All values read as zero or the SunSpec NaN sentinel. Why?

SunSpec Model 701 registers are at model-relative offsets, not fixed absolute addresses. The actual holding register base shifts depending on which models precede it in the device's SunSpec map. Perform a full SunSpec model scan (read from address 40001 and walk the model chain) to locate the correct base address before reading any point.

Power and energy readings look wrong by a factor of 10 or 100. What is happening?

All measurement registers in Model 701 are raw integers that must be multiplied by 10 raised to the power of the corresponding scale factor register (for example, w_sf for active power). The scale factor is a signed int16 and may be negative. Read the relevant _sf register and apply it before displaying or storing the value.

The gateway connects but per-phase registers (wl2, wl3) all return NaN. Is this a wiring problem?

NaN on per-phase registers is expected for single-phase and split-phase devices: only L1 registers are populated in those configurations. Check the actype register first. If actype confirms three-phase but L2 and L3 registers still return NaN, the device firmware may not implement those optional points; consult the device PICS document.

Frequency register hz returns an implausible value. How do I interpret it?

The hz register is a uint32 spanning two Modbus registers. SunSpec encodes all values in big-endian byte order across registers. If your Modbus client is reading the two 16-bit words in the wrong order, the result will be wrong. Confirm your client uses big-endian word order, then apply hz_sf to obtain hertz.

Free Modbus template: SunSpec Model 701 — DER AC Measurement

Name: SunSpec Model 701 — DER AC Measurement
Brand: SunSpec
SKU: 788f465d-ab62-4bc3-a2b8-afbd8a2cb86c

SunSpec Model 701, known as DERMeasureAC, is the approved AC measurement information model for Distributed Energy Resources such as solar inverters and battery storage systems. Accessed over Modbus TCP, it exposes a comprehensive read-only register set covering per-system and per-phase active power, apparent power, reactive power, power factor, current, line-to-line and line-to-neutral voltage, grid frequency, cumulative injected and absorbed energy in both watt-hours and var-hours, six temperature points, throttling state, DER operating mode, alarm bitfields, and SunSpec scale factors. This template gives installers a single standardized interface for monitoring any IEEE 1547-2018 compliant DER without device-specific register hunting.

Registers (72)

72 read / 0 write

Name	Address	Function	Type	Unit	Access
id SunSpec model identifier, fixed value 701 for DERMeasureAC.	0	FC03	uint16		R
l Model payload length in registers, excluding id and l.	1	FC03	uint16		R
actype AC wiring type: single-phase, split-phase, or three-phase.	2	FC03	uint16		R
st DER operational state, enumerated status code.	3	FC03	uint16		R
invst Inverter state, device-specific enumerated status code.	4	FC03	uint16		R
connst Grid connection state: connected, disconnected, or transitioning.	5	FC03	uint16		R
alrm Active alarm bitfield, 32 bits, one bit per alarm type.	6	FC03	uint32		R
dermode Active DER operating mode bitfield, 32 bits.	8	FC03	uint32		R
w Total three-phase active power, watts, positive = export.	10	FC03	int16	W	R
va Total three-phase apparent power, volt-amperes.	11	FC03	int16	VA	R
var Total three-phase reactive power, var, positive = inductive.	12	FC03	int16	Var	R
pf Total power factor, scaled integer using pf_sf.	13	FC03	int16		R
a Total AC current, amperes, sum across phases.	14	FC03	int16	A	R
llv Average line-to-line voltage across all phase pairs.	15	FC03	uint16	V	R
lnv Average line-to-neutral voltage across all phases.	16	FC03	uint16	V	R
hz Grid frequency, hertz, scaled using hz_sf.	17	FC03	uint32	Hz	R
totwhinj Cumulative active energy injected to grid, watt-hours.	19	FC03	uint64	Wh	R
totwhabs Cumulative active energy absorbed from grid, watt-hours.	23	FC03	uint64	Wh	R
totvarhinj Cumulative reactive energy injected, var-hours.	27	FC03	uint64	Varh	R
totvarhabs Cumulative reactive energy absorbed, var-hours.	31	FC03	uint64	Varh	R
tmpamb Ambient temperature at device location, degrees Celsius.	35	FC03	int16	°C	R
tmpcab Internal cabinet temperature, degrees Celsius.	36	FC03	int16	°C	R
tmpsnk Heatsink temperature, degrees Celsius.	37	FC03	int16	°C	R
tmptrns Transformer temperature, degrees Celsius.	38	FC03	int16	°C	R
tmpsw Switching component temperature, degrees Celsius.	39	FC03	int16	°C	R
tmpot Other internal temperature point, degrees Celsius.	40	FC03	int16	°C	R
wl1 Phase L1 active power, watts.	41	FC03	int16	W	R
val1 Phase L1 apparent power, volt-amperes.	42	FC03	int16	VA	R
varl1 Phase L1 reactive power, var.	43	FC03	int16	Var	R
pfl1 Phase L1 power factor, scaled integer using pf_sf.	44	FC03	int16		R
al1 Phase L1 current, amperes.	45	FC03	int16	A	R
vl1l2 Line-to-line voltage between phases L1 and L2, volts.	46	FC03	uint16	V	R
vl1 Phase L1 line-to-neutral voltage, volts.	47	FC03	uint16	V	R
totwhinjl1 Phase L1 cumulative active energy injected, watt-hours.	48	FC03	uint64	Wh	R
totwhabsl1 Phase L1 cumulative active energy absorbed, watt-hours.	52	FC03	uint64	Wh	R
totvarhinjl1 Phase L1 cumulative reactive energy injected, var-hours.	56	FC03	uint64	Varh	R
totvarhabsl1 Phase L1 cumulative reactive energy absorbed, var-hours.	60	FC03	uint64	Varh	R
wl2 Phase L2 active power, watts.	64	FC03	int16	W	R
val2 Phase L2 apparent power, volt-amperes.	65	FC03	int16	VA	R
varl2 Phase L2 reactive power, var.	66	FC03	int16	Var	R
pfl2 Phase L2 power factor, scaled integer using pf_sf.	67	FC03	int16		R
al2 Phase L2 current, amperes.	68	FC03	int16	A	R
vl2l3 Line-to-line voltage between phases L2 and L3, volts.	69	FC03	uint16	V	R
vl2 Phase L2 line-to-neutral voltage, volts.	70	FC03	uint16	V	R
totwhinjl2 Phase L2 cumulative active energy injected, watt-hours.	71	FC03	uint64	Wh	R
totwhabsl2 Phase L2 cumulative active energy absorbed, watt-hours.	75	FC03	uint64	Wh	R
totvarhinjl2 Phase L2 cumulative reactive energy injected, var-hours.	79	FC03	uint64	Varh	R
totvarhabsl2 Phase L2 cumulative reactive energy absorbed, var-hours.	83	FC03	uint64	Varh	R
wl3 Phase L3 active power, watts.	87	FC03	int16	W	R
val3 Phase L3 apparent power, volt-amperes.	88	FC03	int16	VA	R
varl3 Phase L3 reactive power, var.	89	FC03	int16	Var	R
pfl3 Phase L3 power factor, scaled integer using pf_sf.	90	FC03	int16		R
al3 Phase L3 current, amperes.	91	FC03	int16	A	R
vl3l1 Line-to-line voltage between phases L3 and L1, volts.	92	FC03	uint16	V	R
vl3 Phase L3 line-to-neutral voltage, volts.	93	FC03	uint16	V	R
totwhinjl3 Phase L3 cumulative active energy injected, watt-hours.	94	FC03	uint64	Wh	R
totwhabsl3 Phase L3 cumulative active energy absorbed, watt-hours.	98	FC03	uint64	Wh	R
totvarhinjl3 Phase L3 cumulative reactive energy injected, var-hours.	102	FC03	uint64	Varh	R
totvarhabsl3 Phase L3 cumulative reactive energy absorbed, var-hours.	106	FC03	uint64	Varh	R
throtpct Current output throttling level, percent of rated capacity.	110	FC03	uint16	Pct	R
throtsrc Throttle source bitfield indicating which constraint is limiting output.	111	FC03	uint32		R
a_sf Scale factor exponent applied to all current registers.	113	FC03	int16		R
v_sf Scale factor exponent applied to all voltage registers.	114	FC03	int16		R
hz_sf Scale factor exponent applied to the frequency register.	115	FC03	int16		R
w_sf Scale factor exponent applied to all active power registers.	116	FC03	int16		R
pf_sf Scale factor exponent applied to all power factor registers.	117	FC03	int16		R
va_sf Scale factor exponent applied to all apparent power registers.	118	FC03	int16		R
var_sf Scale factor exponent applied to all reactive power registers.	119	FC03	int16		R
totwh_sf Scale factor exponent applied to all active energy registers.	120	FC03	int16		R
totvarh_sf Scale factor exponent applied to all reactive energy registers.	121	FC03	int16		R
tmp_sf Scale factor exponent applied to all temperature registers.	122	FC03	int16		R
mnalrminfo Manufacturer-defined alarm detail string, free-form text.	123	FC03	string		R