SMA Sunny Boy Smart Energy Battery Inverter: Payback in less than 10 years?
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.
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.
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.
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.
Contact us for a free quotation or If you have any questions please get in touch:
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.
By puchasing from Solar Energy Alliance Ltd. you agree to our Terms & Conditions of Sale