I estimate that it has saved us around 3 MegaWatt hours since it was commissioned. In monetary terms, that's roughly £1,000 taken off our electricity bills.

How did I work that out? Well, maths is hard, as Barbie knows, so take all this with a pinch of monosodium glutamate.

Here's a typical month - October 2025:

Yikes! What's going on here?

We use a variable electricity tariff. Prices fluctuate every 30 minutes. At peak times our electricity prices can shoot up to 60p per Kwh. Overnight or when the wind is high, prices can drop to zero. Yes, free electricity! Sometimes the excess in the grid means that prices go negative and we are paid to use electricity. Hurrah!

Our battery knows this. Its Internet connection allows it to download the tariff for the day ahead and plan accordingly. If the electricity prices are cheap, the battery fills up. The battery can decide to discharge when we're using more electricity than solar provides, or it can wait until prices are more expensive after the sun has gone down.

Here's an example, again from October:

In October, about a third of the power stored in the battery came from the sun. About 92% was used by our house with the remainder being sold back to the grid if it was profitable to do so.

By contrast, here's June 2025 - a sunny month in the Northern Hemisphere:

Here, only 12% of the battery charging was done by the grid. 88% was done for free by solar power. But because solar was so plentiful, about 15% of the battery was sold back to the grid.

Maths. Is. HARD!

I've been playing around with various charts, graphs, spreadsheets, modellers, and a bit of calculus. I basically came to the conclusion that the easiest way was to assume I was saving the energy price capped value of a kWh.

That varies from 25p to 35p. If I fudge the numbers just right, it rounds off at an even grand.

It's Payback Time

No-one ever asks what the payback period is of buying a car vs taking public transport. You never see anyone amortising an engagement ring over the length of a marriage. Still, here we are.

We paid £2,700 for the supply, install, and commissioning of our battery.

That means the payback time for the battery will be between 6 and 7 years. If energy prices go up, the payback time goes down. Its capacity is showing no degradation yet and I hope it will provide us with many years of savings before it needs to be repaired or upgraded.

Solar batteries are getting cheaper and their capacity is getting bigger - although not big enough to store all my home's electricity.

If you can afford the upfront costs, it's like pre-paying for a chunk of your energy usage and can help protect you against sudden price rises.

You can sign up to Octopus and get a £50 bill credit if you want to switch to a variable tariff.

Well, after less than 10 months, the battery has given us 1MWh.

To put that in to context, the average UK household uses about 3MWh per year. So (again, very roughly) over a third of our electricity use this year has come from the battery.

But where does the battery get its energy from? We have two sources.

First is solar. When the sun is shining, our solar panels produce electricity. That flows down from our roof and into our mains wiring where it is used by the home. If we are using less electricity than is being produced, the electricity flows into the local grid and we get paid for selling our surplus.

Our battery has sensors attached to the grid connection. When it detects surplus generation, it starts charging. By constantly monitoring our overproduction, it can charge up with free solar power.

But the sun doesn't always shine (ain't that the truth!) so there are days when our solar production is less than our usage.

In these cases, the battery charges from the electricity grid. We have a smart tariff which changes price every 30 minutes. The battery knows the day's prices and can predict our daily usage. If it can see that electricity is cheap at 3am and expensive at 4pm, then it will charge up during the early hours of the day and discharge at peak time.

The battery occasionally sits idle. Mostly when it has fully charged but knows an expensive period is coming up later.

What does that mean for money?

Well... it's complicated! When the battery charges from solar, is the electricity free? No! If we were to sell that surplus electricity to the grid, we would be paid 15p/kWh.

When the battery charges from the grid, is the electricity expensive? No! Because we are on a dynamic tariff, we occasionally get paid to use electricity! Our provider has paid us up to 5p/kWh to charge!

When the battery discharges, how much does it save us? Again, complicated! Because we're on a dynamic tariff our prices change every 30 minutes. Sometimes the rates are as high as £1/kWh, other times they're 1p/kWh. Generally speaking, the battery only discharges if the price of use is higher than the cost of acquisition.

So... I've fudged the figures! For the first year of operation, energy prices have been high. Based on a back-of-a-fag-packet calculation, I reckon the battery saves us an average of about 31p/kWh. Call it about £360 per year in savings.

That gives us a payback time of about 8 years.

Of course, if electricity prices spike, payback will be quicker. If they crater, it'll take longer. If we switch to electrical heating or get an electric car, the savings will be greater.

Domestic battery technology is still a bit of a tough sell. The batteries are large and their fans are noisy. The cost of materials and installation is high and their capacity is relatively small. But the technology behind them is sound. With a dynamic energy price tariff, they're one of the best way to reduce utility bills.

Obligatory referral link

Join Octopus energy and we both get £50. They have regular and dynamic tariffs, and a pretty cool GraphQL API.

Seven years ago, we installed a solar battery. It was part of an experimental project which looked at creating a community power-grid, so it came at a subsidised price.

As I explained to BBC Click, the 2kWh capacity was reasonable - but I expected the future would bring higher capacity, cheaper costs, and smaller sizes⁰.

But, after 7 years the battery was starting to show its age. The little Raspberry Pi inside it needed more frequent reboots, the fans were grinding a bit, and it would occasionally drop off our network.

So Moixa made me an offer I couldn't refuse. Upgrade the battery to the newest 4.8kWh model. Total cost for supply and installation? £2,700.

Ooof! That's a lot.

We did the maths. The previous subsidised battery had paid for itself over the 7 years. And with electricity prices rising, it made sense to be able to use more of our home-grown supply. So we went for it. Also, I like buying new gadgets.

Installation

Someone comes along with a big drill and lots of electrical flex. The whole thing is mounted on the wall like this:

And then covered up like so:

The old battery was sent to be recycled.

A few minutes after it was commissioned, the website was showing power flowing from the solar and going into our battery and home - with enough left over to sell to our neighbours.

The Good

It can store nearly 5kWh of sunshine. That's about £1.60 worth of electrons at today's capped prices.

Smart profiles - it can monitor how much energy the house is using and charge / discharge as necessary. Or, it can look at realtime energy prices and make a decision about whether to charge. We'll move onto a smart-tariff soon and it will charge up from the grid when prices are low and allow us to sell our excess when prices are high.

It can connect via WiFi and Ethernet. Moixa supply some homeplugs for the Ethernet connection. That allows it to look up energy prices and means Moixa can monitor the battery's health.

It has a modular design. Inside are two US2000 batteries. They're of a fairly standard design and - in theory - could be swapped out for something bigger and cheaper in the future.

Oh, also, there's an app! So I can check what the battery is doing while on the go. A bit silly, but lets me know if the battery is full - which might mean I decided to switch on a high-energy device like a tumble-dryer.

The Bad

It's a big brute! There's been a bit of effort made to soften its industrial appearance. But there's no getting away from the fact it is a big box with wires coming out of it. It needs a bit of airflow around it for the fans, and a sturdy wall to be mounted on.

It's a bit noisy. There's the hum of the inverter, the whirr of the fans, and the occasional click of the relays. Unlike a gas boiler, it is on constantly. Moixa recommend installing it out of the way if possible. Ours is in the porch, so we only notice it when entering or leaving the house.

The information screen doesn't say what the state-of-charge is. All you get is whether it is connected to the Internet and whether it is charging, discharging, or idle. A few more stats on it might have been nice.

If the power goes out, so does the battery. The UK has strict rules on "islanding". If the electricity went out but the battery kept feeding back into the grid it could injure people working on the wires. So it can't be used as an Uninterruptible Power Supply.

The battery's network connection doesn't expose any open ports. I mean, I suppose that's good for security - but I wanted to play! The website is great - but I don't think it offers an API.

Economics

*sigh* Money, eh?

What's the return on investment for your new kitchen? Or for getting your garden landscaped? Sometimes it is nice to have cool things. And, as we head further into a climate emergency, being able to reduce our personal dependency on polluting forms of electricity is a good thing.

But let's talk money anyway!

On the first day, the battery charged up to 95% on solar. At about 8pm, it started discharging. At 8am the next morning it was down to about 35%.

60% of 4.8kWh is 2.88kWh. Divided by 12 hours is 240 Watts. That's how much our house uses over night. We paid £0.00 for electricity during those hours.

The average price of electricity is about £0.35 per kWh - so we saved £1.01.

£2,700 / £1.01 / 365 days = 7 years, 4 months.

But… of course, it is a little more complicated than that. Here's what our solar panels do on a rainy winter's day:

Hardly any solar generated, not enough to even half fill the battery. So the system is useless, right?

Nope!

We're moving to a smart-tariff from Octopus (join and we both get £50). When electricity prices are cheap, the battery will charge from the grid. When electricity prices are high, the battery will discharge. We effectively become small-time arbitragers. We buy low and sell high.

And, if electricity prices go higher, our payback time will be shorter.

Come back to this blog in the year 2030 and I'll tell you how the battery performed.

Verdict

Solar batteries are expensive. There's no VAT to pay if you get them installed at the same time as your solar panels - but the Government doesn't seem keen on making it cheaper for people to retrofit energy-saving measures.

Battery tech is still in its relative infancy. We don't have Moore's Law increasing capacity and reducing prices. So for now we're stuck with big expensive boxes.

If you have the space and money for one, I think solar batteries are a reasonable investment. They're the ultimate in "think global, act local" when it comes to electricity.

Sadly, last year, it died. It was prototype hardware, and these things happen. Moixa offered to replace it with an updated model - which was generous of them. While we were waiting for the new model to come in to stock, we moved house. Then COVID happened...

Anyway, long-story-short, we now have a shiny new 2kWh battery installed!

The batteries came delivered like this:

And were installed in this:

And then wired in like this:

Then given a slightly less industrial look like this:

It has many blinking lights to tell us how it is doing.

It was a bit of a chore to get installed. We had holes drilled in walls. Then we needed to get our electrics checked. Then it needed to be commissioned. Not helped by various lockdown restrictions. But we got there in the end. Moixa were superb at keeping us informed all the way through the process.

How it works

It's slightly more complex than you may think.

• Solar power is generated on our roof as DC.
• An inverter in our loft converts this to AC and pumps it into our consumer unit.
• If we are using electricity, the solar power flows into our house.
• If there is surplus solar power, it goes back to the grid. Our SMETS2 smart meter records how much we have exported.
• A clamp on the tails under the meter records the flow of electricity.
• If we are exporting, the battery sucks up the energy to store later.
• If we are importing, the battery pumps out the energy to use immediately.

Phew! Got that?

CONNECT IT TO THE INTERNET!!!!

Every single thing in my home connects to the Internet. EVERY. THING. The battery is no different. This allows for two useful things:

1. Monitoring of the battery - by myself and Moixa.
2. Adaptive charging
3. Being hacked

The monitoring function is available via a website. It shows simple diagrams like this:

You can also see more complex minute-by-minute graphs.

I'll write a later blog post about the API and how it can be used.

The adaptive charging is interesting. It can, theoretically, look up the weather forecast to work out when it is optimal to charge and discharge. Similarly, it could work with your energy provider to see when their spot rates for electricity make it worth selling.

I'm with Octopus Energy who do some interesting things with adaptive pricing.

Power Cuts

One important thing to note - home batteries do not help you if your area has a power-cut. If there was a cut, the battery might pump power back into the grid - this would be a risk for any electrician working on the grid.

Cost

The cost of battery storage is high.

• Initial install: £500
• Removal of old battery: £175
• Fitting of new battery: £450
• Compensation for original battery not working: -£200
• Cost savings from original battery: -£125

Total: £800

By comparison:

• Tesla PowerWall costs around £6,000 for 13.5 kWh
• Duracell costs around £4,500 for 3kWh

More comparisons are on the Which Guide to Solar Batteries.

Is it worth it?

In monetary terms - no. Probably not. Electricity prices are about £0.14 per kWh when purchased from the grid. So the maximum it can store is about £0.28 worth of electricity.

I can sell my surplus solar electricity at about £0.055 per kWh. So the energy I store for later use, I could have sold.

So I "lose" 5p by not selling it, but "gain" 14p by not buying it in. Call it 9p per kWh.

If the battery charged to full every day of the year, it would save us around £100 per year. So a payback period of around a decade. That improves if electricity prices rise.

But it's not (just) about the money. This is an investment in the future. I believe that distributed local energy storage will play a huge part in our future energy mix. I want to make sure that companies like Moixa have customers and that people will see the benefits of home storage.

Our solar panels produce all of the electricity that we use in a typical year. But we can't make use of all of it. Ideally, we'd have a MegaWatt battery which charged all summer long. But, for now, I'm quite happy with this little box whirring away in the corner.

Discounts!

If you buy a Moixa solar battery and mention my name, you'll get a £200 discount - and I'll receive a £200 incentive.

Score!

If you switch to Octopus Energy we both get £50!

Most of our domestic energy use is in the evening. So, when I'm out at work I can schedule the tumble dryer, robot vacuum cleaner, and WiFi rice-cooker to consume energy when the sun is shining. The rest is sold back into the grid for my neighbours to use.

Wouldn't it be great to capture that energy and use it to power my lights and games console in the evening? Yes! Enter the Maslow - a 2kWh wall mounted battery designed to capture solar power and put it to use when it is most needed.

The Maslow gobbles up the surplus power and stores it for later use.

I received a subsidised Maslow battery as part of Project ERIC.

Project ERIC (Energy Resources for Integrated Communities) is an initiative bringing solar PV power and smart energy storage to up to 100 homes in Rose Hill, East Oxford. Project ERIC is led by Moixa Technology and Bioregional and is part-funded by Innovate UK.

Installation

It's a relatively svelte box - smaller than a normal domestic boiler - and fits neatly onto my interior wall.

Here it is before installation and without any batteries.

As you can see, the batteries are designed to be replaceable. If they die unexpectedly, or technology leaps ahead, you should be able to keep your existing installation and just swap out the cells for something newer.

A couple of screws - and a bit of swearing - and it was fitted.

Installation took around 3 hours. The battery needs its own RCD in your consumer unit. A few holes had to be drilled in order to get all the wiring hidden away.

The fans on the side run when the batteries are charging or discharging. They're a little louder than a typical PC - and will be easily drowned out by a boiling kettle or rumbling tumble-dryer. You probably wouldn't want this installed in a bedroom or living room - but it's fine for a kitchen or loft.

They're needed for cooling these chunky capacitors.

Down in the bottom of the unit, you'll find the fairly unremarkable control circuitry.

Wait... wait a moment! Is that...? OMG! This thing is RASPBERRY PI POWERED!

Wooo! I think this is the 5th Pi I have controlling something in my home ?

There's a WiFi antenna which runs to the outside of the unit. You can also connect directly to the Pi's Ethernet port if you don't have a strong WiFi signal.

Hidden behind a panel is a full range of blinkenlights.

A mini-USB port is present for debugging purposes, along with some diagnostic LEDs. Apparently there's also Zigbee for controlling smart appliances in the future.

Network and API

As part of the Project ERIC trial, I've agreed to have my battery's energy usage monitored.

The Maslow collects details of usage every minute, these data are then combined to provide an overview of what our village is consuming and producing:

I also get access to a personalised dashboard - which will hopefully show more details soon!

There's nothing really to control on the battery - it just sits there doing its job. There is an API, more details in a future blog post!

Cost

Because I'm on a trial of this hardware, the total cost of the Maslow battery and installation was £600 (including VAT@ 20%).

What do you get for that?

A typical mobile phone battery holds around 0.015kWh. My electric car has a battery capacity of 19kWh. My house's idle usage overnight (lights, chargers, servers, devices on standby) is around 100 Watts. So a typical night (2200 - 0600) will use around 1kWh.

My electricity costs me 13.08p / kWh - sign up to Ovo Energy and we both get a £25 Amazon voucher.

So, assuming the battery is fully charged once during the day and then fully discharged overnight, how long before the device pays for itself?

£600 / (£0.1308 * 2) ~= 2,300 days.

2,300 / 365 = 6 years 4 months.

At the unsubsidised price of £2,000 the repayment period is around 21 years. That's essentially the guaranteed lifetime of most solar-power systems. It also assumes that energy prices stay static.

Of course, the solar panels don't always generate enough - let alone enough surplus - to fill the battery:

Edent's Solar Panels

@Edent_Solar
Automated

Pretty grim. @edent's solar panels generated ~1.42kWh, earning £0.25
FAQ: shkspr.mobi/blog/solar-gra…
#edentSolar pic.x.com/92wikj4nuy

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There's no doubt the Maslow is an expensive "lifestyle" product. It's for saving the planet rather than fattening the wallet. Built in to the cost of a typical home it could be a real game-changer in how energy is used in this country.

As an aside, the UK Government pays me for every kWh the solar panels generate. They don't measure the actual amount I export. So the Maslow doesn't reduce the Feed In Tariff (FIT) payments.

Features

OK, other than offsetting my grid usage, what does this big ol' box do?

• Powering DC lighting. I decided not to go for this option. I already have energy efficient bulbs, so the extra cost for replacement didn't make sense for my needs.
• DC Power Circuitry. I've not yet installed this, but it should let me charge USB devices without needing to do a costly AC/DC conversion.
• Works during a power-cut. For safety reasons, the Maslow won't power normal household sockets during a power-cut, but it will allow you to use the aforementioned USB sockets and LED lighting. Handy in an emergency
• WiFi for monitoring usages. Which of course means…
• An API available for HACKING!

Alternatives

There are number of alternatives to this sort of technology.

• Divert to immersion heater. I currently have a Solar iBoost which heats up my water and reduces my gas usage.
• Build it yourself! If you have lots of spare batteries and are a qualified electrician.
• Car storage. At the moment, I've been using my electric car to store surplus electricity - but I'm not always at home during the day. I can't "reverse the polarity" and feed back from the car into the house.
• Tesla Powerwall - the elephant in the room!

Tesla battery has the cachet of the Tesla brand - but hasn't yet been released to the UK public. At around US$3,000 for a 7kWh model, the cost/power ratio is pretty good - but it is significantly larger in size to the Maslow.

The Tesla is only generally available in the USA, so it will be very interesting to see what their price is for the UK market. The Maslow is designed for typical UK use, which may be different from Tesla's focus - UK houses don't tend to have air conditioning, for example.

Final Thoughts

I've only just had the batteries installed - but it's obvious that the Maslow provides a vital way to reduce peak grid usage from domestic properties. Even if it is a little costly.

I'm delighted to be part of such an innovative trial - I'd love to see every home in the UK generating and storing their own energy.