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Mr Giesen, different solar systems are not equal to each other. What are the differences?
There are thermic solar systems, the so called solarthermie for heat production, that means heating and hot water. With this system, the sun-produced energy will be saved in a buffer for the heating or the hot water preparation in the house. Than there are solar systems for power generation, called photo-voltaic. They change solar energy into electricity. This electricity will be led into the public electricity net and be remunerated by sets for specific pay. (Note: the electricity may of course be used by oneself. But due to the current laws, the leding in to the public net is more efficient.)
Is a solar system worthwhile on this house?
You can´t answer this in general. It depends from the object. For a photo-voltaic-system you need alt least 20m² up to 30m² area of roof. It might bring a high return of investment of about 6%. The thermic-system has another background. If you use it for example for hot water preparation, the hot water buffer will be designed for a certain number of users. For two people, who take a shower once a day, it won´t be worth it.
Isn´t there too little sun in our latitudes?
The sun is enough. But it can´t profit the optimum with each object. Important is the location and orientation to the sun, the tilt of the roof, respectively the tilt of the solar system, shadowing etc.
The solar thermia depends on the heating surfaces. For old radiators with high supply temperatures the produced energy often isn´t sufficient enough. For a floor heating it´s more advisable, because it works with remarkable lower temperatures.
How many kilowatt-hours can be produced with a solar system? How many does an average household need?
This depends on the location and the roof surface. For a photovoltaic-system you need ca. 10m² of surface for one kilowatt (kW). According to an empirical rule, with one kW solar productive power between 700 up to 1200 kilowatt-hours (kWh) solar electricity can be produced. With 10 kW output on 100m² roof surface it will amount to 7.000 up to 12.000 kilowatt-hours. A single household needs 4.000 kWh on the average per year.
With a solar thermia in the best of cases 60% of the needed energy for hot water can be covered. Concerning the heating support, 30% of the costs may be saved.
How much does a solar system cost, installations included?
For a 1 to 3-family dwelling the costs of a solar system for hot water preparation will amount up to 6.000,- €. The installation of a solar system for heating support will be at about 13.000,- €. In case of assembling a solar system, it´s recommended to change the old low-temperature-boiler by a modern upper-heating-value boiler, because that has much more thermal efficiency. Reason for the increase of efficiency ist the additional extraction of energy from the exhaust gas. Besides this, the modulation of heat output is to be considered.
The costs of investment for a photo-voltaic system depend on the size, respectively the calculated output of the system. It is calculated with maximum 10 kW output. For this, the costs will be at ca. 5.000,- € up to 6.000,- € per kilowatt-peak (kWP), that is 60.000,- € in total. The kiloWatt-peak means the output, one solar module can produce. For a 1 or 2 family dwelling, this will be about 4 kWP up to 6 kWP. Per kiloWatt-peak, about 7m² up to 10m² of roof surface is needed.
The systems have become cheaper. Is this due to the technique?
No. The demand has increased. More and more systems are produced, the competition between the suppliers has mounted. Therefor the systems become cheaper. The increase of demand is also due to the state assistance: the “energy pass” makes regenerative energies more interesting for house owners. And there are special financial supports.
Which one for example?
The state supports solar systems (note: in Germany by the “Erneuerbare-Energien-Gesetz” (EEG)), for example by remuneration for solar electricity. One can make a contract with a public energy supply contract and feed the privately produced electricity into the public net. According to the law, the energy supplier must purchase and pay the electricity for 20 years.
Where and how are solar systems installed?
On flat roofs, a solar system can be installed lying or with studding and tilt angle. On common slanted roofs, the system can be fitted as an on-roof-construction (that means above the roof tile) or as an in-roof-construction (that means integrated in the roof tiles). Besides this, an assembling on the front or the house wall is also realizable. Flat collectors have to be in a special angle to the sun. These are mainly fitting for gabled roofs. Tube collectors are more efficient, but also more fragile. They can be adjustet to the wall or layed out flatly.
A few years ago, there were rumours about the so-called “solar cheat” of the suppliers: 60% up to 70% savings for heating and hot water preparation was criticized as fraudulent advertising. It would be only 5% up to 8% of savings effectively. (About 50,- up to 80,- € per year).
Of course, you can´t reach 60%, if the house is located in the shadow between two skyskrapers. The roof must be in line to the south, and the system must be well adjusted. Than there´s the question: how many hours of sunshine do I have? How long does the winter? The output of energy and so the savings depend on all these factors.
Solar systems are also offered on the internet? What do you think about that?
I would always procure from specialized traders. There one gets guarantee on the equipment and the spare parts.
What must be concerned in general on purchase and installation of a solar system?
That it is designed reasonably. A large surface on the roof, but not sufficient buffer for the produced heat doesn´t use. This happens, if people buy on internet or DIY superstores. A solar system must be planed and applied reasonable: is there enough surface? What output shell be gained? Is it really worth for me?
Are there additional supports or state subsidies?
There´s a support by the federal office for economies and export control (BAFA). At the time, its once 60,- € per square meter for the solar thermia, but at least 410,- €. For a solar heating system it is 105,-€ per square meter of collecting surface. Admittadly this support shall be cut. Besides this, the KfW bank group offers low priced credits.
More useful information on that topic is found on the website of the “Bundesverband Solarwirtschaft, www.solarfoerderung.de. There you´ll also find the nationwide support programme.
For house owners, who want to know if their house is “solar suitable” the “Energy agency NRW” offers the “solar check”. Information under http://www.ea-nrw.de/_infopool/page.asp?InfoID=2343
From 1st to 9th of may the “Woche der Sonne” with activities and festivities, e.g. open day at solar system operators, lecture events and counselling days at workshops, expositions in city halls and banks and projects promotions at schools and universities will take place allover Germany
www.woche-der-sonne.de
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