By Anders Arvesen, industrial ecology researcher and (occasional) blogger

Benefits of variable renewables outweigh costs

By on 8. February 2016 in Ukategorisert with 3 Comments

Replacing fossil fuel power with variable wind and solar power means that more energy storage and power transmission capabilities are necessary. Despite this, we find large climate benefits and a range of other pollution benefits of switching to renewables.

Solar Panel

The variability of wind and solar power makes their large-scale integration into power systems challenging. The wind does not blow on demand. The sun does not always shine. Still, power demand must be met at all times and for all locations. Our new study, lead-authored by one of our Master’s students last year, Peter Berrill, assesses the environmental impacts of high penetration renewable energy scenarios for Europe. By bringing together life cycle assessment (LCA) and power grid modelling, the study is able to capture both life cycle effects and variability issues in one single analysis.

While increased needs to store energy and to transfer electricity over large distances cause additional impacts in systems dominated by renewables, these impacts are small in comparison to the benefits of deploying renewables.

Former estimates present an incomplete picture

Results of LCAs are frequently used to compare the environmental performance of electricity generation options. One example is this graphic from the IPCC, juxtaposing life cycle emission estimates for different power generation options. However, these estimates do not consider impacts associated with accommodating large shares of variable supply in electricity networks.

Considering both life cycle effects and variability issues in one coherent assessment involves a substantial methods and data challenge. The basic reason for this is that impacts occurring as a result of variability is a property of whole systems, not of individual technologies.

How so? Well, we know that the wind does not always blow. This constitutes a challenge, because customer demand for electricity must always be satisfied. Now, we can deal with the challenge in a number of ways. We can expand transmission grids, to exploit the fact that the wind (almost) always blows somewhere. We can combine wind and solar deployment to reduce overall fluctuations. We can invest in energy storage, such as batteries or pumped hydro. We can invest in surplus capacity of flexible natural gas power, ready to be used when needed. Or – as will be the case in the real world – we can combine these measures in one way or another. Then, the impacts that arise as a result of variability depend on how all technologies are combined. The impacts cannot be determined by considering any single technology in isolation.

Our attempt to get a fuller picture

In order to capture both life cycle effects and variability effects, you need both a power system model capable of simulating the operation of entire power systems, and an LCA model capable of estimating life cycle impacts of different power system layouts, and to combine the two in a sound manner.

Our study does exactly this. First, 44 scenarios describing power system configurations for Europe in 2050 were generated by a power system optimization model, REMix, operated by DLR in Germany. Next, the scenarios were examined using NTNU’s prospective LCA modelling framework, THEMIS. This combination allows us to present the first LCA of entire electricity systems while taking into account the effects of variability on storage and transmission requirements, and losses.

Findings: Large climate benefits

Wind turbines in Copenhagen. Photo: NTNU/Maren Agdestein

Wind turbines in Copenhagen. Photo: NTNU/Maren Agdestein

The findings indicate large climate benefits and a range of other emissions reduction benefits of switching to renewables. Adopting variable renewables on a large scale does lead to additional storage and transmission capacity requirements – and hence additional environmental impacts – but these are not large enough to significantly undermine the benefits of renewable power displacing fossil fuel-based power.

Another finding is that solar photovoltaic (PV) power tends to induce larger impacts than wind power, for two main reasons. First, the supply chains of solar power plants generally involve more emissions-intensive material processing and manufacturing activities than that of wind power plants. Second, as wind power plants on average operate closer to their full capacity, systems dominated by wind power show lower needs for storage than solar-dominated systems.

Our findings can help to alleviate fears that large-scale adoptions of variable renewable energy will cause large unintended emissions. At the same time, it is worthwhile to keep in mind that simplifications and assumptions were necessary, and this contributed to uncertainty. Some of the simplifications and assumptions may be replaced by more sophisticated modelling or better data in the future.

The study is reported in Environmental Research Letters.

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  1. paul hofseth says:

    Most interesting and thorough, with the proper caveats in place.

    Since conclusions ad backup and storage may depend more on power profiles than on anuual energy availability, there are three issues that are potentially covered, but not entirely clear in the text. They may of course be covered in detail in the references:

    – It is stated that connections between countries are included:

    * Is the trans-Europe HV grid assumed to be dimensioned so as to transmit the full power generated by the moving wind fields and changing insolation to the load centres, or is just country-to-country transmission considered ? (High windspeeds in Portugal may be seamlessly followed by peaks in France or Switzerland giving a roughly constant contribution, and high-pressure over Italy and max solar there, may well be immediately followed by max solar in Greece or Germany).

    – It is stated that the potential for additional load-shifting is not considered. That of course will be a major task in itself. It would, however be useful if it was emphasized how the trans continental interaction between weather patterns and your projected business-as usual- load patterns for the continent is summed in the current model.

    * When considering existing and projected load patterns does the study examine the correlation between seasonal and daily solar input and projected cooling and ventilation loads and the corresponding correlation between wind speeds and heating loads in winter (including the levelling effect of district-heating hot water storage -if CHPplants and spinning reserves and not just peaking gas turbines are envisaged)?

    * When considering the trans-continental grid (assuming that such a grid is included so as to capture the effects of moving wind-fields), is the evening-out effect of existing and projected differences in peak-load timing resulting from different trans-continental timezones, work patterns and habits accounted for? (The power profiles and time-zone issues become particularly relevant for the eastwards expansion you mention as a future option).

    paul hofseth

    • Thank you for your comment and questions. Your questions are quite detailed concerning the power system optimization model, REMix, used for the study. I should say that the REMix model is owned and operated by DLR in Germany. I have not worked with REMix and I am not an expert in power system modelling. For the study discussed in the blog post, we collaborated with DLR in Germany, and the study has two co-authors from DLR. To my understanding, REMix works with region-specific hourly load profiles and hourly renewable energy generation profiles. To my understanding flexibility offered by CHP are addressed by the model, and the “evening-out effects” that you refer to should be captured. For more detailed information about REMix, I will need to refer to the documentation of REMix (references provided in the paper).

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