How is a solar thermal plant constructed and how does it work?

A solar thermal plant is consisting of solar collectors, a control system with pumps, the heat exchanger, and the thermal storage system. The collector converts solar radiation into heat. A water mixture is flowing through the collectors, transporting heat in a circuit. The heat is transferred to the storage system by the heat exchanger, and so it serves to heat p. e. process water of the household.

Can I also heat with solar thermal power, and how large would such a plant have to be?

There are combined solar plants enabling solar heating together with the heating of process water. These plants operate most efficiently in houses with low-temperature heatings. Solar plants for heating support require a larger collector surface, however, than plants serving only to heat process water. In addition these plants require a special storage system. And always you will still need additional heating. Recommendable is a collector surface of 16-20 m² in size, in connection with a storage buffer of 1,000-1,500 l.

When is my roof suitable for a solar thermal plant?

Solar thermal plants can be installed on surfaces larger than 4 m². The roof should be oriented SE to SW; most ideal was South. The roof should be pitched between 20° and 60°. Roofs oriented W or E still generate 80-85% of the gain which an ideally oriented roof might yield. Losses can be compensated by a larger collector surface.

Will my roof sustain the additional weight of a solar plant? Aren't the collectors very heavy because of all the water?

The filling of solar collectors amounts to ca. 0.5 l/m², the weight of solar collectors to ca. 20 kg/m². The BUSO solar roof thus is lighter than tiles, which amount to 25-35 kg/m².

What benefit has the environment from solar thermal plants?

Using a solar thermal plant may replace conventional power sources such as oil, coal, gas, or uranium. This way you reduce CO₂ emissions and other exhaust gases produced by burning. A solar plant of 6 m² in size can conserve up to 1500 kg CO₂ per year. Solar thermal plants also reduce the transport routes for you need less oil or gas.

What life expectancy may I expect from a solar thermal plant?

A high-quality solar thermal plant has a life expectancy of more than 30 years.

How is the solar thermal plant protected against frost?

The liquid flowing through the collectors is a composition of water and an anti-freeze. Thus the plant may operate in winter, too.

How much maintenance do solar thermal plants need?

The maintenance level of solar thermal plants is rather low by comparison. Like any other technological plant it should however be regularly controlled.

Will my solar thermal plant be funded?

There are various means of funding, especially investment grants. In solar funding, the operator of a plant will receive a funding of 60 € per m² for the heating of process water in up to 40 m². For combined plants that also heat with solar power, the funding increases to 105 € per m². In addition there is p. e. a bonus of 750 € if the old boiler is replaced by a new one or if an eligible bio-mass or heat pump plant is installed to support the collectors.

Do I need a permission to implement a solar thermal plant?

The implementation of a solar thermal plant does not need permission.

Does a solar thermal power plant generate sound?

No - it is part of the fascination of a solar plant that if you look at the heat meter you will perceive how many kilowatt hours are generated without any emissions.

How much oil may I conserve per year with the solar roof?

There are various conservations, depending on collector surface and use of the plant. One example may be a single-family house that is 30 years old and provides 130 m² of living space. Without support of solar power, this house consumes 2,500 l of oil. A collector surface of 5 m² in size, serving to heat process water, may conserve 150 l of oil. A solar roof featuring 24 m² may cover 1/3 of the demand for heating. If you equip the house with improved insulation you may reduce the demand for oil even more.

How much money will have about to invest?

Depending on plant size and funding, about 550-700 €/m2. Buffer and fresh-water systems are included, representing a general improvement of the heating system. The newest generation of our system technology may even include a perfect heating regulation.

How may I combine the solar roof with an additional heating?

It will not be sufficient trying to cover the demand for heating completely with solar power. An additional heating is obligatory. The solar roof may be combined with wood carburator boilers, pellet heaters, pellet stoves, heat pumps, and gas/oil-condensing boilers.

May I connect a wood boiler to the storage buffer (later) without a problem?

Yes – you do not need a heat exchanger, for the buffer is containing heating water, too. The buffer and the fresh-water system may thus serve for solar and wood heating with double benefit. With our new control technology, the solar controller may even monitor the connection to the wood boiler, too.

What if the sun does not shine?

At a cloudy day, the sun still yields about 80% of the radiation at a sunny day.

Can I switch off my heating boiler completely during summer?

Yes – the decisive factor is the flow rate of warm water. Our fresh-water system enables the tapping of the buffer as if it was a boiler. That is, out of a 1,000 l buffer at 50 °C, you may tap almost 800 l of water at 45 °C. This is a difference from systems with interior hot-water preparation by heat exchangers. These latter operate according to the "mixing principle", allowing only a small part of the heating water volume to be tapped for showering and bathing.

What happens if during winter there is snow on the collector?

This snow often will melt faster than on the rest of the roof. Light passes the snow and does access the collector. This generates a water film on the smooth glass. Another advantage against evacuate technology which defrosts only slowly (if not faulty).

What is "intrinsic safety of solar plants"?

An intrinsically safe solar plant benefits from running all operational conditions intrinsic and without interfering actions from the outside. Let us explain this by a practical example: At a beautiful summer day, the storage medium is charged to the highest temperature which the controller is set to (p. e. 65 °C). The controller will switch off the pump to protect it against overheating. Now the heat can no longer be removed from the collector. Its internal temperature will rise until the solar liquid evaporates. The rise in temperature and the evaporation cause the solar liquid in collectors and pipe tubes to expand. Now the solar plant is intrinsically safe if the expansion tank can fully absorb the volume expansion. (Otherwise the volume expansion would increase pressure and finally trigger the safety valve which would exhaust a part of the solar liquid!). After this operational condition has changed, p. e. due to lessening irradiation and cooling of the collector, the expansion tank may return the solar liquid into the collector circuit. The controller decides whether the storage medium may be further charged.

How long will the installation of such a plant take?

A solar roof requires between 0.7-1.5 man-hours/m². The system technology is pre-assembled by us and quite quickly implemented. The time needed for connecting the system may markedly vary, depending on which conception used.

How is your collector fitted to the roof?

The absorber frames are mounted on plywood bars bolted on the joist. These plywood bars may to some extent also be used for „back-coating“ of uneven roofs. Even on assembly with cranes, the plywood bars may serve as guiding systems.

May your collectors also be mounted to a flat roof?

Yes, but for heating support it will be less than ideal unless floor-mounted. The solar roof may also be floor-mounted with a wooden substructure and will then be coated on the back. This solution is of higher quality than classic floor-mounts of on-roof collectors, for pipes and mounts are protected.

Does the effectiveness of the collectors lessen if polluted? Do they have to be regularly cleaned?

No - the collectors will sufficiently clean themselves.

May the whole solar plant be mounted without on-roof?

On-roof mounting is suitable only for small solar plants with prefabricated collectors. For larger surfaces, solar roofs are available only for integration onto the roof. This is the only way to achieve even surface load on the roof and to use inexpensive modular technology.

What if I have a Thermoroof?

Slightly more difficult – because handling has to be very carefully so that the sensitive styrofoam parts will not be damaged. Beneath the collector some wooden bars will have to be fixed with long bolts, and underneath a wider board has to be mounted.

What kinds of collectors are available?

When installing solar thermal plants, the following collector types are used:

1. Flat-plate collectors
2. Evacuated flat-plate collectors
3. Evacuated tube collectors
4. Pool absorber

The first three types of collectors are identically structured: body with transparent cover, insulation, and absorber. The flat-plate collector is essentially a box made of wood, metal, or plastic. Inside there is a metal absorber to convert solar radiation into heat. The box is insulated at the bottom and sides, on top there is a transparent cover, usually made of glass.

Evacuated flat-plate collectors are structured like common flat-plate collectors. However there is no heat insulation. Instead the interior of the body is evacuated. In order to absorb the load invoked by pressure differences, a tight grid of bolts keeps front and back of the collector box at equal distance. A metal absorber converts solar radiation into heat.

Body and transparent cover of evacuated tube collectors consist of a tube of glass. Here as well, heat insulation is replaced by a vacuum. The glass tube contains the metal absorber for heat generation. Pool absorbers consist of absorbing mats or plastic hoses. There is neither a heat insulation nor a transparent cover.

Your collectors are made of wood. Why do you use such a cheap material which may even decay?

It is true that wood is a cheap processing material, but that does not mean it is bad material. Roof frames have been made of wood for millenia. Wood has the advantage of "respiring", i.e. absorbing water and steam and diffusing it out again. Also, wood only decays in persistent contact to water or in case of absent ventilation. Continuous ventilation, however, is achieved by placing the collector on the joist. Because of the considerable seasonal changes of temperature you may also need no wood preservative, for there is a "thermal disinfection". High-ranking institutes also confirm that wood provides a profitable micro-climate.

Why do you offer your collectors so cheaply in comparison to your competitors?

We could answer to that that you should ask our competitors why theirs are so expensive. No, seriously, there are some reasons why we can offer you our products in such a surprising price/performance ratio:

1. The collector is already cheaply produced. It was designed specifically as a solar roof, i.e. in large modular technology. We do not need intermediate plating, we are using an innovative sealing free of silicone, and we install a patented glass coating technology. This enables us to inexpensively produce our collectors.
2. In comparison to our competitors, we may install our collectors on the roof without an expensive crane. The solar roof is “tiled” like any roof of slate or brick.
3. Our high trading turnover and thus advantageous purchase prices enable us to sell our products inexpensively to our customers. The collector is sold in direct sales to the customer, i.e. you do not need to pay for expensive intermediate or wholesale, unlike with many competitors.

Why do you install your solar roofs in individual parts and not as assembled collectors?

This way we can install collector plants that are individually tailored to the customer's desires. The customer may even decide himself where the collector's supply and return lines may enter the roof! Also there are no breakthroughs, tubes, or air bricks on the roof! Besides, such a modularly structured collector system is easy to repair and expand, so that its life expectancy may increase to 50 years.

Why are there often external plate heat exchangers used for the storage buffer? Isn't that impractical?

Not at all. The customer is receiving a pre-mounted system into which the plate heat exchanger has already been integrated. Usage of the external PHT brings further advantages: In contrast to combined storages (integrated potage water blisters) or buffers with interior plain tube heat exchangers we can achieve a very low junction temperature in the buffer, allowing to switch off the boiler from spring to autumn. Also, from an external PHT you may tap a much higher amount of hot water at once.

Why to I have to use high-temperature resistant insulation for the solar circuit?

If the pump is switched off or faulty and there is a strong solar irradiation, collectors may be exposed to stagnation temperatures considerably higher than 200 °C (up to 280 °C for evacuated tubes). If you start operating the plant again after such a stagnation, the entire collector circuit may feature temperatures of up to 130 °C. But pipe insulation commonly used in the heating business is only resistant against constant temperature heights of about 90 °C, thus damage of the collector circuit was imminent.

Why do you not use intermediate platings and silicone seams, in contrast to some other producers?

The usage of intermediate platings and silicone seams has to be considered hazardous to the tightness of the roof. The extremely varying temperatures from summer to winter may cause tensions and breaks, due to different materials, translating into different thermal expansion values. This will ultimately provoke leaks in the roof. With our solar roof, all parts are clamped, so that there is sufficient clearance for thermal expansions.

How much power do the pumps consume that you integrate into your plant?

In the average, our solar plants are yielding a power/heat ratio that it 2 to 4 times better than that of conventional solar plants (just for hot water). Reckon about 1 kWh of power for the pumps vs. 100 kWh of solar heat. Despite of featuring 2 solar pumps, this is made possible by perfect hydraulic tuning and the size of the solar array. The fresh-water pump (0.083 kW) is active for less than half an hour per day.

Does the solar roof provide additional heat insulation?

No - the solar roof is ventilated and thus cannot suit as a heat insulation.

How do I know how high might be the gain of the solar plant? Do you have a heat meter?

A heat meter we integrate by standard into all our solar roof plants.

Does the heat meter provoke additional regular costs?

The heat meter is an electronic component and thus requires an additional power supply of 0.1 Watt. Meaning that the annual power consumption will rise by about 1 kWh (ca. 0.17 EUR) – an almost negligible amount.

May I heat my pool with a solar plant?

Yes. In single- or double-family houses, solar plants made of flat-plate or tube collectors are usually sized so that during the summer months they will provide more hot water than the users will consume. This "heat surplus" can be transferred to the pool water.

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