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Wednesday, November 3, 2010

Solar + Hydro power: winning combination?

In the realm of micro generation (residential buildings, small towns, isolated houses or cabins) you may have heard about the winning idea of combining solar power generation with hydro-electric generation.

Why is this?

It has to do with the intermittent behavior of almost all the renewable energy sources: wind, solar, waves, hydro. Unfortunately the availability of these sources of energy depends on things that are outside of human control, and in particular on the weather and on the season of the year.

There are different ways to deal with this issue.

At the moment, generation from renewable sources is a very little portion of the whole energy production (most of the energy we use come from oil, natural gas, and nuclear). Therefore it is possible to safely ignore the intermittent behavior of renewables, because there will always be thermal power plants ready to backup in case of necessity.

However, if the production from renewable sources increases, this approach is not possible any more. We therefore have to shape our energy demand according to the availability (for example via real time pricing) and, more important, we have to differentiate among different energy sources.
This way, when for example it is cloudy and windy, and solar panels are not working at their full capacity, we can exploit the wind with a turbine and compensate for it.
Solar and hydro power seem to be a winning couple because of their seasonal behavior. In summer the sun shines high in the sky and days are longer, and therefore solar panels work well and compensate for the little water that streams in the rivers. In winter solar panels are almost useless, but water streams increase their volume and hydro power is an effective choice.

Of course, this compensates only for seasonal variations. For hourly or daily variations, you need storage devices like batteries.

However, for larger hydroelectric plants, there is also another option. You can pump the water upwards, above a dam, and store the extra energy coming from the solar panels (or wind) as potential energy. Then you will use this stored water to produce energy when needed. Efficiency is not extremely high, but it is still very effective to enable a more efficient usage of the electrical power coming from intermittent sources like the sun and the wind.