Solar in the morning

It's about 8:30am with light cloud.  We're generating 350W at the moment, which is more than we're using.  It was already running around 200W when Richard got up at 7am.

Last night, we hit the point where we were using all we generated around 5:30 (apart from cooking tea which is obviously a higher load) and power generation went to zero around 6pm.

I imagine the real test of the system will be on days with heavy cloud.  And days are much shorter in winter, of course.

We had 13 panels installed, which is the maximum the roof can take.  The economics are very clear on this.  If you're going to have panels at all, you should have as many as you can take.  There's a large fixed cost for things like erecting scaffolding and installing the inverter - to spread the fixed costs over as many panels as possible makes clear sense.  It would not be easy to add more panels at a later date as you'd have to put scaffolding up again.

The interesting question is how much of our electricity usage can be shifted into the daytime.   Washing and vacuuming are obvious ones, but I'm wondering about cooking - which is the really heavy drain on any electricity system (apart from kettles and electric showers).

We don't have an electric shower, but if we did, I'd be showering in the daytime from now on.

I see some possibilities with regard to cooking.  It may be possible to cook things like potatoes earlier in the day and reduce the amount that needs to be cooked in the evening.  (though anyone can save a lot on cooking this kind of thing by using towels on the hay box principle.  Bring your spuds/stew/whatever to the boil and simmer for a few minutes, then turn off the ring, cover the pan/casserole with some thick, fluffy towels and come back when you want to eat it and it will be cooked though, still warm, and never burnt)

Overcast

I'd describe the sky right now as overcast.  The sky is pretty much covered, but it isn't rain clouds.

Generation at 520W at 12:30  (of which I'm using 200W)

As I get a feel for maximum generation at different times of day and what fraction cloud cover knocks off, I'll probably be able to predict what to expect.  For a very rough figure, I'd say that 'overcast' reduces power generation to around a quarter of 'full sun'.  But at this time of day, a quarter is still enough to cover my consumption.

Overcast = 1/3

I've uprated 'overcast' from 1/4 to 1/3 generation.  I'd forgotten that my power is likely to hit max a little after the middle of the day as my roof isn't directly south.  I'm at about 600W generation now.  (I think my max will be around 18-19KW under ideal conditions)

600W is enough for background, but if I cook toast I go well over.  I was surprised how much difference it made to power use if I turned down the grill temperature by one point.

It pays to remember that the relationship between temperature and the energy required to reach it is definitely NOT linear.

Measuring data

A thought from Alex_Holden.

If I had two sensors with logging (My current one doesn't have a logger), then I could use one after the inverter and one in the usual position and get some really pretty graphs.

I can't currently justify spending £70 to get a pair, but I do like the idea of being able to see both generation and consumption.

sky mostly overcast 3:20pm - generation = 480W

(no subject)

Keris asked a bunch of questions:

----OK, how does that Owl thing show you how much individual things are using? Is it only by turning them off and seeing the difference?

Yes.  but it's advisable to do it several times to get a sample as things like fridges and freezers go through a cycle, which can affect results.  However, some things are easy to spot.  The old fluorescent tube in my kitchen needs replacing as it's about 150W - a lot more than I thought.


----That power is a lot more than I'd expect from solar panels, what area do they cover? And is your roof south-facing? Mine is SE/NW so it's far from ideal.

My roof is within about 25 degrees of south.  The entire roof is now covered in panels - 13 of them.  If you're not within 30 degrees of south, then solar power is unlikely to be cost-effective.  Yours might be worth checking.

----How do you get them to install it free? Since my average power consumption (without heating on) is around 500W that might reduce my costs quite a bit, but not if I have to pay several thousand pounds to have it installed.

Your roof may be too small to qualify for free panels, but see Home Sun  to find out.

How to qualify for free solar panels

The firm I used are Home Sun.  If you want to know if you qualify under their rules, see this page.  The key factors are:

Compass direction of roof.  Must be between SE and SW.

Angle of slope of roof.

Lack of shade from trees/neighbouring properties.

Size of roof - the bigger the better.  (economies of scale on installation)


It's unlikely that you'll ever get more than a third of your electricity from solar power, and it could be as low as a quarter if you're not at home during the day to do things like laundry using the daylight.