Subject: AC PV panels

From: [email-masked] (Nick Pine)
Date: 3 Dec 1995 06:22:24 -0500

Tom Gray  <[email-masked]> wrote:
>Nick Pine writes:
>>Solar panels with built-in inverters that plug into wall sockets
>>to lower electric bills should be coming quite soon.

[email-masked] (Charlie Collins) kindly forwarded the following from
http://www.ultranet.com/~sda, paraphrased below with a few comments...

Solar Design Associates is now developing an AC solar module with Solarex.
The AC module is a DC module with a small integrated inverter.

Solarex calls the product "PowerWall." The first modules are designed for 
curtain walls, the shear wall systems used on modern office buildings. These
modules replace the glass or other sheet material used in curtain walls, eg
in framing manufactured by Kawneer of Norcross, Georgia. A residential roof
product is also in the works.

PowerWall modules are available in AC and DC models, in sizes up to 53" X 87",
[32 ft^2--why not 4' x 8'?] with outputs up to 250 watts.

An ideal solar system should harvest both heat and electricity from the same
aperture [although PV power falls off as temperature rises...] Virtually every
building has thermal as well as electrical energy needs, and roof area is
limited... In 1979, SDA developed a combined, flat-plate, PV/thermal collector.
The device worked well. Unfortunately, no company was willing to produce it.
Now they are revisiting this device... 

[I wonder if it still has a thermal output?]

In 1980, existing PV modules (~ 4 ft^2) were not large enough to integrate
well with building systems. Too many connections were needed to make a
significant electrical output. SDA presented the case to all major PV makers
for building a large-area module of 25 to 30 square feet, which could be
integrated into a building skin to form the structure and weathering surface.
Every manufacturer thought they were crazy - except one.
 
SDA began working with Mobil to develop a 24 ft^2, glass-superstrate PV module
which could be sold with or without a frame. Now the rest of the industry is
following suit. Custom module manufacturers in Europe now offer PV modules of
3 square meters and larger, designing them to architect's specifications for 
direct building integration.
 
DC outputs of PV arrays impose serious limits on the electrical use. Most
electrical loads require AC power, and 30-40% of the cost of a PV system has
been used in the transition from the DC PV module to the load. Such systems
were complex and required special DC-rated components not readily available.
The obvious answer was to create an AC PV module. SDA is now doing that now. 
  
Nick

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From: [email-masked] (Nick Pine)
Date: 5 Dec 1995 16:59:36 -0500

John A. Stanley <[email-masked]> wrote:

>The electric utilities don't take too kindly to folks simply
>pumping juice back into the grid.

Gee I wonder why :-) I think in a few years, what you do with your
electric line inside your house will be mostly your business, the way
it is now with the telephone line. Utilities are exaggerating the
safety problem.

>Most grid intertie systems use two meters, 

In some states, eg Vermont and California, the law says you have to be
able to do this with one meter, if you want to. I imagine this will
become more widespread.

>and there are stringent safety requirements to make
>sure the PV's are disconnected in the event of a power failure.

Not a bad idea. Also not hard to do.

>Grid intertie inverters tend to be costly (several thousand dollars.) 

Sheesh. I've been saying that this is not true for 3 months now, for
technical reasons. I think we will see at least one 500 watt grid-tie-only
inverter on the US market within 6 months, from one of several companies
who are now nearly finished developing this product. At that point,
rational suburbanites and city dwellers would give up their expensive
PV habit and put a $500 400 watt wind turbine on the roof, with one of
these $100 inverters to reduce their electric bills.

Nick