Journey of evolution17 February 2023
Terry Stebbings from Proterra Energy gives an overview of a combined small hydro and solar scheme the company recently worked on in Knoydart, Scotland. He says that in an ever-changing climatic world, Proterra Energy has come to understand the importance of hybrid systems and their potential to provide power
It is surprising to note how many locations in Scotland, a developed country, are not connected to the power grid network. As of this year we have built over 15 off grid power systems, most with hydro at their heart.
Despite our allegiance to, and fondness for, hydro we have come to understand the importance of hybrid systems and their potential to provide power in an ever-changing climatic world. In some ways this small-scale power generation model is symptomatic of much that will be required for national and worldwide generation in years to come.
One scheme on an estate in Knoydart on the far west coast of Scotland is a great example. It comprises five housing properties, one large lodge, a farm and a small campsite was. Originally powered by a total of five diesel generators using 1750- 2000l of diesel per month, we installed a new power grid, battery storage and crossflow hydro in 2019, massively reducing their requirement for diesel.
36kW Crossflow Turbine, installed 2019
However, with a warm and dry summer and the hydro scheme operating on a river with environmentally sensitive areas restricting water abstraction, the backup generator was often called upon. Working within the client’s objectives for the estate of the re-generation of rare natural Scottish Pine variants and bringing people back to work on the land, we were tasked with reducing the use of fossil fuels even further and finding ways of improving the use of hydropower when it was available in the wetter months.
We added 16kW of ground mounted solar in the summer of 2021 and this had a massive effect of reducing generator run hours in the spring and summer months. This year the generator ran for three hours between March and July, a testament to the effectiveness of the hybrid renewable system. Whilst the hydro does the majority of the heavy lifting, power wise, the solar adds a valuable contribution in those months when the hydro is limited.
To make the most of the hydro power we extended the electrical system, from just providing electricity to the nine properties, to providing a significant proportion of the heating requirement too. Two large thermal stores form a “storage” extension to the 75kWhr battery bank. These use 8 x 6kW immersion to sequentially divert power when the batteries are full. One provides heating to the lodge and the other to two staff properties and a third property used by guests.
The battery storage to the left, the solar inverters straight ahead and the edge of the thermal store. Hybrid generation and hybrid storage.
This journey of evolution would not be possible without an open-minded client with a desire to demonstrate what is achievable. It serves as a great example of how not only different renewable energy systems can be harnessed to work together but different storage systems too.
The systems were installed in an environmentally sensitive area including a Wildland Designation, Sites of Special Scientific Interest and a National Scenic area, but by working closely with the Environmental Protection Agency and the Natural Heritage bodies it was possible to find a way to carry out the installations in a way that met everyone’s objectives.
This was an example of an often-rare occasion where compromises were made by all sides, delivered by people who had a pragmatic approach and an understanding of the wider picture. This is something we are going to have to work harder on as we as a nation, country and world, move forward with more projects of this nature.
Increasingly we must appreciate that one single solution will not provide the answer. Hydro is great but works better with solar. Energy storage amplifies the capability of renewable systems, but energy doesn’t have to be electricity. We must try to preserve the environment but that doesn’t preclude us sensibly using its resources to help us achieve our aim.