FINANCE & ECONOMICS

Off-Grid: What Does This Really Mean?

Craig Herbst, Technical Director, South Africa

19 September 2019

Going truly “off-grid” can be an expensive exercise, as you need to cater for the worst-case scenarios of weather and energy consumption. Even if budget isn’t a constraint, your aspirations may be tempered by available roof space – a meaningful off-grid solar system requires significant rooftop real estate.

Becoming “grid neutral”, where you rely on Eskom for peak usage and periods of bad weather, is much easier to achieve. This would often be achieved through a phased approach, first ensuring that you have made your home as energy-efficient as possible by replacing outdated, energy-hungry power appliances and equipment with the most efficient alternatives, and then building your power system, either in one go or in steps as budget allows or circumstances dictate. For example, one may opt to invest in a battery backup system if power security is a pressing issue, and add solar panels at a later stage. It is of absolute importance though, that the end goal is understood, to ensure that the right components are installed from the beginning.

Solar panels have now become very affordable, and the cost of a good inverter also won’t break the bank. The key to becoming substantially grid-independent for residential homes is battery storage, as we use most of our electricity in the early morning, and evening, and not while our solar systems are producing most of their energy.
Until recently, this was not economically viable. Cheaper “deep cycle” lead acid batteries have very short lives when cycled deeply or frequently, and the best lead acid batteries (e.g. Hoppecke’s OPzS batteries) are prohibitively expensive, require maintenance and a lot of space in a secure, ventilated room.

 

Much of this has changed as Lithium Ion battery technology – and particularly LiFePO4 – has become much more affordable.
These batteries offer very long lives (more than 3000 cycles / 10 years, with warranties to match), very deep discharge, small footprint and very high round-trip charge-discharge efficiency, and the ability to scale the battery over time.
A further exciting development is the (limited) availability of “2nd Life” LiFePO4 batteries (see other articles on this page explaining the 2nd Life concept), which enhances the Lithium battery value proposition even further.

“The key to becoming substantially grid-independent for residential homes is battery storage, as we use most of our electricity in the early morning, and evening, and not while our solar systems are producing most of their energy.”

So, where does this leave us? Well, becoming largely grid-independent is no longer a pipe dream,- my own home is good example of this:
I have a medium/large (~400sqm) family home with pool, koi pond, air conditioning and the usual goodies. My wife runs her business from home, and my daughter is a student, so there are various computers, printers, etc in use. My grid electricity consumption for February 2019, thanks to a full week of rain, was 50kWh. Under most conditions, I “buy” less than 1kWh of grid electricity per day.

The house makes use of solar water heating, with a 7kWp solar system providing for the electric requirement. I use a 10kWh 2nd Life Lithium battery for storage, which is just enough for the summer part of the year, but which will be left a little wanting as we move into the longer winter nights.

Follow this link to view my monitoring dashboard, which gives real-time information on the performance of my power system:

GreenHouse Monitoring

A system like this costs R160k (basic) to R190k inc VAT, depending on options.

Watch this space for a write-up on Balance of System costs, and why it’s important not to cut corners on system spec.

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