Batteries

• What is a home battery?

  A home battery allows you to store up cheap electricity to use later when you would otherwise use expensive electricity.

  The best electricity you can store is the surplus solar from your own generation to use in the evening and overnight.

  During the winter there is little or no solar surplus so we fill the battery with cheap nighttime electricity and use it during the day when electricity is more expensive.

  Some people have a battery without solar PV and buy cheap electricity at night to avoid expensive daytime costs.

• What if I already have solar PV WITH a Feed-In-Tariff ?

  If you already have a solar PV system that receives a FiT payment then we must design your battery solution to work with your existing system while keeping your existing system compliant with the FiT rules.

  In practical terms, this means having a separate inverter for your battery. The Tesla Powerwall has its own inverter built in for example or if you wanted more solar PV either now or in the future then we would use a hybrid inverter that can take both solar and battery.

• What if I already have Solar PV WITHOUT a Feed-In-Tariff ?

  If your solar PV system doesn’t receive a FIT payment then we can either leave it exactly as it is like we would if you had a FIT or we can re-design it to be part of a single system perhaps with more solar PV and/or a battery.

  We will take into account the cost of different options as well as how well each alternative might work.

• Will I need to change anything on my Solar PV system?

  Depending on when your Solar PV was installed and if the system is working well, you may need to upgrade your inverter or other components.

  If you receive a FIT payment for your existing system then we need to keep it working and keep it compliant with the scheme.

  Upgrading the system with a new inverter and individual panel optimisers can yield more electricity. With an average inverter lasting around 10 years, a full service and new inverter, with a new warranty sets your system up for greater productivity and reliability going forward.

• Do I need Solar Panels to have a battery?

  The simple answer is no, by purchasing a battery you will be able to access lower tariffs from your energy provider.  These are usually during the night. Your battery can fill up during the night on the lower tariff and you can then use the energy during the day, reducing the amount of energy that you require to import from the grid at a higher tariff.

• What size Battery is best?

  You will need a battery to best suit your household and your electricity usage. Some households require a battery to assist with the morning and evening requirements, some households will be able to use the energy all day and not require importing any electricity from the grid.  The best way to find out when and how much energy you typically use would be to look at your SMART metre.  A battery can then be sized to your usage. Most batteries can have additional batteries added so if your usage changes or your battery isn’t big enough, it is possible to add more battery capability after the initial install.

  A typical household would make good use of a 10kWh battery, a very efficient, low consumption home might be fine with 5kWh and a big home with a heat pump might need 20 or even 30kWh

• What type of batteries are there?

  All modern home batteries are lithium-ion batteries as they can charge and discharge small or large amounts without being degraded very much at all. Older battery chemistry like nickel cadmium (NiCad) would degrade each time you charged or discharged, and their life could be counted by the number of charging cycles but Lithium Ion batteries are more powerful, last longer and are smaller.

  The main difference between home batteries is whether they have an inverter built in like a Tesla Powerwall (AC coupled) or they use a separate inverter which they can share with solar PV such as a Solaredge (DC coupled).

  DC-coupled batteries are better if the DNO restricts how much inverter power you can have as the same inverter is used for Solar PV and battery.

  AC-coupled batteries are great if the DNO are not constraining your inverter power or if you have no solar PV (Ground floor flat, listed building etc)

• What role do the DNO perform?

  The DNO (Distribution Network Operator) usually National Grid (formerly Western Power) are responsible for the transmission of electricity to homes and businesses. They carefully monitor and authorise what is connected to every part of the grid. They calculate what will happen in different normal and fault scenarios and upgrade the network to allow changes.

  When we add solar PV or a battery the DNO are interested only in how powerful the inverter is and how much power it might inject into the grid if you were not using any of the power produced. There is a system to control how much power your system exports for which they test and approve devices from different manufacturers (type approved). A type approved device can monitor your connection to the grid at the same place as your electricity meter and tell the inverter to constrain it’s output to whatever level is safe for the grid. This constrain system takes up to 5 seconds to respond so the DNO give us 2 numbers to work with. The 2 numbers we get when we make an application are 1) Total capacity allowed 2) What the equipment must be constrained to. If we want more then we can always pay for an upgrade to our supply which might be very reasonable, or it might be very expensive if lots of work would be required.

  In the main, there are two different types of battery. An AC and DC battery.

  An DC battery is normally installed between your solar panels and the inverter.  We don’t need to inform the DNO, National Grid, of this install.  It works exactly the same as a DC battery, allowing you to store electricity and use it when you require.

  An AC battery is installed just after your incoming metre.  We do need to inform the DNO, National Grid, of these installations.  On the whole permission is usually granted and in worse-case scenarios the export from the battery may be limited.  The big difference between an AC and DC battery is that an AC battery can operate in an electrical blackout/power cut. With the battery in the Island mode, it will take over the supply of electricity to your home.  In more remote locations some customers feel that this is a necessity and not a luxury, enabling them to carry on with their tasks until the supply is restored.  For this reason, AC batteries are generally more expensive.

• Does a battery work when there’s a power cut?

  As mentioned above, an AC battery is the only type of battery that will work in a blackout or power cut. NOT TRUE

• Will a battery interfere with my FIT payment?

  Yes, some batteries will interfere with your FIT payments.  The main reason being that the electricity companies don’t want you to be able to put energy through your metre twice.  There are several batteries that we can place in your system that won’t interrupt your FIT payments.  If you are on a very low FIT payment, it may be worth considering if a battery would be of more use to you.

• How can I see how much energy is stored?

  All the batteries come with great Apps that can be accessed via Smartphones or iPad to show you how much you have in your battery and when and how much you have consumed.  You, as the owner will be able to change your setting to best serve you and your usage.  Usage will be different in the summer to the winter and can be personalised to your household and needs.

• How big are the batteries?

  Batteries range in physical size depending on the KWh size.  A typical 10KW sized battery is around 790 x 1179 x 250 mm.

• Can the battery be outside?

  Yes, batteries can either be installed inside or outside.  Like anything kept outside the battery would benefit from a little shelter from the elements but is not essential.

• Will I still need to buy electricity from the grid?

  Depending on your household’s usage, you will possibly still need to buy some energy from the grid.  Every household and every day is different, so its not a case of one size fits all. We do have many customers that don’t buy anything from the grid, they have adapted their lifestyles to get maximum from their installation.  These changes can be as small as putting the dishwasher on in the morning rather than at night when its dark, putting the tumble drier on after the washing machine has finished and not having all electrical household items on at once.

• What are time of use tariffs?

  A tariff is a pricing plan for energy use. Time of use (TOU) tariffs use different prices to encourage consumers to use electricity at times when more is available cheaply. This can support a more flexible and sustainable electricity system.

  https://energysavingtrust.org.uk/time-use-tariffs-all-you-need-know/

  https://www.citizensadvice.org.uk/Global/CitizensAdvice/Energy/Citizens%20Advice%20summary%20of%20the%20value%20of%20time%20of%20use%20tariffs.pdf