watervole | Solar power and usage patterns

Although I'm currently minus 5KWh on my electricity meter since Tuesday, I'd warn people to be sceptical of claims by some firms that you'll halve your electricity bills. I still think 1/4 to 1/3 reduction is more likely.

That's because that negative 5KWh is the electricity I didn't use. I suspect some firms take the total you generate and subtract that from your total electricity bill and quietly ignore the fact that electricity produced when you don't need it is no use (unless you're collecting the feed in tariff yourself, in which case you'll also gain financially from the unused amount). I saw a firm in Poole yesterday, making exactly that claim (with a girl on the stand who knew so little that on hearing I already had PV panels suggested that I might be able to install hot water panels on the inside of my roof...). If you're collecting the FIT, then you'll be owning your own panels. That's also a sound route to go, but you need to have the free capital.

I'm looking at the different cycles of my washing machine. I always use the 30 degree setting normally, but just for curiosity I'm trying the others to see what they power usage is like.

today I'm trying the 60 degree eco wash. I've already concluded that it's not a good one for solar power. Although the manual rates it as using just over 1KWh and I'm currently generating 1.25KW, I'm actually negative by 1.4KW. It's clear that most of the power is used at the start of the washing cycle to heat the water. Solar is best for things that use less than 1KW for longer periods of time. (though I'm still saving nearly half the power used on this wash)

Incidentally, it's clear that washing machines get their energy efficiency labels for scoring on particular points. I can think of no other reason why my machine uses less energy (according to the manual) on the 60 degree cycle than on the 40 degree cycle!

Tomorrow, or the weekend, I'll try my normal 30 degree wash and see if it's possible to do that without ever exceeding the generation rate.

I'm also intending to cook the rice for tea early today while power is still plentiful.

Flat | Top-Level Comments Only

Er, if they take the total you generate from the total of the bill, isn't that just as good (from a financial point of view) as collecting the FIT yourself? For instance, that 5kWh which was 'wasted' because you weren't using it at the time, didn't it turn your meter backwards? So you'll still get that as a discount on the bill of 5 'units', yes?

If not, and anything over what you use doesn't count, that makes it a lot less attractive, because very few people can switch their lives around so they do the washing and cooking and vacuuming only when it's light, most of us have employers who want us to work at that time (even though some of us would rather work at night). Similarly, most of us use a lot less energy in the summer (less heating, often less cooking as well because people eat salads etc.), if that is 'wasted' and they aren't paid for it (but do have to pay in the winter) that's going to limit the benefit.

This is, of course, a problem with solar generation in general. Unless you have a really efficient storage system, which will keep the energy over days or weeks or even months (pumped water is about the best so far) it just doesn't produce power when its needed.

What we need is something like Heinlein's 'Shipstone' batteries, where you could store enough energy in something the size of a car battery (luggable) to run a house for a month or a car for thousands of miles, and no degradation with multiple charging (things like NiMH and LIon are good for a few thousand recharge cycles at most, often less). Without it, our power demands are far too erratic and don't correspond to when we actually get the energy from things like wind and sun.

Once they replace the meter (which will happen in a few week's time) then it will no longer run backwards when we generate excess. The feed in tariff will be calculated by some means, but I don't get that part of it.

You're quite right about the limitations - that's why I'm trying to make them clear as some solar companies do, and some don't.

It's a lot more useful for people who are at home in the day (or at least able to maximise use at weekends)

If you own your own system, then you get the feed in tariff yourself and get the daylight money.

If I get panels fitted to my house (survey is happening in the next couple of weeks to see if I can), I will look at setting up some rechargeable batteries and a secondary low voltage lighting system. I reckon I'll be able to put enough charge into a couple of small batteries (or even some old car batteries) to be able to provide light for several hours.

I know that I am NOT dedicated to economy/ecology as much as you would like; while I gain points by always doing my laundry with cold water (and eco-friendly washing powder), I lose a huge amount of points by always using the clothes-dryer. I gave up on hanging the laundry on the clothes line after the Nth time I forgot them, left them out all week and got them rained on. Yes, I do have an indoor clothes-horse. I tend to use it only for things that shouldn't go in the dryer.

You're right about tumble-dryers. They are very energy-intensive.

I get quite a bit of use out of my indoor clothes horse. I dry a lot of stuff on it in winter - often I part dry outside and then finish it off inside when it's cold.

You do get lots of points for doing cold water washes, so it's not all bad.

"It's clear that most of the power is used at the start of the washing cycle to heat the water. Solar is best for things that use less than 1KW for longer periods of time (though I'm still saving nearly half the power used on this wash)" - Obvious now, but it wasn't, until I thought about it, thanks to you. This is quite an education, and intriguing.
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I've had a reply from Homesun. They will arrange a survey. From the details they give, I can't see that we qualify for the free installation, but we can just about get the share system (£500 to install, £5/month from then on). I'll have to do some calculations to see if that is worth it.

One thing I was wondering, is what happens during a (external) power cut? Obviously your panels would still produce electricity (subject to sunlight), but do you get the power, or is it all fed outside, or would the system be overloaded by the drain and shut down/blow a fuse?

unless the system is one which has a battery bank it's a simple grid tie system. When the grid shuts down it shuts down so when there's a power cut you don't have power either.

higher spec systems have a battery bank to smooth over this. In a power cut the tie is dropped and the house is fed by a combination of solar with the battery supplying any shortfall. When the grid reconnects the system tops up the batteries and surplus is fed into the grid.

I've just spoken to someone at the company. They confirm what you say about it shutting down, and they get notified remotely if it doesn't start up again properly.

Oh, that's good to know. One additional reason I'd consider getting a solar power system is so that I wouldn't lose power immediately when there's an external power cut.

You may have to hunt a bit for the higher spec/integrated battery systems. They are more common in Europe and North America than here (several reasons, aside from the cost and weight of several hundred amp hours of deep cycle batteries)

Could the calculations in the manual be assuming that it can get 60 degree water from your hot water system?

No. It doesn't plumb into my hot water sytem - which is something I didn't realise until after I'd bought it. Any energy-friendly system should have the option for a hot-water input - my previous machine did, so I never thought to ask on this one.

Apparently it is considered better for the machine (either washing machine or dish washer) to heat the water itself than to use water from the hot water system. I'm not entirely sure why, and I'm not entirely convinced that is a good thing either. I would guess that the machine is better at heating the exact amount of water the the required temperature compared with getting water that is either too hot and needs to be mixed down, or too cold and needs to be heated an extra bit.

Just a thought, if one had a solar hot water system then plumbing the washing machine into that would allow a hot wash to be carried out much more economically.

My current washing machine doesn't have the option of taking hot water from elsewhere.

(goes and looks at washing machine)
Ah, mine takes its hot water from the hot water system.
My hot water system is gas, which loses points for being fossil fuel, and gains points for being more efficient than electricity. Hmmm.

Solar power and usage patterns - esp laundry

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