Even in the UK the sun does occasionally shine, and what better way to make use of that sunlight, apart from being out in the fresh air, than to use it to provide energy?

Why is it green?

Solar electricity is probably the most common renewable energy source and it doesn’t use a fossil fuel, doesn’t release carbon dioxide nor other pollutants into the air to increase global warming

What’s involved?

Photovoltaic panels are fitted onto a roof, these convert sunlight into electricity.  This electricity can’t be stored (without expensive storage solutions, see below) but it can be used and any excess can be exported to the grid which shows good neighbourliness.

Can you DIY?

Sorry, this is a definite no. It’s a job for a professional

How much does it cost?

Any average system will cost about £7,000, but it will depend on the size of the building and the amount of electricity that is required or wanted.

Does it save money?

Careful use of appliances when electricity is being generated will reduce the reliance on the grid.  Although the electricity can’t be easily stored (again, see below), it can be used to heat water, and hot water can be stored.

Can it be done in a church?

It can, and because the major use of our buildings is during the day, then the time of greatest advantage, makes it something well worth considering.

Other Thoughts?

It’s not always easy to make optimum use of solar-generated electricity.  This has led to a proliferation of research into battery storage solutions that aim to help you maximise solar resource.

The technology is developing rapidly, but is still relatively new. So is it worth considering for your building?  The crux of the issue is that photovoltaic panels can only generate power during daylight hours (and effectively only when the sun is well above the horizon). Cloud cover also reduces output substantially, and in winter the amount of electricity you can produce is very low.

What this means is that power isn’t produced when domestic demand for electricity is at its highest – i.e. in the morning, in the evening and during winter. Unless you’re at home on a bright day when there’s a good sunlight resource, and you are using the array to run electrical appliances, you may not be able to take direct advantage of the power you’re generating.

The timing mismatch between electricity demand and PV supply can be partly addressed through the use of battery storage. Instead of exporting the excess to the national grid, you can stockpile the power on site and use it in the evening and at night, when the panels aren’t generating.

Battery storage systems can be supplied as part of a new PV installation, or retrofitted to existing setups. They are available in AC and DC formats, depending on which point in the system they’re hooked into (basically, AC is used after the PV’s inverter; DC before the inverter).   The batteries are rated in terms of how many kWh of energy they can store. Domestic versions range in capacity from 2kWh to 14kWh, but how you use the electricity is also important.  If your main consumption at night is short bursts of high power uses, such as kettles or electric showers, then a battery with a low output won’t reduce your grid demand that much. But it will still supply devices with a smaller power demand, such as fridges or lighting.

Battery technology has improved recently. The old lead-acid versions were cheap but they tended not to last for long and were inefficient. Lithium ion is the now the norm in many battery storage applications (including PV systems), and has greatly increased efficiency. The underlying technology isn’t likely to change much in the medium term; so it looks like lithium ion batteries are here to stay.

The calculation is a matter of comparing the up front cost of a battery with the savings it provides.

Of course, adding storage technology to a PV system will only reduce electricity bills for the lifetime of the battery. Most systems are warranted for a period of five or 10 years. Some manufacturers also warrant their batteries for a fixed number of cycles (a complete charge up and discharge of the unit). Others work on the basis of a specified number of kWh that will be delivered under the warranty.

To figure out whether investing in a system is worthwhile, let’s look at a simple example. If a battery storage system is expected to deliver 40,000kWh, then based on an electricity price of 15p/kWh you would expect that fitting it would save you a total of £6,000 over its warranted lifetime (40,000 x 15 / 100).  Thus, if the setup cost £6,000 installed, you wouldn’t be saving any money – and you would also be consuming more of the earth’s resources by putting in the system.

Of course, batteries may last for longer than the warranted number of kilowatt-hours, and if so this would improve the economic and environmental payback. Similarly, the cost of installation could fall and the price of electricity is likely to rise.  While battery costs have come down recently, it’s not yet clear-cut that they will deliver a saving (unless you’re totally off-grid).

Investing in batteries will add to the environmental impact of your installation, of course – especially as they are not expected to last as long as the panels themselves. That said, the lithium ion technology currently used is much less toxic than lead-acid, and the units themselves are more compact, which makes them easier to transport.

Battery storage can help to reduce your dependency on conventional power. It can also assist you in making better use of the solar supply, for instance by allowing you to run appliances overnight using your site-generated electricity. But the majority of this benefit will be felt in summertime. However, this is a developing technology – both in terms of on-site generation and large-scale grid supply – and there will undoubtedly be further innovation to come.