Good news first: for a low-usage home like yours, a 4.5kW south-facing array is a strong match, and you're in exactly the profile where summer export credits do real work. Let me take your three in order.
1. Will summer credits cover winter?
For your usage, very likely yes — at least most of it. A 4.5kW array will generate roughly 3,600–4,000+ kWh a year, which is more than you use, and the surplus exported in summer earns CEG credit (typically around 20–24c/unit). Your winter draw of 250–300 kWh/month at day rates is the bit that credit pools against. In practice, low-usage no-battery homes on this setup commonly see minimal or near-zero electricity bills through the darker months once the summer credit has built up — though a stone-cold dull winter and standing charges mean it's "mostly wiped out," not a guaranteed €0.
One tip: a dual-name account (two people on the bill) doubles the tax-free export threshold, which matters if you build a lot of credit.
2. Can export credits pay for the gas?
This depends on your supplier's setup, and it's worth checking with them directly — but the common pattern on dual-fuel:
- Some suppliers pool the credit across the whole account, so a big electricity credit does effectively eat into the gas balance.
- Others ringfence it to the electricity side.
Several owners on dual-fuel report their solar credit reducing the overall bill including gas, so it's often possible — just confirm it with your provider before assuming.
3. String inverter vs optimisers?
For a clean, unshaded standard roof, optimisers usually aren't worth the extra cost — a plain string inverter performs just as well. Where they earn their keep is shading: a chimney, a gable, a neighbour's tree, or a tricky split where one string gets shaded part of the day. Then an optimiser on the affected panels stops one shaded panel dragging the whole string down.
So the real question is: does anything shade your roof? If not, don't sweat it.
One thing I'd flag regardless: get a hybrid inverter even with no battery now. It costs a little more but lets you bolt on a battery later without replacing the inverter — sensible future-proofing if you ever add an EV or heat pump.
Want me to put real euro numbers on the savings and payback for this exact 4.5kW setup? I just need to confirm — shall I run it on 2,900 kWh/year, no battery, grant-eligible?