Belgium: Commercial Customers Can Choose among Several Solar System Variants
 Belgium: Commercial Customers Can Choose among Several Solar System Variants

Belgium: Commercial Customers Can Choose among Several Solar System Variants

In Wallonia, Belgium’s southern region, the favourable incentives make it quite a joy to calculate solar heat prices for retirement homes. The home with 110 flats or rooms described in the case study below achieves solar heat prices of 20 EUR/MWh over 20 years, with a solar fraction of 76.5 % in domestic hot water demand. If the net collector area is at least 2 m² per flat or room, subsidy scheme Soltherm grants EUR 1,500 for each housing unit. “We benefit from an incentive that can be as much as 75 % of the investment costs of the solar thermal system,” Bertrand Fontaine, CEO of Sunoptimo, explains. The Belgium solar thermal system supplier specialises in commercial solar hot water systems with drainback technology and of sizes above 100 m². According to Sunoptimo, drainback systems can reach higher solar thermal shares because larger collector fields do not run the risk of stagnation temperatures in summer. 
Photo: Sunoptimo

“We want the customer to choose the system size and design which best suits their needs and adheres to their specific requirements,” Fontaine explains the marketing principles of Sunoptimo. “We carry out around 50 simulations based on the project’s specifications in order to produce the different graphs, data and tables of our individual customer brochure [see the attached document]. All the parameters specified by the customer will be analysed: fiscal situation, access to incentives, orientation of the roof, hot water consumption and profile, etc.” In its proposal, Sunoptimo distinguishes between three different energy price developments. Scenario 1 assumes an annual energy price increase based on energy price developments over the last 15 years (black lines in the following chart). Scenario 2 predicts a more moderate price trend (pink lines), whereas the third scenario depicts a rather conservative assumption based on energy increases being close to inflation.
Solar thermal ensures fixed heat price over 20 years 
In the chart, which can also be found on page 7 of the customer brochure, the dotted lines show the total costs over 20 years for different scenarios in which hot water is not produced by solar but by fuel or gas. The first scenario, the black dotted line, results in the greatest cost: EUR 250,000. The solid lines illustrate total costs when including both solar system costs and remaining fossil energy consumption. The difference between these two lines allows for a calculation of how much money solar thermal technology saves based on the different collector field sizes. Fontaine notes that the same logic applied to retirement homes in the following can be applied to any other usage as well, be it in hotels, swimming pools, residential or industrial buildings, hospitals etc.
The left-hand side of the chart shows that an increase in collector area results in a strong reduction of total costs. When reaching a certain collector size, it can be observed that the solar saving stagnates. In other words, whether, say, the customer decides to invest in 200 m² or 300 m², total costs will be almost the same. An additional square metre of collector area will not achieve the same yield as it had in smaller fields. Each increase in the number of collectors becomes less economical. However, what also needs to be pointed out is that the graphs expect hot water demand to remain constant. Now, it is up to the client and Sunoptimo to choose the right collector field size together. In its costumer brochure, the Belgium system supplier proposes three different sizes and adds other parameters of each variant (see the following table).
Type of solar thermal system


Drainback 1

Drainback 2

Dot colour in the chart above


Light blue

Dark blue

Solar fraction

45.4 %

76.5 %

78.8 %

Collector area

53 m²

202 m²

252 m²

Storage tank volume

2,500 litres

9,000 litres

12,000 litres

Total cost of solar thermal installation (materials and mounting)

EUR 55,093

EUR 178,996

EUR 217,881

Investment subsidies and tax incentives

EUR 47,185

EUR 158,279

EUR 192,664

Net costs for solar system

EUR   7,908

EUR   20,717

EUR   25,217

Solar heat price over 20 years

13 EUR/MWh

20 EUR/MWh

24 EUR/MWh

Net savings over 20 years

EUR 78,064

EUR 124,294

EUR 124,122

Variants of solar thermal system with parameters based on scenario 2 with moderate energy price increase
Source: Sunoptimo
The second variant of 202 m² (80 collectors) produces the most favourable result. It saves EUR 124,294 over 20 years with a net investment of only EUR 20,717. “Besides good system economy, the most convincing argument for our clients is the fact that solar thermal awards a fixed price for heat over 20 years,” Fontaine says. Through its partners, Sunoptimo has realised numerous solar thermal systems in retirement homes over the last years, and the company says it has plans for several thousand more square metres.
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Baerbel Epp

Bärbel Epp is Founder and Director of the German communication and market research agency solrico and editor-in-chief of