FIGURE 9.A.4 Energy storage options.

Note: CAES = compressed-air energy storage; Caps = capacitor; Li-ion = lithium ion; NaS = sodium sulfur; NiCd = nickel-cadmium battery; NiMH = nickel metal hydride battery; PSB = polysulfide bromide battery; SMES = superconducting magnetic energy storage; UPS = uninterruptible power supplies; VRB = vanadium redox battery; ZnBr = zinc bromide.

Source: Adapted from a presentation by Dan Rastler, Electric Power Research Institute, to the Panel on Electricity from Renewable Resources, March 11, 2008.

setting standards for transformer efficiency can be important in lowering the T&D losses.

The last transformer in the chain is the distribution transformer for residential/small commercial customers, which incurs about 1–2 percent losses. These devices experience about 0.2–0.5 percent constant core losses (in the magnetic material) and load losses that vary according to the load. Core losses are important because they occur all the time, whether the transformer is fully or lightly loaded; the installed capacity of distribution transformers may be two times the total load, causing core losses to add up to a significant and continuous amount.

Grain-oriented steel has generally been used as the core material, though there has been sustained but slow progress both toward improving it and developing alternatives. Transformers with amorphous steel, which have been commercially available in limited quantities for better than 10 years now, have about one-