Key concepts for reliable, small-scale low-carbon energy grids

Recently, I published a guest post by Gene Preston on BNC, which examined the electricity cost comparison for remote solar PV vs small nuclear reactors. This generated considerable discussion (128 comments), much of which focused on whether this was a useful comparison in many circumstances; what if, for various reasons, the small-scale nuclear battery is not a viable option?

Gene has since done further work to consider the problem of how to design a reliable, small-scale, low-carbon energy generation system, which is economically competitive (though not necessarily lowest cost). He uses a case study approach to consider five crucial aspects:

1. System 1: A rooftop solar and wind 100% renewables powered microgrid concept.

2. System 2: Like (1), but the 10 kW rooftop solar is replaced with 5 kW of centralized solar.

3. Analysis 1: Three ways to improve the reliability of a (nearly) 100% renewables system.

4. Analysis 2: The cost of CCS carbon capture and sequestration makes coal power uneconomical.

5. Analysis 3: Small nuclear power provides reliability without needing a new transmission grid.

First, here is a summary of the five cases. Following this overview, the case studies are given in full (for the more dedicated reader — which is probably most BNC readers!). I find these type of empirical studies incredibly useful in understanding the options available to us. Great work Gene.

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In all the cases the microgrid has 150 homes. This number of houses was selected to best match the output of a 1.5 MW wind generator. Of course the size of the system could be scaled to any number of houses. The intent is to design each system to be as independent of the larger grid as possible. Each house has two PHEVs with 50 kWh batteries for a range of 100 miles of city driving for each fully charged vehicle. Each home is assumed to annually use about 12500 kWh plus another 12500 kWh for the PHEVs for a total of 25000 kWh per home annually. The PHEVs are assumed to be bi-directional power sources, being able to both receive power from the microgrid and deliver power to the microgrid in all cases. The microgrid consists of an undergound distribution system connecting the houses as well as the power sources local to the microgrid. All the costs for the distribution system, metering, etc that are the same for each of the above cases are not included in these calculations. The purpose of this analysis is to simply compare the cost and reliability of different types of power sources.

Here are the findings:

Case 1 has 10 kW of rooftop solar fixed panels at each house and a 1.5 MW wind generator for the whole neighborhood. The up front cost of the solar and wind per household is $90,000. This system will suffer occasional power deficiencies if operated as a standalone system. The interconnection costs for backup power from a larger grid were not estimated.

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