Renewable Energy Course: Solar PV & Battery Storage

The UK government has committed to achieving net zero carbon emissions by 2050. Solar PV and battery storage are central to this target, with the government aiming for 70 GW of solar capacity by 2035 (up from approximately 15 GW today). For electricians, this represents one of the largest growth opportunities in the industry.

Solar PV installation is a high-value specialism. A typical domestic installation (4 kWp system with battery storage) charges £8,000 to £14,000, and an experienced two-person team can complete one installation per day. Commercial rooftop installations, ground-mounted arrays, and battery storage retrofits add further revenue streams. The combination of electrical installation skills and specialist solar knowledge means qualified installers are in strong demand.

This Elec-Mate course covers everything from the fundamentals of photovoltaic technology through to advanced system design, battery storage integration, and the BS 7671 requirements for PV installations. Whether you are looking to gain CPD points or preparing for MCS certification, this course provides the knowledge foundation you need.

Solar photovoltaic (PV) cells convert sunlight directly into electricity through the photovoltaic effect. When photons from sunlight strike the semiconductor material in a PV cell, they knock electrons free from their atoms, creating a flow of direct current (DC) electricity. Multiple cells are connected in series within a panel (module) to produce a useful voltage, typically 30 to 50 volts per panel.

Monocrystalline panels use cells cut from a single silicon crystal. They offer the highest efficiency (typically 20 to 23%) and the best performance in low-light conditions, but are the most expensive per watt. Polycrystalline panels use cells made from multiple silicon crystals and offer slightly lower efficiency (17 to 20%) at a lower cost. Thin-film panels use a thin layer of photovoltaic material deposited on glass or flexible substrate — they are the cheapest but have the lowest efficiency (10 to 13%).

Panel output is rated under Standard Test Conditions (STC): 1000 W/m² irradiance, 25 degrees C cell temperature, and AM1.5 spectrum. Real-world output is always lower than STC rating due to temperature effects (output decreases as temperature rises), shading, soiling, cable losses, and inverter conversion efficiency. A realistic annual yield estimate for south-facing panels in the UK is approximately 800 to 1000 kWh per kWp installed.

String sizing is one of the most critical aspects of solar PV system design. Panels connected in series form a string, and the string voltage must fall within the operating voltage range of the inverter's MPPT (Maximum Power Point Tracker) input under all temperature conditions.

The key calculation involves the panel's open-circuit voltage (Voc) and its temperature coefficient. On a cold winter morning with bright sunshine, the panel temperature could be as low as -10 degrees C, causing the voltage to rise significantly above the STC value. The string voltage must not exceed the inverter's maximum input voltage under these conditions, or the inverter could be damaged. Conversely, on a hot summer day with panel temperatures above 60 degrees C, the string voltage drops and must remain above the inverter's minimum MPPT voltage for effective tracking.

Shading analysis is equally important. Even partial shading of a single cell in a string can dramatically reduce the output of the entire string. Micro-inverters and power optimisers can mitigate shading effects by allowing each panel to operate at its individual maximum power point, independent of other panels in the array.

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The inverter converts the DC output from the solar panels into AC electricity that can be used by the property's loads and exported to the grid. Inverter selection significantly affects system performance, reliability, and cost.

String inverters are the most common type for domestic installations. A single inverter converts the DC output from one or more strings of panels. They are cost-effective, reliable, and easy to maintain. Modern string inverters achieve conversion efficiencies above 97%. The main limitation is that the performance of the entire string is limited by the weakest panel — if one panel is shaded or underperforming, all panels in the string are affected.

Micro-inverters are mounted behind each individual panel, converting DC to AC at the panel level. This eliminates the string effect — each panel operates independently at its maximum power point. Micro-inverters are ideal for roofs with multiple orientations or partial shading issues, though they are more expensive per watt and involve more components.

Hybrid inverters combine a solar PV inverter with a battery inverter in a single unit. They manage the flow of energy between the solar panels, battery, property loads, and grid. Hybrid inverters simplify the installation of combined PV and battery storage systems and are increasingly the standard choice for new installations.

Battery storage transforms a solar PV system from a daytime-only energy source into a round-the-clock energy solution. By storing excess solar generation during the day, the battery provides power during the evening peak demand period when electricity tariffs are highest and solar generation has stopped.

The dominant battery chemistry for domestic storage is lithium-ion, available in two main variants. Lithium Iron Phosphate (LFP) offers excellent cycle life (6,000+ cycles), superior thermal stability, and lower fire risk, but has a slightly lower energy density. Nickel Manganese Cobalt (NMC) offers higher energy density (smaller physical size for the same capacity) but fewer cycle life and slightly higher thermal risk. Popular UK battery brands use both chemistries.

Key specifications to understand include: usable capacity (the actual energy available after depth of discharge limits), continuous power rating(the maximum sustained output in kW), peak power rating (short-term maximum for startup loads), and round-trip efficiency (typically 90 to 95%, meaning 5 to 10% of stored energy is lost in the charge/discharge cycle).

BS 7671:2018+A2:2022 Section 558 covers the wiring regulations for electrical energy storage systems, including requirements for disconnection, isolation, marking, and protection against electric shock from stored energy.

Any generation equipment connected to the electricity distribution network must comply with the relevant Engineering Recommendation — G98 for smaller installations and G99 for larger ones.

G98 (formerly G83) applies to installations with a generating capacity up to 16A per phase — that is 3.68 kW for single-phase connections and 11.04 kW for three-phase connections. G98 installations require only a simple notification to the Distribution Network Operator (DNO) within 28 days of commissioning. Most domestic solar PV installations (typically 3 to 4 kWp) fall within the G98 threshold.

G99 (formerly G59) applies to installations above the G98 limits. G99 requires a formal application to the DNO before installation begins. The DNO will assess the network capacity at the connection point and may require network reinforcement before approving the connection. The application process can take 45 to 90 working days, so it must be factored into the project timeline. Commercial rooftop PV installations and larger domestic systems with battery storage may exceed the G98 threshold and require G99.

Both G98 and G99 require anti-islanding protection — the inverter must automatically disconnect from the grid within 0.5 seconds if the grid supply is lost, to prevent the PV system from energising the distribution network while engineers may be working on it.

Solar PV installation involves working at height on rooftops, handling DC circuits that cannot be switched off while the panels are exposed to light, and connecting to the grid supply. A thorough understanding of the safety risks is essential.

DC safety is the primary concern specific to solar PV. Unlike AC circuits that can be isolated at the consumer unit, PV panels generate voltage whenever light falls on them. A typical domestic string voltage can be 300 to 600 V DC, which is potentially lethal. DC isolators must be provided at both the array end (on the roof) and the inverter end. Cable runs between the roof array and the inverter must use double-insulated solar-rated cable (typically 4 mm² or 6 mm² single-core).

Before any roof work, assess for the presence of asbestos-containing materials in the roof structure. Pre-2000 buildings may have asbestos cement roof tiles, soffits, or backing sheets that could be disturbed during mounting rail installation.

Cable sizing for DC circuits follows the same principles as AC circuits but uses DC voltage for the voltage drop calculation. BS 7671 Section 712 contains the specific requirements for solar PV installations, including isolation, protection, and marking requirements.

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