Surge Protection for Solar and Heat Pumps

Solar PV systems and heat pumps both introduce valuable, surge-sensitive electronics into a property. Both require surge protection — solar needs AC protection at the inverter output and DC protection at the string combiner; heat pumps need AC protection at the consumer unit.

As heat pump and solar installations increase across the UK, surge protection has become a standard part of the specification for both technologies. The inverters, control boards, and power electronics in these systems represent significant investment and are highly vulnerable to transient overvoltages arriving via both the AC supply and — in the case of solar — the DC string cables.

Solar PV — AC and DC protection

A solar PV installation has two distinct surge exposure points. On the AC side, surges can arrive via the grid supply and damage the inverter's output electronics. On the DC side, the PV string cables running from panels on the roof act as antennas — in areas of moderate to high lightning activity, nearby strikes can induce significant surge voltages in these cables.

AC protection is provided by a standard Type 2 SPD installed at the consumer unit or at the inverter's AC output distribution point. DC protection requires a dedicated DC SPD rated for the system voltage — typically up to 1000V DC for standard residential and commercial PV systems. The WCED WSPV1000 and WSPV600 provide Type 2 DC surge protection for string voltages up to 1000V and 600V respectively.

Heat pumps — AC protection

Heat pump systems — air source and ground source — contain sophisticated control electronics that are sensitive to supply voltage transients. Unlike solar, heat pumps are AC-only loads, so only AC SPD protection at the consumer unit or heat pump distribution board is required.

Most domestic heat pump installations are adequately protected by a Type 2 SPD at the main consumer unit. Where a dedicated sub-board or heat pump distribution unit is installed, an SPD should be included there too. The WCED WME5/HP4016S heat pump enclosure includes an integrated SPD as standard.

SPD specification by technology

Technology	AC protection	DC protection	WCED products
Solar PV (single phase)	Type 2 SPD at CU	DC Type 2 at string combiner	WSPD240 + WSPV1000/WSPV600
Solar PV (3-phase)	Type 2 4-pole SPD at board	DC Type 2 at string combiner	WSPD440 + WSPV1000
Air source heat pump	Type 2 SPD at CU or HP board	Not required	WSPD240 or WME5/HP4016S
Ground source heat pump	Type 2 SPD at CU	Not required	WSPD240

Shop WCED SPDs for Solar and Heat Pumps

AC Type 2 SPDs, DC solar SPDs (600V and 1000V), and heat pump enclosures with SPD included. In stock.

View SPD range →

Frequently Asked Questions

Is surge protection required for solar PV by the MCS standard?

MCS (Microgeneration Certification Scheme) installation standards recommend surge protection for PV installations, particularly where exposed DC cable runs are involved. Most DNO connection agreements and grid tie-in requirements also specify adequate protection of inverter electronics. Surge protection is considered best practice and increasingly specified as standard on all MCS solar installations.

What happens if a heat pump inverter is damaged by a surge?

Heat pump inverter replacements are typically expensive — often £500 to £2,000 or more. Surge damage is frequently excluded from manufacturer warranties, meaning the full cost falls to the homeowner. An SPD costing £15–30 that prevents this is one of the most cost-effective protections in any renewable energy installation.

Further reading:
DC surge protection (1000V) for solar PV explained
Solar combiner boxes explained
Heat pump protection units explained
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