Updated on December 7, 2023


Created on August 7, 2017

Solar Ear HD-424

Upcoming Update

The Solar Ear Hearing Aid HD-424 is a hearing aid that is charged with a solar powered battery charger.

Developed By
  1. Solar Ear
Tested By
  • Department of Audiology, Bispebjerg Hospital
  • Special Olympics International
  • Stanford University
  • University of Copenhagen
  • Western Michigan University
Content Partners


Product Description

The Solar Ear Hearing Aid HD-424 is a Behind-The-Ear (BTE) hearing instrument that is suitable for mild to severe hearing loss. The hearing aid uses rechargeable batteries that are charged with a solar powered battery charger.

Target SDGs

SDG 3: Good Health and Well-Being

Market Suggested Retail Price


Target Users (Target Impact Group)


Distributors / Implementing Organizations

Solar Ear, Auto Alternative Nig LTD, INOVA Centro Auditivo, ONG Instituto de Rehabilitación de Valparaíso, Rejoice Hearing Systems

Competitive Landscape

Direct competitors include ALIMCO Behind the Ear Hearing Aid.

Manufacturing/Building Method

Hearing Aid HD-424 is manufactured by Solar Ear, formerly Deaftronics, in Botswana and in Brazil and China. The manufacturing sites are independently run, owned, and operated.Interview with representative  Young deaf people are hired by Solar Ear and taught how to manufacture and assemble the hearing aids.

Intellectural Property Type


User Provision Model

Solar Ear has national distributors in Botswana, Brazil, Canada, Chile, China, Egypt, Mexico, Nigeria, Pakistan, and the U.S.A. that can be contacted to purchase the HD-424 Hearing Aid. Customers residing in countries without a national distributor can fill out an online contact form to request a quote.

Distributions to Date Status

18,000 HD-424s have been distributed as of August 2017. 50,000 Solar Ear hearing aids, 100,000 solar chargers, and 250,000 rechargeable hearing aid batteries have been sold as of July 2017. Interview with representative

Peak OSLP 90 (dB SPL)

140 dB SPL

High frequency average (HFA) OSLP 90 (dB SPL)

133 dB SPL

HFA full-on gain (dB)

70 dB

Total harmonic distortion for 500Hz (%), 800Hz (%) and 1600Hz (%)

1.5%, 1%, 1%

Equivalent input noise (dB)

25 dB

Number of frequency channels


Battery type

675Interview with representative

Battery current (mA)

1.8 mA

Memory switch (Y/N)


T-coil feature (Y/N)


Design Specifications

The HD-424 is a rechargeable device suited for profound hearing loss. Features: - Super Power BTE - Optimized DSP hearing aid - 2 Channels WDRC Multi Memories Amplifier - 12 Bands Frequency Shaping - 10 Bands Layered Noise Reduction - Low-level Expansion - Adaptive Feedback Cancellation AFC Technology(Advanced) - Wideband MPO Control - Low Battery Warning - Telecoil function - Up to three programs The Solar Ear Hearing Aid Battery Charger can be charged via solar energy, household light, or a Nokia cell phone charger. The rechargeable batteries and solar battery charger can also be used with 95% of all Behind-The-Ear hearing aids on the market today. Used with a conventional earmold. Interview with representative

Product Schematics

Technical Support

The listening programs must be set by a hearing healthcare professional or the manufacturer. Troubleshooting guidance is available in the user manual. All Solar Ear hearing aids and accessories come with a 2-year warranty.Interview with representative

Replacement Components

Solar Ear will repair or fix any hearing aids or accessories during or beyond the warranty period for no additional charge. Solar Ear will also provide two rechargeable batteries for free upon request. Interview with representative


The rechargeable battery can withstand at least 500 cycles. The lifetime of the hearing aid is approximately five years.Interview with representative

Manufacturer Specified Performance Parameters

Affordable hearing (below ~70 USD) , rechargeable hearing aid Interview with representative

Vetted Performance Status

Results from a clinical trial of a Solar Ear BTE hearing aid with 21 participants found that the hearing aid offers substantial benefit to the hearing impaired with a severe predominantly sensorineural hearing impairment (i.e >60 dB at 2 kHz) and gives amplification in the desired frequency range that is aligned with National Acoustic Laboratories (NAL) recommendations. The HD-424 passed testing at Stanford University. Interview with representative


Patients with middle ear infection should not wear the hearing aid until cured unless otherwise instructed. Disposal Guidance: Return to audiologist where it was purchased. Upon the unit's return to the manufacturer, they will renovate it and donate it to a school for the deaf. Interview with representative

Complementary Technical Systems

Audiometer exam

Academic Research and References

Parving, A., Christensen, B., Nielsen, J., Konradsson, K., Clinical Trial of a Low-Cost High-Power Compression Hearing Aid, Department of Audiology, Bispebjerg Hospital H: S, 2400 Copenhagen NV, Denmark

Parving, A., Christensen, B., 2004, Clinical Trial of a Low-Cost, Solar-Powered Hearing Aid, Acta Otolaryngol, May, 124(4), pp. 416-20.

Compliance with regulations

FDA and CE approved

Evaluation methods

Evaluation: Fitting of the test-HA was based on the NAL-R prescription rule (2) or the POGO-rule (11) depending on the degree of the subject´s HI and all the fittings were validated by insertion gain measurements, using a Siemens Unity-IG equipment. The immediate benefit of the test- HA was measured by the difference in speech recognition scores without and with the test-HA in quiet (SRS) and in background noise (S/N=5 dB)( SRSN). After a 6-8 week trial period the person met for follow-up and completion of a structured interview based on the IOI-HA (3,4). The IOI-HA form includes 7 questions with responses according to a graded scale 1-5, where 5 is the maximum score. At the end of the session the subject should make a preference for the test-HA or the previously fitted HA named HA-AA.

Other Information


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