The solar panel site visit is complete

I mentioned in my last post that I was going to invite one of the companies which quoted me for solar panels to visit the house and check out the setup. Last week that happened.

I spent about 30 minutes chatting to the sales rep/system designer (I'm unclear exactly what his role was) about the house, how we could set up a system, and how much space it would take. We also spoke about Solar Diverters and batteries. I wasn't sure if these two items would be worthwhile in my house.


What is a solar diverter?

A diverter is a thing that seems to get added onto Solar system quotes by default, but you might not need it depending on how your house is set up.

The idea is that during the day your solar system might generate more power than your house needs at that time. You can either send the heat back into the grid (often selling it back to the electricity company) or you can store it in some way. The most obvious way to store it is a battery (which I'll write about below) but a less obvious method of heat storage is to heat water in a tank that would otherwise be heated later with an immersion so that you don't need to do it later (this of course requires a pretty decently insulated water tank).

A Diverter takes the excess generated power and plugs it straight into the immersion heater in your boiler, often heating it beyond the temperature that your built-in immersion will.

Do I need one?

This is something I wasn't particularly clear on. I've got a recently-installed heat pump, so rather than having a gas or oil immersion, the heat pump will very efficiently heat the water. The heat pump is plugged into the house's electric system, so my uncertain assumption was that once I had solar feeding into the house that the heat pump could just sip at its power, avoiding the need for a diverter.

When I spoke to the site visit guy he explained that I was right - a diverter isn't strictly needed. A divert can be plugged into the system heating the water directly, and it can heat water way hotter than the heat pump can. But it would void my heat pump warranty so he recommended not doing it, and I'd still be using solar to heat the water anyway - just less of it. He said he'd always recommend a diverter if you have an old heat pump, but one with an active warranty wouldn't be worth disrupting.


What are they?

Batteries are pretty easily explained - they can charge during the day when you are generating excess solar power, and discharge at times when you don't have enough sun or at night. You can also charge them overnight if you have a night rate and then use that electricity during the day.

Batteries lose some energy while charging and discharging, but you pretty frequently hear of them being installed by default with setups, similar to diverters.

According to the installer, batteries (in Ireland at least) can not be connected to the entire house, but only "critical appliances", I assume so as not to overload them. In my house, I'd probably connect it to the heat pump to power it 24/7.

If you want a battery, you need a hybrid inverter rather than a string inverter connecting your panels to your house's electricity circuit.

Do I need one?

The case for batteries is a little less clear. Batteries are expensive, so you need to ask yourself if the money that you'll save by storing up a few kW is worth the hefty cost. The 5 kW battery that my installer would have recommended costs roughly €3,500. However - it would only reduce bills in the house by a few hundred euros a year in comparison to selling the energy back into the grid.

Do we think that export prices (the price you sell into the grid) will reduce over the coming years? Most likely. Right now a good export price in Ireland is about 21 cents per kilowatt. But export prices are falling across Europe. However, energy prices in general are also falling, offsetting that.

I think batteries are cool and kept trying to convince the installer that maybe I should get one. He argued fairly strongly against it. I'm going to upgrade to a hybrid inverter anyway so that I can get one down the line.


One thing that is a problem for me in the house is that there is almost no storage space. I'd have to cram all of the equipment into an under-the-stairs room that heads up quite a lot when the dryer is running. The installer said that their equipment can all happily be installed outside, so that's a huge draw.

So that's where we are. The quote came to €6,300 for around 5.8 kWh of panels, which the Facebook group I mentioned in my first Solar post saying that it's a pretty decent price, although there has been a debate raging over the weekend around my decision not to get a battery.

I'll keep you all updated as I move forward!

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