Solar Afloat #6 Panel Power

Re: Solar Afloat #6 Panel Power

"Full noon time sun" is around 1,000 Watts per Sq.Meter...

So, the amount of power a panel generates is some fraction of what falls on the panel... Thin film panels tend to be in the 8% efficiency range and crystalline panels are in the 13%+ range.

The number of cells and how they are arranged (series/parallel) does not really affect the panel's output in watts... The the Voltage and Current:

• Power = Voltage * Current

So, if you have two panels with the same surface area and efficiency, the Vmp=35.0 volt panel will output 1/2 the current as a Vmp=17.5 volt panel--However, the power output for both panels will still be the same because P=V*I is the same for both.

However, the thin film/less efficient panel will be larger (more square foot/meter) than the more efficient crystalline solar panel.

But, both types of panels (thin film or crystalline panels) will output roughly the same amount of power if they have the same rating i.e, 205 watts, etc....

-Bill

Re: Solar Afloat #6 Panel Power

Highland_Fling wrote: »

OK thanks so if i have two 185W panels and a 15W controller at max sub the controller will be only able to handle/output 15W but up until then will two 185W panels outperform two 135W panels

I am confused... Are you asking about the MorningStar 15 amp MPPT type charge controller running on a 12 volt battery bank? (instead of a 15W controller?)

If so--then yes, a pair of 185 watt panels will produce more power in "low light" conditions than a pair of 135 watt panels in the same conditions. Once there is sufficient light on the 185 watt panels to for the controller to hit its 15 amp limit (at ~14.5 volts)--then any more sunlight will not result in any more power as the controller is already at its physical limit... For example, the 2x185 watt panels may hit the limit between 10-2pm. Where as the pair of 135 watt panels may hit the limit only a few times a year for an hour or less at a time...

If you had a 30 amp MPPT controller instead, then the 2x185 watt panels would supply enough energy for the 30 amp controller to output more than 15 amps during the (for an example) 10am-2pm period--and you would have more power collected in the day (and that is assuming your batteries are not fully charged by 10am and "tossing away" energy the rest of the day anyway.

Battery Capacity, amount of power used during day/night, size of panels, size of controller, etc. all play together as too how much useful power you can collect from your solar panels on any arbitrary day.

For an off-grid system--You really never plan on using every watt generated by the solar panel every day (100% usage). There are some days where you will use more power than generated (battery bank does not fully recharge) and there are other days when you will use less (bank comes back to 90-100% State of Charge).

i.e. over the whole day will the two bigger more expensive panels outperform two smaller cheaper panels assuming that both can deliver 15W

Well... Yes... Just like if I hooked up my 3.5kW grid to a MS 15 amp MPPT controller--The controller would be capable of outputting 15 amps from about 7:30amp to 6:30pm on a typical July day... However--If I had a larger controller and battery bank, I could instead of harvesting ~217 watts limit during the day time, a larger controller would be able to harvest 2-2.5 kW during the 10am-2pm time frame...

So, there is a place for larger controllers too. For optimum sizing--I use the 0.77 typical derating for solar panels and controller losses so that a "nicely sized" array for a 15 amp MPPT controller running on a 12 volt battery bank would be:

• 15 amps * 14.5 volts * 1/0.77 derating = 282 watts...

The higher a 15 amp MPPT array is over ~280 watts, the more I would think about using a larger (or parallel) charge controller... For example, using PVWatts and the output by hour for a 370 watt array in San Francisco, and 0.77 derating for July 25th:

1970, 7, 25, 07:00, 6.5
1970, 7, 25, 08:00, 62.0
1970, 7, 25, 09:00, 135.0
1970, 7, 25, 10:00, 203.9
1970, 7, 25, 11:00, 241.4
1970, 7, 25, 12:00, 262.9
1970, 7, 25, 13:00, 268.3
1970, 7, 25, 14:00, 258.6
1970, 7, 25, 15:00, 230.8
1970, 7, 25, 16:00, 182.4
1970, 7, 25, 17:00, 112.4
1970, 7, 25, 18:00, 38.0
1970, 7, 25, 19:00, 0.1

We can see that on an average summer day (20 year average/typical day), that the output of a 370 watt array with typical derating of 0.77 fixed mount array tilted at latitude would average 268 watts between noon and 1 pm.

However, the maximum output of the 15 amp controller is ~217 watts--So, during that 1 hour period, such a setup would "lose":

• 268 WH - 217 WH = 58 WH

You can add up the "lost" power--but that would would add up to something like a loss of 150 WH on this typical day with a 370 watt set of solar panels on a 15 amp MPPT controller...

Something like a 10% loss over the whole day with "over-sized" panels on an undersized controller for this one day.

I guess it is your choice as too how much power loss in a day/year vs a cost of a larger power supply is to you...

Is what I wrote above clear?

-Bill