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Solar · The Lead

Maryland signs plug-in solar into law — 1,200W per meter, 391W UL-exempt, effective 1 October

Governor Wes Moore signed HB 1532 (the Utility RELIEF Act) on 12 May, putting Maryland's plug-in solar provisions on the books. Residential customers may run portable PV up to 1,200W per utility meter from 1 October; devices rated 391W or less are exempt from UL certification; systems above that must be UL-listed (or by an equivalent national lab). No utility fees, no interconnection process — but customers must notify their utility and may be required to pay for an automatic locking disconnect switch. Maryland is the fifth US state to legalise plug-in solar, days before Colorado's HB 26-1007 (1,920W cap) follows.

Maryland's Utility RELIEF (Reducing Energy Load Inflation for Everyday Families) Act was signed by Governor Wes Moore on Tuesday 12 May 2026 in the third post-session bill-signing ceremony of the year, as Chapter 353 of the 2026 session laws. The bill is sweeping — data-centre cost-allocation, EmPOWER-program reforms, grid-modernisation provisions — but the line that matters to DC-system builders is the plug-in solar carve-out.

From 1 October 2026, Maryland residential customers may operate a portable solar energy generating system rated up to 1,200W per utility meter that is "designed to feed power into a standard outlet" and certified by UL or an equivalent national testing laboratory. Devices with a rated output of 391W or less are exempt from the UL-certification requirement entirely. Eligible systems are exempt from utility fees and from the standard residential-interconnection process. The trade-off: customers must notify their utility, provide system information, and — if the utility requires it — pay for installation of an automatic locking disconnect switch.

The 1,200W cap is the same number Colorado picked for HB 26-1007 before its legislature raised it to 1,920W; both states copy a 391W lower-tier exemption from utility-tested Maryland and Colorado plug-in-PV working groups. The numbers are not arbitrary. A standard 15A, 120V US branch circuit has 1,800W of headroom; 1,200W leaves comfortable margin for other loads on the same circuit. The 391W floor maps approximately to the smaller class of pre-assembled microinverter-plus-panel kits already on sale in the EU, where Germany's plug-in cap is 800W under EN 50549-1.

Maryland now joins Utah, Maine, Virginia (passed both chambers, awaiting signature) and Colorado in the legal column. Thirty-three states plus DC have plug-in-PV bills in committee. The practical near-term question is product supply: there is currently no widely-available UL 9540-listed plug-in PV kit on US shelves at the 1,200W level. Bluetti, Anker, EcoFlow and Zendure all sell balcony-solar product in the EU; bringing those into Maryland-compliant form is a UL-listing exercise, not an engineering one — but it has to happen before October before the law's intended audience can buy anything off the shelf.

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Charging

Mastervolt ships IP67 waterproof Mac Plus 48V DC-DC family — four bi-directional variants for unenclosed marine installs

Mastervolt announced an IP67 waterproof line of its bi-directional Mac Plus 48V DC-DC chargers on 7–8 May. Four configurations cover the 12V/48V cross-charging market: 48/12-50A, 12/48-15A, 48/24-30A and 24/48-15A. Reinforced aluminium casing, touch-safe connector cover, parallel operation above 100A, supports lead-acid through LiFePO4 with Mastervolt's '3-step+' algorithm. Targeted at fishing boats, trailers and mobile applications where the charger has to live outside an enclosure.

Mastervolt, part of the Navico Group, announced an IP67-rated waterproof variant of the Mac Plus 48V DC-DC charger range on Thursday 7 May (BoatNews) and Friday 8 May (Marine Industry News). Four configurations bracket the 12V/48V cross-charging space: 48/12-50A, 12/48-15A, 48/24-30A and 24/48-15A. All four retain the bi-directional architecture introduced with the existing Mac Plus 48V two years ago — either battery bank can act as input or output, with automatic engine detection preventing accidental starter-battery discharge.

What the IP67 version adds is a reinforced aluminium housing and a touch-safe connector cover, allowing installation in spaces that are unenclosed — bilges, anchor lockers, trailer toolboxes, fishing-platform consoles — without an additional weatherproof enclosure. The "3-step+" charging algorithm is retained, as is multi-chemistry support (open lead-acid, AGM, gel, lithium including LiFePO4) and integration with MasterBus, CZone and NMEA 2000. Multiple units can be paralleled to exceed 100A of effective DC current. The release does not disclose pricing or distributor availability dates; given the existing Mac Plus 48V's pricing band, expect the IP67 variants in the same general region with a modest weatherproofing premium.

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Monitoring

Victron drops the SolarSense 750 — wireless irradiance and panel-temperature sensor at $102

Victron Professional published the SolarSense 750 on 13 May. It's a self-powered Bluetooth Low Energy sensor that reports solar irradiance, estimated PV power, and panel temperature in real time to VictronConnect, VRM and Node-RED. IP65 enclosure, internal 40 mAh / 3.6V battery topped up by an integrated PV cell, $102 USD at Nomadic Supply. Part number SLS300175100. Less for system protection, more for telling you when an MPPT is throttling vs panel-limited.

Victron Energy posted the SolarSense 750 to its Professional news feed on Tuesday 13 May. The device is a small standalone wireless sensor — IP65-rated, 150×85×40mm-class enclosure — that measures real-time solar irradiance, photovoltaic panel temperature, and an estimated PV power figure derived from the two. It speaks Bluetooth Low Energy and surfaces in VictronConnect for direct read-out, in VRM for cloud logging, and via published Node-RED scripts for automation logic. The unit is self-powered: an integrated PV cell trickle-charges a 40 mAh / 3.6V internal battery.

The intended use case is diagnostic and operational rather than protective. In off-grid and grid-limited systems where the MPPT throttles output once batteries are full, the SolarSense gives you the available PV power independent of the charge controller — so you can decide when to switch on discretionary loads (heat-pump pre-heat, EV charging, hot-water dump) or compare expected vs actual production to flag shading, soiling or wiring faults. Pre-sales site assessment is the other use case Victron is pitching: leave a sensor in a candidate location for a few weeks and get a real irradiance profile instead of a TMY estimate. US retail is live at Nomadic Supply at $102 under part number SLS300175100; one-year warranty.

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Solar

Bluetti launches Balco balcony-solar ecosystem in Paris — Balco 260, Balco 500, and a Transfer Hub that retrofits existing power stations

Bluetti unveiled the Balco series on 12 May in Paris: an all-in-one balcony-solar product line built around three pieces. Balco 260 (up to 15kWh expansion, four MPPTs, 2,400W PV), Balco 500 (up to 11kW in three-unit parallel, 70–470V high-voltage MPPT, 4,300W PV), and a Balco Transfer Hub that turns existing portable power stations into grid-tied balcony PV with 800W of grid-compliant output. AI-driven energy management, Wi-Fi linking up to six units via the BLUETTI Space platform, Home Assistant compatible. EU-focused; pricing not yet disclosed.

Bluetti unveiled the Balco series at a Paris launch event on Tuesday 12 May. The product line has three pieces: a compact storage-and-inverter unit (Balco 260) supporting up to 15kWh of total energy via five expansion batteries, with four MPPT inputs that absorb 2,400W of PV; a larger sibling (Balco 500) with a high-voltage 70–470V MPPT design good for 4,300W of PV and up to 11kW of output in a three-unit parallel configuration; and a separate accessory called the Balco Transfer Hub, a grid-tied micro-inverter / controller that lets owners of existing Bluetti portable power stations push their solar surplus to a balcony micro-inverter at up to 800W of grid-compliant output.

The pitch is platform: an AI-driven energy management system (AI-EMS) syncs real-time pricing, generation forecasts and cloud data to decide whether to feed in, store, or discharge; up to six Balco units link wirelessly through a Wi-Fi-based "BLUETTI Space" co-ordination layer; Home Assistant, Google Home, Amazon Alexa, Shelly and Everhome integrations are listed. Standby consumption is quoted at 4.5W and system efficiency at 96.11%. Pricing and country-specific availability were not disclosed at the Paris launch. The geographic emphasis — Paris, EN 50549-grade certifications, 800W Schuko-style grid feed-in — places this firmly in the EU balcony-solar market for now, ahead of the US AHJ catch-up triggered by Maryland's HB 1532 this same week.

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Battery

Anker Solix Solarbank 4 E5000 Pro launches in Berlin — 5kWh stack, 4 MPPTs, Schuko grid feed-in at 800W

Anker Solix announced the Solarbank 4 E5000 Pro in Berlin on 12 May. 5kWh per stack on 314Ah LFP cells, 5kW of PV input across four integrated MPPTs (up to 12 panels), modular to 30kWh, IP66, -20°C to +55°C, 10,000-cycle / 15-year claim. 2.5kW household supply, 800W grid feed-in through a standard Schuko plug, 2.5kW off-grid port with 10ms UPS switchover. Pre-order RRP €1,999 (€1,499 with promo until 11 June); expansion battery €1,049 (from €1,399); German launch date 12 June 2026.

Anker Solix unveiled the Solarbank 4 E5000 Pro in Berlin on Tuesday 12 May, two weeks after the company's Australian Solix XE announcement (covered in our 11 May edition). Despite the family-name overlap, this is a distinct product: smaller (5kWh per stack vs 7kWh on the XE), lower-output (2.5kW continuous vs 5kW bidirectional), explicitly targeted at the German plug-in-solar market with an 800W Schuko grid feed-in port and a 2.5kW dedicated off-grid output for emergencies with 10ms UPS-mode switchover.

The cell chemistry is consistent with Anker's recent direction — 314Ah LFP — and the modular architecture lets owners stack up to six total units for 30kWh of storage. Four integrated MPPTs accept up to 12 solar modules at 5kW combined input. The IP66 housing is rated -20°C to +55°C, and Anker carries over the Anka AI voice assistant and PowerOS firmware platform from the XE. Pre-order RRP is €1,999; an introductory €1,499 promo runs until 11 June, with binding orders accepted 11–21 June and the official German launch on 12 June 2026. The expansion battery is €1,049 (from €1,399 RRP). No US listing has been announced — and won't be straightforward, since the 800W Schuko-plug feed-in design is not a US 120V product.

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Industry

Dragonfly Energy lands a 500-truck Stevens Transport order on a soft RV quarter; relaunches Battle Born e-commerce

Dragonfly Energy reported Q1 2026 net sales of $9.7M (above guidance) on 14 May. The RV channel was soft — March US new-RV retail sales were down more than 20% year-over-year — but the company received its largest-ever trucking order to date: $3M+ from Stevens Transport for nearly 500 trucks, the first tranche of a planned 2,500-truck fleet transition. Q2 guidance is $13.2M (36% sequential growth). On 13 May the company also relaunched the Battle Born consumer e-commerce site and accepted a $527K Nevada Tech Hub award for cylindrical-cell prototyping capacity.

Dragonfly Energy (Nasdaq: DFLI) — parent company of Battle Born Batteries — reported Q1 2026 results on Wednesday 14 May. Net sales came in at $9.7M with a gross margin of 17.6%, split $5.8M OEM and $3.7M direct-to-consumer. CEO Denis Phares characterised the recreational-vehicle environment as soft (US new-RV retail down >20% year-over-year in March), with signs of stabilisation rolling into Q2. Cost-reduction measures and rental-space consolidation are running at roughly $9M of annualised adjusted EBITDA improvement.

The trucking line is more interesting. Dragonfly disclosed a $3M-plus order from Stevens Transport for nearly 500 trucks — the company's largest single trucking purchase order ever — as the first tranche of a planned 2,500-truck fleet transition to Dragonfly's battery platform. Q2 net-sales guidance is $13.2M (36% sequential growth), with adjusted-EBITDA loss narrowing to roughly $1.9M. Separately, on 13 May the company relaunched the Battle Born consumer e-commerce site with an expanded Battle Born Academy content layer aimed at retail-and-installer education, and accepted a $527,000 second-round Nevada Tech Hub award earmarked for cylindrical-cell prototyping equipment and supplier-quality testing infrastructure — capacity that would feed the cylindrical packs Battle Born has been signalling for the heavy-trucking duty cycle.

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The Background · Market Analysis

Plug-in solar's US inflection: policy and product, finally on the same week

Three things crossed each other this week that haven't been in the same calendar square before: Maryland signed plug-in solar into state law, Bluetti unveiled a complete balcony-PV ecosystem in Paris, and Anker Solix launched a 5kWh/Schuko residential storage block in Berlin. The first event happened in a state where, until 12 May, plug-in solar lived in a regulatory grey zone where utilities could refuse interconnection at their discretion. The second and third happened in markets where plug-in PV has been a real consumer product category for the better part of three years. The two trajectories had been moving on separate tracks. They are now crossing, in the US, for the first time.

The product side is mature. Germany counted roughly 1.5 million registered Steckersolar systems by mid-2025 — most of them 600W or 800W microinverter-plus-panel kits sold off Amazon DE or in the local Bauhaus DIY chain, on a regulatory framework (EN 50549-1, the 800W cap, simplified notification to the Marktstammdatenregister) the country progressively eased between 2019 and 2024. Bluetti's Balco and Anker's Solarbank 4 E5000 Pro are the next layer up the stack: integrated storage, AI-EMS, Schuko grid feed-in capped at the German 800W threshold, with optional dedicated off-grid output ports for outage backup. The engineering is mature; the customer-acquisition cost is reasonable; the regulatory friction is low.

The US has had none of that. Until October 2025 there was no state-level statutory basis for plug-in PV anywhere in the country. Utah and Maine moved first; Maryland and Virginia followed; Colorado will be fifth or sixth depending on signing order. Three things are worth flagging about how the Maryland statute is structured.

The 391W threshold has product-design implications, not just paperwork ones

Devices rated 391W or less are explicitly exempt from UL certification under HB 1532. That is not a number plucked from the air — it lines up with the small-microinverter-plus-single-panel kit class that dominates the EU low end. The number is also small enough that it doesn't materially threaten the 15A circuit it plugs into. The above-391W band requires UL listing (or equivalent-lab listing). Today, no mainstream balcony-PV product on the US market carries UL 9540 listing at the 1,200W level. Bluetti and Anker will need to push their EU-stamped designs through US-listing labs before they can be Maryland-compliant in size meaningful to the customer this law is aimed at.

The 1,200W cap is circuit-aware

A 15A, 120V branch circuit is rated for 1,800W continuous. The 1,200W ceiling leaves 600W of headroom for other loads on the same circuit. This is the same calculation the EU used to settle on its 600W/800W limits — there, on a 16A 230V circuit; here, scaled to the smaller US circuit. Colorado went higher (1,920W cap) which makes sense given the state's larger detached-housing stock and the assumption of dedicated plug placement, but it also means a Colorado kit will sit right at the practical limit of a typical 15A circuit and leave essentially no margin. Maryland's choice is the conservative one.

The locking-disconnect option is the implementation question

HB 1532 leaves the utility a discretionary tool: they may require an installed automatic-locking AC disconnect switch, at customer cost. That decision will be made by the individual electric distribution companies — Pepco, BGE, Delmarva Power, Potomac Edison, Southern Maryland Electric Cooperative — and it is the single biggest determinant of how much practical friction a Maryland plug-in-PV install actually carries. If every utility requires a disconnect, the cost stack roughly doubles for a small kit. If none do, the law works as a clean simplification. The October 1 effective date is essentially the deadline for utilities to publish their compliance posture; expect that posture to track the utility's existing attitude toward residential generation.

None of which solves the catalogue problem. There is no UL-listed 1,200W balcony-PV kit on a Home Depot shelf in Hagerstown right now. By 1 October there may be one, and by spring 2027 there will certainly be several. The Maryland legislation is the demand signal that pulls UL listings forward. The Bluetti and Anker launches this week are the suppliers, in EU dress, walking into the room.

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Community Pulse

What the forums are talking about this week

r/diysolar's 14 May thread "Setting up Balcony Solar plug-in with Battery Back-up" lands the same week as the Maryland signing: a SoCal homeowner with a south-facing balcony asking the community how to design a 4×400W in-series, plug-in-plus-battery system to offset wall-outlet load and bank excess for the evening. The replies cycle through the same set of questions Maryland's HB 1532 will surface en masse in October — circuit-shared loads, AC vs DC coupling, AHJ inspection paths, whether to certify or stay sub-391W. Useful reading for anyone in a state that's about to add plug-in-solar legislation to its 2026 session.

On r/diysolar, a 14 May post — "Pylontech Force-L1 + Growatt SPF 6000 ES Plus — CAN (L52) connects but reads SOC as 1%" — surfaces a clean, reproducible Pylontech-Growatt CAN-bus issue. Three SPF 6000 ES Plus inverters in parallel, two Pylontech Force-L1 stacks (BMS FC0048-100S), Main CPU 100.06 / Slave CPU 101.05. With Prog 05 = LI and Prog 36 = L52 selected, the LCD does switch from voltage to percentage display — confirming the handshake works — but the inverter clamps SOC at 1% instead of reporting the real ~40%. Classic BMS-CAN-profile mismatch where the protocol byte-order or scaling is wrong, and the thread is worth reading as a how-to-diagnose template even if you don't have this hardware combination.

r/diysolar's 15 May thread "Network guy trying to build a solar-powered surveillance trailer" is a useful sanity-check case for autonomy-budget design: 2×450W solar, 2 batteries (the OP didn't fully specify chemistry / Ah), loads dominated by cameras, networking and Starlink, expected 24/7 off-grid operation. The replies push hard on actual continuous load (Starlink alone is 50–100W idle), winter-solar derating, and whether the manual-tilt mount is realistic for an unattended trailer. The thread is a good worked example of how the "we'll just throw 900W of panels at it" instinct breaks down against winter days at northern latitudes.

Threads

Product Radar

New and notable components announced or launched this week

SolarSense 750 Wireless PV Monitor — Victron Energy

Monitoring

Self-powered Bluetooth Low Energy sensor that measures solar irradiance, panel temperature and estimated PV power in real time. Surfaces in VictronConnect, VRM and Node-RED. IP65 housing. Internal 40 mAh / 3.6V battery trickle-charged by an integrated PV cell. Part number SLS300175100. Use case: tell when the MPPT is throttling vs panel-limited, drive discretionary-load logic, diagnose shading or maintenance issues; also useful as a multi-week pre-sales site-assessment tool.

$102 Listed at Nomadic Supply (US) and other Victron distributors from 13 May 2026; one-year warranty Find on Amazon →

First Victron-stamped wireless irradiance sensor at a sensible price. The Node-RED hook is the interesting part — easy to use the SolarSense reading as a load-dispatch trigger without bolting on a separate weather station.

Mac Plus 12/48-15 IP67 (and 48/12-50A, 48/24-30A, 24/48-15A variants) — Mastervolt

Charging

Bi-directional DC-DC charger family with IP67 waterproof rating — reinforced aluminium housing and touch-safe connector cover for installation in unenclosed environments (bilges, anchor lockers, trailer toolboxes). Four configurations across 12V/48V and 24V/48V cross-charging. 3-step+ charging algorithm, lead-acid through LiFePO4. MasterBus, CZone and NMEA 2000 integration. Parallelable to exceed 100A combined.

Not disclosed at announcement Announced 7–8 May 2026; distributor listing expected through Mastervolt dealer network

The IP67 variant is the relevant change vs the existing 2024 48V Mac Plus family. For fishing boats, trailers, and marine 12V/48V system charging where the box has to live outside, this is the cleanest off-the-shelf bi-directional option short of Victron's much pricier Orion XS line.

Balco 260 / Balco 500 / Balco Transfer Hub — Bluetti

Solar

Plug-and-play balcony-solar ecosystem launched in Paris. Balco 260: 15kWh stack (with five expansion batteries), four MPPTs absorbing 2,400W, 96.11% system efficiency, 4.5W standby. Balco 500: 70–470V high-voltage MPPT, 4,300W PV input, up to 11kW output in three-unit parallel, 15kWh max storage. Balco Transfer Hub: retrofit accessory that turns existing Bluetti portable power stations into grid-tied balcony PV with 800W of grid-compliant output. Wi-Fi linking up to six units via BLUETTI Space; Home Assistant, Google Home, Alexa, Shelly compatible.

Not disclosed at Paris launch Launched 12 May 2026 in Paris; EU emphasis; country availability not yet published

Genuinely interesting because of the Transfer Hub. Most portable-power-station owners already have several kWh of LFP sitting in their garage; turning that into balcony-PV-compatible grid-feed-in storage for €a-few-hundred is a tighter pitch than buying a new all-in-one box.

Solix Solarbank 4 E5000 Pro — Anker

Battery

5kWh modular residential battery built on 314Ah LFP cells. Five-kilowatt PV input split across four integrated MPPTs (up to 12 panels). 2.5kW household supply; 800W Schuko grid feed-in; 2.5kW dedicated off-grid port with 10ms UPS-mode switchover. IP66, -20°C to +55°C operating range. Modular to 30kWh across six total units. Anka voice assistant, PowerOS firmware. Distinct from the larger Solix XE (7kWh, 5kW bidirectional) launched in Australia 30 April.

€1,999 RRP (€1,499 with introductory promo); expansion battery €1,049 (from €1,399 RRP) Pre-orders open from 12 May 2026; binding orders 11–21 June; official German launch 12 June 2026; US availability not announced

EU balcony-solar plug-in storage with off-grid backup as a built-in feature. The Schuko grid feed-in path is Europe-specific; this is not a US product as currently configured, but the Maryland HB 1532 trajectory is exactly the kind of regulatory environment that pulls a US 120V variant onto the roadmap.