Investigation of the Efficiency of a Big Pilot Solar Thermal Installation

Summary
The objective of the project was to investigate the efficiency of a pilot solar thermal installation, built on a block of flats in district Levski, Sofia.
The efficiency both of the solar and Domestic Hot Water loops, as well as the scheme for financing and paying back of the investments was examined through continuous measurements of the solar energy yield and hot water consumption. The technical and economical analyses indicated the measures needed to be undertaken in order to improve the installation performance and reduce the payback period.
The project is financed under SAVE II Program, Project: 4.1031/A/00-009.
The results proves that constructing combined solar-electrical installations for DHW for residential buildings can be profitable solution for more than 600 buildings in Sofia and others in Bulgaria.

Context

There are more than 600 blocks of flats in Sofia for which the local district heating plants provides heat energy for space heating but not for hot water. The inhabitants use mainly electrical heater, which increases considerably their bills for electricity. The idea of was to create a combined system for DHW utilising the solar energy and adding electricity when the solar radiation is not sufficient to ensure normal supply. The system is decentralised and uses RES - solar energy that is in compliance with the word tendencies for clean energy production and sustainable development.

Objectives

The project objectives were to examine the performance of the big solar thermal installation and propose technical and economical solutions for efficiency improvements. The possibilities for project dissemination were also investigated.

Process

The existing big pilot solar plant for DHW supply for 70 households, built on a block of flats in district Levski (Sofia) was investigated in order to increase its efficiency. The installation consists of 126 m2 Austrian flat-plate solar collectors (Fig.1) and 6500 l store-tanks. The overall target groups were the households living in residential buildings in Sofia and other cities not supplied with DHW from a district heating utility, as well as ESCO companies providing energy service DHW supply.
For reaching project objectives all project documentation was inspected and several on-site visit of experts was realized. A one-and-half year monitoring of the solar energy yield was conducted in order to prove and verify the suggestions from the walk through audit of the installation and 2 months work in the real beginning. The monitoring results were analysed and compared to the theoretical computations. The energy balance and the data from system operation revealed the weaknesses of the installation and possibilities for its improvement.
The project was implemented in 2 phases:
First phase: On-site visits, preliminary investigations and assessment, analysis of the project documentation and system construction, examination of the operational data for the firs 2-3 months of work of the installation.
Second phase: Design and installation of equipment for system monitoring and additional measuring devices. The data received were analysed and measures for system improvement were proposed.

Results

The solar energy yield for the period September 2003 - September 2004 (one year) was 90 MWh (Fig.2). This means 714 kWh per square meter collector area per year renewable energy. This numbers show the high potential of using solar systems for DHW in Bulgaria. As a comparison in Germany the average value for thermal energy production from flat plate collectors is 400 kWh/m2.year. On the other hand it is very important to find out a proper technical solution for a given building (existing or newly constructed) in order to avoid problems with high level of thermal losses in the internal loop - about 45% in our case. After undertaking measures for performance optimisation these losses were reduced to less than 20%. Another important issue is the financial aspect of the project. It was estimated that the payback period for big solar installation could be reduced up to 8-10 years and hence make the systems more attractive for the investors, particularly taking into account the lifetime of such a project - 20-25 years.
The project opens perspectives for constructing similar solar DHW installation for residential and non-residential buildings and hence reducing greenhouse gases emissions and ensuring new job opportunities for collector manufacturers, installers and ESCO companies who will coordinate and organise the process of construction and exploitation of the systems.

Lessons learned and repeatability

The project proved that using solar energy for DHW in Bulgaria could be profitable both for households and for ESCO companies who could build and operate big solar installations proposed to ensure DHW for residential and non-residential buildings with high hot water consumption (like hospitals, sport centres, etc.).
Measures foreseen to be implemented and included in the future design of solar installations will facilitate designing and proving the financial effectiveness of such a solution as a renewable and distribute source of energy and will open the door for wide-spread use of solar installations for DHW supply in Bulgaria.