There are two distinctly different reasons for wanting to store energy: to provide backup or to match the energy supply with the demand. For the former you can use batteries but for the latter application you can use much less expensive approaches like exergy storage, which uses electricity for its input but delivers demand reduction for its output. Both approaches deliver the same results if you are struggling to match supply and demand on a power grid. It would be useful if articles on electricity storage kept these differing objectives separate.
Three of the four 'building blocks' are counter-productive:
1) Make fossil fuel plants more efficient
2) Dispatch low-emissions sources, namely natural gas, more often
4) Expand use of energy efficiency
They propose that we should continue to rely on the use of fossil fuels instead of replacing such fuels with alternatives that do not produce GHG's. The EPA is proposing that we should protract the fossil fuel era, which is the opposite of what we really need to do - replace such fuels with the abundantly available non-GHG-emitting alternatives.
REW is doing us all a disservice by referring to carbon as the culprit. Carbon is not poisonous and it is not a greenhouse gas. We certainly DO need to stop polluting the atmosphere by burning coal but curbing pollution and curbing GHG's are separate issues so REW should take care to treat them separately.
The same goals can be met if you employ energy storage in general instead of assuming the use of battery storage. We use energy in two forms: electricity and thermal, and in most places the thermal form dominates. Moreover, it is the thermal demand that fluctuates the most from season to season. If you store the thermal energy in thermal form then you do not need to keep converting the energy back and forth between the two forms, which entails losses. While you might still want to use batteries for the part of the energy that is used in electrical form the size of the batteries can be reduced by a couple of orders of magnitude so they are more cost effective. The fluctuations in the electrical component are short term (daily) variations rather than long term (seasonal) variations so the required storage capacity is small.
The rate of solar insolation in the UK is less than 120 W/sq. m and the country is legendary for its long gaps between sunny periods. That does not imply that solar energy is useless in the UK but it does suggest that its role should be niche applications that take advantage of the potential to store solar thermal energy.
Neil: I assume that you have dropped a few zeroes in citing 4 kWh/year as your output. A solar thermal collector (with storage) for a house would be only one quarter the size of a PV collector and in spite of that small size the storage system would deliver about five times as much energy. Most of that energy would be extracted from the air, but air-source systems have difficulty delivering the temperature that is needed for DHW and in handling peak demands. The solar input fixes both problems. Homes that use such systems burn no fuels at all and they reduce the peak demands for electricity. A given reduction in peak demand is more useful than the equivalent amount of power generation because it does not have to be transmitted.
Solar thermal collectors are five times more efficient than solar PV collectors and heat storage is about 1000 times cheaper than batteries. Used together they can shift the power demand from daytime to the night, and in the north from winter to summer (see exergy storage). The reduction in peak power demands is just as useful to a power grid as the generation of the same amount of electricity, especially as it also reduces the need for power distribution.
Stored heat does not have to be converted back into electricity. The primary energy needs for most buildings are thermal, not electric (for heating, cooling and hot water). An exergy store can provide heat at 60 degrees C (for hot water), 40 degrees (a viable temperature for space heating) and 4 degrees for cooling, all without needing any power at the time of extraction. The resulting reduction in power demand during the peak demand periods is more useful than the equivalent amount of power generation. Exergy storage systems both meet the needs for thermal energy and also shift the time of their power demand from the peak demand periods to times when there is ample power. From the point of view of the grid operator they act like giant batteries.
At the present time there are 40 million square feet of building space in Toronto that are cooled by cold that is extracted from the winter air, stored at 4 degrees C, and is then used to air condition the buildings without needing heat pumps. That means they are not taking up space, they are not adding to the costs, and they are not using power.
Many millions of dollars are currently being spent on supply-side storage, such as batteries. It would be about 1000 times cheaper to use consumer-side storage for that task and consumer-side storage like exergy stores can also deliver most of the energy the buildings need. That has a down side - the power generators and distributors expect the building owners to pay for the stores, which would leave the building owners with all of the expense while the generators reap most of the economic benefits.
In considering energy storage it is essential to consider both of the forms in which we use energy for buildings - electricity and thermal. Thermal energy includes heat for space heating, cold for cooling, and DHW. The two forms of energy are highly interactive - we use electricity for both cooling and heating, for example - so if we store either heat or cold we can reduce our consumption of electricity.
In considering electricity storage it is common practice to assume that stored electricity must be returned as electricity. It is often more practical to return the accumulated electricity in the form of demand reduction. Reducing the demands on the grid accomplishes the same end as returning electricity to the grid, with the added advantage that the costs and losses associated with power transmission are avoided.
The articles on storage that REW has been publishing on the subject of energy storage have mostly failed to take either of these basic factors into consideration.
The EPA uses a Global Warming Potential (GWP) of 21. The latest IPCC value for the GWP of methane is 72 (20 year). The implication is that natural gas is NOT better than coal in terms of its GHG emissions even if you use the EPA's questionable low estimates for fugitive methane. As the author observes, we should not be using either coal or natural gas. There are better alternatives.
In Alberta solar thermal collectors are more cost effective than solar PV systems. The reason stems from the need to supply a lot of heat in cities that have very cold winters. Solar heat plus heat extracted from the summer air and stored in the ground can meet that need for heat (plus the need for cooling and DHW). That could eliminate the dependence on fossil fuels for heating and it also reduces the consumption of electricity since about one third of the present power consumption is used for thermal applications. The potential for power demand reduction is considerably greater than the potential for generation via PV systems, and the collectors are smaller as well. See http://kanata-forum.ca/kegs.pdf