# Solar Panel Efficiency

Darryl Said:

Solar Panel Efficiency?

I’ve operated a 25 kilowatt (kw) solar panel system for two years (144 panels, rated at 190 watts each, just about like yours). It averages 110 kilowatt hours (kwh) per day, but clear days get about 160 kwh. My system generates about 3300 kwh per month (we dump directly to grid), worth about \$4,000 per year. Payback for my system, which cost \$100,000 (after utility rebates and tax credits), is 25 years (the expected lifetime, coincidentally). Under similar conditions, your 200 watt solar panel would average 820 watt-hours per day, or about 25 kwh per month, worth \$2.50.

Jay Said:

What is the present efficiency of a high-tech solar panel and how much would it cost per unit area?

Max eff: 12%
Material: Amorphous Silicon
Cost: Little

Max eff: 38%
Material: single crystal silicon
Cost: Lots

Nicholas Said:

Why is solar panel efficiency so low?

About 70% of the loss is due to the photons not having the correct energy level to be converted:
http://science.howstuffworks.com/environ…

Regarding reflections, if the light hits the surface on the perpendicular, very little of it is reflected. As the angle of incidence decreases, more of the light reflects from the surface. Manufacturers of tracking devices that keep the panel pointed at the sun claim that the tracking will increase the panel’s output by up to 20%. But a large part of the gain comes from the panel presenting a full surface area pointed toward the sun. At an oblique angle, the panel doesn’t intercept as much of the sun’s rays. So the 20% increase isn’t due just to fewer reflections, but also due to a full interception area. The latter is quantified on some web sites. Subtract that from the 20% and you could attribute the remainder to losses from reflections (as an approximation).

Jennifer Said:

What Solar Panel Efficiency would replace Coal?

I’m with g.aidono. The efficiency of the panel is not the issue, it’s the cost.

I believe photovoltaic panels are hovering at around 14% efficiency right now – when you see high numbers like 41%, that’s an exotic cell, and not in a sturdy glass and metal frame suitable for domestic use. But even at 14%, if they cost \$2 / watt, they would be a cost winner in a majority of US homes. Even at \$4 / watt today, they are a winner in some places, such as supplying the last few, very expensive kWh’s on someone’s bill. If panels got to \$1 / watt, even without any subsidies, people would be clamoring to connect panels – so many, in fact, that it would threaten the stability of the grid, and new architectures would be necessary.

Leslie Said:

Does anyone have a graph showing the efficiency of a solar panel vs temperature?

nope

Peter Said:

solar panel efficiency in space?