Over in South Australia, the power networks are working with Enphase Energy to trial another new distributed energy storage system. Compared to Tesla's Powerwall (and some other existing battery storage), the system promises to be more flexible and has a smart management system -- but at what cost?
The stand out difference is that the Enphase system has opted for a much smaller capacity battery - just 1.2 kWh (vs 7 kWh for the Powerwall). That sounds too small to be much use, but the Enphase batteries can be ganged up together to work as a larger battery.
This actually has an advantage over the Powerwall, where adding in an extra battery is a significant investment that is hard to adjust to a home's individual power draw. Instead of being able to up the capacity bit by bit, you need to add an entire 7 kWh module.
The downside to the modular system is that it will likely always be more expensive to buy 5 or 6 batteries vs 1, to get the same capacity. This could be offset by lower install costs, as each unit is smaller and lighter and can be put into place by one person. It also allows homes to easily upgrade their storage capacity down the track.
Right now Enphase estimates that the system could cost $1150 per kWh, but that does not include installation and is only for volume partners. In comparison, the Powerwall costs around $600 per kWh - based on a $3000 US purchase price, and current exchange rates.
The $1150 per kWh figure is problematic, as (depending where you live) power costs around $0.25 a kWh (though whether this will increase or decrease in the future is hard to know). Assuming a free charging source (solar) and no install costs, it would take almost 13 year of operation just to give the same cost per kWh as buying the power from a utility.
Enphase suggest that two battery cycles are a day is possible, which essentially reaches the break even point in half the time - but how well that works in the real world remains to be seen. Factoring in all the costs and efficiency losses then the system is unlikely to pay for itself in 20 years, yet alone it's 10 year rated battery life.
Of course battery storage technology is about more than just the pure financials for an end customer, so we will be very interested to see the results of the tests. One application could be the power utilities offering the units at a subsided cost, as it could lessen their own operating costs by helping to handle peak loads.
What Enphase is doing is not exactly ground breaking - existing lead acid systems have a similar modular setup. But by combining Lithium Iron Phosphate batteries and some smart tech, Enphase could have a solid system that makes upgrades 'plug and play'.
Enphase also promises a 96% round trip efficiency, compared to the Powerwall's 92%. While the overall system efficiency, as well as battery capacity degradation is just as important, extra efficiency savings can help offset a higher cost.
Of course the true cost and subsequent savings won't be known until there is an actual installed price for the system. We did some preliminary calculations for Powerwall, and pending an exact sale price here in Australia, the numbers don't yet stack up for it either - at least from a purely financial perspective.
The Enphase system also has the Envoy S Wi-Fi connected smart power management system, which will let users monitor and control their power use from an app for best efficiency.
Just like other storage systems, the key points are better load management, especially with solar, as well as offsetting power bills with cheaper stored energy.
South Australia in particular has a lot of solar (25% of homes), but most of that electricity is generated outside of the peak draw time. The result is that the power stations can be throttled back during the day as solar takes over, but it needs to running full bore for the evening surge in power use.
With battery storage, some of that solar power can be saved and used to handle part of the evening peak. This puts less load on the power stations and electricity delivery infrastructure.
Right now the electrical distribution system has to be powerful and robust to ensure it can handle the peak load every day. With a distributed battery system, the peak load can be covered, meaning the power system only needs to cover the average load.
Helping start the shift to distributed energy storage systems is the Powerwall, which will be first available here in Australia.