Plans2Reality

Efficiency Doesn't Matter

Not for mass-market solar panels, anyway.

The goal of mass-market solar, otherwise known as grid-tied PV, is to generate electricity for the grid, so we don't have to burn as much coal, oil, etc. It's a fine idea.

But anyone in the fild will tell you that PV electricity is still a lot more expensive than coal-fired electricity, even when the sun is shining - never mind darkness. (And even if you factor in a pretty high carbon tax. Coal is cheap.)

Therefore, the goal is to get the cost of PV electricity down as far as possible - ideally as cheap as coal, even cheaper if possible.

Now, electricty is sold in units of kilowatt-hours (kWh). So we need to get the cost of PV, in terms of dollars per kWh, as low as possible. It doesn't matter how EFFICIENT a PV panel is, only how much it costs. Sunlight (unlike coal) is free, so it really doesn't matter if a panel is 10%, 15%, or 20% efficient - not if such efficiency comes at a cost.

There's nothing _wrong_ with efficiency, per se. And I am sure the boffins will find ways to improve it. But anyone who asks what a panel's efficiency is doens't understand the problem. The only meaningful question is, what's the cost per kilowatt-hour?

Solar Panels: Why Quote the Wrong Spec?

Here at Plans2Reality World Headquarters, we have been looking at solar panels for electricity. This has provided an interesting and instructive lesson in marketing along the way. I shall christen it:

Bragging About the Wrong Thing

Solar panel makers love to brag about two things: their watt-peak (Wp) rating and their efficiency. Oddly enough, neither one matters. Nope, not a bit. Not one d*mn bit at all. 

(Let me interject here that _all_ panel makers are equally involved. In private conversation, many have told me they agree with the analysis I am about to present.)

First, Wp. The peak-watt rating is a measurement of instantaneous power output from the panel, taken under an incident light intensity of 1000 watts per square meter, and at a cell temperature of 25C.

So what's wrong with this? The panel will never actually see these conditions in the real world, and there is poor correlation between these "STC" ratings and real-world performance.

1000W/m2 does approximate the noon-day sun, but most of the time it isn't noon. Furthermore, most solar panels are NOT installed in sun-tracking mounting systems, so at best the panel "sees" full sun only at noon. The oblique angle the rest of the day reduces incident light. (Actually, most smaller arrays are installed so the panels aren't at the optimum angle even at noon - residential rooftops are usually not at the correct angle, but it's easier, and nicer-looking, to mount them flat against the roof.)

So your panel will never generate its Wp rating, due to sun angle. But wait, there's more!

PV panels are quite temperature-sensitive - some more than others, but all are to a fair degree. And when you place an object in the sun, it gets warm - warmer than 25C most of the time.

How much warmer? Well, That Depends.

The exact amount of heat gain depends on the specific PV material. Some panels will get warmer than others. In addition, the degree to which the panel cools off, that is, sheds heat via conduction and convection to the environment, varies substantially among panels. There have been attempts to quanity this (NOCT, PTC) but these are at best compromises.

Net-net of all this: the Wp rating of the panel represents a power output you will never see in real life. Couldn't be much more meaningless than that, huh?

So what specification SHOULD we be talking about? 

We should be talking about kilowatt-hours per dollar. Why? The answer is quite simple: Solar panels are installed to generate electrical energy. Electrical energy is measured - and sold - in units of kilowatt-hours. So why not measure our PV installation the same way the electric utility measures the electricity it sells us?

It's just that simple. Really.  I am putting up PV panels so I don't have to buy kilowatt-hours from the utility. Great. So tell me how much the kilowatt-hours from the PV panels will cost.

Nothing else matters, folks. Nothing.

Next installment: Efficiency doesn't matter either.  ;-)

A Modest Proposal

Even solvent banks don't seem to be lending much, and the VC community has pulled up the gates. So, a modest proposal to get the economy going that probably will not cost too much:

A tax holiday for the proceeds from any new VC or similar business investment made in the next 12 months. No capital gains, no income tax, no nothin'.

I will leave it to the boffins and policy wonks to hammer out the definitional details, but this is the gist of it.

Note that this is NOT the usual investment tax credit. Those are okay, but are more loop-hole than incentive. This is aimed at venture-oriented, higher-risk investments - new businesses or LARGE expansions of existing ones.

Write your Congress-person!

Eli's Coming......

Yes, Eli is coming. Stay tuned for details.

Photovoltaic Panels, Part One

Here at Plans2Reality World Headquarters we have been evaluating various solar technologies with an eye to getting our electricity bill down a little bit. Of course, we could just buy a system from a local contractor on a turnkey basis, but where's the fun in that?  ;-)

Market research led us to the usual vendors of traditional silicon flat panels, but also to another company with a novel idea: Solyndra. (http://www.solyndra.com)  

These guys make what looks like a giant barbeque grill. It's a bunch of tubes, each about an inch in diameter and about 36 inches long. Each tube is itself a PV panel. Forty of them in a row makes the grill.

They are designed expressly to be place on the flat roofs common to most large commercial buildings. Think of the roof of you average big-box store, or for that matter about 95% of the buildings here in Silicon Valley.

The panels sit on little legs, but they aren't tilted. You just carpet the roof with them and wire them up. Clever idea, huh?

More to come.