Getting ready for PV storage

Storage is a buzzword in the PV community at the moment and it seemed like half the stands in some of the halls at InterSolar in Munich in June had storage products on display. But do they make sense in the UK yet – especially when most of the products on display seemed to cost upwards of ten thousand euros?

I am very familiar with battery storage systems: I lived off grid for a while, relying on my daily charge and discharge cycles to keep the lights lit; I have also installed a fair number of battery systems, as this was the main market for PV when I started (there were no grid connected PV systems back then).

So what has this familiarity with batteries taught me? Well, mainly to avoid them where possible. Yes, there are technology improvements being made all the time (and I am not even going to get into the merits of the various battery technologies), but in general batteries are still:

  • Expensive – the best ones particularly so;
  • Hazardous – varies depending on type, but issues exist in both operation and manufacture/recycling;
  • Have limited lifetimes – batteries will typically need replacing at least once within the system lifetime;
  • Wasteful – many battery systems will waste 20% of all the energy put into them through inefficiencies in the charge/discharge cycle

This is generalising I know. I also recognise improvements are being made in all these areas and I am sure system and battery manufacturers would love to take me to task on each of the above points. However, the fact remains that given the above, there still needs to be a good reason to use a battery.

For off-grid PV systems, batteries obviously provide a vital function, storing energy during sunny periods until the time it is needed. In these systems they generally can’t be avoided, so we live with the negatives. But why consider them for grid-connected systems? Unless you are installing at a site where there are regular power outages, the wisdom for the last few years has been avoid batteries – why live with all the hazards, inefficiencies and expense unless you have to. So what has changed?

In Germany, the success of the PV industry means that there are now large numbers of systems spread across the German electricity grid. These high penetration levels have consequences (such as voltage control) and mean that for further expansion, measures have had to be brought in to limit the amount of PV electricity that is injected into the grid at certain times. Rather than switching off or reducing the output of a system, one very sensible alternative is to dump the surplus energy into a battery for use later.

Most of the storage systems I saw in Germany looked to add at least €10,000 (£8,600) to a project, though there were a few notable exceptions that used smaller batteries to keep the price down. However, changes to the German feed-in tariff scheme and other incentives now mean that installing a battery storage system in conjunction with your PV system can be a financially sensible option. For the increasingly stressed German grid they also make sense, and ensure that surplus energy doesn’t go to waste.

In the UK we do not yet have the penetration levels (in most areas) to warrant peak lopping of PV system output. We also don’t have any financial incentives to install a battery storage system. So for the moment they do not in general really make sense – either in terms of energy husbandry or for financial reasons. But how long until this changes?

Grid storage isn’t new – after all, pumped hydro systems have been doing it for years. What is new is the prospect of the mass installation of distributed micro storage systems. That comment may sound familiar to some of you who have been in the PV industry a while – this is because it echoes the comments aimed at PV when (as the “new” distributed micro generators) they began to appear on the electricity network. In other words, we are at a development stage with storage systems that we have seen before in the PV industry. And if there is one thing we have learnt, given the right commercial and technical drivers, installation levels can very quickly multiply.

It may not be long until these technical and commercial drivers kick in, and when they do we need to be ready. We need to have in place a set of standards and regulations that ensure systems are fit for purpose, reliable and safe.