I must confess I am just about the furthest thing from an actual engineer – while I have a great deal of curiosity about the nature of solar power and its possible impact on household energy consumption at a micro level, on certain technical matters I will be a small kid with armbands swimming in the deep end.
What do we do when we are potentially out of our depth? We consult a real world expert. So for that reason, this week we speak to Martin King and Bryn Bennett of Degree Limited, who specialise in the installation of all things heating and cooling.
Balance Transfers: Just to give us a bit about your background, can you tell us a bit about Degree? In your own words, what do you do?
Bryn: We specialise in heat pumps and electrical and air conditioning and solar.
Balance Transfers: You’ve commented in the past that a lot of the gains from a solar power installation can essentially be overstated. What are the main things that someone should take into account when looking at installing solar power?
Bryn: I would certainly say their consumption. How much power is going to be used during the day while the sun’s up. And I would certainly not look at what’s being exported back to the grid, because that is not a constant known, and then there is the fact that the power companies give you almost nothing for what you export back. So you really need to monitor what you’re using during the day, compared with what you can use and produce.
Balance Transfers: So basically it’s important to match your own consumption to the power that you’re generating? What impact would that have on return on investment?
Bryn: I would say it would probably maximise your return on investment, in the sense that you’re not putting too much on the low generation, so you’re keeping your initial install costs down, and maximising your consumption (of solar power) against the cost of it.
Balance Transfers: What are your concerns around selling power back to the grid?
Bryn: Well, not all companies will give you money for it, and it’s not a guarantee that in the future that they will give you money for it. So if you base (your assumptions) on selling power back to the grid, and in a year’s time they stop giving you anything for it, then your calculations are out the window.
Balance Transfers: So a lot of companies in the past used to offer at least some wholesale energy rate for selling back to the grid. But some of the retailers have actually switched off that. So is that something that people should factor into their calculations?
Bryn: I would certainly base myself around getting nothing from the power companies and consuming whatever you can.
Balance Transfers: So it’s really important again just to match it to your own consumption. Batteries are on offer for many solar power installations to help store solar energy overnight. Do batteries actually represent a good option, in your view?
Martin: At the moment, for what you’ve got to pay in to pay back those batteries before they actually die out – I know lithium is better now, but I don’t think it’s at a point where it’s worth buying them yet. Like Bryn was saying, you’re better off by using that power that you have instantly.
Bryn: The dishwashers and iron and dryer – consuming during the day and spreading that over so you don’t just fire all of your load on at once, you know, you actually spread it out over the day and consume whatever you can over the period of the day to match your system.
Balance Transfers: How often would you have to replace batteries?
Bryn: Oh, I’m not sure what the lifespan of the batteries are, but it would probably give you maybe five to seven years, something like that?
Balance Transfers: So, in addition to the once-off cost of installing solar, you’d then be looking every five to seven years to replace the batteries. How would that affect return on investment?
Bryn: I would say the return on investment would probably be a lot worse if you’re replacing batteries every seven years. They’re about 2,000 to 3,000 full charge life cycles.
Balance Transfers: That’s only a few years.
Bryn: Pretty much.
Balance Transfers: How much energy loss from solar panels do you need to factor in? If you’ve got a 3 kWh system, not all of that’s going to translate to usable energy?
Bryn: No, so you do get some losses, but in this system micro inverters can be extremely energy efficient so they come on a lot sooner and they go off a lot later in the day. If there’s any slight shadings, they can (compensate) because each panel is working independently to save a whole string. So you may lose a little bit (with good micro inverters) if you use a 3 kWh system, but you should still be getting up close to 3 kWh on a bright sunny day.
Over the period of the panels, so a 20 year to 25 year life span, they drop down to about 80% (efficiency).
Balance Transfers: Not all installers would offer good quality micro inverters, is that right?
Bryn: No, you can get some cheap Chinese string inverters.
Balance Transfers: And then what sort of loss would you be looking at?
Bryn: They’re all different. But yeah, a big loss. And the lifespan of them might not be that great either, so then you’re up for new inverters. Like the inverters, the ones we’re using, there’s a 10 year warranty on them.
Balance Transfers: So lower power generation to begin with (if you use the wrong inverters), more replacement costs potentially, and I take it that would in turn affect return on investment for your solar installation, is that right?
Bryn & Martin: Yep.
Balance Transfers: This is just based on what you told me – but it seems like the best solar power installation is a good, small, simple one that is actually tied to the amount of power that you use during the daytime. Less is more, basically.
Bryn: Yep.
Balance Transfers: Any other thoughts?
Martin: The position of them in the first place, being on the right side of the roof at the right angle. If you’ve got a north facing, 30 degree roof, that’s the best. Slightly off north, it’s still good. If you want an optimise it, it’s important to get the north facing roof at 30 degrees.
Balance Transfers: So it’s important to find the right spot.
Martin: Yeah. So if you have a lot of roofs, you want to pick the best option out of all of them. In general, you’re going to pick the right roof.
Bryn: And obviously, on really hot sunny days, it changes the output because the panels get hotter. And when the panels get hot they generate slightly less as well.
Balance Transfers: Oh, really?
Martin: Yeah. On a day that’s really hot, it might produce slightly less than a day where there’s a nice cold breeze. And a fair amount of sun will probably do more than when it’s a really hot day.
Bryn: And on an overcast day, when there’s a lot of clouds around, it gets a lot of reflected light off those clouds as well, which increases (the solar power generation).
Martin: If you put solar power panels in front of a lake, you’re going to get even more power off of that because of the reflection.
Balance Transfers: So it’s all about location location location!
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