(Solar) efficiency isn’t everything?

To be a truly sustainable, energy independent, energy efficient house I need some way to generate my own electricity. At the moment I can only see two viable options (although I’m open to suggestions!), photovoltaic (PV) solar panels and/or a micro wind turbine.

I was leaning toward trying to do both, but my spirirts were dampened slightly when I learnt how poorly the turbine at 3 acorns had been performing.

So despite the fact that the UK has been on ‘amber alert’ this weekend due to the ‘near gale force’ winds of the storm called St Jude, I think I’m going to have to put my trust in solar panels for the majority of my electricity generation.

I’ve been looking in to solar panels quite a lot recently, and there’s a lot of information out there regarding thin-film solar, mono-crystalline and poly-crystalline, etc.

It seems the important figure to pay attention to is solar module (panel) efficiency (different to the solar cell efficiency, which is a bit higher). The efficiency is how much of the sun’s energy gets converted in to electricity.

At the time of writing this, the most efficient solar panel is SunPower’s X-Series that is 21.5% efficient. If you’ve only just started reading up on solar panels, this seems like a fairly low number, but the thing to bear in mind is that theoretically the most efficient solar panel we can ever produce will only achieve 44% efficiency (as only a certain range of light within the spectrum is used in PV).

Of course you’ll see news stories of record breaking solar cells of 44.7% efficiency, but these are CPV, or Concentrated Photovoltaic cells that use a concentrator to effectively shine more than 1 sun’s worth of light on to the panels. So it’s not quite the same.

Sounds good right? Sign me up, I’ll take some solar panels and a concentrator please. But unfortunately they aren’t available for residential use, and the cost is prohibitive anyway.

But it’s not important. 21.5% is more than good enough for most people’s uses. Even 15% is good enough to make a real difference. And people are very good at pointing out that you shouldn’t be an efficiency snob.

I don’t think I’m an efficiency snob, but what does concern me is a slightly different issue. It seems like advances in PV technology are happening every week. And the price of solar panels is decreasing all the time. I worry that I’ll get some solar panels and then 6 months later there will be residential panels available for half the price that are an extra 10% more efficient.

Just in the last 2 weeks I’ve seen the following stories which always make me think in a few months to a year solar panel efficiency is just going to leap forward massively:

A quarter more efficient?

A potential breakthrough in efficiency? (and good news for LED lighting)

And a possible 80% efficiency?!

Of course this talk of efficiency may be irrelevant to me when the time comes and we've actually bought our house. You also need to pay attention to positioning. A south facing roof is ideal (south-west and south-east are fine too). You can put them on roofs facing other directions too, but you lose efficiency (about 15-20% for west or east. I think it’s far worse for north).

And then there’s the angle of your roof too. A 35 degree angle is ideal in London, but the optimum angle changes depending on where you are in the world (or even just the UK).

So I’m not an efficiency snob, I’m really not. But depending on what house we end up with, I might end up having quite an unsuitable roof to place my panels on, so every percentage of efficiency may count!

Lessons in LED lighting

I’ve been trying to write this post for a few weeks now but work has been so busy.

I thought a post about LED lighting would be a good way to ease in to looking at energy efficiency. It’s one of the cheapest and quickest ways to make a difference in your energy usage. However if you don’t know anything about lightbulbs other than how to change one, it can be slightly confusing at first.

So what prompted me to look in to lighting was a combination of two events. 1: my girlfriend Anne bought a new LED bulb for her bedside lamp from Tesco, and 2: I saw this buyers guide on twitter.

I knew there were different types of light bulb and that LEDs are the new efficiency kings, but beyond that my knowledge was pretty basic. Also I could never remember what CFL stood for or what it looked like. So after looking around I made my own quick guide to remind me:

Really the important thing to note is that the more efficient a bulb is, the less electricity it will use (in Watts) to produce the same amount of light (measured in Lumens).

So for instance, the LED mini globe Anne bought is 4W and 250lm. It says on the box that the equivalent conventional bulb is 25W. I’m not sure what ‘conventional bulb’ means. Whether it’s incandescent, or CFL (which are now pretty common that I’d almost call them conventional). But anyway, that’s potentially a change from 25W to 4W (I’m not sure what kind of bulb she replaced). If you were to do this with every bulb in your house that’s quite a saving. You could cut the electricity use in your house (on lighting) to less than a fifth of what you are using currently (although this is likely a big exaggeration if you are already using CFL bulbs).

The other benefits of LED lighting is the bulbs last for a very long time (25 years if used for an average of 2.7 hours per day, the Tesco packet says). Also LED lights produce hardly any heat as a by product of creating light, so they don’t get hot to the touch. And they don’t have a ‘warm up’ period like CFL bulbs, where you have to wait for them to reach their full brightness once you turn them on.

The downside? They are quite expensive. Buying a lot of LED bulbs is not cheap. But you can easily earn your money back in the savings on your energy bill over the years. Also as LED light become more ubiquitous the price will come down (If they’re selling them in Tesco that’s a good sign!).

So having been totally sold on the use of LED lights I’ve decided I’m going to replace every bulb in our new house as soon as we move in. I was so enthusiastic that I pestered Ecotopia on their range of LED lighting (among other things…). As previously mentioned I am slightly obsessed with Ecotricity, and as I already use Ecotopia I was keen to get them to stock the bulbs I was anticipating needing.

They will be getting some in stock, but in the meantime I found a good range on Nigel's Eco Store.

The other thing to take in to account though is that LED light can come in different ‘shades’ of white. The names vary depending on what website you’re looking on, but you can choose from ‘warm white’ ‘pure white’ or ‘cool white’. Which basically means a orange tinge, white, or a blue tinge. This depends on the Kelvin number. I won’t go into this in further detail though, more can be found here.

Also I read that the Wattage needed for a room is the square footage of a room multiplied by 1.5. So for a room 10 foot by 10 foot (100 feet) you would need 150W of lighting. Again I assume this is for incandescent bulbs. So using LED lighting you need the equivalent, which is about 30W.

I don’t think I’m actually going to worry about the Kelvin of my light, or the Wattage needed yet though until there are actually some real life rooms to apply my newfound knowledge to.

Although while reading up on bulbs I did come across this kickstarter, the Nanolight!

It had already been funded by the time I’d seen it, otherwise I probably would have backed it to get myself a Nanolight. I can see they’ve rebranded now to nanoleaf so maybe I’ll revisit their site when the time comes.

And finally. If anyone is looking to switch energy suppliers to Ecotricity (which I can highly recommend) if you quote this referral code ( RAFE-4WKE5 ) when making the switch, we will both receive a £50 voucher for Ecotopia. So I can use it to buy my LED light bulbs once they get their new stock, and so can you! (or you can spend it on toilet paper and dishwasher tablets)

Until next time.