The limits of efficiency
vs generation trends (click to enlarge)
We take it as a given that buildings should operate as efficiently
as possible. Efficiency is one of the foundations of sustainable
design, affecting all aspects of a project, from siting, to space
planning, material usage, and systems.
Energy efficiency is central to current green design practice: the
largest category of LEED points, for example, has to do with energy.
And energy efficiency has a very long way to go: in recent years,
overall building energy intensity (the amount of energy used per
unit area, square foot or square meter) has not declined dramatically.
State of the art buildings have made a great deal of progress in
efficiency, but they are a small percentage of the total building
But for leading-edge buildings, energy efficiency is a process with
diminishing returns. Generally, each new increment in efficiency
will come at increasing cost, and energy use in most buildings will
never – and should never – reach zero, since the (efficient) use
of energy is one of the essential attributes of civilization. Light
at night, refrigeration of food, communications, and computation
for entertainment and work, are dependent on the use of energy.
The paradigm shift of energy generating buildings.
first BIPV commercial building in the US
Though they are often seen as part of a continuum, energy
is qualitatively different from energy efficiency.
The techniques of energy saving are well advanced (though they have
a long way to go), but the practice of on-site energy generation
is in its infancy.
Energy can be generated on site from non-renewable sources, like
microturbines or fuel cells, which have efficiency and reliability
benefits when compared to grid energy. However, true sustainability
is based on renewable energy as the only clean source of energy.
All real renewable energy comes from just one source – the sun –
whether directly as light or heat, or transformed (with decreasing
efficiency) into wind, hydropower, or biomass. In our work, we have
concentrated on the direct use of solar energy in buildings, as solar
offers technical benefits, and importantly for us, has architectural
implications, as the basis of multifunctional architectural
The implications of integrated energy production go beyond individual
building components. Energy generating buildings will
lead to an operational and architectural paradigm shift, from total
consumption to net production of energy; from minimizing and mitigating
the external environment, to integrating and embracing it.
Building Integrated Photovoltaics: BIPV
|PV housing in IJsselstein,
BIPV is defined as solar-electric generators that are also part
of the building envelope, or serve an architectural function. Kiss
+ Cathcart are pioneers in this field, having built some of the world’s
first BIPV projects in the 1980s and 1990s, performed early research
and technical studies for industry and government agencies such as
the US Department of Energy and the New York State Energy Research
and Development Authority, and designed and developed BIPV products
and architectural systems.
BIPV interests us for two reasons. First, for the architectural
opportunities afforded by a productive building skin. Second, the
economics: BIPV has the potential to be the lowest cost source
of energy, period. Some BIPV materials are inherently similar
to architectural materials – thin film photovoltaics are physically
almost the same as laminated architectural glass, for example – and
ultimately the costs will be similar as well. It is possible today
to construct a BIPV curtain wall that costs less than a high end
conventional facade. Done properly, BIPV can produce free renewable
Terminal BIPV train shed, Coney Island
In economic terms, the story of BIPV to date is one of unfulfilled
promise. Rather than low or zero net cost, the vast majority of BIPV
installations to date have been extremely expensive. The reasons
for this are many, having to do with technology, the state
of the PV industry, subsidy programs, regulatory issues, and lack
of understanding by designers and developers. Nevertheless the potential
is real, and completely economic, architecturally exciting BIPV projects
can be done today. We can say this because we have built such projects
as much as 20 years ago.
Building Mounted Wind
|2020 tower - top
with wind array
The only renewable source other than solar that can be included
in a building is wind (hydropower may have applications in some buildings,
but it will be very rare that a building site has hydropower potential,
whereas the sun and wind are available almost everywhere). Building
mounted wind is a compelling idea to many in the green community,
presenting a visible, kinetic expression of renewable power. Unlike
centralized equipment like microturbines, wind turbines are inherently
visible, either directly (fully exposed) or indirectly (screened
or ducted). In this sense they have strong architectural implications;
but unlike PV, they have no potential for integration, which is defined
as a multifunctional architectural element. For this reason we refer
to Building-Mounted, not Building-Integrated wind.
There have been a number of elegant designs that incorporate wind
turbines in buildings; to us the problem with them is that the architectural
integration is all cost and no benefit, the opposite of multifunctional
PV cladding, for example. Wind turbines in these types of buildings
occupy space that cannot be used for any other purpose, may inspire
costly aerodynamic manipulations of the building massing, and create
issues involving noise and vibration. A more fundamental problem
with building mounted wind turbines is that often they will not work
well. Wind is a highly site-specific resource and in an ideal location
(offshore, mountain ridges) produces very economical electricity.
Wind is highly sensitive to turbulence, however, and urban and built-up
areas are very disruptive to air flow.
|2020 Tower - wind
turbines at 120th floor
Despite these issues we are very interested in the potential of
building mounted wind. In our 2020 Tower project, which is designed
to be energy self-sufficient in a very dense urban environment, we
were able to generate only about 2/3 of the project’s energy from
the BIPV facade and glazing. Assuming that a very tall tower (150
stories or 700m+) would have a good wind resource at the top, we
included a large array in the upper 20% of the building. Without
actual monitored results we cannot be sure whether even this configuration
would work effectively. We remain interested in the idea but are
skeptical about the feasibility in most cases. (see Environmental
Building News on the subject).
integrated landscape >