Is a proposed Tucson Metropolitan microgrid of solar energy feasible and cost effective?

A guest opinion in the Arizona Daily Star (Jan. 23, 3015) by Terry Finefrock proposed that Tucson build a system of photovoltaic solar energy facilities and connected electrical storage units (see article here). Finefrock claims “By using rapidly developing energy storage equipment on feeder circuits we can manage fluctuations in demand or supply, essentially creating a metropolitan microgrid.” He also claims that photovoltaic generation of electricity is less expensive than fossil fuel generation.

I emailed him asking what”rapidly developing energy storage equipment on feeder circuits” was and whether such equipment is at a stage sufficient for commercial deployment. He responded the same day referring me to http://www.greentechmedia.com/. The answer seems to be a whole bunch of batteries.

At the website, I found a story on British pumped hydro storage (not likely to work in Tucson); a story saying “General Electric is significantly scaling back production of its sodium-ion Durathon batteries, a move that comes amid what the company says is a slow-to-develop market for grid-scale energy storage”; and a story on “Faulty Solar Panels Are Creating ‘Uncertain Risk’ for Chinese PV Projects.” I searched the site for the word “storage” and got several more articles about batteries connected to the grid.

I know from other sources that several schemes are in the works. For instance, a solar-thermal plant in Gila Bend proposes to store excess heat in molten salt containers that they claim will provide 12 hours of generation. Tucson Electric Power was also planning a solar-thermal system with heat storage in Tucson. But what happens if it is cloudy two or three days in a row?

The biggest problems with solar and wind electrical generation, other than cost, is their intermittency and unreliability. Solar panels can deliver significant energy only from 9am to 3pm on a clear day – a maximum of 25%of the time. A good storage system for electricity could possibly help extend that time, but much of solar’s peak generation would need to be used for recharging the storage equipment rather than providing for consumer demand.

Typically, solar systems provide less than 25% of their rated capacity whereas fossil fuels provide at least 85% of their rated generating capacity according to the Energy Information Administration (EIA). This is what EIA calls capacity value “which depends on both the existing capacity mix and load characteristics in a region. Since load must be balanced on a continuous basis, units whose output can be varied to follow demand (dispatchable technologies i.e. fossil fuels and nuclear generation) generally have more value to a system than less flexible units (non-dispatchable technologies such as solar and wind), or those whose operation is tied to the availability of an intermittent resource.”

Dr. John Morgan, Adjunct Professor in the School of Electrical and Computer Engineering at RMIT (Australia), claims “energy storage cannot solve the problem of intermittency of wind or solar power. Not for reasons of technical performance, cost, or storage capacity, but for something more intractable: there is not enough surplus energy left over after construction of the generators and the storage system to power our present civilization.” Morgan claims that the energy required to manufacture and operate solar photovoltaic systems and battery storage for electricity is about equal to the energy produced over the life of the facility, so there is little to no net energy produced. (See article here)

In the Star article, Finefrock claims that solar energy is less expensive than coal or natural gas fueled generation, but he seems to ignore manufacturing and capital costs for solar systems and batteries.

The U.S. Energy Information Administration (EIA) takes a different view when comparing energy sources. They use a metric called “Levelized cost of electricity (LCOE)” which “represents the per-kilowatt-hour cost (in real dollars) of building and operating a generating plant over an assumed financial life and duty cycle. Key inputs to calculating LCOE include capital costs, fuel costs, fixed and variable operations and maintenance costs, financing costs, and an assumed utilization rate for each plant type.”

In EIA’s latest report, they estimate LCOE for solar photovoltaic to be 230 $/MWh, and solar thermal at 243 $/MWh versus 96 $/MWh for conventional coal and 66 $/MWh for conventional natural gas.

As to the question in the article title, yes, a microgrid connected storage system is possible, but

given the facts that solar energy is unreliable and expensive; that storage equipment is expensive and could provide a backup for only a limited time; and that a very large number of batteries to make it beyond a few days would take most of the PV output to charge them, it makes little sense to retire fossil-fuel fired plants in favor solar energy as Finefrock suggests.