Hydropower vs solar – a quick investigation
Alex Andriatis 29-07-2021
Summary
Hydro less carbon than solar. Hydro much more land than solar. But hydro = freshwater and irrigation.
Intro
The hypothesis is that hydropower is significantly more damaging than solar power. Because hydro can provide reliable baseload power vs intermittent solar, the solar figures really need to be combined with battery storage. Turns out batteries are pretty much negligible, with a cost of 0.03 gCO2/kWh, as seen below. Batteries are omitted from the rest of the discussion.
Carbon Cost
Hydro – 24 gCO2/kWh
Solar – 48 gCO2/kWh
Batteries – 72.9 gCO2/kWh of capacity.
https://www.mdpi.com/2313-0105/5/2/48
A solar-only grid needs three days of battery backup. Let’s say we have a large 100 MW solar plant. Three days of production would be 7.2 GWh. A 7.2 GWh battery would have a carbon cost of 525 tCO2. A typical service life for a battery is 20 years, during which time the solar plant will have produced 17,532 GWh. Dividing the carbon cost gives 0.03 tCO2/GWh = 0.03 gCO2/kWh. Turns out batteries are pretty much negligible somehow.
Land Use
Hydro - 25,000 m^2/GWh.
There aren’t good references for this number, and it varies wildly based on geography. Mountainous regions require far less reservoir space than flat areas.
Solar – 402 m^2/GWh
Discussion
While hydroelectric power is about half as carbon intensive as solar, it requires 1-2 orders of magnitude more land. The land used in solar power can be chosen to be open desert, farmland, or rooftops, resulting in a small impact on existing people and ecosystems. By contrast hydroelectric land use is by necessity along rivers, that support either very important ecosystems or are existing homes to human populations. Hydroelectric land use is, from this point, much more ecologically damaging. The cobenefits, however, of hydroelectricity are much greater. Damming rivers provides 1) freshwater reservoirs for human consumption and irrigation and 2) predictable water flow, increasing land area downstream by preventing floods, allowing it to be used for human settlement and agriculture. I would venture to make the argument that most hydroelectric reservoirs in the world would have been built regardless of their power generation ability because of these cobenefits – rivers are very important for human life and making them predictable and controllable has been a major source of growth in the 20th century. The cobenefits of utility solar are none, while rooftop solar, especially in cities, has the negative impact of decreasing albedo and taking space that could otherwise be used for rooftop greenery.