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Sunday, April 10, 2022

Distributed power generation in urban areas

An interesting article in today's Washington Post newsletter talked about the issues around getting power from wind farms in rural areas to electric car charging stations in urban areas over existing grids. (Click here to see the article). The article mentions a study showing that the US will need to invest $125 billion into the grid by 2030 to meet the need for electric car recharging. 

This got me to thinking about distributed power generation in urban areas. After all, this is where the majority of cars are located today, and where the power will be needed tomorrow. I live in a dense urban neighbourhood characterised by 100-year old row houses with flat roofs, all fronting on narrow streets. The image shows the area as seen by Google Maps.

My house has a surface area of 1100 sq. ft, on a lot 25' by 100'. If I include the total distance from the middle of my street to the middle of the alley in back, I get a total depth of 125'. (Street centrelines are 250' apart.) So 1100 sq. ft., divided by the total urban area attributable to my property (25' x 125'), gives 35% of the urban area taken up by flat roofs when extrapolated to the larger neighbourhood. 

A quick check of the Interweb gives a year-round average solar power generation capacity of about 4 kWh per square metre, per day, for solar panels located along the border between New York state and Quebec. (Click here for the maps.) Assuming this is representative of Montreal, about 100 km north of the border, that works out to an average of 165 Watts per square metre, again on an annual basis -- it will be much lower in winter months, of course. Still, 1100 sq. ft. equals 100 square metres, so this is a year round potential average power generating capacity of 16.5 kW using solar panels with tracking systems to keep them aimed directly at the sun. Regular readers will know I've been tracking my own power use for Hydro Quebec over the last two winters, and I know that my peak power use in a cold snap on turning up the heat immediately after a Hydro-mandated pricing event was never more than 8 kW. Winter average power use this year was closer to 4 or 5 kW, even with a fairly cold January, helped by the fact that as the resident of a ground floor flat surrounded by other buildings, I have very few exposed outside walls. So in theory 100 square metres of solar panels on the roof would provide me with excess capacity, especially in those really cold but bright sunny winter days. 

I extended the analysis to the entire borough, which has a total area of 8.1 square kilometres. I suspect potential usable area of 35% of this is a large number; to start with, there are wider streets as well as parks and other areas where solar panels could not be mounted. But assuming 15% of the borough were covered with panels, the neighbourhood could make, on average, 200 MW. While this is only 0.5% of the 40 GW peaks Hydro hit last winter, it is still requires only 8 square kilometers of urban area, and no need for extended transmission lines. As well it would go a long way towards recharging a local electric vehicle fleet, especially if augmented by storage systems of some kind such as masses of parked electric car batteries all plugged into the grid. (Most cars sit 90% of the time).

I haven't taken the time to go through the economics, but one online source suggested costs of $3 per installed Watt in Ontario. Covering my roof would thus cost close to $50,000, which I wouldn't want to do on my own without serious subsidies; but the neighbourhood could make 200 MW for $600 million. And $3 per W is about 5 times cheaper than Site C in BC ($16B for 1.1 GW), without the need for long-distance transmission lines. 

In Quebec the main issue will be Hydro Quebec's mandate, which does not encourage small-scale or distributed generation unless it is off-grid, but I assume that could be changed by an act of Parliament. But I've met people in Alberta who have put solar panels on the roof of the garage to charge the Tesla; the open-access grid there allows excess power (when the owner of the car is at work on a sunny day, for instance)  to be trickled back into the grid for a credit.

Food for thought.

1 comment:

  1. See a newer article in the same vein here: