Submitting InstitutionUniversity of Cambridge
Unit of AssessmentGeneral Engineering
Summary Impact TypeEconomic
Research Subject Area(s)
Engineering: Electrical and Electronic Engineering, Materials Engineering
Technology: Communications Technologies
Summary of the impact
Research by the University of Cambridge Department of Engineering (DoEng)
on high-reliability micro-inverters for use in solar power systems was
commercialised by DoEng spin-out company Enecsys Limited. Since 2008,
Enecsys has attracted GBP34M in private investment, increased its number
of employees from 7 to 75 people across three offices in Europe, North
America and Asia-Pacific, and shipped more than 150,000 micro-inverter
units. Its revenue in financial year 2012/13 was USD11.7M. Solar power
installers have confirmed that Enecsys' products, in comparison with
traditional string inverters, are: easier, cheaper and safer to install;
more reliable; and able to extract more energy from an array of solar
panels. Enecsys products are also changing the market for solar power with
simple plug-in solutions that home owners buy from retailers and install
Gehan Amaratunga became a Professor in the DoEng in 1998 and led the
Power Electronics Group. Amaratunga set his strategic research aim to be
power electronics for energy efficiency and renewable energy sources,
particularly solar photovoltaic (PV) power. He reviewed the
state-of-the-art of solar PV technologies in 1998 to refine his research
aim and to inform the creation of a new teaching module. During this
analysis, Amaratunga realised that the deployment of solar PV systems for
integration with mains voltage circuits and the grid was being hampered by
the cost and reliability of "string" inverters. A typical installation
would use one or two of these inverters to convert the 200-800V DC output
from a string of PV panels in series creating a complex, expensive and
hazardous single point of failure. Micro-inverters had been proposed by
others, but the high component count created cost and reliability
problems. Amaratunga's systems-level analysis and detailed knowledge of
power control devices led to his conclusion that micro-inverters of
sufficiently low cost and reliability could be deployed on each panel to
great advantage with a control architecture that eliminated a single point
of failure and allowed optimisation of energy transfer from each panel.
Amaratunga published his broad vision (Ref 1).
Amaratunga secured funding from Semelab, a UK-based semiconductor firm
for an ambitious research project (1999-2003) to investigate the ideal
option for a solar PV micro-inverter: a monolithic integrated circuit
using Silicon On Insulator (SOI) technology for both the management and
control functions of the micro-inverter. The research used simulation to
explore the design of such an integrated circuit, Semefab (a subsidiary of
Semelab) made experimental circuits for the team, and these circuits were
tested at the DoEng. The project was successful. It showed that
multi-voltage-level power electronic circuits working at different
switching frequencies could be integrated on the same substrate.
Specifically, it showed that low-voltage (~70V rated) first stage Metal
Oxide Semiconductor Field Effect Transistor switches and high-voltage
(~300V rated) second stage LIGBT (Lateral Isolated Gate Bipolar
Transistor) switch bridge inverter circuits could be integrated on a
single chip and applied to micro-inverters for solar PV.
In 2000-05, Amaratunga undertook another research project in parallel
with the first. This project focussed on control aspects of solar PV
systems, which were now viewed as key. It was funded by the Cambridge
Commonwealth Trust and an EC FW5 project called USHER "Urban Integrated
Solar Hydrogen Economy Realisation". This research was focused on the
system-level performance of solar installations. The first challenge was
to maximise the energy harvest of an array of panels by minimising the
impact of individual panel output variations caused by factors such as
shading. The second challenge was to achieve electronic control and
efficient transfer of small amounts of power to the grid, for instance,
when a micro-inverter was handling only 25W from a single 250W-rated panel
running at 10% of its capacity (in comparison, it was relatively easy to
design a traditional string inverter for a typical array of 20 similarly
rated panels, which would be handling 500W at 10% capacity).
The research was not published because Amaratunga and his research team
founded Enecsys Limited in July 2003 to exploit their results and they
needed to apply for patents. The first patent (Ref 2 with a priority date
of 6 May 2003) describes the fundamental architecture of a micro-inverter
together with its control strategy. It also includes the invention of a
single chip monolithic integrated circuit implementation of the
micro-inverter. It embodies the results of the research carried out by
Amaratunga and his team during the period 1999-2003 and underpinned
Enecsys. Amaratunga led further research in the DoEng with funding from
Enecsys between 2003 and 2006.
The research at the DoEng combined theoretical studies, analysis and
simulation with practical experiments. Solar PV arrays were built in the
DoEng and used extensively for trials. The focus shifted substantially
from the single chip concept to address the complex issues of the dynamic
stability of grid-connected solar PV systems and their control. In
particular stable and novel methods for Maximum Power Point Tracking
emanated from the research (Refs 3 and 4 with these results protected in
US patent 8405367). A number of new strategies and methods for improving
the dynamic stability of micro-inverters also resulted from the research.
This systems-level analysis then moved forward to address the long-term
performance of solar PV micro-inverter systems (Ref 5). Another major
outcome of the research was the elimination of the need for electrolytic
capacitors, which are unreliable and limit the period over which failure
free operation can be obtained. This was achieved with a novel
architecture which drastically reduced the amount of capacitance required
for energy ballasting in a single phase inverter (where the grid power
periodically transitions through a zero point, while the solar panel keeps
generating power). This enabled the use of long-life time polypropelene
capacitors, which are not available at high capacitance, and solution of
the reliability limitations (Ref 6 with the results protected in US patent
References to the research
1. Amaratunga, G.A.J. and Lorenz, L. Electronic devices for power
switching and power integrated circuits: the enabling technology for clean
energy. Invited paper. World Microtechnologies Congress, Expo 2000,
Hannover, Germany, September 2000, 1, 407 (VDE Verlag, 2000), ISBN
2. *Power Supply Circuits. Patent. Inventors: Mumtaz, A., Chisenga, L.
and Amaratunga, G.A.J. Priority date: 6 May 2003. PCT publication date: 18
November 2004. Patent number: US8067855.
3. Rodriguez, C. and Amaratunga, G.A.J. (2006) Lyapunov's stability and
operational margin of grid-connected photovoltaic modules. Proceedings of
the IASTED International Conference on Energy and Power Systems, Chiang
Mai, Thailand, 2006. pp. 178-183, ISBN 0-88986-586-8
4. Rodriguez, C. and Amaratunga, G.A.J. (2007) Analytic solution to the
photovoltaic maximum power point problem. IEEE T Circuits and Systems-I,
54. pp. 2054-2060, DOI: 10.1109/TCSI.2007.902537. ISSN 1549-8328
5. *Rodriguez, C. and Amaratunga, G.A.J. (2006) Dynamic maximum power
injection control of AC photovoltaic modules using current-mode control.
IEE P-Elect Pow Appl, 153. pp. 83-87, DOI: 10.1049/ip-epa:20050246. ISSN
6. *Rodriguez, C. and Amaratunga, G.A.J. (2008) Long-lifetime power
inverter for photovoltaic AC modules. IEEE T Ind Electron, 55. pp.
2593-2601, DOI: 10.1109/TIE.2008.922401. ISSN 0278-0046.
*Outputs that best represent the quality of the research.
Details of the impact
In 2003, Enecsys Limited was founded by Amaratunga (as Chairman), his
research team and an MBA student from the Judge Business School, who led
the development of the financial business plan. This followed their
success in winning the Cambridge Business Plan Competition earlier in the
same year (with the name "Cambridge Solar Electronics"). Enecsys aimed to
commercialise Amaratunga and his team's solar PV research. All relevant
DoEng intellectual property was assigned to Enecsys. Amaratunga continued
as Chairman until 2009, when the first round of venture capital funding
was completed. He remained as a Director until October 2010.
Enecsys won initial funding from Cambridge Enterprise (2005), the East of
England Development Agency (2004 and 2008) and the Carbon Trust 2008.
Enecsys funded further research in the DoEng, while Enecsys worked in
parallel to develop micro-inverter products. Enecsys has 36 issued patents
of which 13 have been granted in the US, a further 5 have been allowed,
with 39 pending (2013) (Ref 7).
Enecsys made sufficient progress with initial product development to win
A-round funding of GBP9M in November 2009 from Wellington Partners, Good
Energies and NES partners. The funding supported the development and
launch of three market-ready micro-inverter products: the single
micro-inverter (one inverter per solar PV panel), the monitoring system
and communications gateway. These were launched into the European and
North American markets in June 2010.
Enecsys secured further B-Round funding of GBP25M in May 2011 from its
existing investors and Climate Change Capital Partners, bringing the total
investment in Enecsys during the REF period to GBP34M. The funding led to
further product development and subsequent announcement of a dual
micro-inverter (one inverter for every two solar PV panels) in 2011.
All of the Enecsys micro-inverter products are founded on the
underpinning research that was undertaken in the DoEng. Enecsys reported
its first revenue in March 2011. It achieved USD1.4M in this first year of
sales, which grew to nearly USD11.7M in the financial year 2012/13.
Enecsys has shipped more than 150,000 micro-inverter units between 2008
and 2013. In 2013, it employs 75 people based in three offices in Europe,
North America and Asia-Pacific, which is an increase of 68 from the
beginning of 2008. Enecsys has established distribution agreements with
installers in: Australia, Austria, Belgium, Croatia, Denmark, France,
Germany, Greece, Hungary, Italy, Luxembourg, Malta, Mexico, Netherlands,
Spain, Switzerland, Turkey, UK, Canada, and USA (Ref 7).
These installers have achieved high-profile sales, for example, Afresh
Energy Limited has completed solar PV installations on over 225 homes in
the 2014 Commonwealth Games athletes' village in Glasgow using Enecsys
micro-inverters (Ref 8).
Enecsys products offer benefits versus traditional string inverters for
solar PV installations that were made possible by the underpinning DoEng
- Each individual solar PV panel can be controlled, so that the
performance of the panel can monitored and optimised for maximum energy
harvest. A domestic customer and Professor at Stanford University said
of his Enecsys equipped domestic system: "We decided to go with the
Enecsys micro inverter system rather than a more old fashioned string
inverter system because our roof situation here is pretty complex.
We've got a lot of shade. We've got a complicated roofline. Concerns
that would really make one these older systems impractical. The folks
at Enecsys estimated that we would be able to cover about two thirds
of our electricity needs with this installation. In practice, it turns
out to be more like 90%" (Ref 9)
- Installation is less complicated, faster and cheaper because the
design and location of the PV array is not influenced by shade.
PowerPac, a UK-distributor, states: "The new Enecsys solar micro
inverter solution is the latest breed of advanced solar technology
delivering a simplified PV array design. The new solar micro inverter
solution can now be installed on any available roof space due to its
new and innovative design. Whereas older versions are more difficult
to install, this one is a lot easier in comparison and therefore makes
it faster and cheaper to implement" (Ref 10). German PV system
installer, Mini Joule, gives similar evidence: "We trust Enecsys
micro inverters, because the system is easy to install, it is totally
`plug-and-play' and for complex installations with shading there are
no problems. And of course our clients love the monitoring system"
(Ref 9). Abakus Solar (USA) states: "Enecsys Micro Inverters
liberate installers from many previous shading-related constraints"
(Ref 11). An installation integrator based in Hawaii said, "The
Enecsys system allowed us to change the layout without having to get
new parts to install the inverters" (Ref 11).
- Less maintenance is needed, while lifetime and reliability is
increased, with Enecsys guaranteeing an operational lifetime for its
inverters that matches the typical 25-year lifetime of the solar PV
panels. Enecsys presents analysis of expected total lifetime maintenance
costs for a typical installation that shows reduction from GBP3000 using
string inverters to just GBP500 with Enecsys micro-inverters. PowerPac,
a UK distributor notes that "[Enecsys] maintenance levels are
significantly less" (Ref 10).
- Safety for system installers working at roof-top level is improved,
because Enecsys micro-inverters eliminate the need for high DC voltages.
The Managing Director of Powercon BV, who has 30 years' experience of
the PV industry, said "I've become aware of the safety issues
affecting solar installations" and chose Enecsys micro-inverters
for the installation on his own house "because the system is safer
due to the lower operating voltages" (Ref 9).
In addition to selling micro-inverters for permanent roof-top solar PV
arrays, Enecsys has worked with PV-panel manufacturers to create plug-in
solar power solutions in the home. The home owner sets up the solar PV
panel and simply plugs it into a standard mains outlet in the house. The
Enecsys micro inverter manages the conversion to alternating current and
synchronisation with mains electricity. In this way, the home owner
benefits from solar power substituting for grid power without any need for
expensive, professional installation. These kits sold by retailers in the
range from 200W to 1kW. Sales figures were not released (Ref 7).
The Global Cleantech Group, a leading global research and advisory firm
focused on innovation in energy and the environment, listed Enecsys in its
Global Cleantech 100 awards in each of 2010, 2011 and 2012 (Ref 12).
Sources to corroborate the impact
- Founder and now Principal Engineer at Enecsys can corroborate all
information about Enecsys
- Client page on Afresh Energy Limited website at http://afreshenergy.co.uk/clients
- Corporate video on Enecsys website at http://www.enecsys.com/resources/videos/
- Enecsys installers page on PowerPac Limited website at http://www.powerp.co.uk/enecsys-installers.html
- Case studies page on the Enecsys website at http://www.enecsys.com/resources/case-
- Global Cleantech 100 at http://www.cleantech.com/global100/global-cleantech-100/