Monthly Archives: July 2013

OXIS Energy to scale up production of Li-S batteries in 2014

OXIS Energy is planning on commercial production of their Lithium Sulfur batteries in 2014. The cells are expected to be around 200Wh/kg (low for Li-S but its still early) and achieve a little more than 1500 cycles to 80% capacity. They have been tested to be very safe (a nail puncture test resulted in a 1.4C rise in temperature and no expansion or pouch rupture).

These batteries are suited well for EVs and marginally for EREVs.

For EVs, the energy density is about double of what was in first generation EVs (Nissan Leaf). This means that replacing the pack with the new cells would provide almost double the range, from 75 miles to 130-150 miles. The cycle life of 1,500 cycles would provide for about 195,000-200,000 miles to 80% capacity (a nominal range of 104-120 miles). This would be a big boost for EVs.

For EREVs, the weight and size of the pack could be reduced by 1/2 over the 2010 baseline with the same electric range, or by 1/3 to achieve a 25-30% range increase. For something like the Volt, this would mean a return of the 5th seat and a boost in electric range from 38 miles to about 45 miles in a 19kWh pack using 13kWh of energy. Because cycle life is non-linear in Lithium batteries (well, it is for Li-Ion, I’m assuming that it is also that way for Li-S), by using only 70% of the battery we extend the cycle life by almost 60%, increasing the cycle life from 1500 to 2400 to 80%, which would be good for 108,000 electric miles – just barely exceeding the 8-year, 100,000 mile warranty supplied by auto manufacturers on EREVs and EVs (notwithstanding any gas-powered miles that also count under the warranty). This just-clearing-the-hurdle approach however doesn’t leave a lot of margin for environmental factors (heat, cold) and time-based degradation of the cells. Cycle life would need to be extended more (from 1500 to 2000 cycles), or cell energy density would need to be improved (more miles per battery cycle) to remedy this.

Ultimately, the biggest issue facing OXIS Energy isn’t the performance of the cell in 2014, rather what is promised by other companies for 2015 and 2016 – 300 and 400Wh/kg energy densities that will revolutionize EVs. If they can keep their Li-S chemistry competitive (and outrun Li-Ion in the mid- and long-term race), or if their competitors fail to deliver on their promises, they will be successful.

Grid Storage set for prime time?

Its been a long while since I published anything renewable energy related – I had become burnt out by extravagant promises and the green bubble bursting in 2010. But things are starting to look up – solar leasing is a huge success, more and more projects are being built using renewable energy, and even thrifty casinos are getting in on the game.

So what happens when we start to scale up to even more renewable energy generation? The intermittent nature of renewables both in the immediate (sun goes behind a cloud) and daily dispatch (sun goes down at night) requires that there be some sort of grid stabilization and storage capacity.

A slide deck from EOS Energy Storage shows off their energy storage product – a 6MWh, 1MW capacity grid-scale battery storage system. The most impressive piece here isn’t the technology or scale, its the price they’re promising. Now I don’t know if that’s their off-the-line price when they start to ship in volume down the road, or the price they are debuting in 2014 when they start to ship their product for its first field deployment, but its a very compelling price for grid storage.

However I’m not entirely ready to jump on board yet, especially with the 2014 release date since they released a slide deck about a year earlier, where they said that they would ship product in 2013 (and they haven’t). They have acquired a customer since then, which is a promising sign.


Their quote price of $160/kWh and $1000/kW and promise of 10,000 cycles and 75% round-trip efficiency translates to a cost of 2.1 cents per kWh – which is more than the typical spread between off- and on-peak wholesale (spot market) prices along the west coast, which is around 1 to 1.5 cents per kWh. However, a net cost increase of half a cent per kWh to be able to include more renewable energy into the grid is a rather small price to pay. As solar and wind prices continue to decline, renewable energy will become more of a player, and storage and buffering of that power source will be needed. It wont take much storage – maybe 3-5% of total plant capacity (250MW solar would need 7.5MW of generation from battery storage) to smooth out bumps in the grid, and around 20% (50MW) to be able to store power for after-hours usage.

Where and How to install public EV charging stations

I’ve been bitten by some poorly placed EV charging stations, so I thought I would write this up…

1. Are the charging stations located somewhere where they will be used?

In other words, are people going to keep their car there for sufficient periods of time to have a meaningful charge. The amount of time someone will spend with their car in the parking spot must match the amount of time to get a useful charge from the charging station. Installing an “slow-charge” 240V 3.3/6.6kW EV station at a fast-service place (e.g. McDonald’s) makes little sense – you’re better off installing a fast-charge station for a fast-service place (DC fast charging – although not many cars will support this anytime soon, and stations are relatively expensive). A 20-minute DC fast-charge can replenish up to 100 miles of range.

At places like movie theaters, shopping malls, etc. it makes more sense to install the 240V chargers – patrons will be there for 2-4 hours using the facilities. This translates to anywhere from 20-50 miles of charge, depending on how quickly the car can charge.

2. Do you plan on charging a fee for the charging stations? If so, can you set a reasonable price or is it too much of a headache? 

For most 240V charging stations, the amount of electricity doled out is about $1 per session. How do you monetize this small of a transaction profitably? Can you do it at all, or is it better to just give it away for free? Charging on a per-session level is difficult because the amount of time people charge and the amount of electricity they will draw will vary from person to person. Charging on a per kWh basis is problematic because it doesn’t scale well the longer you charge. Charging on a time-basis means that people who can only charge a 3.3kW pay twice as much for the same amount of electricity as compared to charging at 6.6kW.

An alternate system would have a both session and kWh cost – 50c per session, plus 1.5x the cost of a kWh. So in my area, that would be 50c per session plus 18c kWh. A full charge would cost me $2.48 (11kWh for the Volt) for roughly $1.20 of electricity. Its still cheaper than a gallon of gas (which is what people will compare it to) and would take me about 35 miles. This also would cause cars with smaller batteries (Plug-in Prius, Ford Energi series models) to stay away and leave the spots open for pure EVs and longer range plug-in cars.

One of the best options is the traditional all-you-can-eat style flat rate plan. This would allow unlimited charging at your EV charging stations for users. This works best at a place like a parking garage or gym membership where it can be added on to another annual charge, reducing per-transaction costs. The charge for this will vary depending on the expected usage pattern (charging every night vs. a few times a week at a gym or occasional use).

Finally, there is always the free option – the one-time cost of construction, plus a small amount of money each month (in the neighborhood of $100 per charger) considered the cost of attracting customers, a marketing expense. The free plan also might be required – if your state has stringent rules about who can offer electricity for retail sale, you might have no other option but to give it away for free.

3. Are they public or behind a valet or in a private lot?

A charging station in a public lot might be ICE’d (occupied by a non-EV). But behind a valet or in a private lot, its easier to keep them free for EVs. At places like hotels, you will want to put some charging stations behind a valet, so that they can manage the car charging (e.g. when a car is full, have the valet move it to a regular spot and then bring in the next EV to charge).

4. What is the EV sales in the area? Are they common or uncommon? What outside conditions (state rebates, climate) affect purchasing an EV? 

Installing a charging network in a region or locale where EV cars are uncommon may not be a good idea. Check the utilization of current facilities before adding more.

5. Are you planning on expanding this charging infrastructure in the future? 

If you want to have just more than one or two token charging stations, it may help to install the electrical and underground infrastructure in one go – things like circuit breakers, transformers, conduit, etc, should be sized to handle your future expansion plans when EVs become more common. You wont need to have every spot in your parking lot charger-accessible, but build out for 5-10% of all parking spots having a charger, at 6.6kW for each car.

You may want to consider designs that allow for four cars to share two charging posts, this will reduce infrastructure costs and allow more flexibility for cars who want finish their charge and unplug but don’t have to move their car immediately.

6. Can you cost-share with others that share the parking lot or neighborhood? 

In the early stages of EV adoption, it may help to have multiple companies advertise that they have EV charging stations available for use. This may increase utilization initially and bring down initial costs.