This white paper discusses guidelines for installing photovoltaic (PV) solar panels to generate electricity locally. Key points include: - Panels should face south in the northern hemisphere and north in the southern hemisphere, at an inclination of around 35 degrees. - The roof must be able to support the weight of panels and mounting systems. Sufficient space around panels is needed for maintenance. - Around 30 square meters of panels can meet the electricity needs of an average family, generating about 120 kWh per year per square meter. - Micro-inverters allow each panel to operate independently, avoiding losses from partial shading of individual panels.

1. ECI Publication no. Cu0249
Available from www.leonardo-energy.org
WHITE
GENERATING ELECTRICITY LOCALLY
energy.org
HITE PAPER
Y LOCALLY
Guy Kasier
October 2016

2. Publication no. Cu0249
Issue date: October 2016
Page i
Document Issue Control Sheet
Document Title: Generating electricity locally
Publication no: Cu0249
Issue: 01
Release: Public
Author(s): Guy Kasier
Reviewer(s): Carol Godfrey (English Upgrade)
Document History
Issue Date Purpose
1 October
2016
Initial public release
2
3
Disclaimer
While this publication has been prepared with care, European Copper Institute and other contributors provide
no warranty with regards to the content and shall not be liable for any direct, incidental or consequential
damages that may result from the use of the information or the data contained.
Copyright© European Copper Institute.
Reproduction is authorised providing the material is unabridged and the source is acknowledged.

3. Publication no. Cu0249
Issue date: October 2016
Page ii
CONTENTS
1. Introduction................................................................................................................................................ 1
2. A few rules for a good PV installation ......................................................................................................... 2
2.1. Direction and inclination .................................................................................................................................2
2.2. Roof .................................................................................................................................................................2
2.3. How many panels are needed? .......................................................................................................................3
2.4. Built-in or surface-mounted? ..........................................................................................................................3
2.4. What is the financial return?...........................................................................................................................3
2.5. Avoiding shade ................................................................................................................................................4
2.5.1. Traditional PV installation ..............................................................................................................4
2.5.2. Partial shading................................................................................................................................4
2.5.3. Micro-inverters...............................................................................................................................4
3. Useful links ................................................................................................................................................. 6

4. Publication no. Cu0249
Issue date: October 2016
Page 1
1. INTRODUCTION
This white paper is one of a series of thematic white papers covering various aspects of electrical installations
in houses, flats and residential units. They are aimed at architects, designers, specification writers, decision
makers and students.
In this white paper we focus on people generating electricity themselves using renewable energy sources,
especially through the installation of photovoltaic (PV) panels. It is well enough known that, despite the
reduction in installation subsidies in many places, the financial return for the user is still sufficiently high. An
additional advantage for society as a whole is that no CO2 is emitted during the generation of electricity.
Therefore, every installed PV panel helps to work towards a better environment for us all.
We only discuss here the issues that are important to designers and decision makers as specialised installers
have adequate knowledge and experience to make the installation process go smoothly. In the design of a
residence, a number of items have to be considered in order to be able to fit a PV installation either right away
or at a later stage.
Small wind turbines that generate electricity are not taken into consideration in this white paper as they create
more of a disturbance to their direct environment and so, in principle, can only be installed on large plots of
land. A farm can benefit from them, but they do not belong in residential areas. In addition, in most cases a
building permit will need to be obtained in order to install them. During that process, an investigation will be
carried out to ensure they do not cause a disturbance to nearby residents.

5. Publication no. Cu0249
Issue date: October 2016
Page 2
2. A FEW RULES FOR A GOOD PV INSTALLATION
To ensure the investment in a PV installation gives the best possible return, it is important to respect a few
rules.
2.1. DIRECTION AND INCLINATION
In principle a PV installation can be fitted on any roof, but the wind direction in which the roof is installed is of
utmost importance to obtain the highest output from the installation.
The direction in which the PV panels must be fitted is the one where the sun is highest at midday, which
immediately implies that there is a difference between the northern and southern hemisphere. In the
northern hemisphere the sun rises in the east, climbs towards the south and sets in the west. Conversely, in
the southern hemisphere the sun also rises in the east but then climbs towards the north before setting in
the west.
In the northern hemisphere the panels must therefore face south for maximum efficiency. Southeast or
southwest is also possible, but generation then falls to approximately 90%. In the southern hemisphere the
ideal direction is towards the north, with a possible shift to the northeast or northwest.
The slope of the roof is also important and for solar panels the ideal inclination is 35°. While 30° to 50° is also
feasible, there will be a slight loss of generation. Therefore, during the design of a residence it is important, if
possible, to take account of the direction and slope of the roof.
With flat roofs there is a greater range of options as we are free to choose the direction in which the panels
are fitted ourselves, to a certain extent anyway. A mounting system ensures that the PV panels are fitted at
the most efficient inclination.
2.2. ROOF
With a new build it is not a problem to design the roof strong enough to support the additional weight of the
PV panels. A solar panel weighs approximately 13 kg/m², and traditional roof constructions will therefore
usually be adequate - e for sloping roofs, anyway. The situation is a little different for flat roofs because, in
addition to the weight of the panels, the weight of the mounting system has to be taken into account.
Furthermore, the strength of the wind can also be a factor in the calculations for the construction. On flat
roofs the mounting systems are often held in place by heavy tiles used as ballast and, in some cases, the
mounting system is physically anchored to the roof.
Since the PV panels will be installed on the roof for 20 to 25 years on average, with existing residences it is
advisable to inspect the construction in advance and essential to check the water tightness. After all, it would
be most regrettable if any necessary roof works had to be carried out after the installation of the PV panels.
This might also be the perfect moment to consider installing good roof insulation if that hasn’t already been
done.
When designing the PV installation it is important to ensure that there is still adequate room to move on the
roof around all sides of the PV panel installation, without the need to support oneself on the actual PV panels.
Maintenance works can then be carried out more easily.

6. Publication no. Cu0249
Issue date: October 2016
Page 3
Figure 1: Provide sufficient space around the PV panels on the roof. (Photo source: Fotolia)
2.3. HOW MANY PANELS ARE NEEDED?
Every m² of solar panelling generates approximately 120 kWh per year. The electricity consumption of an
average family is 3,500 to 4,000 kWh, so a surface area of PV panels of 29 to 33 m² will comfortably suffice.
Smaller surface areas are of course also possible, but in that case part of the electricity requirement will have
to be obtained from the electrical mains circuit in the street (and paid for).
Excess generation is usually not rewarded, so calculate in advance the annual electricity use and adjust the
number of m² of PV panels accordingly. Another tip: a more economical use of electricity means that fewer
panels need to be installed and thus a lower investment cost.
2.4. BUILT-IN OR SURFACE-MOUNTED?
In a sloping roof PV panels can be integrated in the roof structure and, while this is indeed sometimes done for
aesthetic reasons, it is not recommended. When the sun shines on PV panels they get hot, which just happens
to be one of the things that makes them less efficient. Therefore, for optimum efficiency it is better to install
the panels above the roof, with a little gap between them and the roof. In this way both their upper and lower
sides can be cooled down by the wind, leading to better performance.
2.4. WHAT IS THE FINANCIAL RETURN?
An example: with an investment of EUR 8,000, approximately 30 m² of solar panels can be installed. At an
electricity price of EUR 0.21/kWh this yields an annual saving of approximately EUR 735. The saving will of
course be greater in regions with a lot of sunshine than in regions with a lot of cloud cover. If electricity prices
do not go up in future (but you probably don’t believe in fairy tales), the investment will be recouped after 11
years. Over a period of 20 years the investment will have yielded EUR 14,700. If electricity prices do go up, and
if there are subsidies in the region where the residence is built, this figure will of course be higher.

7. Publication no. Cu0249
Issue date: October 2016
Page 4
2.5. AVOIDING SHADE
2.5.1. TRADITIONAL PV INSTALLATION
In a traditional installation, multiple PV panels are linked with each other in series to make up a so-called
string. An installation can then, depending on the total capacity, consist of multiple strings. Every string is
linked via special cables to the central inverter that transforms the generated DC voltage to the 230V AC
voltage used inside homes.
2.5.2. PARTIAL SHADING
Due to leaves, a tree, a post, a chimney, bird droppings, or the higher roof of an adjacent residence or other
building, it is possible for the PV panels to be in the shade to a certain extent and for a certain time. A partially
or wholly shaded panel will generate drastically less, and therefore so will the whole string. The total energy
yield will drop considerably, as a result of which the payback time of the investment will become much longer.
For this reason, the key element is to install the panels on the roof in such a way that no shade, or the least
possible shade, can be cast on them.
2.5.3. MICRO-INVERTERS
In certain circumstances it will not be possible to avoid temporary, partial shading. In such installations it is
then recommended to work with micro-inverters.
Figure 2: Each PV panel is connected to its own micro-inverter. (Photo source: Enphase)
A traditional installation works with a central inverter to which all PV strings are connected, but here partial
shading on a panel will cause the whole string to perform less well. In an installation with micro-inverters
every PV panel has its own small inverter, meaning there is no central inverter at all in the system. The great

8. Publication no. Cu0249
Issue date: October 2016
Page 5
advantage here is that a shaded panel has no influence on the non-shaded panels and only the shaded panel
doesn’t supply its full capacity.
A micro-inverter is installed behind each panel and the outgoing voltage is immediately 230V AC. Such systems
also communicate with the user via an internet link, and the user can then see on his or her computer, tablet
or smartphone which panels might be performing less well.
A defective micro-inverter can be replaced by a new one, and that is of course cheaper than having to replace
a central inverter.

9. Publication no. Cu0249
Issue date: October 2016
Page 6
3. USEFUL LINKS
Is the sun part of your roof partially shaded?
https://pitchbook.copperwire.org/is-the-sun-part-of-your-roof-partially-shaded#
Are you harvesting your own power yet?
https://pitchbook.copperwire.org/are-you-harvesting-your-own-power-yet#