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KWH output is not the main objective of photovoltaic

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KWH OUTPUT IS NOT THE MAIN OBJECTIVE OF PHOTOVOLTAIC Dipl. Ing. Christof Erban

Scientist at the Fraunhofer ISE Heidenhofstraße 2, D-79110 Freiburg

Tel.: +49-(0)761 4588-5358 E-Mail: Christof. Erban@Ise.Fraunhoder.de

Promevendus at TU Delft Building 8, Julianalaan 134

NL 2628 BL Delft Tel.: +31 (0)15 27-84094

c.w.erban@tudelft.nl

ABSTRACT: The fast increasing amount of electricity generated by photovoltaic systems does often not match the profile of electricity consumption. Ideas to utilize the surplus of PV-electricity by generating additional demand, such as energy storage in lakes or car batteries are in consideration, but not available in the required size and time. This paper introduces the alternative that omits any storage by providing the possibility of broadening as well as shifting the peak of photovoltaic generated electricity. It furthermore highlights the correlation of annual yield due to changes in orientation and inclination of PV-Systems in respect to time shift and energy yield.

Not the mere generation of as many kWh as possible is the main objective of photovoltaic, but the generation of as much kWh as possible at the suitable time.

Keywords: Peak shift, adapted feed-in tariff

The usage of photovoltaic panels has been proven to be very successful. EPIA states an average growth rate of >45% over the last decade [1]. Photovoltaic contributes significantly to the production of electricity especially at peak times as table 1 shows exemplarily for Germany in week 25, 2011. PV-products that ensure a reliable and optimized kWh production have been developed and are available worldwide.

Table 1: Electricity production in Germany week 25 2011 [2]

But with the further increasing capacity of photovoltaic to come, a problem for the conventional suppliers arises, as is indicated by the already today occasionally occurring small dips in the electricity provided by conventional sources at noon time. The increasing amount photovoltaic installed is about to split the formerly uniform noon time peak of the electricity provided by conventional sources resulting in double peaks of short duration by providing a high amount of electricity only for a very distinct time span. As the inertia of conventional power plants is rather high, this results in a high probability of idle operation of those plants, causing avoidable costs. Photovoltaic in those times does not replace conventional electricity, but causes idle operation of power conventional plants. The reason for this is simple: Feed-in tariffs in general consider only the total annual amount of

electricity provided by photovoltaic. That’s why the majority of all photovoltaic systems are oriented toward due South and thus provide their electricity almost at the same time, without any respect of the actually amount of electricity being required. Due to the feed-in tariffs that do not consider the fact that the time of electricity production follows a pattern that does not necessarily correspond to its consumption, photovoltaic continuously increases its impact by providing electricity with its distinct peak around noon time. As in addition feed-in tariffs continuously decrease, the pressure upon project-developers, installers and owners of PV-systems rises to focus exclusively on more or less southward oriented PV-systems as this will be the crucial issue to maintain the highest energy yield and thus a high payback for a desired location.

This will not only cause an increasing threat to the stability of the public grid (the fact that the boundary conditions to limit the number of PV-systems being shut off at the same time - e.g. in case of a too high grid frequency - are under discussion, indicates that the contribution of PV in the grid can not be neglected any more), but furthermore will have a tremendous effect on the pricing of electricity.

Wind generated electricity already occasionally effects the general electricity pricing in times when a large supply of wind generated electricity coincides with times of little consumption. The lowest yet reported price for electricity traded at EEX occurred on Sunday, the 4th of

October 2009, where between 2 AM and 3 AM one MWh of electricity cost -500,02 € [3]. Thus one did not only get any money for the electricity provided but had to pay a significant amount in order to find consumers with a suitable demand of electricity at this specific time.

This might be an upcoming thread for photovoltaic even more than for wind, for the two reasons:

- the amplitude of the photovoltaic electricity peak at noon time will increase fast with the ongoing success of photovoltaic, as all European feed-in tariffs promote the

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“as much as possible” paradigm. The problem thus will not occur randomly as it does for wind, but it will occur almost every day.

- in contrast to wind with its regional distribution, photovoltaic generated electricity peak occurs at the same time for all locations of identical longitude.

Most of the ideas to balance the photovoltaic generated surplus are based on the attempt to create a additional consumer demand for electricity around noon time, e.g. using the electricity to pump water into storage lakes or using batteries of electric cars as short term storages.

All those ideas do not utilize the fact that in contrast to wind, photovoltaic is much more predictable. While considering wind, where the accuracy of both: the amplitude and the time of occurrence is reciprocally proportional to the number of days forecasted, the time when photovoltaic systems provide the peak of their annual electricity not only can be predicted but more so can be modified to a large extend.

By changing orientation and/or inclination of a PV-System the conventionally existing noon peak –caused by PV-systems that mostly face South at optimum tilting angle for maximum annual yield - can be shifted to earlier or later hours depending on necessities e.g. given by consumer profiles.

The graphs in Figure 1 show the time shift of PV-systems when varying orientation and/or inclination and their related of the annual yield [4].

E.g. a peak shift of ± 2h can already be achieved when changing the orientation 35° from due South towards either East or West. Possible inclinations range from 15° to 55°.

100%95% 90% 80% 70% 60% 50% 40% 30%

Figure 1: Annual electricity-peak shift as function of orientation and inclination

The correlated loss in total annual electricity generated is ≤ 5%, which can be considered small when being compared to the losses that are related to alternatively discussed storage techniques.

Conclusion:

Not the mere generation of as many kWh as possible is the main objective of photovoltaic, but the generation of as much kWh as possible at the suitable time. By developing feed-in tariffs that consider the amount as well as the time when the electricity is provided, any further increase in photovoltaic capacity can be managed easily, as a fit-to-purpose generation of electricity would be possible.

[1] Hoffmann, W., 25 anniversary of TNC, Die PV Roadmap der EPIA, p 6, Zürich 25.10.2010 [2] Data provided by www.transparency.eex.com

[3] Data provided by www.transparency.eex.com [4] Irradiation data provided by W: Sprenger, Fraunhofer

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