Environmental Engineering Reference
In-Depth Information
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single-axis tracking around the vertical rotation axis for inclined mounted mod-
ules, and
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two-axes tracking.
All in all, single-axis tracking systems are less demanding in terms of engineering
expenditure than double-axes systems. According to tracking mode and the site
specific conditions, single-axis tracking systems permit the increase of energy
yields by 20 to 30 %. Two-axes systems achieve the highest energy yields, how-
ever, the yields of latter two single-axis options are only slightly lower. Tracking
systems only require little energy varying between approximately 0.03 to 3 % of
the annual energy yield. When the solar radiation is characterised by a high share
of direct radiation, the energy demand of the tracking system is close to the lower
value of the above mentioned interval. If the available solar energy dominated by
diffuse radiation the situation is vice versa.
Small grid-connected photovoltaic systems are usually fixed mounted on house
roofs, and are usually not equipped with tracking systems for civil engineering or
esthetical reasons. For flat roofs - e.g. on garages and industrial buildings - the
situation is different, as advanced tracking systems could be favoured with regard
to the cost-to-benefit ratio. Also passive tracking systems that are currently being
investigated have shown favourable perspectives.
However, it must be observed that tracking systems tend to become less attrac-
tive with increased cost reductions for photovoltaic modules. Compared to fixed
systems, tracking systems need more space, have higher maintenance costs, re-
quire more expensive mounting equipment and only offer low cost reduction po-
tentials under Central European meteorological conditions.
Under Central European conditions, even for solar power stations with high in-
stalled electrical power (i.e. MW-range), also mainly fixed mounting systems are
used. When comparing the achievable additional energy output to the additional
costs required for tracking systems compared to a fixed installation, tracking sys-
tems are, so far, always connected with higher costs. However, this situation may
be different for sites with a high share of direct radiation.
Especially high concentrating systems provided with lenses require very pre-
cise two-axes tracking systems. As for all concentrating systems, only direct ra-
diation can be concentrated. Thus, this technology is hardly applied in Central
Europe in view of the annual diffuse radiation share of approximately 50 % but is
of interest e.g. in Spain or Northern Africa with a share of direct radiation of more
than 80 % (see Chapter 2.2).
Batteries and charge controllers.
While only in very special cases grid-
connected photovoltaic systems are connected with batteries, batteries are integral
components of stand-alone power supply systems. Batteries store the electric en-
ergy provided by the photovoltaic modules or additional generators, and provide it
to consumers when they need it. Typically, prior to consumption, between 70 and
100 % of energy is intermediately stored within such systems. Batteries also per-
mit to connect consumers with higher power requirement than the corresponding
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