is more or less charged.

4. PWM "throws away" the extra voltage and operates at the battery voltage. MPPT does not do this, which means charging, at least in theory, may be faster.

5. high voltage input makes equalization voltages easier to maintain (yes I know li don't need or want that)

6. As panels heat, their voltage output drops. By having "voltage to spare", one still gets an adequate charging current. "As the temperature of the solar panel increases, its output current increases exponentially, while the voltage output is reduced linearly."

7. "lensing effect" excursions are turned into more current sent to the battery bank.

Here are some negatives of MPPT

1. The charge controller is less efficient in MPPT mode (94 to 95%) than in PWM.

2. More heat needs to be dissipated, requiring the controller to be oversize to keep from letting out the magic blue smoke.

3. Since all MPPT controllers have a PWM "hiding inside them", the controller may be a lot more expensive.

4. Panels are now the cheapest component of a solar charging system, so adding an extra panel gets you to about the same charging capacity--but only under ideal conditions. (i.e. 77 f, no clouds)

I'm sure there are many other "trade offs". I chose MPPT because, in 2005, it was a good way to drag as many watts from the panels as possible--and the cost of panels was $5.50 per watt (and that was a GREAT buy, at the time).

I do get 5 amps of charging in the rain. I do get 7 amps in leafy shade. But my panels have bypass diodes on each and every cell. They are LARGE.

So far as I am aware, no one makes a panel with bypass diodes on each cell any more.