Solar Power Self Consumption

What is solar power self-consumption?

The concept of solar power self-consumption applies to grid connected solar power systems.  When your solar panels are producing power you will either be exporting the power to the grid or you will be using the power for electrical appliances within your home or business.  Self-consumption is when you use solar power directly for your electrical appliances.

SMA Explains what solar power self-consumption is;

Why should you aim for solar power self-consumption?

Off-setting your electricity bill with solar power is more valuable than exporting your power to the grid, and this is why self-consumption is ideal.

By using solar power directly you are eliminating the need to buy power from the grid, which is approximately 30¢ per kWh. If you were to export that power to the grid energy companies will only get paid around 8¢/kWh for your power, which is not as valuable as using the power yourself.

Power consumption vs. solar power generation

In a typical New Zealand household, most energy / power demand occurs at the start of the day when people are having breakfast, getting ready for work and at the end of the day when dinner is made, lights and heaters are turned on.  In contrast, the majority of solar power generation happens around the middle of the day, as seen in the bell curve below.

Solar Power Self Consumption with Typical Energy Demand Graph

The typical power consumption and generation graph above shows very little self-consumption, i.e. solar power used directly (shown in the pink shading).  It shows that there is a lot of power being drawn from the grid in the morning and the evening at the expensive energy retailer price of around 30¢/kWh (orange shading).  There is also a lot of solar power being exported to the grid at the low rate of around 8¢/kWh (dark blue shading).

Note:  If you have panels on an east facing roof you will generate more power before mid-day as show by the blue dotted bell curve.  Likewise with panels on a west facing roof, they will generate more power in the afternoon.  This factor will change the dynamics of self-consumption versus exporting the solar power.

The aim is to get more self-consumption happening so we end up with something similar to the graph below.

Increase Solar Power Self Consumption Graph

Here's an example of a scenario that could achieve higher solar self-consumption as pictured in the graph above; the dishwasher could be programmed to turn on at 10am, the washing machine is programmed to turn on at 12pm as well as a robotic vacuum.  At 2.30 pm the heat pump could be timed to turn on then to start warming or cooling the house to achieve the perfect temperature for when you arrive home.

How do you achieve solar self-consumption when you are at home during the day?

It's really easy to achieve more solar self-consumption if you are often at home during the day.  If you have monitoring on your solar power system you will be able to see when solar is being produced and you can aim to turn on appliances at that time, i.e. the vacuuming, ironing, heating.

Charging electric vehicles is also a very good option to use up solar power.  At present you can buy a Nissan Leaf (EV) cheaper than what you can buy a home storage system for with the same size battery, so buying a Nissan Leaf makes a lot of sense. You can now buy a Nissan Leaf second hand on trade me starting at $20,000.  The cars come with wall chargers so you just need to plug it into the wall, so it will use any solar power if available.  You can also buy fast charging stations you can install in your garage, the Delta EV Charger is an example of one available in New Zealand.

How do you achieve solar self-consumption when you're not home?

Well here is some good news; there is now automated ways to achieve higher solar power self-consumption.

You can use appliances with delayed start times which can help you use solar power directly, for example setting your dishwasher to turn on at 11am and then your washing machine at 1pm.  Turning on a heat pump at 3pm to start either cooling or heating the house before you get home from work is another good option (starting early means the heat pump won't use as much energy in the evening to achieve a comfortable temperature).  Robotic vacuum technology has now come a long way and is a great alternative from conventional vacumming.  I personally own a Neato XV, I would highly recommend it to anyone. You can combine it with a appliance timer so the vacuum's battery only charges during the middle of the day. 

Plug in appliance timers come in a wide range of functionality.  The HPM Plug in Digial Timer can be brought from Bunnings at $13.88, you can schedule your appliance to turn on and off at different times of the day for 7 different days of the week.  The Belkin WeMo Switch can be scheduled to turn off and on and can be remotely controlled via an downloadable app for your smart phone.

A relatively new to the market, sophisticated option for getting appliance to use solar power directly is appliance controllers.

Appliance Controllers

These are automated gadgets that will turn on your appliances when the suns out, even when your not at home.  The controller is alerted as to when and how much solar power is being generated.  You can program appliances to turn on when there is a sufficient amount of solar electricity being generated.

For example, a hot water cylinder is the perfect appliance that you would want controlled.  Because your cylinder can store the hot water for extended periods of time, the cylinders element can be turned on at any time during the day.

Other appliances that could be controlled are pool pumps, washing machines and heat pumps.

Appliance control products include: Power Genius and Immersun.

Enasolar Immersun

Enasolar Immersun

The Enasolar Immersun is an appliance controller that only directs solar power to the hot water cylinder, the retail price is approximately $1,200.

The Power Genius allows appliances to be wirelessly or hardwired into the system, and there's virtually no limit to the amount of appliances you control and monitor.  The retail price is approximately $2450.  If you have a 3kW system or larger you will find this well worth while as it will add $500 to $600 value each year for a 3kW system.

Battery Storage

The obvious way to increase solar power self-consumption is by storing power in batteries, which can be used at any time of the day.

Batteries systems are still quite expensive, but there is a lot of hype in the solar power industry at the moment about battery storage technology improving and becoming more affordable. 

If you choose to purchase a grid connect system and if batteries are still looking out of your budget then you can always add batteries to your system in the future.

There are some really cool battery storage systems about to hit the market (all lithium-ion), if you can hold off a little longer it might be worth the wait;

Below is Enphase's "AC Battery".  It is a modular system where you can stack on more as you need them.

Enphase ac battery installed on wall

Below is Tesla's Powerwall, these battery units are now being sold in New Zealand by Vector.  Because Tesla are making them, you know they will be good!

Tesla Powerwall Home Energy Storage

Finally SMA's new innovation is their Sunny Boy Smart Energy system.  A complete inverter and battery storage in one unit.

SMA Smart Energy

West and East Facing Solar Panels

You can increase the percentage of self-consumption if you install solar panels on an east and/or west-facing roof.  If you put panels on your east-facing roof this will generate more power in the morning, more power will be generated in the afternoon with west facing panels.  If you live in the typical NZ household and use a lot of power first thing in the morning and in the evening, then you would benefit from this particular arrangement.

If you install solar panels on your east and west facing roof you will get a flatter, wider bell curve showing the solar power generation.  Below is what the self-consumption graph will look like with both east and west facing solar panels (this is without any appliance controllers or batteries).  In this case the amount of power used directly his increased and the imported power decreased.

Self Consumption With East & West Facing Panels Graph