Off-grid design – consider the variables carefully

One Step Off The Grid

Going off-grid is a big step. It requires careful consideration, good design and engaged users.

Recently trailblazer Michael Mobbs wrote about his own experience, and the unexpected challenges he has faced.

Having supplied equipment to Mobbs in 2015, Alpha-ESS was particularly interested in drawing out lessons for others looking to ‘cut the wire’.

Living Off-Grid is a Mindset

When you are effectively the power customer and the power provider, energy comes into sharp focus.

The first step we always advise our customers is to become an ‘energy bloodhound’.  Cut energy use any way you can.

Lesion 1: Reduce your load, and plan to use energy when it is available.  Also design essential circuits that still operate when power is scarce.

Same Solar Output?

Mobbs is right to point out that in an off-grid situation, when your battery is full and there is not much power being used in the home, the excess solar energy has no-where to go, so is curtailed by the inverter.

Lesson 2: Depending on the design, an off-grid solution may yield less solar energy than a grid connected system (that exports excess solar energy to the grid regardless of local loads).

System design is critical.  Getting the right sizing of both solar and storage will reduce this problem.

A System Bug?

Mobbs also says there is a bug causing the system to trip.

In this case our measurements show that large concurrent loads are shutting the 5kW inverter down.

The size of the inverter puts a ceiling on the amount of energy that can be drawn at any one time.

In Mobbs’ case the inverter has an absolute capacity of 5kW.  This in turn means running power hungry devices concurrently may trip the system. Increasing the size of the inverter may help.

Lesson 3: Bump up your inverter even if you have cut your load, and avoid using big loads such as water pumps, irons, washing machines and microwaves all at the same time.

Expect the Unexpected – Back up is Smart

Australia’s weather is changing as extreme and unusual weather events become more commonplace.  A system designed on assumptions of the ‘average pattern’ is fine – until it isn’t.

Battery storage is finite, so you either have to design for the ‘outlier events’ (and get a battery that is oversized for the rest of the time), or have back up for exceptional circumstances.

Most off-grid customers will design in a small emergency generator for that backup.  Mobbs did not want a generator, and that is fine, but that will lead to beefing up your storage capacity.

Lesson 2: Think about your options in managing outlier weather events and have a plan.

Our Solution

Going off-grid takes careful planning and requires expert advice. Alpha-ESS are experts in this field.

Given all of the variables, our advice to others in a similar situation is:

Monitor and model the variables, we can do this for you, to come up with an ideal design.

Get a backup generator (only for extreme events). It will be much cheaper than getting a larger battery bank to increase the days of autonomy.

Potentially look at upgrading to a larger inverter, and adding some more solar PV. We have other inverters in the range that might suit the purpose.

Make the most of sunny days and target times when your battery is full to run appliances.

Alpha-ESS stands by our customers.  We are very happy to measure all of Michael Mobbs’ unique energy flows, and provide further design advice at no charge.

Dong Lin, Managing Director – Alpha ESS Australia

This article was originally published on RenewEconomy’s sister site, One Step Off The Grid, which focuses on customer experience and ambitions with distributed generation. To sign up to One Step’s free weekly newsletter, please click here.