Solar Panel Control via Mobile App

Implementing Solar Panel Management via Mobile Applications

A solar system is not just panels. It's a chain: panels → inverter → battery pack (optional) → grid connection point. Mobile applications manage not the panels directly, but the inverter and energy storage management system. Each inverter manufacturer — Huawei FusionSolar, SolarEdge, Fronius, SMA, GoodWe — has its own API or protocol. There is no unified standard.

Inverter Protocols

For most small systems, use the manufacturer's cloud API — simpler and doesn't require opening ports on the local network. For industrial installations and offline operation — use local Modbus TCP.

Huawei FusionSolar OpenAPI

One of the popular inverters in Europe and CIS countries. The API requires authentication via HTTPS Basic + systemCode:

// iOS
struct FusionSolarClient {
    let baseURL = URL(string: "https://intl.fusionsolar.huawei.com/thirdData")!
    var token: String?

    mutating func login(userName: String, systemCode: String) async throws {
        let body = ["userName": userName, "systemCode": systemCode]
        let response: LoginResponse = try await post("/login", body: body)
        token = response.data.token
    }

    func getStationList() async throws -> [Station] {
        let response: StationListResponse = try await post(
            "/getStationList",
            body: ["pageNo": 1]
        )
        return response.data.list
    }

    func getRealTimeData(stationCode: String) async throws -> RealTimeData {
        return try await post("/getStationRealKpi", body: ["stationCodes": stationCode])
    }
}

Key metrics from getStationRealKpi: radiation_intensity (insolation), theory_power (theoretical power), inverter_power (actual generation), power_profit (generation in kWh per day), use_power (consumption).

Fronius Solar API: Local REST

Fronius inverters provide REST API directly from the inverter without cloud:

GET http://192.168.1.20/solar_api/v1/GetPowerFlowRealtimeData.fcgi

Response:

{
  "Body": {
    "Data": {
      "Site": {
        "Mode": "produce-load-grid",
        "P_Grid": -1250.5,
        "P_Load": -2800.0,
        "P_PV": 4050.5,
        "P_Akku": null,
        "E_Day": 18.4,
        "E_Year": 4230.0
      }
    }
  }
}

P_Grid — negative value means feeding to the grid. P_Load — home consumption. P_PV — current generation. The difference is clear: 4050 W is generated, 2800 W is consumed, 1250 W is fed to the grid.

Fronius API is queried directly from the application only within the local network. For remote access — use a reverse proxy with authentication or Fronius Solar.web API.

Dashboard: Energy Flow Visualization

The key screen is an energy flow diagram: panels → home → grid → battery. Animated arrows show flow direction. In Flutter:

class EnergyFlowPainter extends CustomPainter {
  final double pvPower;    // generation
  final double gridPower;  // <0 to grid, >0 from grid
  final double loadPower;  // consumption
  final double batteryPower; // <0 charging, >0 discharging

  @override
  void paint(Canvas canvas, Size size) {
    _drawNode(canvas, pvIcon, pvPosition, '$pvPower W');
    _drawNode(canvas, homeIcon, homePosition, '$loadPower W');
    _drawNode(canvas, gridIcon, gridPosition, '${gridPower.abs()} W');

    if (pvPower > 0) {
      _drawAnimatedArrow(canvas, pvPosition, homePosition,
          color: Colors.green, active: true);
    }
    if (gridPower < 0) {
      _drawAnimatedArrow(canvas, homePosition, gridPosition,
          color: Colors.orange, active: true);
    }
  }
}

Control: Inverter Operating Modes

SolarEdge and Huawei allow switching modes via API: Self-Consumption (maximize own usage), Time-of-Use (charge battery during off-peak hours), Export Limitation (restrict grid feed to a set value).

Command via SolarEdge API:

suspend fun setStorageCommand(siteId: String, command: StorageCommand): Result<Unit> {
    return withContext(Dispatchers.IO) {
        runCatching {
            val response = api.setStorageCommand(
                siteId = siteId,
                body = StorageCommandBody(
                    mode = command.mode.apiValue,
                    chargeLimit = command.chargeLimit,
                    dischargeLimit = command.dischargeLimit,
                )
            )
            if (!response.isSuccessful) {
                throw ApiException(response.code(), response.message())
            }
        }
    }
}

Changing inverter settings is an operation with consequences. UX must require explicit confirmation and show the current mode separately from the pending command.

Developing a mobile application for monitoring a single solar system via cloud API: 2-3 weeks. Supporting multiple inverters, local Modbus TCP, mode management and automation: 5-8 weeks. Cost is calculated after clarifying equipment.