How To Get The Best Out Of Your Solar Panels

Having recently got a set of solar panels fitted to our roof, I've been trying to work out how to get the most out of them.

This isn't quite as easy as you might imagine.

The Problem
For a start, even on a cloudless day, the energy I can get from the sun varies according to the angle of the sun relative to our roof. Then you have to throw in things like the effect of cloud cover, and the length of day. So the amount of energy we get from the panels at any given moment is changeable.

This is important because, if we move the washing machine run from the overnight, cheap rate to the daytime rate, we'd better have enough power, otherwise it could cost us more!

Since the day rate is just over twice the cheap rate, that means the solar panels need to be generating over half of what we're using to make the move cost effective.

The Numbers
To figure out whether it's worth switch an appliance during the day, I need to know 3 things:

• Our 'base load' electric usage (i.e. From all those items that are always on. Like fridges, freezers, and things on stand-by). This can be done with an energy monitor.

• How much energy our panels are creating at the time (Can be read off the solar panel inverter).

• The maximum amount of power the appliance uses (using the energy monitor again). Some appliances use electric unevenly (e.g. dishwasher) and others use high kW e.g. kettle at 3kW and showers 8-10 kW. Better behaved items are lighting, dvd players, tv, computers, toasters, tumble dryers,  and vacuum cleaners.

This sounds like an awful lot of mucking about (and it is) but if we end up being able to use our washing machine, dish-washer, and tumble dryer for free, then I think it's worth it.

Obviously it'll take some work to get these figures to begin with, but I think it'll get easier as I get used to it. 

The Solution

The day's electric is generated in a bell curve which gets bigger until it peaks in the Summer. So the recommended time period to use power hungry items (usually ones with a heat cycle) is from 10 am to 3 pm when the sun is at it's strongest. However, it's important to note the Summer peak electric may be up to 8 times that in the Winter.

As a result, dull days in Winter will probably only cover the base load, whilst you may not be able to 'use up' all the power generated in the Summer.


Keeping that in mind, and the individual quirks of my appliances, I should be timing their use accordingly.

That's easy enough if there's someone at home most of the time but, in our case, we're usually at work during the week. So we need to keep an eye on the weather forecast and use timers for the major appliances, aiming for that 10 am - 3 pm window. If possible we will save the biggies for the weekend when we have more control.

Two major pieces of advise I've discovered elsewhere are:

• Don't run them all at the same time, stagger them, i.e run them one after the other

• Don't be tempted to run part loads (Because you'll increase the amount of water, detergent, conditioner etc you use!).

Bottom line: It'll all be a bit of a juggling act balancing usage against generation, but it should be worth the effort.