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Transition Matters

This section is used to list tried or potential practical solutions for individuals and communities across North Cornwall and beyond. To get more details or to arrange a trainig session/ seminar on one of the Solutions, just contact the originator of the message.

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Energy Storage for Grid Connected PV/Wind Systems


Self Consumption. Install batteries and charge them from your solar PV system. Never be without power.

Install a home battery backup system and protect yourself from looming power cuts. Bright Green Energy Ltd has developed the @HOME battery storage system. Utilising existing technology our @HOME battery system consists of batteries, inverter charger, battery monitor and a few minor adjustments to your electrical fuse board; not only will you continue to receive the FiT but you can charge your batteries direct from your solar PV system.

The Electricity Grid and your Solar PV System.

Grid connected solar PV systems do not work during a power outage. Regrettably, the solar PV system remains idle until mains power is restored to the property. Straight grid connected solar PV systems are “battery less”. The solar PV inverter requires a connection to the electricity supply to function properly. If there is no grid supply available then the solar PV inverter does not operate. t

The obvious question is: if a solar PV system produces energy whenever the sun shines then why can't we use that energy even if the grid is not available? The answer is not so clear cut.

It has to be remembered that a solar PV system is a constant current source and therefore cannot increase or decrease the amount of energy it produces to handle normal, everyday, appliances and home load demands. If the solar PV system produces 8A then it cannot produce more than that. Of course, appliances that operate at 8A or less could be run, but fridges and appliances with motors would not work as they require a higher “surge” current to turn their motor over.

If you suffer from frequent loss of power or that any loss of power lasts a long time and assuming that you’re not already living off the grid then you may want to consider having a battery backup system installed. In fact, if there are some appliances that you absolutely must run all the time, you should definitely consider a battery backup system. You may have a water pump; lights and computer equipment; TV and radio; fridge freezer or similar appliances.

Battery backup system considerations

There are two types of battery backup system for solar PV systems

System 1: DC - coupled systems. These systems are better known as true "off-grid" systems. The solar panels are connected via a solar controller to a battery bank, to which an AC inverter is connected. These systems have efficiencies of 92-94% as opposed to grid connect inverter efficiencies of 95-97%. Batteries are either GEL or lithium-Ion, the latter are becoming more and more popular.

System 2: AC - coupled systems. These are generally considered if there is one or more renewable energy source in a single system, such as a combination of wind, hydro and solar. To incorporate all of these sources of power together and take advantage of them during a loss of grid supply is best done via AC coupling, thus taking advantage of the high-voltage energy sources of supply.

All homes and offices that have solar PV systems installed can also have a battery backup system installed. We prefer the AC coupled system.

The Advantages of AC Coupled Systems.

The trick to AC coupled systems is keeping the grid-connected inverter operating during a power cut with the battery backup source acting as a utility power supply so that the inverter operates in the normal way.

At a first glance this seems impossible, not least because it flouts the G83/1 rule that the inverter must disconnect itself during a power cut to prevent "islanding".

In fact, AC coupling is pretty straightforward if a 240V battery backup inverter is used in conjunction with a 240V grid connected inverter.

The system design is based upon a well kept secret that the AC output of inverter chargers can accept power flow in either direction. There is more to it than just that, but this is the principle around which the inverter chargers operate.

Battery backup system sizing is much more critical than typical grid-connect system and details are essential. The more detail the better. Of course, running loads on a grid connected solar PV system is simple. If the solar panels cannot provide the required power then the extra comes straight from the grid, if it is available. If you size a battery backup system and it is too small to meet your load requirements then you may (most likely will) run of our power during a power cut. What’s the point of that?

Assuming that you do want to add batteries to your grid connected solar PV system then it is our opinion that the backed up loads must be separated from non-backed up loads and placed in a separate distribution board or separated out in a split, dual RCD board.
Never run out of power. Add batteries to your solar PV system makes perfect sense and has considerable benefits:
Benefit: Protect essential appliances from power cuts with batteries which function as an Uninterruptible Power Supply (UPS). A UPS will keep appliances running during a blackout.
Benefit: Run any appliances you want, when you want. For example: charge your batteries during the day from your solar panels and run appliances at night, for free!
Benefit: Reduce your electricity bill even more. Don't export the electricity generated by your solar PV system simply store it in batteries and use it when you want.
Benefit: Don't waste excess energy when your batteries are full. Use the excess energy to heat your hot water, for example.
Why you should add batteries to your grid connected solar PV system.

If you have paid for solar panels to be installed on your home, office or leisure centre you must be happy that not only is your electricity bill is being reduced, but that you're receiving feed-in-tariff payments for all the electricity generated regardless of whether it is consumed or not.

If you have had solar panels fitted for free you do not receive the FIT but you do reduce your electricity bill.

In both cases you may be wondering how else you can further reduce your electricity billfurther without resorting to switching off all your appliances. Indeed, can else anything be done?

Bright Green Energy firmly believes that 100% of the electricity generated by your solar PV system should be consumed and not exported. If you are out at work all day and you discover that you are exporting more electricity that you would like then you can install a device to switch your immersion heater on & off dependent on the power produced by the solar panels. This approach is simple and easy to achieve regardless of whether you receive the FIT payments or not.

However, what if you simply cannot achieve 100% consumption and are still exporting?

Exporting unused electricity really does not make financial sense whatsoever. If you can't use it then what else can you do with it? The simple answer is to store the electricity in deep-cycle batteries and use it when you want.

Demand for battery storage systems to compliment grid-connected solar PV systems will become increasingly popular in the UK. Demand is rising for three main reasons:

1) Concern about ever increasing energy price rises. Ofgem have forecasted that energy prices will rise at least 5% per annum for the foreseeable future. That should be read as: expected to rise by a minimum of 5% per year, every year. Recent price hikes indicate that 5% is very conservative;

2) Concern over reliability of supply. The UK energy generation sector is in crisis. Lack of investment, coupled with aging power stations means that security and reliability of supply is in doubt. If you already live in a rural area then you will probably already have experienced power cuts though not on a regular or predictable basis. Indications are that the situation will continue to get worse.

3) Enhanced return from your Feed-in-Tariff. If you have installed a solar PV system then adding batteries to your solar system makes perfect, practical and financial sense. Practical because energy can be stored in batteries and used when required; financial because it is pointless to export any energy if it is not consumed. Why not use the energy generated to charge batteries?

Adding batteries to your solar PV system offers a wide range of advantages:

1. Reduce export. Charge your batteries "free" during the day.

2. Reduce your electricity bill still further by running appliances from batteries during the night when your solar PV system is not working.

3. Secure power supply to vital appliances. In the event of a power cut keep your Fridge/Freezer operating.

4. Batteries can be added at any time to any existing solar PV system.

Background - you already have a solar PV system installed.

Battery storage can be added to solar PV systems in three main ways:

1. Manual Extension

Implementation: achieved through the addition of batteries,battery charger, inverter (or inverter charger), separate fuse-board, if required, and manual changeover switch.

2a) Inverter Extension - achieved through addition of new and separate battery inverter system, such as SMA’s Sunny Backup.

2b) Inverter Extension - achieved through addition of battery inverter system and solar switch. Victron being a good example.

3) Inverter with in-built battery support. - Ideal for new solar PV systems as inverter supports direct battery connection. Can be installed as a replacement inverter for existing solar PV inverter.

Let's look at the options in more detail

Scenario 1 - Manual Extension

The cheapest way of adding battery support to an existing solar PV system is to use a simple battery charger, inverter, (or inverter charger) manual changeover switch and new separate fuse-board, if required. The decision to install a separate fuse-board should be based on sensible approach to home wiring already in place.

This simple and easy to install system means that the batteries can be charged during the day - (charged free from the solar PV system) and then used at night. This system is designed for low power use and is operated manually. Operation depends upon switching over to battery power after solar PV system shuts down at night.

Battery size (storage capacity) depends upon load demand but a minimum of 2 x 220Ah AGM batteries should be considered to be of practical use though 4 x 220Ah is much more practical.

A qualified electrician is required to install the system.

Note: this small battery system will be able to run reasonable loads but will not power an entire house.

Note: load analysis is important as batteries are affected by how often and how deep they are cycled.

Anticipated cost: £2500 depending on the size of components used. Cost does not include electrical installation.

Scenario 2 - Inverter Extension

Some inverter manufacturers such as SMA already produce a battery backup inverter that is installed as an add-on to the solar PV system. The Sunny Backup will automatically switch to battery backup with no effect on the efficiency of the solar PV system and the batteries can be utilised to power appliances during night time hours.

The Sunny Backup should be used in conjunction with the SMA Meter Box. The Meter Box ensures that maximum self-consumption takes place during the night. This results in greater independence from the electricity grid and reduces the amount of power drawn from the grid.

The result? Increased efficiency and effectiveness of self-consumption systems as well as increased efficiency of the battery.

Capacities from 2.2 kW to 100 kW available


Sunny Backup Inverter, 2.2kW, 24V, 0-90A charge Inc. remote: £call

Sunny Backup Inverter, 5.0kW, 48V, 0-100A charger: £call

Please note: The Sunny Backup is not currently certified for use in the UK

Scenario - Inverters with in-built battery support

Some inverter manufacturers offer built-in battery support. A good example is the Nedap PowerRouter.

The PowerRouter is a modular smart inverter with an integrated battery manager, which can be used for on grid or off grid applications. The inverter is designed to maximise self-use, in other words the available solar electricity can be “routed” directly to the loads or stored in batteries for later use.

The Nedap approach to “routing” allows the batteries to be correctly cycled thus extending their life. Just like the Sunny Portal, the PowerRouter can be connected directly to the internet via the web portal: my

The PowerRouter is available in 3.0 kW, 3.7 kW and 5.0 kW versions and can easily be expanded with batteries for storing energy.

Please don't hesitate to get in touch if we can be of any further help.

CALL US ON: 01959 570 728
Bright Green Energy