Very new to the Green Power life - Lithium Ion

[Nick Chan]

Hi all,

I am a new member, and recently bought a property that requires my wife and my to maintain a PV and wind system. The current system uses a LA battery setup that obviously requires regular maintenance. I've been trying to search for systems that have switched to Lithium Ion. Are these ready from a practical and cost perspective? As well, do companies out there install them? I have read some articles stating that they have a higher upfront cost, but much better discharge cycles (I think I'm saying that right).

Any help would be very much appreciated. Happy to look at links as well.

Cheers,

Nick

[Rob Beckers]

Hi Nick,

First, welcome to the forum!
I've been pondering the same question as you lately, though from a somewhat different perspective. We supply off-grid items (panels, inverters, batteries and such) to quite a few customers these days, and I am wondering if we should add lithium-ion batteries to the lineup (i.e. haul them in from China).

I'm talking about lithium-iron-phosphate (LiFePO4) prismatic cells. Those are different from what's in your laptop, which is lithium-cobalt. Lithium-iron is much less temperamental, no spontaneous combustion and such. The downside is that it store less energy.

The tough part is getting reliable data on long-term performance of these batteries: Supposedly they have several thousand charge cycles at 100% DOD, and live semi-indefinitely if you don't go below 80% DOD (with regular lead-acid batteries you shouldn't go above 50% DOD on a regular basis, with the occasional 80% as the absolute maximum if you want any longevity).

Lithium-ion batteries also need a charge management system that monitors voltage for every cell, and makes sure they get charged evenly. Adding cost and electronics.

To compare prices:

A mid-range Surrette S-530 goes for about US$420 (street price). Those are about 500Ah @ 72h, and they are 6V cells. If treated well, with a bank sized to normally not go beyond 50% DOD, about 10 years of life can be had out of them.

For the initial cost, that means 500 * 6 = 3000 Wh * 50% = 1500; $420 / 1500 Wh = $0.28 per Wh

For long-term cost, let's see how much energy we can get out of the battery over its life. Rolls/Surrette states that one can expect 1280 cycles at 50% DOD. Each cycle is 1500 Wh, so that makes 1280 * 1500 = 1920 kWh. The cost per kWh comes then to $420 / 1920 = $0.22 per kWh

(As an aside, the above should give those getting their electricity from the grid an idea of just how expensive it is to make your own electricity! That 22 ct/kWh just for batteries! Then there's PV modules, inverters, charge controllers etc.).

Moving on to Thunder-Sky's 400Ah LiFePO4 battery type LFP400. Street price (what I can find) is US$1,800. Capacity is 400Ah @ 3.2V. Thunder-Sky lists "greater than 3000 cycle life for 80% DOD".

For the initial cost that works out to 400 * 3.2 = 1280 * 80% = 1024Wh; $1800 / 1024Wh = $1.76 per Wh

The long-term cost, assuming 3000 cycles works out to: 3000 * 1024Wh = 3072 kWh. Cost per kWh is $1800 / 3072 = $0.59 per kWh

Those prices for Li-ion don't include a battery management system, so actual cost may be a bit higher.

In short, barring mistakes in math (of which there may well be many!), it looks like Li-ion is about 3x as expensive to run vs. plain old flooded lead-acid.

Of course, feel free to poke holes in my calculations. That's what the forum is for. If anyone can make a better case for lithium-ion I'm all ears!

-RoB-