Residential Solar Storage Systems - Comparison

Introduction

We offer five different residential storage systems, as follows:

• Tesla Powerwall 3
• Tesla Powerwall 2
  
• MyEnergi libbi
• GivEnergy domestic and commercial systems (domestic - Modular + All in One)
  
• Victron Energy Storage Systems (Victron + BYD / Pylontech batteries)
  
  
  

We have presented a comparison of our offering in the tables below. You can also download this comparison as a PDF.

All storage systems consist of a charger and battery. The Powerwall 2, Powerwall 3, GivEnergy All-in-One and libbi are 'all-in-one' systems, with the charger and battery combined into one unit. The GivEnergy modular and Victron systems have separate charger and battery units, making them less compact and aesthetically pleasing, but more 'modular' with greater design flexibility.

There is no 'one-size-fits-all' solution. The right choice for you will depend on your budget, space availability, house usage, solar output, and whether you want a back-up in a power cut or not. You may not want cobalt in your battery, in which case the Powerwall 2 is not for you.

Storage Cost / Benefit

Installing storage affords the following potential benefits:

• increased on-site use of solar generation – with a correctly sized solar energy storage system, 65%-80% of solar generation should be used on site, thus reducing the owner’s electricity bill;
• emergency power supply in a power cut;
• the ability to buy electricity off-peak and store it for use at peak;
• the potential to increase on site power output by around 20% (useful when fast-charging an electric vehicle);
• potential to access future opportunities including the export and sale of electricity at peak charge times, and the provision of grid balancing services.

A re-chargeable battery essentially consists of thousands of 'kWh storage slots', charging one kWh by the grid or excess solar, and then discharging one kWh (minus about 10% losses). In economic terms, one of the key questions is - how much does each kWh storage slot cost? The answer depends on the chemistry, since lithium ferro phospate (LFP) typically offers twice as many 'lifecycles' or storage slots per kWh battery capacity than lithium manganese cobalt (LMNC). With the correctly sized system, the lifetime cost per kWh of stored electricity is around  9p per kWh for LFP (all our batteries except the Powerwall) and around 16p per kWh for lithium manganese cobalt (Powerwall). This compares to an average domestic grid cost of around 22.36p per kWh. 

The lifetime cost per kWh typically assumes an expected lifetime of between 10 years and 25 years (or between 4,000 lifecycles (LMNC) and 10,000 lifecycles (LFP), and whilst the overall economic case is favourable, solar energy storage should undoubtedly be seen as a long-term investment. 

System Comparison: Rough Cost, Use, Components and Sizing

(1) Lithium ferro phosphate is a superior chemistry to lithium manganese cobalt for two reasons:
a) It offers many more lifecycles (one lifecycle being a round-trip in and out of a kWh) – i.e. many more storage slots. Typically 6,000 – 10,000 lifecycles for lithium ferro 
phosphate, compared to 4,500 for lithium manganese cobalt.
b) There are reports of possible child labour issues associated with cobalt mining. Therefore lithium ferro phosphate is generally preferred.
(2) Emergency Loads require a second distribution board separating emergency loads from non-emergency loads. Whole House does not require this; however in a power-cut 
usage will be limited to the power output of the storage system. Setting up a second distribution board with loads that will function in a power cut is best practice (and 
good discipline!) but the additional electrical work does increase upfront cost.
(3) Solar PV panels generate DC electricity, and batteries charge and discharge with a DC current. DC coupled storage systems allow you to combine the solar PV and battery 
storage into one inverter; AC coupled storage systems do not. DC coupled systems are ideal for new or extension PV installs. They are most efficient, keeping AC/DC 
conversion losses to a minimum, and they also reduce the upfront system cost and the on-going maintenance cost. AC coupled storage systems are best used when retrofitting storage to an existing solar system. Flexible (AC and DC Coupled options) systems allow for both AC and DC coupled solar. They offer the best of both worlds.
(4) 5kW can be limited to 3.6kW if required by DNO operator (SSE etc), 
(5) Reduced to 2.5kW for emergency loads in a power-cut. Further limited in a power cut to 1.3kW with 2.6kWh battery. 

System Comparison: Normal Operating Modes / Functionality in a power cut (Islanded Mode)

It is important to know what happens in a power cut. Does the storage system work? Does the solar PV still work? Will everything in the house work ('Whole House' back up), or just pre-defined 'Emergency' loads connected to a separate board?

Note that all of this functionality is subject to prior approval from the network operator (SSE, Western Power etc).

System Comparison: Monitoring, installation and warranty

System Comparison: Three phase (400V) grid connections

If you have a normal single phase (230V) grid connection, ignore this section.

With a three phase grid connection, you have a choice:

• connect storage to one of your three phases only, in which case only loads and single phase PV inverters connected on this phase will work in a power cut; or
• connect storage to all three phases, which is more expensive, but, with Victron (or GivEnergy's commercial three phase storage units), will enable you to back-up all three phases.
  
  

  	Tesla Powerwall 3	Tesla Powerwall 2	MyEnergi libbi	GivEnergy Modular	GivEnergy All-in-One	Victron + BYD/Pylontech
  Can the system be installed on a three phase connection?	Yes, one Powerwall 3 per phase, plus 3 expansion packs per Powerwall 3 unit. Power cut protection capability on three phase connection unknown.	Yes, up to three Powerwall 2's per phase. Note that ONLY one phase will work in a power cut.	Not recommended. But is technically possible, up to three libbi's per phase.	Not recommended. Use GivPCS-30, GivPCS-50, GivPCS-100 instead (GivEnergy’s three phase systems).	Not recommended. But is technically possible, up to three All in One's per phase.	Yes, typically up to four or five units can be installed per phase.
  Will the system work in a power cut?	TBC Contact Spirit Energy for latest information.	Only one phase can work in a power cut, even if Powerwall 2's are installed on more than one phase.  Three phase loads and three phase solar PV will not work in a power cut.	N/A	N/A	N/A	Yes, any phase to which a Victron unit is installed will work in a power cut. Three phase loads and solar PV will work if Victron units are installed on every phase.