At $8/watt installed, PV is expensive. But more than half of the cost is installation and conversion to AC. Eliminate the installation cost with BIPV, then eliminate the inverter with a DC standard (choose a voltage and a plug/receptacle design). If Nanosolar (or anyone) then gets modules costs near $1/watt, it takes over.

Can we please call for a DC standard? Thank you.

E-mail the IEEE regarding setting a household+commercial DC standard.

When you talk about the cost of PV, or any generation, you need to talk about the cost per kWh, not per watt. $1/watt PV might sound great, but when it’s mounted vertically you don’t actually ever get a watt of power (assuming it’s rated at a 90 degree tilt to the sun). And then only one wall can be facing true south, there’s clouds and shade, not to mention night. On the other hand, $/kWh can be compared meaningfully.

Nonethless, inverters are coming way down in price and solar is competitive in many markets with the rebates power companies offer. I have many friends that spin back their meters for many months, and their payback is ~8-11 years.

Best,

D

Dano, it is not the cost of inverters are the issue (since even many off-grid houses with lots of DC appliances have them for the oddball stuff). It is the efficiency loss. The inverter is usually 90-94% efficient at their peak (feed something other than a resistive load at peak power and you’ll get lower numbers). That’s pretty good (a few years ago it was more like 80-90% I think). But all those wall warts, power bricks, and similar vampire loads are usually pretty inefficient. You’re probably luck to get one at 80% efficiency. (One reason power bricks can get hot is that they are inefficient.)

Multiply and you find that you might be losing 25% of your PV output to stupid DC to AC to DC.

For comparison, I’ve seen DC to DC converters rated at 98% efficiency (e.g. the Outback MX60).

The industry must be using something else to compare PV’s.

DC appliances are just too expensive and most are not very efficient. Better to get an Energy Star refrigerator off the appliance store floor and buy a few extra panels and batteries than to pay thousands more for a super-efficient DC model. There’s a manufacturing economy of scale that makes losing some power converting to AC worth it.

As for bricks and phantom loads, we switch stuff off when we’re not using it.

The cost curve analysis suggests to me that we need a strong price on carbon from either a tax or emissions trading (with an aggressive cap). The cost curve also suggests the importance of implementing the mitigation opportunities with negative costs, and addressing the market failures that have prevented these opportunities from being realised.

BIPV = Building Integrated Photovoltaics. Check out Steve Strong’s work at solardesign.com. Some of his stuff has the PV in the windows!

Yes, the cost of energy from PV varies depending upon where you are, in addition to your system’s attitude to the sun, construction costs, etc. Which is fine, because it’s real, and the cost of energy is what interests us, not the cost of power.