Since 2004 Paradigma has been providing solar-thermal systems which are operated and connected to the conventional systems like the existing boiler. Since 2006 about 50 installations have been put into operation including the FESTO instalment, a 1,330 m2 CPC-ETC-field, the worldwide largest of its kind, providing heat for the largest adsorption chiller in the world and cooling 27,000 m2 of office space in summer and heating in winter (fig. 1, 2, 3). The interface to the heating system is a small and simple storage tank with only 17 m3 volume and without heat exchanger, so the existing huge hydronic net can be used as heat store as well.

The collector field does not contain any de-aerators, valves or other devices in the outdoor area. The planning of self-filling and self-de-aerating LSS requires extended mathematical hydraulic simulation means.

solar application cooling at 75-95 °C heating at 50-70 °C

collector area 1,330 m2 gross

volume flow 30 m3/h

storage tank 17 m3

peak power 1.2 MW

max. continual power 0.65 MW

guaranteed yield 500 MWh per year

electrical energy req. 2.5 MWh per year

FESTO, hydraulic scheme, source (HfT-Stuttgart, FESTO AG)

According to the monitoring up to now this will probably be the first LSS that delivers more energy for the customer than the planners promised in advance.

On sunny winter days nearly 4.3 MWh were fed into the tank at temperatures of more than 80 °C (fig. 4). These are after all 3.2 kWh per square meter gross collector area — an outstanding result for a day in February. No flat plate collector could probably reach the same result on a sunny day, not even in August.

In other installations an additional storage tank was expendable because the hydraulic system was able to absorb the solar input almost completely. This is very often the case in large industrial building complexes if the solar heat input can be absorbed permanently by the already existing instalment.

As a prototype a solar-thermal system for a large sauna bath has exactly been installed like an additional boiler (fig 5, 6). The solar heat is directly fed into the existing heating network (fig. 7).

solar application all-season support of an existing

heating network at about 65 °C

collector area 98 m2 gross

storage tank none

guaranteed yield about 50 MWh or 500 kWh/m2

respectively per annum

electrical energy req. 380 kWh per annum

fig. 7 direct supply of hydraulic networks

The sauna bath installation proves that this hydraulic principle is easily usable for the most district heating networks. The prospects for this principle are very promising because professional solar support for district heating could be a huge business field in the near future.

Many of non-spectacular but well-running systems like multifamily buildings, condominiums, hospitals, schools and gyms, hotels, restaurants, convention centres, barracks, prisons etc deserves to be especially mentioned, but that is impossible. All of them work amazingly simple because the heating water is also used as collector heat transfer fluid (fig. 8)

fig. 8 — large-scale solar-thermal systems for domestic hot water and space heating

3. History

At the end of the 90’s the conventional technique for solar-thermal collectors led in a dead end road. The flat plate collectors achieved high stagnation temperatures but the real efficiency for temperature ranges from 60 °C to 150 °C was not exactly promising. The problem of stagnating glycol-filled collector fields was enlarged. State of the art is that large-scale glycol-filled collector arrays must be prevented from stagnation situations by all means. Standard solutions are huge storage tanks which indeed partially solve the problem of stagnating collectors but in reality reduce the cost effectiveness considerably.

Paradigma has been involved the research and development of collectors since 1988 and launched the most innovative flat plate collectors on the market many years. In 1997 Paradigma treaded a new path and turned to vacuum tube technology. Today Paradigma has an ETC market-share of

50 % in Europe. The tubes were improved considerably, fitted in collectors from Paradigma’s own production and complemented with self-produced, high-precision CPC mirrors. This vacuum tube system is combined with minimal heat losses and ensures a very comfortable technical application on the building site. The technology to overcome the most serious problems concerning the use of water in all-year-round pressurized solar systems, which is frost protection, has been developed. Only with very high-efficient collectors with lowest heat losses it makes sense to prevent the collector field from freezing with a minimum of low temperature heat of about 2 % of the yearly solar energy gain. Operating temperatures of 60 °C — 130 °C can be achieved with high efficiency. The high sophisticated feeding algorithm provides the thermal energy at a temperature level which is preset by the user. So the solar systems operate like conventional boilers, the only difference is, that the solar irradiation is not steady.