Tallinn University of Technology

Recently, Tiit Hõbejõgi defended his doctoral thesis "Possibilities to Optimize Low Voltage Network Investments in Rural Areas" at the TUT Department of Electrical Power Engineering.

Estonian rural areas face a consistent decline in population. At the same time, the length of the power lines per inhabitant in these areas exceeds considerably the Estonian average, which in its turn means that the corresponding investments are unreasonably high. The issue is topical, because, regardless of regulatory methodologies, the reduction of costs and the increase of network reliability is always the focus point for all distribution network strategies.

Firstly, Tiit Hõbejõgi, Leading Financial Controller at Eesti Energia AS, provides a methodology in his doctoral thesis for finding favourable investment sites in the power supply network. The methodology identifies remote connection points located far from the sub-station where electricity can be provided from a nearby medium voltage line element. A mathematical model is used to find the shortest distance between a connection point and a medium voltage cable line.
Secondly, use of other voltage levels is investigated and a methodology is provided for finding potential investment sites.
Both methodologies were tested in Elektrilevi OÜ where these proved to be very effective.

Lastly, the doctoral thesis provides a framework to calculate the use of off-grid (i.e. without any connection to the electricity grid) as a more cost-effective alternative to the traditional power line construction. As a rule, an off-grid solution consists of a renewable power plant, a storage battery, an inverter and a diesel generator. As the prices for these components have a negative trend, the use of off-grid becomes more feasible in the rural areas, where the density of population is smaller.

The supervisor of the doctoral thesis, Juhan Valtin, Professor at the Faculty of Power Engineering said: "The results of the doctoral thesis show that, already today, the use of off-grid, i.e. a stand-alone power supply option, can be a more cost-effective solution."

The supervisor of the doctoral thesis was Professor Juhan Valtin (TUT).

The opponents were Matti Lehtonen (Aalto University) and PhD Mart Landsberg Elering AS, Estonia).

The doctoral thesis has been published in the digital collection of TUT library at http://digi.lib.ttu.ee/i/?4123