My friend Ian Woofenden has this to say about using batteries on the grid:
Tesla Battery Perspective
There’s been a lot of buzz recently about the Tesla battery. My attitude and ideas toward it are tempered by 30+ years of living off-grid with renewable energy technology and watching the industry progress. There’s plenty to say – my summary looks like this:
* It’s just a battery. Off-grid folks have been living with batteries for decades. They are not magic, and in fact they are often the biggest problem components in renewable energy systems. If you can avoid batteries, I advise you to do it!
* Batteries are actually a load on a system, since they are not 100% efficient and they have a standing loss. Adding more battery adds more load (and more cost). If you can grid tie without batteries, you’ll have the most efficient and environmentally friendly renewable energy system. If you need batteries (off-grid or utility back-up), I suggest you keep your battery relatively small, and invest in more generating capacity instead of more heavy metals that need care and replacement.
* It’s not a real product until it has a price tag, a warranty, and a track record.
* Early specs on the product make me scratch my head about whether the engineers even looked at the current renewable energy technology and how their product might interface with existing systems and gear.
* If the grid needs more storage, it is not your problem. Let the utilities solve that issue; they have a sweetheart deal with a profit-guaranteed monopoly – they can figure out any real storage problems. If you think you need storage personally, ask yourself the hard questions — how often and how long do you actually have utility outages, and do you really have critical loads?
* Perhaps the biggest drawback of the media focus on this prospective product is that people will get distracted from a true star of the renewable energy show — photovoltaics. Solar-electric modules are warranted for 25 years of energy production, and just sit on your roof or in your yard making electricity for you. They are ultra reliable, almost maintenance free, and will last longer than many of you reading this will live. My first modules went on the roof above me in 1984 and are still making clean electricity for my homestead.
* Perhaps the biggest benefit of the Tesla hoopla is that people will start thinking harder about renewable energy. Once they realize that this product is not magic, is expensive, and in itself really does very little for the average homeowner, they might start to ask smarter questions and make better energy decisions. Reputable and experienced renewable energy dealers and consultants are getting plenty of inquiries due to the Tesla hype; the wise ones are using the opportunity to help people understand the practical and cost-effective ways to achieve their energy goals. There is no silver bullet that can solve your energy problems quickly, easily, or cheaply.
In the United States (where Ian lives) they often have a Net Metering arrangement where the electricity they export to the grid is credited at the same value as what they use. This reduces the incentive for storage. But even when the exports are “lost”, as in “not credited to the householder”, there is not a big financial case for using a battery. The latest new battery announced in the UK for example (article here) stores only a couple of kW hours. Even if used to the full every day this would earn less than £100 over a whole year. Batteries are expensive and they only last a few years. Let’s focus on making renewable energy and investing in the equipment that makes the energy.