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SMA-solar-PV-inverter-with-battery-storageSMA Sunny Boy Smart Energy Battery Inverter: Payback in less than 10 years?
SMA have just released their new Smart Home energy storage system.  The Smart Home system has a modular design, to ensure that the solar power you produce is used in the best possible way and, as an option, stored in batteries.  As energy costs continue to rise, it is becoming mroe important to consume and store the energy you generate, but do not instantly consume.  This means that a large portion of your energy needs can be covered and offers greater independence and protection from ever rising energy costs.  The simple fact of the matter is that you should consume all the energy you generate or store it in batteries.  The greater the amount of energy that i self-consumed, the lower your electricity bill and the greater the returns from feed-in tariffs and your investment.
The coming years will see home battery storage become the essential add-on to solar PV systems. Batteries have been used for a long time with off-grid solar systems, but have only recently begun to be used with grid-connected systems. SMA's new Sunny Boy Smart Energy Battery Inverter is now available in the UK for the first time and could well be the solution for your customer's battery storage requirements.
The advantages of having a battery system in the house are multiple, primarily the end-customer likes the idea that they can keep some of the energy generated during the day to use it when they need it, during the evening. This increase in self-consumption is valuable, but in fact the advantages of home battery systems go beyond that and in the UK can even mean that the payback time of installing such a system in the house, when combined with a sufficiently large PV array, can bring payback times of less than 10 years.

AC Coupled vs DC Coupled
There are two types of battery systems combined with solar PV; the principle difference concerns the 'Bus' the solar array and the battery charging are connected with. 
An AC Coupled system, such as the SMA Sunny Island, is essentially an add-on to an ordinary PV system. The PV modules and SMA inverter are sized and installed as normal on the house, and then an additional charger/inverter unit such as the Sunny Island, can be wired into a circuit in the house. Such a system is called AC Coupled because there is an AC bus in-between the solar inverter and the battery inverter. The advantage of such a system is that it can be retrofitted onto existing installations and the installer can be flexible about the technology and size of battery bank they are using.
The second type of battery system is a DC Coupled system. With a DC Coupled system using an SMA Smart Energy inverter, the batteries are connected on the DC side of the inverter and are charged with a charge controller unit. Excess energy which cannot be used by the inverter is stored in the battery for later use. This system is ideal for new installations and installation is far simpler than with AC Coupled systems: You simply clip the battery into the side of the inverter and you are ready.
SMA Smart Energy AC Coupled
 AC Coupled Battery Storage – The Sunny Island Battery charger unit is connected onto the AC side of the PV system. The Sunny Boy inverter converters Solar DC to AC, while the Sunny Island converts battery DC to AC.

SMA DC Coupled Smart Energy Inverter System
DC Coupled Battery storage – PV modules charge batteries directly on DC bus, one inverter converts both solar and battery energy to AC.


Increased self-consumption

Both AC and DC Coupled systems give the advantage of increased self-consumption. How much electricity can be saved depends a lot on the load profile and behaviour of people living in the property as well as the size of the PV array and battery. There may be days that the battery does not fully charge or discharge.

For example on an overcast winter day there might not be enough generation to fully charge the battery, or on some days the household might not use electricity in the evenings and so the energy is simply stored for the next day. But the theoretical maximum of any savings from a battery system are the capacity of the battery itself, so for example a 2.2 kWh battery like the Sunny Boy SE can save a maximum of 2.2 units of electricity every day, roughly 30 pence at current electricity prices, or £110 a year. Currently, this increased self-consumption by itself would not give very fast payback times for a battery system, however there is an additional, more important benefit.

Installing 6 kW arrays on a 3.6 kW inverter

The main advantage of home battery systems, but only DC coupled battery systems, is the fact that the inverter can be massively undersized with respect to the PV array. On SMA's Sunny Design Web you can configure a 'Self-Consumption' system (a system with battery storage) and configure a 6 kW array.

The inverter that configures is the 3600-SE, a 16 Amp, G83/2 compliant, 3.6 kW inverter, splitting the array over 2 power point trackers. The inverter is almost half the size of the PV array in terms of power rating. However, because of the battery being on the DC side of the array, this is not a problem. The peak energy is stored in the battery and released later.

During the day, the energy coming from a PV array is shaped like a curve. On a 6 kW array, for most of the day the production from the array is not even at 3.6 kW, so the inverter can simply convert all the energy and send it to the house. During some parts of the year such as winter, the peak might never reach 3.6 kW, so the inverter would never clip. However, a 6 kW array is very large compared to the inverter, and so on sunny days it is quite likely the power curve will exceed 3.6 kW during the middle of the day. In that moment, the inverter works at full capacity to convert what it can, while the additional energy is stored in the battery. The energy is not ‘clipped’ or wasted, and instead it is released later on in the day.

An example of the behaviour of Smart Energy Inverters can be seen on theSMA Sunny Portal.

SMA Smart Energy Behaviour 

SMA Smart Energy Flow


The performance of a 5.2 kW array on a summer day. With a battery, an inverter can be undersized more than normal, because some energy that would have been clipped is instead stored in the battery for later use.


Less than 10 year payback

According to Sunny Design Web, this system configuration generates 5,315 kWh a year in London, which using generation tariff of 13.03p and export tariff of 4.77p (50% deemed export), leads to an income from the tariff of £819.30 every year.

Having a battery and home energy manager of course increases self-consumption, but the array is generating so much electricity that in fact a household might actually struggle to find use for all the power produced. In the same Sunny Design Web, different load profiles can be chosen. Because the array is so large, self-consumption of the array will still hover around the 40-50% mark. (A more energy hungry household will have higher self-consumption, but an energy efficient household will have higher self-sufficiency).

In the case below, the household has been buying 6,200 units of electricity every year and so the system could offset roughly 50% of that or 2,723.33 kWh. Taking electricity prices of 14 pence a unit, we can modestly assume a saving of £381.26 a year, irrespective of any electricity price inflation.

SMA Smart Energy 04

The total yearly benefit of such a system is therefore £819.30 in tariffs and £381.26 in electricity savings, for a total of £1,200 every year. Inflation in electricity prices will increase the benefit, as will any attempts by the household to increase self-consumption further.

It is reasonable to expect the entire system of modules, inverter and battery could be installed for less than £12,000, meaning payback time could be less than 10 years. 

Supporting the grid

The inverter only produces 16A on a single phase and therefore it can be fitted under G83/2 regulations and conform without having to incur the potentially difficult costs of upgrading the grid or even being refused a connection where the grid has reached capacity. Such a battery system is advantageous for the grid, because it flattens the generation peak of the system. On a sunny day it is broad shouldered and flat at the top, giving greater support to the grid in the mornings and evenings and a constant, steady contribution to the grid during the middle of the day.

SMA Smart Energy Potential Export Profile
Potential Generation Profile of 6 kW array with SMA Smart Energy on a clear summer day showing a constant 3.6 kW power output across the middle part of the day.

Replacing the battery

Batteries have a finite lifetime. The SMA Lithium-Ion battery has an expected lifetime of 10 years, with a warranty of 7 years, meaning that by the time the system has reached the point of paying for itself, the battery will be reaching the end of its life. However, when the time comes to replace the battery, it will be the only component that needs replacing, not the modules, nor the inverter itself. A new battery can simply be clipped into the side of the SMA inverter so installation time is a simple site visit. However this will slightly extend the payback time, increasing the initial system cost by whatever a Lithium-Ion battery will cost in 10 year's time.

So in conclusion...

The SMA Smart Energy inverter gives birth to a new system concept that PV installers can take to customers. It is possible now to install larger 6 kW systems on an undersized, G83/2 compliant, 3.6 kW inverter and battery. The array can be split over 2 MPPT trackers if required. Such a system is a larger up-front capital cost, but allows for greater self-sufficiency and an overall greater return on investment. It is also an architecture that offers greater support to the grid by ironing out production spikes.
Our team of solar PV engineers are available to discuss any aspect of specifying and installing an SMA's Sunny Boy Smart Energy Battery Inverter. Feel free to give them a call on 01502515532 
Some important information:
Due to battery storage and transportation restrictions the Sunny Boy 3600SE-10 Smart Energy Inverter is not held in stock, all orders are delivered direct from SMA's production facility in Germany.
You should allow for a minimum of two weeks delivery time, ideally direct to the installation site to minimise further transportation.
Download the ‘SMA Smart Energy Battery Pack Transport and Storage Information’ document from the link below and call our sales team on 01502 515532 for more information ahead of placing your order.

Related Downloads

SMA Sunny Boy 3600 5000 Battery Storage Inverter Datasheet

SMA Smart Energy Battery Pack Transport and Storage Information

SMA Smart Energy Battery Pack Warranty Conditions

SMA Smart Energy Battery Pack Replacement Info

SMA Smart Energy Battery Pack Special Liability and Conditions Information

SMA Smart Energy Battery Pack Service Manual

SMA Smart Energy Battery Pack Additional Information



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Solar Energy Alliance Ltd.
Tel: 01502 515532
8/9 Battery Green Road, Lowestoft, Suffolk, NR32 1DE

We do not use sales staff, your site survey will be carried out by our Energy Performance Assessor who will give you advice, talk you through your options, take measurements and asses roof suitability or any shading issues. He will also be able to give advice about (EPCs) Energy Performance Certificates. He will then compile a detailed quotation which will be posted or emailed to you, we will not try to sell you a system at your home and we do not use high pressure sales. We believe in presenting information, answering questions and leaving you to make up your own mind.


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