A big topic of conversation in Silicon Valley this week is "cleantech", from the launch of Bloom Energy - which the company claims will deliver cheap, emission-free power - to the gathering of minds at the Cleantech Forum, where the focus is on business.

Add to the mix 19 companies from the UK working in this space who have come to the Valley for a variety of reasons: from finding partners to raising cash; from looking to set up an office to getting some press attention.

The mission has been called "Clean and Cool" and has been organised and bankrolled by UK Trade And Investment, the Technology Strategy Board, BP, Orrik, Polecat and the Cleantech Group among others.

"The companies involved are all really trying to solve some quite similar problems but in really different ways," said Oli Barrett, an entrepreneur and one of the people involved in the event.

"We are talking about everything from the very large pieces of technology through to various innovations in battery cells to gadgets you might find in your house to making your building more energy-efficient. There is a real breadth and depth to the kinds of companies who have come to the Valley this week."

A total of 140 start-ups competed for a place at the trade week that has seen attendees pitch their wares to investors, meet industry peers and make contacts.

I caught up with a few of them to see what they have to offer in a space where the Valley likes to consider itself as a leader.

Breathing Buildings is a company that is selling the idea of low-energy natural ventilation. Or as I put it, a hole in the wall.

"In a very crude way, that is what it is - and in fact, the most wonderful ventilation is an amphitheatre which doesn't have a roof but in reality won't work for all seasons and climates," said managing director Shaun Fitzgerald.

He said that instead of using fans and pumps, his system uses "the forces of nature, namely wind and buoyancy to drive the exchange of fresh air".

Mr Fitzgerald reckons that the energy consumption of a naturally-ventilated building over an air-conditioned one can be halved.

"In a typical school classroom you are looking at a saving of $500 or £300-400 per classroom. In a typical school, you have ten classrooms and the savings could add up to a half a teacher just by using the right ventilation strategy," claimed Mr Fitzgerald.

Today the business has an order book of over £2 million in the UK education sector and wants to expand in the US and Europe.

At DIYKyoto the focus is also on saving money but on an individual basis.

Co-founder and director Richard Woods said he wants to empower one person at a time to change the amount of energy he or she uses, to save money and to save the planet, all at the same time.

"We are trying to create consumer cleantech-branded products that will be about more than just energy. The concept is really about do-it-yourself towards the Kyoto protocol, which is all about reducing green house gasses.

"We are saying: don't wait for government or big business. We are about giving people the chance to do something positive and proactive themselves," said Mr Woods.

The company's first product is called Wattson and is an energy monitor that shows you how much electricity you are using in terms of pounds and pence and also how much you can save.

"The focus is on design but also showing you as simply as possible how much you are using. For example, if you turned on a 100-watt lightbulb. Wattson will go up £120 per year because that is what it would cost you to keep that bulb on. Switch it off and you will see what you save. It gives you a context as to what is good value and what isn't," said Mr Woods.

Wattson is already on sale in the UK and Mr Woods said he hopes being part of Clean and Cool will help him find partners here in the US to expand sales.

Addressing a bigger energy problem, this time for the telecommunications industry, is Diverse Energy.

The company makes green, low-cost power plants for off-grid cell phone towers mainly in emerging markets. With 4 billion cellphones in use already and another 3 billion untapped customers, operations director Dr Alistair Livesey said his company presents a cost-effective and low-emission solution to a big problem.

"In these emerging markets, where there are no landlines and no electricity, these cellphone towers are being powered by diesel generators," said Dr Livesey.

"The problem is they are very expensive and over 50% of the cost of running the cellphone tower goes on diesel. In 2008, when the price of fuel rocketed, it was an enormous problem. They are also highly polluting and give out a lot of CO2. Added to that is the issue of theft because a lot of this diesel is stolen."

Dr Livesey said his company's PowerCube solves these issues. It is the size of a small garden shed and costs about $90,000 or £55,000.

The secret sauce is the use of ammonia as fuel, which Dr Livesey said is the basis of fertilizer and can be found on farms even in the remotest communities.

Diverse Energy claims the technology would deliver an 80% CO2 reduction and 25% reduction in total cost of ownership with a two-year pay-back.

The PowerCube is already on trial with Motorola on the east coast of Africa.

Dr Livesey hopes his week in the Valley will help him attract investors to a product he said is "really a 21st-Century power plant for a 21st-Century industry".

The problem Xeros is trying to solve is as old as the hills. The company wants to change the way you do your laundry.

"We aim to save you 90% of the amount of water you use, 40% of electricity and a third of the detergent," said chief executive officer Bill Westwater.

The solution lies in replacing most of the water you use with little plastic beads.

"You still need to dampen the clothes - but rather than use lots of water to get all the stains away, you roll them in these plastic beads which have a unique property that attracts and absorbs the dirt. This lets you reduce the amount of water you use, the amount of electricity and the amount of detergent," said Mr Westwater.

"It's a new way of washing clothes that is going to be better for the environment and better for you wallet."

So far, so good - but the gnarly problem with all of this is, of course, the washing machine which today uses too much water.

"What we are selling here is a whole new system and that requires not just the plastic beads but, yes, a new machine," admitted Mr Westwater.

He said in time the price of a new machine, which they are still developing, should not be too prohibitive because it will use most of the same components that present-day machines use.

In the first instance, Xeros is going after the commercial laundry market where the results will be most marked.

"One of the problems we face is getting this new technology into the market and fighting inertia because, of course, most people are satisfied with their current laundry process. You throw dirty clothes in, switch on the machine, walk away and come back later to clean clothes," said Mr Westwater.

He said while he faces something of an uphill task, he has come to the Valley for inspiration and a bit of that can-do attitude that is prevalent here.

"This laundry proposition is really exciting, but sometimes you can get worn down in the UK by how is it going to get started.

"Here people work out of their garage against big established businesses all the time and make a real go of it. That is the sort of inspiration I would like to take back to the UK. People are so expansive and positive and I am hoping a bit of that rubs off on me," said Mr Westwater.