In this opinion piece, energy consultant Patrick Waterfield asks: are batteries worth it for photovoltaic (PV) panels, and what is the fuss all about?
In this article we cover:
- Battery types
- Cost of installation
- Are batteries worth the investment
Energy storage has long been seen as a holy grail of energy supply, especially where intermittent renewable energy sources are concerned.
This applies both on a national/regional level, with an increasingly decarbonised electricity supply grid, and also with domestic renewables systems.
The most common approach, with domestic renewables, has been to use the grid as an effective storage medium, exporting excess output to the grid and importing back from it during periods of low production or high demand.
Although the price paid for exported output has tended to be much lower than the unit rate for imported supply, the economics are generally favourable, as you avoid the need for a storage medium on site and the standing charge (where applicable) would be payable anyway.
Increasingly these days, however, people are considering battery storage for their home renewables systems. I have written pieces for this publication in the past on the subject of battery storage for renewables, including integration with electric vehicles.
The verdict overall has been that the technology and/or economics was not sufficiently well progressed to make a persuasive argument for batteries. So, has anything changed in the past couple of years?
Well, technological advances have certainly been made. The rise of electric vehicles has seen improvements in Lithium-ion technology, while sealed lead acid cells offer reduced maintenance
requirements for that type of battery.
NiCad batteries, meanwhile, are durable and require simple management systems. There are also emerging technologies, such as flow batteries, which promise long lifespan with good safety (though slower charge/discharge times).
However, disadvantages of batteries include high capital cost (varies according to technology), limited capacity (relevant to overall system size), maintenance requirements (especially floodedLead Acid), concerns regarding safety (especially Li-ion), short lifespan (especially Lead Acid), issues around toxicity and disposal/recycling (especially Ni-Cad).
Solar battery providers cite in excess of 100 per cent savings in annual electricity costs, including export income (where grid-connected). Considering an average annual electricity usage of 3,500kWh and overall unit cost of 30p (or around 45c in ROI) the average yearly bill would be around £1,050 (€1,575) not including standing charge (where applicable).
At a capital cost (for a 5kWh lead acid system) of ca £5,000 (€6,000), the payback period would be of the order of four or five years. This equals the maximum lifespan of lead acid cells. Li-ion batteries are more expensive to buy, ca £11,000 (€13,500) for the same size system, giving a payback period of up to 10 years. Again, around the system lifespan.
So, unless you are faced with high grid connection costs, for example in more remote areas (which effectively improve the economics of the storage medium), or maybe are motivated by more ideological goals of net zero, energy autonomy and off-grid living, the case for solar battery storage, in my opinion, is still not compelling.
NOTE: Please note that this is my opinion, as an energy consultant not associated with any manufacturer or supplier of solar PV or battery systems. The figures cited above may vary for different suppliers, different technologies and differing levels of usage. Capital costs for battery systems will be lower if part of a new installed solar PV system, compared to retrofitting to an existing one. You should carry out a basic cost benefit analysis based on your own circumstances and proposed systems.
