Getting rid of US hydro- replacing it with solar

An intriguing  US study  looks to looks to getting rid of hydro dams, and at compensatory ‘solar-power replacement as a solution for hydropower foregone in US dam removals’. It notes that ‘there is a growing dam removal movement in the United States, driven in part by environmental, safety and cost considerations. These include electricity-producing hydro-dams, many of which are ageing and will require substantial maintenance or removal over the coming decades’.  And it looks to solar PV to replace the lost power.  

According to Dr John Waldman, an aquatic conservation biologist from the City University of New York who led the study, many environmentalists have come to see dams as ‘blood clots in our watersheds’ owing to the ‘tremendous harm’ they have done to ecosystems.  Carbon Brief quotes him as as saying that the ‘poster children’ for this effect are migratory fish, such as salmon and shad, whose numbers have declined by several orders of magnitude in some regions due to their migration paths being blocked. Dams can also lead to declines in local biodiversity, trapped sediments and changes in river temperature as water sitting in reservoirs warms up. They can even become sources of emissions, as flooding great areas of land leads to microbes living in the water pumping out methane and other greenhouse gases.

Not all dams are a problem, but some may be, as another new study concluded, with its lead author commenting : ‘We need to be really careful that new facilities we develop don’t fall into the category that have emissions that lead to climate impacts that are worse than fossil fuels.’ 

Solar to the rescue

The Waldman study is focused more on the existing projects, although he recognizes that hydropower has been and remains an important source of energy in the US, ‘generating about 6% of the nation’s electricity while providing essential grid services’. It says that as a potential solution to the conflict between these imperatives, ‘industrial-scale photovoltaics (PVs) could be used for replacement of the energy foregone from hydro-dam removals either by installing the PV infrastructure in the area formerly inundated by the dam reservoir or through offsite replacement’. It claims that ‘PVs could replace the total annual energy produced from these dams while requiring only 13% of their existing reservoir area. If all the hydro-dams in the United States were removed and only 50% of the emergent land was used for PVs, 945,062 GWh yr power could be generated, which is 3.44 times the current hydropower generation’.

Carbon Brief quotes Waldman’s view that ‘When you drain a reservoir, you get back a lot of land. You have the opportunity to put solar on part of the reservoir bottom, and maybe even floating solar in some places.’ He thinks the potential could be large: ‘Because many reservoirs are in valleys, you might be able to put wind power on the ridge lines and you also have the possibility of capturing some of the power of the water using hydrokinetic or diversionary approaches, which allow you to capture some power but don’t block the river’.

Displacement problems

The study admits that its analysis is theoretical and does not consider costs, which ‘would be highly site specific’. In addition, ‘replacement by PVs without energy storage could not replicate the dispatchability and grid services provisions of existing hydropower facilities’. However, it says ‘improving battery storage capabilities may ameliorate this shortcoming’. That seems a little fanciful for PV, given that battery storage only make sense for relatively short periods. Focused-solar CSP, with linked molten salt heat stores, might do better, although, even then, it would be hard to replicate the large scale grid-balancing and pumped storage options hydro projects offer. Indeed, the US Dept. of Energy’s Hydropower  Vision  report, says the contribution of hydro to grid planning & operations will actually increase in the future: ‘In particular, hydropower’s flexibility to rapidly ramp generation up and down in response to changes in the balance between electrical loads & generators facilitates integration of renewable variable generation, such as wind & solar energy, into the grid.’ £25m has just been allocated to new flexible US hydro projects.

Nevertheless, Carbon Brief quotes Waldman as saying that ‘even though I recognise we are never going to take down all 2,603 dams in the US, and switch to this notion, there is a lot of room to push the idea of doing this in selective circumstances’, e.g. as old hydro projects are retired. He adds  ‘over 1,000 US dams have been dismantled in the past three decades, and scientists have noted marked improvements as a result’. Most of the hydro dams removed have been relatively small, so the power loss issue has not been great. And the new study is not against some new or revamped projects if well designed and located. It says ‘There are opportunities for new hydropower capacity expansion in the United States that could avoid the environmental challenges of the existing fleet, including upgrading and optimizing existing hydropower reservoirs, installing hydropower units in the existing water conveyance infrastructure and increasing pumped storage hydropower’. Nevertheless, the study suggests that, in theory, ‘PVs could replace much of the annual electricity output of hydro-dams in the United States while using substantially less land area and providing considerable environmental & ecological benefits’.

Can and should it be done?

That would be a huge project. Will and should it happen? Will the idea spread around the world?  It seems unlikely…but large hydro certainly has eco-impacts and dam failure problems, as I reported in an earlier post, and it is also facing reduced water available due to climate change. And some Dam removal projects are underway in Europe.

However hydro, large and small, supplies about 16% of global power, with around 1.2 TW installed and more planned. It’s the largest renewable so far- wind and solar combined only just about match its capacity globally at present, and their outputs are variable. Although the scale of any new projects maybe should be reduced, and their role may have to shift more to pumped storage support for variable renewables, replacing the existing hydro input quickly with other renewable sources would be very tricky in many parts of the world. For good or ill, several developing countries rely on hydro for the bulk of their power.

That reliance might be reduced in time, and large hydro might be cut back elsewhere, but, in general, without a hydro input, and the balancing services hydro can offer, even with major commitments to energy saving, it would initially be harder for other renewables to see off fossil fuel- and to avoid nuclear.  Big new hydro projects can perhaps be avoided, and new smaller run of the river projects with out reservoirs promoted, but new pumped storage projects may also be needed, and, as the Waldman study notes, some existing reservoirs are actually a good site for floating PV, reducing PV land use! That may actually give some old hydro projects a new lease of life.  Meantime a recent study suggested that there could be a huge potential for new pumped hydro storage projects around the world.  Hydro doesn’t seem likely to be go away anytime soon.