diff --git a/src/main/java/home/gateway/adapters/solarman/ModbusRtuFrame.java b/src/main/java/home/gateway/adapters/solarman/ModbusRtuFrame.java
new file mode 100644
index 0000000..3329c24
--- /dev/null
+++ b/src/main/java/home/gateway/adapters/solarman/ModbusRtuFrame.java
@@ -0,0 +1,54 @@
+package home.gateway.adapters.solarman;
+
+import java.io.IOException;
+
+/** Modbus RTU frame: unit id, PDU, CRC16 with the low byte first. */
+final class ModbusRtuFrame {
+
+    private static final int CRC_LENGTH = 2;
+    private static final int MIN_LENGTH = 1 + 1 + CRC_LENGTH;
+
+    private ModbusRtuFrame() {
+    }
+
+    static byte[] build(int unitId, byte[] pdu) {
+        byte[] frame = new byte[1 + pdu.length + CRC_LENGTH];
+        frame[0] = (byte) unitId;
+        System.arraycopy(pdu, 0, frame, 1, pdu.length);
+        int crc = crc16(frame, frame.length - CRC_LENGTH);
+        frame[frame.length - 2] = (byte) crc;
+        frame[frame.length - 1] = (byte) (crc >> 8);
+        return frame;
+    }
+
+    static boolean hasValidCrc(byte[] frame) {
+        if (frame.length < MIN_LENGTH) {
+            return false;
+        }
+        int crc = crc16(frame, frame.length - CRC_LENGTH);
+        return frame[frame.length - 2] == (byte) crc && frame[frame.length - 1] == (byte) (crc >> 8);
+    }
+
+    static byte[] parse(byte[] frame, int expectedUnitId) throws IOException {
+        if (!hasValidCrc(frame)) {
+            throw new IOException("Modbus RTU frame has a bad CRC or is too short");
+        }
+        if ((frame[0] & 0xFF) != expectedUnitId) {
+            throw new IOException("Modbus RTU frame from unit " + (frame[0] & 0xFF) + ", expected " + expectedUnitId);
+        }
+        byte[] pdu = new byte[frame.length - 1 - CRC_LENGTH];
+        System.arraycopy(frame, 1, pdu, 0, pdu.length);
+        return pdu;
+    }
+
+    static int crc16(byte[] data, int length) {
+        int crc = 0xFFFF;
+        for (int i = 0; i < length; i++) {
+            crc ^= data[i] & 0xFF;
+            for (int bit = 0; bit < 8; bit++) {
+                crc = (crc & 1) != 0 ? (crc >>> 1) ^ 0xA001 : crc >>> 1;
+            }
+        }
+        return crc;
+    }
+}
diff --git a/src/main/java/home/gateway/adapters/solarman/SolarmanV5Transport.java b/src/main/java/home/gateway/adapters/solarman/SolarmanV5Transport.java
new file mode 100644
index 0000000..cef249e
--- /dev/null
+++ b/src/main/java/home/gateway/adapters/solarman/SolarmanV5Transport.java
@@ -0,0 +1,176 @@
+package home.gateway.adapters.solarman;
+
+import home.gateway.adapters.modbus.ModbusTransport;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.time.Duration;
+import java.util.Arrays;
+
+/**
+ * Modbus RTU carried in Solarman V5 frames over the Wi-Fi logger's TCP port (usually 8899).
+ * One connection is kept and reused, one request at a time; after any error it is closed and
+ * the next call reconnects. All V5 fields are little endian, the RTU frame inside is not.
+ */
+public final class SolarmanV5Transport implements ModbusTransport {
+
+    public record Settings(String host, int port, long loggerSerial, Duration connectTimeout, Duration readTimeout) {
+    }
+
+    private static final int START = 0xA5;
+    private static final int END = 0x15;
+    private static final int REQUEST_CONTROL_CODE = 0x4510;
+    private static final int RESPONSE_CONTROL_CODE = 0x1510;
+    private static final int HEADER_LENGTH = 11;
+    private static final int TRAILER_LENGTH = 2;
+    private static final int REQUEST_PAYLOAD_PREFIX = 15;
+    private static final int RESPONSE_PAYLOAD_PREFIX = 14;
+    private static final int INVERTER_FRAME_TYPE = 0x02;
+    private static final int DOUBLE_CRC_LENGTH = 2;
+
+    private final Settings settings;
+    private Socket socket;
+    private int sequence = (int) (Math.random() * 256);
+
+    public SolarmanV5Transport(Settings settings) {
+        this.settings = settings;
+    }
+
+    @Override
+    public synchronized byte[] exchange(int unitId, byte[] requestPdu) throws IOException {
+        try {
+            Socket connection = connection();
+            int requestSequence = nextSequence();
+            OutputStream out = connection.getOutputStream();
+            out.write(requestFrame(requestSequence, ModbusRtuFrame.build(unitId, requestPdu)));
+            out.flush();
+            byte[] rtu = readResponseRtu(new DataInputStream(connection.getInputStream()), requestSequence);
+            return ModbusRtuFrame.parse(rtu, unitId);
+        } catch (IOException | RuntimeException e) {
+            closeConnection();
+            throw e;
+        }
+    }
+
+    @Override
+    public synchronized void close() {
+        closeConnection();
+    }
+
+    private Socket connection() throws IOException {
+        if (socket == null) {
+            Socket candidate = new Socket();
+            try {
+                candidate.connect(new InetSocketAddress(settings.host(), settings.port()),
+                        (int) settings.connectTimeout().toMillis());
+                candidate.setSoTimeout((int) settings.readTimeout().toMillis());
+            } catch (IOException e) {
+                candidate.close();
+                throw e;
+            }
+            socket = candidate;
+        }
+        return socket;
+    }
+
+    private void closeConnection() {
+        if (socket != null) {
+            try {
+                socket.close();
+            } catch (IOException ignored) {
+                // already failing; the next call reconnects
+            }
+            socket = null;
+        }
+    }
+
+    // Only the low byte is echoed by the logger; it counts the high byte itself.
+    private int nextSequence() {
+        sequence = (sequence + 1) & 0xFF;
+        return sequence;
+    }
+
+    private byte[] requestFrame(int requestSequence, byte[] rtu) {
+        int payloadLength = REQUEST_PAYLOAD_PREFIX + rtu.length;
+        ByteBuffer frame = ByteBuffer.allocate(HEADER_LENGTH + payloadLength + TRAILER_LENGTH)
+                .order(ByteOrder.LITTLE_ENDIAN);
+        frame.put((byte) START)
+                .putShort((short) payloadLength)
+                .putShort((short) REQUEST_CONTROL_CODE)
+                .putShort((short) requestSequence)
+                .putInt((int) settings.loggerSerial())
+                .put((byte) INVERTER_FRAME_TYPE)
+                .put(new byte[REQUEST_PAYLOAD_PREFIX - 1]) // sensor type and three timers, all zero
+                .put(rtu);
+        frame.put((byte) checksum(frame.array(), frame.position()));
+        frame.put((byte) END);
+        return frame.array();
+    }
+
+    private byte[] readResponseRtu(DataInputStream in, int requestSequence) throws IOException {
+        byte[] header = new byte[HEADER_LENGTH];
+        in.readFully(header);
+        ByteBuffer head = ByteBuffer.wrap(header).order(ByteOrder.LITTLE_ENDIAN);
+        int payloadLength = head.getShort(1) & 0xFFFF;
+        if ((header[0] & 0xFF) != START) {
+            throw new IOException("V5 response does not start with 0xA5");
+        }
+        if (payloadLength < RESPONSE_PAYLOAD_PREFIX) {
+            throw new IOException("V5 response payload too short: " + payloadLength);
+        }
+        byte[] rest = new byte[payloadLength + TRAILER_LENGTH];
+        in.readFully(rest);
+        verify(head, header, rest, requestSequence);
+        byte[] rtu = new byte[payloadLength - RESPONSE_PAYLOAD_PREFIX];
+        System.arraycopy(rest, RESPONSE_PAYLOAD_PREFIX, rtu, 0, rtu.length);
+        return withoutDoubleCrc(rtu);
+    }
+
+    private void verify(ByteBuffer head, byte[] header, byte[] rest, int requestSequence) throws IOException {
+        int controlCode = head.getShort(3) & 0xFFFF;
+        if (controlCode != RESPONSE_CONTROL_CODE) {
+            throw new IOException("Unexpected V5 control code 0x" + Integer.toHexString(controlCode));
+        }
+        if ((head.getShort(5) & 0xFF) != requestSequence) {
+            throw new IOException("V5 response answers another request");
+        }
+        if (head.getInt(7) != (int) settings.loggerSerial()) {
+            throw new IOException("V5 response from another logger");
+        }
+        byte[] checked = new byte[header.length + rest.length - TRAILER_LENGTH];
+        System.arraycopy(header, 0, checked, 0, header.length);
+        System.arraycopy(rest, 0, checked, header.length, rest.length - TRAILER_LENGTH);
+        if ((rest[rest.length - 2] & 0xFF) != checksum(checked, checked.length)) {
+            throw new IOException("V5 response has a bad checksum");
+        }
+        if ((rest[rest.length - 1] & 0xFF) != END) {
+            throw new IOException("V5 response does not end with 0x15");
+        }
+    }
+
+    // Deye loggers append a second, always zero CRC. Check the trimmed frame first: a frame
+    // followed by its own CRC also passes the CRC check, with the CRC taken as payload.
+    private static byte[] withoutDoubleCrc(byte[] rtu) {
+        if (rtu.length > DOUBLE_CRC_LENGTH) {
+            byte[] trimmed = Arrays.copyOf(rtu, rtu.length - DOUBLE_CRC_LENGTH);
+            if (ModbusRtuFrame.hasValidCrc(trimmed)) {
+                return trimmed;
+            }
+        }
+        return rtu;
+    }
+
+    /** Sum of all bytes between the start byte and the checksum, modulo 256. */
+    private static int checksum(byte[] frame, int end) {
+        int sum = 0;
+        for (int i = 1; i < end; i++) {
+            sum += frame[i] & 0xFF;
+        }
+        return sum & 0xFF;
+    }
+}
diff --git a/src/test/java/home/gateway/adapters/solarman/ModbusRtuFrameTest.java b/src/test/java/home/gateway/adapters/solarman/ModbusRtuFrameTest.java
new file mode 100644
index 0000000..30f2745
--- /dev/null
+++ b/src/test/java/home/gateway/adapters/solarman/ModbusRtuFrameTest.java
@@ -0,0 +1,47 @@
+package home.gateway.adapters.solarman;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.IOException;
+import org.junit.jupiter.api.Test;
+
+class ModbusRtuFrameTest {
+
+    private static final byte[] READ_10_AT_0 = {0x01, 0x03, 0x00, 0x00, 0x00, 0x0A, (byte) 0xC5, (byte) 0xCD};
+
+    @Test
+    void buildsTheStandardExampleWithCrcLowByteFirst() {
+        byte[] pdu = {0x03, 0x00, 0x00, 0x00, 0x0A};
+        assertArrayEquals(READ_10_AT_0, ModbusRtuFrame.build(1, pdu));
+    }
+
+    @Test
+    void crcOfAKnownResponse() {
+        byte[] frame = {0x01, 0x04, 0x02, (byte) 0xFF, (byte) 0xFF};
+        assertEquals(0x80B8, ModbusRtuFrame.crc16(frame, frame.length));
+    }
+
+    @Test
+    void parsesBackThePdu() throws IOException {
+        assertArrayEquals(new byte[] {0x03, 0x00, 0x00, 0x00, 0x0A}, ModbusRtuFrame.parse(READ_10_AT_0, 1));
+    }
+
+    @Test
+    void rejectsBadCrc() {
+        byte[] frame = READ_10_AT_0.clone();
+        frame[7] ^= 1;
+        assertThrows(IOException.class, () -> ModbusRtuFrame.parse(frame, 1));
+    }
+
+    @Test
+    void rejectsOtherUnit() {
+        assertThrows(IOException.class, () -> ModbusRtuFrame.parse(READ_10_AT_0, 2));
+    }
+
+    @Test
+    void rejectsTooShortFrame() {
+        assertThrows(IOException.class, () -> ModbusRtuFrame.parse(new byte[] {0x01, 0x03}, 1));
+    }
+}
diff --git a/src/test/java/home/gateway/adapters/solarman/SolarmanV5TransportTest.java b/src/test/java/home/gateway/adapters/solarman/SolarmanV5TransportTest.java
new file mode 100644
index 0000000..b6c8476
--- /dev/null
+++ b/src/test/java/home/gateway/adapters/solarman/SolarmanV5TransportTest.java
@@ -0,0 +1,277 @@
+package home.gateway.adapters.solarman;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.DataInputStream;
+import java.io.IOException;
+import java.net.ServerSocket;
+import java.net.Socket;
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import java.time.Duration;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+import java.util.function.Function;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+class SolarmanV5TransportTest {
+
+    private static final long SERIAL = 3112107147L;
+    private static final int UNIT = 1;
+    private static final byte[] READ_REQUEST = {0x03, 0x00, 0x00, 0x00, 0x02};
+    private static final byte[] READ_RESPONSE = {0x03, 0x04, 0x00, 0x2A, 0x01, (byte) 0xF4};
+
+    private FakeLogger logger;
+    private SolarmanV5Transport transport;
+
+    @BeforeEach
+    void start() throws IOException {
+        logger = new FakeLogger();
+        transport = new SolarmanV5Transport(new SolarmanV5Transport.Settings(
+                "localhost", logger.port(), SERIAL, Duration.ofSeconds(2), Duration.ofMillis(500)));
+    }
+
+    @AfterEach
+    void stop() throws IOException {
+        transport.close();
+        logger.close();
+    }
+
+    @Test
+    void sendsDocumentedRequestFrame() throws IOException {
+        logger.respondWith(request -> response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE)));
+
+        transport.exchange(UNIT, READ_REQUEST);
+
+        byte[] frame = logger.requests.get(0);
+        byte[] rtu = ModbusRtuFrame.build(UNIT, READ_REQUEST);
+        ByteBuffer buffer = ByteBuffer.wrap(frame).order(ByteOrder.LITTLE_ENDIAN);
+        assertEquals(28 + rtu.length, frame.length);
+        assertEquals((byte) 0xA5, frame[0]);
+        assertEquals(15 + rtu.length, buffer.getShort(1));
+        assertEquals(0x4510, buffer.getShort(3));
+        assertEquals(SERIAL, buffer.getInt(7) & 0xFFFFFFFFL);
+        assertEquals(0x02, frame[11]);
+        for (int i = 12; i < 26; i++) {
+            assertEquals(0, frame[i], "timer byte " + i);
+        }
+        assertArrayEquals(rtu, Arrays.copyOfRange(frame, 26, 26 + rtu.length));
+        assertEquals(sum(frame, 1, frame.length - 2), frame[frame.length - 2] & 0xFF);
+        assertEquals(0x15, frame[frame.length - 1]);
+    }
+
+    @Test
+    void returnsTheResponsePdu() throws IOException {
+        logger.respondWith(request -> response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE)));
+
+        assertArrayEquals(READ_RESPONSE, transport.exchange(UNIT, READ_REQUEST));
+    }
+
+    @Test
+    void acceptsTheDoubleCrcOfDeyeLoggers() throws IOException {
+        byte[] rtu = ModbusRtuFrame.build(UNIT, READ_RESPONSE);
+        byte[] doubled = Arrays.copyOf(rtu, rtu.length + 2);
+        logger.respondWith(request -> response(request, doubled));
+
+        assertArrayEquals(READ_RESPONSE, transport.exchange(UNIT, READ_REQUEST));
+    }
+
+    @Test
+    void reusesOneConnectionForSuccessiveRequests() throws IOException {
+        logger.respondWith(request -> response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE)));
+
+        transport.exchange(UNIT, READ_REQUEST);
+        transport.exchange(UNIT, READ_REQUEST);
+
+        assertEquals(1, logger.connections);
+        assertEquals(2, logger.requests.size());
+    }
+
+    @Test
+    void usesIncreasingSequenceNumbers() throws IOException {
+        logger.respondWith(request -> response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE)));
+
+        transport.exchange(UNIT, READ_REQUEST);
+        transport.exchange(UNIT, READ_REQUEST);
+
+        int first = logger.requests.get(0)[5] & 0xFF;
+        int second = logger.requests.get(1)[5] & 0xFF;
+        assertEquals((first + 1) & 0xFF, second);
+    }
+
+    @Test
+    void rejectsBadChecksumAndReconnects() throws IOException {
+        logger.respondWith(request -> {
+            byte[] bad = response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE));
+            bad[bad.length - 2] ^= 1;
+            return bad;
+        });
+        assertThrows(IOException.class, () -> transport.exchange(UNIT, READ_REQUEST));
+
+        logger.respondWith(request -> response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE)));
+        assertArrayEquals(READ_RESPONSE, transport.exchange(UNIT, READ_REQUEST));
+        assertEquals(2, logger.connections);
+    }
+
+    @Test
+    void rejectsBadRtuCrc() {
+        byte[] rtu = ModbusRtuFrame.build(UNIT, READ_RESPONSE);
+        rtu[rtu.length - 1] ^= 1;
+        logger.respondWith(request -> response(request, rtu));
+
+        assertThrows(IOException.class, () -> transport.exchange(UNIT, READ_REQUEST));
+    }
+
+    @Test
+    void rejectsWrongControlCode() {
+        logger.respondWith(request -> {
+            byte[] frame = response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE));
+            frame[4] = 0x17;
+            return withFixedChecksum(frame);
+        });
+
+        assertThrows(IOException.class, () -> transport.exchange(UNIT, READ_REQUEST));
+    }
+
+    @Test
+    void rejectsResponseToAnotherSequence() {
+        logger.respondWith(request -> {
+            request[5]++;
+            return response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE));
+        });
+
+        assertThrows(IOException.class, () -> transport.exchange(UNIT, READ_REQUEST));
+    }
+
+    @Test
+    void rejectsResponseFromAnotherUnit() {
+        logger.respondWith(request -> response(request, ModbusRtuFrame.build(2, READ_RESPONSE)));
+
+        assertThrows(IOException.class, () -> transport.exchange(UNIT, READ_REQUEST));
+    }
+
+    @Test
+    void reconnectsAfterTheLoggerDropsTheConnection() throws IOException {
+        logger.respondWith(request -> null);
+        assertThrows(IOException.class, () -> transport.exchange(UNIT, READ_REQUEST));
+
+        logger.respondWith(request -> response(request, ModbusRtuFrame.build(UNIT, READ_RESPONSE)));
+        assertArrayEquals(READ_RESPONSE, transport.exchange(UNIT, READ_REQUEST));
+        assertEquals(2, logger.connections);
+    }
+
+    @Test
+    void timesOutWhenTheLoggerStaysSilent() {
+        logger.respondWith(request -> new byte[0]);
+
+        assertThrows(IOException.class, () -> transport.exchange(UNIT, READ_REQUEST));
+    }
+
+    /** A V5 response as the logger sends it: echoes sequence and serial, status 1, three timers. */
+    private static byte[] response(byte[] request, byte[] rtu) {
+        ByteBuffer frame = ByteBuffer.allocate(11 + 14 + rtu.length + 2).order(ByteOrder.LITTLE_ENDIAN);
+        frame.put((byte) 0xA5)
+                .putShort((short) (14 + rtu.length))
+                .putShort((short) 0x1510)
+                .put(request, 5, 2)
+                .put(request, 7, 4)
+                .put((byte) 0x02)
+                .put((byte) 0x01)
+                .putInt(100)
+                .putInt(200)
+                .putInt(300)
+                .put(rtu)
+                .put((byte) 0)
+                .put((byte) 0x15);
+        return withFixedChecksum(frame.array());
+    }
+
+    private static byte[] withFixedChecksum(byte[] frame) {
+        frame[frame.length - 2] = (byte) sum(frame, 1, frame.length - 2);
+        return frame;
+    }
+
+    private static int sum(byte[] frame, int from, int to) {
+        int total = 0;
+        for (int i = from; i < to; i++) {
+            total += frame[i] & 0xFF;
+        }
+        return total & 0xFF;
+    }
+
+    /** Local stand-in for the Wi-Fi logger. A null answer drops the connection, an empty one stays silent. */
+    private static final class FakeLogger implements AutoCloseable {
+
+        final List<byte[]> requests = new CopyOnWriteArrayList<>();
+        volatile int connections;
+        private final ServerSocket server = new ServerSocket(0);
+        private final List<Socket> accepted = new CopyOnWriteArrayList<>();
+        private volatile Function<byte[], byte[]> responder = request -> null;
+
+        FakeLogger() throws IOException {
+            Thread.ofVirtual().start(this::acceptLoop);
+        }
+
+        int port() {
+            return server.getLocalPort();
+        }
+
+        void respondWith(Function<byte[], byte[]> responder) {
+            this.responder = responder;
+        }
+
+        private void acceptLoop() {
+            try {
+                while (true) {
+                    Socket socket = server.accept();
+                    accepted.add(socket);
+                    connections++;
+                    Thread.ofVirtual().start(() -> serve(socket));
+                }
+            } catch (IOException closed) {
+                // server closed at the end of the test
+            }
+        }
+
+        private void serve(Socket socket) {
+            try (socket) {
+                DataInputStream in = new DataInputStream(socket.getInputStream());
+                while (true) {
+                    byte[] request = readRequest(in);
+                    requests.add(request.clone());
+                    byte[] answer = responder.apply(request);
+                    if (answer == null) {
+                        return;
+                    }
+                    socket.getOutputStream().write(answer);
+                }
+            } catch (IOException closed) {
+                // client went away
+            }
+        }
+
+        private static byte[] readRequest(DataInputStream in) throws IOException {
+            byte[] header = new byte[11];
+            in.readFully(header);
+            int payload = ByteBuffer.wrap(header).order(ByteOrder.LITTLE_ENDIAN).getShort(1);
+            byte[] frame = new byte[11 + payload + 2];
+            System.arraycopy(header, 0, frame, 0, 11);
+            in.readFully(frame, 11, payload + 2);
+            return frame;
+        }
+
+        @Override
+        public void close() throws IOException {
+            server.close();
+            for (Socket socket : new ArrayList<>(accepted)) {
+                socket.close();
+            }
+        }
+    }
+}