Solar storage batteries have been a popular add-on for years with those installing solar panels in their own home rooms.
Save the excess electricity you generate in the middle of the day to power your home during the evening. What’s not to love? It turns out there are a few things.
The changing economics, combined with some difficult ecological questions, has led some to start questioning the former eco-poster-child. We’ve been looking into why.
The economic argument for solar storage batteries
Most domestic solar panel installations will generate more power than the house can use during summer day times. In many countries, any excess electricity generated is given back to the grid for free.
This means that many homeowners spend their day giving away electricity for free, only to spend their evenings paying to buy that power back from the grid.
That is only half the benefit, a storage battery can do much more than just saving midday power for evening use.
Solar panels tend to produce nice steady electricity, whereas most houses use electricity in short sharp peaks followed by big troughs. A battery can help smooth this all out.
Here’s the generation from the solar panels installed on a 3-bed home in Ireland that we studied:
Here’s the usage pattern for the same house – a very different story.
Most homes follow this pattern of low background demand, broken up by large spikes in usage. Items such as kettles, ovens and electric showers demand a lot of electricity, but only in short bursts.
A solar storage battery here will charge and discharge many times during a day – discharging to help cover the demands of every spike, then charging up in the trough in between ready for the next spike. Every time, saving the homeowner money.
How the numbers add up
We checked the numbers for the house above, and on average, the 5.1 kWh battery would store then release a total of 1660 kWh per year. At an average price of 25 cents/kWh, that would save this homeowner €415 per year.
Adding a battery to a solar panel installation like this adds around €2,400 to the total price, meaning that the battery would have paid for itself in just under six years. Financially, this is looking good, so far.
The economic arguments against solar storage batteries
The upfront cost is pretty hefty when compared to the rest of the solar panel system. A typical 4 kWp solar panel installation in Ireland might cost about €5,800.00 to the homeowner (after grant subsidies). Add on a battery, and that jumps by a whopping 47% to around €8,500. Good idea or not, that can lift the whole system above the affordability of many households.
The second factor is feed-in tariffs. In an effort to meet the net-zero targets, many countries are rolling out feed-in tariffs, so that homes with solar panels will get paid for every unit of electricity they send back to the grid.
The whole economic argument for solar storage batteries was to save the electricity you would have given away for free. Now that you can sell it, the financial argument for batteries is seriously diminished.
The above numbers assume excess power is given away for free. But if you are getting paid, that’s a very different story.
It’s common to get a lower rate for the electricity you sell compared to the electricity you buy. In Ireland (where the house above is located) you get anything between 25% and 50% for electricity sold back to the grid, which pushes the payback period on the battery to anything between 9 and 14 years. Considering the average lifespan of a solar storage battery is around the 10 to 12 year mark, it means the economic argument for batteries does not stack up nearly as well.
The environmental argument for solar storage batteries
If you ask most homeowners why they got solar installed in the first place, environmental benefits are almost always a significant factor. Yes, economics is one part, but it is rarely the sole driver. So we would be only looking at half the story if we just considered the economic arguments.
Balancing the electricity grid is a big issue, and grid balancing has a big carbon footprint. Many households follow a similar usage pattern, needing the largest amount of power in the early evening as everybody goes home and starts turning on their cookers.
This has led to the infamous “peaker” power plants. Often fuelled by natural gas, these electricity generation stations only run for a few hours a day just to cover these spikes in demand. Building a whole infrastructure just to run a small amount of the time has a serious carbon footprint.
Governments worldwide have been grappling with how to spread the load more evenly throughout the day. Many countries will need five times more electricity during these few peak hours than in the quiet times in the middle of the night. If we could spread the electricity usage, just that change alone would lead to a very significant carbon footprint reduction.
Initiatives rolling out include such things as smart meters. Utility companies can charge peak rates just for those few hours a day to encourage homeowners to change their usage patterns.
Also, more and more devices now have delayed start controls built in. Load the dishwasher like normal, but with one more button press, it will not turn on until after the peak period. Good for your pocket, good for the grid, and good for the environment.
Even more, controls are built into electricity-intensive devices such as electric cars, which can easily be programmed to only charge during the middle of the night when demand on the grid is slow. There are also moves for super smart systems, where the grid operators can pause all car charging just for small periods where unexpected spikes in demand come in.
Coming back to our battery question, domestic solar storage batteries are another tool to help spread the load on the grid. A 5 kWh battery can store enough power to run a house for the evening, and that’s one less home contributing to the spike. If household batteries mean just one less peaker power station needs to be built, then that in itself is a huge environmental benefit.
The environmental argument against solar storage batteries
If you Google the pros and cons of electric cars, one theme you will see time and again is the dubious supply chain of lithium-ion batteries. Cobalt is an infamous example, with the Democratic Republic of Congo being the world’s largest producer and having the largest known cobalt reserves[1]. There are many question marks over the extraction, on both human rights and ecological issues, and this is true of other raw materials required as well.
This same black mark against EV batteries is true in solar storage, with lithium-ion being the most common technology for domestic solar storage batteries.
Yes, a solar storage battery might just be one of the countless lithium-ion batteries in any one particular house, with everything from mobile phones and tablets to PCs and smart devices containing lithium-ion batteries. But when you consider a typical solar storage battery might be 2000 times the capacity of a mobile phone battery, suddenly the problem is at a new scale.
So, where does this leave us?
The jury seems to be out on the future of solar storage batteries. Once a popular add-on to home solar panel installations, the demand may be waning.
The economics will depend on the future of feed-in tariffs and how they evolve compared to the ever-increasing energy costs.
The environmental impact is, as always, never clear-cut. The need to reduce the CO2 footprint of electricity grids on one side, and the ecological and human rights impacts on the other. Even if you put ecological and human rights as the most important factor, we cannot ignore the fact that more CO2 released itself creates other ecological and human rights issues.
Time will tell which way this one goes. But with some governments cutting grants towards solar storage batteries whilst others invest in electricity storage capacity, there’s no clear consensus yet.
