Thursday, April 29, 2021

Sun cents

My solar power system was switched on a week ago today, and I’ve been both monitoring and adjusting to it. It’s been interesting.

I kept checking the output on Friday, the first full day it was running, beginning a little before 9am. At that time, the system was generating 500 watts, about 10% of its maximum. That has to do with the time of year and the position of my house.

It’s the latter part of Autumn now, so the sun rises around 7am. That means that it takes around an hour before the sky starts getting light, and so, my system starts generating real power. Beyond that, the front of my house faces northeast, and that means that the peak of the roof runs northeast to southwest. This matters because the solar panels are on the western side of the roof ridge, and so, full sunlight doesn’t start hitting the panels until later in the morning. I knew all this, of course.

As it turned out, I could watch the output increasing reasonably quickly: By 9:30am it was at 1.6KW (1.6 kilowatts, or 1,600 watts). An hour later, it was nearly double, at around 3KW. It peaked out at 4.6KW, just 400 watts shy of its maximum output.

Since then, we’ve had several rainy days, and the output was on the lower end on those days (like, say, 1.6KW). I expected that, too.

Because the amount of power I generate varies according to time of day and the weather, what electrical things I can run for free on a day also varies. I shouldn’t run everything at once for a good reason: If the power I’m using exceeds the power I’m generating, I have to buy power from the electricity company. I’d rather use free power, of course.

This is typical for how I manage this: Yesterday morning, I ran the dishwasher by itself, and the power was free. Later, after the dishwasher was done and the sun was moving higher, I did a load of washing, and then put it in the dryer. Then, when my power generation was peaking, I started another load of washing while the first was drying. Today, with no more laundry to do at the moment, I ironed my shirts using free electricity. Tomorrow will be a partly cloudy day, so I’ll probably just vacuum (I’d normally do that on a Friday, anyway).

What may be obvious is that this actually isn’t very different from what I’d normally do, apart from running the dishwasher in the daytime (I used to put it on when I went to bed). On the other hand, if it’s a bright sunny day, I know I can run more electrical stuff for free, and other days I can run less to have it free.

All of this is stuff I more or less knew would be the case, however, there was one surprise: Noise. It turns out that when the inverter (which converts the DC from the PV panels to the AC the house needs) is under load (probably at least 2KW), it sort of hums. I’m pretty sure that’s the cooling fan, which doesn’t run at lower load levels because the heatsink is enough.

The inverter is mounted in the garage, on the wall next to the power panel (circuit breaker). It needs to be there because it has to connect into the house’s power distribution, but, unfortunately, that spot is also on the other side of the kitchen wall. It’s not an obnoxious sound inside the house, and barely noticeable if I’ve switched on the jug or the TV us on, but when the house is quiet and I’m standing in the kitchen, I can hear it. It’s much louder in the garage, of course, where it sounds like an older PC (Nigel once built one that sounded just like it, and it’s louder than the computer servers, also in the garage). Fortunately the pitch is neither too high nor too low, which means it’s not a problem, just something that I didn’t expect.

It’s too early to know how this will affect my power bills—the system was turned on the same day the meter was read. Even so, I do know that my bill for last month was up about 18% on the previous month, but even that’s not straightforward: Last month’s bill was for 29 days (and not a full month) because I switched power providers last month. Also, I’m now turning on the heat at night. On the plus side, the bill’s total is after subtracting the $1.44 credit I received for my power generation—which was actually only for the few hours the system was on and generating that day (I think I did a load of laundry that day, too).

Even though it was fun to pay close attention in the first few days, I won’t be keeping track of my power generation in real-time. However, I am planning to talk about how it’s going at 3 months, six months, and at one year. By then I should have a pretty good idea how it’s affecting my power bills. I know some other people who will be as interested as I am in seeing how this works out.

Any rate, this is just the start, of course. That’s also part of why I think it’s so interesting.


Roger Owen Green said...

My wife loves watching her miles per gallon on her hybrid car in a manner, not unlike the monitoring of your energy consumption.

It's vaguely adorable in a nerdy sort of way.

Arthur Schenck said...

I think so, too! Interestingly, I don't feel that way about my car: When I bump something at it shows fuel efficiency, I always reset it to "distance remaining" before I run out of petrol, because that matters more to me in a car.