photovoltaic systems - pearson...

Photovoltaic systems

Home systems

The German experience with the 10,000 Solar Roofs Program was, from the point of view

of some participants, frustrating. At the beginning, the photovoltaic (PV) systems were

found to have many defects. After more experience (the learning curve), there were fewer

defects. However, participants experienced a substantial number of failures, and repair

bills were high and waits for repairs were prolonged, both because of lack of spare parts

and because the repair services were so busy.(133)

Grid-connected PV energy is still not cost competitive in Germany. The authors of Ref.

133 list several reasons that Germans invest in PV energy anyway:

“Shock the neighbors;”

environmental awareness of PV cleanliness and long life;

eventual higher energy costs in the future expected;

innovative funding schemes; and

ability to replace a conventional roof with a new material.

Both subsidies and advertisements have played large roles in the growth of German

PV.(133)

There are advantages to utilities in having grid-connected photovoltaic arrays either sited

in individual homes or in farms. Peak loads can be handled better by some utilities, which

can remedy or delay the need to construct peaking plants; the fuel is free, and does not

enhance dependence on oil imports; such installations are easy to site; and customers are

pleased that a nonpolluting renewable resource is being tapped.(134) For some utilities, the

benefits at present may outpace the (still relatively high) costs.(134)

Energy, Ch. 21, extension 5 Photovoltaic systems 2

Fig. E21.5.1 The net metering of electricity is not available nationwide. This chart shows where solarphotovoltaic systems are most useful. The greater the value shown, the more effective a PV solar systemwill be.(U.S. Department of Energy, National Renewable Energy Laboratory, Ref. 58)


One utility leader in investigating solar energy in private homes is the Sacramento

Municipal Utility District (SMUD). Figure E21.5.1 shows that Sacramento is well-

situated to utilize solar energy in the region between 1800 and 1900 on the map. The PV

Pioneer program of SMUD began as the utility (for a small fee, $4/mo) came to roofs in

its service area and installed photovoltaic systems that fed directly into the SMUD grid

(that is, the homeowners got no benefit other than self-satisfaction).(135,136) SMUD

installed 2 to 4 kW systems on what they characterize as “borrowed” rooftops.(132)

More than 550 home energy pioneers turned their roofs into miniature power plants, and

gave SMUD valuable expertise in connecting home PV systems, as well as dealing with

the ancillary problems.

However, California subsequently passed a net metering law that changed the program

into what SMUD after April, 1999 calls “PV Pioneers II.”(137) The SMUD website now

says “own a piece of the sun and watch your meter turn backwards.” The point is that

the PV system can turn the meter backwards when the Sun is high; of course, this

backwards meter movement does not occur at night! According to SMUD, the typical 2

kW residential rooftop solar system they install produces around 3,600 kWh/yr. “This

solar system therefore avoids the need to burn 3.7 tons of coal to produce the same

amount of electricity, and thus prevents 10,000 lbs. of greenhouse gases from entering the

atmosphere.”

The program is very popular (even more so after the California deregulation energy crisis

of 2000-2001). The waiting time is 4 months before any response could be anticipated,

and the utility warns it may take 1 to 1.5 years before the roof is installed.(132) By mid-

2001, the utility had on hand 1,500 signed letters of intent from customers.(137)


The modules SMUD uses (they call them SunSlate®, and are made by Atlantis) are 64 cm

by 124 cm each and each one can produce 32.5 W alternating current after connection

through an inverter (which produces AC from the DC current of the solar cell). The

modules have an estimated 40 year life and adhere even under conditions of high winds

(greater than 200 km/h). SMUD estimates that their south-facing, 2 kW SunSlate PV

system will supply the owner of a typical new home with about 60% of total electricity

needs, approximately 4,000 kWh per year.(132)

Solar subdivisions?

SMUD is also touting the SMUD Solar Advantage Homes.(138) These homes are built by

the developer with the solar photovoltaic systems already installed and have other

features as well. Table E21.5.1 shows the benefits claimed by SMUD for its Solar

Advantage Homes. Figure E21.5.2 shows how the PV system is connected.

TABLE E21.5.1

Benefits of Solar Advantage Homes as Suggested by SMUD

The Solar Advantage Homes ...

Produce their own energy.

Reduce the monthly energy bill.

Quietly produce clean/green energy.

Increases the value of the home.

Incur no additional property tax on the PV system.

Give virtually free energy after the 8-15 year payback period.

Have a 30-year system lifespan.

Provide energy savings that help finance the PV system.

Help keep the energy bill in lower tiers, so owners don’t pay at peak rates.

Do one’s part to help out during the California energy crisis.

Provide a turnkey PV system.


Fig. E21.5.2 How SMUD homes photovoltaic systems are connected.(SMUD)

Solar subdivisions seem to be blooming in California (which has some fine territory for

solar energy, as Fig. E21.5.1 showed).(139,140) Developers such as Shea Homes and U.S.

Home Corp. have embraced solar energy.(140) Part of this is because a photovoltaic

system, which costs anywhere between $12,000 to $20,000, is subject to state rebates

that can take from $6,000 to $9,000 off those prices.(141) California pays the lesser of

$4.50 an installed watt or 50 percent of cost. The rebate program has $56 million to

distribute.

Some cities are trying to make solar energy more attractive. In Santa Clara, California, ten

families were able to share $232,000 in city money to install rooftop solar systems. The

ten residents were winners in an essay lottery.(142)

Other solar roofs

Sacramento-area churches have been part of the photovoltaic program of SMUD.(137,143)

As with the German churches, it is part of the idea of stewardship. The churches


apparently have experienced no problems in their solar roofs. The typical church in the

program has a 15 kW system, costing about $36,000. Sacramento churches are trying to

spread the idea to other California churches, and are calling their initiative (perhaps tongue

in cheek)”California Interfaith Power and Light.”(143)

The Los Angeles Convention Center had a solar roof installed in 2000. About 1400 m2 of

photovoltaic arrays were mounted. City Hall and the Zoo are next.(144) The Santa Rita jail

has a solar roof. The company PowerLight installed a 500 kW system that cost $4

million.(145) It is expected to save the County money in the long run. A State of California

office building in Sacramento will utilize part of its built-in curtain wall as a solar

array.(146)

And it’s not just governments. The Palo Alto Ace hardware store put photovoltaic panels

on its roof. The hardware store roof system only covers 370 m2, but it provides a peak of

30 kW. The only bigger rooftop system in the Bay Area is on the building owned by the

company, PowerLight, that installed the hardware store’s roof.(147) The hardware store

benefits not only from the state subsidy program, but from the Palo Alto city program

that supplies a tax credit of $4/kW. PowerLight is also installing a solar roof for the

International Brotherhood of Electrical Workers Local 332 in San Jose.(148)

Utility use

Energy utilities may also reap benefits from use of solar cells. A 1 MWe solar cell test

installation was built at Kobern-Gondorf in the Mosel valley of Germany in 1989 by a

German utility. ARCO Solar, now Siemens Solar, one of the companies involved in silicon

photocell development for large-scale use, in 1984 built a 1.0 MWe solar facility at the

Lugo substation near Hesperia, California, that sold electricity to the local utility (Fig.


E21.5.3), and a 6.5 MWe facility at Caresa Plains, California that sold electricity to

Pacific Gas and Electric. A 2 MWe installation was built in Sacramento, California in two

stages in the mid-1980s.

Fig. E21.5.3 The ARCO solar installation at the Southern California Edison substation at Hesperia,California. ARCO Solar was later sold to Siemens Solar and the station was dismantled.

Fig. E21.5.4 The Rancho Seco photovoltaic array in the SMUD. The plant is a 2 MW installation, theworld’s largest solar photovoltaic facility.


(U.S. Department of Energy, National Renewable Energy Laboratory)

The Hesperia installation was sold to Southern California Edison and the Caresa Plains

station to Pacific Gas and Electric. The stations were dismantled by the utilities and sold

in pieces.(128)

Other utilities maintain solar presence. SMUD recently won an award for having 8.5 MW

from solar energy (they now have over 9 MW, with 3.5 MW coming from the PV Pioneer

programs).(137,149) The other 6 MW is in large stations, such as the one on the site of the

former SMUD nuclear reactor at Rancho Seco seen in Fig. E21.5.4.

Where do the solar systems come from?

Many solar arrays are manufactured in the United States. Figure E21.5.5 shows the total

area manufactured each year for which data exist.

Fig. E21.5.5 Solar collector array area manufactured in the United States.(U.S. Department of Energy, Ref. 15, Table 10.3)


At present, the major exporting nation for solar arrays is the United States. Much of the

developmental work was originally done here, and entrepreneurs have been very active in

designing assembly-line techniques for manufacturing the arrays on a large scale. Figure

E21.5 6 shows the growth of the photovoltaic industry in the 1990s.(150)

Fig. E21.5.6 Most photovoltaic arrays manufactured in the U.S. are exported.(U.S. Department of Energy, Ref. 150, Fig. 10)

Amazingly, most output is exported rather than used domestically. The U.S.

manufactures about 40% of the world’s solar cells,(151,152) but only 30% of solar cell

sales are in the U.S.(153) California laws aim to change that, however, and other states are

at least considering how to embrace PV technology. A very bright spot is the huge

increase in output—U.S. output rose sevenfold between the mid-1980s and the late

1990s.(152)


Fig. E21.5.7 Most photovoltaic arrays are single crystal silicon, but other forms of solar cell are growing.(U.S. Department of Energy, Ref. 150, Fig. 11)

Fig. E21.5.8 This glass coating furnace processes 12 meters of substrate at 500 °C. Solar Cells, Inc., wasable to perfect their processes so that the furnace can run 24 hours a day, processing 1400 substrates at100% yield. Solar Cells, Inc., of Toledo, Ohio, manufactures cadmium telluride solar panels.(U.S. Department of Energy, National Renewable Energy Laboratory)


Obviously, the Southwest is a center of photovoltaic deployment. The report

Repowering the Midwest suggests that PV has a role even in the Midwest because the

seasonal peaks of demand occur in midsummer at midday due to air conditioning

demand.(57)

Crystalline solar cells still lead in the volume of arrays manufactured, but other types of

solar cell have captured important market segments (Fig. E21.5.7). Even in the Midwest,

the Sun’s energy can reduce peak demand. The Midwest also contains successful solar

companies, as seen in Fig. E21.5.8. However, one Ohio company, First Solar, is struggling

to remain viable.(154)

If enough roofs have grid-connected solar cells on them, especially in the Southwest,

which is generally sunny and has high insolation, it is possible that the daily demand

curves could be altered significantly. Even in less sunny regions, it is the sunniest of days

that result in the highest electricity demand (for air conditioning),(57) and grid-connected

roofs could be advantageous. This will especially be true if the materials and energy costs

of solar cell fabrication can be reduced significantly.

Energy use in the United States is 9470 kWh/person/yr,(155) while in Germany it is 3270

kWh/person/yr.(131) Clearly, Germany is also a developed country with a standard of

living similar to the United States (admittedly with less climatic variation), so there is a

message here that energy economies are possible without loss of lifestyle. And, if the

United States decides to maintain the higher demand, there are opportunities to substitute

renewable energy for nonrenewable energy sources everywhere. The demand on

nonrenewables could be reduced substantially with solar cell installations, for example, in

Germany to only 700 kWh/person/yr,(131) but such a change is not yet economically

feasible.


By the early 2000s, solar cells are expected to be competitive with baseload.(119) Since

the costs of mounting, weatherproofing, and onsite installation come to 3 cents/kWh

alone, the cost for cell fabrication must be made very small.(119) There is also need for a

backup to solar or for energy storage (Chapter 23) because of the fact of intermittancy

and lack of light for half the day. This complicates the picture for solar as an energy

source.

Off-grid systems—the developed world

Several demonstration totally solar homes have been built. One recent home that attracted

attention is that of NREL engineer Otto Van Geet.(156) Built about 30 km west of

Golden, CO, of course it has a photovoltaic system (1200 W). However, it also

incorporates many active and passive solar ideas discussed at length in Chapter 24. The

house was built entirely separately from the lab, having a typical mortgage but utilizing

many of the NREL’s ideas. The $200,000 home is a long way from the grid, and

connection would have added an additional $100,000 to the home’s cost; solar electricity

was considerably less expensive. The Van Geets use a propane generator as backup for

those times when there is no sunlight for days on end, and spend under $100 per year on

fuel.(156) Clearly, if there had to be a house here, only the solar features would have made

it possible. The house is shown in Fig. E21.5.9.


Fig. E21.5.9 Otto Van Geet’s 280 m2 (3,000 ft2) mountain home comes without an electric bill.(U.S. Department of Energy, National Renewable Energy Laboratory)

Fig. E21.5.10 The Chase home, a demonstration project of the Department of Energy. Solar arrays arevisible on the roof of the home.(U.S. Department of Energy)

A photovoltaic totally solar home in Massachusetts has operated over two decades

without a major problem. The Chase family of southwest Florida along the Peace River

went totally solar after they found it would have cost them $15,000 to connect to the

grid. The U.S. Department of Energy partially funded their home (Fig. E21.5.10).(157)


Florida and California, being in the south, and being in the high-value region of Fig.

E21.5.1, are easier to support than in, say, Wisconsin. The 300 m2 Davenport home is

about the most efficient in Wisconsin, according to WisconSUN.(158) The house has

active solar thermal, passive solar, and PV systems, as well as a masonry wood-burning

stove. The PV system meets only half the needs, even though it cost $4000 and has more

solar arrays than the SMUD homes.(158) (The SMUD solar subsidiary has suffered some

setbacks, however.(159)) A similar result was experienced in the Bircher home in DePere,

Wisconsin. Its PV system cost $4800, but saved only $37 per year in electricity costs

(the passive heating and cooling, which cost about $11,000, saved the Birchers about

$500 per year).(160) These illustrate the difficulties in making PV economic in the upper

Midwest as opposed to Florida and California. Despite this, solar continues to make

gains in the Midwest.(12)

A partial counterexample is provided by the Lord’s 270 m2 (2900 ft2) home in

Kennebunkport, Maine, also in a low-value region for solar energy.(161) Environmental

features accounted for $32,000 of the $300,000 cost of the house. The home features both

active and passive solar, solar hot water, and PV. The PV system provides 4.5 MWh/yr,

and supplies 590 kWh more than the house uses. The major energy expense is for

propane for cooking, backup heating, and drying. Without net metering, the payback

would be 57 years.(161)

Even in developed countries, remote villages can best be served by solar electricity. The

tourist village of Schluchsee in the Black Forest of Baden-Württemberg, Germany, saved

money by buying a 4.5 kW solar installation instead of connecting to the grid.(162)

Flanitzhütte, Bavaria, Germany, found the upkeep on the power lines too expensive, and

installed instead 30,000 solar cells with a surface area of 380 m2 at a cost of DM10/kW

(about $6/kW).(163) For night and overcast days there is a 3-day battery. For backup, a


liquid gas-powered generator is used. Alpha Real, a Swiss firm, has designed and built a

photovoltaic installation with 3-kW capacity for apartments. It sells for SF40,700 (about

$22,000).(131)

One novel idea that was recently announced is the solar backpack. The pack has a mass of

just 10 kg and fits into a backpack. The system can provide 120 Wh/d of AC or DC

electricity. The inventor suggests that the backpack could contribute to humanitarian

relief efforts.(164,165) The unit sells for $549. Greenpeace ordered 20 units for use in

India. One unit is currently being tested at the South Pole.(165)

The National Park Service (NPS) and Utah’s Department of Natural Resources joined

forces with the Department of Energy to use PV at Devil’s Garden in Arches National

Monument, Canyonlands, Natural Bridges National Monument, and Dangling Rope

Marina, at Glen Canyon.(166) Overall, diesel fuel use has been reduced by $104,500 per

year. At Pinnacles National Monument (Fig. E21.5.11), visitor experience was enhanced

by reduced emissions and noise when the 9.6 kW PV system was installed.

Fig. E21.5.11 Solar PV system at Pinnacles National Monument. S(U.S. Department of Energy, Ref. 166)

Three comfort stations were installed at the Chickasaw National Recreation Area by the

NPS, and uses solar hot water (Fig. E21.5.12).(166) The Visitor Center at Zion National

Park (Fig. E21.5.13), which is some distance from the grid, was served by a diesel


generator. A 7.2 kW photovoltaic array provides a significant portion of the electricity

needs by the building.

Fig. E21.5.12 A comfort station at the Chickasaw, Oklahoma National Recreation Area. S(U.S. Department of Energy, Ref. 166)

Fig. E21.5.13 Ron Judkoff and Paul Torcellini from NREL inspecting rooftop PV panel at the VisitorCenter at Zion National park.(U.S. Department of Energy, National Renewable Energy Laboratory)

As mentioned briefly in the Chapter, the most important use of photovoltaic energy is in

off-grid applications at the present time because solar cells are still more expensive

(amortized over 20 years) than competing systems. However, the spectacular price drops

in this technology are expected to continue. When the cost from photovoltaics gets below

5 cents per kWh, the spread to other states envisioned in Repowering the Midwest will be


realized.(57) While the examples in this extension so far have been from the United States,

one of the reasons that so many solar cells are exported is that in less-developed

countries, solar technology is often the only option.

Grid failure systems—the developed world

The August, 2003 blackout that affected 50 million people might have been prevented if

some of the load could have been switched to solar installations. Solar cells do best on

very sunny days, and that August was hot and sunny. If solar backup had been available,

it might have prevented the cascade of trips that blacked out such a wide awath of

territory (see extension Extension 4.5, The 2003 blackout).(167) And, of course,

individuals who are totally off-grid, or even partly grid-independent, are better able to

withstand assaults on the system.(168)

Off-grid systems—the less developed world

So where are those solar cells America exports going? To many applications in Germany

and Japan, at least since 1997, when these two countries financed a big push into

renewable energy.(152) Of the 1996 production of 90 MW, 35 MW went to these

purposes; another 30 MW were sold for remote telecommunications applications; 20

MW were sold for off-grid signs; 20 MW for motor homes, vacation cottages, etc.; and 20

to 25 were sold for powering homes and clinics not connected to a grid in less-developed

countries.(152) That had grown to about 40% of the total by 2000, and should constitute a

$2.5 billion/yr market in 2005.(169) According to experts, this still hasn’t reached 2 billion

people who depend on traditional biomass for all their energy needs, many of whom have

the means to pay for the energy were it available.(169,170)


Something as simple as supplying electricity to a school “out in the boondocks” for

computer access can increase its graduation rate from 30% to 70% as occurred at Myeka

High School in Natal, South Africa.(169) Changing people from kerosene to solar should

cause a local “explosion” of change because of the much greater versatility of electricity as

compared to kerosene for a family’s energy supply. Even amortizing the very long-lived

systems (lifetimes of 30 to 50 years, with little or no maintenance) over 10 years brings

the cost of off-grid electricity down to 18 cents/kWh, competitive with or below other

off-grid energy costs.(169) Of course, to get the family there takes a large initial investment

that may be beyond the reach of many of those in that market.

One company, Greenstar, put up the $75,000 it took to set up a system in a rural Indian

village, which now sells art and other items over the internet to great profit, which is split

with Greenstar. Greenstar expects to be paid back fully within 4 years, but will collect

10% of profits into the future to help finance other projects. Meanwhile the village of

Parvathapur has benefited in other ways. Farmers are better aware of when to sow and

reap harvests, and are making more money.(169) The Grameen Bank, which gives low-cost

loans to poor people on the Indian subcontinent (mostly in Bangladesh), has also financed

solar energy projects.(169)

PV systems have been popular in Kenya. Over 1% of the rural population is served by

such systems, which collectively total about 2 MW. Only 2% of rural homes are

connected to the grid, and the system grew without subsidy after the price of the PV

systems fell enough to be within reach of the well-to-do, but not superrich.(170) China has

used wind turbines and small hydro to bring electricity to its rural areas; for most

Chinese, PV is still to expensive. The most important lessons from success stories seems

to be that support should be given for institutions rather than for specific projects,

support for regional networks should be pursued, and to promote public-private


collaborations.(170) In the spirit of E. F. Schumaker’s book Small is beautiful,(171) the

appropriateness of the technology, composed of affordability and understanding of local

customs, is crucial.

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