Battery Storage Options
SMA Sunny Boy Storage 2.5
Connects to an existing Solar PV installation. It connects to the AC bus and contains an inverter. It charges and discharges a high voltage DC battery, 120V-500V, at the maximum rate of 2.5kW.
An LG Chem Li-Ion comes in 7 or 9.8kWh 400V battery packs.
Cost: 10kWh £6.7k; 10 year warranty
SMA Integrated Storage System
SMA Sunny Boy Smart Energy is the heart of the system. It is a Sunny Boy with attached 2kWh Li-Ion battery storage unit. An SMA energy meter is required. An SMA Sunny Home Manager is recommended which can control remote switches and provide detailed home energy consumption information. Models to support either 3.6 or 5.0 kW solar array. AC bus connect.
Cost: 2kWh 5kWarray, £4.5k; warranty ?
SMA Flexible Storage System
SMA Sunny Island inverter (SI-3.0M-11) 2.2kW. LG Chem 6.5kWh Li-Ion battery storage unit. An SMA energy meter is required. An SMA Sunny Home Manager is included which can control remote switches and provide detailed home energy consumption information. AC bus connect.
Cost: 6.5kWh, £6.3k; warranty ?
Mercedes Energy Storage & SMA Sunny Island Inverter
Mercedes have moved into the home energy storage market. They provide Li-Ion battery in floor standing units, each stack takes up to 4 x 2kWh units, weighing in at 32kg each unit. Units cost just over £1k each. They are designed to work with SMA equipment and are being rolled out using Wind & Sun as a distributor (not necessarily exclusive). Wind & Sun provide a kit with 2 units of storage and an SMA Sunny Island 2.2kW (SI-3.0M-11) inverter. Includes a Sunny Island Remote Control and a Sunny Home Manager.
Cost: 5kWh storage, £5.5k; 10kWh storage, £7.5k. 20kWh storage £12.5k. warranty ?
Victron, Salt Water Battery
Victron also do a system, but max storage is 6kWh.It uses a salt water battery.
Cost: 5kWh storage, £5.2k; warranty ?
Tesla Power Wall 2
The Powerwall 2 is recently released in Australia, though not available in the UK yet (Sept 2017) and the price is not announced. Li-Ion battery storage in 10kWh chunks, extendable many times. Only new batteries used.
Assumptions: Connects to the AC bus without interface to existing system; Has it's own built in inverter. Must have an energy meter plugged somewhere into the existing system.
Cost: 10kWh , £6-7k ? ; 10 year warranty.
Why Battery Storage?
Pros but mostly Cons
A 10kWh battery storage system makes energy available when your energy generation stops, typically at night or on a dull day for solar. It will save you 10 units of electricity being purchased from the grid which could be £1.50 with a full discharge of the batteries. It's cheaper to buy it from the grid! It is useful if you need backup when the grid goes down, but needs to be aimed at essential items like fridges, lights, but won't touch that 9kW electric shower unit or the 3kW oven. It might allow you to have a shave, charge the iPhone or do your hair in an emergency. Most users will not benefit significantly from a battery storage system.
Battery storage will only capture, in this example, the 10kWh it is capable of storing, the rest going into the grid as usual.
You can capture far more of your surplus energy currently flowing into the grid. The challenge is to find a process that has a greater storage capacity at a lower cost. Yes, you can increase the size of your batteries, but at over £1000 per 2kWh it is expensive. How about capturing the surplus energy as heat? BUT: it won't come back as electricity!
Hot Water Cylinder
Maybe you have an immersion heater in your hot water system, though probably not if you run on gas! It is possible to divert your surplus generated energy into your hot water until it is up to temperature. This gives an immediate benefit, requiring investment in a black box of tricks (it's actually white) costing around £500 for the all singing all dancing version, which reads the flow of energy into the grid and diverts most of it into heating the water. It works the same way as most laptop battery chargers do these days using PWM - pulse width modulation, basically sending pulses of energy to the immersion heater, reducing the amount of energy going into the grid. The capacity of the system can be enhanced by adding an extra water tank, costing whatever your local plumber thinks appropriate to your system, but for those capable of doing it themselves, it can be very cost effective.
Underfloor Heating (Water)
Heat is often lost when the wind is blowing, so this can be an ideal solution when your surplus energy is from a wind turbine. Underfloor heating has a high storage capacity and uses low grade heat as its source of energy. A typical underfloor heating system may use a flow heater, say 6kW, 9kW, basically comprising a collection of immersion heaters arranged in a copper mass around a tube of water flowing through its core. There is a separate pump to ensure water always flows when the heater elements are active. Again, a white 'black box' is installed to divert the surplus energy from its grid journey (£500) into the underfloor heating system. This can be a little more complicated, requiring mods to the flow heater, allowing the surplus energy to go into the floor whilst allowing extra heat to be bought in from the grid when typically required on a cold winter's day.
Underfloor Heating (Electric)
Currently under investigation... more to come.
Electrolysis of Water
Why not make your own hydrogen and oxygen and power a car... we have absolutely NO experience of this but love the idea...
Make Sea Salt
One of our customers' loves this idea, use all the spare energy to evaporate salt water and get your own sea salt full of minerals and iodine and... And why not?