Stroomwerk Energy

Solar Basics

Solar power; clean, quiet and renewable
The production of solar power does not produce any dangerous gasses or gasses that harm the environment. Next to that it uses an eternal source like the sun, instead of volatile fuels like coal and natural gas. But as you know “it takes money to make money”. This also counts for the production of solar modules “it takes energy to save energy”. How long should a solar power system be active to produce as much energy as it has cost to produce the same system? In the Netherlands that is about 2,5 years. So during it’s lifetime a solar power systems produces 12 times the amount of energy that was needed to produce the system it self. In this chapter you will find more technical information about solar cells, solar modules and different solar power systems.

solar cells	solar modules		performance and insolation

solar power systems		FAQ

Solar cells

Photovoltaic transformation or PV is the name of the process when a solar cell transforms the light into electricity. The process of photovoltaic transformation is based on the principle that a current will flow when two not identical semi conductors make contact under the influence of light.

Most solar cells are made of silicon. Silicon is a semi conductor material and it is very common on our earth; the basis is sand. The silicon which is used for solar cells exists of two prepared layers. A bit of phosphorus is put on one layer, in the other layer you can trace a bit of borium. Between these two layers there is a kind of separation layer. Thin contact lines are attached at the front of the cell. At the back you will find a small metal line, often made of silver or nickel. Electrons are set free in the cell under the influence of light (insolation). Then a voltage drop will develop between the plus (frond side of the cell) and the minus (back of the cell). This creates a current flow. To start this process you don’t need bright sunlight. Even on a cloudy day the cells will produce electricity.

Roughly you can distinguish three types of solar cells:

Monocrystalline solar cells are made of silicon slices, cut from a big monocrystal. Because this crystal has ‘grown’ under very controlled circumstances is has a very even structure.

Polycrystalline solar cells (or multicrystalline) are also made of silicon slices, cut from a big crystal. The efficiency of these cell is often a fraction less than the efficiency of the monocrystalline cells.

Amorphous silicon Amorphous silicon is not cut from a big crystal, but the silicon is directly ‘blown’ on a surface, glass for example. Less silicon is used and the power output of a square meter of amorphous solar module is less than the output of a square meter of crystalline modules.

Celtype	Monocrystalline cells	Poly/Multicrystalline cells	Amorphous modules
Abbriviation	mono-Si	poly-Si or multi-Si	amorf-Si (thin film)
Material	stiff, hard	stiff, hard	flexible or stiff/hard
Production process	slices of silicon	slices of silicon	‘blown’ on the surface (less silicon, but less power)
Market share	85 %		15 %
Efficiency	15 %	14 %	6 - 8 %
Colour	dark blue, dark grey	blue	black/brown/gold

Solar modules

There a several kinds of brands, types and sizes of solar modules. The global development of modules still goes on. Different techniques are developed to convert the solar energy into electricity on the most efficient way. The most common techniques are described here. Often, a solar module consists of a collection of solar cells, for example 72 cells. You create a monocrystalline solar module by using monocrystalline cells, and polycrystalline modules by using polycrystalline cells.

Production process crystalline solar modules
The first step is connecting all the cells together with soldered ribbons. This is also called ‘stringing’. Depending on the number of cells that are connected to each other, the module will deliver a current of 12 V, 24 V or 36 V.

Then the string of cells is put on a kind of melting foil called EVA. The EVA and cells are transferred to the glass. Then another foil, called tedlar is put on top. The tedlar is the back of the module. And you will also see the tedlar at the front side of the modules, between the cells. Tedlar is available in many colours and also in a transparent version. The most common colour is white.

Then the complete ‘tower’ of layers (glass, melting foil, cells, tedlar) is put in the laminator, a kind of oven. All layers melts together and a waterproof connection arises.

Then most of the modules are framed. This aluminium frame increases the stability and strength of the modules. And the frame helps you install the module because you use the frame for mounting. A solar module without a frame is called a laminate. Laminates are mostly used in roof integrated systems.

On the back of the modules, a junction box with diodes is mounted. And here the plus and minus cables are connected which simplify the connection of the modules to each other. All modules are flashed. That means that every module is exposed to a certain amount of light in a conditioned environment. The power the module provides at that moment is measured and determines the Wp power of the module. This data is called flash data. All modules have a unique serial number and the flash data shows the exact result of the test of that specific module.

Solar module sizes The size of solar modules varies enormously. For example, in a pocket calculator extremely little solar cells are used. But in the meantime there are also modules manufactured with a size of 2x2m. Manufacturers will mostly use standardised sizes. Manufacturing of special sizes is an expensive possibility. Stroomwerk realised a project with two of the largest modules ever manufactured. Each module was 3m high and had a width of 1,5 m. Now they forfill their task as a roof of a waiting room for boat trips.

Transparent modules Some architects will choose for transparent solar modules for esthetical reasons. The effect of the square shade spots is very typical for this kind of solar module. The manufacturer of this module can use for example transparent tedlar to get this effect. It is also possible to use a second glass layer, the so called “glass-glass” modules.These modules can also be used for insullating glass units. The glass-glass modules are mechanically stronger but they are also heavier in weight. The junction box has been removed by this kind of module; otherwise the junction box will be in sight. Transparent modules are often higher in price than normal modules.
Amorphous silicium modules Silicum is also used as a base material, but there are no cells manufactured of it. The raw material is vaporised on a base. With glass as a base, you will get amorphous solar modules. When a plastic foil is used as base, you will get flexible solar modules or even solar modules on a roll! This technique, which is much cheaper, will offer lots of possibilities. The disadvantage of this kind of modules is that they produce less power. One square meter will produce half of the power compared to one square meter of mono- or multi crystalline modules To get the same power results you will need twice as much surface and installation costs. An advantage is the better performance of the amorphous modules on a “rainy, grey day” Warrantees with crystalline solar modules Solar modules have two kinds of warrantees, product warrantee and power output warrantee. Product warrantee: You can compare this to the normal warrantees you get when you’ll buy a product. For example a bread toaster has a product warrantee of 1 year. Most of the solar modules have a product warrantee of two years. Vermogensgarantie: You can compare this to the normal warrantees you get when you’ll buy a product. For example a bread toaster has a product warrantee of 1 year. Most of the solar modules have a product warrantee of two years.

Solar power systems

A solar module is always a part of a solar power system, which has more components, such as cables, inverters, batteries, power regulators and a supporting framework. A loose solar module will not function. Depending of the need of electricity a solar system is assembled. There are two kinds of solar power systems:

Stand-alone systems
Grid connected systems

Stand alone systems
This type of solar power system can be used where there is no power supply or when a connection to the grid is too expensive and there still is a need of electricity. Sometimes a generator set is used to produce electricity. Those systems are not always wanted because of the side effects (noise, presence of fuel, emission) or they are not technically fitted for the specific situation.

Solar modules are a permanent, maintenance free and very reliable alternative. You can think of areas in Africa, buoy in the sea, space travelling etc. But there are also mobile light masts, ticket machines and water pumping systems which operate on solar power. The electricity whis is produced during daytime is stored in batteries, so the produced electricity can also be used in the evening and at night. The batteries need to have enough capacity to bridge dark days, especially in wintertime. A battery charger is essential with a stand-alone system. It will regulate the charge and discharge current to the batteries.

The batteries will provide 12 V. There are special lamps, fridges, pums and other devices that worjk on 12V

Stand alone systems are not used as a general power supply which is aiming to a maximal year production. Most important is quarantee of power supply over the year.

Grid connected solar systems
These solar systems are connected to the main electricity grid. The inverter will convert the DC voltage, which is produced by the solar modules, into the correct voltage (230 V AC)

When a building needs more electricity than the modules provide, the lack is filled by the electricity grid. When a a solar system provides more power than is needed, for example during when you are on a holiday, the surplus will be returned to the electricity grid. The electricity meter will count backwards*

The solar system will stop immediately for safety reasons when the electricity grid is dropping out. So you’re not independent from the electricity grid with a grid connected system.

Applications
Solar power systems are available in many features and applications. The solar systems are classified in their application areas. The different application areas are; stand alone systems for consumers, stand alone systems for professional use, grid connected systems for buildings and other constructions. In the schedule below you can find typical examples for each application area.

Application area	Examples
Stand alone for consumers	garden houses, trailers, boats, remote houses
Stand alone for professional use	public lighting, emergency telephones, buoys, beacons, sluices
Grid connected	decentred electricity supply on houses, buildings and other constructions

*provided that your electricity meter is suitable for this. Most moving coil meters will count backwards, unless they are provided with a back-flow pawl. Electronic meters don’t count backwards. In that case there has to be installed a digital meter, which can register the backflow. You can contact your power supply company for more information. Consumers who installed small solar systems (up to 500 Wp) probably will not see the meter count backwards. There are always some appliances which will use electricity, for example a fridge, an alarm clock or VCR. Such “sneaky” users will consume about 600 kWh a year.

Profit and solar insolation

The amount of solar energy which reaches the earth is enormous. In one hour the earth will intercept an energy flow which is equal to the yearly energy usage. The Netherlands receive yearly an amount of energy which is equal to almost 500 times our yearly energy usage! The amount of energy which a solar module will produce from this is depending of 3 factors, the surface of the module, the efficiency of the module and the insolation of the sun.

Profit
To make a clear statement of the effective power of a solar module we calculate with peak power of a module. This is the maximum electric power which a solar module can provide at a certain insolation under specific circumstances. We call this Watt peak (Wp). There are solar modules with all kinds of power. This varies from 10 Wp to over 200 Wp. In the solar power annual you will find an overview of the used measures and figures, which are used in the solar world.

In the Netherlands a stand alone solar system of 4 m2 will provide energy of approximately 160 kWh. A grid connected system of the same size will provide approximately 320 kWh a year. The energy yield of such a grid connected system is equal with 10% of the yearly power usage of an average household, or the energy consumption of a fridge.

The difference in yield of those two systems is related to the use of a battery in case of a stand alone system. When the battery is fully loaded the solar modules are switched of so there is no conversion of sunlight into electricity.

The yield of a solar module is depending of the angle of inclination of the module and the positioning of the module to the south. Determination of the most optimal angle of inclination fo the solar system depends on the application and location of the system. In the Netherlands the maximuml yield on a yearly base is realised by positioning the module at an inclination angle of 36 degrees positioned southwards. Not everybody has a roof which is positioned southwards where they can put their modules. That doesn’t have to be a problem. You have to find the best possible inclination angle at the best positioning. With the use of the radiation insolation diagram, you can find the optimal inclination angle. Between the positions southeast and southwest you can always find a roof angle where the insolation is 95% of the maximum insolation. When the positioning is east or west you can get a maximum possible insolation of 80% till 85% with an inclination angle of 20 degrees.

In yhe Netherlands you can expect a yearly energy yield of 75 to 80% of the Wp-capacity at an optimal positioning. A system of 3000 Wp generates yearly approximately 2250 kWh. Of course it is normal that a solar module will generate more power in the summer than in winter. You can imagine there will be more sun shine at the coasts than in the east of the Netherlands. Also the conversion of light into electricity works better in a cooler environment. So that is also important for positioning your modules. This is visible in the schedule below. At (almost) the same hours of sunshine, the month June will generate more power. The reason is that the month July is expected to have a higher temperature.

Month	Days	Hours of sunshine in the norm year	Energy yield of the norm year in percentages
January	31	69,9	3,41%
February	28	97,2	5,16%
March	31	126,9	7,91%
April	30	168,5	11,24%
May	31	202,6	12,41%
June	30	204,1	13,22%
July	31	204,4	11,55%
August	31	201,5	11,78%
September	30	141,3	9,75%
October	31	117,2	6,42%
November	30	68,0	3,82%
December	31	56,7	3,33%
total	365	1658	100%

The radiation insolation diagram
The radiation insolation diagram displays the yearly average for different inclination angles and orientations expressed in percentages of the maximum insolation. The middle of the diagram displays a maximum insolation of 85% with an inclination angle of 0 degrees. In the Netherlands the maximum is reached with an inclination angle of 36 degrees orientated on the south. This is almost 1100 W/m2. The diagram covers the area from Denmark to the Northern of Spain.

FAQ

Here you can find the answers to the most common questions about solar systems.

1) Is power, which is generated by a solar module, profitable?

Without a financial impulse (subsidy, feed-in tariff,…) it is difficult to get your investment back within a reasonable term. With subsidy, a do-it-yourself system can be earned back within the power-guarantee terms of the modules (mostly 25 years). So in the end you’re system is profitable. With your own solar system you also invest in the environment. A solar system with a surface of 24 m2 makes a difference of 1000 kg CO2 in the atmosphere a year. And you’ll become the owner of your own electrical power company. The prices for the “regular” electrical supplies will increase in the next years due to growth of environmental taxes, the supplies of fossil fuels will become scarce. The costs will decrease to a minimum once you are the owner of a solar power system.

2) How much energy can a solar module provide?

In the Netherlands the yield of a solar module of 145 Wp is about 109 kWh a year. A system with four modules (580 Wp) will provide 435 kWh every year, which is the same as 13% of the average annual electricity use of a household.

3) Will I produce power when the sun doesn’t shine?

Yes, a solar module also works on diffuse light. Diffuse light is solar insolation which reaches the earth not directly, but is absorbed in the atmosphere and then is reflected to earth for example due to cloudy weather. The yield of a solar module is at a maximum in full sunlight with clear white clouds.

4) Will my electricity meter count backwards??

Almost all kinds of electricity meters will count backwards as long as your household needs less electricity than your solar modules will provide. “Old” meters (moving coil meters) will count backwards, unless they are provided with a back-flow pawl. Digital meters will normally not count backwards, but the newest models can register the energy that is delivered to the power company. With the small solar power system (<500Wp) you probably won’t see your meter counting backwards. It is important to watch out for energy consuming devices. These are devices which continuously are consuming energy, such as the doorbell, the fridge, the deepfreeze, alarm clocks, the television and the video recorder (stand-by mode). Such consuming devices will use about 25 Watts, this is 250 kWh pro year.

5) Do I need permits to place a solar power system?

Since 1 July 2002 you don’t need any local permits anymore in the Netherlands. There are a few exceptions, such monumental buildings or buildings which are placed under protected village or city sights. Besides that there are some reasonable guidelines which you need to take care of. Please check the local authorities if you need any permits.

6) Has the module to be orientated south?

No. The south is the most optimal orientation for the module, but there is a wide range possibly from the east till the west. North is not suitable for the modules.

7) What is the power output warrantee of a module?

The most solar modules have a warrantee of 12 years at 90% of the nominal power output, and 25 year at 80% of the nominal power output. The product warrantee is mostly 2 years. Inverters have warranties which can vary from 1 to 5 years.

8) Are the modules determined against the weather conditions in the Netherlands?

Yes, when the modules have been placed properly, they are determined against extreme weather conditions, such as storm, hailstones, snow and heavy frost.

9) Is mounting of the modules on the roof difficult?

No. With the help of good guidelines and the mounting materials everyone shoudl be able to mount the modules on the roof. Mounting modules on a leaning roof needs a little bit more skills and some safety facilities. When you think it’s to difficult or to dangerous for you you can always hire a person or company who will mount the modules for you.

10) How do I know if my modules generate power?

When you place an performance measuring device, you’ll always know how much power your system provides. You also can look at your electricity meter when the weather is beautiful or after you switched off all other electronic devices in your house.

11) Are there any funds for a solar energy system?

In the Netherlands there was a special national funding “Energie premie” for private owners of solar energy systems. Unfortunately this funding has been vanished since January 2004. We still are waiting for new funding from the government.

12) Can solar modules be mounted on any kind of roof?

Almost every kind of roof is suitable for mounting modules. There are special mounting constructions for not insulated corrugated plates and bitumen roofs.

13) Does the module need maintenance or cleaning?

No, because of the construction with an inclination angle and the special glass layer of the module, the rain will clean the modules. When you like to clean the module yourself, please use a mild natural soap.

14) Do I need adjustments for my house or electrical installation?

Your house or electrical installation barely needs any adjustments when you buy a grid connected system. The modules can be mounted on top of the roof tiles without any adjustments to the construction. With a flat roof, he modules are mounted on a loaded construction which is placed loose on the roof. Solar energy systems with a power output over 600 Wp need to be installed on a separate group in your electricity switchboard. Furthermore a cable need to be installed to the nearest grounded wall socket or to the electricity switchboard.

15) How do I put my cable from the modules through the roof to the inverter?

With a tiled roof you can drill al hole beneath the tiles. With a flat roof construction it is wise to carry the cable through a vertical wall.

16) Are the modules insured with the house insurance?

We advise you to contact your insurance company or person to inform yourselves if you need a separate insurance for your solar modules.

17) Do solar modules increase the danger of being hit by a flash of lightning with a thunderstorm?

No. The chance your house is hit are not bigger than normal. The modules are double isolated. With large solar systems there is no need to put extra conductors on your roof.

18) Are the modules getting any cheaper in the future?

The demand for solar modules is expanding in the last couple of years. The production capacity of the manufacturers can not be expanded just like that. The production capacity is behind in the need of the rising demand. Because of this the prices will rice in the near future. When the manufacturers have expanded their production capacity, the prices can decrease again. But we expect that the (governmental) funding then also has become less.


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