Grid-tied solar could have a siginificant role in the smart grid--if we can get the lithium ion battery technology right.

People living off the grid using photovoltaics (PV) or other renewable energy to generate power typically depend on maintaining banks of lead-acid batteries and carefully managing the amount of energy they store and use as well as maintaining those batteries for long-term durability.

As the move toward renewable energy gains traction, especially in Europe, an intriguing possibility is beginning to take hold: the use of next-generation batteries in grid-connected systems to store and manage energy capacity.

Time-shifting for peak demand

In current grid-tied PV, any excess energy produced by a home or business PV array is sent back to the grid. This works well because demand for electricity is high during the sunniest part of the day, but it also has limitations since peak demand can occur in the early evening and so does not coincide with PV power generation.

Storing this power generated at mid-day would allow the power to be accessed, or "time shifted," for use later in the evening. A joint pilot project between the U.S. Department of Energy and the Sacramento Municipal Utility District (SMUD) is attempting just such a project, and at the heart of the system are lithium-ion batteries.

Bursting the lead balloon

Lead-acid batteries were invented in the mid-19th century, and flooded deep-cycle versions necessary for power storage continue to be the workhorses of off-grid PV installations. They are inexpensive and have established, reliable performance, but the mining, transport, and use of lead have significant environmental drawbacks. And lead-acid batteries have to be maintained and used in well-ventilated areas because they produce explosive hydrogen gas.

Lithium ion batteries use lithium salts and organic solvents rather than lead and acid to generate the electric charge. We have all used the consumer version of lithium ion batteries in laptop computers, cell phones, and even electric cars like the Tesla. These are the batteries we use when we need a long service life and better performance than alkaline or nickel cadmium can provide.

Deep-cycle versions are sealed and do not generate explosive gases; they're also lighter than lead (what isn't?), almost maintenance free, and companies estimate a 20-year lifespan (though the technology for PV applications is still new). On the down side, they require rare earth minerals, you have to have additional electronics to run them safely, and they are at least three times the cost of lead-acid.

GreenSpec shows the best of both battery worlds

But the advanced design and performance might just be worth it when it comes to grid-tied applications such as those run by SMUD, and the cost of these batteries should drop as demand increases and technology advances. GreenSpec lists a number of the best lead-acid and lithium-ion batteries.

One of the manufacturers we list has been making lithium iron magnesium phosphate batteries since 2002 and offering them for renewable energy systems since 2006. Another company's lithium-ion batteries are RoHS-compliant and can be equipped with energy management controls and designed for specific energy demands and uses, including 12-, 24-, and 48-volt options.

Though lithium ion battery technology is not new, its use in renewable energy storage is. If you are trying to avoid toxic lead, need a sealed system because of ventilation concerns, and are willing to pay the price, these are worth a look. Yes, it will take years for the performance and cost to balance out for most consumers, but if these prove successful in smart-grid applications, utilities might find subsidizing use of these batteries is less expensive than building additional power plants.