Lecture 3

The third lecture of Ene-59-4210 Special Course in Energy Economics was held on 24th January 2011. The lecture was follow-on for last Friday’s lecture. The main topics discussed on the third lecture were PV systems, solar thermal systems and small scale wind systems in developing countries.

In the PV system section it was discussed about rating of PV modules and various technical aspects related to designing of PV system. For me it was new information that outside temperature in typical rating conditions is only 25’C. In most of the countries where PVs are widely used or will be widely used in future, the temperatures are clearly above 25’C when sun is shining. Because efficiency of crystalline silicon solar modules (most used technology at the moment) decreases when temperature increases, a little bit higher temperatures in the rating of PV modules might be in my opinion more informative.

Siting of PVs was also discussed on the lecture. PV modules should be installed so that there are no obstacles that can overshadow the modules. Even if relatively small part of whole PV system is shadowed, the output of the system may decrease a lot. To get as much electricity as possible from PV systems with no tracking, the modules should be tilted at around the latitude angle of the location. With tracking the output could be increased. However there is also increase in costs, so tracking is not always economically viable. Usually it is economically more viable when the efficiency of the modules is high. So the best PV technology for the systems with tracking could be mono crystalline silicon technology. However, First Solar Inc, the largest manufacturer of solar modules in the world, has invested to tracking technology despite of relatively low efficiency of their CdTe modules.

The second topic on the lecture was solar thermal systems for heating of water or buildings. The basic technology here is simple flat collector. Tracking is not used usually in solar thermal solutions, especially in developing countries. Also there usually is no need for vacuum tube collectors in developing countries, because there simply is no use for very hot water produced by vacuum tube collectors.

Design of wind power system as a part of RAPS was third topic on the lecture. Technical aspects of small scale wind power and measuring of wind energy potential were discussed. It is for example very important to know average wind speed and the distribution of wind speed (Weibull parameter) to estimate the amount of wind generation in local conditions. Unlike in PVs (without tracking), wind turbines have moving parts and so they need service. It would have been very interesting to hear how maintenance of the turbines is arranged in rural conditions in developing countries. Wind turbine have not been used so much before in these conditions so there might be lack of spare parts and knowledge of servicing turbines.

Micro and pico hydro power were discussed very briefly on the lecture.

The last topic on the lecture was applying of wind and solar power in water pumping. In many places in developing countries there is water shortage. The only way to get fresh water may be to pump it from deep underground. Traditionally human and animal power has been used for this but today solar and wind energy can be also utilized.