In the UK’s fledgling PV industry there are some unexpected issues emerging.
One of those is related to the grid or ‘mains’ voltage. This should be, as
in the rest of Europe, fixed at 230V. However it can vary, and in reality
the legal limit is 230V plus or minus 10 percent, generally being higher
voltage close to the nearest transformer, and getting lower voltage as you
move away.

This is important for PV systems because the inverter must convert direct
current into mains compatible AC with an acceptable voltage level. Inverters
are also designed to shut down if there is a problem with the grid for
safety reasons.

In Germany, the voltage level is very precise (perhaps as you might expect)
and since Germany is the world’s largest solar market by far, most inverters
in Europe have their settings with Germany in mind. This means that when the
grid strays slightly away from 230V, the inverter temporarily shuts down. In
the UK, the grid is much more likely to deviate from 230V, meaning that with
German settings, an inverter could well spend more time off than on.

Luckily the problem is generally easily fixed by changing the inverter to
new settings which make it tolerant to a wider voltage range. The key point
to remember is that with the inverter shortage, products are being sold
which are completely unchanged from their German settings. This means you
need to be extra vigilent when buying an inverter to ensure compatibility.

A related topic, that I will soon cover, is to do with how lots of solar
energy connected to the grid can actually affect the grid voltage and
frequency – but that’s another issue.

If an inverter is used in the UK without any change in settings then chances
are, with our fluctuating grid, you will have peaks or dips in the voltage
that shut off the inverter from time to time. The solution is simply to
change the settings via the firmware to allow the inverter to carry on
working in a wider range of voltages.

The sun shone upon the festival goers at Glastonbury last week with usual scenes of rain and mud put on hold as thousands flocked to that corner of Somerset. With sunburn and dehydration an obvious risk for the crowds, the UV rays would have proved a welcome sight for Michael Eavis who plans to build the biggest solar farm in the UK. Eavis, the founder of Glastonbury festival hopes to take advantage of the recently introduced feed-in tariff to earn money for the energy he generates on the site.

The plan will consist of 1500sqm of panels at a cost of £550,000 on Pilton Farm and will be situated on the cow shed dubbed ‘Mootel’. With an obvious substantial outlay involved in the construction of the 1100 panels, Eavis will utilize the feed-in tariff to generate an income based on the units of energy his solar farm produces.

The feed-in tariff works by offering a guaranteed, premium rate for the units of renewable energy produced by the solar panels be they fed-back into the national grid or simply consumed by the owner of the farm. Eavis’ system for example expects to generate around 200 kilowatts of electricity a year generating £45,000 in income from the tariff, enough to pay for the installation in six years. With a 25 year lifetime of the project, Eavis can hope to generate a healthy profit once the high cost of the installation is recovered.

Although Michael Eavis is investing £50,000 of his own money into the solar farm, the rest is being invested by Triodos Bank who specialize in green investments. Eavis, explaining why he chose to invest his money in solar power stated,

“I’ve been planning this for a long time but the Gulf of Mexico oil spill has brought home just how urgent it is that we move to renewable electricity. We have already bought all the recycled fat from chip shops that we can find to run the generators during the festival and we wanted to create a permanent source of renewable energy. It makes sense to use some of the massive amount of free energy that comes from the sun.”

Understanding how to design a PV system is not rocket science, but it is more complex than many people consider. Here’s a very quick overview of the important points.

Solar panels produce direct current (DC). This means you need an inverter to turn that electricity into mains frequency alternating current (AC).  Inverters come in a range of power ratings. The more solar panels you have, the more power the inverter has to deal with, so the size and cost increases. It’s very important to match the size of the inverter to the number of solar panels.

If the inverter is too small, you will lose out on some of the energy that your system produces. If it is too large, the inverter may not perform at its optimum efficiency, and you will have paid for more than is necessary. In the UK, the optimum situation is to have an inverter that is rated at 80% of the power rating of your PV system, since it is rare you will be producing at 100% power.

More critically than getting the power right, you need to ensure the voltage and current of your solar panel system remains within the input range of the chosen inverter. To re-cap, solar panels on your roof are generally connected together in series, in a ‘string’. This increases the system voltage, but does not increase the current. Once a certain number of solar panels have been connected in series, the voltage will become too high and the system needs to be arranged in two strings, each of the same number of panels, connected in parallel. This generally occurs after a string exceeds 8 – 11 solar panels. When strings are connected in parallel, the currents add-up, but the voltage remains constant.

By adding more and more strings in parallel, the current and voltage can be controlled to remain in the inverter limits. For large solar installations, inverters can used that that have a very high power capacity, or alternatively it is possible to use many small inverters connected in parallel.

It is important to remember certain constraints. Inverters come in several sizes, but there may be some numbers of solar panels for which no inverter is ideal. For instance, because it is necessary for all stings to be equal in size, you can only use an even number of solar panels when using multiple strings. In addition, all solar panels must receive the same amount of sunlight when connected to the same inverter. It is no good to have some solar panels facing different directions on different parts of the roof. New technologies, soon to become widely avaialable that will make this process much easier. Namely micro-inverters, which convert DC to AC at every solar panel, will mean that solar panels can face different directions, however these are not yet widely available.

If you have a sales visit from a solar company, make sure the salesman understands these points as he’s designing your system.

With the huge oil disaster in the Gulf of Mexico still fighting for column inches with the FIFA World Cup in most parts of the world, it still remains a highly emotive subject in the country where it is having the most devastating impact. The Gulf states of the US are reeling under the blow to their economy, environment and way of life with an understandable backlash now both in the media and in Washington towards the oil industry and in particular, BP.

With this public maelstrom directed at the hapless BP, a leading energy attorney, Greg Chaffee has stated that the disaster will inevitably lead to more investments in green energy. Chaffee who practices at Morris Manning & Martin and also acts as the chairman of the MMM Green Industry Practice stated that,

“This is more evidence that the Gulf spill disaster has become a wakeup call for a nation that remains firmly addicted to oil.”

With specific reference to BP, Chaffee added,

“Not only should the federal government hold BP accountable for its errors and misjudgments leading up to the disaster, the federal government is now positioned more than ever to be the catalyst for funding research and development on alternative fuels.”

The Obama administration has already given its commitment to leading the way in green technologies with other leading countries such as China giving backing to funding in renewable energy sources. Chaffee however believes that what is really needed is not government legislation but a root change in the culture of the public.

“If we do not mobilize our resources now to concentrate on our energy future, we will be missing a key opportunity to positively re-shape the economic and environmental future of our nation. Weaning ourselves from our addiction to oil does not begin at the White House. It begins at home.

Each decision we make daily – from the cars we drive, to the containers in which we store our food, to how high we set the thermostat has an impact on our demand for oil. It’s that demand which led us to drill a mile beneath the ocean floor in the Gulf of Mexico.”