How to save money with solar while Eskom suspends load-shedding

While there has been no load-shedding in over two weeks, solar power system users can still ensure their investment is providing some returns by using self-generated power to reduce their electricity bills.

The first way to get the most out of your solar power system is to ensure you shift as much of your usage as possible to the daytime.

If you have an entry-level 5kWh battery, chances are that even a small four-panel array consisting of 460W units will be able to charge it to full with around three to four hours of sunshine.

All the additional energy it could provide while the sun is shining is wasted while you are away from home.

Although you could upgrade your system with an additional battery use of the extra energy, these are very expensive at about R18,000–R20,000 for a 5kWh unit.

People with bidirectional meters can benefit from excess generation by pushing their additional electricity back into the grid when they don’t require it.

However, these meters cost around R10,000 or higher, and feed-in tariffs are generally much lower than consumption tariffs.

Therefore, it might take a long time for the cost of the meter to be amortised with excess energy feed-in.

Shift your loads to the day

Instead, setting certain appliances to run during the day rather than the night will ensure as little as possible excess solar goes to waste.

First and foremost should be electric geysers, which can consume nearly half of a household’s electricity.

By putting your geyser on a smart switch or timer, with prices starting from around R400–R500, you can configure it to heat water late in the morning or early afternoon.

This can be followed up with a small top-up later in the afternoon to ensure the geyser is at its correct temperature for evening usage.

Ideally, you should use a switch that can be controlled with a mobile app in cases where the solar’s optimal production shifts around.

If you have a large household that uses copious amounts of water in the evenings, the geyser might need an additional top-up with battery or grid power, or a combination of the two.

However, if you use as much of the solar power and ambient heat of the day to get the geyser’s temperature up, your overall consumption during these periods should be lower than when you allow the geyser to heat up at any time.

Remember that your geyser can also effectively act as a type of supplementary battery due to its ability to hold heat energy over a long period.

While setting a geyser’s maximum temperature lower can reduce consumption, using a higher but safe target temperature could be beneficial in ensuring you still have hot water many hours after it is switched off.

A timer could also be of benefit if you use a solar geyser, as you can choose when to supplement its element with grid power.

Another appliance that is notoriously power-hungry and will benefit from a smart switch to shift much of its usage to the day is a pool pump.

Some appliances — even older washing machines — won’t require adding a smart switch or timer but come with delayed starting or ending.

This allows you to set them to only turn a few hours after leaving for work, or to complete their cycle just before you arrive home.

The second important habit you should develop is to consume as much of your generated battery power as safely as possible.

Most modern lithium-ion batteries can last for over 5,000 cycles, so even if you consume their full capacity twice a day, they will retain 80% of their original storage after nearly seven years.

Of course, you should consider that Eskom could implement load-shedding at any time, and you don’t want insufficient battery capacity during an outage.

For this reason, it is good practice to leave a bit of breathing room between your absolute battery cutoff that will only apply when there is no grid power and a minimum for when grid power is available.

To determine a safe gap, calculate how much power you typically consume in a load-shedding slot.

For example, drawing an average of 500W per hour would consume about 1,000Wh over the typical two-hour load-shedding period.

On a 5kWh battery, this is equal to around 20% of the capacity.

Therefore, if your rated depth-of-discharge is the typical 80%, you should set the minimum discharge level with grid power to 40% while your absolute battery cutoff is 20%.

The 20% gap between these numbers will ensure that you always have sufficient battery power available for general consumption when load-shedding begins.

If you have a larger 10kWh battery and the same level of consumption, the gap lowers to 10% of the capacity.

However, if Eskom announces load-shedding from stage 5 and above, some consumers in areas with 4-hour load-shedding slots should revise their percentage gaps to support power supply over this longer period.

Use the grid sparingly

Lastly, you should make minimal use of grid power. This can be done without cutting down on your overall consumption.

There are two ways to achieve this, starting with not switching on enough appliances to exceed your inverter’s capacity.

This will be more of an issue for those households with the conventional 5kW entry-level hybrid inverter than those with an 8kW or 10kW model.

While the inverter won’t trip if you exceed its maximum capacity while there is no load-shedding, it will draw additional power from the grid.

Instead of turning on your airfryer, microwave, and kettle at the same time, run them in sequence whenever possible.

Your overall usage remains unchanged, but you will avoid grid usage due to inverter capacity constraints.

Secondly, you can set the battery to only charge from the grid overnight and limit its charge level to a certain percentage sufficient for your morning consumption before the solar panels start producing electricity and recharging your battery from the sun.

For example, if you are only at home for two hours from waking up to leaving for work, you will only need 1,000Wh of power — 20% on a 5kWh battery or 10% on 10kWh unit.