Efficiency Question

adam1984

I see panels (monocrystalline) can have up to 16-18% efficiency. Can that be right? Meaning of 100% of energy it takes in from the PV array, it can only use 18% of that. Since energy and wattage are related by time, does that mean that 100 watts from a pv turns into 18 watts being used? That would be awful efficiency. Is the other 82% lost in heat? This is the best forum thank you all for the help

niel

Re: Efficiency Question

that is the efficiency of what the sun inputs to the pv and what the pv outputs. this of the pv as a glass is to taking water from a 2 gallon bucket of water. until we figure a way to increase the glass capacity (conversion efficiency in converting the sun's energy to electricity) that is all she wrote. it isn't wasted so much as it wasn't harvested.

icarus

Re: Efficiency Question

The best PV panels convert sunlight to electricity at about ~15%. This is somewhat misleading however.

In simple terms, a PV panel will return ~80% of name plate rating into power under STC (standard test conditions) so a 100 watt panel might deliver say ~80 watts of power.

The issue gets further clouded by the fact that various wiring schemes rob more power. For example, a grid tie system might have an over all efficiency of ~90% (system loses!) While a battery based system will only run ~52%.

So in a battery based system a 1000 watt system might deliver 1000 watts *.53= 530 out the inverter.

A similar grid tie system might deliver 1000*.9=900. The amount of total power is entirely dependent on the number of hours of "good" sun, seldom more than ~4.

So the battery system might then produce 1000*.53*4=2120 watt hours/day

The grid tie would be 1000*.9*4=3600 watt hours/day

Remember, all systems have loses. Wiring loses, charge controller loses, more wiring loses, basic battery charging loses (a big one ~20%) plus battery charging loses, more wiring loses, inverter loses.

Tony

adam1984

Re: Efficiency Question

So does that mean that a 100 watt panel (ideal, no losses past the panel) would put out 100watts, or would it put out 15W? Sorry still a little confused.

niel

Re: Efficiency Question

a 100w pv idealy would output 100w. if it is at 15% efficiency that means the sun was impending about 667w to the pv.

BB.

Re: Efficiency Question

Full sunlight is ~1,000 Watts per square meter

A 15% efficient panel that was 39"x39" (1 meter x 1 meter) at high noon and 77F in a light breeze will output:

• 1,000 Watts/sqmtr * 0.15 = 150 watt panel

The rest of the sun's energy goes into making the panel hot, re-radiated IR energy, heating air, etc...

Refer back to your first thread--I put the I*V curves of a generic crystalline solar panel in there:

data sheet for a crystalline silicon panel

-Bill

icarus

Re: Efficiency Question

adam1984 wrote: »

So does that mean that a 100 watt panel (ideal, no losses past the panel) would put out 100watts, or would it put out 15W? Sorry still a little confused.

Under ideal conditions the panel might put out 100 watts. On the other hand, warm panels will drop that by a considerable amount (~.05v/DegreeC if memory serves) On the other hand, if the temperature drops substantially below STC (25C?) out put could be considerably MORE than 100 watts.

Under very unusual circumstances, my small system will on occasion put our ~50% more than name plate rating. (very cold temperatures, bright sky with edge of cloud events etc).

Give us an idea of what you might be interested in doing and folks here will be more than willing to steer you in the right direction.