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Energy Blog magic box provides your house with night time power

magic box provides your house with night time power

Caroline Robertson
by Caroline Robertson July 1, 2015
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The ability to store solar power for use when the sun isn’t shining would be a dream come true for home owners who have invested in solar panels.

Many thousands of houses are now using hi-tech blackboxes to store solar energy for use at night.

At the moment, solar panels provide “free” energy to households while it is being generated, but they must still buy power from the National Grid at night like everyone else.

Now though, manufacturers are claiming that the blackboxes could cut energy bills as much as 60 percent.

Experts remain sceptical however. Many have labelled the new gadget as “overpriced and oversold”, commenting that any savings made are cancelled out by the £2,500 cost of buying and installing a blackbox, as well as the continuous task of replacing the batteries.

How do the ‘blackboxes’ work?

The boxes are roughly the size of a dishwasher, contain a set of rechargeable batteries and are designed to go in the kitchen. They silently charge during sunny periods and monitor whether electricity is flowing in or out of the house. When the solar panels stop bringing in power, the box switches to “discharging mode” and begins powering appliances in the home.

The result is that the “base level” consumption in a home, i.e. the use of constantly running appliances, for example a modem, is always powered from solar energy rather than by the grid.

The theory goes that the device will cancel out the usage of small gadgets and appliances in the home, something that pushes up energy bills due to constant power use.

The most costly background gadgets according to energy firm Ecotricity are wireless routers (£21.92 per year), desktop PCs on standby (£3.65), mobile phone chargers left plugged in (£2.44), electric toothbrush chargers (£1.22) and night lights for children (73p).

During the day the device will even switch to “discharge” mode if you need a sudden burst of energy to power a kettle, for example.

Joe Warren, from the start-up company Powervault, the only British firm the manufacture blackboxes, said: “They perform best if you have large solar panels that generate plenty of electricity, but you’re not at home during the day to use it.”

Surplus energy generated after the blackbox is fully charged is exported back into the grid.

While only 25 homes have a Powervault box installed, Mr Warren said the technology is in its “early stages” and the firm recently gained £750,000 worth of investment through crowdfunding to develop more boxes.

How much money can be saved?

Solar panel use in itself could save a household up to 50 percent on their energy bills. This can be increased to 60 percent by using a battery system, according to Powervault.

The cost of the blackbox could cancel out these savings however.

The units tend to last roughly 15 years and the battery requires replacing every five, costing £500 each time. Over 15 years the annual cost of a blackbox amounts to £233.

What’s more, using appliances the require a lot of energy in a short period, such as taking a shower or using a kettle, could rapidly drain the batteries, leading to them needing to be replaced more frequently.

On the bright side, battery prices are dropping rapidly, having already fallen by 40 percent in the last year, according to Renewable Economy, an energy efficiency research centre from Australia.

Currently households are paid money for every kilowatt hour (kWh) of energy their solar panels put back into the grid, and this will be unaffected by the boxes.

Every kWh earns the owner 13.39p, which half of this earns an extra 4.89p per kWh. This is due to the assumption that the homeowner will use half of what they generate, and export the other half to the National Grid. This returned energy therefore earns a “bonus” 4.89p.

Installing solar panels in the south of the UK will usually save roughly £135 a year in bills, while generating an extra income of £600 in export tariff payments.

Households in Scotland earn slightly less, according to the Energy Saving Trust.

The solar blackbox could make a marked improvement on the amount of money saved per year, although it will have no affect on the income from exporting electricity back to the grid, nor on the amount of energy generated by the panels.

The bottom line

Although the technology is promising, the blackboxes do not store enough energy yet to power high-consumption appliances, and therefore people will still need to rely on the grid, says Chris Rudge, a solar expert at YouGen, an online community for home owners with renewable energy devices.

Things like electric showers, hot tubs and induction hobs would run the batteries out in under a couple of minutes, he said. He added that “the battery unit is there to keep low wattage domestic appliances running, like lights and the television” and is not designed to handle large energy demands.

Costs of the boxes and batteries are falling however, thanks to large companies such as Bosch joining the market. US pioneers Tesla have also become involved, announcing that they will soon be making batteries that can power homes.

Available in the US this summer, the wall-mounted energy battery, which costs $3,000 (£1,954), will “change the entire energy infrastructure of the world”.

Foreign companies have been selling battery storage devices in the UK for the past few years, but Mr Rudge said a some of them “look very doubtful”.

These batteries are mostly designed for people who want to store energy for use at night. “This will save them buying in power when they get back from work,” Mr Rudge said.

The “Sunny Boy”, which sells for £4,700, is made by German company SMA, and boasts the ability to cut energy bills by 52 percent. This number is based on a comparison with households that use solar panels on their own.