Q&A: Battery and solar developments

Q: I HAVE read and heard that the next generation solar batteries superseding lithium will be available and ready for market in two years time. That being the case, can you please indicate whether a hybrid solar system currently working on lead-acid batteries can be retrofitted with the upgrade?

Also, are you aware of any developments whereby solar panels can be wirelessly connected to the inverter/batteries i.e. the solar equivalent of wireless internet connectivity on a laptop?

Lastly, are you aware of any double-glazed, aluminium or wood-framed window systems with integrated solar panels, either already available or coming to market? Would ReNew be able to run a feature on this subject at some stage?


A: THERE IS a lot going on in battery development at the moment, but most of it is focused on modifications to lithium chemistries, such as using silicon nano-wires in the electrodes to reduce degradation and improve lifespan and energy density. There are some other chemistries around, such as the Aquion Energy sodium ion battery, as well as rechargeable zinc-air batteries, flow batteries and a few others. However, for the moment the two industry workhorses are lead-acid and lithium chemistry units, in particular lithium iron phosphate (LiFePO4) for larger storage requirements.

The cost of lithium batteries is steadily decreasing and with the commissioning of Tesla’s Gigafactory next year, the price is expected to go below US$150/kWh by 2020, possibly as low as US$100/kWh. So, for the next decade or so, lithium batteries are most likely to be the best bet. All of the other chemistries are really in their infancy as far as development is concerned.

Whether you can upgrade to a newer battery type will depend on the other system components and the proposed battery system. For example, a battery system with similar voltage range during charge/discharge will probably be able to be used, provided that the solar charge controller in the system can meet the charge requirements. Some charge controllers have fully programmable voltage setpoints, so that sort of controller is more likely to be able to handle a new battery chemistry. However, most battery chemistries in development have their own management systems, so they may not need a charge controller at all: the management system will control charge and discharge of the battery.

The other issue will be your inverter and whether it can handle a possibly wider voltage range of a new battery chemistry. Many inverters also have programmable minimum and maximum voltages, so there’s no way to know without knowing your current inverter model and the new proposed battery chemistry.

Wireless data transfer and wireless energy transfer are very different things. Data transfer only takes milliwatts of power, whereas energy transfer for a typical domestic solar power system would need to be in the kilowatts—a million times more power at least. There are prototype energy transfer systems being developed and some have reached the stage where 100 watts or more of usable power can be transmitted over a short distance (inside the same room, for example), but these have relatively low efficiency compared to running cables, as well as much greater cost and complexity. They also require the room to be filled with an alternating magnetic field of considerable strength—something that many people might find disconcerting. So far, all domestic-scale wireless energy transfer devices have been aimed at the gadget market—charging mobile phones and the like.

Regarding solar windows, there have been a number of companies working on these, and we have covered some installations in the past, such as in ReNew 101 where we looked at windows at Ballarat University, Schott Solar’s ASI transparent thin-film panels. However, it appears they no longer make them. Most of the manufacturers that were using their glass modules also seem to have disappeared, except one, although they don’t appear to be using the Schott modules: www.ertex-solar.at/en/products.

Kaneka still make transparent PVs, but in the last PV buyers guide (ReNew 126, just over a year ago), we found no transparent PVs available here.
There are several companies working on new transparent glazing materials, including Oxford Photovoltaics (www.oxfordpv.com), New Energy Technologies (www.newenergytechnologiesinc.com) and SOLPROCEL (www.solprocel.eu).

When interesting products hit the market we always try to include them in the Products section, so that’s the best place to keep an eye out for them.

—Lance Turner

To read more questions and answers, buy ReNew 131.