Most people don’t realise there are different types of solar power. So here’s a quick overview of what solar power is, and the different types you can get.
It’s All About The Sun
The first thing to quickly acknowledge is that all types of solar power need sunshine to work. They don’t work at night, and don’t work very well on cloudy days.
Nelson might win out on yearly sunshine hours, but this is New Zealand. So Auckland, Christchurch and Wellington all get more than enough sunshine too. Yes, if you live in Stewart Island things aren’t going to be quite so effective – but it will still work, you just need the right solar system design for where you live.
There are also ways to store the energy but more on that in a moment.
This is what most people think of when we talk about generating solar energy. PV panels are those flat panels that sit on your roof and generate electricity.
The PV stands for ‘PhotoVoltaic’. In simple terms this just means electricity from the suns energy. It comes from the Greek word ‘photo’ which means ‘light’, and ‘voltaic’ which refers to voltage (which essentially means electricity). So the name is just describing the process by which we use materials like silicon and convert that light from the sun into electrical energy.
The panels themselves connect up to a box of eletronic trickery, typically tucked away in your garage. This box is able to convert the constant energy (DC – or direct current) into the varying energy (AC – alternating current) that our homes normally use. That clever box also takes care of things like feeding energy back into the grid so your energy company can pay you for energy generated above what you use.
More modern systems can now also include advanced battery techonology to store the energy generated during the day time so you can continue to use this ‘free’ energy at night. These are really just big advanced rechargeable batteries – the types now being used in electric cars.
This is the solution most people are now looking for to install in their own homes. But it’s not the only option.
Solar Hot Water
This technology has been available to homeowners for a lot longer. It’s very effective and can save you a lot of money, as a large percentage of our electricity bill comes from heating our hot water supply.
The options vary a little, but most modern systems work the same way. Water flows around pipes or tubes in a panel on your roof. The sun directly heats up that water, which is then stored in an insulated hot water tank (as most of us do already).
If you think what happens to a bottle of water if you leave it out in the sun – that really is all there is to these systems!
They are designed to maximise absorption of the heat though (black panels/pipes absorb heat better – white things reflect heat more). And they do work very well indeed – in New Zealand in Summer you can easily heat a 250 litre hot water tank up to 80°C and keep it there through a whole family of daily showers! It would go even hotter but systems have safety features built in to prevent it getting too hot.
For most sunnier areas of NZ they will provide all of your hot water needs for Spring through to Autumn. Even through a lot of Winter if there is some sun. But for extended periods of bad weather or heavily cloudy days, systems also include an electric back-up – just a regular electric heating element inside the tank. This can be all be controlled by the system itself – which can give you a readout of your roof and tank temperatures – or you can manually turn it on when you want a ‘boost’.
For larger families or to help cover for longer cloudy periods you can simply install a larger system – a bigger tank to store water, and more panels to gather heat.
An older style of system you will still see around New Zealand looks like a big black or silver drum on the roof attached to a solar panel. These systems have smaller storage capacity and are not quite as efficient at holding heat on cold days (because they are outside!). But they do benefit from being very simple – they don’t require a pump and controller system to move water from the tank to the roof and back again.
These are more of a barbecue type toy in NZ, but in some parts of the world where mains electricity is not available this is how food is cooked! So there is no reason you couldn’t get one of these to use at home on your deck, and cut your electricity bills by not using your electric oven.
The principle is simple – reflect and concentrate as much of the suns rays as possible onto a central point. Which is where you stand your cooking pot. A lot of these ‘solar ovens’ look like an upturned silver satellite dish or umbrella. But there are also designs based around a solar tube with reflectors too.
On a good sunny day they can easily generate regular oven level temperatures.
Passive Solar Houses
This is not something you can easily add to an existing house, but it can make an incredible difference to your energy consumption. Great house design can mean the sun alone is enough to keep your house a comfortable temperature nearly all year round. I know, I know, this sounds revolutionary to us kiwis who are used to leaky homes, and rental homes with no insulation at all 🙂
But it is possible. It mostly works by aligning your house on an East/West alignment, with lots of windows facing South. That way, the house soaks up lots of sun.
There’s more to it than that of course. The house design also has to include lots of ‘thermal mass’. That means plenty of solid materials that can absorb the heat throughout the day, and then slowly release it again at night. This is what keeps that temperature constant. When you partner this with insulation done properly (and I mean properly, not just the way we are starting to do it, but the way countries like Germany and Scandinavian countries do it) — and you end up with a super efficient house that is incredibly comfortable to live in.
And for the days when it’s really cold and there hasn’t been much sun, a tiny log burner or small heat pump is more than enough just to top things up.
There aren’t many houses in this country built that way yet, but some do exist (have a look at examples in Nelson and Golden Bay for example).
Once you’ve lived in a passive solar house you wouldn’t want to go back to any other way!