Saturday, October 03, 2015

Micro Solar - The Future is Bright

Micro-Solar - A New Approach to Increasing the Installed PV Capacity


Recent changes in the solar grant scheme have had a very negative effect on the UK's fledgling solar pv industry. The rug has been pulled out from under the feet of all those that set up installation businesses. The FITs have been decimated - and so now there is virtually no reason why anyone would make a large, long term investment in a permanent pv installation.

Feed in tariffs (FITs) have been reduced to the point where there is no longer an incentive to invest in a photovoltaic solar installation.  Our current Government seem to be more interested in kickstarting the UK fracking industry and selling off large sections of our critical electricity generation infrastructure to the Chinese.

The reduction in FITs to just 1.63p/kWh in January 2016 is going beyond miserly, and at such levels completely removes any economic reason to export to the grid.

Without the grid export option, the pv output can only be used locally, and if used efficiently will help reduce the amount of power consumed from the grid.

In this post, I propose a new way to look at solar pv, in a way that could appeal to a much greater customer base, and at a price that is much more affordable.

A single 250 W pv panel, could reduce your electricity bills by up to 10%, and if repeated by millions, rather than 10's of thousands of consumers around the country, it would significantly increase the installed solar capacity.

There are many potential customers for micro-solar. Those who can afford an expenditure of up to £1000,  but not the £6K - £10K for a full system.  With the FITs gone, the market for larger systems will have evaporated.

Sources of PV Panels

A recent web-search revealed small solar systems being made and marked in China for about £750, complete with inverter, battery and controller.

If you choose to shop around on Taobao (Chinese ebay) you can find 250W panels for about £60 each. Even if these prices doubled by the time you had shipped to the UK.

If you want to search for your own panels - the Chinese term is 250W 太阳能板  - Happy Hunting!


A unit from the grid (Southern Electric October 2015) is currently 14.0385p (incl VAT). My annual consumption is approximately 2400 kWh.

A small system consisting of 4 x 250Wp panels would yield between 850 and 900kWh per annum, displacing about 35% of my grid consumption.

If we think that 800kWh of this can be used in the home, it could reduce the incoming electricity bill by
£112 per year.

Importing 250W panels from China at £0.50 per peak watt, means that the system could recover its costs in 5 years - without a grant or FITs, nor the additional expense of a grid-tied inverter and professional MCS installation.

The Case for Microsolar

I will define a Micro-Solar system as an installed system of 1000Wp or less.  With currently available panels this would consist of up to 4, 250Wp panels.  These panels are typically 1.6m x 1m and weigh about 21kg.

The emphasis being that microsolar should be small, cheap and portable.  Portable in the sense that it's not a permanent installation, can be deployed on a wall mounted bracket, especially if roof access is not available, and can be moved from property to property a required - a benefit for young adults in the rented sector. As it is a small system, typically it would be a DIY installation, not requiring specialist tools or equipment. One attractive use would be on a south facing balcony, with the panel securely clamped to the balcony rail.

As the system is small, it is essential to get the best use from it, and the best conversion efficiency. This will entail the use of high efficiency dc/dc converters and LiFePO4 batteries used for energy storage.

Whilst we are all familiar with ac mains electricity, and almost all of our appliances and consumer electronics products are intended for ac plug in use - for some products the ac is an inconvenience, and a huge source of inefficiency. With the rise of portable computing products, smart phones and other mobile gadgets - these increasingly require a 5V charge - from a standard "USB" style charger.

If you are interested in USB chargers - this excellent post covers them in great detail, in terms of efficiency, power quality and safety.

The underlying message is that small ac powered USB chargers are at best only 65 to 80% efficient, and this is a figure that has a lot of room for improvement.  Direct dc/dc conversion could improve this considerably.  Starting with a 12V input, this can be converted with 92% efficiency to 5V using a synchronous switching converter - such as this one from ON Semiconductor.

With the increase in electric bike technology - LiPo battery packs are available with high capacities and low cost.  The real benefit of Lithium battery chemistry is that it has a very high charge efficiency. Packs of welded lithium cells are typically available in 350W to 1kWh capacities.

What can you power with 1kWh per day?

Several years ago, when I was working from home, I mused on the idea of a home-office workspace that ran on just 200W. At the end of that post, I speculated that perhaps even 100W was possible. In the 10 years since that post we have had the benefit of  more power efficient laptops and netbooks, LCD monitors, LiPo batteries and LED lighting. I now believe that I can run the same work environment on an average power budget of  just 100W - and that puts home working well within the reach of a microsolar installation.

Whilst thinking about the e-bike battery packs, it occurred to me that a lot more people are cycling these days, particularly within our urban cities.  An e-bike consumes typically about 20Wh per mile, and so a 36V 10A pack could offer a range of about 15 to 18 miles between charges - depending on terrain and how much you pedal.  By using several e-bike battery packs as the basis of the modular battery store, it is possible to have a freshly charged pack every morning. Three or four interchangeable packs would form the system, so on any day there is always about 1kWh of storage.

Having arrived back home after a day at the office, the battery is fully charged and ready for the evenings use.  This would involve recharging of portable computing devices, smart phones and LED lighting in the evening.

A quick check on the specs of a 43" Samsung smart tv - showed a 51W consumption - so 6 hours of TV gaming or web-browsing in the evening is going to be well within the capability of a microsolar system.

What about the Winter?

Microsolar systems will run at much reduced capacity during the Winter months.

The graph below shows monthly output, for south facing panels, in southern England, averaged over 3 years (2012-2014) - scaled to reflect the output of a single 250 Wp panel.
Normalised output for a 250Wp panel
It shows that useful output is available from March until September - approaching 1kWh per day, but for 4 months of the year, you are getting only about a third of the summer peak.  If you are reliant on the solar contribution to charge your bike pack, then you will need to find an efficient means to recharge your pack from the ac mains during the winter months.

Fortunately, the designers of switched mode power supplies have made significant advances over the years in improving power supply efficiency. This is particularly important in the server farm and telecoms applications where efficiency and reliability is paramount.  These efficiency improvements have filtered down to the PC power supplies - and you can now buy a desktop PC supply with better than 95% efficiency.

Combining a high efficiency psu with a LiPo battery bank, means that you can top up your store when required, at maximum efficiency. It also helps maintain your output on cloudy days.

In summary, all the components for a high efficiency microsolar system are available and affordable.

In the next post I will go into some more detail of the proposed system.

1 comment:

Jean-Claude Wippler said...

Here's another source of energy...